Subject: SNA, IP, and MPTN

From: "Jim (J.) Cobban" <[email-masked]>
Date: Fri, 30 Apr 1993 11:16:00 +0000

It seems to me that using TCP/IP to provide the reliable data-link
connection for SNA, as is done in DLS, is an unnecessarily expensive
implementation.  That is DLS places the logical link control sub-layer of
SNA data link control on top of the transport layer of TCP/IP.  This causes
several layers worth of duplicate functionality to be performed.  It also
does not agree with the architectural direction proposed in the
Multi-Protocol Transport Network model.

This discrepancy becomes even more obvious when the evolution of APPN to
high-performance routing is considered.  In HPR the reliable logical link
control of SDLC is abandoned, the connection-oriented network (path control)
layer is replaced with an IP-like (or CLNP-like) connectionless network
layer, and the required reliable connection-oriented transport is
re-inserted by a TP4-like transport layer.

Although this point is beyond the immediate concern of the DLS working
group, it would seem to me that DLS, as currently conceived, is only a
short-term solution to the problem of carrying SNA over an IP network.
Therefore, rather than making DLS perfect we should invest some effort in
the question of how to provide the SNA transport semantics, required for APPN
over HPR, over an underlying TCP/IP (or TP4/CLNP) fabric.

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From: John Pickens <[email-masked]>
Date: Fri, 30 Apr 93 09:13:57 -0700

I suggested at the last AIW that in June we have an extended discussion
about APPN/ISR and APPN/HPR link layer alternatives - as you suggest,
APPN/HPR over IP is one candidate (RTP/ANS/IP).  I still think DLS
should be standardized in its current form, as it is a transitional
layer 2 extended bridging method for SNA and Netbios traffic.  The
work on more optimized flows then can be reserved for SNA routing,
i.e. APPN.

JP