[cisco-nas] TCP header compression....questions

[Benoit GRANGE]

> The following doc says it is possible to have fast/cef 
> switching enabled + TCP header 
> compression enabled at the same time.
> 
> http://www.cisco.com/univercd/cc/td/doc/product/software/ios12
> 0/120newft/120t/120t7/rtpfast.htm

I had numerous tries, it seems to be somewhat platform specific, and can kill your box when it decides to process switch instead of cef. Plus it it CPU intensive.

> How much will be the throughput gain (%) for DSL 
> (PPPoE/PPPoA) clients when tcp header 
> compression is enabled? I have heard it goes till 5%, not more.

TCP header compression was done to lower the TCP latency mostly in interactive (telnet) mode which was way too high on 9600 bps PPP lines (a single character to be sent by telnet requested a 40 bytes packet instead of 1 byte in async mode).

I think it is useless for DSL. In this environment you see tons of TCP sessions (for P2P) and header compression can only handle a limited amount (I don't remember how much), and HTTP sessions usually carry big packets where the overhead of the TCP header is negligible.

I would expect the gain to be less than 5% in a real world application, probably more likely 1 to 2%.

Regards,

--
Benoît Grangé
Directeur réseau, Tiscali Télécom
37 rue Greneta, 75002 Paris
Tel: 01 45 08 24 68	
Fax: 01 45 08 20 01