[SIPForum-discussion] What to do if sent-by value is missing in responses while proxy processing them ?

Tomasz Zieleniewski tzieleniewski at gmail.com
Tue Apr 21 09:29:51 UTC 2009

For instance

REGISTER sips:ss2.biloxi.example.com SIP/2.0
  Via: SIP/2.0/TLS *client.biloxi.example.com:5061*;branch=z9hG4bKnashds7
  From: Bob <sips:bob at biloxi.example.com <sips%3Abob at biloxi.example.com>
  To: Bob <sips:bob at biloxi.example.com <sips%3Abob at biloxi.example.com>>
  Call-ID: 1j9FpLxk3uxtm8tn at biloxi.example.com
  Contact: <sips:bob at client.biloxi.example.com<sips%3Abob at client.biloxi.example.com>
  Content-Length: 0

According to SIP ABNF:
sent-by = host [ COLON port ]

- Tomasz

2009/4/21 Yevgen Krapiva <ykrapiva at gmail.com>:
>> Section 18.1.1 Sending requests
>> ....
>> Before a request is sent, the client transport MUST insert a value of
>> the "sent-by" field into the Via header field.  This field contains
>> an IP address or host name, and port.  The usage of an FQDN is
> Here is a SIP call flow examples http://www.ietf.org/rfc/rfc3665.txt
> Can anybody show me any sent-by parameters there ? :)
> Noone uses sent-by values. Checked with Xlite, Ekiga softphones.
> But in anyway, I try to make correct proxy, but this issue makes me stuck.
> Can anybody comment this ?
> 2009/4/18, Tomasz Zieleniewski <tzieleniewski at gmail.com>:
>> Hi,
>> If the sent-by value is not present then it means that it doesn't match
>> proxy
>> address. In such case as it it written message is discarded by proxy.
>> Regards
>> - Tomasz Zieleniewski
>> 2009/4/17 Yevgen Krapiva <ykrapiva at gmail.com>:
>>> Hi all.
>>> This is quotation from RFC3261 about stateless response processing:
>>>>  Response processing as described in Section 16.7 does not apply to a
>>>>  proxy behaving statelessly.  When a response arrives at a stateless
>>>>  proxy, the proxy MUST inspect the sent-by value in the first
>>>>  (topmost) Via header field value.
>>>>  ...
>>>> If the address does not match the
>>>> proxy, the message MUST be silently discarded.
>>> What to do if sent-by value is not present in responses ? :)
>>> For example, I didn't find any in rfc3665 (sip call flow examples).
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