From: Joe Martin (jmartin@xxxxxxx)
Date: Sun Jun 03 2001 - 12:40:48 GMT-3
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
This archive was generated by hypermail 2.1.4 : Thu Jun 13 2002 - 10:31:17 GMT-3