INTRODUCTION
With standardized hardware and software, the microcomputers provide user-friendly
environment. It meets the computing requirements of most users. But, the need for interaction
with other computer users and with other computer systems for exchange of data etc., has
increased over the years. Networks are increasingly meeting this need. From the users’ point of
view the networks may be of two types: Local area network and Wide area network.
Computer networking is the process of inter connecting two or more computers so that
the users can communicate with each other, share resources and overcome other limitations of
stand-alone systems. The network can be established with a variety of combinations of
computers such as a net of only microcomputers, microcomputers and one or more
minicomputers and a set of microcomputers connected to a mainframe computer. The computers
in typical network are autonomous in the sense that they have processing capability independent
of the network.
The main advantages of networking are:
(i). Hardware resource sharing:Network enables sharing of expensive resources such as processor, storage space and
peripherals like modern, fax, and laser printer.
(ii). Sharing of databases:The network permits concurrent access to the same data file by many users in the
network. Thus, user in the sales department, production department, inventory department etc
share corporate databases.
(iii). Sharing of Software:Any user in a network can load and use the software installed on any of the computer of
file server in the network.
(iv). Communication between users:The Network users can communicate between them. E-mail facility can also be used for
communication.
(v). Decentralized data processing:In a network, the data processing can be decentralized by enabling local offices to capture
and store data, and generate information to meet most of their requirements a local level itself.
(vi) Security of data:In a networked environment the data is backed up with duplicate storage. Adequate
security measures are also put in place to product the data.
The networks can be classified into three; local area network (LAN), metropolitan area
network (MAN) and wide area network (WAN). They are explained in the following sections:
1. Wide Area Network (WAN)
WAN is made up of number of autonomous computers distributed over a wide
geographical area. WANs were originally developed in the late 1960s to enable communication
between computer centers and sharing of hardware, software and other communication facilities.
WAN can be implemented using private or public networks. In a private network an
organization takes on lease telephone lines to connect such sites into a network. It is also
possible to connect computers in different locations using microwave or satellite transmission.
Public networks are installed by the Government owned telecommunication agencies. WAN
spans large geographic distances. It is also called long-haul network. WAN is usually operated
at lower speeds then MAN and involves delay.
Most organizations use private networks for communication. Society for Worldwide Inter bank Financial Transactions (SWIFT), a non-profit organization of banks, owns a private network. The network exchanges financial transactions between the participating financial
institutions, about 3000 in number in over 60 countries. The terminals of these participating
banks are hooked with SWIFT’s access centers. The network offers data communication service
24 hours a day, 7 days a week.
INDONET, NICNET, SBINET and WELCOMENET are some of the private network in
India. CMC’s INDONET offers e-mail service to customers for a fee. NICNET is a network of
National Informatics Center that connects all the district headquarters in the country. SBINET is
a private network of State Bank of India and connects its branches across the country.
WELCOMNET connects the hotels of the Welcome Group.
A wide area network (WAN) is used to connect LANs and nodes that are separated by
great physical distance. Generally speaking it is larger version of LAN with several differences:
1. It operates by means of the international telephone network
2. Unlike LANs which owned by their users, WANs operate on public and leased
telephone lines provided by licensed common carriers, or by other means such satellite
and microwave, which are regulated by government agencies.
3. Data transmission is somewhere slower.
4. The WAN compose any of the following system configurations:
5. Single nodes
6. Clusters
7. LANs
Suppose a company has its central headquarters in Coimbatore and the Coimbatore site
contains all departments and equipment for product manufacturing prod distribution, accounting,
and sales. The information pertaining to these operations is tracked by a single centralized
database system. As the company becomes more profitable and expands, it established additional
sales offices on Mumbai and Delhi. Each sales office maintains its own system to record and
track customer orders for its region. At the same time the two sites are linked to the mode at
corporate headquarters and relay each order shipment and inventory and invoice processing.
provides the following advantages:
1. The WAN allows access to database at remote sites, enabling exchange of data.
2. If a remote node fails, remaining nodes on the network can still exchange data.
3. If the network fails, the local mode can still access its own database.
4. The data used on daily basis by the sales offices resides at the local site, making it easier to
retrieve quickly.
