[Sis-SCPS-INTEREST] SCPS + WAN Compression

[travis at globalprotocols.com]

Frank,

> At the moment the WAN bandwidth is limited by the throughout of the
> uncompressed data. I am trying to find a way to inform the SCPS system that
> instead of logging the transmit of x bytes for a particular segment, an
> amount of x/[compression ratio] should in fact be logged. The current
> compression ratio is available in real-time as each packet is transmitted.
> Our theory then is that SCPS should be able to increase the rate at which it
> transmits data over the WAN interface as it would then have a correct
> reading of the amount of unack'ed data in the 

My guess would be that you are being throttled by the rate-pacing mechanism.
The token-bucket credit deducted (probably in iovCoalesce(), but maybe in 
tp_Send() immediately after the call to the former) is deducting the size of
the uncompressed segment from the available credit.  What you would really 
like it to do is deduct the size of the compressed datagram...

The simple *test* for this being the case is to just increase the configured 
rates by the anticipated compression ratio and then measure the actual utilization
of the path between the gateways versus the throughput measured by the endpoints.

Two options for addressing these from the old engineering notebooks:

     Construct a feedback control mechanism to dynamically tune the token-bucket
     associated with each interface to conform with the observed compression 
     ratio.

     Construct a feedback mechanism to re-credit the size reduction of the 
     compressed datagram to the token-bucket associated with the interface.

OK... a third option:

     If possible migrate the segment (de)compression into the gateway itself, but 
     depending on how/what is being compressed this might be more disruptive than 
     either of the above. 

Regards,

Eric