Subject: [AVT] Re: [MMUSIC] RTP packets and MTU

From: Magnus Westerlund <[email-masked]>
Date: Tue, 09 Sep 2003 17:01:54 +0200

Hi Lorenzo

First, lets move this question to AVT where it belongs.

No, you can't fragment the RTP packet over multiple UDP packets as there 
is no fragmentation and reassembly mechanisms on this level. You will 
have to either rely on IP-fragmentation or use RTP payload level 
fragmentation.

It is recommend that one ensures that the RTP payloads one want to send 
is smaller than the MTU. The best way is to let the encoder produce 
output that are suitable to the network.

Some payload formats has a mechanism for fragmenting the ADU. However 
fragmentation of application data (ADU) units should always be avoided.

When it comes to MPEG-2 please read RFC 2250 which seems to have clear 
rules on how to fragment slices.

Best Regards

Magnus

Lorenzo wrote:

> Hi all,
> 
> I have a question about the RTP packet encapsulation in UDP packet. I have
> to send MPEG2 Elementary Stream (ES) video frame over RTP. First of all: can
> I fragment an RTP packet across some UDP packets or it is mandatory to
> insert the entire RTP packet in the UDP packet payload? and about MPEG2: can
> I fragment an MPEG slice in two or more RTP packets?
> I have a UDP Maximum Segment Size (MSS) of 1460 byte and I can encapsulate
> easly an entire MPEG slice in a UDP packet, but if I had a little MTU, i.e.
> 256 byte?
> 
> Best Regards,
> Lorenzo
> 
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-- 

Magnus Westerlund

Multimedia Technologies, Ericsson Research EAB/TVA/A
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