5. The local offices can maintain the data more effectively. The corporate office can access the
data as needed.
6. As a site's database grows larger, its system's storage capacity can be easily upgraded without
affecting the transfer of data between other nodes on network.
One of the most significant aspects of a wide area network when comparing it with
freedom of a local area network is the involvement of a public telecommunications authority.
Regardless of whether the network is made up from system, the controlling authority is almost
always the public authority. In order to protect their equipment and employees, the authority lays
down rules, which must be observed by anyone connecting to their lines. In most countries
stringent requirements are also imposed on the characteristics of the data transmissions.
2. Metropolitan Area Network (MAN)Metropolitan area network covers a wider area than a local area network. Usually MAN
covers a large metropolitan city and is a scaled down version of wide area network. It operates
at high speeds over distances sufficient for a metropolitan area.
3. Local Area Network (LAN)A LAN is a system of interconnected microcomputers, sharing common resources like
disks, printers etc., and links a number of computers workstations) together to allow many
people to use the same software and data files. Each user in such a multi-user environment
accesses the resources through his microcomputer workstation. The network operating system
integrates all the network components and makes operation smooth and transparent. LAN works
in restricted geographical area such as within a large building or offices within a few kilometers.
The LAN is an interconnection of computers that need to communicate with each other in a
limited geographical area. The network may have other sharable devices attached such as fax,
laser printers and copiers. The network includes a central facility with huge storage capacity for
the requirements of the organization. It also has a network operating system for managing the
network.
a) Client / Server LANClient Server LAN has servers and clients. The server is a computer that manages shared
resources: hardware as well as software and data. It is usually a powerful computer with large
RAM and secondary storage capacity. The LAN has a number of microcomputers, called
clients, the request the server for services. The LAN may have many servers each specializing in
one area of service such as file server, printer server, database server etc. A file server stores
program and data files. A database server stores data and a printer server controls printers on the
local area network.
b) Peer-to-Peer LAN:In a Peer-to-Peer LAN every computer is equal in status and functioning. All the
computers on the network are capable of communicating independently with any other computer
on the network without using a server. Thus, any computer on the network can access data and
programs stored on any other computer. The peer-to-peer LAN is less expensive than
client/server LAN. But at the same time this LAN may be slower than a client/server LAN.
LAN TopologyThe design of network requires selection of a particular topology and an architecture for
the interconnection of network component.
Topology refers to the way the computers are physically connected into the network. The
network architecture includes the specifications of the components that can be connected to the
network. IBM’s Systems Network Architecture (SNA) is an example of vendor developed
network architecture. Such network architecture specifies network components such as
terminals, workstations, printers, cluster controllers, host computer and communications
controllers.
There area a number of network topologies. Of them ring, star and bus are popular network
topologies.
In star network the nodes are connected to a central computer called the host computer.
The nodes cannot communicate directly. Each node can communicate with the host computer.
The host computer takes the message and routes it to the other node or nodes.
The host is the main computer to which other nodes are connected by communication
links. The host computer is responsible for the overall functioning of the network. The node
may be a microcomputer, terminal or any other device like storage device, printer etc.,
In a star network centralization of control over the network resources is easy. It is also
possible to network minicomputer or mainframe with other microcomputers and dumb terminals.
It eliminates single point failure of a common wire. If one of the host computers fails, it does not
usually affect the others in the network. But the hub becomes a central point of failure in a ring
network. If the host computer breaks down, the entire network breaks down.
the central computer. The nodes are connected to a line that is closed like a loop. The ring
network is more reliable than star network. Even if the central computer in the network fails, the
other computers can continue to communicate with each other.
connected to the network share the same bus or communication channel. Bus wiring is easy and
needs much less wring for small segments.
