1926 lines
109 KiB
HTML
1926 lines
109 KiB
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<HTML>
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<HEAD>
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<TITLE>The HYDRA file transfer protocol.</TITLE>
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</HEAD>
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<!-- Background white, links blue (unvisited), navy (visited), red (active) -->
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<BODY
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BGCOLOR="#FFFFFF"
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TEXT="#000000"
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LINK="#0000FF"
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VLINK="#000080"
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ALINK="#FF0000"
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>
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<PRE>
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Document: FSC-0072
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Version: 001
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Date: 21-Feb-1993
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The HYDRA file transfer protocol
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Joaquim H. Homrighausen and Arjen G. Lentz
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Status of this document:
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This FSC suggests a proposed protocol for the FidoNet(r) community,
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and requests discussion and suggestions for improvements.
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Distribution of this document is subject to the restrictions listed
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below.
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Fido and FidoNet are registered marks of Tom Jennings and Fido
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Software.
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---------------------------------------------------------------------
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Copyright 1991-1993 Joaquim H. Homrighausen. All rights reserved.
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Copyright 1991-1993 Lentz Software Development. All rights reserved.
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---------------------------------------------------------------------
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Restrictions
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=====================================================================
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You are granted a license to implement the HYDRA file transfer
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protocol, HYDRA hereafter, in your own programs and/or use the sample
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source code and adapt these to your particular situation and needs;
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subject to the following conditions:
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o You must refer to it as the HYDRA file transfer protocol, and you
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must give credit to the authors of HYDRA in any information screens
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or literature pertaining to your programs that contains other such
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information (credits, your own copyrights, etc.).
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o HYDRA will always remain backwards compatible with previous
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revisions. HYDRA allows for expansion of its features without
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interfering with previous revisions. It is, however, important that
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different people do not expand the protocol in different directions.
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We therefore ask you to contact us if you have any needs/ideas
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regarding HYDRA, so development can be synchronized and beneficial
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to all.
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o If your implementation cannot converse with past or future revisions
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as supplied by us, then you must refer to it as "HYDRA derived", or
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as "a variation of HYDRA", or words to that effect.
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Permission is hereby granted to the FTSC (FidoNet Technical Standards
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Committee) and other technical organisations to republish this
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document in its entirety. Librarians may change the title page and
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page headers to match their library format as long as all copyrights
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and body text remain unaltered. The original document name and source
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must be mentioned in any republished versions of this document.
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No organization, company, person, or other being may impose any fees
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for any reason for providing this document. This document may not be
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sold or otherwise transferred for personal or company gain under any
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circumstances.
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Disclaimer
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=====================================================================
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This information is provided "as is" and comes with no warranties of
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any kind, either expressed or implied. There is no support available
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for this package. It's intended to be used by programmers and
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developers.
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In no event shall the authors be liable to you or anyone else for any
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damages, including any lost profits, lost savings or other incidental
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or consequential damages arising out of the use or inability to use
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this information.
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Revision timestamps
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=====================================================================
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001 0x2b1aab00 Dec 01, 1992
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Introduction
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=====================================================================
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This document will not attempt to convince the reader that HYDRA is
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of value to him/her or that it is better than other file transfer
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protocols, it will simply describe the protocol. Just to get it out
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of the way, HYDRA is not the ultimate file transfer protocol.
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The authors do, however, feel that it offers an significant
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improvement over those file transfer protocols available today. HYDRA
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is a bi-directional protocol with the ability to receive and send
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files simultaneously. There are other bi-directional file transfer
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protocols, but to the authors' knowledge no public specifications
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exist.
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HYDRA owes much to Zmodem and its designer, Chuck Forsberg as well as
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to Janus, designed by Rick Huebner. We would like to think of HYDRA
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as a combination of both with a few extra options installed.
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The basic concept of a bi-directional file transfer protocol is
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simple. Both data channels are utilized to transmit and receive files
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simultaneously. I.e. two 100 kb files can be exchanged between two
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parties in the time it takes a fully streaming uni-directional file
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transfer protocol to transmit one of the files.
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Protocol design
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=====================================================================
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The ultimate goal when designing HYDRA was to design a protocol that
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is as simple and robust as possible; complexity increase the problem
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of faulty implementations.
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The obvious function of a file transfer protocol is to transport a
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collection of data from its source to its destination as efficient
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possible and without jeopardizing the integrity of the data.
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The lack of data compression and lost packet management (as used in
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Kermit and Super Kermit) is intentional. The authors feel that this
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unnecessarily increases the complexity of the protocol.
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While HYDRA performs to its best on full duplex links, it should be
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possible to use it on links using proprietary protocols such as the
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US Robotics HST protocol which features one 14.4 kbps data channel
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and one 450 bps back channel.
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The protocol design should be flexible enough for future enhancements
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while maintaining backward compatibility.
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Protocol requirements and restrictions
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=====================================================================
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HYDRA require that the link can handle ASCII character 24 (DLE) as
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well as all ASCII characters in the range 32 through 126. All other
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characters can be escaped or encoded by the protocol as required by
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the link.
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Capability of the computer to perform simultaneous serial I/O as well
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as simultaneous serial I/O combined with disk access is preferred,
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but can be circumvented by opting for windowed transmission instead
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of full streaming.
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HYDRA calls for the ability to check whether there is anything in the
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serial input buffer (i.e. "peek-ahead"), but it doesn't mind if it
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has to wait for a second if there is no data available (using for
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instance the UNIX alarm() mechanism).
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The protocol is extremely tolerant with timeouts (i.e. satellite or
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network delays) while still maintaining maximum reliability,
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robustness, and throughput.
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Terms and definitions
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=====================================================================
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A BYTE An 8-bit unsigned character.
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A WORD A 16-bit unsigned integer.
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A DWORD A 32-bit unsigned integer.
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A LONG A 32-bit SIGNED integer.
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FILE OFFSETS (position) A long.
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NUL The ASCII character 0.
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BS The ASCII character 8.
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CR The ASCII character 13.
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XOFF The ASCII character 17.
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XON The ASCII character 19.
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H_DLE The HYDRA link escape character, ASCII 24
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(^X).
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SP or SPACE The ASCII character 32.
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UNIX timestamp A specific time and date expressed as the
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number of seconds since midnight, January
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1st, 1970. All UNIX timestamps used in HYDRA
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are expressed in local time.
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Multi-byte items are transmitted in "low-byte first" order, so big-
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endian CPUs (like 680xx) need to do some byteswapping, depending on
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the implementation.
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Values preceded by '0x' are in hexadecimal notation (base 16, 0..9
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a..f). All values transmitted in hexadecimal notation must be
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converted to lowercase characters and left-padded to their full
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size with '0' prior to transmission. E.g. a WORD with the value 255
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(decimal) is expressed as 00ff. A LONG with the value 255 (decmial)
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is expressed as 000000ff.
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In formulas, "AND" means bitwise AND, "XOR" means bitwise Exclusive
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OR, "NOT" is ones complement (i.e. all zeros become ones, all ones
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become zeros). The ">>" is a shift operation to the right, "R >> 3"
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means shift R three bits to the right.
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General packet format
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=====================================================================
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All data exchange is done with framed packets protected by 16 or 32
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bit CRC values appended to the packet data and packet type (low-
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byte first). The only exception to this is the cancel sequence of 5
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consecutive H_DLE characters.
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All packets except those with the type DATA are followed by a CR
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(ASCII 13) to help get through some buffered environments and aid
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possible debugging and/or tracing. If requested by the other side in
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its INIT packet, packets can also be prefixed by a specific data
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string which can include NULs, delays or break signals. Refer to the
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section on the INIT packet for more information.
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Format of unframed packet
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+------------------------------------------+
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~ Zero or more bytes packet dependent data ~
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+------------------------------------------+
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| Packet type byte |
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+------------------------------------------+
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| CRC-16/32 of packet data and packet type |
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+------------------------------------------+
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Table of packet types
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+--------+---------+-----+--------------------------------+
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|Name |Character|ASCII|Description |
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+--------+---------+-----+--------------------------------+
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|START | 'A' | 65 |Startup sequence |
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|INIT | 'B' | 66 |Session initialisation |
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|INITACK | 'C' | 67 |Response to INIT packet |
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|FINFO | 'D' | 68 |File information |
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|FINFOACK| 'E' | 69 |Response to FINFO packet |
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|DATA | 'F' | 70 |File data packet |
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|DATAACK | 'G' | 71 |File data position ACK packet |
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|RPOS | 'H' | 72 |Reposition request packet |
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|EOF | 'I' | 73 |End of file packet |
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|EOFACK | 'J' | 74 |Response to EOF packet |
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|END | 'K' | 75 |End of session |
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|IDLE | 'L' | 76 |Idle (just saying I'm alive) |
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|DEVDATA | 'M' | 77 |Data to specified device (1)|
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|DEVDACK | 'N' | 78 |Response to DEVDATA packet (1)|
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+--------+---------+-----+--------------------------------+
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(1) Support for DEVDATA and DEVDACK types is optional and indicated
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in INIT state of a HYDRA session.
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Format of framed packet
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+----------------------+--------------------+
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| H_DLE |Packet format byte |
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+----------------------+--------------------+
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~ Encoded packet ~
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+----------------------+--------------------+
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| H_DLE |End of framed packet|
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+----------------------+--------------------+
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Table of packet formats
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+----+---------+-----+--------------------------------+
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|Name|Character|ASCII|Description |
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+----+---------+-----+--------------------------------+
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|END | 'a' | 97 |End of framed packet |
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|BIN | 'b' | 98 |Binary packet |
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|HEX | 'c' | 99 |Hex encoded packet |
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|ASC | 'd' | 100 |Shifted 7-bit encoded packet (1)|
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|UUE | 'e' | 101 |UUencoded packet (1)|
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+----+---------+-----+--------------------------------+
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(1) Support for ASC and/or UUE formats is optional and indicated in
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the INIT state of a HYDRA session.
