Capwap Mailing List: Re: CAPWAP and congestion control

[Pat Calhoun (pacalhou) (pcalhoun]

Any objections before I go ahead and change the spec? Do we want to run this by the transport ADs and advisors?

 

PatC

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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.