Subject: Proposal for APPN Class of Service

From: "J. G. Dudley (444/4358)" <[email-masked]>
Date: Mon, 31 Jul 95 16:34:17 EDT

Jim Cobban has made a very thoughtful proposal that includes TG
characteristics for the QoS services of a public data switched network
and modified COS tables.  I would like to suggest a way to improve his
proposal.

When a subnet offers multiple service levels (such as priority or delay
sensitivity as Jim suggests), the TG characteristics should be defined
in a manner that suggests the real trade offs that route selection must
make.  For example, a high priority service offers less delay but at
higher cost than a lower priority service.  Likewise, I believe a
delay-sensitive service would offer similar cost and delay trade offs
relative to a satellite service.  I'm not sure how delay and cost compare
between a high-priority satellite circuit and a low-priority delay-sensitive
circuit, but the following TG characteristics illustrate the idea.

            lowpri/sat  lowpri/delsen   hipri/sat   hipri/delsen
Cost/byte       64           128           144         192
Delay           99            91            81          71

Use of TG characteristics such as these may not eliminate the need for
COS table modifications because the current COS tables did not anticipate
all services that are now available.  However, such characteristics should
remove the need for COS tables that appear to favor more expensive circuits
that offer no improvement in delay, capacity, or security; as a result,
the tables should be easier to change for other services as they become
available.

Gary Dudley
IBM APPN Architecture Team