Transmission Network of BTTB

Mashiur Rahman

Divisional Engineer, BTTB

Optical Fiber links:

Digital Microwave Radio Links:

Telecommunication sector, both PSTN and Mobile (PLMN), of the country experienced a revolutionary development in the last few years. BTTB has converted all it’s telephone exchanges at district level into digital by the end of 2001. The backbone transmission network of BTTB as well as the spur transmission links, connecting various districts with the backbone, are now fully digital. The transmission network of BTTB consists of both optical fiber and radio links.

Optical Fiber links:

In the last three years BTTB built about 1375 Km optical fiber network in the country under two projects. The most modern SDH technology was adopted in all these optical fiber links. Dhaka – Comilla – Feni – Chittagong backbone optical link and Feni – Choumuhini – Noakhali, Choumuhini – Lakshmipur, Comilla – B. Baria spur optical links were implemented under Dhaka – Chittagong high capacity optical fiber project. The total length of optical cable laid under this project is about 450 Km. 18 core optical cables were used in backbone link whereas spur links were built with 12 core O.F cables. The transmission capacity of the backbone is 2.5 GB/s (STM-16). Transmission capacity of Feni – Choumihini spur link is 622 MB/s (STM-4) whereas the transmission capacity of Choumuhini – Noakhali, Choumuhini - Lakshmipur and Comilla – B. Baria spur links is 155 MB/s (STM-1). Some short haul optical links like Tongi – Gazipur and B.Baria Microwave Station – B.Baria Exchange of STM-1 capacity were also built under this project. The SDH transmission equipment used in this network are from Alcatel CIT.

 Major Optical Fiber Links of BTTB (Click for Coloured Diagram)

Under the project entitled “Installation and Expansion of Digital Telephone Exchanges in various District Head Quarters of Bangladesh” which is commonly known as 216 KL project, about 925 Km 12 core optical fiber cable network was built. The SDH transmission equipment used in this network are also from Alcatel CIT. The backbone optical link built under this project is Bogra – Palashbari – Rangpur – Saidpur – Dinajpur – Thakurgaon – Panchagarh. Bogra – Palashbari – Rangpur portion of this backbone is of STM-4 capacity and rest is of STM-1 capacity. Now the present requirement of E1 claims that the Rangpur – Saidpur – Dinajpur section of the link should be upgraded to STM-4. Some spur links also were built in different areas of the country under 216 KL project. They are:

            1. Rangpur – Kurigram                                         STM-1

            2. Rangpur – Lalmonirhat                                      STM-1

            3. Saidpur – Nilphamari                                        STM-1

            4. Pabna – Shahjadpur – Sirajgonj                    STM-1

            5. Kushtia – Meherpur – Chuadanga                 STM-1

            6. Khulna – Satkhira                                             STM-1

            7. Sherpur – Mymensingh – Netrokona             STM-1

            8. Betbunia – Rangamati                                       STM-1

A proposal to upgrade the Comilla - B.Baria optical link from STM-1 to STM-4 and to build a new optical link of STM-4 capacity in B.Baria – Shahjibazar – Maulavibazar – Sylhet route from 216 KL project is now under active consideration in MOPT.

Besides the links listed above, some short haul optical links connecting several exchanges to the respective Microwave stations were also built under this project. Those are:

·        Bandarban Exch. – MW station                  STM-1

·        Cox’s Bazar Exch. – MW station                STM-1

·        Rangamati Exch. – MW station                   STM-1

·        Sherpur Exch. – MW station                       STM-1

·        Narshingdi Exch. – MW station                  STM-1

·        Satkhira Exch. – MW station                      STM-1

·        Narail Exch. – MW station                            STM-1

·        Jhenaidaha Exch. – MW station                  STM-1

·        Jessore Exch. – MW station                       STM-1

·        Bogra Exch. – MW station                            STM-1

·        Dinajpur Exch. – MW station                      STM-1

·        Barguna Exch. – MW station                      STM-1

·        Kishorgonj Exch. – MW station                  STM-1

Some short haul optical links connecting Exchanges to the corresponding Microwave stations were also constructed under different projects. Some of them are:

            a. Sylhet Exch. – MW station                            140 Mb/s PDH (Alcatel)

            b. Tangail Exch. – MW station                          140 Mb/s PDH      “    

            c. Mymensingh Exch. – MW station                  140 Mb/s PDH      “

            d. B.Baria Exch. – MW station                     STM-1     SDH (Alcatel)

            e. Ramna Exch. – Moghbazar Exch.             140 Mb/s PDH (Fujitsu)

            f. Jessore Exch. – MW station              34 Mb/s PDH       “

            g. Comilla Exch. – MW station             STM-1  SDH   (ZTE)

