[Serusers] UDP Fragmentation Problem

[Giudice, Salvatore]

How large are the sip messages? Do you have an SBC deployed at one/both
locations?

I've observed that SER will truncate message that it forwards if they
become too large. This is usually happens with two clients behind an SBC
when large via parameter have been inserted to maintain SBC state within
the sip dialog. Both Ingate and Jasomi products do this for example. The
result of these large via's is that the message become too large and SER
tend to truncate the SDP portion of the message. The connection
generally sets up with regard to signaling, but the media path always
fails.

I have observed this behavior while making a sip to sip call between two
xten clients, both positioned behind an ingate separator. Both clients
were registered to the same SER with RtpProxy (Redhat Enterprise AS
3.0).



-----Original Message-----
From: Andrei Pelinescu-Onciul
[mailto:pelinescu-onciul at fokus.fraunhofer.de] 
Sent: Monday, November 01, 2004 12:32 PM
To: Bastian Schern
Cc: serusers at lists.iptel.org
Subject: Re: [Serusers] UDP Fragmentation Problem

On Oct 30, 2004 at 01:28, Bastian Schern <ml01 at in-bln.de> wrote:
> Hi everybody,
> 
> I've got no success to get a friend in Bogota (Colombia) connected to
my 
> SER. He has got a ISDN Internet connection and the UDP packets will be

> fragmented. It seems that the MTU of this connection is round about
400 
> to 500 Bytes. Therefore most UDP-SIP packages are fragmented.
> Is SER not able to handle fragmented UDP packages?

The packets are defragmented by the ip stack of the OS, so ser doesn't
really care if they arrive fragmented or not.

> Is it possible to use SIP over TCP with X-Lite?
> Or has somebody another hint for me?

If you plan to use TCP, keep in mind that nat traversal won't work (if
you use it).


Andrei

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