BTCL is Bangladesh's primary telecommunications provider. It operates landline telephone services across urban areas of Bangladesh and provides international calling. While BTCL previously had a monopoly on phone services in Dhaka, several other operators have entered the market since 2004. BTCL's network uses digital and analog switching technologies. Exchanges like the ZTE and Shanghai Bell switches route calls between local loops, trunks, and switching offices. Services include landlines, wireless networks, leased lines, fax, and prepaid cards. Calls are established through switching cards like the ASLC cards which provide dial tones. Maintenance of the network involves equipment like cable cabinets, distribution frames, and distribution points. Cables connect these

1. 1
Chapter -One
Introduction to BTCL
BTCL or Bangladesh Telecommunications Company Limited, formerly BTTB, began operations
on July 1, 2008. The Bangladesh government initially owns all shares of BTCL but it would
offload shares in the next one year for public. The value of BTCL is estimated to be at Tk 15,000
crore. BTCL has a total of 12,636 officials and staffs.
BTCL provides land-line telephone services in the urban areas, domestic long-distance calling
and international services. In 2004, Bangladesh Government issued a number of PSTN licenses
but they were barred to provide service in the lucrative Dhaka market (which account for
majority of the nationwide market). This monopoly of BTCL was broken when 6 other operators
started to receive their licenses from 2007. These 6 operators include PeoplesTel, RanksTel,
National Telecom Limited, WorldTel, Dhaka Phone and Telebarta.
Telephone operating work in Federal agencies requires knowledge of telephone regulations and
procedures and skill in operating telephone equipment and lines to route incoming and outgoing
calls. It requires the use of telephone courtesy and tact in dealing with a diversity of callers,
sometimes under very difficult and stressful circumstances. The work also requires speed and
accuracy, and in some locations it requires observing strict security measures.
Telephone operators typically perform combinations of some or all of the following tasks:
operating a console telephone switchboard;
placing and receiving local calls;
placing and receiving regular and special long distance calls over commercial circuits,
timelines, or other systems and networks, such as a wide area commercial system, a
military system, a civilian Federal system, or a Federal overseas exchange;
providing organizational information to callers using computerized or printed directories;
keeping records of calls for computing charges;
providing primary routing or alternative routing service for high priority calls;
handling calls of varying priority and preempting circuits if necessary;
keeping statistics on system use to inform managers of trends concerning capacity and
utilization; and
Operating associated equipment, such as radios, alarms, paging systems, and secures voice
equipment.

2. 2
1.1 Telephone network
Telephone networks use circuit switching. The telephone network had its beginnings in the late
1800s.The entire network, which is referred to as the plain old telephone system (POTS), was
originally an analog system using analog signals to transmit voice. With the advent of computer
era, the network in the 1980s began carry data in addition to voice. During the last decade, the
telephone network has undergone many technical changes. The network is now digital as well as
analog.
1.2 Major components of telephone network
The telephone network, as shown in figure is made of three major components:
Local loops,
Trunks, and
Switching offices.
The telephone network has several levels of switching offices such as end offices, tandem
offices, and regional offices.
1.3 Services provided by BTCL
Telephone – Land Phone.
WLL – Wireless in Loop Line.
Lease line - for different mobile company, ISP, Bank, BTV etc.
Telegraph or Telegram.
Fax and other related facilities.
Prepaid calling card system.
1.4 Telephone exchange
In the field of telecommunications, a telephone exchange or telephone switch is a system of
electronic components that connects telephone calls. A central office (CO) 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.
The term exchange area can be used to refer to an area served by a particular switch, but is
typically known as a rate center or wire center in the telecommunications industry (local calling
areas, in which it is not necessary to pay a long-distance rate, typically cover more than one rate
center even in metropolitan and small metropolitan areas). The exchange code or central office
code (often called the prefix by the public) refers to the first three digits of the local number
(NXX), though most non-rural exchanges have more than one code or prefix.

