Mitel MiVoice Business: Understanding Class of Restriction

Class of restriction (COR) is an important feature on MiVoice controllers for protection and control over what calls can access an outgoing trunk group.

COR can be split into two parts, the class of restriction group themselves, and its members which are defined by an Class of Restriction number.

Confusion can occur since class of restriction group are also identified with a number, so it’s important to distinguish between a class of restriction group and a class of restriction number.

If a class of restriction number if part of a class of restriction group, the station associated with that number will not be able to access the outgoing route. To summarise, if a class of restriction is a member of a class of restriction group, it is blocked.

Classes of restriction can assigned to groups in the form System Properties > System Feature Settings > Class of Restriction Groups

Different parts of the system will utilise a class of restriction group to control its use, or can be assigned a class of restriction identifier to be used within groups.

Utilises a Class of Restriction Group

ARS Route (Blocks access to route)

ARS Leading Digits (Blocks access to a route as soon as leading digit is received)

Assigned a Class of Restriction Number

Station Attributes (COR assigned to individual phones)

Trunk Attributes (COR assigned to external trunks)

Use cases of class of restriction can include:

  • Stopping voicemail ports from dialing out of an external trunk
  • Only allowing international dialing for a select class of stations
  • Preventing an incoming trunk call from being able to dial out of another trunk



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