opensipstack-devel

[OpenSIPStack] By Looking at the UDP packet, How to find out if Packet is SIP/RTP

[Ashish K. <ash...@gm...>]

Hi Joegen,

I ahve one query.
By Looking at the UDP packet, how to find out if the packet is SIP or RTP.
We cannot use the destination port information as the there are no standard
fixed port for SIP/RTP. Although the Default port for SIP is 5060, but still
some servers may use different ports.
What information you use while parsing to identify if the packet is SIP or
RTP.

Please reply.

regards
Ashish

Re: [OpenSIPStack] By Looking at the UDP packet, How to find out if Packet is SIP/RTP

[Joegen E. B. <joe...@gm...>]

A  simple approach would be to search for the pattern "via:" until the 
last occurrence of CR/LF.   If the search algo finds the string, then 
it's a SIP message.   This is based on the assumption that all SIP 
messages will have a via header.   If it's not a SIP message, you may 
get the version bit of the RTP packet from the first byte  
(((packet[0]>>6)&3) == 2) .  If the version is 2, then it might be an 
RTP packet.  You can then proceed in parsing the entire RTP header and 
see if it is indeed an RTP packet.  

A much better approach is to dig into the ethereal/wireshark code and 
see how it determines which protocol a packet belongs to.  

 HTH

Ashish Khare wrote:
> Hi Joegen,
>
> I ahve one query.
> By Looking at the UDP packet, how to find out if the packet is SIP or RTP.
> We cannot use the destination port information as the there are no standard
> fixed port for SIP/RTP. Although the Default port for SIP is 5060, but still
> some servers may use different ports.
> What information you use while parsing to identify if the packet is SIP or
> RTP.
>
> Please reply.
>
> regards
> Ashish
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