[SR-Users] Remove a CODEC in the Invite

[Alex Balashov]

Johannes,

On 11/24/2010 05:19 AM, Johannes Wagner-Meingassner wrote:

> I have to remove the Transparent Codec in the INVITE-Message to a dedicated
> SIP-Client, because the Client can not work with it.
> What do you think is the best methode to do this?

While the motive is understandable, this is a bad idea.  Proxies are 
supposed to relay messages, not modify them.  There are certain fields 
of a message (for example, the Request URI in an initial request) that 
they can modify, and they can add additional headers, but in general, 
that is not their purpose an.d their modification capabilities are 
formally very restricted.  It is fundamentally contrary to the purpose 
of a proxy in every way to do something like modify the SDP body.

On a practical level, the problem with modifying the SDP offer is that 
without stateful reversion applied to every answer sent (rather in the 
way that uac_replace_from() and 'topoh' work for other data), the sender 
of the offer is fully entitled to refuse an answer whose content does 
not reflect the original offer sent (since modifying SDP on the proxy 
would be opaque to the sender).

You really need to use a B2BUA for something like this.

-- 
Alex Balashov - Principal
Evariste Systems LLC
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