RE: [pacnog] Allot Netenforcer AC-401

["Alex Abraham" <alex.abraham@samoatel.ws>]

Hi Alo,

I have similar issue where our Retail ISPs are asking how we can maximize
the use of the links.  Based on the TCP/IP principles I understand that
delay plays an important part in utilization of the links.  

Joe's comments that making changes to the routers will make no difference
because the routers are just forwarding.  There is a Cisco IOS which has a
feature to deal with Satellite latency but it requires the far end to also
have this feature enabled.  

I am interested in how this can be done?  What would you need on both ends
to do implement this?  Also what are the impacts?  The issue I can see is
that you can run out of bandwidth faster than if you had this not enabled.
Is this correct?

Thanks.

Alex


-----Original Message-----
From: pacnog-bounces@pacnog.org [mailto:pacnog-bounces@pacnog.org] On Behalf
Of Alo Anesi
Sent: Monday, 20 November 2006 12:34 p.m.
To: pacnog@pacnog.org
Cc: pacnog@pacnog.org
Subject: [pacnog] Allot Netenforcer AC-401

All-

Thanks for the replies to my TCP/IP question.

On a related note, is anyone else using the Netenforcer from Allot
Communications?

So far, we've had good experiences, but are now running into a problem
bandwidth will start to degrade by about 2M. Restarting the flows clears the
problem and bandwidth jumps back up to 6.5M and above, but we're having to
do this daily. Support has been unable to find any problems, and I was
hoping someone had any insight.

Thanks,
Alo	

-----Original Message-----
From: Joel Jaeggli [mailto:joelja@uoregon.edu] 
Sent: Sunday, November 19, 2006 6:57 AM
To: Alo Anesi
Cc: pacnog@pacnog.org
Subject: Re: [pacnog] TCP Send/Receive Window



Alo Anesi wrote:
> I have a 7.5Mb down by 2.5Mb up satellite connection with about 700ms
latency. Would there be any reason to look into modifying the TCP
Send/Receive window on my 7206VXR gateway router? Would I ever need to
change it for this router? If so, how much bandwidth can I scale up to on a
satellite connection?

If you need to move data from your router over the link then playing
with window scaling might be a good idea. However in this case the knob
you really want to tweak is actually on the end hosts since the router
isn't meddling with the receive window of flows going through it (there
are middle boxes that do this).

You probably already know this, but bandwidth delay product (the size
you need the window set to in order to achieve a given throughput given
a certain amount of latency is expressed as:

bandwidth × delay product = link capacity (which is also the size of the
receive window required to fill the link.

7.5Mb/s with 700 ms rtt = requires an rwin of about 640KB.

Of course you probably don't want to fill the link with only one flow,
but tcp slow-start will prevent that in the presence of other traffic
anyway. On some platforms (ie linux) you can set your tcp congestion
avoidance algorithm via a sysctl which in conjunction with a a larger
rwin can dramatically increase your link utilization for a given flow
but not all algorithm's play nice with others...

> Thanks,
> Alo
> 
> _______________________________________________
> pacnog mailing list
> pacnog@pacnog.org
> http://mailman.apnic.net/mailman/listinfo/pacnog

-- 
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Joel Jaeggli             Unix Consulting              joelja@uoregon.edu
GPG Key Fingerprint:   5C6E 0104 BAF0 40B0 5BD3 C38B F000 35AB B67F 56B2

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