Article_031

IMPLEMENTATION OF NEW TECHOLOGICAL SYSTEMS OF TELEPHONE SWITCHING IN Bangladesh

A H. M. Shafiqul Islam

1. Evolution of telephone switching system.

Telephone switching in the world is existing for more than a century. During this long period many types of switching system have been designed and used in the telephone networks. Following are the chronological major stops in the evolution of the telephone switching techniques.

a) Magneto type manual exchange with local battery system.

b) CB type manual exchange with central battery system.

c) Automatic exchange will electromechanical step-by-step system.

d) Automatic exchange with electromechanical systems with register control

e) Automatic exchange with cross bar systems employing multi-stage switching networks according to the link principle and with marker controlled switching stages

I) Analogue automatic exchange with electronic control system.

g) Digital automatic exchange with Stored Programme Control (SPC) System.

A new concept of digital upto-electronic switching technique is under research stage which will in future be very much useful for the purpose of switching among the broad hand transmission superhighways.

2. Advantage and disadvantage of SPC system.

Electronic stored Programme control (SPC) equipment have some advantage and disadvantages which are summarized in the lolloping paragraphs.

2.1 Operational benefits

i) Flexibility to change traffic routing data;

ii) Flexible numbering plan;

iii) Possibility of remote operation and supervision;

iv) Integration of traffic supervision and measurement

v) Easy adaptation to future network requirements;

iv) Large overflow possibility;

2.2 Maintenance benefits

i) Reduced manpower quantity;

ii) Integrated automatic testing of subscriber lines, inter exchange, and internally circuits;

iii) Automatic fault detection and location programs;

iv) Greatly expanded centralized maintenance capability.

2.3 Administrative benefits

I) Reduced floor space requirements;

ii) Software events recording counters with records on magnetic tape;

iii) Memory update capabilities for subscribers and features;

iv) Itemized automatic billing.

2.4 Subscriber Service benefits

i) Many classes of service and new services are possible;

ii) Faster and more reliable service;

2.5 Disadvantages of SPC system

i) Much higher skill level personnel needed;

U) More intensive and detail training required;

Hi) Can he ‘note prone to complete system outages affecting a larger ha e of customers;

iv) More care in maintenance of office records;

v) A heavier dependence on manufacturers for software and training;

vi) Possible higher initial costs;

vii) Need for accurate forecasts of Busy Hour Call Attempts (BHCA);

viii) Possible susceptibility to malicious interference by maintenance personnel.

3. Economic consideration for replacement of existing equipment.

Development of new systems to take advantage of technological progress to meet new needs take into consideration for economy, reliability and compatibility with existing systems. Some of the economic considerations for replacement studies include combinations of the following 7

I) Building space savings;

ii) Operations and maintenance expense savings;

iii) Existing network inefficiencies;

iv) Numbering plan limitations;

v) Very rapid growth;

vi) changes in call charging arrangements;

vii) Possibility of additional revenue;

viii) Need for flew services;

ix) Reduction in subscriber complaints;

x) Availability and cost of new capital.

4. Alternative strategies for upgrading the telephone network.

Telecom Administrations must effectively plan to implement a smooth introduction of new technological systems into the existing network while maintaining high quality communications services to its subscribers. The evolution and expansion of a telephone network requires an Administration to cosider several alternatives for upgrading its network3:

a) Continued expansion by the addition of similar equipment to that already existing.

b) Continued expansion by adding, modifications or upgraded equipment to the existing network.

c) Early retirement of the old equipment and its replacement with a mordern SW system. Sonic telephone Administrations have decided that no non-SPC systems shall remain in the network.

d) Creation of an overlay network, by installing the modern equipment in newly established exchanges while replacing old equipment with new equipment in older exchanges when economically feasible.

In actual practice, all above four alternatives may he used simultaneously in different exchanges within the network depending upon the economic and administration’s policies appropriate to conditions encountered in each exchange.

