PSTN Calculation Plan Accepted Elements
Most countries’ calculation affairs allotment some accepted elements. They usually abutment the
following types or classes of numbers:
■ Emergency services: Some countries accommodate a distinct cardinal for all emergency
services, admitting added countries accept abstracted numbers.
■ Information or agenda services: Most countries accept a cardinal for directory
services. In the United States, it is about 411.
■ Bounded calls: Bounded calls are usually chargeless and aural a bounded geographic area.
■ Adaptable calls: Most countries bill a addition for calls to a adaptable phone. The United
States. is a notable exception. Billing the addition requires that the adaptable phones be
assigned a specific cardinal range. In the United States, the addition is billed for incoming
and approachable calls, so adaptable phones can be assigned numbers from the same
pool as acceptable phones.
■ Long ambit or toll: Long ambit calls are calls alfresco of the bounded geographic
area. These calls usually crave an admission cipher (when placed from abaft a corporate
telephony system) as able-bodied as an breadth cipher and subscriber number.
■ Toll free: Toll-free calls are chargeless to the being authoritative the call. The alarm is billed to the
recipient by the account provider.
■ Premium: Premium calls acquire per-minute or per-call charges. These calls are usually
blocked by companies because they are frequently acclimated for “entertainment” purposes,
usually accepted in the United States as 900 numbers.
■ International: International calls are placed to added countries application an admission code,
followed by the ITU E.164 country code, and again the abounding subscriber number
including breadth code.
North American Calculation Plan Example
The archetype illustrated in Figure 6-10 shows the operation of the North American numbering
plan.
Chapter 6: Identifying Dial Plan Characteristics 351
Calling
Party
Called
Party
Long Distance
Carrier (Virginia)
Dialed Number:
1 7...
703...
Texas Virginia
Long Distance
Carrier (Texas)
Path to 703
(An breadth cipher of “703”
summarizes an
area in VA.)
Path to 1
(A “1” indicates
that the destination
is NOT local.)
Local
CO
Local
CO Path to 0123
(Subscriber)
Path to 555
(A prefix of “555”
summarizes a
smaller breadth in VA.)
1
2
4
5
3
Figure 6-10 North American Calculation Plan
The alarm acquisition action is as follows:
1. A subscriber in Texas dials 1 703 555-0123.
2. The bounded CO in Texas recognizes that the 1 agency this is not a bounded alarm and forwards
the alarm to a long-distance carrier in Texas.
3. The long-distance carrier in Texas recognizes 703 as an breadth cipher in Virginia and forwards
the alarm to a long-distance carrier in Virginia.
4. The long-distance carrier in Virginia assiduously the alarm to the bounded CO.
5. The bounded CO delivers the alarm to the actual subscriber.