            h. Barisal Exch. – MW station               STM-1  SDH       “

            i. Nawabgonj Exch. – MW station                    STM-1   SDH      “

            j. Naogaon – Santahar                                      STM-1   SDH     “

The first optical network in BTTB was built in Dhaka city by M/S NEC, Japan in the year 1988. It is a PDH network of 140 Mb/s capacity which connected different exchanges of Dhaka multi exchange area. Later M/S Alcatel, France built several PDH optical networks of 4´140 Mb/s, 140 Mb/s and 34 Mb/s capacity in Dhaka, Chittagong, Khulna, Rajshahi and Sylhet cities. They are used to interconnect different exchanges of these cities or to connect MSUs to RSUs.

Another very important optical link of STM-4 capacity in Dhaka – Gazipur – Mymensingh – Tangail – Sirajgonj – Bogra route is now awaiting implementation under 266 KL project. The present traffic forecast claims that this link should be of STM-16 capacity instead of STM-4.  

Digital Microwave Radio Links:

a. PDH Radio links in district level

BTTB commissioned it’s first digital backbone microwave link in the year 1991. It is a 140 Mb/s PDH link of 2+1 configuration from Fujitsu, Japan. There are seven hops in this link which are: Dhaka – Manikgonj – Faridpur – Magura – Jessore – Khulna and Magura – Jhenaidaha – Kushtia.

Two more digital backbone microwave links were installed and commissioned by M/S Alcatel, France in 1993-1994. They are also 140 Mb/s PDH link with 2+1 configuration. One of them is in Dhaka – Narshingdi – B.Baria – Shahjibazar – Maulavibazar – Sylhet route and the other in Dhaka – Talibabad – Tangail – Sirajgonj – Bogra and Tangail – Modhupur – Mymensingh route. M/S Alcatel also installed and commissioned a point to point 140 Mb/s PDH microwave link between Chittagong and Betbunia.

Meteorological department of Bangladesh built two PDH microwave backbone links of 34 Mb/s capacity in the year 1994 and handed over to BTTB for operation and maintenance. Major portion of the capacity of these links is used by BTTB. Equipment of these links are from JRC, Japan. One of the backbone is in Khulna – Sripur (Pirojpur) – Barisal – Patuakhali route and the other is in Chittagong – Satkania – Chiringa – Cox’s Bazar route.  

Besides the backbone links listed above, there are a number of 34 Mb/s and 8 Mb/s PDH spur links now working in various districts. These are:

 ·         Khulna – Gopalgonj                                     34 Mb/s            Siemens

·         Madaripur – Shariatpur                                8 Mb/s              Haris

·         Rajbari – Faridpur                                       8 Mb/s              Haris

·         Barisal – Bhola                                           8 Mb/s              Nokia

·         Barisal – Jalokathi                                       2+2 Mb/s          Nokia

·         Barisal – Pirojpur                                        8 Mb/s              Tata

·         Khulna – Bagerhat                                      8 Mb/s              Haris

·         Patuakhali – Barguna                                  34 Mb/s            Nera

·         Jessore – Narail                                          34 Mb/s            Nera

·         Barisal – Gournadi – Madaripur                   34 Mb/s            Nera

·         Chittagong – Fatikchari -

      Manikchari – Alutila                                    34 Mb/s            Nera

·         Alutila – Khagrachari                                  8 Mb/s              Nokia

·         Bogra – Gobindagonj – Gaibandha                34 Mb/s            Nera

·         Mymensing – Gafargaon – Kishorgonj          34 Mb/s            Nera

·         Mymensingh – Jamalpur                              34 Mb/s            Nera

·         Mymensingh – Sherpur                                8 Mb/s              Nokia

·         Sylhet – Sunamgonj                                     34 Mb/s            Nera

·         Hobigonj – Maulavibazar                             34 Mb/s            Nera

·         Rajshahi – Nawabgonj                                 34 Mb/s            Nera

·         Dhaka – Manikgonj                                     34 Mb/s            Alcatel

·         Dhaka – Munshigonj                                    34 Mb/s            Alcatel

