Automated Alternate Routing Configuration

Introduction

Cisco Unified Communications Manager automatically reroutes calls through the PSTN or other networks when Cisco Unified Communications Manager blocks a call due to insufficient location bandwidth. With automated alternate routing, the caller does not need to hang up and redial the called party. The Automated Alternate Routing (AAR) feature enables Cisco Unified Communications Manager to establish an alternate path for the voice media when the preferred path between two intra-cluster endpoints runs out of available bandwidth, as determined by the locations mechanism for CAC. This document provides a sample configuration for Automated Alternate Routing.

Prerequisites

Requirements

Ensure that you meet these requirements before you attempt this configuration.
Here in this scenario you already have CAC implemented after the configuration of locations and deployment of RSVP agents to prevent WAN bandwidth oversubscription. You implement AAR to route calls over the PSTN if they were not admitted by locations-based CAC. The AAR feature applies primarily to Centralized Call Processing deployments.
Note: Use of globalized call routing simplifies AAR implementation in international deployments.

Components Used

The information in this document is based on these software and hardware versions:

• Cisco Unified Communications Manager 8.x (Centralized Deployment)
  
• Cisco IP Phones
  
• Cisco IOS MGCP Gateway
  

The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, make sure that you understand the potential impact of any command.

Conventions

Refer to the Cisco Technical Tips Conventions for more information on document conventions.

Background Information

When a call is made from the device of one location to the device of another location, location bandwidth gets deducted from the maximum available bandwidth that is available for the call at either location. If not enough location bandwidth for the call exists at either location, instead of blocking the call, Cisco Unified Communications Manager uses the table of AAR groups and the external number of the terminating directory number to supply the alternate number that is used to reroute the call through the PSTN or other network. The Cisco Unified IP Phone displays the Network congestion, rerouting. message. Use Service Parameters Configuration for the Cisco CallManager service in order to configure this message.
AAR supports these call scenarios for insufficient bandwidth:

• Call originates from a line or directory number (DN) of an IP phone within one location and terminates to a line or DN of another IP phone within another location. This scenario includes calls that terminate at the shared line with terminating IP phone devices that are resident in multiple locations and calls that terminate at the Cisco voice-mail port.
  
• Incoming call through a gateway device within one location terminates to a line or DN of an IP phone within another location. This scenario includes calls that terminate at the shared line with terminating IP phone devices that are resident in multiple locations and calls that terminate at the Cisco voice-mail port.
  

Cisco Unified Communications Manager automatically attempts to reroute calls, due to insufficient bandwidth, through the PSTN or other network only when the AAREnable enterprise parameter is set to true. Cisco Unified Communications Manager uses the device-based AAR calling search space, which is assigned to Cisco Unified IP Phone station devices and gateway devices, when it attempts to route the call to the gateway device that connects to the PSTN or other network. Cisco Unified Communications Manager uses the external phone number mask and the directory number of the line or DN and the Cisco voice-mail port to derive the alternate number that is used to reroute the call.

Configure

For example, if a phone in the headquarters calls a phone in branch A and the available bandwidth for the WAN link between the branches is insufficient (as computed by the locations mechanism), AAR can reroute the call through the PSTN. The audio path of the call is IP-based from the calling phone to its local PSTN gateway, TDM-based from that gateway through the PSTN to the branch A gateway, and IP-based from the branch A gateway to the destination IP phone.
The implementation of AAR includes these steps.

1. Enable AAR.
   
2. Configure partitions and CSSs.
   
3. Configure AAR groups.
   
4. Configure phones for AAR:
   
   1. ApplyAARCSS and (source) AARgroup to IP phones.
      
   2. Configure IPphone directory numbers:
      
      1. Apply (destination) AAR group.
         
      2. Set individual AAR destination mask (CFNB)
         
      3. Forward to voice mail if no bandwidth is available.
         

Note: Use the Command Lookup Tool (registered customers only) to obtain more information on the commands used in this section.

Network Diagram

This document uses this network setup:

Enable AAR

In these steps, you set the Cisco CallManager service parameter Automated Alternate Routing Enabled to True in order to enable AAR.

1. Choose System > Service Parameters and choose the Cisco Unified Communications Manager.
   
2. From the Service drop-down menu, choose Cisco CallManager.
   
3. Locate the Clusterwide Parameters (System—CCM Automated Alternate Routing) pane.
   
4. Set the Automated Alternate Routing Enable parameters toTrue.
   
   
5. Click Save.
   

Configure an AAR Group

Complete these steps:

1. Choose Call Routing>AAR groups and click Add New.
   
2. Enter the name hq_aar.
   
3. Click Save.
   
   Note: These same previous steps have to be performed in order to create another AAR group called br_aar for Branch office also.
   

Configure Phones for AAR

Complete these steps:

1. Choose Device > Phone and click Find.
   
2. Choose any phone which is in the HQ partition.
   
3. Click Line 1 in order to get to the Directory Number Configuration window.
   
4. In the AAR Settings pane, choose hq_aar for the AAR Group. For branch office phones, this has to be br_aar.
   
5. Verify that the external phone number mask is in globalized format.
   
6. Click Save.
   
7. From the Related Links, choose Configure Device and click Go.
   
8. At the Phone Configuration window, choose Global_css for the AAR CSS.
   
9. Click Save and then OK in the pop-up window.
   
10. Reset the phone.
    
11. Click Save.