Mitel SX-200 Documentation page 539

SECTION MITL91 OS/91 1 o-096-21 3-NA
Page 2
2.04 The subscriber number may be any series of digits from 0000
to 9999. Once again there are assigned numbers such as 1212
and 1000 that are generally reserved for special services.
Interchangeable Codes
2.05 The requirement for the total number of office codes within an
area may require the use of office codes other than the NNX
format outlined in paragraph 2.02 (i.e., the employment of codes in
NXX format). Conversely, the need for area codes eventually may be
such as to exhaust the available area code universe (NO/lx)
then also expands to an NM format. In either event the office and area
codes are known as Interchangeable codes.
2.06 When Interchangeable Office codes are used, the prefix digit "1"
has to be used to identify a long-distance call. This requirement
is met by setting a system option (System Option 242). The Home
(Local) Area code requires it to be identified when programming the
system.
Area Code Office Code Subscriber Number
where X
N
O/l
Figure 2-l North American Numbering Plan
2.07 Time, as previously mentioned, is a major factor in trunk usage.
Certain trunks will be cheaper if used at certain times of the
day. For example, consulting Figure 2-2, it is seen that regular tele-
phone service from 08:OO to 17:OO provides no discount. At this time it
would be desirable to use a WATS (Wide Area Toll Service) line to
achieve a lower cost. After 17:00, it may be more economical to use a
regular line.
NNX
= any number from 0 through 9
= any number from 2 through 9
= either the number 0 or 1
No Discount
Figure 2-2 Time Periods
which