Hierarchical Numbering Plans
The previous section discussed the Public International
Telecommunications Numbering Plan (E.164), national numbering plans, and private
numbering plans. Each of the numbering plans can benefit, in terms of
scalability, from a hierarchical design. A hierarchical design has the following
advantages:
-
Simplified provisioning Refers
to the ability to easily add new groups and modify existing groups
-
Simplified routing Keeps local
calls local and uses a specialized number, such as an area code, for
long-distance calls
-
Summarization Establishes
groups of numbers in a specific geographical area or functional group
-
Scalability Provides
additional high-level number groups
-
Management Controls number
groups from a single point in the overall network
The North American Numbering Plan (NANP) serves as a good role
model for a scalable numbering plan. Consider how the NANP might be adapted to
your environment. To illustrate the operation of the NANP, examine Figure 5-11.
In Figure 5-11, the
calling party dials 1-703-555-0123. The calling party's local central office
(CO) forwards the call to a long-distance carrier because the first digit (that
is, the 1) indicated the call was a long-distance call. The long-distance
carrier then forwards the call, based on the dialed area code, to a Virginia
long-distance office. The Virginia long-distance office forwards the call, based
on the CO code (that is, the NXX code), to an
Alexandria CO. Finally, the Alexandria CO, based on the last four digits,
forwards the call out to the called party.
While the NANP acts as a good starting point in designing a
numbering plan, it is not always easy to design a hierarchical numbering plan.
Existing numbering plans in the network might include proprietary PBXs, key
systems, and telephony services such as a Centrex service. The necessity to
conform to the PSTN at the gateways also contributes to the complexity of the
design. Translation between these systems is a difficult task. If possible,
avoid retraining system users. The goal is to design a numbering plan that has
the following attributes:
-
Minimal impact on existing systems
-
Minimal impact on users of the system
-
Minimal translation configuration
-
Consideration of anticipated growth
Span Engineering LLC will use the full ten-digit DID numbers
that are assigned by the PSTN for the company's internal numbering plan. Using
the ten-digit numbers provides Span Engineering with the following benefits:
-
Allows easy integration to the PSTN at each local campus with
minimal digit manipulation
-
Allows dial plans to summarize call routing for sites that use
multiple number ranges
-
Provides flexibility for the dial plan to use shorter dialing
patterns as extensions within the voice network
Sections
Comments (0 posted)
Syndication