3. 3
1.4.1 Digital room
Digital room consists of two main exchanges system. These are:
I. ZTE exchange &
II. S12 exchange / Shanghai Bell
I. ZTE exchange (Zhongxing Telecommunication Equipment)
ZTE Corporation is a Chinese multinational telecommunications equipment and systems
company headquartered in Shenzhen, China. It is the world's fourth-largest mobile phone
manufacturer measured by 2012 unit sales and the world's fifth-largest telecoms equipment
maker measured by 2011 revenues.
There are various types of cards that are used in ZTE exchange. Some of them are described
below:
ADSL card
Asymmetric Digital Subscriber Line. This is used for internet purpose. There are 400 connections
and bandwidth can be used maximum 1 MB per sec. It uses S7, R1, and R2 signaling channel.
But it prefers R1 channel.
DTI card (Digital Trunk Interface Card)
The different subscriber’s lines come to the exchange’s DTI by the trunk interface from different
upazilla. DTI connects the local exchanges & also one exchange with another exchange.
COMM card (Communication card)
COMM card are used for communication set up. It connects trunk to trunk & trunk to DTI.
PEPD card
It is used for dial tone purpose.
MP card (Main Processor)
All the calls are processed and stored in the computer hard disk through main processor. It
process call duration, call charge, call waiting, call forwarding etc.
ASIG card
It is mainly used for the call establishment. It also performs dial tone, ring tone etc.
ASLC card (Subscriber Line Circuit)
There are two wires that come from the MDF and connect to the ASLC card. There are 24 line
channels. Each card provides dial tone, busy tone, ring tone etc. for 24 subscribers.
FASL card
If there is any fault then this card is used for communication.

4. 4
SP, SP1 card (Speech Card)
It controls all the cards that are situated in the same rack.
MTT card
In the switching panel MTT control the SP, SP1 panels. It is known as the distribution card.
SMEM card
Same as MTT card.
TAX card (Telecommunication Exchange)
Tax card is like a distributor which sends the total signal in a desired bandwidth.
Power card
Supplies power to the rest of the cards.
II. S12 exchange / Shanghai Bell
ADSL modem is used in this exchange. It provides services like billing system, observing
internet connection, mailing and communication system. It has a mother server. Under this
exchange 7500 subscribers are served. There are various types of cards that are used in S12 exchange /
Shanghai Bell exchange. Some of them are described below:
MO Card (Metering operating disk): It can take data from hard disk like as a CD.
SLCL/ALCN card:
It is a subscriber line card. There are 16 subscribers in each card so from the 8 cards there are 128
subscribers are served in one rack.
RNGF card
It is known as ringing and signaling card. When one subscriber uses the local exchange then the
RNGF card sends a dial tone to another subscriber that is in the same exchange.
MCUE card
It controls the 8 ALCN card. That means it controls 128 subscribers in one rack.
MCUG card
It is known as power card.
WLL (Wireless Local Loop)
It works within the 23 km distance.
GTU card
It is like a sub exchange. It can serve 900 subscribers.
DTUA card:
It is known as PCM (Pulse Code Modulation Card). When a subscriber wants to call from differ-

5. 5
ent exchange then PCM card is used for switching. In the PCM card there is 32 time slot.
1.5 The way of communication in telephone system
There are three types of way to communicate with one user to another user in the telephone
system. These are:
1. Direct Communication
2. Microwave Link
3. Optical Fiber Link
1. Direct Communication
In direct communication the subscribers that are communicating with each other must remain in
the same exchange.
DP= Distribution Point
CC= Cable Chamber
MDF= Main Distribution Frame

6. 6
Chapter -Two
Equipment’s & Maintenance
2.1 Cabinet
In the cabinet mainly two types of cable are used.
1. Primary
2. Secondary
From the cable chamber the cable comes to the cabinet through duct, main hall etc. From
MDF to cabinet primary cable are used. Primary cable may be 200 to 2400 pair.
The secondary cable is approximately twice of primary cable. There is 200/300 pair cabinet,
400/600 pair cabinet. That means if the primary cable is 400 pair then the secondary cable is
600 pair.
In Shanghai china Bell cable, there are five main colours for every pair.
a) White
b) Red
c) Black
d) Yellow
e) Violate
This same type can also be found in Bangla China cables. But difference in colour.
a) Red
b) Green
c) Gray
d) Yellow
e) White
These colours are divided into two main pairs:
Pair number one
a) No ring
b) One ring
Pair number two
a) two ring long
b) two ring short
2.2 MDF (Main Distribution Frame)
All the subscriber line that comes from the exchange connect to the MDF through switch board

