Subject: An Alternate Approach to SNA over IP

From: Robin Layland <[email-masked]>
Date: Wed, 22 Sep 93 16:49 GMT

Quick Reply to Shannon proposal:

>When we at Netlink began thinking about SNA over IP a couple years ago,
>we were favoring a different approach from the one this group has undertaken.  
 
>The key difference is:
 
>With DLSW, IBM has chosen to multiplex SNA data links over one or more 
>reliable TCP connections.  While we considered this approach, we were favoring 
>encapsulating LLC-2 sessions inside of IP datagrams.
 
1. Thee is a big problem with assume that people can having properly tuned LLC
endpoint. That requires changing every end-station plus it needs to be done at
once since LLC2 pacing doesn't exchange values. Get properly tuned LLC 2 is very
hard in any size network from my experience (I tried).
 
2. This doesn't solve the LLC2 time out problem. Again, with properly set values
there is no problem (see #1)
 
3.This doesn't solve the problem of SDLC to LLC2. Someone must convert.
 
4. The LLC flow control is end-to-end. How does the intermediate (router)
station slow things know and ensure fairness.

Some more at the next meeting.
 
Robin Layland

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From: "Alan K. Bartky, Manager of Technology" <[email-masked]>
Date: Wed, 22 Sep 93 11:08:24 PDT

Shannon - 

A couple of comments

One of the problems that DLSw/SSP is supposed to solve
is the fact that IP networks can't always guarantee LLC RR response time
in bridging environments due to things like no priority, IP bursts, etc.
If nothing else you would have to address this.

DLSw is supposed to guarantee this to not happen by breaking up
an end to end LLC connection used in bridging into an LLC to Router
connection, a Router to Router connection using SSP, and then another
LLC to end station connection.

Running LLC over IP is an interesting idea but I don't think it
applies to the DLSw SIG goals.  In addition there are other vendors that
have implemented SNA to IP conversion (e.g. RAD and McData).  McData has
promised to submit their proposal as an RFC to the IETF (It was also 
summarized by handouts at Interop).  It is a much simpler approach that
replaces LLC with TCP/IP with simple headers.  It is a much simpler approach
for just plain conversion of SNA over IP and is worth considering by
end system vendors that do not do want to implement DLSw/SSP but would
like to simply do conversion.  I don't know what RAD's approach is but
from what I have read, it is similar.

DLSw is more of a protocol that is appropriate to routers, it is one that
is implemented by IBM and it is the main focus of the group.  You yourself
indicated the importance of interoperability with current 6611s in
your contributions.  It is important we keep working with DLSw in
documenting how it works and add the features as specified in the working
groups.

I think that alternatives to DLSw could be discussed in a different group
than the DLSw SIG.  I certainly think the McData approach (or others)
should discussed as alternatives when only simple conversion is desired,
but not in the DLSw SIG.

Regards,

Alan K. Bartky
Mgr. of Technology
Sync Research

P.S. Does IBM have opinions on McData's or other SNA conversion approaches
besides DLSw?

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