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Packet sender and receiver state charts
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---------------------------------------------------------------------
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TXPKT (Sender)
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+--------+------------------------------+--------------------------+----------+
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|State |Predicate(s) |Action(s) |Next state|
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+--------+-+----------------------------+--------------------------+----------+
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|Begin |1|pkttype == START or |format = HEXPKT |Format |
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| | |pkttype == INIT or | | |
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| | |pkttype == INITACK or | | |
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| | |pkttype == END or | | |
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| | |pkttype == IDLE | | |
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| +-+----------------------------+--------------------------+----------+
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| |2|Escape 8th bit (7 bit link) | |Coding |
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| +-+----------------------------+--------------------------+----------+
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| |3|else (no spc.pkt, 8bit link)|format = BINPKT |Format |
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+--------+-+----------------------------+--------------------------+----------+
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|Coding |1|escape all control chars & |format = UUEPKT |Format |
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| | |UUENCODED packets allowed | | |
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| +-+----------------------------+--------------------------+----------+
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| |2|ASCII packets allowed |format = ASCPKT |Format |
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| +-+----------------------------+--------------------------+----------+
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| |3|7 bit link & |format = HEXPKT |Format |
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| | |escape all control chars & | | |
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| | |UUE/ASC pkts not allowed | | |
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+--------+-+----------------------------+--------------------------+----------+
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|Format | |Append format byte to data|CRC |
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+--------+-+----------------------------+--------------------------+----------+
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|CRC |1|format != HEXPKT & |Calc CRC-32 (data,pkttype)|Encode |
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| | |CRC-32 allowed |Append one's complement of| |
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| | | |CRC to data, lowbyte first| |
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| +-+----------------------------+--------------------------+----------+
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| |2|else (HEXPKT or no CRC-32) |Calc CRC-16 (data,pkttype)|Encode |
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| | | |Append one's complement of| |
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| | | |CRC to data, lowbyte first| |
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+--------+-+----------------------------+--------------------------+----------+
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|Encode |1|format == BINPKT |BIN escape databuf |Prefix |
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| +-+----------------------------+--------------------------+----------+
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| |2|format == HEXPKT |HEX encode databuf |Prefix |
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| +-+----------------------------+--------------------------+----------+
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| |3|format == ASCPKT |ASC encode/escape databuf |Prefix |
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| +-+----------------------------+--------------------------+----------+
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| |4|format == UUEPKT |UUE encode databuf |Prefix |
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+--------+-+----------------------------+--------------------------+----------+
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|Prefix |1|No more prefix characters | |Transmit |
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| +-+----------------------------+--------------------------+----------+
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| |2|Prefix character ASCII 221 |Send 1 second break signal| |
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| +-+----------------------------+--------------------------+----------+
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| |3|Prefix character ASCII 222 |1 second delay | |
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| +-+----------------------------+--------------------------+----------+
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| |4|Prefix character ASCII 223 |Transmit NUL (ASCII 0) | |
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| +-+----------------------------+--------------------------+----------+
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| |5|else (any other character) |Transmit character | |
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+--------+-+----------------------------+--------------------------+----------+
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|Transmit| |Transmit H_DLE,format byte|Suffix |
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| | |Transmit encoded buffer | |
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| | |Transmit H_DLE,pktend byte| |
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+--------+-+----------------------------+--------------------------+----------+
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|Suffix |1|pkttype != DATA & |Transmit CR,LF (ASC 13,10)|Done |
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| | |pktformat != BINPKT | | |
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| +-+----------------------------+--------------------------+----------+
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| |2|else (pkttype == DATA or | |Done |
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| | | pktformat == BINPKT) | | |
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+--------+-+----------------------------+--------------------------+----------+
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RXPKT (Receiver)
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+--------+------------------------------+--------------------------+----------+
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|State |Predicate(s) |Action(s) |Next state|
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+--------+------------------------------+--------------------------+----------+
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|Reset | |rxdle = 0 |NextByte |
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| | |format = 0 | |
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| | |pktlen = 0 | |
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|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|NextByte|1|User wishes to abort session|Report reason for abort |Abort |
|
||
|
|
| | |or carrier lost | | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|Byte available in inputbuf | |StripIn |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |3|braintimer expired |Report braindead situation|Abort |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |4|Any other timer expired |Tell responsible party | |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|StripIn |1|Escape 8th bit (7 bit link) |c = c AND 0x7f (strip 8th)|StripC |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|else (8 bit link) | |StripC |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|StripC |1|Escape ctlchars with 8th set|n = c AND 0x7f (strip 8th)|Process |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|else (let 8 bit ctl through)|n = c |Process |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|Process |1|c == H_DLE |increment rxdle |DLE |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|Escape XON/XOFF & |Eat these |NextByte |
|
||
|
|
| | |n == XON or n == XOFF | | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |3|Escape all control chars & |Eat these |NextByte |
|
||
|
|
| | |n < 32 or n == 127 | | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |4|rxdle > 0 | |Escape |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |5|else (no eating or escaping)| |Store |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|DLE |1|rxdle == 5 |Report remote wants abort |Abort |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|else (rxdle < 5) | |NextByte |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|Escape |1|c == PKTEND | |PktEnd |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|c == BINPKT |format = BINPKT |PktStart |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |3|c == HEXPKT |format = HEXPKT |PktStart |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |4|c == ASCPKT |format = ASCPKT |PktStart |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |5|c == UUEPKT |format = UUEPKT |PktStart |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |6|else (normal escaped char) |c = c XOR 0x40 |Store |
|
||
|
|
| | | |rxdle = 0 |Store |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|Store |1|format == 0 |Garbage |NextByte |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|pktlen >= maximum |Pkt too long / lost PKTEND|Reset |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |3|else (fmt > 0 & len < max) |Append c to databuffer |NextByte |
|
||
|
|
| | | |increment pktlen | |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|PktStart| |rxdle = 0 |NextByte |
|
||
|
|
| | |pktlen = 0 | |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|PktEnd |1|format == 0 |End without start, garbage|Reset |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|format == BINPKT |(No more decoding needed) |CalcCRC |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |3|format == HEXPKT |ok = Decode HEXPKT |CheckDec |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |4|format == ASCPKT |ok = Decode ASCPKT |CheckDec |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |5|format == UUEPKT |ok = Decode UUEPKT |CheckDec |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|CheckDec|1|ok (no errors during decode)| |CalcCRC |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|else (errors in decoding) |Bad encoding, ignore pkt |Reset |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|CalcCRC |1|format != HEXPKT & |Calc CRC-32 over databuf |CheckCRC |
|
||
|
|
| | |CRC-32 allowed |ok = (crc == 0xdebb20e3) | |
|
||
|
|
| | | |pktlen = pktlen - 4 | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|else (HEXPKT or no CRC-32) |Calc CRC-16 over databuf |CheckCRC |
|
||
|
|
| | | |ok = (crc == 0xf0b8) | |
|
||
|
|
| | | |pktlen = pktlen - 2 | |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|CheckCRC|1|ok (CRC matched magic) |pkttype = last byte of buf|Reset |
|
||
|
|
| | | |pktlen = pktlen - 1 | |
|
||
|
|
| | | |Hand pkt to higher level | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|else (CRC check failed) |Bad CRC, ignore packet |Reset |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
BIN packet format
|
||
|
|
---------------------------------------------------------------------
|
||
|
|
The binary packet format require an 8-bit data channel. If requested
|
||
|
|
by either side, one or more sets of control characters are escaped.
|
||
|
|
In this case, when one of these characters appears in an unframed
|
||
|
|
packet, a H_DLE is sent followed by the character XOR 0x40. The H_DLE
|
||
|
|
character itself is always transmitted in this fashion. On the
|
||
|
|
receiver side, if the character after a H_DLE is not one of the
|
||
|
|
packet format bytes, this character is decoded using XOR 0x40 again.
|
||
|
|
|
||
|
|
|
||
|
|
BINPKT Escaping
|
||
|
|
+--------+------------------------------+--------------------------+----------+
|
||
|
|
|State |Predicate(s) |Action(s) |Next state|
|
||
|
|
+--------+------------------------------+--------------------------+----------+
|
||
|
|
|Begin | |txlastc = 0 |NextByte |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|NextByte|1|No more bytes to process | |Done |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|Escape ctlchars with 8th set|n = c AND 0x7f (strip 8th)|Escape |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |3|else (let 8 bit ctl through)|n = c |Escape |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|Escape |1|n == H_DLE |Output H_DLE |Output |
|
||
|
|
| | | |c = c XOR 0x40 | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|Escape XON/XOFF & |Output H_DLE |Output |
|
||
|
|
| | |n == XON or n == XOFF |c = c XOR 0x40 | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |3|Escape Telenet & |Output H_DLE |Output |
|
||
|
|
| | |n == CR & |c = c XOR 0x40 | |
|
||
|
|
| | |txlasc == '@' | | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |4|Escape all control chars & |Output H_DLE |Output |
|
||
|
|
| | |n < 32 or n == 127 |c = c XOR 0x40 | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |5|else (any other character) | |Output |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|Output | |Store c |NextByte |
|
||
|
|
| | |txlastc = c | |
|
||
|
|
+--------+------------------------------+--------------------------+----------+
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
HEX packet format
|
||
|
|
---------------------------------------------------------------------
|
||
|
|
Supported by all implementations, this packet format is used in
|
||
|
|
worst-case situations and upon startup of a session when it is not
|
||
|
|
yet known what restrictions the line and the other side will place on
|
||
|
|
the link.
|
||
|
|
|
||
|
|
Packet types always transmitted in HEX format are: START, INIT,
|
||
|
|
INITACK, IDLE, END.
|
||
|
|
|
||
|
|
HEX format packets always use a 16-bit CRC.
|
||
|
|
|
||
|
|
HEX packets assume a 7-bit link, escaping all control characters and
|
||
|
|
filtering all control characters upon receipt.
|
||
|
|
|
||
|
|
ASCII characters in the range 128-255 (high bit set) are encoded by
|
||
|
|
first transmitting a backslash ('\') character (ASCII 92), followed
|
||
|
|
by the character in two lowercase hex-digits (bits 4-7 in first
|
||
|
|
digit, bits 0-3 in second).
|
||
|
|
|
||
|
|
Uppercase hex-digits are not permitted.
|
||
|
|
|
||
|
|
The backslash character itself is transmitted as two backslashes.
|
||
|
|
|
||
|
|
ASCII characters in the range 0-31 and 127 (all control characters)
|
||
|
|
are escaped with H_DLE in the same fashion as in binary (BIN)
|
||
|
|
packets.
|
||
|
|
|
||
|
|
Decoded byte 1
|
||
|
|
+------+
|
||
|
|
76543210
|
||
|
|
+--++--+
|
||
|
|
Encoded h1 h2
|
||
|
|
|
||
|
|
|
||
|
|
HEXPKT Encoding/Escaping
|
||
|
|
+--------+------------------------------+--------------------------+----------+
|
||
|
|
|State |Predicate(s) |Action(s) |Next state|
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|NextByte|1|No more bytes to process | |Done |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|High bit of c set |Output \ (backslash) | |
|
||
|
|
| | | |Output hexdigit(c bit 4-7)| |
|
||
|
|
| | | |Output hexdigit(c bit 0-3)| |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |3|c < 32 or c == 127 |Output H_DLE | |
|
||
|
|
| | | |Output (c XOR 0x40) | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |4|c == \ (backslash) |Output \ (backslash) | |
|
||
|
|
| | | |Output \ (backslash) | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |5|else (any other character) |Output c | |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|
||
|
|
|
||
|
|
HEXPKT Decoding
|
||
|
|
+--------+------------------------------+--------------------------+----------+
|
||
|
|
|State |Predicate(s) |Action(s) |Next state|
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|NextByte|1|No more bytes to process | |Done OK |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|c == \ (backslash) | |Escape |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |3|else (any other character) |Output c |Escape |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|Escape |1|No more bytes to process |Premature end of data |Error |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|c == \ (backslash) |Output \ (backslash) | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |3|c == lowercase hexdigit |Save c, move ptr to next |NextHex |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |4|else (all other characters) |Invalid character |Error |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|NextHex |1|No more bytes to process |Premature end of data |Error |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|c == lowercase hexdigit |Output (1st << 4 OR 2nd) |NextByte |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |3|else (all other characters) |Invalid character |Error |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|
||
|
|
|
||
|
|
ASC packet format
|
||
|
|
---------------------------------------------------------------------
|
||
|
|
Support of this packet format is optional and signalled in the INIT
|
||
|
|
packet with the ASC flag in the "Supported options" field. 8-bit data
|
||
|
|
is transformed into 7-bit data by a simple shift operation. Each byte
|
||
|
|
is inserted at the top of a shift register, the lower seven bits are
|
||
|
|
moved out. So seven 8-bit bytes are encoded into eight 7-bit
|
||
|
|
characters.