7. 7
cable.There is a pair of cable for a subscriber. These cables are connected to the horizontal
section in the MDF. In the horizontal section the number and the position of the subscriber
number are fixed. It can’t be changed. Then the numbers are connected to the vertical section of
the MDF through jumper wire. Then the connections are connected through a fuse. The color
code of the jumper wire is Red, Green, Grey, Yellow and White.
If a user wants to use voice and data at a time that means internet connection then the subscriber
needs an extra connection that serves voice and data at a time.
2.3 DDF (Digital Distribution Frame):
From the Mask unit of ODF the fiber that comes to the DDF connects with the exchange through
the E1 line. Here 1 channel is used for 24 users.
2.4 Distribution point (DP)
The cable which goes from cabinet to DP is known as secondary cable. When the pair of cable
comes from cabinet to DP the DP distribute this pair of line to the subscriber through drop wire.
2.5 Rozzet Box
It is the connector between the distribution point and telephone of a subscriber.
2.6 Board of information of Dinajpur BTCL:
Fig:Information Board
2.7 Cable chamber
All the cable from the MDF comes to the cable chamber and adds 100 pair or 200 pair or 400
pair of cable into a one cable in the cabinet wise. There is co-axial cable, optical fiber cable are
used here.
2.8 Rectifier room
In this system the input voltage is (220-230) AC voltage. Then it rectifies into -48 DC voltages

8. 8
through the rectifier. In the rectifier the single face is used 220V and the phase to phase is 400V.
The rectifier is a 3 phase connection and the input voltage supply is 400V. It supplies the DC
voltage to the exchange and charges the battery at a time. In the rectifier for this purpose, step
down transformer are used. The positive terminal of the rectifier is done as earthing and the
negative terminal are connected to the exchange.
2.9 Battery room
The Rectifier charges the Battery. There are 24 battery connected with each other. Each cell is
2.2 volt. The Battery is charged at 53.6 volt. Here hydrometer is used for measuring the liquid
substance of the battery. The amount of Sulfuric Acid and Water is 1:3.
When the PDB line is failed then the battery supplies voltage to the exchange automatically.
Thus it protects exchange from losing any information.

9. 9
Chapter -Three
Radio room of BTCL
3.1 SDH (Synchronous Digital Hierarchy):
Synchronous Digital Hierarchy was a European development, where SONET was a North
American development. They are very similar. The older version of SDH is PDH that means Pre
Synchronous Digital Hierarchy. In the PDH the channels are used by the process 2, 4, 8, 16, 32,
and 62 serially. But in the SDH the 64 channels are used at a times.
In the SDH section STM1, STM4, STM16, STM64 are used.
Here STM1 means 64 E1 line. From 64 line, 1 line is used for synchronization rest of the line are
used for speech.
For STM4, 64*4= 256 E1 lines are used.
For STM16, 64*16=1024 E1 lines are used.
For STM16, 64*16=4096 E1 lines are used.
3.2 Microwave link
Microwave transmission refers to the technology of transmitting information or energy by the use
of radio waves whose wavelengths are conveniently measured in small numbers of centimeter;
these are called microwaves. This part of the radio spectrum ranges across frequencies of roughly
1.0 gigahertz (GHz) to 30 GHz. These correspond to wavelengths from 30 centimeters down to
1.0 cm.
A microwave link is a communications system that uses a beam of radio waves in the microwave
frequency range to transmit information between two fixed locations on the earth. They are
crucial to many forms of communication and impact a broad range of industries. Broadcasters
use microwave links to send programs from the studio to the transmitter location, which might be
miles away. Microwave links carry cellular telephone calls between cell sites. Wireless Internet
service providers use microwave links to provide their clients with high-speed Internet access
without the need for cable connections. Telephone companies transmit calls between switching
centers over microwave links, although fairly recently they have been largely supplanted by
fiber-optic cables. Companies and government agencies use them to provide communications
networks between nearby facilities within an organization, such as a company with several
buildings within a city.
One of the reasons microwave links are so adaptable is that they are broadband. That means they
can move large amounts of information at high speeds. Another important quality of microwave

