[sr-dev] double record-routing also at outbound edge

[Peter Dunkley]

Hi Juha,

This sounds like a bug with the outbound specification.  I can't believe
that the ability to re-target dialogs would be deliberately removed by the
outbound enhancement without it being mentioned in the RFC.

Perhaps the right thing to do would be to raise this issue on the
appropriate IETF mailing lists and seeing if the designers of the
specification have an opinion rather than just using a proprietary
solution like contact aliasing?

Regards,

Peter

> i have one more comment on flow token vs. contact aliasing.
>
> flow token is part of a route uri that represent a proxy in the route
> set.  route set cannot be changed during the dialog, but remote target
> uri can.  from rfc3261:
>
>    Requests within a dialog MAY contain Record-Route and Contact header
>    fields.  However, these requests do not cause the dialog's route set
>    to be modified, although they may modify the remote target URI.
>    Specifically, requests that are not target refresh requests do not
>    modify the dialog's remote target URI, and requests that are target
>    refresh requests do.  For dialogs that have been established with an
>    INVITE, the only target refresh request defined is re-INVITE (see
>    Section 14).  Other extensions may define different target refresh
>    requests for dialogs established in other ways.
>
>       Note that an ACK is NOT a target refresh request.
>
>    Target refresh requests only update the dialog's remote target URI,
>    and not the route set formed from the Record-Route.
>
> if flow token is used instead of contact aliasing to store the remote
> target uri, then it is not possible to modify the remote target uri via
> target refresh requests (e.g. when moving from wifi to mobile network)
> and such setup is violating the above text of rfc3261.
>
> this problem does not exist with contact aliasing, because
> add_contact_alias() is called on each in-dialog target refresh request,
> which allows changing of remote target uri during the dialog.
>
> -- juha
>
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>


-- 
Peter Dunkley
Technical Director
Crocodile RCS Ltd