|
||
|
|
|
||
|
|
The end of the packet is padded by a maximum of six bits of 0 to make
|
||
|
|
the number of bits a multiple of seven and thereby creating
|
||
|
|
complete characters (so the receiver stops decoding when there are
|
||
|
|
less than seven bits left). The output can contain control
|
||
|
|
characters, so if escaping of these characters is required, this is
|
||
|
|
done as in BIN packets using the H_DLE method.
|
||
|
|
|
||
|
|
|
||
|
|
Decoded byte 7 byte 6 byte 5 byte 4 byte 3 byte 2 byte 1
|
||
|
|
+------++------++------++------++------++------++------+
|
||
|
|
76543210765432107654321076543210765432107654321076543210
|
||
|
|
+-----++-----++-----++-----++-----++-----++-----++-----+
|
||
|
|
Encoded c8 c7 c6 c5 c4 c3 c2 c1
|
||
|
|
|
||
|
|
|
||
|
|
ASCPKT Encoding/Escaping
|
||
|
|
+--------+------------------------------+--------------------------+----------+
|
||
|
|
|State |Predicate(s) |Action(s) |Next state|
|
||
|
|
+--------+------------------------------+--------------------------+----------+
|
||
|
|
|Reset | |n = 0 (16 bit wide!) |NextByte |
|
||
|
|
| | |bitshift = 0 | |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|NextByte|1|No more bytes to process | |Flush |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|else (more bytes to process)|n = n OR (c << bitshift) |Shift |
|
||
|
|
| | | |BINPKT escape (n & 0x7f) | |
|
||
|
|
| | | |n = n >> 7 | |
|
||
|
|
| | | |increment bitshift | |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|Shift |1|bitshift == 7 |BINPKT escape (n & 0x7f) |Reset |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|else (bitshift < 7) | |NextByte |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|Flush |1|bitshift > 0 |BINPKT escape (n & 0x7f) |Done |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|else (bitshift == 0) | |Done |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|
||
|
|
ASCPKT Decoding
|
||
|
|
+--------+------------------------------+--------------------------+----------+
|
||
|
|
|State |Predicate(s) |Action(s) |Next state|
|
||
|
|
+--------+------------------------------+--------------------------+----------+
|
||
|
|
|Begin | |n = 0 (16 bit wide!) |NextByte |
|
||
|
|
| | |bitshift = 0 | |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|NextByte|1|No more bytes to process | |Done OK |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|else (more bytes to process)|c = c AND 0x7f |Shift |
|
||
|
|
| | | |n = n OR (c << bitshift) | |
|
||
|
|
| | | |bitshift = bitshift + 7 | |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|Shift |1|bitshift >= 8 |Output (n AND 0xff) |NextByte |
|
||
|
|
| | | |n = n >> 8 | |
|
||
|
|
| | | |bitshift = bitshift - 8 | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|else (bitshift < 8) | |NextByte |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
UUE packet format
|
||
|
|
---------------------------------------------------------------------
|
||
|
|
Support of this packet format is optional and signalled in the INIT
|
||
|
|
packet with the UUE flag in the "Supported options" field. The 8-bit
|
||
|
|
data is transformed into printable ASCII using the UUENCODE
|
||
|
|
algorithm. Three 8-bit bytes are encoded into four printable ASCII
|
||
|
|
characters. This done by taking the bottom six bits left and adding
|
||
|
|
'!' (ASCII 33) to move this character value into printable ASCII
|
||
|
|
range.
|
||
|
|
|
||
|
|
The end of the packet is padded by a maximum of five bits of 0 to
|
||
|
|
make the number of bits a multiple of six and thereby creating
|
||
|
|
complete characters (so the receiver stops decoding when there are
|
||
|
|
less than six bits left). The output of this coding scheme does not
|
||
|
|
need any further escaping before transmission.
|
||
|
|
|
||
|
|
Decoded byte 3 byte 2 byte 1
|
||
|
|
+------++------++------+
|
||
|
|
765432107654321076543210
|
||
|
|
+----++----++----++----+
|
||
|
|
Encoded c4 c3 c2 c1
|
||
|
|
|
||
|
|
|
||
|
|
UUEPKT Encoding
|
||
|
|
+--------+------------------------------+--------------------------+----------+
|
||
|
|
|State |Predicate(s) |Action(s) |Next state|
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|NextByte|1|Less than three bytes left | |Flush |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|else (three or more left) |UUE(in[0]>>2) | |
|
||
|
|
| | | |UUE(in[0]<<4 OR in[1]>>4) | |
|
||
|
|
| | | |UUE(in[1]<<2 OR in[2]>>6) | |
|
||
|
|
| | | |UUE(in[2]) | |
|
||
|
|
| | | |(UUE: (c AND 0x3f) + '!') | |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|Flush |1|No more bytes left | |Done |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|One byte left |UUE(in[0]>>2) |Done |
|
||
|
|
| | | |UUE(in[0]<<4) | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |3|Two bytes left |UUE(in[0]>>2) |Done |
|
||
|
|
| | | |UUE(in[0]<<4 OR in[1]>>4) | |
|
||
|
|
| | | |UUE(in[1]<<2) | |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|
||
|
|
UUEPKT Decoding
|
||
|
|
+--------+------------------------------+--------------------------+----------+
|
||
|
|
|State |Predicate(s) |Action(s) |Next state|
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|NextByte|1|Less than four bytes left | |Flush |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|else (four or more left) & |UD(i[0])<<2 OR UD(i[1])>>4| |
|
||
|
|
| | |(c AND 0x7f) is in UUE range|UD(i[1])<<4 OR UD(i[2])>>2| |
|
||
|
|
| | | |UD(i[2])<<6 OR UD(i[3]) | |
|
||
|
|
| | | |(UD: (c - '!') AND 0x3f) | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |3|else (all other characters) |Invalid character(s) |Error |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|Flush |1|No bytes left or | |Done OK |
|
||
|
|
| | |Less than two bytes left | | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|Two bytes left & |UD(i[0])<<2 OR UD(i[1])>>4|Done OK |
|
||
|
|
| | |(c AND 0x7f) is in UUE range| | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |3|Three bytes left & |UD(i[0])<<2 OR UD(i[1])>>4|Done OK |
|
||
|
|
| | |(c AND 0x7f) is in UUE range|UD(i[1])<<4 OR UD(i[2])>>2| |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |4|else (all other characters) |Invalid character(s) |Error |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
START packet (HEX format)
|
||
|
|
---------------------------------------------------------------------
|
||
|
|
This packet is sent to tell the remote to initiate a HYDRA session.
|
||
|
|
|
||
|
|
The complete framed packet as transmitted looks like:
|
||
|
|
|
||
|
|
ASCII values 24 99 65 92 102 53 92 97 51 24 97
|
||
|
|
+-------+---+---+---+---+---+---+---+---+-------+---+
|
||
|
|
Characters | H_DLE | c | A | \ | f | 5 | \ | a | 3 | H_DLE | a |
|
||
|
|
+-------+---+---+---+---+---+---+---+---+-------+---+
|
||
|
|
|
||
|
|
Applications may scan for this sequence to automatically start HYDRA
|
||
|
|
when the remote transmits this packet (AutoStart). Prior to the START
|
||
|
|
packet, a special string is transmitted to enable remote starting
|
||
|
|
from a command prompt, hydra<CR> (the word hydra in lowercase):
|
||
|
|
|
||
|
|
ASCII values 104 121 100 114 97 13
|
||
|
|
+---+---+---+---+---+----+
|
||
|
|
Characters | h | y | d | r | a | CR |
|
||
|
|
+---+---+---+---+---+----+
|
||
|
|
|
||
|
|
The special string combined with the START packet is transmitted at
|
||
|
|
five second intervals until either a START or INIT packet is received
|
||
|
|
from the remote, or the maximum number of retries is reached. Any
|
||
|
|
other packet types received in this stage must be ignored as they
|
||
|
|
could be remains of a previous session.
|
||
|
|
|
||
|
|
|
||
|
|
INIT packet (HEX format)
|
||
|
|
---------------------------------------------------------------------
|
||
|
|
The INIT packet contains file transfer session options. The remote
|
||
|
|
acknowledges this packet by returning an INITACK packet.
|
||
|
|
|
||
|
|
|
||
|
|
INIT packet data
|
||
|
|
|
||
|
|
+---------------------------------------+
|
||
|
|
~ Application ID string, NUL terminated ~
|
||
|
|
+---------------------------------------+
|
||
|
|
~ Supported options, NUL terminated ~
|
||
|
|
+---------------------------------------+
|
||
|
|
~ Desired options, NUL terminated ~
|
||
|
|
+---------------------------------------+
|
||
|
|
| Desired transmitter window size or 0 |
|
||
|
|
+---------------------------------------+
|
||
|
|
| Desired receiver window size or 0 |
|
||
|
|
+---------------------------------------+
|
||
|
|
~ Other general options, NUL terminated ~
|
||
|
|
+---------------------------------------+
|
||
|
|
~ Packet prefix string, NUL terminated ~
|
||
|
|
+---------------------------------------+
|
||
|
|
|
||
|
|
The application ID string contains a printable ASCII string with the
|
||
|
|
document revision date, product name, product revision number, and
|
||
|
|
optionally the product serial number. The format of the string is:
|
||
|
|
|
||
|
|
<RevDate><ProductName><,><ProductRevision>[<,><ProductSerial#>]
|
||
|
|
|
||
|
|
RevDate is the UNIX timestamp (the hour, minute, and second portion
|
||
|
|
is assumed to be zero), in hexadecimal notation, of the HYDRA
|
||
|
|
document that the application is supposed to support. None of the
|
||
|
|
following three fields should exceed thirty characters in length and
|
||
|
|
must not contain any control characters (ASCII 0-31) or the comma
|
||
|
|
character (ASCII 44). The field separator is a comma (ASCII 44)
|
||
|
|
character.
|
||
|
|
|
||
|
|
Capability flags
|
||
|
|
|
||
|
|
XON Escape <XON> and <XOFF> characters.
|
||
|
|
TLN Escape the <CR>@<CR> sequence (Telenet escape).
|
||
|
|
CTL Escape ASCII characters 0-31 and 127.
|
||
|
|
HIC Escape above three with high bit set.
|
||
|
|
HI8 Escape ASCII characters 128-255 and strip the high bit.
|
||
|
|
BRK Can transmit a break signal.
|
||
|
|
ASC Can handle ASC packets.
|
||
|
|
UUE Can handle UUE packets.
|
||
|
|
C32 Can receive packets with 32-bit CRC error detection.
|
||
|
|
DEV Can receive device packets.
|
||
|
|
FPT Can receive filenames with paths.
|
||
|
|
|
||
|
|
Capability flags are always three characters long, in uppercase, and
|
||
|
|
seperated by a comma character (ASCII 44). Please note that the first
|
||
|
|
five flags must be supported by all applications that implement the
|
||
|
|
HYDRA specifications.
|
||
|
|
|
||
|
|
The "Supported options" string contain the capability flags of the
|
||
|
|
options that the application support. The "Desired options" string
|
||
|
|
contain the capability flags of the options that the application
|
||
|
|
would like to use/enable for the session. Some flags do not have to
|
||
|
|
be specified in both strings. E.g. if the C32 flag is present in the
|
||
|
|
"Supported options" string and the remote system indicates support
|
||
|
|
for the same flag, 32-bit CRC error detection will be used. An
|
||
|
|
application may not ask for an option it does not support.
