Call Handling, Routing and Signaling | Digital Telephone Switching Systems


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Call Handling, Routing and Signaling | Digital Telephone Switching Systems

5.30.1 Numbering Capability

The exchange shall have the capacity to provide for five, six and seven digit subscriber numbers, plus one, two, or three digit area codes, and one zero (0) or two zero (00) access codes. International numbers shall have up to sixteen (16) digits.

A minimum of 256 classes of service shall be provided for lines, and also a minimum of 256 classes of service shall be supplied for trunks.
The CO exchange shall be part of the integrated national numbering scheme of the Saudi Telephone Company (STC) for Saudi Aramco.
The exchange shall be capable of providing the following services (depending upon the requirements of each individual site), consistent with the numbering plan and relevant originating and terminating classes of services:
a) Local Services.
b) Special Services.
c) National and International long-distance services.
d) Optional services to subscribers.

5.30.2 Digit Processing, Storage and Analysis

The exchange shall have the capacity to store up to 16 digits and analyze the relevant digits according to the specified numbering plan.
The offered exchanges shall allow sufficient analysis to satisfy the requirement of the present and future numbering plan. The analysis shall be able to deal with a number of digits that may range up to eight (8).
It shall be possible to modify the analysis tables during exchange operation without interrupting traffic handling.
In addition to the ability to recognize the digit key signals, exchanges shall have the capacity (via the DTMF calling devices) to store and respond to the signals (*) and (#), and to signals A, B, C, and D, corresponding to the fourth column of the DTMF (Dual Tone Multi Frequency) keyboard.

5.30.3 Number Allocation

The system shall allow the allocation of a subscriber line to any equipment position in the exchange, without changing the directory number assigned to it.
PABX numbering shall not require a special series of numbers. The facility to analyze all digits of PABX directory numbers, whatever the size of PABX route, shall be available. PABX number need not be consecutive.

5.30.4 Call Hold and Call Release

Under normal conditions, calls shall be held under control of the calling party. Exceptions to this rule will be as follow:
a) Malicious Calls (Harassment/Nuisance Calls)
Call release will be under control of the called party.
b) Manual Hold
Manual hold by the operator is required, under the following special cases:
1. When the called party does not answer, ringing is applied until the calling party or a programmable time out (90 seconds) releases the call. After the release, the calling party and the called party shall be free.
2. When the called party releases first, the calling line will revert to a busy tone after a time of 4 to 120 seconds (adjustable).
3. When the calling party releases first, the called line is put into line lockout until the called party hangs up.
c) Release Supervision
Supervision of call release shall be as follows:
1. For intra-office and outgoing calls release of the connection shall be controlled by the calling subscriber after completion of the call.
2. For the combined line recording calls, release of the connection shall be controlled by, both the operator and the calling subscriber.
3. For local calls, the exchange equipment shall automatically release (force release) either party, if one of them fails to hang up within a time period of up to 45 seconds after the other party hangs up.
4. DDD/IDDD Calls
When the exchange switch serves as the charging point for DDD and IDDD calls, control of the circuit release shall be as follows:

 If the calling line goes on-hook first, the circuit shall be release within 240 ms.
 If the called line goes on hook first and the calling line remains off hook for longer than 10 seconds after the succeeding office has returned a clear back signal (an on hook), the exchange shall send an on hook toward the succeeding office with a minimum duration of 240 ms to force release of the succeeding office and the reorder tone shall be returned for 30 seconds to the originating office. However, if the succeeding office returns an off hook signal before 10 seconds have elapsed after the exchange receives the clear back signal from the succeeding office, the clear back signal shall be ignored.
d) Special Cases of Call Handling
The call handling of special cases shall be as follows:
1) When the called line is busy or in line lockout, a busy tone shall be returned to the calling line.
2) When the called line is out of order, denied, spare, or temporarily out of service, connection to a recorded announcement shall be made.
3) When a subscriber dials a code or number not permitted according to his class of service, the call shall be routed to a recorded announcement.
4) Malicious Calls (Harassment/Nuisance Calls)
When a subscriber’s line is set up for malicious call trace, the following procedures shall apply:
 Printout report of a called line
If subscribers on a particular line or PABX group complain of receiving malicious calls, the group may be marked for observation as a “malicious call receiver.” In that case, each time that a call is completed to a “malicious call receiver,” a printout report shall be made indicating the identity of the calling line or trunk, the called number, the date, and the time of day.
 Printout report of calling line or trunk
When a particular line or trunk group is suspected of originating malicious calls, it can be marked for observation as a “malicious call originator.” Each time that a call is originated by a “malicious call originator,” a printout report shall be made indicating the identity of the calling line or trunk, the called number, the date, and the time of day.
 Exchange alarm in response to switch-hook flashing
When a subscriber line has been marked as a “malicious call receiver,” this party can give a “switch-hook flash” when receiving a malicious call. The “switch-hook flash” must cause an audible alarm at the local exchange where the party is connected and printout the calling subscriber number.
5) PABX Direct Inward Dialing (DID)
Provision for direct dialing shall be provided for all PABXs (Private Automatic Branch Exchange). The numbers allocated for DID PABXs shall be integrated within the national numbering plan. For billing purposes, the local exchange shall be equipped to send answering signals to the PABX when the called party answers.
6) PABX Outward Dialing
Outward dialing shall be possible from a PABX to the local exchange.
e) Verification Calls
Operators shall be able to place verification calls by dialing the subscriber line number receiving an audible tone from the switch.
f) Trunk Offering
Local exchanges shall be equipped with trunk offering facilities to enable operators or test personnel at a remote center in the network to override an engaged subscriber without breaking the establish connection. The exchange shall supply a warning tone. Also the local exchanges shall be equipped to allow marking of subscriber lines by category in order to inhibit operator intrusion.

