[Serusers] Reg. SIP Parsing, SIP Protocol

Nils Ohlmeier nils at iptel.org
Tue Feb 3 00:06:02 CET 2004


Am Monday 02 February 2004 23:48 schrieb Balaji Bapulal Thoguluva:
>    I am writing a software to parse SIP messages. I have couple of
> questions that I would like to clarified.

maybe your questions are better placed at the SIP mailing lists.

> 1. How to recognise if a packet is a SIP or a non-SIP packet?. SIP uses
> TCP, UDP as underlying transport.

How to recognise that a request is a HTTP request or not? Parse it! If you can 
parse it, it is a valid request of that protocol. If you fail it is probably 
not a valid request (or your parser is faulty).

> 2. How to know the direction of the SIP message if it is from SIP proxy or
> from SIP client?. I ask this question because in most of the SIP messages,
> the header fields are copied from previous messages and so the from, To
> header fileds doesn't always signify he direction

If you dont know if the IP/host is a proxy or a UA i dont know a safe way to 
determine if the type/class of the device.

> 3. Can Call-ID be used to find the number of distinct phone call taken
> place between different SIP UA's?.

No. The content of the Call-ID depends on the UA implementation and e.g. can 
be randomly.

> 4. What is the significance of dialog-ID? and how can it be used?

AFAIK it's the internal identifier of an UA for one dialog state. This can be 
equal to the To or From tag, but can also be something completely different.


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