Old Ethernet bus wiring is prone to cable failure. If the bus wiring connection is broken
at any point, the entire network fails.
greater flexibility and reliability. Hybrid network combines features of Star, Ring and Bus
network:
Features of LANThe features of LAN include the following
a) Limited geographical area say within a few kilometers.
b) Common communication link for sharing information, software and peripheral devices
without regard to proximity of user to such resources on the network.
c) High transmission capability.
d) Low error rate as the network contains built-in component for detecting for system errors.
e) Private ownership by the user.
f) Not subject to regulation by the telecom service.
LAN interconnects computers and computers and components within a limited
geographical area. Such LANs are normally set up within a single site can have one or more
business complex, a hospital, an office- building etc. The site can have one or more buildings but
they should not be too for a way, say less then5 kilometers. A LAN can also include a variety of
computer systems and devices such as workstations, microcomputer, file servers, plotters,
scanners, graphic terminals and printers.
A large personal computer or mini computer serves as the LAN’s hub. A high capacity
hand disk is attached to the hub as data files and software are stored on the network file server.
The users can load the software on the file server and retrieve data files for processing. The
output can be directed to the printer attached to the LAN.
Any the communication network that meets most or all of the following characteristics
can be classified as LAN,:
a) All the devices on the network share a common transmission medium, that is, the cable and/
or the controller.
b) The devices connected to the network can operate independent of the network.
c) Any device connected to it can communicate with any other device on the network, and
d) The network is capable of supporting heavy data traffic over short distances compared to
telecommunication network.
e) The network covers a limited area usually a few kilometers in radius or a single site like a
university campus, an office or a factory.
LAN ComponentsThe components of LAN are File server, workstation, network operating system, LAN
cable, Active and Passive hubs etc.a) WorkstationIt is a single-user microcomputer with high power communication facilities. It can
exchange message with other workstations or file server.
Workstations can be of two types: user workstation and server workstation. User
workstation is a microcomputer on the network, which is used to access the network. Service
workstation performs service to process other workstations on the network. User workstation
normally does not process requests from other workstations. Server workstation makes available
all sharable network resources to other workstations. More than one server workstations may be
added to the network such as printer server and fileserver. Normally the server workstation is
the most powerful workstation. Server workstation may be dedicated or non-dedicated. In case
of dedicated workstation, it is not available for other user applications. Non-dedicated server
workstation doubles as an individual workstation and at the same time performs network-related
functions.
b) File ServerFile server is actually a process running on a computer that provides the clients access to
files on that computer. The term is loosely applied to mean computer that runs file server
software. In this sense, it is a powerful computer with special software to serve files to other
workstations on the network. The files, which may be program files or data files, are
simultaneously shared by a number of workstations. Novell Netware is a popular network
operating system.
c) GatewayThe gateway assists in communicating between LANs. A workstation may be dedicated
to serve as gateway. This is required particularly when two networks with different technologies
have to communicate with each other. Gateway may also be used to connect LAN with a
mainframe computer.
d) Network Interface UnitThe network interface is a printed circuit board installed in the microcomputer. It may be
called network card, network adapter or network interface unit. It connects the workstations
functionally and physically with the network.
e) Active HubHub is an electronic device to which multiple computers are attached usually using
twisted pair cables. Active hub is a powered distribution point with active devices that drive
distant nodes up to one kilometer away. It can connect up to eight nodes on the network. The
maximum distance carried by an active hub is about 2000 ft.
f) Passive HubThis hub is a distribution point that does not use power or active devices in a network to
connect up to four nodes within a short distance. The maximum distance covered by a passive
hub is nearly 300 ft.
g) LAN CableLAN requires superior cable capable of transferring data at high speed. Coaxial cables or
fiber optic cables may be used for networking computer.
