[sr-dev] ideas on dialog spiral distinction

[Klaus Darilion]

Am 25.08.2011 11:16, schrieb Timo Reimann:
> On 25.08.2011 10:31, Klaus Darilion wrote:
>> > Am 25.08.2011 10:14, schrieb Jason Penton:
>>> >>
>>> >> From some initial work and testing I can confirm that this works ONLY
>>> >> when using the top Via *without* branch tags. Not sure what impact this
>>> >> could have?
>>> >> This is because a BYE results in a different set of branch tags from the
>>> >> original set of invite branches - I am investigating why and how this
>>> >> works now.
>> > 
>> > Sure. the branch tag is a transaction identifier and must be unique in
>> > space and time. Thus, BYE must have another tag. That's why I said you
>> > have to put some data into RR cookies - this is the only data which
>> > stays the same during the dialog (except tags and call-id).
>> > 
>> > If you only want to know if an in-dialog request is from orig->term or
>> > from term->orig, then the is_direction function is already sufficient.
>> > 
>> > If you want to detect a certain spiral leg in dialog module, IMO you
>> > have to add another matching parameter (besides tags and call-id) to
>> > dialog module which will be set as RR-cookie and retrieved from Route
>> > header for in-dialog requests. Every time the initial requests spirals
>> > through the proxy, you have to add such a cookie which of course must be
>> > different to the previous inserted cookie (therefore ftag is not
>> > sufficient anymore) - either generate a random identifier or reuse some
>> > data from the message (e.g. you could copy branch-tag to RR header as it
>> > should be unique)
> Let me emphasize that you don't need to add a new RR cookie: You can
> re-use the existing one that implements DID mode and simply extend the
> hash function to cover that extra value you choose. (Random number or
> branch parameter, as Klaus mentioned; see my comments below though.)

Indeed - I have not thought about this parameter. If it would be
extended to be unique it should work - as long as the DID value in
in-dialog requests is correct. Thus, DID_FALLBACK mode would not work
anymore.

regards
Klaus