|
||
|
|
|
||
|
|
Escaping certain characters or bits also means filtering any
|
||
|
|
occurrence of them in the incoming data stream. At the start of a
|
||
|
|
session, it is assumed that the first five capability flags are in
|
||
|
|
effect, i.e. the high bit is stripped off every received character
|
||
|
|
and all control characters are filtered out.
|
||
|
|
|
||
|
|
The "Desired transmitter/receiver window size" fields are long
|
||
|
|
integers expressed in hexadecimal notation. With these options each
|
||
|
|
side tells the other to use window management of the requested size
|
||
|
|
when transmitting file data, instead of using full streaming (0).
|
||
|
|
The window setting is completely seperate for both directions.
|
||
|
|
If one side requests a smaller window size than the other, that
|
||
|
|
smaller size will be used for that direction; also, a window of any
|
||
|
|
size takes precedence over no window (0).
|
||
|
|
Please note that the terms 'transmitter' and 'receiver' used for the
|
||
|
|
fields in the INIT packet are from the view of the side transmitting
|
||
|
|
that packet, so the other side should merge the 'transmitter' window
|
||
|
|
field from the received INIT packet with its own 'receiver' window
|
||
|
|
field.
|
||
|
|
|
||
|
|
The "General options" string currently has no other fields than
|
||
|
|
"Desired tx/rx window size"; the string is NUL terminated.
|
||
|
|
|
||
|
|
The packet prefix string is normally empty, but may be provided by
|
||
|
|
the remote if required. The maximum length of a packet prefix string
|
||
|
|
is 30 characters. All characters should be transmitted as specified,
|
||
|
|
with the following exceptions:
|
||
|
|
|
||
|
|
|
||
|
|
Table of special packet prefix string chars
|
||
|
|
|
||
|
|
+-----+--------------------------------------+
|
||
|
|
|ASCII|Description |
|
||
|
|
+-----+--------------------------------------+
|
||
|
|
| 221 |Transmit a break signal for one second|
|
||
|
|
| 222 |Delay one second before next character|
|
||
|
|
| 223 |Transmit a NUL (ASCII 0) character |
|
||
|
|
+-----+--------------------------------------+
|
||
|
|
|
||
|
|
|
||
|
|
INITACK packet (HEX format)
|
||
|
|
---------------------------------------------------------------------
|
||
|
|
The INITACK packet is used to acknowledge the receipt of the remote's
|
||
|
|
INIT packet.
|
||
|
|
|
||
|
|
Duplicate INIT packets should be acknowledged too, as the remote may
|
||
|
|
have missed previous INITACK packets; the reception of such a
|
||
|
|
duplicate packet should not however reset the braindead timer, as it
|
||
|
|
does not mean a change of state and is not actual file data.
|
||
|
|
|
||
|
|
|
||
|
|
FINFO packet
|
||
|
|
---------------------------------------------------------------------
|
||
|
|
File information packet, sent to notify the remote that another file
|
||
|
|
is to be transmitted, or to signal end of batch. After the FINFO
|
||
|
|
packet has been transmitted, the timer is set to the normal timeout
|
||
|
|
value. The sender then waits for an FINFOACK packet from the remote
|
||
|
|
or for the timer to expire. In the event of a timeout, the transmit/
|
||
|
|
wait sequence is repeated with half the normal timeout value until
|
||
|
|
the maximum number of retries has been reached.
|
||
|
|
|
||
|
|
|
||
|
|
FINFO packet data
|
||
|
|
+-------------------------------------+
|
||
|
|
~ File information, NUL terminated ~
|
||
|
|
+-------------------------------------+
|
||
|
|
|
||
|
|
|
||
|
|
File information End of batch
|
||
|
|
+-----------------+ +-----------------+
|
||
|
|
| Timestamp or 0 | | NUL |
|
||
|
|
+-----------------+ +-----------------+
|
||
|
|
| Filesize or 0 |
|
||
|
|
+-----------------+
|
||
|
|
| Reserved (0) |
|
||
|
|
+-----------------+
|
||
|
|
| Transaction # |
|
||
|
|
+-----------------+
|
||
|
|
| File count or 0 |
|
||
|
|
+-----------------+
|
||
|
|
~ Short filename ~
|
||
|
|
+-----------------+
|
||
|
|
~ Real filename ~
|
||
|
|
+-----------------+
|
||
|
|
| NUL |
|
||
|
|
+-----------------+
|
||
|
|
|
||
|
|
End of batch is signalled by an empty string (only the terminating
|
||
|
|
NUL).
|
||
|
|
|
||
|
|
The first five fields are long integers expressed in hexadecimal
|
||
|
|
notation.
|
||
|
|
|
||
|
|
Timestamp is a UNIX timestamp representing the creation time of the
|
||
|
|
file. If the creation time is not known, this is zero.
|
||
|
|
|
||
|
|
Filesize is the size of the file in bytes. If the size of the file is
|
||
|
|
not known, this is zero. This field should not be used as an exact
|
||
|
|
measure of the size of the file. It is safe to assume that you should
|
||
|
|
not receive less data than specified in this field, but the file may
|
||
|
|
grow while it is being transferred (e.g. the result of a background
|
||
|
|
process).
|
||
|
|
|
||
|
|
Transaction # is a unique number for each set of files being sent
|
||
|
|
during the session. This is primarily used to allow the receiving
|
||
|
|
application to group several files together and store them in
|
||
|
|
specific directories as a result of automated file requests. If the
|
||
|
|
file being sent is not a result of an automated file request, this
|
||
|
|
field must be set to zero.
|
||
|
|
|
||
|
|
File count is the session file counter. For the first file in a
|
||
|
|
session, this field contains the total number of files to be sent
|
||
|
|
during the session; for subsequent files, it contains the file number
|
||
|
|
in the session, starting with two (2). If the total number of files
|
||
|
|
is not known, this field contains zero for all files.
|
||
|
|
|
||
|
|
The first filename field must be specified in lowercase characters.
|
||
|
|
It must conform to MS-DOS filename conventions and not exceed 12
|
||
|
|
characters in length (excluding the terminating NUL character). The
|
||
|
|
second field, real filename, is the actual filename on the sending
|
||
|
|
system. If this field is not present, the short filename field is
|
||
|
|
used.
|
||
|
|
|
||
|
|
No directory paths may be specified in the short filename. Directory
|
||
|
|
paths may be specified in the real filename field if the "Desired
|
||
|
|
options" of the receiver contains FPT. If the real filename field
|
||
|
|
contains a path, it may include any ASCII character in the range 32
|
||
|
|
(0x20) through 255 (0xff) with \ characters translated to /. A drive
|
||
|
|
specifier may be present in the <Drive>: (e.g. c:) format. If both
|
||
|
|
the short and real filename fields are present, they are separated
|
||
|
|
by a NUL character. There is never more than one NUL character
|
||
|
|
terminating the packet.
|
||
|
|
|
||
|
|
|
||
|
|
FINFOACK packet
|
||
|
|
---------------------------------------------------------------------
|
||
|
|
Sent in response to an FINFO packet. If the FINFO packet contained
|
||
|
|
file information, the FINFOACK packet is also used to instruct the
|
||
|
|
remote how to proceed with the transfer.
|
||
|
|
|
||
|
|
|
||
|
|
FINFOACK packet data
|
||
|
|
+---------------------------------------+
|
||
|
|
| Long file offset, special code, or 0 |
|
||
|
|
+---------------------------------------+
|
||
|
|
|
||
|
|
The only data in this packet is a long integer. In response to an
|
||
|
|
an end of batch FINFO packet, the file offset is set to zero (0). In
|
||
|
|
all other cases, file offset is one of the following:
|
||
|
|
|
||
|
|
|
||
|
|
File offsets and special values
|
||
|
|
+------+----------------------------------------------+
|
||
|
|
|Offset|Description |
|
||
|
|
+------+----------------------------------------------+
|
||
|
|
| >=0 |Seek to specified offset and start sending (1)|
|
||
|
|
| -1 |Already have file (2)|
|
||
|
|
| -2 |Send file during another batch (not now) |
|
||
|
|
+------+----------------------------------------------+
|
||
|
|
|
||
|
|
(1) This can only be something other than zero if the FINFO packet
|
||
|
|
specified a filesize other than zero (i.e. the size of the file
|
||
|
|
is known to the receiver).
|
||
|
|
|
||
|
|
(2) The sending application should consider the file as having been
|
||
|
|
sent successfully. This is primarily used to prevent duplicate
|
||
|
|
files from being transmitted.
|
||
|
|
|
||
|
|
|
||
|
|
DATA packet
|
||
|
|
---------------------------------------------------------------------
|
||
|
|
Packet containing actual file data.
|
||
|
|
|
||
|
|
|
||
|
|
DATA packet
|
||
|
|
+-----------------------------------------+
|
||
|
|
| Long file offset of file data block |
|
||
|
|
+-----------------------------------------+
|
||
|
|
~ Variable length data block 0-2048 bytes ~
|
||
|
|
+-----------------------------------------+
|
||
|
|
|
||
|
|
If the file offset corresponds with what is expected by the receiver,
|
||
|
|
the data block is saved and the file position increased accordingly.
|
||
|
|
If the file offset is not correct, DATA packets may have been lost or
|
||
|
|
failed the CRC check. Bad packets are ignored because it is not
|
||
|
|
certain that the bad packet was an actual DATA packet and not some
|
||
|
|
other type of packet. The file offset comparison is therefore the
|
||
|
|
only way to find out about lost or bad data.
|
||
|
|
|
||
|
|
When a bad data packet is detected, an RPOS packet is transmitted by
|
||
|
|
the receiver to force the sender to seek to the desired file offset
|
||
|
|
and resume transmission from it. After transmitting the RPOS packet,
|
||
|
|
the receiver initializes a timer and continues to monitor received
|
||
|
|
DATA packets while comparing their file offset with its desired
|
||
|
|
offset.
|
||
|
|
|
||
|
|
If the offset of a newly received DATA packet is greater than the
|
||
|
|
offset received in the last DATA packet prior to transmitting the
|
||
|
|
RPOS packet, the sender has not yet seen the RPOS packet, or the
|
||
|
|
DATA packet was already in the data stream when the RPOS packet was
|
||
|
|
transmitted.
|
||
|
|
|
||
|
|
If the received offset matches the requested offset, the transfer is
|
||
|
|
resumed, otherwise, a new RPOS packet is transmitted by the receiver
|
||
|
|
and the timer restarted.
|
||
|
|
|
||
|
|
If the timer expires, another RPOS packet is transmitted by the
|
||
|
|
receiver. This is repeated until the maximum number of retries has
|
||
|
|
been reached.
|
||
|
|
|
||
|
|
If the receiver encounters more missing or invalid DATA packets at
|
||
|
|
the same offset than it finds acceptable and it is not the originator
|
||
|
|
of the session, it may decide to revert to a one-way transfer and
|
||
|
|
wait with sending the remainder of its own files until the remote has
|
||
|
|
transmitted its end of batch signal. It is possible that some hard-
|
||
|
|
ware is not capable or well suited for a bi-directional file transfer
|
||
|
|
involving large volumes of data (see description of the IDLE packet).
|
||
|
|
|
||
|
|
|
||
|
|
DATAACK packet
|
||
|
|
---------------------------------------------------------------------
|
||
|
|
Transmitted by the receiver with its current file offset after
|
||
|
|
receiving a valid DATA packet.
