QSig
Q.SIG voice signaling on the Cisco AS5300 provides the following benefits. It enables the Cisco AS5300 to connect with digital PBXs that use the Q.SIG form of common channel signaling. It also provides access to multiple remote PBXs with a single connection to a Cisco AS5300. It provides transparent support for supplementary PBX services, so that proprietary PBX features are not lost when connecting PBXs to Cisco AS5300 networks. It also presents Q.SIG support based on widely used ISDN Q.931 standards.
Q.Sig is made for private integrated services network exchange (PINX) applications. Based on Q.931, Q.Sig is an evolving technology that allows communication with legacy PBX and key systems. When used with Cisco routers, Q.Sig can connect PBX systems with private IP networks or other service provider network service offerings. Using Q.Sig with private IP transport allows businesses long-haul transport of voice traffic without the need for inter-exchange carrier (IXC) interconnection, which saves on long distance charges.
You should make sure to check the ISDN network status when you are reconfiguring. You are looking for Q.921 to be MULTIPLE_FRAME_ESTABLISHED. If that is the case, you should be able to make ISDN calls. If you are in a TEI_UNASSINED or AWAITING_ESTABLISHMENT state, you need to verify your configuration. Remember that if you are in a back-to-back configuration you have to set one of the sides to emulate the network. After you can place calls, the debug isdn q931 command becomes your greatest asset in troubleshooting ISDN calls. The first thing to monitor is the direction of the disconnect.
You also want to see if the bearer capability is correct. In other words, if you are making a voice call, but it's coming in as data, you have a problem. Receiving a disconnect cause code of "Bearer Capability not Implemented" typically means that a command such as isdn incoming-voice modem is missing from the D channel configuration.
Make sure you recheck the channel ID, in order to discover out what the status of the attempted channel is with the show isdn status command. If the channel the call is being attempted on is B, for some reason it has been busied out. You can manually attempt to reset that B channel or the entire range. Do not forget that the q931 debug tells you what the cause code is, although it does not necessarily spell out the problem for you.
