Describe the characteristics and requirements of a numbering plan

Exam: 642-437 - Cisco Voice over IP (CVOICE)


Telecommunications define a numbering plan as a process of allocating numbers to an appliance. If we need to amalgamate the prevailing voice networks and VoIP networks, we need to draw a suitable numbering plan. Moreover, we should be equipped with the required knowledge for successful execution of call routing. There are two types of numbering plans:

Private Numbering plans - As the name suggests private numbering plans need not stick to a format. It can be mutilated according to the requirement. But, a good private numbering plan operator will draft it accordingly so that it coincides with PSTN network.

Public or PSTN numbering plans - Every country has a distinctive numbering plan. Appended below are the common numbering plans:

  • North American Numbering plan - This plan was introduced by AT and T in the year 1951. It is an incorporated plan which is a simplified version of direct dialing the long distant calls. The pattern is NXX-NXX-XXXX which is defined as area code-central office code-station number.

  • European telephony numbering space - ETNS corresponds to the national numbering spaces. It feeds pan-European services. The purpose s to have an effectual numbering for European international services. Four ETNS services are available which are as follows:

    • Public service application
    • Customer service application
    • Corporate networks
    • Personal numbering

Plans may be fixed or of variable length. A fixed plan will depict a fixed length of area and local code where as a variable length being not standardized will consist of different lengths of area code or local code or both. A numbering plan can incorporate various parameters such as country code, area code, subscriber number, trunk prefix and international prefix.

Fixed and Variable-Lenght Numbering Plan Comparison

Scalable numbering plan - This plan has a management, scalability, summarization, simplified routing and provisioning. If we want that a numbering plan should be exceptionally executed, it should have nil or least impact on existing systems, users of the systems, least translation configuration and of course should have a path of anticipated growth.

Scalable plans can be non-overlapping or overlapping plans. The same are described underneath:

Non overlapping numbering plan - A plan should be developed within the system uniformity. The number of digits used should be uniform so as to maintain the simplicity. There should be a similar way from each calling point. But this plan carries a major disadvantage. In real life it is considered as unrealistic.

Overlapping numbering plans - These plans are poorly structured and difficult for a user to use at the end point. But, it has been noticed that it is useful in real life. It can be enforced any time depending upon the need of the organization and does not require any cautious approach in designing.

Private and public numbering plan integration

Though the integration is important as the private numbering can reach the public numbering end point but this plan integration still faces certain challenges. These challenges can be in the form of varying number lengths or there can be addition or subtraction of area codes.


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