[asterisk-ss7] Some sessions hangs. Is it possible with SS7

Jacob Tinning tinning at sifira.dk
Mon May 15 00:02:12 MST 2006

On Sat, 13 May 2006, Storer, Darren wrote:

> the state of CICs can become unsynchronised between SS7 nodes although it
> doesn't happen too often. Sometimes Node A thinks that a particular CIC is
> "In Service Free" whilst Node B thinks that Node A didn't handle the last
> call correctly and places the same CIC into a blocked state at a higher
> application layer.

Oh. There was a case I didn't think of...

> When this situation occurs we normally use MML to "flex" the CICs by
> manually taking each suspect CIC out of service and then returning it back
> to service. I have seen that chan_ss7 appears to support these maintenance
> messages but I haven't used them myself.

Thats right. The user can unblock and block single circuits og groups of
circuits manually if such a situation should occur.

We implemented that feature to make users able to block a single E1 group
for maintanance and unblock it when the maintanance is done, but it can
probably be quite usefull if the nodes get out of sync.

> When an SS7 node is started for the first time (cold start) it has no
> knowledge of the state of the CICs as maintained by another SS7 node that it
> is connected to. To synchronise the state of the CICs after a cold start it
> is common to see many block and unblock messages (including Circuit Group
> Resets) after the signalling links are aligned but before the route starts
> to handle live traffic.

I think chan_ss7 initially send a RESET message on all circuits. Anyway I
hope Anton can make an ISUP dump of what is happening. If there is a bug
in chan_ss7 which can make circuits hang, We would like to fix it :)

Mvh. Jacob

Jacob Tinning
System Developer                                           SIFIRA A/S

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