Re: RING vs. ETHER - Theory and practice


John Leong (leong@andrew.cmu.edu)
Mon, 21 Jul 86 14:44:56 edt


Mark,

Re : 802.2 Type 2 operation

802.2 offers you Type 1 or Type 2 operation. Type 1 is pure datagram stuff with
the ARPANET's "take your chance" approach while Type 2 goes the other extreme
and do both flow control and error recovery.

The general idea is that if you are going for a heavy weight Tranpsort Layer
already such as TCP or TP-4, you should leave every thing to that layer and
chose Type 1. If you are going to use light weight Tranpsort layer such as TP-0,
then Type 2 is for you. (Interestingly, IBM is using Type 2 since under SNA,
the link layer is the only level that will do error recovery).

Hence unless we can get IEEE802.2 to create a Type 1.5, we don't think it is
worth our while to spend the cycles required for Type 2. (Actually, having a
Type 1.5 that will do low level acknowlegement but without flow control and
error recovery procedure may be quite useful - particularly for network level
gateway machines).

Leong



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