Capwap Mailing List: Re: CAPWAP and congestion control

[Margaret Wasserman (mrw]

<wgchair hat="off">

Personally, I thought we reached a different conclusion from the  
discussion in Chicago.  I thought that we were going to specify a  
mandatory to implement congestion control mechanism that could be  
turned off when administrators know that the traffic on their network  
will be IP-only and/or when they know that all of the traffic on  
their network is generated by systems that implement some type of  
congestion control.

Margaret



On Aug 28, 2007, at 8:00 PM, Pat Calhoun (pacalhou) wrote:

> Any objections before I go ahead and change the spec? Do we want to  
> run this by the transport ADs and advisors?
>
> PatC
>
> From: Abhijit Choudhury (achoudhu)
> Sent: Tuesday, August 07, 2007 4:45 PM
> To: capwap
> Subject: [Capwap] CAPWAP and congestion control
>
> Another issue that the transport A-Ds raised was that
> congestion control needs to be considered for CAPWAP.
> The concern was that in case of congestion in the network,
> packets could get discarded and the sources may not be
> notified or may not realize it. This could lead to
> congestion collapse and fairness issues.
>
> In reality, almost all data traffic being tunneled over
> CAPWAP is IP.  Note that the CAPWAP tunnel is
> between the WTP and AC only. TCP already has its own congestion
> control mechanism between the source and the sink, and
> I'd argue that creating another congestion control loop
> in the path would interfere with TCP's congestion control loop
> and lead to undesirable effects.
>
> I'd suggest we add a Transport Considerations section
> to the CAPWAP spec recommending that non-IP traffic not be
> sent over the Internet when using CAPWPAP.
> Some proposed text is provided below.
>
> Thoughts/comments ?
>
> Thanks,
> Abhijit
>
> -------------PROPOSED TEXT ---------------
>
> Transport Considerations
>
> The CAPWAP protocol does not provide a congestion control mechanism.
> The underlying assumption is that data being tunneled by CAPWAP is
> IP. Since it is essentially a tunneling protocol between two  
> intermediate
> points in the path between the wireless client and the end host, it
> was felt that having a separate congestion control for CAPWAP would
> actually interfere with the congestion control mechanisms already
> in place.
>
> In order to prevent congestion collapse and fairness issues from
> happening in the Internet, it is recommended that non-IP traffic
> not be tunneled over CAPWAP.
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