h) Network Operating System (NOS)
The NOS integrates all the network components. The NOS facilitates file and print
serving along with other functions like communications and e-mail between workstations. In
most LANs the NOS exists along with the computer’s operating system.. The computer’s
operating system processes the system requests first and processes them if they can be done with
the workstation resources. If it is not a local request, meaning that the network resources have to
be used, the request is transferred to NOS for carrying out. Thus, the NOS is responsible for
controlling access to data, storage space and sharing of other peripheral resources.
i) Applications SoftwareAnother component of LAN is application software. It has to be ensured that the
application software works in the multi-user environment.
j) ProtocolsData transmission between devices requires protocol. Protocols are sets of rules and
procedures to control the data transmission between computer and other devices. They are
common technical guidelines for communication between devices. They specify the order in
which signals will be transferred, the signal for completion of transfer etc. Only Devices using
the same protocol can communicate directly. Both the sending and receiving devices must use
the same protocol for effecting communication. For communication between devices using
different protocols requires intermediate interpretation device or software.The protocol performs the following functions:
a) Set up a link with the other device in the communication.b) Identify the component to other components in the communication (sending device’s
channel ID)c) Send and interpret the datad) Provide a continuous feedback on data transmission like data is not being received and
understood.e) Request for retransmission of garbled data.f) Engage recovery procedure when error occurs.g) Provide an acceptable way of terminating transmission so that all devices have completed the
process.
The protocol is embedded in communication software designed to use a particular protocol.
The user need not bother about the protocol as the components involved in the communication
perform the protocol matching. The data communication protocols are of two main types:
asynchronous and synchronous. The synchronous protocol permits continuous data
transmission. The devices in communication must be synchronized with the other. The
transmission is governed by a time interval and not by start-stop bits. For example, clock, in the
modern, sets the time interval
With standardized hardware and software, the microcomputers provide user-friendly
environment. It meets the computing requirements of most users. But, the need for interaction
with other computer users and with other computer systems for exchange of data etc., has
increased over the years. Networks are increasingly meeting this need. From the users’ point of
view the networks may be of two types: Local area network and Wide area network.
Computer networking is the process of inter connecting two or more computers so that
the users can communicate with each other, share resources and overcome other limitations of
stand-alone systems. The network can be established with a variety of combinations of
computers such as a net of only microcomputers, microcomputers and one or more
minicomputers and a set of microcomputers connected to a mainframe computer. The computers
in typical network are autonomous in the sense that they have processing capability independent
of the network.
ADVANTAGES OF NETWORKING
The main advantages of networking are:(i). Hardware resource sharing:Network enables sharing of expensive resources such as processor, storage space and
peripherals like modern, fax, and laser printer.
(ii). Sharing of databases:The network permits concurrent access to the same data file by many users in the
network. Thus, user in the sales department, production department, inventory department etc
share corporate databases.
(iii). Sharing of Software:Any user in a network can load and use the software installed on any of the computer of
file server in the network.
(iv). Communication between users:The Network users can communicate between them. E-mail facility can also be used for
communication.
(v). Decentralized data processing:In a network, the data processing can be decentralized by enabling local offices to capture
and store data, and generate information to meet most of their requirements a local level itself.
(vi) Security of data:In a networked environment the data is backed up with duplicate storage. Adequate
security measures are also put in place to product the data.
TYPES OF NETWORK
The networks can be classified into three; local area network (LAN), metropolitan area
network (MAN) and wide area network (WAN). They are explained in the following sections:
1. Wide Area Network (WAN)
WAN is made up of number of autonomous computers distributed over a wide
geographical area. WANs were originally developed in the late 1960s to enable communication
between computer centers and sharing of hardware, software and other communication facilities.
WAN can be implemented using private or public networks. In a private network an
organization takes on lease telephone lines to connect such sites into a network. It is also
possible to connect computers in different locations using microwave or satellite transmission.
Public networks are installed by the Government owned telecommunication agencies. WAN
spans large geographic distances. It is also called long-haul network. WAN is usually operated
at lower speeds then MAN and involves delay.
