AAR simplified in 5 minutes

In brief, AAR is for Automated Alternate Routing in case the WAN/IP network routing or bandwidth is restrictive to pass voice calls. Don't confuse this with SRST which is another subject

Procedure to setup AAR:

1. Decrease the bandwidth between sites so that a voice call wont have enough bandwidth, i.e change location bandwidth to 20K (minimum is 24K for g728 and 80K for g711).
2. on CUCM, Call-Routing / AAR-Group, add AAR-HQ, AAR-BR1 ...
3. Depend on the DialPlan configured previously, there 're 2 scenarios here for AAR routing. 
4. If you configured global Route-Pattern  \+!  then adding Translation-Pattern to route calls , there 're no need to add Dial_prefix between sites since the global RP  \+! should match all routes.
5. If you configured multiple RP for local/LD/INTL numbers, then calls using PSTN from HQ to BR1 should include prefix 9 (if BR1 External Phone Number Mask is 11 digits , i.e 1312301XXXX)  or prefix 91 (if BR1 External Phone Number Mask is 10 digits , i.e 312301XXXX)  and local calls inside HQ should use prefix 9 .
6. Update both HQ and BR1 Device/Phone AAR-CSS and AAR-Group with appropriate info. 
7. Update both HQ and BR1 Device/Phone/Line  AAR Settings with appropriate AAR Group.
8. Update both HQ and BR1 Gateway  AAR-CSS and AAR-Group with appropriate info.

Test by changing Location bandwidth of BR1 site to 20K. Calls from HQ phone to BR1 phone should be using PSTN with message "Network Congestion - Rerouting" appears on the HQ phone.