From: Roman Rodichev (rodic000@xxxxxxxxxxx)
Date: Sun Jun 03 2001 - 14:35:27 GMT-3
Hey, that's cool! :) But... Remember my question? How does the receiving
router know what is in the packet?
>From: "Joe Martin" <jmartin@gte.net>
>To: "Chuck Church" <cchurch@MAGNACOM.com>, "Roman Rodichev"
><rodic000@hotmail.com>, <ccielab@groupstudy.com>
>Subject: RE: RTP header compression
>Date: Sun, 3 Jun 2001 08:40:48 -0700
>
>Actually IP RTP HEADER-COMPRESSION does compress the IP/UDP/RTP header from
>40 bytes (IP=20, UDP=8, RTP=12) down to 2-4 bytes total. Due to this it is
>a hop-by-hop method of compression/decompression. It also tax's the CPU
>heavily as such. CEF is helping with this loading but you must be aware of
>limitations on the quantity of simultaneous calls passing thru the router
>using cRTP. For example a 2600 can handle about 24 simultaneous calls with
>cRTP before the CPU load gets tooo high for it to do other things. While
>cRTP seems to be an awsome tools, remember that is designed for low
>bandwidth situations where the quantity of calls is small.
>
>Joe
>CCIE #5917
>
>-----Original Message-----
>From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
>Chuck Church
>Sent: Sunday, June 03, 2001 8:21 AM
>To: Roman Rodichev; ccielab@groupstudy.com
>Subject: RE: RTP header compression
>
>
>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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