An ARPANET update


Ken Pogran (pogran@ccq.bbn.com)
Tue, 15 Dec 87 19:01:04 EST


Several problems with regard to the New End-to-End Protocol
deployed on the ARPANET with PSN Release 7 were discussed in
messages to this list over the past couple of days. Here's a
report on what we at BBN have uncovered so far.

We are working on three general problems and one problem that is
specific to a particular host. The "general" problems affect
communication with some hosts (including some gateways) connected
to the ARPANET with X.25 interfaces.

1. The "one packet problem." The scenario has been described by
    several folks, and runs about like this: An 1822-connected
    gateway has traffic for an X.25-connected host. Sending the
    first datagram into the net causes an X.25 VC to be opened to
    the destination host. One and only one packet is received by
    the host, and the flow stops. Various events can cause the
    flow to become "unblocked", such as sending traffic FROM the
    host back over the same VC. This problem has been observed
    with several, but by no means with all, DDN Standard X.25
    implementations.

    This problem has especially been seen in situations where an
    X.25-connected ARPANET host establishes communication with a
    MILNET host (or vice-versa). In this situation, because of
    the Mailbridge "homing rules", traffic often flows across a
    different Mailbridge in each direction. Thus, user data flow
    is essentially unidirectional across each of two VCs. With
    other patterns of communication, a symmetric, bidirectional
    user data flow would generate one of those "events" that
    seems to "unblock" the flow over the VC.

    This problem is not observed in communication between pairs
    of hosts that are BOTH X.25-connected, or BOTH



This archive was generated by hypermail 2.0b3 on Thu Mar 09 2000 - 14:40:15 GMT