[sr-dev] Kamailio at SIPit 30

[Peter Dunkley]

On 20/02/13 16:28, Iñaki Baz Castillo wrote:
> Let me a question: does not the TCP buffer size affect to the WS 
> module? This is, if I send via SIP over WS or MSRP over MSRP a very 
> big WebSocket messsage (i.e. an ISO image) does it not deal with 
> Kamailio's TCP buffer settings?

Kamailio has fixed size TCP receive buffers.  The size can be set in the 
configuration file and changed live (using an MI command), but has to be 
manually set.  If you want to receive any request (SIP, HTTP, or MSRP) 
on Kamailio that exceeds the buffer size that is currently in use you 
will have problems.

It is currently the case that receiving large HTTP (for example, for 
XCAP), SIP, and MSRP messages requires this buffer to be increased from 
the default.  WebSocket is no different at all, and the problem is no 
different here than it is for anything else in Kamailio.

The reason it is noticed more with WebSockets is that SIP over WebSocket 
tends to be using WebRTC generated SDP - which is quite a bit larger 
than that produced by most clients.

I plan to modify the TCP receive code and MSRP module so that when large 
MSRP SEND requests (for example, a single SEND containing an ISO image) 
are received Kamailio will chunk them into smaller outgoing SENDs at a 
size that is less than the TCP receive buffer size.  This chunking by a 
relay is permitted by RFC4576.  I haven't gotten around to this yet, but 
even when done it won't help with large SIP or HTTP requests.

At the moment we work-around this with our Javascript MSRP stack by 
doing chunking there and:

 1. Limiting the chunk size to something small
 2. Limiting the number of outstanding chunks (that is chunks for which
    we have not received a 200 response) for a particular file transfer

In effect, we have kludged our MSRP stack to have flow-control at a 
level higher than just TCP.

Regards,

Peter

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