Uniform On-Net Dial Plan Example Best CCSP Certification in Gurgaon

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 A dial plan should be designed so that all extensions within the system are reached in a
uniform way. A fixed number of digits is used to reach a given extension from any on-net
origination point. Uniform dialing is desirable because of the simplicity it presents to users.
A user does not have to remember different ways to dial a number when calling from
various locations.
Table 11-1 is an example of a four-digit uniform on-net dial plan. Various sites in Table 11-1
were assigned numbers in the following ways:
■ Site A, the company headquarters, requires more than 1000 extensions, so two ranges
of numbers have been retained (1XXX and 5XXX). Note that the corresponding DID
ranges must also be retained from the site’s local exchange carrier (LEC).
■ Site B has been assigned the range (2XXX), allowing for up to 1000 extensions.
IP WAN
IP
2001
IP
2002
IP
2003
IP
3001
IP
3002
4001
555-2001
408 555-4001
Dials 4001
Dials 9 555-2001
Dials 3001
HQ
Site 1
Site 2
IP IP
4002
V
V V
PSTN
On-Net
Abbreviated
Off-Net
254 Chapter 11: Call Routing Components
■ Site C was assigned a four-digit range, but it has been split between 100 DID extensions
(415 555-30XX) and up to 900 non-DID extensions. If growth requires more extensions
for DID, any unassigned numbers from the non-DID range could be used.
■ Sites D and E were each assigned 500 numbers from the 4XXX range. Note that their
corresponding DID ranges must match each of the site’s respective portions of the
4XXX range. Because the DID ranges are for different sites (probably from different
PSTN service providers), more coordination effort is required to split ranges between
sites. As the number of sites assigned within a given range increases, it becomes
increasingly difficult (sometimes impossible) to make full use of an entire range.
■ Site F’s range is split between 900 DID numbers (6[0–8]XX) and 100 non-DID
numbers (69XX).
■ The ranges 7XXX and 8XXX are reserved for future use.
Table 11-1 Uniform Dial Plan Example
Directory
Number
Range Usage DID Ranges Non-DID Ranges
0XXX Excluded: 0 is used to
reach the operator.
1XXX Site A extensions. 418 555 1XXX Not applicable
2XXX Site B extensions. 919 555 2XXX Not applicable
3XXX Site C extensions. 415 555 30XX 3[1–9]XX
4[0–4]XX Site D extensions. 613 555 4[0–4]XX Not applicable
4[5–9]XX Site E extensions. 450 555 4[5–9]XX Not applicable
5XXX Additional Site A
extensions.
418 555 5XXX Not applicable
6XXX Site F extensions. 514 555 6[0–8]XX 69XX
7XXX Future extensions.
8XXX Future extensions.
9XXX Excluded: 9 used as
access code.
Call Routing 255
When the enterprise consists of few sites, such an approach can be used with few
complications. Large enterprises (in terms of number of extensions and sites) may
face more of the following challenges in designing a uniform dial plan:
■ The number of extensions necessary can exceed the range afforded by the number of
digits being considered for the dial plan. For instance, if more than 8000 extensions are
required (considering the exclusions of the 0XXX and 9XXX ranges), the system may
require that an abbreviated dial plan use more than four digits.
■ Matching on-net abbreviated extensions to DID numbers means that when a new DID
range is obtained from a local exchange carrier, it cannot conflict with the preexisting
on-net abbreviated dial ranges. For example, if the DID range of 415 555-1XXX exists
in a system using a four-digit uniform abbreviated dial plan, and DID range 650 556-
1XXX is also being considered, it might be desirable to increase the number of digits
for on-net dialing to five. In this example, the five-digit on-net ranges 51XXX and
61XXX would not overlap.
■ Most systems require the exclusion of certain ranges because of off-net access codes
and operator dialing. In such a system where 9 and 0 are reserved codes, no dial plan
(uniform or not) could accommodate on-net extension dialing that begins with 9 or 0.
This means that DID ranges could not be used if they would force the use of 9 or 0 as
the first digit in the dial plan. For instance, in a five-digit abbreviated dial plan, the DID
range 415 559-XXXX (or any subset thereof) could not be used. In this example,
alternatives include increasing the length of the abbreviated dialing to six or more
digits or avoiding any DID range whose last five digits start with 9.