Calling privileges describe the types of calls that a phone, or a class of phones, is able to place. For example, you might not want your lobby phones to be able to place long-distance calls, or you might want to restrict some employees from placing international calls. The call processing system typically controls these types of restrictions. When the router is the call processing system, running either SRST or CallManager Express, you implement calling privileges using COR.
COR is required only when you want to restrict some phones from making certain types of calls while allowing other phones to place those calls. If you do not want to allow any phones to call 1-900 "premium" calls in the United States, you can build your dial peers to prevent these calls. This is much simpler than implementing COR to restrict all phones from placing 1-900 calls.
COR is often described as a lock and key mechanism. Locks are assigned to dial peers using an outgoing COR list. Keys are assigned to dial peers using an incoming COR list. For a call to succeed, the inbound dial peer must have the key for each of the locks that is assigned to the outbound dial peer.
Assume that you want to allow users in Dept. A to make international calls, but users in Dept. B should not be allowed to call internationally. In that case, you would assign an International outgoing COR list containing a lock called "International" to the outgoing dial peer. You would assign an incoming COR list that contains "International" (and possibly other types of calls) to the incoming dial peers associated with Dept. A. The incoming dial peers that are associated with Dept. B would not include "International." Figure 12-1 illustrates the concept of incoming and outgoing COR lists.
Figure 12-1. Incoming and Outgoing COR Lists
As always, some exceptions cause the lock and key analogy to break down. The most important exception is when no incoming COR list is assigned to the inbound dial peer. In this case, the call succeeds even if an outgoing COR list is assigned to the outbound dial peer.
Part I: Voice Gateways and Gatekeepers
Gateways and Gatekeepers
Part II: Gateways
Media Gateway Control Protocol
Session Initiation Protocol
Connecting to the PSTN
Connecting to PBXs
Connecting to an IP WAN
Influencing Path Selection
Configuring Class of Restrictions
SRST and MGCP Gateway Fallback
Using Tcl Scripts and VoiceXML
Part III: Gatekeepers
Part IV: IP-to-IP Gateways
Cisco Multiservice IP-to-IP Gateway
Appendix A. Answers to Chapter-Ending Review Questions