|
||
|
|
|
||
|
|
|
||
|
|
DATAACK packet data
|
||
|
|
+------------------------+
|
||
|
|
| Long file offset |
|
||
|
|
+------------------------+
|
||
|
|
|
||
|
|
This packet is only transmitted if there is a window in operation
|
||
|
|
for that direction (selected in the INIT stage of the session), in
|
||
|
|
which case the sender uses the DATAACK file offsets to manage its
|
||
|
|
transmit window. If the sender's file offset is greater than or equal
|
||
|
|
to the last DATAACK offset received plus the window size, no more
|
||
|
|
data is transmitted by the sender until a DATAACK packet is received
|
||
|
|
which allows the sender to proceed without exceeding the window size.
|
||
|
|
|
||
|
|
While waiting for the DATAACK packet, the sender checks its timer
|
||
|
|
and retry counter. If the timer expires before a valid DATAACK packet
|
||
|
|
is received, the next DATA packet is transmitted, the retry counter
|
||
|
|
incremented, and the timer restarted with half the normal timeout.
|
||
|
|
This system ensures that the two sides do not end up waiting for
|
||
|
|
each other in case packets are lost; the receiver will respond with
|
||
|
|
either a DATAACK or RPOS packet. Receipt of a DATAACK packet does not
|
||
|
|
reset the braindead timer.
|
||
|
|
|
||
|
|
There are two windowing systems the receiver can use: sliding window
|
||
|
|
or segmented streaming.
|
||
|
|
|
||
|
|
If the receiver is capable of simultaneous serial and disk I/O, it
|
||
|
|
will transmit a DATAACK packet for every received DATA packet, or
|
||
|
|
every few DATA packets if it wants to be more economical with line
|
||
|
|
capacity.
|
||
|
|
Sliding window transmission is just a method of keeping the runahaid
|
||
|
|
of the transmitter within reasonable limits (for sattelite or network
|
||
|
|
links with long delays), thereby allowing for faster error recovery.
|
||
|
|
Because of Hydra's tolerancy to delays and method of error recovery,
|
||
|
|
sliding windows transmission is not normally required and full
|
||
|
|
streaming can be used.
|
||
|
|
|
||
|
|
If however the receiver is not capable of simultaneous serial and
|
||
|
|
disk I/O, it will will process received DATA packets until the window
|
||
|
|
size is reached (or slightly exceeded), write the received packets to
|
||
|
|
disk, and then transmit one DATAACK packet to signal that it can
|
||
|
|
receive the next segment of data.
|
||
|
|
|
||
|
|
If the sender cannot handle simultaneous serial and disk I/O, it can
|
||
|
|
apply the segmented streaming technique for reading data segments of
|
||
|
|
the negotiated window size from disk.
|
||
|
|
|
||
|
|
|
||
|
|
RPOS packet
|
||
|
|
---------------------------------------------------------------------
|
||
|
|
Transmitted by the receiver to force the sender to seek to a specific
|
||
|
|
position in the file and resume the transfer (as described above).
|
||
|
|
|
||
|
|
The RPOS packet is also used by the receiver to skip a file once the
|
||
|
|
transfer has been initiated. This is done by transmitting a RPOS
|
||
|
|
packet with -2 as the desired offset and then waiting for a EOF
|
||
|
|
packet with the same offset (-2). Once the EOF packet is received,
|
||
|
|
the receiver responds to it by transmitting a EOFACK packet and then
|
||
|
|
proceeds to wait for the next FINFO packet.
|
||
|
|
|
||
|
|
|
||
|
|
RPOS packet dependent data
|
||
|
|
+----------------------------------------+
|
||
|
|
| Long file offset |
|
||
|
|
+----------------------------------------+
|
||
|
|
| Desired datablock size (word, 64-2048) |
|
||
|
|
+----------------------------------------+
|
||
|
|
| Long RPOS packet ID |
|
||
|
|
+----------------------------------------+
|
||
|
|
|
||
|
|
|
||
|
|
File offsets
|
||
|
|
+------+-------------------------------------------+
|
||
|
|
|Offset|Description |
|
||
|
|
+------+-------------------------------------------+
|
||
|
|
| >=0 |Seek to specified offset and resume sending|
|
||
|
|
| -2 |Send file during another batch (not now) |
|
||
|
|
+------+-------------------------------------------+
|
||
|
|
|
||
|
|
The desired data blocksize field tells the sender what blocksize
|
||
|
|
to use when it resumes transmitting from the specified file offset.
|
||
|
|
|
||
|
|
Each new RPOS packet should be given a different packet ID. This
|
||
|
|
allows the sender to identify and ignore duplicate RPOS packets.
|
||
|
|
The ID need not be sequential, but it must not have the same value as
|
||
|
|
any other RPOS packet sent during the transmission of the same file.
|
||
|
|
A RPOS ID value of zero (0) is not permitted. The same ID value is
|
||
|
|
only used when sending multiple RPOS packets due to an expired RPOS
|
||
|
|
packet timer as described above (DATA packet).
|
||
|
|
|
||
|
|
|
||
|
|
EOF packet
|
||
|
|
---------------------------------------------------------------------
|
||
|
|
Indicates that the end of the file has been reached by the sender.
|
||
|
|
The packet is transmitted after the last DATA packet with file data.
|
||
|
|
The EOF packet only contains one field which holds the current file
|
||
|
|
offset of the sender (i.e. the actual size of the file).
|
||
|
|
|
||
|
|
After the EOF packet has been transmitted, the timer is set to the
|
||
|
|
normal timeout value. The sender then waits for an EOFACK packet
|
||
|
|
from the remote or for the timer to expire. In the event of a
|
||
|
|
timeout, the transmit/wait sequence is repeated with half the normal
|
||
|
|
timeout value until the maximum number of retries has been reached.
|
||
|
|
|
||
|
|
In the event that the receiver requests to skip the file by
|
||
|
|
transmitting a RPOS(-2) packet (see RPOS packet), the EOF packet
|
||
|
|
contains the same value (-2). If the sender wants to skip the file
|
||
|
|
currently being transmitted, it issues an EOF packet with -2 as the
|
||
|
|
offset value.
|
||
|
|
|
||
|
|
EOF packets with an incorrect offset should be treated by the
|
||
|
|
receiver as if it was an incorrect DATA packet (i.e. transmitting an
|
||
|
|
RPOS packet). Accepted EOF packets are acknowledged by transmitting
|
||
|
|
an EOFACK packet.
|
||
|
|
|
||
|
|
|
||
|
|
EOF packet data
|
||
|
|
+----------------------------------+
|
||
|
|
| Long file offset or special code |
|
||
|
|
+----------------------------------+
|
||
|
|
|
||
|
|
|
||
|
|
File offsets and special value
|
||
|
|
+------+----------------------------------------+
|
||
|
|
|Offset|Description |
|
||
|
|
+------+----------------------------------------+
|
||
|
|
| >=0 |Final offset in file (size of file) |
|
||
|
|
| -2 |Send file during another batch (not now)|
|
||
|
|
+------+----------------------------------------+
|
||
|
|
|
||
|
|
|
||
|
|
EOFACK packet
|
||
|
|
---------------------------------------------------------------------
|
||
|
|
Transmitted in response to an accepted EOF packet. After transmitting
|
||
|
|
this packet, the receiver waits for the FINFO packet of the next file
|
||
|
|
or end of batch.
|
||
|
|
|
||
|
|
|
||
|
|
END packet (HEX format)
|
||
|
|
---------------------------------------------------------------------
|
||
|
|
Once all files have been transmitted by both sides and no device
|
||
|
|
packets remain to be transmitted, the end of session sequence is
|
||
|
|
initiated. END packets are always sent in HEX format.
|
||
|
|
|
||
|
|
Two END packets are transmitted and the transmit timer set to half
|
||
|
|
the normal timeout. The application then waits for an END packet from
|
||
|
|
the remote or for the transmit timer to expire. In the event of a
|
||
|
|
timeout, the transmit/wait sequence is repeated until the maximum
|
||
|
|
number of retries has been reached. At this point, the HYDRA session
|
||
|
|
may be considered to be successful as both batches were completed.
|
||
|
|
|
||
|
|
If an END packet is received before timeout, another three (3) END
|
||
|
|
packets are transmitted and the protocol exits. Both sides need to
|
||
|
|
transmit END packets and receive at least one from the remote.
|
||
|
|
|
||
|
|
|
||
|
|
IDLE packet (HEX format)
|
||
|
|
---------------------------------------------------------------------
|
||
|
|
The IDLE packet is used to let the remote know that the application
|
||
|
|
is still alive. This is only applicable in uni-directional transfer
|
||
|
|
mode to let the remote know that your application is still alive when
|
||
|
|
it is receiving files, and after having transmitted an end of batch
|
||
|
|
signal to the remote and not having any more files to send for the
|
||
|
|
remainder of the session.
|
||
|
|
|
||
|
|
When applicable, the IDLE packet is transmitted every 20 seconds. The
|
||
|
|
remote resets its braindead timer upon receipt of an IDLE packet. If
|
||
|
|
an application receives an IDLE packet while it is in a state where
|
||
|
|
it is transmitting IDLE packets to the remote, something is wrong.
|
||
|
|
This could occur if both sides have accidentally switched to one-way
|
||
|
|
mode waiting for the remote to finish its batch. In this situation,
|
||
|
|
one-way should be disabled to prevent a complete deadlock. Note that
|
||
|
|
if both sides have finished their batch, the end of session sequence
|
||
|
|
(see END packet) should be initiated.
|
||
|
|
|
||
|
|
|
||
|
|
DEVDATA packet
|
||
|
|
---------------------------------------------------------------------
|
||
|
|
Support for the DEVDATA and DEVDACK packets is optional and indicated
|
||
|
|
in the INIT packet with the DEV flag in the "Supported options"
|
||
|
|
field. The ID value is a long, different for each new device data
|
||
|
|
packet sent. A value of zero (0) is not permitted.
|
||
|
|
|
||
|
|
Only one DEVDATA packet may be transmitted at a time; the side
|
||
|
|
issuing it then waits either for a timeout of the device transmit
|
||
|
|
timer, or for a DEVDACK packet with the correct ID value to be
|
||
|
|
received from the remote. If the timer expires before a correct
|
||
|
|
DEVDACK packet is received, the DEVDATA packet is again transmitted,
|
||
|
|
and the nnumber of device transmit retries incremented. If the
|
||
|
|
maximum number of retries is reached, the HYDRA session is aborted;
|
||
|
|
apparently the other is not functioning properly, or data is not
|
||
|
|
getting through. In either case, the normal operation of the
|
||
|
|
protocol (transferring files) will also fail.
|
||
|
|
|
||
|
|
The name of the device to which the data is addressed is transmitted
|
||
|
|
as an uppercase fixed-length three character NUL terminated string.
|
||
|
|
There are two pre-defined device names as described below. If an
|
||
|
|
unknown device name is specified, or a duplicate DEVDATA packet is
|
||
|
|
received (one with the same ID value as a previously received and
|
||
|
|
acknowledged DEVDATA packet), the packet is simply discarded after
|
||
|
|
transmitting a DEVDACK packet with the corresponding ID value.
|
||
|
|
|
||
|
|
DEVDATA and DEVDACK packets do not reset the braindead timer. They
|
||
|
|
operate independently from the normal protocol. Device packets may
|
||
|
|
only be transmitted after the initialization sequence, and before
|
||
|
|
both sides have completed their batch. If a DEVDATA packet has not
|
||
|
|
yet been acknowledged, the end of session sequence is delayed until
|
||
|
|
a DEVDACK packet has been sent in response.
