[Serusers] Modifying "From" header field of an INVITE message

[Alberto Cruz]

Hi Jan I found this response from you where you explain is possible to 
modify any header field in SER.

I have exactly the same issue like SCM. My service provider is asking me 
to send a fixed user part at From URI header for all my calls for 
billing purpose.
For example If I have 4 users registered at SER like the following
user1 at sipserver.mydomain.com
user2 at sipserver.mydomain.com
user3 at sipserver.mydomain.com
user4 at sipserver.mydomain.com

I should translate all the user part before to forward their calls to 
the Service Provider by the following:
2102456787 at sipserver.mydomain.com

Where could I find information related to the command(s)/funcion(s) that 
make this possible?

If I change the From header, what should I do to keep the original value 
in order to avoid loosing the call flow? Is it enough with the 
"Contact:" field?

Regards

Alberto Cruz
Jan Janak wrote:

>On 06-02 08:44, John Todd wrote:
>  
>
>>Asterisk Operational Note:
>>  From Asterisk, try something similar to this:
>>
>>exten => _1XXXXXXXXXX.,1,SetCIDNum(+1${CALLERIDNUM})
>>exten => _1XXXXXXXXXX.,n,Dial(SIP/+${EXTEN}@ser.mydomain.com)
>>
>>  This assumes you have ten digit North American caller ID digits, 
>>and that you need to hand numbers to Level3 like "+13015551212" for 
>>both ANI and DNIS.
>>
>>
>>SER Development/Usage Note:
>>  While I agree that changing the "From:" is generally a bad idea, 
>>there certainly are instances in which is is a desirable thing for a 
>>SIP proxy to do.  The instance below is a good example.  Other 
>>examples are when the recommended privacy options are not used, so 
>>despite privacy settings elsewhere in the headers the "true" Caller 
>>ID is shown on the remote side.  The only way to avoid this would be 
>>to not include the origin AOR on the outbound call.  Of course, to 
>>process replies correctly, it may be necessary to mangle the headers 
>>in the inverse manner on the way back in... but that level of voodoo 
>>is left to the administrator.
>>
>>  I agree that a b2bua is a way to do this - it may be necessary to 
>>keep state in that manner.  (specific note: Asterisk _is_ a glorified 
>>b2bua.)  However, it seems natural that all headers should be subject 
>>to modification if required within the proxy - not always is it 
>>required to keep state, as in this case.  Is it truly the case that 
>>SER does not allow re-formatting of the From: header in any way?
>>    
>>
> 
>  It does require you to keep state -- you have to restore the original
>  value on the way back, and not just in replies, but in subsequent
>  mid-dialog requests (BYE, for example) as well.
>
>  You can do it statelessly only if you know that no user agent uses the
>  From/To URI for dialog matching. Suprisingly many implementations do,
>  Cisco is one well-known example.
>
>  Another option would be encoding the original value into the
>  Record-Route header field generated by SER, that way SER could restore
>  the original value from the Route header field later. It will be the
>  user agents in this case who would keep the state.
>
>  You can rewrite any header field in SER, even From/To but
>  expect interoperability problems if you do so statelessly. Unless you 
>  are sure that all SIP implementations behave exactly as described in 
>  RFC3261, you need a B2BUA that would keep state during calls.
>
>    Jan.
>
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>
>  
>
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