From: Chuck Church (cchurch@xxxxxxxxxxxx)
Date: Sun Jun 03 2001 - 12:20:44 GMT-3
Roman,
I don't think that neither RTP nor TCP header compression touch the
layer 3 (IP) header. Only the layer 4. Otherwise, every router would have
to decompress it to find the destination. But if an intermediary router has
an extended ACL which needs to look at layer 4 info, I'm not sure what will
happen on a compressed packet. Guess I've got something to play with later
on today!
Chuck
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
Roman Rodichev
Sent: Sunday, June 03, 2001 3:06 AM
To: ccielab@groupstudy.com
Subject: RTP header compression
This question was bothering me for a long time. RTP header compression
reduces IP/UDP/RTP header size from 40 bytes to 2-4 bytes. I suppose that
happens only each hop (between two adjacent routers). I still don't
understand how receiving router will recognize what's in the packet? Does
anyone know approximate header structure of the header-compressed RTP
packet?
IP header is 20 bytes.
1-Version,1-TOS,2-Length,2-ID,2-Fragm,1-TTL,1-Type,2-Checksum,4-Source,4-Des
t.
If the header gets compressed down to 2 bytes (including UDP and RTP), how
will receiving router identify that it is an IP packet, that it has protocol
number 17 (UDP) and what the source/destination is?
Is there a different Ethertype or something? I don't get it
Roman
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