|
||
|
|
|
||
|
|
|
||
|
|
DEVDATA packet dependent data
|
||
|
|
+--------------------------------------------------+
|
||
|
|
| Long DEVDATA packet ID value |
|
||
|
|
+--------------------------------------------------+
|
||
|
|
| 3 character uppercase device name, NUL terminated|
|
||
|
|
+--------------------------------------------------+
|
||
|
|
~ Variable length device data block (0-2048) ~
|
||
|
|
+--------------------------------------------------+
|
||
|
|
|
||
|
|
|
||
|
|
Predefined device names
|
||
|
|
+---+-------------------------------------+
|
||
|
|
|Dev|Description |
|
||
|
|
+---+-------------------------------------+
|
||
|
|
|MSG|Print data in protocol message window|
|
||
|
|
|CON|Print data to user console |
|
||
|
|
+---+-------------------------------------+
|
||
|
|
|
||
|
|
The MSG device may be used to notify the remote of protocol-specific
|
||
|
|
issues, i.e. "One-way transfer mode". Such messages may be logged,
|
||
|
|
but should not be considered to be machine-readable.
|
||
|
|
|
||
|
|
The CON device may be used to implement a "chat" or conversation
|
||
|
|
feature. This is a special case in which a session *can* be prolonged
|
||
|
|
after end of batch, but not against the remote's will.
|
||
|
|
While chat is enabled, there is no transition from the REND to the
|
||
|
|
END transmitter state. When a CON device packet is transmitted in
|
||
|
|
chat mode and the txstate is REND, the own braindead timer is reset.
|
||
|
|
If the other side does initiate the end sequence by sending an END
|
||
|
|
packet, the chat mode is immediately terminated and the session ended
|
||
|
|
in a clean manner. If one side does not want to (continue) chat, and
|
||
|
|
the other side does not comply, the one side will abort after a
|
||
|
|
braindead timeout, so this chat system does not mean a security flaw.
|
||
|
|
Each side is responsible for keeping the session going on his end
|
||
|
|
until its own user has finished chatting. It is suggested that the
|
||
|
|
software apply a timeout of say 1 minute to keyboard input, ending
|
||
|
|
the chat automatically if the user stops typing but does not exit
|
||
|
|
chat mode. Also, the chat mode should be initiated with a special key
|
||
|
|
so that it can not erronously be started or prolonged.
|
||
|
|
|
||
|
|
|
||
|
|
DEVDACK packet
|
||
|
|
---------------------------------------------------------------------
|
||
|
|
Transmitted in response to a DEVDATA packet. The device data ID value
|
||
|
|
must correspond to the ID of the previously received DEVDATA packet.
|
||
|
|
|
||
|
|
|
||
|
|
DEVDACK packet data
|
||
|
|
+---------------------------+
|
||
|
|
| Long device data ID value |
|
||
|
|
+---------------------------+
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
DEVICE sender (devtxstate HTD_...)
|
||
|
|
+--------+------------------------------+--------------------------+----------+
|
||
|
|
|State |Predicate(s) |Action(s) |Next state|
|
||
|
|
+--------+------------------------------+--------------------------+----------+
|
||
|
|
|Begin | |devtxid = 0 |DONE |
|
||
|
|
| | |reset devtxtimer | |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|DONE |1|wish to send device data & |increase devtxid |DATA |
|
||
|
|
| | |other side allows DEV pkts |devtxretries = 0 | |
|
||
|
|
| | | |reset devtxtimer | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|wish to send device data & |Tell calling function | |
|
||
|
|
| | |other doesn't allow DEV pkts|it's not on... | |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|DATA |1|devtxretries == 10 |Report too many errors |Abort |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|else (devtxretries < 10) |txpkt DEVDATA(id,dev,data)|DACK |
|
||
|
|
| | | |devtxtimer = timeout | |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|DACK |1|rxpkt DACK & |reset devtxtimer |DONE |
|
||
|
|
| | |DACK(id) == devtxid | | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|devtxtimer expired |Report devtx timeout |DATA |
|
||
|
|
| | | |increase devtxretries | |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|
||
|
|
DEVICE RECEIVER
|
||
|
|
+--------+------------------------------+--------------------------+----------+
|
||
|
|
|State |Predicate(s) |Action(s) |Next state|
|
||
|
|
+--------+------------------------------+--------------------------+----------+
|
||
|
|
|Begin | |devrxid = 0 |DONE |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|DONE |1|rxpkt DEVDATA |txpkt DEVDACK(id) |CheckID |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|CheckID |1|DEVDATA(id) != devrxid |devrxid = DEVDATA(id) |Process |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|else (apparent duplicate) | |DONE |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|Process |1|DEVDATA(dev) == MSG |Print protocol message |DONE |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|DEVDATA(dev) == CON |Output to user console |DONE |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |3|DEVDATA(dev) == known&ok |Call processing routine |DONE |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |4|else (unknown/not-ok device)|One-way into bitbucket |DONE |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|
||
|
|
|
||
|
|
Packet length and data block size
|
||
|
|
---------------------------------------------------------------------
|
||
|
|
The maximum length of a source data block (i.e. raw, non processed
|
||
|
|
input file or device data) is 2048 bytes. The maximum allowed length
|
||
|
|
of the packet data is 2048 + 8 = 2056 bytes. The eight bytes are to
|
||
|
|
provide sufficient room for the additional fields in the DATA and
|
||
|
|
DEVDATA packets. Packetizing adds an additional three to five bytes.
|
||
|
|
The maximum length of a framed packet being transmitted can be three
|
||
|
|
times the size of its source data depending on what type of encoding
|
||
|
|
scheme is used (ASC, HEX, UUE, BIN). The minimum length of a data
|
||
|
|
block is 64 bytes.
|
||
|
|
|
||
|
|
The block size of DATA packets is based on the physical (DCE) link
|
||
|
|
speed and is established as follows:
|
||
|
|
|
||
|
|
+---------+------------------+-------------------+
|
||
|
|
|DCE speed|Maximum block size|Starting block size|
|
||
|
|
+---------+------------------+-------------------+
|
||
|
|
| 300 bps| 256 bytes | 256 bytes |
|
||
|
|
| 1200 bps| 512 bytes | 256 bytes |
|
||
|
|
| 2400 bps| 1024 bytes | 512 bytes |
|
||
|
|
|>2400 bps| 2048 bytes | 512 bytes |
|
||
|
|
+---------+------------------+-------------------+
|
||
|
|
|
||
|
|
The blocksize is initialized to the starting blocksize when a session
|
||
|
|
is first started. After each kilobyte of file data transmitted, the
|
||
|
|
blocksize is doubled until it reaches the maximum allowed blocksize.
|
||
|
|
|
||
|
|
When the maximum allowed blocksize has been reached, the variable
|
||
|
|
keeping track of how many bytes are needed to increase the blocksize
|
||
|
|
is reset to zero.
|
||
|
|
|
||
|
|
If a request for retransmission (RPOS packet) is received from the
|
||
|
|
receiver, the blocksize is immediately set to that specified in the
|
||
|
|
retransmission request. Every time this occurs, the number of bytes
|
||
|
|
needed to double the blocksize is increased by 1024 with a maximum of
|
||
|
|
of 8192 bytes. The end result is that more data has to be
|
||
|
|
successfully transmitted before the blocksize is increased for each
|
||
|
|
error that occurs.
|
||
|
|
|
||
|
|
The length of a data block is dynamic and always in the range 0-2048
|
||
|
|
bytes. A data block is never padded. If there is insufficient data
|
||
|
|
to fill a block of the current blocksize, the blocksize is adjusted
|
||
|
|
to the amount of remaining data.
|
||
|
|
|
||
|
|
The blocksize logic is not reset between files in a session.
|
||
|
|
|
||
|
|
|
||
|
|
Timers and retry counters
|
||
|
|
=====================================================================
|
||
|
|
Each process in the protocol (transmit, receive and device transmit)
|
||
|
|
has its own timer and retry counter, and there is one overall
|
||
|
|
braindead timer. Allowed are 10 tries, the braindead timeout is 120
|
||
|
|
seconds, and the other timeouts are based on the speed of the line
|
||
|
|
and the state of the protocol. It can be calculated as (40960/DCE
|
||
|
|
rate), with a minimum of 10 seconds and a maximum of 60 seconds.
|
||
|
|
|
||
|
|
+---------+----------+----------+
|
||
|
|
|DCE speed|Timeout |Half |
|
||
|
|
+---------+----------+----------+
|
||
|
|
| 300 bps|60 seconds|30 seconds|
|
||
|
|
| 1200 bps|34 seconds|17 seconds|
|
||
|
|
| 2400 bps|17 seconds| 8 seconds|
|
||
|
|
|>2400 bps|10 seconds| 5 seconds|
|
||
|
|
+---------+----------+----------+
|
||
|
|
|
||
|
|
If the output buffer is empty, the timeout value is halved. In
|
||
|
|
general, this is the case if the number of tries is greater than zero
|
||
|
|
and during the init and end sequences. These timeouts are not fatal
|
||
|
|
situations, they just give the remote a reasonable amount of time to
|
||
|
|
receive and respond to a packet before a retry occurs. Duplicate
|
||
|
|
packets are always identified and ignored. A retry counter is reset
|
||
|
|
if there is a change of state, or a reposition different from the
|
||
|
|
previous file offset occurs.
|
||
|
|
|
||
|
|
The braindead timer monitors useful data from the other side: a first
|
||
|
|
response to a transmitted supervisiory packet, or a received packet
|
||
|
|
with file data at the correct offset. Device packets and packets that
|
||
|
|
do not signify any progress of the protocol do not affect the
|
||
|
|
braindead timer.
|
||
|
|
|
||
|
|
No other timers (such as one between characters in a packet) are
|
||
|
|
necessary.
|
||
|
|
|
||
|
|
|
||
|
|
Aborting a session
|
||
|
|
=====================================================================
|
||
|
|
A session is aborted with five consequetive CAN (^X or ASCII 24)
|
||
|
|
characters. Whenever a state table mentions "Abort", the following
|
||
|
|
procedure is to be followed:
|
||
|
|
|
||
|
|
Clear the output buffer and transmit eight CAN characters followed by
|
||
|
|
ten BS (^H or ASCII 8) characters; wait a few seconds for the data to
|
||
|
|
be transmitted to the remote, purge the input buffer and exit the
|
||
|
|
protocol code.
|
||
|
|
|
||
|
|
|
||
|
|
GENERAL sender (txstate HTX_...)
