[e2e] TCP Performance with Traffic Policing

Barry Constantine Barry.Constantine at jdsu.com
Wed Aug 17 10:09:32 PDT 2011

Hi Detlef,

The client was running iperf with the "-w 64K" option which controls the client's send buffer.

The server was configured to advertise 4 MB RWIN; I used the client side to control all in-flight data.


-----Original Message-----
From: end2end-interest-bounces at postel.org [mailto:end2end-interest-bounces at postel.org] On Behalf Of Detlef Bosau
Sent: Wednesday, August 17, 2011 11:19 AM
To: end2end-interest at postel.org
Subject: Re: [e2e] TCP Performance with Traffic Policing

On 08/12/2011 04:03 PM, Barry Constantine wrote:
> Hi,
> I did some testing to compare various TCP stack behaviors in the midst 
> of traffic policing.
> It is common practice for a network provider to police traffic to a 
> subscriber level agreement (SLA).
> In the iperf testing I conducted, the following set-up was used:
> Client -> Delay (50ms RTT) -> Cisco (with 10M Policing) -> Server
> The delay was induced using hardware base commercial gear.
> 50 msec RTT and bottleneck bandwidth = 10 Mbps, so BDP was 62,000 bytes.
> Ran Linux, Windows XP, and Windows 7 clients at 32k, 64k, 128k window 
> (knowing that policing would
> kick in at 64K)

What do you mean by 32k, 64k, 128k Window?

You surely don't fix rwnd to a fixed value, because you would undermine 
TCP flow control then.

Are you talking about rwnd? Or about window scaling?

In the latter case, please keep in mind that scaling rwnd to larger 
units might make it difficult to announce small receiver windows, when 
this is necessary e.g. due to load or memory reasons. So, when you scale 
a window in units of 128 kByte, you should careful consider what you're 
doing and whether this is what you really want to do.

Detlef Bosau
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