5.30.5 Signaling

The signaling of the exchange shall be compatible with the Saudi Aramco’s existing signaling systems. Furthermore, the exchange shall be able to operate with Common Channel Signaling (CCS), and support ITU-T recommended Channel Associated Signaling (CAS) in time slot 16 of the 2.048 Mb/s (E1) facilities terminating on the switch.
(For “data link layer specification” see ISDN on section 5.23 of this standard).
a) National Signaling System
The exchange shall be capable of supporting, as a minimum, the basic signaling codes and schemes identified bellow:
1. DC Loop Line Signaling (2-Wire)
The DC loop line signaling is used for one-way operation over 2 wire circuits in combination with Multi Frequency Code (MFC) register signaling.
2. Discontinuous Line Signaling
The discontinuous line signaling is used for one-way or both way operations over 4 wire circuits in combination with MFC register signaling. The signals can be sent out-band or in a digital form Pulse Code Modulation (PCM) circuits.
3. PCM Line Signaling for 32 Channels (E1)
The 32 channel PCM signaling is for one-way operation over 32 channel PCM circuits.
4. Register Signaling
A Multi Frequency Code (MFC) with six frequencies in the forward direction and four in the backward direction is used for register signaling. Any signal, in either direction, is distinguished by the simultaneous transmission of two frequencies. The numeric signals are sent in the forward direction and the control signal in the backward direction. The signals are transmitted from a sender and are received in a register (or a receiver); hence, there are registers and senders at each end of the signaling path.
 ITU-T Signaling System No. 7
The national version of ITU-T SS No. 7 shall be according to ITU-T Q.701 – Q.707 [Message Transfer Part (MTP)], and ITU-T Q.721 – Q.725 [Telephone User Part (TUP)]. The interface for the 2048 kb/s primary shall conform to ITU-T G.704 (synchronous frame structures), where there are 32 time slots per frame, numbered 0 to 31, and the number of bits per frame is 256 (8X32). The 8-bit frame alignment occupies position 1 to 8 in time slot 0 of every other frame in the CEPT30+2 format. See section 5.23 for additional information about ISDN.
 Signaling for International Traffic
The CO digital exchanges shall comply with ITU-T Signaling Systems No. 1, No. 5, No. 6, and R2. Also, the CO digital exchanges shall comply with ITU-T Signaling System No. 7 regarding ISDN capabilities, unless otherwise will be stated by Saudi Aramco in writing.
Commentary Note:
The following reference information, associated with the R2-Multi-Frequency Code (R2-MFC) register signaling requirements, is provided for the design of the switching system and shall be verified during the detailed design of each project.
(For “data link layer specification” see ISDN on section 5.23 of this standard).
R2 – MFC
Generally, as is defined in the ITU-T Recommendations Q.440 and Q.441. Specifically, frequencies shall be as specified in Table 4/Q.441. At the present time, Saudi Aramco is using the ETSI-PRI signaling for the Lucent’s No. 5ESS Central Office (CO) & PABX switches, and the EURO-ISDN signaling for the Nortel’s DMS & Meridian switches. However, the Saudi Telephone Company (STC) and Saudi Aramco’s implementation of multi-frequency compelled register signaling varies somewhat from the ITU-T Recommendations. The exact meaning of the forward and backward signals within the Saudi Aramco’s network, and between the Saudi Aramco’s and STC’s networks, are defined below:

1. Digits 1-10 are used as address digits
2. ITU-T = same as ITU-T Recommendations Q.440 through Q.480.
3. Same as first forward digit if line status is marked by the digital Central Office (CO), associated with the PABX, as Charged Number Intercept. The call is routed to Charged Number Intercept Recorder. (“I” trunk group to be dedicated at time of data base engineering). “I – 11” is never sent to STC.
4. NS = Never sent within the Saudi Aramco network or to STC.
5. INV = Treat as invalid if received.
6. II-5 is sent and received within the Saudi Aramco network.
7. A-5 following any other Group A signal indicates request for calling party’s category. A-5 immediately following an A-5 indicates send first or next digit of calling party address [Automatic Number Identification (ANI)]. The receiving exchange may request return to sending called party address by returning A-1, A-2, A-7 or A-8 at any time during transmission of category or ANI.
The CO digital switching system shall be capable of meeting the requirements of ITU-T Recommendation ITU-T G.121 for digital switching interfacing to the Saudi Aramco telephone network, and capable of sending and receiving Multi-Frequency Code (MFC), Dual Tone Multi-Frequency (DTMF), and Dial Pulse (DP) signaling.

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