Subject: Re:

From: "Ray Bird" <[email-masked]>
Date: Wed, 16 Aug 95 09:26:07 EDT

Dave,
  Thanks for the comments.  My replies follow.

** As it turns out, the only product that has implemented SDLC so far
** is NCP and they do not support UI frames.  So, in order to run
** with NCP, you cannot use UI frames on SDLC.

*I'm sorry, NCP is not the only SDLC product. Do you mean only IBM SDLC
*product*?

Sorry, I meant the only product that has implemented and shipped running
HPR over SDLC.

*I don't understand why it is necessary to preclude SDLC from using UI,
*although I agree it is not a strategic direction for APPN/HPR. Surely
*if NCP (or anything else) knows that it does not support datagrams on
*the underlying DLC, it can simply indicate ERP mode in XID ? Am I
*missing something here ?

If products want to do UI over SDLC we will do it.  However, some
rules regarding polling, send window sizes, etc. need to be decided
on.  This is true especially on multidrop where the secondary stations
cannot send without being polled by the primary.  Perhaps they should
send maxout (maximum window size used for I-frames) UI frames each time
they are polled.  But this approach questions the advantage of using
UI because you have about the same number of flows as when sending
I-frames.  Using UI frames on point-to-point SDLC is easier but it
would still be nice to suggest how many buffers should be allocated
for UI frames.  I am not an SDLC expert so I've probably not covered
everything.  My main point is that it's not quite as simple as
we originally thought and the benefits may not be all that great.

If it is decided to go ahead with UI on SDLC I would still like
the base SDLC support to be non-UI (ERP mode) for HPR so that all HPR
products are capable of interconnecting over SDLC links.

Ray

---

From: Dave Finnie <[email-masked]>
Date: Thu, 17 Aug 1995 07:39:24 +1000

Ray,

I now understand your concerns about SDLC. If there are unresolved
issues, then I'll agree that we don't want to spend time working them
out instead of doing something more productive !

Dave