|
||
|
|
+--------+------------------------------+--------------------------+----------+
|
||
|
|
|State |Predicate(s) |Action(s) |Next state|
|
||
|
|
+--------+------------------------------+--------------------------+----------+
|
||
|
|
|Begin | |txretries = 0 |START |
|
||
|
|
| | |reset txtimer | |
|
||
|
|
| | |blksize = startblksize | |
|
||
|
|
| | |goodbytes = 0 | |
|
||
|
|
| | |goodneeded = 1024 | |
|
||
|
|
| | |braintimer = 120 | |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|START |1|txretries == 10 |Report too many errors |Abort |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|else (txretries < 10) |txstr AutoStart |SWAIT |
|
||
|
|
| | | |txpkt START | |
|
||
|
|
| | | |txtimer = 5 | |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|SWAIT |1|rxpkt START or |txretries = 0 |INIT |
|
||
|
|
| | |rxpkt INIT |reset txtimer | |
|
||
|
|
| | | |braintimer = 120 | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|txtimer expired |Report tx timeout |START |
|
||
|
|
| | | |increment txretries | |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|INIT |1|txretries == 10 |Report too many errors |Abort |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|else (txretries < 10) |txpkt INIT(linkinfo) |INITACK |
|
||
|
|
| | | |txtimer = timeout/2 | |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|INITACK |1|rxpkt INITACK |txretries = 0 |RINIT |
|
||
|
|
| | | |reset txtimer | |
|
||
|
|
| | | |braintimer = 120 | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|txtimer expired |Report tx timeout |INIT |
|
||
|
|
| | | |increment txretries | |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|RINIT |1|rxstate != INIT | |NextFile |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|NextFile|1|No files left? |Report end of batch |ToFName |
|
||
|
|
| | | |Set NULL fileinfo | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|Can access next file? |Set up fileinfo |ToFName |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |3|Can't access file? |Report access failure |NextFile |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|ToFName | |txsyncid = 0 |FINFO |
|
||
|
|
| | |txretries = 0 | |
|
||
|
|
| | |reset txtimer | |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|FINFO |1|txretries == 10 |Report too many errors |Abort |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|txretries > 0 |txpkt FINFO(fileinfo) |FINFOACK |
|
||
|
|
| | | |txtimer = timeout/2 | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |3|else (txretries == 0) |txpkt FINFO(fileinfo) |FINFOACK |
|
||
|
|
| | | |txtimer = timeout | |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|FINFOACK|1|NULL fname (end of batch) & |txtimer = idletimeout |REND |
|
||
|
|
| | |rxpkt FINFOACK |braintimer = 120 | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|rxpkt FINFOACK & |txpos = FINFOACK(pos) |DATA |
|
||
|
|
| | |FINFOACK(pos) >= 0 |txretries = 0 | |
|
||
|
|
| | | |txlastack = 0 | |
|
||
|
|
| | | |braintimer = 120 | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |3|rxpkt FINFOACK & |They already have file |NextFile |
|
||
|
|
| | |FINFOACK(pos) == -1) |braintimer = 120 | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |4|rxpkt FINFOACK & |Skip this file for now |NextFile |
|
||
|
|
| | |FINFOACK(pos) == -2) |braintimer = 120 | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |5|txtimer expired |Report tx timeout |FINFO |
|
||
|
|
| | | |inrease txretries | |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|DATA |1|rxstate != Done & |txtimer = idletimeout |XWAIT |
|
||
|
|
| | |hdxlink == True | | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|rxpkt DATAACK & |txlastack = DATAACK(pos) | |
|
||
|
|
| | |DATAACK(pos) > txlastack | | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |3|rxpkt RPOS & |Skip this file for now |SkipFile |
|
||
|
|
| | |RPOS(pos) < 0 |braintimer = 120 | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |4|rxpkt RPOS & |Report too many errors |Abort |
|
||
|
|
| | |RPOS(id) == txsyncid & | | |
|
||
|
|
| | |inc txretries == 10 | | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |5|rxpkt RPOS & |txpos = RPOS(pos) | |
|
||
|
|
| | |RPOS(id) != txsyncid & |txsyncid = RPOS(id) | |
|
||
|
|
| | |RPOS(pos) >= 0 |txretries = 1 | |
|
||
|
|
| | | |blksize = RPOS(blksize) | |
|
||
|
|
| | | |goodbytes = 0 | |
|
||
|
|
| | | |inc goodneeded + 1024 | |
|
||
|
|
| | | |if (goodneeded > 8192) | |
|
||
|
|
| | | | goodneeded = 8192 | |
|
||
|
|
| | | |braintimer = 120 | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |6|File seek/read error or |Skip this file for now |SkipFile |
|
||
|
|
| | |user wishes to skip file | | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |7|txwindow & |if (txretries > 0) |DATAACK |
|
||
|
|
| | |txpos >= txlastack+txwindow | txtimer = timeout/2 | |
|
||
|
|
| | | |else | |
|
||
|
|
| | | | txtimer = timeout | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |8|Enough room in output & |txpkt DATA(pos,data) | |
|
||
|
|
| | |more filedata(blksize) to go|txpos += datalen | |
|
||
|
|
| | | |inc goodbytes + datalen | |
|
||
|
|
| | | |if goodbytes > goodneeded | |
|
||
|
|
| | | | Store txpos,blksize | |
|
||
|
|
| | | | blksize * 2 (max.2048) | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |9|End of filedata reached | |EOF |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|SkipFile| |txpos = -1 |EOF |
|
||
|
|
| | |txretries = 0 | |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|DATAACK |1|txretries == 10 |Report too many errors |Abort |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|rxpkt DATAACK & |txlastack = DATAACK(pos) |DATA |
|
||
|
|
| | |DATAACK(pos) > txlastack & |txretries = 0 | |
|
||
|
|
| | |txpos < DATAACK(pos) + txwin|reset txtimer | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |3|rxpkt RPOS |Handle RPOS in state DATA | |
|
||
|
|
| | | |but stay in this state | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |4|txtimer expired |Report tx timeout |DATA |
|
||
|
|
| | | |increment txretries | |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|XWAIT |1|rxstate == Done |reset txtimer |DATA |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|rxpkt DATAACK & |txlastack = DATAACK(pos) | |
|
||
|
|
| | |DATAACK(pos) > txlastack | | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |3|rxpkt RPOS |Handle RPOS in state DATA | |
|
||
|
|
| | | |but stay in this state | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |4|rxpkt IDLE |hdxlink = False |DATA |
|
||
|
|
| | | |reset txtimer | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |5|txtimer expired |txpkt IDLE | |
|
||
|
|
| | | |txtimer = idletimeout | |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|EOF |1|txretries == 10 |Report too many errors |Abort |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|txretries > 0 |txpkt EOF(txpos) |EOFACK |
|
||
|
|
| | | |txtimer = timeout/2 | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |3|else (txretries == 0) |txpkt EOF(txpos) |EOFACK |
|
||
|
|
| | | |txtimer = timeout | |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|EOFACK |1|rxpkt EOFACK |braintimer = 120 |NextFile |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|rxpkt DATAACK & |txlastack = DATAACK(pos) | |
|
||
|
|
| | |DATAACK(pos) > txlastack | | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |3|rxpkt RPOS & |rxpos == -2 |EOF |
|
||
|
|
| | |RPOS(pos) == -2 & | | |
|
||
|
|
| | |rxpos != -2 | | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |4|rxpkt RPOS & |Handle as in state DATA |DATA |
|
||
|
|
| | |RPOS(pos) >= 0 | | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |5|txtimer expired |Report tx timeout |EOF |
|
||
|
|
| | | |increment txretries | |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|REND |1|rxstate == DONE & |txretries = 0 |END |
|
||
|
|
| | |devtxstate == DONE | | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|txtimer expired |txpkt IDLE | |
|
||
|
|
| | | |txtimer = idletimeout | |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|END |1|txretries == 10 | |Abort |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|else (txretries < 10) |txpkt END (twice) |ENDACK |
|
||
|
|
| | | |txtimer = timeout/2 | |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|ENDACK |1|rxpkt END |txpkt END (thrice) |Done |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|txtimer expired |Report tx timeout |END |
|
||
|
|
| | | |increment txretries | |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
GENERAL RECEIVER (rxstate HRX_...)
|
||
|
|
+--------+------------------------------+--------------------------+----------+
|
||
|
|
|State |Predicate(s) |Action(s) |Next state|
|
||
|
|
+--------+------------------------------+--------------------------+----------+
|
||
|
|
|Begin | |reset rxtimer |START |
|
||
|
|
| | |lastrxdlen = startblksize | |
|
||
|
|
| | |(tx handles braintimer) | |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|INIT |1|rxpkt INIT & |txpkt INITACK |FINFO |
|
||
|
|
| | |INIT(options) are compatible|Set options | |
|
||
|
|
| | | |braintimer = 120 | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|INIT(options) not compatible|Report link failure |Abort |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|FINFO |1|rxpkt INIT (apparent dup) |txpkt INITACK | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|rxpkt FINFO & |Report end of batch | |
|
||
|
|
| | |FINFO(fileinfo) == Empty |txpkt FINFOACK |DONE |
|
||
|
|
| | | |braintimer = 120 | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |3|rxpkt FINFO & |do not want this file | |
|
||
|
|
| | |we already have file |txpkt FINFOACK(-1) | |
|
||
|
|
| | | |braintimer = 120 | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |4|rxpkt FINFO & |Skip this file for now | |
|
||
|
|
| | |open/diskspace error |txpkt FINFOACK(-2) | |
|
||
|
|
| | | |braintimer = 120 | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |5|rxpkt FINFO & |rxpos = resume offset |ToData |
|
||
|
|
| | |file we want to resume | | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |6|rxpkt FINFO & |rxpos = 0 |ToData |
|
||
|
|
| | |new file for us | | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |7|rxpkt EOF (apparent dup) |txpkt EOFACK | |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|ToData | |txpkt FINFOACK(rxpos) |DATA |
|
||
|
|
| | |rxsyncid = 0 | |
|
||
|
|
| | |rxlastsync = 0; | |
|
||
|
|
| | |rxretries = 0 | |
|
||
|
|
| | |reset rxtimer | |
|
||
|
|
| | |braintimer = 120 | |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|DATA |1|rxpkt FINFO (apparent dup) |txpkt FINFOACK(rxpos) | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|rxpkt DATA & |Store data | |
|
||
|
|
| | |DATA(pos) == rxpos |rxpos += datalen | |
|
||
|
|
| | | |rxretries = 0 | |
|
||
|
|
| | | |rxlastsync = rxpos | |
|
||
|
|
| | | |reset rxtimer | |
|
||
|
|
| | | |braintimer = 120 | |
|
||
|
|
| | | |if (rxwindow) | |
|
||
|
|
| | | | txpkt DATAACK(rxpos) | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |3|rxpkt DATA & |Report bad rxpos |BadPos |
|
||
|
|
| | |DATA(pos) != rxpos | | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |4|rxpkt EOF & |Close file, received ok |OkEOF |
|
||
|
|
| | |EOF(pos) == rxpos | | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |5|rxpkt EOF & |Close, save for resume |OkEOF |
|
||
|
|
| | |EOF(pos) == -2 | | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |6|rxpkt EOF & |Report bad EOF |BadPos |
|
||
|
|
| | |EOF(pos) != rxpos | | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |7|File write error or |Close, save for resume | |
|
||
|
|
| | |user wishes to skip file |rxpos = -2 | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |8|rxpkt IDLE & |braintimer = 120 | |
|
||
|
|
| | |hdxlink == False | | |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|BadPos |1|DATA/EOF(pos) <= rxlastsync |rxretries = 0 |Timer |
|
||
|
|
| | | |reset rxtimer | |
|
||
|
|
| | | |rxlastsync = pos | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|DATA/EOF(pos) > rxlastsync |rxlastsync = pos |Timer |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|Timer |1|rxtimer expired | |HdxLink |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|else (rxtimer not expired) | |DATA |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|HdxLink |1|rxretries > 4 & |hdxlink = True |Retries |
|
||
|
|
| | |txstate < REND & |rxretries = 0 | |
|
||
|
|
| | |originator == False & | | |
|
||
|
|
| | |hdxlink == False | | |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|else (above not the case) | |Retries |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|Retries |1|inc rxretries == 10 |Report too many errors |Abort |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |2|rxretries == 1 |increase rxsyncid |RPos |
|
||
|
|
| +-+----------------------------+--------------------------+----------+
|
||
|
|
| |3|else (rxretries > 1) | |RPos |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|RPos | |lastrxdatalen/=2 (min.64) |DATA |
|
||
|
|
| | |txpkt RPOS (rxpos, | |
|
||
|
|
| | | lastrxdatalen,rxsyncid)| |
|
||
|
|
| | |rxtimer = timeout | |
|
||
|
|
+--------+------------------------------+--------------------------+----------+
|
||
|
|
|OkEOF | |txpkt EOFACK |FINFO |
|
||
|
|
| | |reset rxtimer | |
|
||
|
|
| | |braintimer = 120 | |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|DONE |1|rxpkt FINFO (apparent dup) |txpkt FINFOACK(-2) | |
|
||
|
|
+--------+-+----------------------------+--------------------------+----------+
|
||
|
|
|
||
|
|
|
||
|
|
HYDRA in FidoNet technology mailers
|
||
|
|
=====================================================================
|
||
|
|
HYDRA is suitable for use in FidoNet mailers. It can be implemented
|
||
|
|
for EMSI and FTS-6 mail sessions. The FTS-6 (YooHoo) capability bit
|
||
|
|
for HYDRA is 0x0020 (DOES_HYDRA). The EMSI and IEMSI protocol
|
||
|
|
capability flag is HYD.
