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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