Subject: [Tsvwg] VoIP and Congestive Collapes: QoS vs. Best Effort

From: Cyrus Shaoul <[email-masked]>
Date: Thu, 03 Jul 2003 00:23:02 -0400

TSVWG list members, 

After lurking for a bit, I wanted to try asking a question of the other
list members. I have been reading the recent IAB draft relating to
congestive collapse of VoIP traffic, called draft-iab-congestion-00.txt,
and I wanted to see if my understanding of the issues relate to the work
of the TSVWG and to the recent draft that Naotaka Morita recently
submitted (draft-morita-tsvwg-pps-00.txt)

As I see it, one way to compare the two is to look at the level of QoS
support in the routers that are assumed. In draft-iab-congestion-00, the
IAB authors assume that all nodes are not capable of Diffserv or other
QoS functions, and all traffic is treated equally with best effort.
Morita's draft assumes that all packet forwarding nodes support Diffserv,
and have configurable PHB. (This is not currently the case, but it may
be the case in the future)

Another comparison is the type of communication targeted. draft-iab-congestion-00
only considers voice, which has a range of 4 to 64kpbs in most cases.
In draft-morita-tsvwg-pps-00.txt, video calls and other broadband
services, around 1Mps per call, are the focus.

A final comparison can be made between the reactive vs. proactive
natures of the solution. One of the conclusions, as I understand them,
of the IAB draft is that in cases of certain specific amounts of congestion
and packet loss, the application should end the call instead of using
any of the remaining resources. I feel that this is a very different
user experience for the one that the VoIP user expects. (Other than
during emergencies, PSTN phone calls rarely terminate in mid-call due to
high call volume). The Morita proposal acts like a preventative measures,
and instead of reacting to congestion, it proactively prevents voice
traffic from ever getting to the point of failing. By using admission
control, the user can be informed of the lack of available bandwidth
before the call begins, reducing the change to the standard telephone user
experience.

Are these two drafts trying to solve different problems? Or are they
solving the same problem in different ways because they begin with
different assumptions?

Thanks for your time, 

Cyrus

Cyrus Shaoul
NTT Advanced Technology Corp.
[email-masked]
http://www.ntt-at.com/

_______________________________________________
tsvwg mailing list
[email-masked]
https://www1.ietf.org/mailman/listinfo/tsvwg

---

From: Sally Floyd <[email-masked]>
Date: Sun, 13 Jul 2003 06:20:34 -0700

>My point as is proposed in the following draft is
>a kind of preventative control or admission control.
>http://www.ietf.org/internet-drafts/draft-morita-tsvwg-pps-00.txt

Thanks for the pointer.  We are planning to add a brief section in the
document with pointers to efforts towards QoS in the Internet (though the
draft only addresses that traffic that might be competing directly
with best-effort traffic on some congested link).

- Sally