Most organizations use private networks for communication. Society for Worldwide Inter bank Financial Transactions (SWIFT), a non-profit organization of banks, owns a private network. The network exchanges financial transactions between the participating financial
institutions, about 3000 in number in over 60 countries. The terminals of these participating
banks are hooked with SWIFT’s access centers. The network offers data communication service
24 hours a day, 7 days a week.
INDONET, NICNET, SBINET and WELCOMENET are some of the private network in
India. CMC’s INDONET offers e-mail service to customers for a fee. NICNET is a network of
National Informatics Center that connects all the district headquarters in the country. SBINET is
a private network of State Bank of India and connects its branches across the country.
WELCOMNET connects the hotels of the Welcome Group.
- Features of Wide Area Network
A wide area network (WAN) is used to connect LANs and nodes that are separated by
great physical distance. Generally speaking it is larger version of LAN with several differences:
1. It operates by means of the international telephone network
2. Unlike LANs which owned by their users, WANs operate on public and leased
telephone lines provided by licensed common carriers, or by other means such satellite
and microwave, which are regulated by government agencies.
3. Data transmission is somewhere slower.
4. The WAN compose any of the following system configurations:
5. Single nodes
6. Clusters
7. LANs
Suppose a company has its central headquarters in Coimbatore and the Coimbatore site
contains all departments and equipment for product manufacturing prod distribution, accounting,
and sales. The information pertaining to these operations is tracked by a single centralized
database system. As the company becomes more profitable and expands, it established additional
sales offices on Mumbai and Delhi. Each sales office maintains its own system to record and
track customer orders for its region. At the same time the two sites are linked to the mode at
corporate headquarters and relay each order shipment and inventory and invoice processing.
- Advantages of WAN
provides the following advantages:
1. The WAN allows access to database at remote sites, enabling exchange of data.
2. If a remote node fails, remaining nodes on the network can still exchange data.
3. If the network fails, the local mode can still access its own database.
4. The data used on daily basis by the sales offices resides at the local site, making it easier to
retrieve quickly.
5. The local offices can maintain the data more effectively. The corporate office can access the
data as needed.
6. As a site's database grows larger, its system's storage capacity can be easily upgraded without
affecting the transfer of data between other nodes on network.
One of the most significant aspects of a wide area network when comparing it with
freedom of a local area network is the involvement of a public telecommunications authority.
Regardless of whether the network is made up from system, the controlling authority is almost
always the public authority. In order to protect their equipment and employees, the authority lays
down rules, which must be observed by anyone connecting to their lines. In most countries
stringent requirements are also imposed on the characteristics of the data transmissions.
2. Metropolitan Area Network (MAN)Metropolitan area network covers a wider area than a local area network. Usually MAN
covers a large metropolitan city and is a scaled down version of wide area network. It operates
at high speeds over distances sufficient for a metropolitan area.
3. Local Area Network (LAN)A LAN is a system of interconnected microcomputers, sharing common resources like
disks, printers etc., and links a number of computers workstations) together to allow many
people to use the same software and data files. Each user in such a multi-user environment
accesses the resources through his microcomputer workstation. The network operating system
integrates all the network components and makes operation smooth and transparent. LAN works
in restricted geographical area such as within a large building or offices within a few kilometers.
The LAN is an interconnection of computers that need to communicate with each other in a
limited geographical area. The network may have other sharable devices attached such as fax,
laser printers and copiers. The network includes a central facility with huge storage capacity for
the requirements of the organization. It also has a network operating system for managing the
network.
