[Serusers] 305 Use Proxy

[Nils Ohlmeier]

Hi Rick,

> I am trying to setup a redirecting proxy server with Ser, but I find that
> my GXP-2020 phone gets into an endless loop.  Is this common?
>
> The phone is configured to use my ser service which is set as a proxy.
> If it tries to dial things that this proxy shouldn't handle, it sends
> back a "305 Use Proxy" response.  The phone seems to ignore the proxy
> and tries again.

unfortunately the usage of 305 is totally under specified. And I haven't
it being used in the field ever. Anybody else maybe?

On a first look this seems to be the perfect response if you want to make
the sender of a request to retry this request on a different proxy, BUT:
- is a proxy on the path back allowed to consume the 305 and retry it by
himself on behalf of the originator?
- or is only the originator (UAC) allowed to follow the URI from the reply?
- if it is only the originator: how can the originator assure that the
request will traverse exactly the same path except for the last hop? Use a
Route header? But when it receives the 305 response it does not know which
path the original request took.
- in case of the the originator trying to follow this reply: what should
the UAC do in case it uses an fixed outbound proxy? Use a pre-loaded Route
header with two entries?
- and the biggest question: how should the URI look like which you send
back in the 305 response? Just the URI of the proxy without usernames? Or
should it be the complete URI which should be retried at that proxy?

> 1) Is it common for the proxy redirection not to work?  I've seen it being
>    ill-advised on iptel.org because the RFC isn't too clear how it works.
>
> 2) What would be the proper formula to get Ser to send back a proxy
>    redirect?  I may be approaching it wrongly, but I cannot find much
>    documentation about it online.

I would recommend you to avoid the 305. Which also means there is nothing
like a proxy redirect.
You could either try to use a 301 response instead. Or you just configure
the proxy to froward the request to the correct proxy instead of replying
with a 305.

Best regards
  Nils Ohlmeier
  VoIP Freelancer