About BTCL

About BTCL

 The Telegraph branch under the Posts and Telegraph Department was created in 1853 in the then British India and was regulated afterwards under the Telegraph Act-1885. The Telegraph branch was reconstructed in 1962 in the then East Pakistan as Pakistan Telegraph and Telephone Department. In 1971, after the independence of Bangladesh, Bangladesh Telegraph and Telephone Department was set up under the Ministry of Posts and Telecommunications. This was converted into a corporate body named 'Telegraph and Telephone Board' by promulgation of Telegraph and Telephone Board Ordinance, 1975. In pursuance of an ordinance of 1979, Telegraph and Telephone Board was converted into Bangladesh Telegraph and Telephone Board (BTTB), as a Government Board. From 1^st, July, 2008, as per the Telecommunication policy,1998, BTTB was converted into a public limited company - Bangladesh Telecommunication Company Limited through another ordinance.

Bangladesh Telecommunications Company Limited (BTCL), a state owned premier telephone company, to fulfill government’s pledge to provide access to affordable and effective internet connectivity all over the country has launched broadband services under brand name ‘BCube’ through its existing fixed phone connections.

Timeline of BTCL

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1853		Formation of Posts and Telegraph Department in British India
	1885		Telegraph Act-1885
1933		Wireless Act-1933
1962		Renamed as Pakistan Telegraph and Telephone Department
1971		Renamed as Bangladesh Telegraph & Telephone Department under Ministry of Posts  & Telecommunications
1975		Telegraph and Telephone Board Ordinance
1979		Bangladesh Telegraph and Telephone Board (BTTB) Ordinance with right to issue license  for Telecom & Wireless services.
1998		Telecommunication Policy-1998
2001		Telecommunication Act-2001 to form Bangladesh Telecommunication Regulatory  Commission (BTRC). Jobs of former Frequency and Wireless Board (under Ministry of  Posts and Telecommunications) were vested upon BTRC.
2008		BTTB was converted into BTCL (Bangladesh Telecommunications Company Limited) from  1st July 2008. Bangladesh Government owns all shares of BTCL. Shares will be offloaded  later to the public

Related Terminologies:
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# PSTN: Public Switched Telephone Network
# MSU: Main Switching Unit
# MDF: Main Distribution Frame
# TAX: Trunk Automatic Exchange
# ITX: International Trunk Exchange
# PCM: Pulse Code Modulation
# DP: Distribution Point
# SPDT: Single Pole Double Through
# EN: Enterprise Network
# SLN: Subscriber Line Number
# TSW: Tactical Switching
# IPLC: International Private Leased Circuit
# ADSL: Asymmetric Digital Subscriber Line
# INS: International Network Subsystem
# CCS: Control Circuit Subsystem
# STM: Synchronized Transfer Module
# LPD: Lens Photo Diode
# DDF: Digital Distribution Frame
# SDH: Synchronized Digital Hierarchy
# EOC: Embedded Operations Channel
# OLT: Optical Light Transmission
# TANDEM: the exchange that is used to connect other exchanges
# E1: A communication line that multiplexes thirty voice channels and two control
channels onto a single communication line. The E1 line uses 256 bit frames and
transmitted at 2.048 Mbps.

SERVICES: 
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                                   Fig 1 : services provided by BTCL

PSTN: Phone, ISDN, Value Added Service

Internet: Dial-up & ADSL Broadband (BCube)

Web hosting & DNS: .bd domain registration & ,bd whois

 IPLC: Voice/Data leased line at nx64Kbps

DDN: Digital Data Network (WAN) (BLink)

IN: Toll Free Phone, Prepaid Phone, Prepaid Card

Transmission: E1, E3, STM-1, STM-4

PSTN (Public Switched Telephone Network) or Landline

 Ø   LOCAL call (within same exchange or multi-exchange) (call rate: 30 paisa/minute)

 Ø  NWD:  Nation Wide Dialing, requires NWD code  (call rate: 30 paisa/minute)

 Ø   EISD: Economy ISD

(From any NWD phone, dial 012, then country code & number in 55 countries)

 Ø ISD: International Subscribers’ Dialing

(From an ISD phone, dial 00, then country code and number)

 Ø   ISDN (Integrated Services Digital Network)

    Ø  BTCL provides Value Added Services (VAS) like  Call barring,  Abbreviated dialing,  Call  Conference, Call waiting, Wake up call  (Alarm),  Subscriber absence message facilities,  Call establish facilities to busy subscriber, Hotline facilities,  Call Forwarding,  Temporary disconnection on request, Don’t disturb message etc.         

INTERNET

 Ø   Dial-up Internet: Available around the country. Requires a dial-up modem. Voice call is unavailable   vcvwhen logged in.

 Ø Dial-up Premium Internet: Available around the country. No need to apply. Requires a dial-up  fgmodem.

 Ø      Broadband Internet: ADSL (Asymmetric Digital Subscriber Line) over telephone line requires an    vbADSL modem and allows us to browse and talk at the same time.

   IPLC (International Private Leased Circuit))

 Ø  Voice or data at 64 kbps, nX64 kbps, E1, E3, STM-1, STM-4 etc. 

 Ø   International bilateral Voice Carrier Service

IN (Intelligent Network)

·         Toll Free Phone Service (FPS):

This is the brand name of BTCL’s Toll free phone service.

     ·Pre-Paid Telephony (PPT):

The PPT (Prepaid Telephony) Service enables the subscriber to transfer the balance of a Prepaid Card to the account of a telephone number. When subscriber makes Prepaid Phone call by this telephone, the call will be charged to the prepaid account of this telephone number.

