From: [email-masked] (Himanshu C. Shah)
Date: Wed, 16 Jun 93 13:45:29 EDT

<[email-masked]>
Subject: More DLSw RFC related questions/issuess

>In Mr. Himanshu's C. Shah's comment that the DSAP should be hard coded to
>0x04 for SNA frames, we at Sync Research disagree.

>SNA (in IBM manuals) defines using 4, 8, or 0x0c in many of the IBM manuals.
>Sync Research's and Netlink's current SDLC to LLC converters use those SAPs
>and others.  This is required as most 3725s, 45s and 3174 Gateways use SAP
>4 and only 4, and a converter must be able to use SAPs other than 4 in order
>to establish multiple LLC connections between the converter and the remote
>SNA device as each PU requires it's own LLC connection.  Since the remote
>SNA device typically has 1 MAC address and 1 SAP (SAP 4), the converter only
>has one MAC address, so the only way to establish more than one LLC connection
>is to use SAP values other that 4.

Given the nature of SNA where clients are initiating the connections
to server (via test/xid frames), one can form multiple LLC connections
by having DSAP hard-coded to 0x04 and SSAP to any other value, which I
believe you use to denote an SDLC device/port.

By having DSAP set to SSAP in CUR data link ID, you are stuck with
data link ID that represents nothing. For example, if SSAP used is
0x12 (some user configured value), the data link ID formed as per RFC is
DA-SA-0x12-0x12. Neither server nor client produce any LLC frame that
matches this DSAP/SSAP combination. If hard-coded, data link-Id would
look like DA-SA-0x04-0x12.

This is my understanding. Please correct me if I am wrong.

Himanshu.