[Sis-SCPS-INTEREST] SCPS + WAN Compression

[Frank Lynam]

Hi Pat,

Thanks for the quick response. I now have the following setup:

[LOCAL RFILE]

BIF_BUF		1000000
BIF_RATE		440000
BIF_CC		2

[LOCAL CODE]

sWAN->rt_route->current_credit -= (currentbuffer->size /
current_compression_ratio);
Note that I'm not editing sWAN->rt_route->min_current_credit as I don't have
MIN_RATE_THRESH defined.

[REMOTE RFILE]

BIF_BUF		1000000
BIF_RATE		4000000
BIF_CC		2

[REMOTE CODE]

NO CHANGES

[NETWORK]

NISTNET NET SIMULATOR: RTT=900->2400msecs, BANDWIDTH=400000bps

I am doing FTP uploads from the local LAN. I now get a slight improvement
(average 78KBps) overall. Looking at the data throughput from the PC, it
looks like the entire BIF_BUF amount is accepted by the LOCAL SCPS peer at
the start of the transfer and then it slowly builds to just above the
network bandwidth (50KBps). This improvement doesn't equate to the
compression ratio (around 10 to 1 in places) of the packets. Looking at a
NISTNET real-time network bandwidth display shows that the bandwidth is not
being fully utilized. Sometimes it's as low as 10KBps.

What do you think?

Best regards,

Frank Lynam

-----Original Message-----
From: sis-scps-interest-bounces at mailman.ccsds.org
[mailto:sis-scps-interest-bounces at mailman.ccsds.org] On Behalf Of Feighery,
Patrick D.
Sent: 09 June 2006 15:33
To: Frank Murray; sis-scps-interest at mailman.ccsds.org
Cc: Cian Masterson
Subject: RE: [Sis-SCPS-INTEREST] SCPS + WAN Compression

You are on the right track with your question about the rt->route structure.
Essentially this structure contains information that is shared amount
different connection's control blocks - this includes the rate control
mechanisms.

There are two fields in the rt_route structure
	current_credit
	min_current_credit

These values are decremented in tp_output.c when a packet have been emitted,
by the size of that packet.  You need to adjust these two variables
accordingly.

Now as for the buffer sizes -- SCPS needs to buffer data at the sender in
case retransmission is necessary and buffer data at the receiver in case it
was received out of order.  Just because you compress the data over the RF,
SCPS still needs to buffer it.  The buffer size control the maximum amount
of data that can be emitted by the sender, until it receives an
acknowledgement by the receiver.  Typically in a gateway environment, as a
rule of thumb, I set the buffer sizes to twice the
bandwidth delay product.   So if the bandwidth is 1Mbps and the round
trip delay is 600 msec or 150 KBytes.

By compressing the data, you are essentially increasing the bandwidth of the
pipe; thus the buffer sizes will need to be increased.  You many to need to
experiment a bit for an 'optimal value' based on both single and multiple
flows.

Does this make sense..

	Pat


>>-----Original Message-----
>>From: sis-scps-interest-bounces at mailman.ccsds.org
>>[mailto:sis-scps-interest-bounces at mailman.ccsds.org] On Behalf Of 
>>Frank Murray
>>Sent: Friday, June 09, 2006 9:23 AM
>>To: sis-scps-interest at mailman.ccsds.org
>>Cc: Cian Masterson
>>Subject: [Sis-SCPS-INTEREST] SCPS + WAN Compression
>>
>>
>>
>>Hi all,
>>
>>We are using SCPS in gateway mode to accelerate TCP traffic running 
>>over a satellite link. Native IP is used as the network protocol.
>>For congestion
>>control we are using Vegas. I've got a question about compressing data 
>>on a per packet basis after it has left SCPS on the WAN side. The 
>>setup looks something like this:
>>
>>LAN INTERFACE
>>|
>>SCPS
>>|
>>COMPRESS/DECOMPRESS DATA
>>|
>>WAN INTERFACE
>>|
>>SAT LINK
>>|
>>WAN INTERFACE
>>|
>>COMPRESS/DECOMPRESS DATA
>>|
>>SCPS
>>|
>>LAN INTERFACE
>>
>>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 network.
>>
>>Up to now I hold the following assumptions:
>>
>>sWAN->snd_cwnd:		WAN Congestion Window. This is 
>>decremented when new
>>unack'ed data is introduced into the network and incremented when the 
>>data is ack'ed.
>>
>>sWAN->sndwin:		WAN Send Window. This seems to behave as
>>sWAN->snd_cwnd. I presume I'm wrong here.
>>
>>sWAN->snd_awnd:		WAN Receive Window Of Remote 
>>Peer. Again this is
>>decremented when new unack'ed data is introduced into the network and 
>>incremented when the data is ack'ed.
>>
>>All these variables are decremented in tp_iovCoalesce. I have tried 
>>updating this change proportionally using the current compression 
>>ratio. However the transfer still seems to be limited by the BIF_RATE 
>>and BIF_BUF parameters set at SCPS startup. If I set BIF_RATE and 
>>BIF_BUF to be much greater at startup, the WAN throughput increases as 
>>expected. This however isn't an option as it is not dynamic and causes 
>>problems if compression is turned off or it's affects are negligible.
>>
>>I also assume that these variables are incremented as the data is 
>>ack'ed and these too would have to be changed proportionally based on 
>>the compression ratio.
>>
>>Finally I'm not sure what part the sWAN->rt_route structure plays in 
>>the limiting of throughput on the WAN interface. I have noticed though 
>>that the current_credit variable is updated in a similar way to the 
>>variables listed above. The range of values seen here though seem to 
>>be lower.
>>
>>Let me know if you need any further information. I'd greatly 
>>appreciate any help forthcoming.
>>
>>Best regards,
>>
>>Frank Lynam
>>
>>
>>
>>
>>
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>>

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