[Serusers] Re: rewrite the FROM part of SIP INVITE
Greger V. Teigre
greger at teigre.com
Sat Sep 9 16:54:12 CEST 2006
Hi Steve, Thanks for elaborating and providing the reference to the
"anonymous RFC."
I have written up a FAQ item on this for future reference:
http://www.iptel.org/FAQ_To_From_change
To all: Anyone with an account at http://iptel.org/ can add content like
FAQs, how'tos etc. If you don't have the answer, but rather a FAQ item
you think should be described, you can create a new FAQ question and
leave the answer to others :-)
g-)
Steve Blair wrote:
>
> Greger:
>
> Thanks for addressing this. I've had a few questions about From
> rewriting over the years. I'd like to add one more point. RFC3323 does
> permit the display name and uri in the From header to be rewritten for
> privacy concerns providing the tag is maintained. So rewriting the
> From header to somthing like the following is acceptable for
> applications such as caller ID blocking.
>
> From: "Anonymous" <sip:anonymous at anonymous.invalid>;tag=873345996
>
> That being said I've moved away from this technique for caller ID
> blocking because it presents problems with call detail record
> generation. I generate CDRs in my gateways. With this form of caller
> ID blocking the CDR record shows the called number but the calling
> number is the word "anonymous". To get around this I now use
> Remote-Party-ID headers with a display name of "anonymous" but a uri
> which preserves the original calling number.
>
> We are looking at using P-Asserted-Identity next to remain current
> with the standards but we aren't there yet.
>
> -Steve
>
> Greger V. Teigre wrote:
>
>> Ok, I've written this before, but it's important and worth another try.
>> First of all some clarifications:
>> - From and To have nothing to do with routing
>> - The requirement to not touch From and To has nothing to do with SER
>> implementation
>> - The tags in From and To together with Call-Id form a dialog and is
>> important for matching SIP messages in a transaction (ex. an INVITE -
>> OK - ACK sequence) and a dialog (ex. later reINVITEs, BYE etc)
>> http://www.tech-invite.com/Ti-sip-abnf-hf.html#from
>>
>> Thus, in order to be RFC3261 compliant, you need to:
>> 1. NOT touch the tags in From and To
>> 2. NOT touch the remainder of From and To
>>
>> If you break #1, you mess up transaction and dialog matching and
>> pretty much everything breaks. If you break #2, you violate the
>> requirement to be backwards compatible.
>>
>> That being said, if ALL your UAs and gateways support and use
>> RFC3261, changing From and To names/uris (while leaving tags) will
>> probably work, but as all subsequent SIP related IETF documents and
>> implementation try to be RFC3261 compliant, it is assumed that From
>> and To are only changed two places:
>> a. In the UAs
>> b. In a B2BUA, i.e. a server that terminates a dialog with UA1 and
>> creates another one with UA2 and thus is a go-between
>>
>> New SEMS can be used for b.
>>
>> So, regardless of using uac module or subst for replacing From/To,
>> you will be MUCH better off if you follow the intentions of the RFCs,
>> i.e. change the From/To in the UAs through the provisioning systems
>> you use. Having lots of non-compliant SER installations is a recipe
>> for trouble in the future.
>>
>> Note that there is an exception to the anonymization of a call. I
>> tried to find the reference, but I couldn't find it. Does somebody
>> sit on the reference?
>>
>> I hope that was clarifying.
>> g-)
>>
>> Ricardo Carvalho wrote:
>>
>>> It isn't necessary to restore those from-header fields to maintain
>>> the call leg of transactions taking place. As far as I know, by the
>>> tests I made, Ser routes SIP messages based on Call-Id and not as
>>> well From and To tags of messages.
>>> Although this is only true if all UAs that you use are
>>> RFC3261compliant. If some phones that you use implement the old
>>> protocol, uses the full content of From/To for the same purposes,
>>> you may get some problems... It's risky manipulate From/To tags...
>>>
>>> Regards,
>>> Ricardo.
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>> G.Jacobsen wrote:
>>>
>>>> Ricardo,
>>>>
>>>> Ok, but how do you restore the from-header when you send answers of
>>>> the
>>>> downstream party to the upstream party again ?
>>>>
>>>> Cheers
>>>>
>>>> Gerry
>>>>
>>>>
>>>> ----- Original Message ----- From: "Ricardo Carvalho"
>>>> <rcarvalho at iric.up.pt>
>>>> To: "Alex Fler" <alexfler at yahoo.com>
>>>> Cc: <serusers at lists.iptel.org>
>>>> Sent: Friday, September 08, 2006 5:15 PM
>>>> Subject: Re: [Serusers] Re: rewrite the FROM part of SIP INVITE
>>>>
>>>>
>>>>
>>>>
>>>>> I've used subst() function for substituting From and To URIs and
>>>>> calls
>>>>> succeed well! I think that this indicates that Ser uses in fact
>>>>> only the
>>>>> Call-Id to keep track of calls and not as well From and To tags of
>>>>> messages. Although I this may end up biting me later...
>>>>>
>>>>> You can do that for example with the following syntax:
>>>>>
>>>>>
>>>>
>>>> subst('/^From:(.*)sip:.*@your_domain(.*)/From:\1sip:what_ever_number at what_ev
>>>>
>>>> er_domain\2/');
>>>>
>>>>
>>>>> Greetings,
>>>>>
>>>>> Ricardo.
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> Alex Fler wrote:
>>>>>
>>>>>> Hello guys,
>>>>>>
>>>>>> Sorry for a stupid question, but how do you actually rewrite the
>>>>>> FROM
>>>>>> part of SIP INVITE ?
>>>>>>
>>>>>> Do you use avp ? Could someone give me an example ?
>>>>>>
>>>>>>
>>>>>>
>>>>>> Thanks to all
>>>>>>
>>>>>>
>>>>>>
>>>>>> Alex Fler
>>>>>>
>>>>>>
>>>>>>
>>>>>> ------------------------------------------------------------------------
>>>>>>
>>>>>>
>>>>>> _______________________________________________
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>>>>>> Serusers at lists.iptel.org
>>>>>> http://lists.iptel.org/mailman/listinfo/serusers
>>>>>>
>>>>>>
>>>>>
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>>>>>
>>>>
>>>>
>>>>
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>>>
>>>
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