5. Telephone exchanges in the country before liberation of Bangladesh.

The telegraph department of the British India had installed telegraph lines in our country at the later part of 9th century. Telegraph lines at that time of initial stage was mostly erected along the railway lines establishing railway control circuits and telegraph services in order to setup a communication infrastructure basically for the interest of colonial administration and trade, Limited operator dependent telephone facilities were initially introduced over the land line telegraph routes. During the British India period the evolution of telephone switching in the country was achieved n three stages viz. magneto type manual exchange. CB type manual exchange and Strowger type step-by-step automatic exchange. During Pakistan period between 1947 to 1971, a number of automatic electromechanical step-by-step system telephone exchange were installed which were Siemens designed Fl type exchange manufactured in the TIC, Haripur, Pakistan. During Pakistan period most of the exchanges in the country were of Magneto and CB type.

6. General approach of evolution of telephone switching in BTTB.

6.1 Initial take off.

After Liberation of Bangladesh, Telephone Shilpa Sangstha (TSS) in Tongi near Dhaka started manufacturing of Siemens designed EMD model automatic electromechanical unimotion switched telephone exchanges. Telegraph and Telephone department of Bangladesh (presently BTFB) extensively installed EMD exchanges after liberation of Bangladesh which created an initial take-off atmosphere for making wide expansion of telephone services to the people of various regions of the country. Especially expansions in the then subdivision head-quarters made a great contribution in making general awareness and habitual development of the people living there in about necessity of use of telephone in their every day life.

6.2 Approach of evolution of Telephone switching by BTTB

Bangladesh T&T Board (BTTB) is presently operating with four types of telephone exchanges in the country, which are Magento (Manual), CB (Manual), Analogue (Auto) and Digital (Auto) and country’s digital local exchanges were first introduced in 1990-91 fiscal year. Regarding manual exchanges, B1ITB’s oldest version magneto exchanges are working mostly in the remote rural areas and these are gradually been replaced by Central Battery (CB) exchanges. some C.B. exchanges are replaced by analogue automatic exchanges and some analougue automatic exchanges are replaced by digital exchanges. Some new digital telephone exchanges are also being gradually installed. At few places, old generation obsolete Fl model exchanges have been replaced either by EMD exchanges or by digital exchange. There are few F-I exchanges still in service giving very poor quality of service, which are badly in need of early replacement.

BTFB’s telephone exchange status as on June 1994 and June 1995 (Table-I) will give an idea on trend of change in the exchange setup.

TABLE - 1

BTTB’S telephone exchange status as on June of ‘94 & 95

7. Installation of NEC-NEAX version digital exchanges in Dhaka.

Six digital exchanges were installed in 1990-91 in the multi-exchange area of Dhaka city, the capital of Bangladesh. Optical fibre link was also introduced to interconnect these digital exchanges. These exchanges were later on expanded in two phases. Initial capacity and present capacity of these six exchanges are shown in the following Table - 2.

TABLE - 2

Capacity of NEAX version digital exchanges in Dhaka.

8. installation of ALCATEL-E-1O series digital exchanges under Chittagong Project.

A project for installation of digital exchange (ALCATEL E-l0 Version) along with replacement of an old F-I model analogue auto exchange has been undertaken by the BTTB The project consists of MSUs (Main Switching Unit), RSU’s (Remote Switching Unit), Tandem, TAX etc. switching units and optical fibre network to interconnect different switching units. The project has three phases for installation of 22,000 & 11,000 subscriber line units. Phase I portion has been completed in 1995, the phase 11 is almost completed and the contract amendment between ALCATEL and BTTB has been made for phase III portion of the work. The subscriber L.U provision in this project is shown in the Table - 3.

TABLE - 3

Exchange wise subscriber LU. of ALCATEL system under Chittagong Project.

* It includes the replacement of 7400 lines F-i analog auto exchange switching equipment by digital version.

9. Installation of ALCATEL E-1O series digital exchanges KL (Kilo line) Project.

in five cities under 130Installation of 150,000 subcriber lines capacity digital telephone exchanges (AICATEL E-10 series) in five cities of Bangladesh has been undertaken by BTTB under its largest project. The project comprises installation of new 10 MSU. new 7RSU and expansion of 2 MSU in Chittagong. The project also consists of Tandem, TAX etc. switching centers and optical fibre junction network in multi-chachange areas. This project is an on going project. A revised project Paper is submitted by BTTB to upgrade the project for installation ot’ total 200,000 subscriber lines capacity along with some other interrelated works. The subscriber L.U provision in this project is shown in Table e-4.

TABLE - 4

Exchange wise subscriber LA]. of ALCATEL System under 130 KL Project

Out of 700 lines actual expansion is 3000 because 4000 LU. connection of motijheel area releases ealier connections from Moghbazar & Nilkhet NEC digital exchange.

