[Serusers] [Serdev] loose_route behaviour, detecting single Route with myself

[Klaus Darilion]

This discussion is quite interesting ...

Nils Ohlmeier wrote:
> No. The To-tag is not enough as criteria for in-dialog. And unfortunately the 
> presence of Route isn't as well.
> 
> You can basically have these type of ACKs (ACKs illustrate the worst case):

> - the UAC uses an outbound proxy without a Route header
(A) >   - the in-dialog ACK will have a To-tag and a Route header
(B) >   - the out-of-dialog ACK will have a To-tag and no Route header

> - the UAC uses a Route header for its outbound proxy
(C) >   - then in-dialog ACK will have a To-tag and a Route header (same 
as above)
(D) >   - the out-of-dialog ACK will have a To-tag and a Route header 
(and this is
     > the problematic case!)

ACK. Lets consider the different forwarding scenarios: tm + sl

tm:
(A) loose_route=true,  --> just t_relay
(B) loose_route=false, --> just t_relay (will be absorbed by tm)
(C) loose_route=true,  --> just t_relay
(D) loose_route=true,  --> just t_relay (will be absorbed by tm)

sl:
(A) loose_route=true,  --> just forward
(B) loose_route=false, --> lookup()*, forward
(C) loose_route=true,  --> just forward
(D) loose_route=true,  --> lookup()**, forward

* if lookup() was done for corresponding INVITE then lookup() then it 
also has do be done here. Usually lookup() is done if RURI=myself.

** if lookup() was done for corresponding INVITE then lookup() then it 
also has do be done here. This scenario is more complicated - if the 
proxy is just used as relay (Route=myself, RURI!=myself) then lookup() 
is not necessary. If this is the authoritative proxy (Route=myself, 
RURI=myself), then lookup will be performed.

I think all scenarios can be handled with current functionality, 
although I would prefer the behavior suggested by JF to have 
loose_route=false if there is only one route header which points to the 
proxy itself because regardless if the outbound proxy is addressed 
directly or with a preloaded route set it has to be routed identically.

regards
klaus

sl dispatcher

> The only thing which distinguishes the in-dialog ACKs from the last 
> out-of-dialog ACK might be the length of the Route header. If the Route 
> header has the length one it might be an out-of-dialog ACK. But in the worst 
> case this is equal to an in-dialog ACK with only one Route header. In this 
> case the only difference will be the RURI.
> 
>>    process_routes(); # may have different return values
>>                      # -1: no routes found
>>                      # -2: only a single route pointing to "myself"
>>                      # 1: loose routing done
>>                      # 2: strict routing done
>>    ... NAT traversal, security checks, ....
>>    t_relay();
>>    exit;
>> }
>>
>> process_routes();
>> # here proceed according to policy, e.g.
>> # -1, -2: handle now incoming request
>> # 1, 2: reject out-of-dialog loose/strict-route request
>> ...
> 
> Ok, what would be the difference then between this new process_routes() 
> function and adding more different return values to the existing 
> loose_route() function?
> 
>   Nils