Why PRI Bachhauling?

[rnarayana]

Hello ,

What is the use of PRI backhauling in MGCP.

Thanks in advance.

[ROBERT Clark]

In the context between Call Manager and a voice gateway using MGCP.

When terminating an ISDN PRI connection on a gateway, the Q.931 messages from the PSTN are backhauled via TCP to Call Manager for processing.

My understanding of why this is done is due to the master/slave relationship between endpoints in MGCP. All intelligence resides in the Call Agent (i.e Call Manager), not the gateways. As opposed to H.323, which assumes each endpoint possess a full or near full "knowledge" of the H.323 protocol suite. Since Q.931 manages call set up/ call tear down, it is logical to assume these functions should be processed on the device with the intelligence (i.e Call Agent).

hth,

Rob

[pbarman]

Rob is correct, and PRI Backhauling is enabled by default on MGCP-controlled PRI. It establishes a tcp link to port 2428 on the Callmanager and communicates all D-channel Q931 signaling information with CallManager for call processing. This also means that the gateway will not bring up the D-channel unless it can communicate with Cisco CallManager to backhaul the Q.931 messages contained in the D-channel. In a MGCP gateway, give the command "show ccm" to find whether the PRI backhaul connection is active.