10. 10
links is that they require no equipment or facilities between the two terminal points, so installing
a microwave link is often faster and less costly than a cable connection. Finally, they can be used
almost anywhere, as long as the distance to be spanned is within the operating range of the
equipment and there is clear path (that is, no solid obstacles) between the locations. Microwaves
are also able to penetrate rain, fog, and snow, which mean bad weather doesn’t disrupt
transmission.
The block diagram of microwave link is given below:
Fig 2: The block diagram of microwave link
It is a point to point communication system. It uses microwave and ultra-high frequency for
communication within different exchanges in a long distance. The transmission frequency is
945.5 MHz and receiving frequency 940.6 MHz The microwave range is .3 to 30 GHz. For point
to point communication in microwave link dish parabolic and grid parabolic antenna are used.
The transmission power is 40, 60, 80 watt. 80 watt does not used in our country.
3.3 Optical fiber link
Fiber-optic communication is a method of transmitting information from one place to another by
sending pulses of light through an optical fiber. The light forms an electromagnetic carrier wave
that is modulated to carry information. Because of its advantages over electrical transmission,
optical fibers have largely replaced copper wire communications in core networks in the
developed world.
The process of communicating using fiber-optics involves the following basic steps: Creating the
optical signal involving the use of a transmitter, relaying the signal along the fiber, ensuring that
the signal does not become too distorted or weak, receiving the optical signal, and converting it
into an electrical signal. The block diagram of optical fiber is given below:

11. 11
Fig: The block diagram of optical fiber
All the procedure of fiber link is same as microwave link. But there is used an additional part that
is SDH which is known as Synchronous Digital Hierarchy.
3.4 ODF (Optical Distribution Frame) :
It is used in the STM system. The Optical fiber which comes from another exchange is connected
to the chamber of the ODF. There is 6 pair of cable in one optical fiber. The capacity of this
optical fiber is 10 GB. The cable is connected to the external part of ODF within two pair. One is
active and another is standing by. Then the fiber connects to the DDF (Digital Distribution
frame).
3.5 BTS (Transmission Section)
3.5.1 Transmission section
In the transmission section the transmission frequency are analog
and the signal is digital. In this section the voice frequency 30Hz to
3400Hz or 3.1 kHz is used. Pulse Code Modulation is used here
which is 2.60 MB and it contains 8000 samples. In each frame there
is 32 time slot. There are 3 channels such as Synchronous,
Signaling, and Speech.
Among the 32 slot of a frame 1 slot is used for synchronous and 1 slot is for signaling and the
rest 30 slots are used for speech. Here 1 multi frame consists from 16 frames. In one multi frame
0th and 16th
frame are used for signaling and the rest are used for speech.
In the transmission section mask unit is also called IDU (Indoor Unit). Here both modulation and
demodulation are performed. Here the transmission power is used 33 dB
The ODU (Outdoor Unit) is a kind of transceiver.
The block diagram is given below:
Exg= Exchange
RSU=Remote Switch Unit
Dnj= Dinajpur
Rng= Rangpur
TAX= Telephone exchange

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Fig: The block diagram of transmission in Telephone exchange
3.5.2 Transmission system
A system by which data transmission is occurred. Through the transmission the BTSs connect
with BSC. The is called A- interface.
3.5.3 Transmission media
Information can be transferred through some carrier. Carrier is required because information
can’t go beyond a certain distance without the aid of carrier.
Properties of Carrier:
Should be capable of carrying information
Can take it through long distance
Should have good speed
Some Medium is also required for transferring information from Transmitter to Receiver.
3.5.4 Types of medium
Wired (Guided media)
Twisted pair
Co-axial Cable
Optical
Wireless (Unguided media)
Satellite
Microwave
3.6 Power system
Power is most important issues in BTS. Without power nothing can do. If everything is okey but

13. 13
have not power to active the BTS there is no communication.
2.6.1 Power equipment’s used in the exchange
1. Rectifier
2. Battery
3. Air Cooler
4. Energy Meter
5. Distribution Board
6. Stabilizer

