Subject: RE: [Speermint] Re: UPD ?

From: "Lee, Yiu" <[email-masked]>
Date: Fri, 7 Jul 2006 12:17:21 -0400

Hi Andy,

I work in operator, so I can share some of our experience in regard to
TCP/UDP for SIP. You are right that persistence TCP connection affects
load balancing and fault tolerance schemes, Cullen is also right that IP
fragmentation causes many problems especially our firewalls in
production. We can't avoid the fact that SIP messages are getting bigger
and bigger. So our current way to solve the problem is to have UDP
connection between user-endpoint to our edge SIP proxy (P-CSCF/CMS) and
have TCP connection between proxies. Since PacketCable eMTA connects to
the cable plan directly, so we do not expect any firewall between the
eMTA and our edge SIP proxy. However, the IP fragmentation will become
problem when we introduce PC based soft client to the market for
PacketCable Release 2.0.

Using TCP connection between proxies is a natural decision. Normally
connections between these proxies are long-lived. Also, we don't expect
to have many of those connections between proxies. Since we have
firewall between the edge proxy and other internal proxies or
application servers, TCP can help us to simplify the firewall rules.

Cullen's SIP outbound draft is a potential solution for handling
persistent TCP connection between user endpoint and edge proxy. But this
is a more expensive solution compared to using simple UDP connection.
Another way may help is to use compression to the SDP before sending.
This may help to reduce the total message size. However, if one day the
SIP header size alone is larger than 1300 bytes, then we may have to
work on TCP connection.

Yiu

-----Original Message-----
From: Andrew Newton [mailto:[email-masked]] 
Sent: Friday, June 30, 2006 12:48 PM
To: Cullen Jennings
Cc: Khan, Sohel Q [[CTO]]; [email-masked]; Adam Uzelac
Subject: [Speermint] Re: UPD ?

On Jun 30, 2006, at 12:00 PM, Cullen Jennings wrote:
> My real concern is IETF is acting as if we will move to TCP, 
> deployments are acting as if this is not possible. This mismatch seems

> like a growing problem for us and I am concerned about it. I think 
> that this speermint WG has operators that are connected with the real 
> issues so this seems as good a place as any to discuss this.

For us the UDP vs. TCP issue is much more important on the registrar
part of the network thanks to the ever cursed NAT.  But even with
peering, UDP is better performance wise.  Persistent TCP connections
also tend to cause problems with load balancing and fault tolerance
schemes, which is a big issue.

I do agree that TCP is important and strategies will need to be
developed to better handle it.

-andy

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