|
||
|
|
|
||
|
|
When utilizing HYDRA in a mail session, two complete batches are
|
||
|
|
always performed. Little else differs from a normal FTS-6 ZedZap mail
|
||
|
|
session. The first batch is used to transmit all mail, files, and
|
||
|
|
file requests by both sides. The second batch is always performed,
|
||
|
|
sending nothing if there are no file requests to honor. The data
|
||
|
|
buffers are not purged between the two batches since HYDRA ignores
|
||
|
|
any leftovers from the previous batch (END packets, etc.).
|
||
|
|
|
||
|
|
To integrate HYDRA into an existing mailer, the same code used for
|
||
|
|
the ZedZap session flow can be used, but instead of one transmit and
|
||
|
|
one receive session, two transmit sessions (or batches) are used.
|
||
|
|
When the HYDRA end of batch is initiated it will not be terminated
|
||
|
|
until an end of batch has been received from the remote and the end
|
||
|
|
of session sequence has been finished.
|
||
|
|
|
||
|
|
Fido and FidoNet are registered marks of Tom Jennings and Fido
|
||
|
|
Software.
|
||
|
|
|
||
|
|
|
||
|
|
Error detection using CRCs
|
||
|
|
=====================================================================
|
||
|
|
CRC (Cyclic Redundancy Check) values only provide their promised
|
||
|
|
maximum error detection capability when properly applied, which
|
||
|
|
involves calculating and transmitting low-bit first, presetting the
|
||
|
|
CRC with all ones, and transmitting the ones' complement of the
|
||
|
|
result. The receiver also initializes to all ones, processes all of
|
||
|
|
the data AND the following CRC, and the result should match a "magic
|
||
|
|
value" which is 0xf0b8 for the 16-bit CRC and 0xdebb20e3 for the
|
||
|
|
32-bit CRC.
|
||
|
|
|
||
|
|
The easiest and fastest way to perform CRC calculations is by using a
|
||
|
|
table that does the algorithm's shift-operations in 8-bits at a time.
|
||
|
|
|
||
|
|
|
||
|
|
CRC-16 error detection
|
||
|
|
---------------------------------------------------------------------
|
||
|
|
16-bit CRC using the CCITT CRC-16 polynomial. This is the default at
|
||
|
|
startup, and always used for HEX packets even if both sides are
|
||
|
|
capable of handling 32-bit CRCs.
|
||
|
|
|
||
|
|
This CRC-16 is not identical to the one used by the Xmodem and Zmodem
|
||
|
|
file transfer protocols. The polynomial is the same
|
||
|
|
(X^16+X^12+X^5+X^0 or 0x8408) but the bit-ordering is the opposite,
|
||
|
|
and preconditioning and postconditioning is used as in 32-bit CRCs.
|
||
|
|
This method is also used by the European version of X.25.
|
||
|
|
|
||
|
|
The 16-bit CRC table is created as follows (pseudocode, the variable
|
||
|
|
CRC16 and the table of 256 entries are 16-bit unsigned integers):
|
||
|
|
|
||
|
|
FOR (i=0 TO 255)
|
||
|
|
{
|
||
|
|
CRC16=i
|
||
|
|
FOR (N=1 TO 8)
|
||
|
|
{
|
||
|
|
IF (CRC16 AND 1)
|
||
|
|
CRC16=(CRC16 >> 1) XOR 0x8408
|
||
|
|
ELSE
|
||
|
|
CRC16=CRC16 >> 1
|
||
|
|
}
|
||
|
|
CRC16TAB[i]=CRC16;
|
||
|
|
}
|
||
|
|
|
||
|
|
When processing data, each byte is run through the CRC calculation
|
||
|
|
routine as follows (variable CRC stores the 16-bit CRC value/result,
|
||
|
|
C is the next 8-bit char):
|
||
|
|
|
||
|
|
CRC=CRC16TAB[(CRC XOR C) AND 0xff] XOR ((CRC>>8) AND 0x00ff)
|
||
|
|
|
||
|
|
|
||
|
|
CRC-32 error detection
|
||
|
|
---------------------------------------------------------------------
|
||
|
|
32-bit CRC using the CCITT CRC-32 polynomial. Support of CRC-32 is
|
||
|
|
optional and signalled in the INIT packet.
|
||
|
|
|
||
|
|
If both sides indicate they can handle CRC-32, all packets except
|
||
|
|
those transmitted in HEX format use this algorithm instead of CRC-16
|
||
|
|
to improve error detection.
|
||
|
|
|
||
|
|
This CRC-32 is identical to the one used by the Zmodem protocol.
|
||
|
|
The polynomial is (0xedb88320):
|
||
|
|
|
||
|
|
X^32+X^26+X^23+X^22+X^16+X^12+X^11+X^10+X^8+X^7+X^5+X^4+X^2+X^1+X^0
|
||
|
|
|
||
|
|
The principal method of calculation, transmission, and checking is
|
||
|
|
identical to CRC-16 as described above, but the "magic value" for
|
||
|
|
32-bit CRC is 0xdebb20e3.
|
||
|
|
|
||
|
|
The CRC-32 table is created as follows (pseudocode, the variable
|
||
|
|
CRC32 and the table of 256 entries are 32-bit unsigned integers):
|
||
|
|
|
||
|
|
FOR (i=0 TO 255)
|
||
|
|
{
|
||
|
|
CRC32=i
|
||
|
|
FOR (N=1 TO 8)
|
||
|
|
{
|
||
|
|
IF (CRC32 AND 1)
|
||
|
|
CRC32 = (CRC32 >> 1) XOR 0xedb88320
|
||
|
|
ELSE
|
||
|
|
CRC32 = CRC32 >> 1
|
||
|
|
}
|
||
|
|
CRC32TAB[i] = CRC32;
|
||
|
|
}
|
||
|
|
|
||
|
|
When processing data, each byte is run through the CRC calculation
|
||
|
|
routine as follows (variable CRC stores the 32-bit CRC value/result,
|
||
|
|
C is the next 8-bit character):
|
||
|
|
|
||
|
|
CRC=CRC32TAB[(CRC XOR C) AND 0xFF] XOR ((CRC>>8) AND 0x00ffffff)
|
||
|
|
|
||
|
|
|
||
|
|
The authors
|
||
|
|
=====================================================================
|
||
|
|
The authors can be reached at the following addresses:
|
||
|
|
|
||
|
|
Joaquim H. Homrighausen Arjen G. Lentz
|
||
|
|
389, route d'Arlon Lentz Software Development
|
||
|
|
L-8011 Strassen Langegracht 7B
|
||
|
|
Luxembourg 3811 BT Amersfoort
|
||
|
|
The Netherlands
|
||
|
|
joho@ae.lu
|
||
|
|
FidoNet 2:270/17 aglentz@fido.lu
|
||
|
|
FidoNet 2:283/512
|
||
|
|
|
||
|
|
|
||
|
|
The name HYDRA
|
||
|
|
=====================================================================
|
||
|
|
Hydra is a greek mythological creature (the watersnake). Like the
|
||
|
|
Nemeic lion, Hydra is the daughter of the giant Typhon and the snake
|
||
|
|
Echidna.
|
||
|
|
|
||
|
|
She grew up in the marshes of Lerna near/in Argolis (Argos). There
|
||
|
|
she ate entire herds of cattle and destroyed large cropfields. Later,
|
||
|
|
she lived in caves on a hill near the spring of Amymone.
|
||
|
|
|
||
|
|
Hydra is a monstrous large snake with nine heads: eight mortal ones,
|
||
|
|
and one (the middle one) immortal. She was defeated and killed by
|
||
|
|
Heracles (Hercules) - son of Zeus and Alcemene, grandson of Perseus -
|
||
|
|
as the second of his twelve tasks, with the help of his cousin
|
||
|
|
Iolaos. Every time he cut of one of the heads with his sword, two new
|
||
|
|
heads grew in its place. So Iolaos scorched the wound of each cut off
|
||
|
|
head with burning branches so the head couldn't grow on again.
|
||
|
|
|
||
|
|
Heracles buried the last and immortal head under a stone nearby. He
|
||
|
|
also dipped his arrows in Hydra's poisonous blood, thereafter the
|
||
|
|
wounds caused by those arrows were incurable.
|
||
|
|
|
||
|
|
|
||
|
|
Also star constellation (sign of the watersnake) in the equatorial
|
||
|
|
zone.
|
||
|
|
|
||
|
|
|
||
|
|
Also a type of sweetwater polip (the Hydroidea Thin, tubeshaped body
|
||
|
|
can be full contracted, just like the six (or more) tentacles. There
|
||
|
|
is no generation change, the gender-products grow directly on the
|
||
|
|
body.
|
||
|
|
|
||
|
|
The animals catch their prey with nettlecells, and are very verocious.
|
||
|
|
They can be found in various stilstanding and flowing water and were
|
||
|
|
first described by Anthonie van Leeuwenhoek in the year 1704.
|
||
|
|
|
||
|
|
|
||
|
|
Also small island (spelled Idhra in modern Greek) of the Sargonic
|
||
|
|
group in the Aegean Sea, just of the eastern tip of the Argolis
|
||
|
|
peninsula of the Peloponesus (Attika). Its length (NE/SW) is 21 km,
|
||
|
|
with a total area of 49,6 square km. Its highest point is 597 meters
|
||
|
|
above sea level. Population of 2794 (latest census: 1981). Only one
|
||
|
|
real city with the same name as the island. Once quite wooded and
|
||
|
|
well watered, now denuded and dry, with almost no arable land
|
||
|
|
(infertile limestone). Certain times of the year the people have to
|
||
|
|
ship in water from the main land. Its Turkish name is Camliza which
|
||
|
|
means "Place of Pines".
|
||
|
|
|
||
|
|
References:
|
||
|
|
Dutch: Oosthoeks Encyclopedie
|
||
|
|
Grote Winklerprins Encyclopedie
|
||
|
|
English: Encyclopaedia Brittannica
|
||
|
|
|
||
|
|
</PRE>
|
||
|
|
|
||
|
|
<A HREF="index.htm"><IMG SRC="../images/b_arrow.gif" ALT="Back" Border="0" width="33" height="35"> Go Back</A>
|
||
|
|
|
||
|
|
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|
||
|
|
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|
||
|
|
|