[Sis-SCPS-INTEREST] SCPS with jitter

[Frank Murray]

Should I set BIF_MINRTO to the minium RTT that I expect (say 700ms) and 
the BIF_SNACK_DELAY to the max deviation from BIF_MINRTO (say 600ms)?

I gave this a try but from a performance point of view it gives similar 
results. I will dig into the traces to get a clearer picture of what's 
happening

Regards,
Frank

Feighery, Patrick D. wrote:

>Keith asked me to pull the traces and take a look a them.
>
>When I looked at the traces, I noticed that each data packet processed
>by NISTNET appears twice in the tcpdump while TCP ACKS only appeared
>once.  This made it a little harder to get a handle of what was going
>on.  The short answer is NistNet's jitter does not preserve packet
>ordering.  Therefore you are getting a plethora of unnecessary
>retransmissions.  Setting the BIF_SNACK_DELAY and also the BIF_MINRTO
>to ensure RTOs do not occur unnecessary should do the trick.  Let me
>know if this helps...
>
>The bigger question is...  Is the jitter that NistNet produces mimic
>the environment you are trying to emulate...
>
>Hope this help. 
>
>	Pat
>
>
>  
>
>>>-----Original Message-----
>>>From: Scott, Keith L. 
>>>Sent: Monday, January 23, 2006 10:43 AM
>>>To: 'frankm at klasonline.com'
>>>Cc: 'sis-scps-interest at mailman.ccsds.org'; Feighery, Patrick D.
>>>Subject: Re: [Sis-SCPS-INTEREST] SCPS with jitter
>>>
>>>Great, thanks.  I'm on the road at the moment and will pull 
>>>the dumps when I get a chance.
>>>
>>> --keith
>>>
>>>
>>>-----Original Message-----
>>>From: Frank Murray <frankm at klasonline.com>
>>>To: Scott, Keith L. <kscott at mitre.org>
>>>CC: sis-scps-interest at mailman.ccsds.org 
>>><sis-scps-interest at mailman.ccsds.org>; Feighery, Patrick D. 
>>><feighery at mitre.org>
>>>Sent: Mon Jan 23 10:38:57 2006
>>>Subject: Re: [Sis-SCPS-INTEREST] SCPS with jitter
>>>
>>>Keith,
>>>I think you're probably right about nistnet reordering the packets.
>>>
>>>I've uploaded 2 dumps to our website:
>>>http://www.klasonline.com/download/Klasrouter/scps_logs/tcp2_krt.log
>>>http://www.klasonline.com/download/Klasrouter/scps_logs/tcp2_nist.log
>>>
>>>tcps_krt.log is taken at the FTP server end of the connection in the 
>>>non-SCPS portion while tcp2_nist.log is taken between the 2 SCPS 
>>>gateways. The FTP client is at 192.168.0.41 and the FTP server is 
>>>192.168.150.254. FYI the link between the SCPS gateways over 
>>>nistnet is 
>>>GRE'd to make it easier to mask all traffic with nistnet.
>>>
>>>Thanks for your prompt reply,
>>>Frank
>>>
>>>Scott, Keith L. wrote:
>>>
>>>      
>>>
>>>>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
>>>>Tel: VoIP 3123 at blueface.ie
>>>>
>>>>
>>>>
>>>>www.klasonline.com - 'making PC encryption easier'
>>>>
>>>>
>>>>_______________________________________________
>>>>Sis-SCPS-INTEREST mailing list
>>>>Sis-SCPS-INTEREST at mailman.ccsds.org
>>>>http://mailman.ccsds.org/cgi-bin/mailman/listinfo/sis-scps-interest
>>>>
>>>>        
>>>>
>>>-- 
>>>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
>>>Tel: VoIP 3123 at blueface.ie
>>>
>>>
>>>
>>>www.klasonline.com - 'making PC encryption easier'
>>>
>>>
>>>      
>>>
>
>  
>

-- 
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
Tel: VoIP 3123 at blueface.ie



www.klasonline.com - 'making PC encryption easier'