2002-02-16 21:38:40 +00:00
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<TITLE>Reduced seen-by lines.</TITLE>
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<PRE>
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| Document: FSC-0093
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| Version: 001
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| Date: 13 September, 1996
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| Title: Reduced seen-by lines
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| Author: Frank Ellermann, 2:240/5815.1
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Reduced seen-by lines
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Frank Ellermann, 2:240/5815.1
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Abstract
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--------
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A way to save great amounts (estimated 10 %) of echo mail traffic by
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reducing "seen by" informations, compatible with existing echo mail
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tossers conforming to FTS-0004.
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Definitions
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-----------
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A thorough understanding of FTS-0004 is required, the reader should
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be familiar with PATH and SEEN-BY lines in echo mail, illegal and
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legal echo mail distribution topologies, i.e. dup-rings, as well
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as with some pre-requisite knowledge of zones, 4D and 2D addresses,
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and the "sticky" 2D notation in PATH and SEEN-BY lines.
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PATH: path lines as specified in FTS-0004
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FSB: full seen-by informations as specified in FTS-0004
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TSB: tiny seen-by informations as mentioned in FTS-0004, see below
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RSB: reduced seen-by informations specified below
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dupe: multiple arrival of the same echo mail (e.g. different paths)
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Examples of echo mail distribution topologies
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---------------------------------------------
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In all examples a) to d) echo mail entered at system 1 is sent to
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systems 2 and 3 with FSB 1 2 3. Therefore system 2 (3) knows, that
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system 3 (2) already got this mail, topology a) is perfectly legal.
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a) 1 - 3 b) 1 - 3 c) 1 - 3 d) 1 - 2
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| / | | | / | | X |
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2 2 - 4 2 - 4 2 - 4
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In the exanmples b) and c) both systems 2 and 3 forward all mails
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from system 1 to system 4, these topologies contain a dup-ring and
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are therefore illegal following FTS-0004.
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The examples a) and d) show fully connected polygons with three or
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four nodes. In example d) a mail entered at system 1 is sent to
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systems 2, 3, and 4 with FSB 1 2 3 4. The topologies a) and d) are
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perfectly legal, there are no dupes caused by distribution.
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In example b) each mail entered at system 1 reaching system 4 via
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system 2 carries FSB 1 2 3 4, therefore system 4 will not forward
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such mails to 3. Using TSB at system 2 the same mails would carry
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TSB 2 4, therefore system 4 would forward them to 3 as dupes.
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Note that illegal topologies as in example b) and c) cause dupes
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with either FSB or TSB. The real problem with TSB is example b),
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as it allows for loop mails on the dup-ring 1 - 2 - 3 - 4 - ...
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and vice versa, if no additional checks for dupes are employed.
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With RSB (specified below) systems contained in the PATH are not
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stripped from the seen-by informations, therefore RSB avoid loop
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mail much like FSB.
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FSB algorithm
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-------------
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1) add own system to the PATH.
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2) all area links not contained in the FSB qualify as recipients.
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3) add own address(es) to the FSB set if not already contained.
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4) add recipients to FSB, sort FSB, forward mail to recipients.
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TSB algorithm
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-------------
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1) add own system to the PATH.
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2) all area links not contained in the TSB qualify as recipients.
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3) strip old TSB and start new TSB with own address(es).
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4) add recipients to TSB, sort TSB and forward mail to recipients.
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RSB algorithm
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-------------
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1) add own system to the PATH.
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2) all area links not contained in the RSB qualify as recipients.
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3) strip RSB addresses not matching an address in the PATH, then
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add own address(es) to the RSB set if not already contained.
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4) add recipients to RSB, sort RSB and forward mail to recipients.
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PATH considerations
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-------------------
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There are 2 problems with the PATH kludge as specified in FTS-0004:
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First like in the FSB the addresses in the PATH are 2D, and having
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the same 2D address in different zones is possible. Therefore zone
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gates are required to use the TSB algorithm. Unfortunately the PATH
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is forwarded without regarding zone gating, therefore detection of
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loop mail based solely on the PATH could be erroneous.
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Further FTS-0004 (written 1989) expects future echo mail tossers to
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implement PATH support, but doesn't require this support from old
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implementations. Strictly spoken the PATH is still only an option.
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In some areas of FidoNet (e.g. in zone 2) at least all non-terminal
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nodes are required to fully support the PATH line, therefore this
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problem will probably not show up in praxis. Of course any tosser
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implementing the RSB feature is required to fully support the PATH.
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Summary
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-------
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To show the benfits of RSB compared with FSB assume the following:
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An echo mail travels from node to echo hub, host, major star, echo
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host, hub, and finally arrives at a recipient. Each routing system
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has 10 links, i.e. FSB at the recipient contain 51 addresses, about
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400 characters, but RSB only 15 addresses in about 150 characters.
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Therefore in an echo mail with 2500 characters about 10 % of its
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size can be reduced using RSB in favour of FSB. If this estimation
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is applicable on world wide FidoNet echo mail traffic, RSB can save
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us an immense amount of costs.
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This document can be adopted by the FTSC as FTS, in this case it
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has to be regarded as an addition to FTS-0004 with the extension,
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that all non-terminal nodes are required to support PATH lines as
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specified in FTS-0004.
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For additional informations (e.g. aspects of zone gating) feel free
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to send mails to Frank Ellermann 2:240/5815 or leo@bfispc.hanse.de
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- eof -
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