[asterisk-ss7] changeback

[Horacio J. Peña]

Hola!

I've a doubt about how changeback should work, let's say we have a linkset with 4 links (1-0 to 1-3, SLS 0 to 3) and the following happens:

1. link 1-0 fails, changeover to 1-1 (COO on 1-1 with SLS=0)
2. link 1-2 fails, changeover to 1-1 (COO on 1-1 with SLS=2)
3. link 1-0 gets available, changeback from 1-2 (CBD on 1-1 with SLS=0)

What happens with the traffic normally going thru 1-2 ?

Q.704 reads:

4.4.1 When a previously unavailable signalling link becomes available again (see
3.2), signalling traffic may be transferred to the available signalling link by
means of the changeback procedure. The traffic to be transferred is determined
in accordance with the following criteria.

4.4.2 In the case when the link set, to which the available signalling link
belongs, already carries signalling traffic on other signalling links in the
link set, the traffic to be transferred includes the traffic for which the
available signalling link is the normal one. Note that the assignment of the
normal traffic to a signalling link may be changed during the changeback process
taking into account, for example, system performance.

The normal traffic is transferred from one or more signalling links, depending
on the criteria applied when the signalling link became unavailable (see 4.3.2),
and upon the criteria applied if any of the alternative signalling link(s)
themselves became unavailable, or available, in the meantime.
If signalling links in the linkset are still unavailable, and if it is required
for load balancing purposes, signalling traffic extra to that normally carried
by any link might also be identified for diversion to the signalling link made
available, and to other available links in the linkset. This extra traffic is
transferred from one or more signalling links.

---------------

My understanding of it is that the traffic from 1-2 should continue going
thru 1-1. libss7's interpretation differs and send that traffic thru 1-0. 

Is libss7 right? If so, where am I wrong?

All the ss7 linksets I've access to are one-link, so cannot test what do other
implementations do.

Thanks,
-- 
Horacio J. Peña
horape at compendium.com.ar
horape at uninet.edu