- Types of LAN:
a) Client / Server LANClient Server LAN has servers and clients. The server is a computer that manages shared
resources: hardware as well as software and data. It is usually a powerful computer with large
RAM and secondary storage capacity. The LAN has a number of microcomputers, called
clients, the request the server for services. The LAN may have many servers each specializing in
one area of service such as file server, printer server, database server etc. A file server stores
program and data files. A database server stores data and a printer server controls printers on the
local area network.
b) Peer-to-Peer LAN:In a Peer-to-Peer LAN every computer is equal in status and functioning. All the
computers on the network are capable of communicating independently with any other computer
on the network without using a server. Thus, any computer on the network can access data and
programs stored on any other computer. The peer-to-peer LAN is less expensive than
client/server LAN. But at the same time this LAN may be slower than a client/server LAN.
LAN TopologyThe design of network requires selection of a particular topology and an architecture for
the interconnection of network component.
Topology refers to the way the computers are physically connected into the network. The
network architecture includes the specifications of the components that can be connected to the
network. IBM’s Systems Network Architecture (SNA) is an example of vendor developed
network architecture. Such network architecture specifies network components such as
terminals, workstations, printers, cluster controllers, host computer and communications
controllers.
There area a number of network topologies. Of them ring, star and bus are popular network
topologies.
a) Star Topology:
In star network the nodes are connected to a central computer called the host computer.The nodes cannot communicate directly. Each node can communicate with the host computer.
The host computer takes the message and routes it to the other node or nodes.
The host is the main computer to which other nodes are connected by communication
links. The host computer is responsible for the overall functioning of the network. The node
may be a microcomputer, terminal or any other device like storage device, printer etc.,
In a star network centralization of control over the network resources is easy. It is also
possible to network minicomputer or mainframe with other microcomputers and dumb terminals.
It eliminates single point failure of a common wire. If one of the host computers fails, it does not
usually affect the others in the network. But the hub becomes a central point of failure in a ring
network. If the host computer breaks down, the entire network breaks down.
 |
| STAR TOPOLOGY |
b) Ring Topology:
In a ring network the computers can communicate directly with each other and also withthe central computer. The nodes are connected to a line that is closed like a loop. The ring
network is more reliable than star network. Even if the central computer in the network fails, the
other computers can continue to communicate with each other.
c) Bus Topology:
A bus network configures computers to a single non-looping channel. The computersconnected to the network share the same bus or communication channel. Bus wiring is easy and
needs much less wring for small segments.
Old Ethernet bus wiring is prone to cable failure. If the bus wiring connection is broken
at any point, the entire network fails.
d) Hybrid Network:
In most cases, instead of a single topology, a combination of topologies may be used forgreater flexibility and reliability. Hybrid network combines features of Star, Ring and Bus
network:
Features of LANThe features of LAN include the following
a) Limited geographical area say within a few kilometers.
b) Common communication link for sharing information, software and peripheral devices
without regard to proximity of user to such resources on the network.
c) High transmission capability.
d) Low error rate as the network contains built-in component for detecting for system errors.
e) Private ownership by the user.
f) Not subject to regulation by the telecom service.
LAN interconnects computers and computers and components within a limited
geographical area. Such LANs are normally set up within a single site can have one or more
business complex, a hospital, an office- building etc. The site can have one or more buildings but
they should not be too for a way, say less then5 kilometers. A LAN can also include a variety of
computer systems and devices such as workstations, microcomputer, file servers, plotters,
scanners, graphic terminals and printers.
A large personal computer or mini computer serves as the LAN’s hub. A high capacity
hand disk is attached to the hub as data files and software are stored on the network file server.
The users can load the software on the file server and retrieve data files for processing. The
output can be directed to the printer attached to the LAN.
Any the communication network that meets most or all of the following characteristics
can be classified as LAN,:
a) All the devices on the network share a common transmission medium, that is, the cable and/
or the controller.
b) The devices connected to the network can operate independent of the network.
c) Any device connected to it can communicate with any other device on the network, and
d) The network is capable of supporting heavy data traffic over short distances compared to
telecommunication network.
e) The network covers a limited area usually a few kilometers in radius or a single site like a
university campus, an office or a factory.
