[Sis-SCPS-INTEREST] SCPS with jitter

[Scott, Keith L.]

I wonder if NISTNET delivers packets out of order when the jitter is
high enough?  That could be bad, but shouldn't be too bad with pure
rate control.

With pure rate control (no congestion control) there's no way to get
stuck in slow start.

Can you tcpdump both ends of the inter-gateway interface?

  --keith


-----Original Message-----
From: sis-scps-interest-bounces at mailman.ccsds.org
<sis-scps-interest-bounces at mailman.ccsds.org>
To: sis-scps-interest at mailman.ccsds.org
<sis-scps-interest at mailman.ccsds.org>
Sent: Mon Jan 23 05:15:45 2006
Subject: [Sis-SCPS-INTEREST] SCPS with jitter

All,
I am currently testing 2 SCPS gateways in the configuration below:

PC1->SCPS GW1---->Satellite simulator--->SCPS Gw2----->PC2

I use nistnet as a sat sim with a round-trip time of 1s and a symmetric
bandwidth of 512K. I'm using FTP to test performance and as it is a 
dedicated link I'm using pure rate control for BIF_CC. The results have
been good and I get to wire-speed very quickly with this setup. I've 
injected errors and the performance is still very good.

Problems arise however when I simulate jitter on the sat sim. I've set 
the jitter to have a standard deviation of 100ms and on 2 in 3 ftp 
uploads I get wire speed as before but on the other I get average 
bandwidths of about 30 kbits/s. The speed never builds up so I'm 
guessing that we get stuck in slow start because an ack gets delayed at
startup. Is this behaviour to be expected with pure rate control?

I switched to Vegas but got similar results. I read in one of the FAQs 
that jitter *can* be interpreted as congestion so played around with
the 
alpha/betta/gamma parameters without things improving but there was an 
amount of trial and error about this. Any advice on how to tune these 
parameters would be great.

Regards,

-- 
Frank Murray
KlasRouter Project Manager
Klas Ltd

-------------------------------------------
mail to : frankm at klasonline.com

Tel: International +353-1-662-4270
Tel: Direct line +353-1-4361768
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www.klasonline.com - 'making PC encryption easier'


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