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Chapter -Four
Regional Operation & Maintenance
4.1 Operation and maintenance subsystem
The OMSS is responsible for handling system security based on validation of identities of
various telecommunications entities. These functions are performed in the Authentication Center
(AUC) and EIR. The AUC is accessed by the HLR to determine whether an MS will be granted
service. The EIR provides MS information used by the MSC. The EIR maintains a list of
legitimate, fraudulent, or faulty MSs. The OMSS is also in charge of remote operation and
maintenance functions of the PLMN. These functions are monitored and controlled in the OMSS.
The responsibilities for Regional operation are given below:
4.2 Fault handling
Field operation is the owner of all kind of equipment’s at sites and any site itself.
Fault handling of all kinds of equipment’s of Transmission, power a BTS equipment’s.
For Handling faults there is specified service level agreement which is popularly known as
SLA (allowed time varies from Fault to Fault) for each type of fault.
4.3 Preventive maintenance
Preventive maintenance means ‘To take initiative to remove all sorts of possible causes of
fault before fault appears’
In other word, PM is called preventive Maintenance.
There is specified preventive maintenance form/check list, which is to be fulfilled while
doing any preventive maintenance.
Preventive maintenance is a periodic routine work, 2 cycles in a year at each site.
Ensure the security of optical fiber, coordinating with patrolling team of Admin department
4.4 External power maintenance
All sorts of power maintenance are our responsibility. When commercial power is
unavailable, power backup ensuring by generator running is one responsibility of engineers.
When any fault occurs with the commercial power, Energy meter/service lone/Transformer
related or what else, its engineer’s responsibility to take care for removing the fault and
ensure power to site.
First line maintenance of battery, auto generators, portable generators, fuel loading at all
auto generators are engineers responsibility.

15. 15
Chapter -Five
Mobile Systems
5.1 Mobile systems
Mobile communication systems have become one of the hottest areas in the field of
telecommunications and it is predicted that within the next decade a considerable number of
connections will become partially or completely wireless. Rapid development of the Internet with
its new services and applications has created fresh challenges for the further development of
mobile communication systems.
Provides the necessary background information on digital communication systems, such as
speech and channel coding, digital modulation (including OFDM) and basic access
protocols
Presents the properties of a mobile radio channel and describes mobile radio propagation
models.
Explains the concept of cellular systems and their design.
Covers GSM and IS-95 and reviews paging systems, first generation cellular systems,
wireless telephony, trunking systems and wireless local loops.
Features HSCSD, GPRS, EDGE, UMTS and WLAN technologies and smart antenna.
The block diagram of mobile system is given below
Fig: Call set-up MS to PSTN
5.2 MSC (Mobile Services Switching Center)
The primary node in a GSM network is the MSC. It is the node which controls calls both to MSs
and from MSs the primary function of the MSC include the following:
1. Switching and call routing
2. Charging
3. Communication with HLR
4. Communication with VLR

16. 16
5. Communication with other MSCs
6. Direct Access to internet services
7. ISDN primary rate access
5.3 BSC (Base Station Controller)
The BSC controls are major part of the radio network. It’s most important task is to ensure the
highest possible utilization of the radio resources. The BSC manages all the radio-related
functions of a GSM network. It is a high capacity switch that provides functions such as MS
handover, radio channel assignment and the collection of cell configuration data. A number of
BSCs may be controlled by MSC. In one BSC there are mainly 8 modules. A BSC can take
maximum 1024 site/cell. The main functional areas of the BSC are:
1. Radio Network Management
2. Multi Band Support
3. Transmission Network Management
4. Positioning Services.
5. Handling of MS connections.
6. Internal BSC Operation and Maintenance
7. TRC handling
8. RBS Management.
5.4 BSS (Base Station Subsystem)
The BSS is the physical equipment that provides radio coverage to prescribed geographical areas,
known as cells. It contains equipment required to communicate with the MS. Functionally; a BSS
consists of a control function carried out by the BSC and a transmitting function performed by
the BTS. The BTS is the radio transmission equipment and covers each cell. A BSS cab serves
several cells because it can have multiple BTSs. The BTS contains the Transcoder Rate Adapter
Unit (TRAU).
5.5 RBS (Radio Base Station)
The RBS handle the radio interface to the mobile station. The BTS is the radio equipment
(transceivers and antennas) needed to services each cell in the network. A group of BTSs are
controlled by a BSC.A BTS is a network component that serves one cell and controlled by a
BSC. A BTS compares radio transmission and reception devices, up to and including the
antennas and also all the signal processing specific to the radio interface.
5.6 NSS (Network and Switching Subsystem)
The NSS includes the main switching functions of GSM, data-base required for the subscribers,

