Connected: An Internet Encyclopedia
APPENDIX C: CHANGES FROM RFC-1072, RFC-1185
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APPENDIX C: CHANGES FROM RFC-1072, RFC-1185
APPENDIX C: CHANGES FROM RFC-1072, RFC-1185
The protocol extensions defined in this document differ in several
important ways from those defined in RFC-1072 and RFC-1185.
- SACK has been deferred to a later memo.
- The detailed rules for sending timestamp replies (see Section
3.4) differ in important ways. The earlier rules could result
in an under-estimate of the RTT in certain cases (packets
dropped or out of order).
- The same value TS.Recent is now shared by the two distinct
mechanisms RTTM and PAWS. This simplification became possible
because of change (2).
- An ambiguity in RFC-1185 was resolved in favor of putting
timestamps on ACK as well as data segments. This supports the
symmetry of the underlying TCP protocol.
- The echo and echo reply options of RFC-1072 were combined into a
single Timestamps option, to reflect the symmetry and to
simplify processing.
- The problem of outdated timestamps on long-idle connections,
discussed in Section 4.2.2, was realized and resolved.
- RFC-1185 recommended that header prediction take precedence over
the timestamp check. Based upon some scepticism about the
probabilistic arguments given in Section 4.2.4, it was decided
to recommend that the timestamp check be performed first.
- The spec was modified so that the extended options will be sent
on <SYN,ACK> segments only when they are received in the
corresponding <SYN> segments. This provides the most
conservative possible conditions for interoperation with
implementations without the extensions.
In addition to these substantive changes, the present RFC attempts to
specify the algorithms unambiguously by presenting modifications to
the Event Processing rules of RFC-793; see Appendix E.
Next: APPENDIX D: SUMMARY OF NOTATION
Connected: An Internet Encyclopedia
APPENDIX C: CHANGES FROM RFC-1072, RFC-1185