    · Pre-Paid Card Service (PPS):

The PPS service (prepaid calling card service) allows a user to make any call (local, NWD, EISD, ISD) from any Digital telephone set by using a scratch card. This call will be charged to the card number (account number in IN system) and will not be included in telephone bill.  The PPS subscriber will be given a personal Identification Number (PIN),

Transmission Services

·         Inter-Operator Connectivity (E1, E3, STM-1, STM-4 etc)

·         For E1 connectivity, ISPs are requested to apply with necessary documents to the following address:

Several Components used in BTCL MSU:
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1. TXE equipments:

2. E1 card schematic view:

3. Two storied E1 shelf:

Exchange:

A  telephone exchange or telephone switch is a system of electronic components that connects telephone calls. A central office is the physical building used to house inside plant equipment including telephone switches, which make telephone calls "work" in the sense of making connections and relaying the speech information.  Here maximum 20000  lines can be extracted .

MDF:

From the exchange, all connections are gone to Main Distribution Frame (MDF). MDF transfers all the signals to the main-hole/hand-hole through wires. From the mainhole/ hand-hole all wires are divided and go to several different cabinets. A cabinet can control at best 500-600 connections. Cabinets are reached at distribution points, from which, through drop-wires, subscribers are connected.Two types of cables are used in this long connection. One is called primary cable and the other is called secondary cable. Primary cable is used to connect the exchange with the cabinets while secondary cable is used to connect the cabinets with thesub scribers. Secondary cable is thinner than the primary cable. Usually,secondary cable = 1.2×primary cable.

Main Distribution Frame (MDF):

The wire connection point (wire rack) that is located at or near the central switching that is the point where all local access loops are terminated. The MDF connects cable pairs to the line and trunk equipment terminals of a switching system. The frame also serves as a test point between individual telephone lines and central office equipment. The vertical side carries the outside lines and protective devices. All connections to central office equipment are made on the horizontal side. The main distributing frame also is referred to as a mainframe.

Hand Hole (Handhole):

A handhole is a plastic, steel, or tile enclosure used in buried cable distribution systems that includes a cover that is used as a splice or pull box. Handholes are smaller versions of manholes and do not enable outside plant personnel to enter for splice work. The splice closure or cable sheath is pulled out of the handhole, spliced or repaired above ground and then laid back in the enclosure. Handholes are common in residential and commercial subdivisions served by 200 pair or smaller cables between buildings.

Man Hole (Manhole):

An access hole that allows entry of service personnel into a system or facility.

Cabinet

In communication systems, a cabinet is an enclosure that is used to hold equipment or electronic assemblies. An enclosure assembly that allows the installation of electronic assemblies or components. Common equipment racks are 7 feet tall by 24 to 26 inches wide. The inside mounting area is often 19 or 22 inches wide (the rack). Some equipment cabinets come with power supplies and cooling fans.

Max. line : 500.

Distribution point:

In telephony, a  distribution point (DP)is a signal distribution frame for connecting equipment (inside plant) to cables and subscriber carrier equipment (outside plant).

Types of exchanges:

1.    Local exchange

It is utilized to connect line within small region. Here direct line are  used only.

2.   TAX exchange

To connect other district or country.

3.   TANDEM exchange

The connection of the output terminals of one network, circuit, or link directly to the input terminals of another. (2-message network) A switching system that establishes trunk-trunk connections but has no subscriber lines connected to it. Tandem types include local tandems, LATA tandems, and access tandems. No local subscriber are under tandem exchange.

4.   ITX

Means International Trunk eXchange.

When a number is dialed by the subscriber, it is immediately sent to the nearest
exchange. The exchanges decides whether the call should be transferred to another
exchange, TAX exchange or to the tandem exchange. Usually, the mobile operators are
connected to the telephone network via the tandems. So, in the above figure, when a
number beginning with 017 is pressed, the nearest exchange considers it either ISD
(beginning with 00) call or mobile phone calls. It waits for the second digit. When the
second digit comes, it treats the number as a mobile phone number and transfers the
signaling control to the tandem. The tandem, in turn, waits for the third digit. If it is 7, as
in our example, it considers it as a Grameen Phone number and chooses the suitable
mobile operator MSC from several operators’ list and transfers the calls immediately.
Counting Capacity of an Exchange:
One E1 card can handle 31 calls together, having 32 slots.
One Tandem has 512 E1 i.e. 512×31= 15872 call handling capacity.
Since E1 has 32 time slots and each slot transmits/receives 8 bits. 16 bits makes a
frame.
We get, 32×8 bits
In a second, it can transmit/receive 8000 frames.
We get, 32×8×8000 bits/sec = 1.95 Mbps
But, actually, a frame uses one bit for framing/synchronization and one bit for
signaling. Thus, 30 bits are in used.
Hence, 30×8×8000 bits/sec = 1.92 Mbps.
STM-1 has 63 E1. Therefore, STM-1 may have 1.92×63 = 120.96 Mbps data rate.
Therefore, STM-16 has 1.92×16×63 = 1.89 Gbps.
STM-64 has 1.92×64×63= 7.56 Gbps.

POWER CONNECTION: 
The power connection is controlled from a power supply room. The arrangement
is shown in the following figure.

CONCLUSION:

BTCL or Bangladesh Telecommunications Company Limited, BTCL is the core of the telecommunication in our country. It does not onlysupport normal digital telecommunication service, but also it has a license for working as ISP. BTCL is currently providing internet of 64 STM capacity, a little of which is in practical use. A tour to BTCL’s exchange has provided us with practical knowledge of aswitching center along with several various components used in modern telecommunication technology.

As of May 2008, the total number of subscribers of BTTB was 0.87 million.The BTCL also has plans to offer a wide range of broadband internet services soon..