Subject: Question on hop-by-hop versus end-to-end in HPR

From: "Marcia Peters (8-444-4380)" <[email-masked]>
Date: Fri, 8 Oct 93 09:41:38 EDT

Robin Layland sent the following question and OK'd my sharing the
answer with the SIG.

> Marcia...When in a HPR environment and using Adaptive rate flow control
> (instead of in a ISR and adaptive flow control environment) are the
> intermediate Network Nodes involved in (a) session pacing and (b)
> network level pacing.  If I have four network nodes my understand under
> the older APPN is that each NN is involved in pacing (a hop by hop
> involvment).  With HPR is only the first and last NN involved?  Another
> way of asking is:  Is the flow control at the RTP level and thus the
> intermediate NN don't get involved or is it still Hop by Hop at the HPR
> level?
>
> Thanks.....Robin Layland

Let's say we have the following HPR configuration (maybe not very
realistic, but illustrative):

                            :
APPN       APPN       APPN  :  HPR         HPR         HPR
 EN         NN        NN    :   NN         NN           EN
+---+     +---+      +---+  :  +---+       +---+       +---+
| A |-----| B |------| C |-----| D |-------| E |-------| F |
+---+     +---+      +---+  :  +---+       +---+       +---+
                            :

Adaptive session level pacing is performed between A(LU)-B(ISR),
B(ISR)-C(ISR), C(ISR) and F(LU).  Adaptive BIND pacing is performed
between ASM components in the same node pairs:   A-B, B-C, and C-F.

An RTP connection is established between D and F. ARB is performed only
between D and F. E is not involved with (1) adaptive session pacing (2)
adaptive BIND pacing, or (3) ARB.  During stead-state data flow, E just
(1) checks checksums and discards any errored incoming packets (2)
routes packets and (3) honors the priority indicated in the
network-layer header.

HPR eliminates all hop-by-hop elements of procedure.

Marcia Peters ................................ IBM Networking Systems