17. 17
and mobility management. Its main role is to manage the communication between GSM and
other network users. Within the NSS, the switching functions are performed by the MSC.
Subscriber information relevant to provisioning of services is kept in the HLR. The other
database in the NSS is the VLR.
5.7 MS (Mobile Station)
The MS consists of the physical equipment used by the sub-scriber to access a PLMN for offered
telecommunication services. Functionally, the MS includes a Mobile Termination (MT) and
depending on the services it can support, various Terminal Equipment (TE) combinations of TE
and Terminal Adapter (TA) . Various types of MS, such as the vehicle-mounted station, portable
station, or handheld station are used. The MSs come in five classes which define the maximum.
Basically, an MS can be divided into two parts. The first part contains the hardware and software
to support radio and human interface functions. The second part contains terminal/user- specific
data in the form of smart card, which can effectively be considered a sort of logical terminal. The
SIM card plugs into the first part of the MS and remains in the duration of use. Without the SIM
card, the MS is not associated with any user and cannot make or receive calls. The SIM card is
issued by the mobile service provider after subscription, while the first part of the MS would be
available at retail shops to buy or rent. This type of SIM card mobility is analogous to terminal
mobility, but provides a personal-mobility-like service within the GSM mobile network.
An MS has a number of identifies including the International Mobile Equipment Identity (IMEI),
the International Mobile Subscriber Identity (IMSI), and the ISDN number. The IMSI is stored in
the SIM. The SIM card contains all the subscriber-related information stored on the user’s side of
the radio interface.
There are various types of cards in BSC. Some of them are given below:
PWC card:
It is known as power card. It supplies -48V to the system.
BAM card (Back Administrative Module Card):
It makes the connection between the BSC and MSC through E3 line. They are connected through
optical fiber or microwave.
Fig: Connections between BSC and MSC through BAM

18. 18
GCTN card (Global Central Switching Network):
It is used for central switching.
CDB card:
It shows the cell zone of a mobile handset.
DDN (Digital Data Network):
The functions of digital data network are provided by I manager through router and switch.
CDU4 card (Combined Duplexer Unit):
It combines the carrier signal and the original signal.
A BSC can take maximum 1024 site.
5.8 BTS (Base Transceiver Station)
The BTS controls the radio interface to the MS. The BTS comprises the radio equipment such as
transceiver and antennas which are needed to serve each cell in the network. A group of BTSs are
controlled by BSC.
In the BTS there are DTRU unit. It combines the two TRX. If TRX is increased the number of
subscriber are increased. First time the number of subscriber is 6 then the number of subscriber is
8.The number of BTS under a BAM depends on the number of in a BIE. There is a half
rate or full rate in the BTS. In BTS for half rate 84 users can talk and for full rate 42 users can
talk.
The number of BTS in a BAM is given below:
Fig: Number of BTS in a BAM

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Chapter – Six
Different Antenna Types
Antenna types
There are various types of antenna are used for connecting BTS to BTS. Some of them are
described below.
6.1 Yagi antenna:
Multi-element highly directional antennas, Light, but strong construction for easy deployment.
Available for medium duty 150 W or heavy duty with 300 W. It uses very VHF (3GHz).
6.2 Parabolic antenna:
The small round size antennas connect the long distance BTS. These types of antennas are known
as parabolic antenna. They are used for point to point communication. There are two types of
parabolic antenna:
1. Dish parabolic
2. Grid Parabolic
6.3 Omni directional or GSM antenna:
An antenna system which radiates power uniformly in all directions in one plane. GSM antenna
is 360 . It may be maximum 270 and minimum 45 . If considers 3 antenna then the antennas
are situated at 120 .
6.4 Horn antenna:
A type of directional antenna shaped like a horn.
6.5 WLL antenna:
Wireless Loop Line antenna. From this antenna a local number is allocated for a subscriber in a
long distance.
6.6 Gateway:
In telecommunications, the term gateway has the following meaning:
In a communications network, a network node equipped for interfacing with another
network that uses different protocols. A gateway may contain devices such as protocol
translators, impedance matching devices, rate converters, fault isolators, or signal
translators as necessary to provide system interoperability. It also requires the establishment
of mutually acceptable administrative procedures between both networks. A protocol

20. 20
translation/mapping gateway interconnects networks with different network protocol
technologies by performing the required protocol conversions.
Loosely, a computer or computer program configured to perform the tasks of a gateway.
For a specific case, see default gateway.
Gateways, also called protocol converters, can operate at any network layer. The activities
of a gateway are more complex than that of the router or switch as it communicates using
more than one protocol.
Figure: Communication by Gateway