Digital Telephone Switching System | Subscriber Services
5.33.1 Telephone Service
Telephone service provided by the digital exchanges shall include Dual Tone Multi Frequency (DTMF) dialing and rotary dialing, with access to local calls, toll calls, international calls, all operator services and all other special subscriber features.
5.33.2 Classes of Service Required
The digital exchanges shall include but not be limited to the following classes of service: (The actual Classes of Service Required and the percentage of exchange lines, for each class of service, shall be determined and verified during the detailed design of each project).
a) Line under service observation for observing quality of service on subscriber calls. This may be local or centralized, as required.
b) Line under malicious call hold: 0.5% of exchange lines.
c) Spare line.
d) Changed number of service interception with rerouting to operator.
e) Changed number with rerouting to announcement circuit.
f) Line temporarily out-of-service.
g) Abbreviating dialing, if required, with entry of code under subscriber’s and/or exchange control. It must be possible to store at least 30 numbers per subscriber: 0.5% of exchange lines.
h) Call waiting service, which permits a subscriber engaged in conversation to receive an audible signal, indicating that a third party wishes to talk to him: 0.5% of exchange lines.
i) Hot line, with path set through switching equipment giving callers direct access to predetermined party without dialing: 0.5% of exchange lines.
j) Three-way Calling Service: This service permits a subscriber to add a third party to an existing conversation. This is done on any call placed by or received by the subscriber: 0.5% of exchange lines.
The manufacturer shall assume that a subscriber having the three-way calling feature shall use the feature 10% of the time. The following shall be considered acceptable average holding times for both local and toll exchanges combined:
1. 120 seconds: Average call holding time.
2. 300 seconds: Average conference call holding time.
k) Call Forwarding: This service permits a subscriber to have all incoming calls transferred to some other local or toll destination. The system is arranged to allow the customer to specify this destination when activating the service, and to be able to activate or deactivate the service, from his telephone: 0.5% of exchange lines.
l) Do Not Disturb: When a line has the service activated, it is not rung on incoming calls. The calling party receives an announcement. The line can originate calls while the service is activated: 0.5% of exchange lines.
m) Wake Up: The system is arranged so that a subscriber with this feature can be recalled at a requested time. The subscriber can assign any hour and minute within the next 24 hours: 0.5% of exchange lines.
The wake up call is made at the requested time, and the line is rung for 35 seconds. If the first attempt reaches a busy line or results in no answer, a second trial is made 10 minutes later. If there is no answer to the second trial, a printout is made.
n) Manual line (off-hook) service, which is providing an automatic connection to an operator for handicapped subscribers: 0.5% of subscriber lines.
o) Multiline Hunting: This feature is applicable to individual lines, in WATS, PABX, and CENTREX lines, to provide associated lines. The feature includes a choice of station number. The maximum number of multilane hunting groups shall be 250 with up to 500 lines per group.
p) Call Diversion: With this service, all calls directed to a subscriber line while busy or if not answered within 30-45 seconds are forwarded (diverted) to an alternate local destination: 0.5% of exchange lines.
q) Automatic Call Back: 0.5% of exchange lines.
r) Inward and Outward Dialing:
1. Direct Inward Dialing (DID): 2.5% of exchange lines.
2. PABX Direct Outward Dialing (DOD): 2.5% of exchange lines.
3. Total Exchange Capacity: 2.5% + 2.5% = 5% of exchange lines.
5.33.3 Optional Classes of Service
The following classes of service shall be available to the digital switching system, along with full details of methods, limitations, and required equipment, including additional processors if needed.
a) Automatic waiting (camp-on-busy) for Centrex.
b) Radio paging.
c) Automatic credit card.
d) Long-line subscriber (providing up to 3,000 ohm loop resistance by using different techniques, including extenders).
e) Conference call: 0.5% of exchange lines.
5.33.4 Rearranging of Service Features
The digital exchange shall be equipped with sufficient flexibility to permit alterations due to a change in service requirements. It shall be possible to rearrange classes of service, routing trunk assignments, and similar service options by command through input/output devices, or through modifications to the existing store programs. The required operating terminals to accomplish such modification shall be included as interfacing peripheral devices.
5.33.5 Call Restriction
Cal-barring capabilities shall be available and shall be activated by command, under the control of the administration only. The following classes of restriction shall be provided:
a) Trunk offering barred.
b) All outgoing calls barred.
c) All terminated calls barred.
d) LDD calls barred.
e) LDD and IDDD calls barred.
f) Access to certain operator services barred.
5.33.6 Non-Telephone Services
The digital exchange shall have the capability of handling non-telephone services as well, in order to form part of an Integrated Services Digital Network (ISDN).