LAN ComponentsThe components of LAN are File server, workstation, network operating system, LAN
cable, Active and Passive hubs etc.a) WorkstationIt is a single-user microcomputer with high power communication facilities. It can
exchange message with other workstations or file server.
Workstations can be of two types: user workstation and server workstation. User
workstation is a microcomputer on the network, which is used to access the network. Service
workstation performs service to process other workstations on the network. User workstation
normally does not process requests from other workstations. Server workstation makes available
all sharable network resources to other workstations. More than one server workstations may be
added to the network such as printer server and fileserver. Normally the server workstation is
the most powerful workstation. Server workstation may be dedicated or non-dedicated. In case
of dedicated workstation, it is not available for other user applications. Non-dedicated server
workstation doubles as an individual workstation and at the same time performs network-related
functions.
b) File ServerFile server is actually a process running on a computer that provides the clients access to
files on that computer. The term is loosely applied to mean computer that runs file server
software. In this sense, it is a powerful computer with special software to serve files to other
workstations on the network. The files, which may be program files or data files, are
simultaneously shared by a number of workstations. Novell Netware is a popular network
operating system.
c) GatewayThe gateway assists in communicating between LANs. A workstation may be dedicated
to serve as gateway. This is required particularly when two networks with different technologies
have to communicate with each other. Gateway may also be used to connect LAN with a
mainframe computer.
d) Network Interface UnitThe network interface is a printed circuit board installed in the microcomputer. It may be
called network card, network adapter or network interface unit. It connects the workstations
functionally and physically with the network.
e) Active HubHub is an electronic device to which multiple computers are attached usually using
twisted pair cables. Active hub is a powered distribution point with active devices that drive
distant nodes up to one kilometer away. It can connect up to eight nodes on the network. The
maximum distance carried by an active hub is about 2000 ft.
f) Passive HubThis hub is a distribution point that does not use power or active devices in a network to
connect up to four nodes within a short distance. The maximum distance covered by a passive
hub is nearly 300 ft.
g) LAN CableLAN requires superior cable capable of transferring data at high speed. Coaxial cables or
fiber optic cables may be used for networking computer.
h) Network Operating System (NOS)
The NOS integrates all the network components. The NOS facilitates file and print
serving along with other functions like communications and e-mail between workstations. In
most LANs the NOS exists along with the computer’s operating system.. The computer’s
operating system processes the system requests first and processes them if they can be done with
the workstation resources. If it is not a local request, meaning that the network resources have to
be used, the request is transferred to NOS for carrying out. Thus, the NOS is responsible for
controlling access to data, storage space and sharing of other peripheral resources.
i) Applications SoftwareAnother component of LAN is application software. It has to be ensured that the
application software works in the multi-user environment.
j) ProtocolsData transmission between devices requires protocol. Protocols are sets of rules and
procedures to control the data transmission between computer and other devices. They are
common technical guidelines for communication between devices. They specify the order in
which signals will be transferred, the signal for completion of transfer etc. Only Devices using
the same protocol can communicate directly. Both the sending and receiving devices must use
the same protocol for effecting communication. For communication between devices using
different protocols requires intermediate interpretation device or software.The protocol performs the following functions:
a) Set up a link with the other device in the communication.b) Identify the component to other components in the communication (sending device’s
channel ID)c) Send and interpret the datad) Provide a continuous feedback on data transmission like data is not being received and
understood.e) Request for retransmission of garbled data.f) Engage recovery procedure when error occurs.g) Provide an acceptable way of terminating transmission so that all devices have completed the
process.
The protocol is embedded in communication software designed to use a particular protocol.
The user need not bother about the protocol as the components involved in the communication
perform the protocol matching. The data communication protocols are of two main types:
asynchronous and synchronous. The synchronous protocol permits continuous data
transmission. The devices in communication must be synchronized with the other. The
transmission is governed by a time interval and not by start-stop bits. For example, clock, in the
modern, sets the time interval
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