·         Comilla – Hazigonj – Chandpur                    34 Mb/s            Alcatel

b.      SDH Radio links

  BTTB entered into the era of digital SDH radio link with the commissioning of two point to point STM-1 Radio links, one between Dhaka & Savar and the other between Dhaka & Zinjira. These two Radio links were installed under 67.5 KL project and the Radio equipment of these links are from NEC, Japan. Later, in the year 2000 – 2001 STM-1 SDH Radio links from Nortel Networks, Canada were commissioned in Bogra – Naogaon – Natore – Rajshahi, Natore – Pabna – Kushtia – Jhenaidaha – Magura and Dhaka – Manikgonj – Faridpur – Magura – Jessore – Khulna* backbone routes. After completion of Dhaka – Bogra SDH optical link the above mentioned microwave backbone will be connected to this optical link in STM-1 level at Dhaka and Bogra stations and thus it will form a SDH transmission ring connecting Dhaka, Gazipur, Mymensingh, Tangail, Sirajgonj, Bogra, Naogaon, Natore, Pabna, Kushtia, Magura, Faridpur and Manikgonj stations. Total 18 hops STM-1 SDH Radio links from Hariss, Canada were also installed in Rajbari – Faridpur – Sadarpur – Madaripur – Gopalgonj – Khulna – Bagerhat – Pirojpur – Jalokathi – Barisal – Bhola – Lakshmipur and Chittagong – Satkania – Chiringa – Cox’s Bazar backbone and Madaripur – Shariatpur, Barisal – Patuakhali, Bogra – Joypurhat, Satkania - Bandarban spur routes under 216 KL project in the year 2002. The Rajbari – Khulna – Lakshmipur backbone is connected to Khulna – Satkhira optical link in STM-1 level at Khulna station and the Bogra – Joypurhat spur link is also connected to Bogra – Rangpur – Dinajpur – Panchagarh optical backbone in STM-1 level at Bogra microwave station. It is also possible to connect the Rajbari – Khulna – Lakshmipur backbone radio link with the Feni – Choumuhini – Lakshmipur spur optical link in STM-1 level at Lakshmipur station. Out of 18 Radio hops, 15 hops are already commissioned and the rest 3 hops will be commissioned within June 2003. After commissioning of all the 18 Radio hops several PDH spur radio links listed in the previous page will become spare.

Besides the PDH and SDH digital microwave Radio links listed above, some analog microwave Radio links also are still in operation in BTTB’s transmission network. Among them some important links are Dhaka – Chittagong 1800 channel NEC microwave link and Bogra – Fulbari – Ataoari 960 channel Fujitsu microwave link.< Microwave Links under 216 KL Project (Large Format Diagram)

Large Format
Microwave Links under 266 KL Project.( Coloured Large Format Diagram)

  c.       Radio network in rural area

BTTB’s transmission network for rural area is almost fully digital. Almost all the upazilas, except the upazilas of hilly districts, are connected to the respective districts by low capacity digital radio links. Upazilas of northern and western part of the country are connected to their respective districts by Bell Radio links of 8 Mb/s capacity. Upazilas of southern and eastern part of the country are connected to their respective districts by Nokia Radio links of 2+2 Mb/s or 8 Mb/s capacity. Upazilas of Cox’s Bazar, Feni, Noakhali, Lakshmipur, B.Baria, Comilla, Chandpur, Satkhira and Bagerhat are connected to their respective districts by TRT Philips Radio links. The Bell radio links have become very old and because of unavailability of spare parts it became very difficult to keep the Bell radio links operational. So, some of the Bell radio links were replaced by Tata radio links of 8 Mb/s capacity.  BTTB is also planning to replace the remaining Bell radio links gradually. Though the TRT radio links are digital still they can not support point to point E1. So, these links are not suitable for connecting the RSUs, installed at different upazilas, to the respective MSUs at district levels. For this reason BTTB is now replacing most of the TRT radio links with 8 Mb/s Alcatel radio links.  Among all the radio links of rural area, performance of Nokia radio links are most satisfactory. But these links also have become very old (2+2 Mb/s links) and their performance also are degrading day to day. So, BTTB is also planning to replace the old Nokia links gradually in near future. The upazilas of hilly districts are connected to their respective districts through 120 channel Motorola analog radio links. BTTB is planning to put small digital exchanges in the upazilas of hilly districts along with digital radio links from these districts to their upazilas.

  In the present socio-economic stage, it is not possible to connect the upazilas optically. But with the vast improvement of road communication system in the last few years, it is now possible to bring the major cities, like Khulna, Sylhet and Barisal, under optical fiber network. Khulna can be connected to the backbone optical network from Pabna through Pabna – Kushtia – Jhenaidaha – Jessore – Khulna route. Sylhet can be connecting from B.Baria if the proposal lying in MOPT is implemented and Barisal can be connected through Jessore – Magura – Faridpur – Madaripur – Barisal route. Optical network is certainly costlier than Radio network but it is much more reliable than radio network and it can carry huge traffic also. Equipment failure rate of optical network is also less. The only difficulty with optical network is the danger of cable break down. But this danger can easily be overcome by creating conscious among people through strong publicity in mass media.