SARK UCS/MVP Class of Service Implementation.

Introduction

Class of Service has been a feature of high-end PBX systems for many years. It tends not to be found on low-end and low mid-range offerings. Essentially, Classes of Service define selections, or restrictions, based upon either time, or the dialled number domain. In this way, a degree of control can be exercised upon telephone extensions in terms of which subsets of the telephone number domain they are allowed to dial.

SAK COS Implementation.

SARK/SAIL implements Class of Service through the "Class of Service" relation in the SARK/SAIL database. Each tuple references a set of restrictions, or selections, drawn upon the underlying telephone number domain (or, at least, that part of the domain which is of interest to an individual PBX implementation). There is no imposed limit to the cardinality of the Class of Service relation (other than those imposed by the underlying database manager). It may freely vary from user-implementation to user implementation and, since the restrictions themselves are freeform and user-defined, it is extremely extensible in nature and can vary to accomodate the physical numbering schemes of individual countries and regions. Provided a target sub-set can be defined using regular Asterisk number matching nomenclature then it can be used as a restriction in a Class of Service tuple.

Class of Service tuples can be created and deleted at will. Once a new tuple exists it is automatically exposed in the extensions-update panel and it may be nominated as a restriction for the selected extension. Referential integrity is enforced across the two domains such that physical deletion of a Class of Service tuple will drop that restriction from any extension upon which it is imposed.

Creating a Class of Service tuple to restrict International Dialling from the United Kingdom.

Tuples are defined, updated and deleted in the Class of Service panel within the server-manager. To create a new tuple, click on the "New COS" button.

In the United Kingdom, the IDD code (International Direct Dial code), is 00. Thus to create an international dialling restriction we can create a tuple as follows...

Let's look at the specification. We have given the tuple a name (key) "International" and declared it active, which meanbs that this tuple will generate restrictions at the next system commit. Declaring a tuple inactive will cause it to be ignored at the next system commit. This is useful for temporarily removing a restraint from the system without physically deleting it.

The two defaults "open" and "closed" dictate whether this restraint will be automatically applied to new extensions' open and closed outbound routes when they are created.

Finally, the dial plan specifies a regular set of one or more Asterisk dial plan statements separated by whitespace. In this case there is only one statement; _00. which will match the entire set of UK Internationally dialled numbers.

A sample Class of Service Relation.

Above is an example Class of Service relation for the UK. It has restrictions for International, National, Mobile, Local and Premium Rate number sub-sets. The PremiumRate? tuple is interesting in that it uses two dial plans to restrict 09 numbers and 087 numbers, both sub-sets are charged at premium rate in the UK.

Applying Class of Service to individual extensions.

Class of Service restrictions are selected for an extension in the extension update panel. Here is an example of a Cisco 7960 with restrictions applied...

This extension is allowed to call all but International and Mobile numbers during open hours and only allowed to call other extensions and emergency numbers during closed hours.

The special class EMERGENCY

EMERGENCY numbers can always be called from any extension, irrespective of any class of service restrictions applied. You define the EMERGENCY sub-set in Globals panel...

In the above example we have chosen the US emergency code 911, the UK emergency code 999 and the European international emergency code 112. These codes will ALWAYS be dialable from any phone in the system.