ss7box and MTP3 Route Management

ss7box has a partial implementation of MTP3 route management. Route management is needed when ever SS7 linksets are connected to a signal transfer point (STP). The ss7box implementation needs to be advanced for passing network acceptance testing, automatic restart, and improved fault tolerance. Up to this point, ss7box has not been connected to an STP where route management has been a critical issue. STPs tolerate nodes that ignore route management messages which also supports why the implementation is incomplete. As is often the case with ss7box, things changed suddenly this week, and now having a more complete route management is important.

Route management in MTP3 consists of procedures and messages per ITU Q.704 Section 13 Signalling Route Management:

• TFA - allow traffic to route
• TFP - prohibit
• TFR - restrict, don't allow unless no better choice to reach destination
• TFC - controlled, for communicating congestion levels
• SRST - signal route set test for asking and STP about the status of a route
• SRSC - signal route set congestion test for asking an STP about the congestion status of a route

In ss7box, route management is already designed and implemented at the core of the ss7box routing mechanism. The route management values assigned to each linkset are initialized to TFA and are never changed, but the values are checked for every outbound MSU passing through ss7box. Inbound route management messages are being decoded. These functions have been thoroughly tested in the field.

Inbound route management messages need to affect the route table and the values from the route table need to affect the related status of each linkset. If a route becomes completely unreachable, ss7box needs to send out a Destination UNAvailable (DUNA) M3UA message to all connected ss7boost clients. Conversely if a destination becomes reachable, a Destination AVAvailable (DAVA) M3UA message needs to be sent.

A signaling route set test procedure needs to be implemented to periodically query an STP that has prohibited a destination on its linksets to see if the prohibited destination is available.

A tool is needed to inject and receive route management messages for unit testing in the lab. This will most likely take the form of ss7box_cli commands for injection. In the lab two ss7box will be connected back-to-back. One will be the device under test (DUT) and the other will be the tester. The cli commands will be issued on the tester to the DUT. Messages from the DUT will be captured and decoded n the tester using normal ss7box route management procedures with some added debugging code.

The route set congestion messages and procedures will not be supported at this time as they are options in the spec and not frequently encountered.