Centralized Call Processing – Automated Alternate Routing

The CUCM locations Call Admission Control (CAC) mechanism is not turned on by default. CAC should be aligned with the priority queue (PQ) configuration in the WAN. The will PQ QoS configuration with the CAC mechanism will guarantee call quality over the IP WAN. Intermittent call quality issues can result if CAC and QoS are not properly configured. Call Manager uses bandwidth variables of 24kbps and 80kbps for G.729 and G.711 respectively. CAC alone will reject calls over the WAN when there is not enough bandwidth. End users will hear reorder tone (or an annunciator message) and see “Not Enough Bandwidth” displayed on the LCD of their phones when calls over the IP WAN are rejected. Automated Alternate Routing (AAR) is a CUCM feature that will transparently re-route rejected calls over the IP WAN in centralized call processing models. The calling party phone will display “Network Congestion. Rerouting” on the LCD when the call is re-routed. Automated Alternate Routing depends on the external phone number mask of each destination directory number. AAR works in environments with direct inward dialing (DID), but CUCM 4.2/6.0 introduced the call forward no bandwidth (CFNB) feature which will allow directory numbers to be configured with an AAR destination mask that will forward CAC rejected calls to an operator, automated server (AA)/ IVR), cell phone, or voice mail. AAR is not turned on by default. AAR must be activated in the Call Manager service parameters. Set the Automated Alternate Routing Enable from False to True. The Out of Bandwidth Text and AAR Network Congestion Rerouting Text service parameters can be changed to propagate LCD messages different than the two described in the previous paragraph. AAR groups are used to configure a dial prefix which will be pre-pended to the dialed digits after the dialed digits are manipulated by the destination directory phone number mask. AAR groups are normally configured as 91 in environments where a 9 access code is used for an outgoing line and a 1 is required by the long distance provider. External phone number masks are normally configured to change the corporate abbreviated dial plan to a fully qualified 10 digit PSTN number. A five digit phone number of 11001 with an external phone number mask of 21255XXXXX would result in a phone number of 2125511001. The external phone number mask parameter of the called party is used to manipulate the dialed digits and the AAR group is used to prefix the access codes and the long distance code if necessary. AAR groups are configured from the call routing menu. AAR groups are applied on the phone configuration page. The calling search space (CSS) of the calling party may not include long distance dialing capabilities. AAR calls that require long distance dialing would fail in this situation if a separate AAR calling search space is not configured at the phone. The AAR calling search space (CSS) will override the device or Line/Device CSS. In the next blog, we will start talking about the distributed multi-cluster call processing model. REFERENCES: CUCM 7.x Solution Reference Network Design (SRND) Guide: http://www.cisco.com/en/US/netsol/ns818/networking_solutions_program_home.html www.cisco.com/go/srnd