** Replaces F-1 exchange from Dhaka central exchange location.

* * * Replaces EMD exchange.

**** It makes expansion to the ALCATEL MSU installed earlier from Chittagong Project.

10. Istallation of ITALTEL Linea UT digital switching system in seven to was under SADE Programme.

A Programme for installation of 20,500 susbscriber lines capacity ITALTEL Linea UT digital switching system in 7 towns of Bangladesh is under implementation process. The scope of work for this SADE Programme is given below in Table-S.

TABLE - 5

Exchange wise subscriber capacity of ITALTEL system under SADE Programme.

Existing 3,500 EMD lines wilt work together.

** Existing 3100 EMD lines will work together

11. Recent like by like emergency expansion of EMD exchanges at various towns of Bangladesh.

In order to meet up pressing telephone demand 12,100 EMD tines expansion was made at 16 small district headquarters. The switching part of the same had been completed by the TSS with new equipment and handed over to BTPB before August1993. Considering the EMD system as obsolete technology, the TSS, manufacturer of EMD switching equipment in Bangladesh, decided to stop manufacturing and installation of EMD tines any further.

reusable portion of EMD switching equipment going to be released from the EMD exchanges of the cities under replacement by the digital exchanges. This way of planning for equipment reuse is an innovative and thrifty solution for maximisation of our resource utilisations.

12. Conclusion.

Bangladesh T&T Board determined to implement modern digital telephone switching system to achieve improved quality of service. Proiority of such digitalisation is given to the large cities through creation of overlay network by installing new medium or large capacity local exchanges with modern equipment, while replacing old analogue switching equipment with new digital equipment as and when found economically feasible. Most of the switching equipment of old analogue automatic exchanges in the country are EMD type. TSS has stopped production of EMD lines equipment. Under this circumstances the only economic solution to operate all the working EMD exchanges is to ensure tiny expansion and collect maintenance spare parts, from the EMD equipment released and replaced by digital exchanges. Apart from modernization of telephone exchanges by BTTE, two private operators named M/S Bangladesh Rural Telecom Authority (BRTA) and MIS Sheba Telecom will also install digital exchanges in gradual phases at the rural Thana locations to provide modern digital SPC telephone services to the rural areas. Besides the land leased PSTN services described above Cellular telephone services will also spread throughout the country very soon. Ultimately a day will come probably at the beginning of 21st century when people of everywhere in the country will enjoy benefits of telephone services from modern digital switching systems.

References

1. Choice of Telephone Switching System - GAS 6, ITUICCIYI’, Geneva 1981 (P-96)

2. Ibid (P-89)

3. Ibid (P-90)

Engr A.H.M. Shafiqul Islam obtained B.Sc. Engg. (Electrical) from Rajshahi University, Bangladesh. He joined in Bangladesh T&T Board in 1978 and did his Post Graduate Diploma in Telecom System from the University of Essex, England in 1985. He also participated in training on network planning in South Korea & India and on optical fibre cable transmission system in France. He is an associated member of Bangladesh. Computer Society & member of IEB & IEEE (USA). He is now student mentar, IEEE Bangladesh section, Presently he is Divisional Engineer, Multi-Exchange Planning, Bangladesh Telegraph and Telephone Board.

B’ITB is going to make expansion of 6500 EMD lines at 29 small district headquarters to meetup very urgent need of pressing telephone demand. For this purpose EMD switching equipment will he made available from the 

reusable portion of EMD switching equipment going to be released from the EMD exchanges of the cities under replacement by the digital exchanges. This way of planning for equipment reuse is an innovative and thrifty solution for maximization of our resource utilizations.


Engr A.H.M. Shafiqul Islam obtained B.Sc. Engg. (Electrical) from Rajshahi University, Bangladesh. He joined in Bangladesh T&T Board in 1978 and did his Post Graduate Diploma in Telecom System from the University of Essex, England in 1985. He also participated in training on network planning in South Korea & India and on optical fibre cable transmission system in France. He is an associated member of Bangladesh. Computer Society & member of IEB & IEEE (USA). He is now student mentar, IEEE Bangladesh section, Presently he is Divisional Engineer, Multi-Exchange Planning, Bangladesh Telegraph and Telephone Board.