What happens when the phone cannot reach the call manager (for any reason really)? Well, hopefully there is some fault tolerance built into your design. The IP phone likely has an SRST gateway defined and will loyally register to the SRST gateway in the event that it cannot reach the call-manager.
By default, what kind of call can the user place from an SRST-registered IP Phone? Well, if you have not implemented any kind of restrictions - they can call ANYWHERE.
Imagine a fiber cut that is going to take the local provider a couple of days to restore. This cut has prevented your IP Phones from reaching your call-manager. Luckily, you have a functioning SRST gateway local to the phones. Unluckily, even your lobby phones can now make international calls! Your phone just rang and your manager's manager wants to know how to stop this!
Class of Restrictions (COR) Overview
Class of Restrictions (COR) is a Cisco voice gateway feature that enables Class of Service (COS) or calling privileges to be assigned. It is most commonly used with Cisco Survivable Remote Site Telephony (SRST) and Cisco CallManager Express but can be applied to any dial peer.
COR is often described as a lock and key mechanism. Locks are assigned to dial peers with an outgoing COR list. Keys are assigned to dial peers with an incoming COR list.
The COR feature provides the ability to deny certain call attempts based on the incoming and outgoing CORs provisioned on the dial-peers. COR is required only when you want to restrict the ability of some phones to make certain types of calls but allow other phones to place those calls.
COR is used to specify which incoming dial-peer can use which outgoing dial-peer to make a call. Each dial-peer can be provisioned with an incoming and an outgoing COR list. The corlist command sets the dial-peer COR parameter for dial-peers and the directory numbers that are created for Cisco IP phones associated with the Cisco CallManager Express router. COR functionality provides the ability to deny certain call attempts on the basis of the incoming and outgoing CORs that are provisioned on the dial-peers.
If the COR applied on an incoming dial-peer (for incoming calls) is a super set or equal to the COR applied to the outgoing dial-peer (for outgoing calls), the call goes through.
WARNING, WARNING: By default, an incoming call leg has the highest COR priority and the outgoing COR list has the lowest COR priority. This means that if there is no COR configuration for incoming calls on a dial-peer, then you can make a call from this dial-peer (a phone attached to this dial-peer) going out of any other dial-peer, irrespective of the COR configuration on that dial-peer.
Class of Restriction (COR) Configuration
With this configuration:
- dn 1001 can call all numbers
- dn 1002 can call all number except "call1900"
- dn 1003 can call only emergency and local calls
- dn 1004 can call all numbers (has no corlist applied)
dial-peer cor custom
dial-peer cor list Manager
dial-peer cor list Facilities
dial-peer cor list Guest
dial-peer voice 1 voip
session target ipv4:18.104.22.168
corlist outgoing calllocal
dial-peer voice 2 voip
session target ipv4:22.214.171.124
corlist outgoing call1800
dial-peer voice 3 pots
corlist outgoing call1900
dial-peer voice 4 pots
corlist outgoing emergency
dial-peer voice 5 pots
cor incoming Manager
cor incoming Facilities
cor incoming Guest
Configuring Class of Restrictions