Subject: RE: Routing for UDP/real-time vs TCP

From: "Mangtani, Robindhra" <[email-masked]>
Date: Thu, 5 Oct 2000 14:27:49 +0100

Bogdan, can give some comments on the router question
 
Routers discard traffic when experiencing congestion in the Wide Area,
packets are not usually discarded as a result of protocol or port numbers
unless policies are set up to deliberately do this e.g IP precedence bits
mapping to WFQ classes. Weighted Fair Queueing is usually switched on  by
default for <2Mbit/s WAN links, this would ensure small packets such as ICMP
packets get serviced along with larger packets e.g FTP. The set-up for WFQ
can prioritise segregating traffic into multiple flow or classes and then
scheduling traffic on outputs to meet specified bandwidth allocation.
Therefore I believe your assumption would be correct, particularly when
using DiffServ at Ingress resulting in Priority at Egress based on a policy
which may rely on Precedence bits, source/dest IP address, Port no etc.
 
Regards, Robindhra

 

-----Original Message-----
From: Bogdan Ghita [mailto:[email-masked]]
Sent: Thursday, October 05, 2000 09:04
To: [email-masked]
Subject: Routing for UDP/real-time vs TCP

Dear all
 
I have a question related to general routing issues:
I am looking into measuring RTT for a specific path using 2 different
methods: TCP acknowledgements and RTCP NTP/LSR/DLSR fields.
Is there any specification regarding different handling by the servers of
packets that carry TCP segments vs packets carrying UDP datagrams? I had
several discussions lately about how some/all routers tend to drop first
ICMP traffic, then TCP traffic and, at the end, UDP traffic, as the first
category is not critical and the second can recover. If so, it would mean
that there are several different transport performance rates for the same
path, depending on the type of traffic being sent. Are the
assumption/conclusion correct? Could you point me to some materials that
detail this matter?
 
Thank you very much
 
Best regards
Bogdan Ghita