Computer Networks
Computer Network
A computer network is defined as the
interconnection of 2 or more independent computers
or/and peripherals.
Network
Source
Destination
Need of Networks
– Communicate and collaborate
– Share information
– Share resources
– Sharing computer files and disk space
– Sharing high-quality printers
– Access to common fax machines
– Access to common modems
– Multiple access to the Internet
Classification of Networks
1. Local Area Networks (LANs) - a computer
network covering a small geographic area, like
a home, office, or group of buildings. Typically
within 5-mile radius.
2. Metropolitan Area Networks (MANs)- are
large computer networks usually spanning a
city. (within 30 miles)
3. Wide-Area Networks (WANs) - any network
whose communications links cross
metropolitan, regional, or national boundaries.
Network Topology
The way in which the computers are
interconnected together is known as
TOPOLOGY.
Types of topologies
• Physical topology
• Logical topology
Types of physical topologies
• Bus/Linear
• Star
• Ring
• Tree
• Mesh
Linear or bus topology
• Consists of a main cable, known as
backbone cable, with a terminator at
each end .
• All nodes (file server, workstations,
and peripherals) are connected to the
cable.
• Ethernet and LocalTalk networks use
bus topology.
Advantages of Bus Topology
• Easy to connect a computer or peripheral
to a linear bus.
• Requires less cable length.
• Easy to extend.
• If one node of the N/W is faulty, the N/W
can still remain working.
Disadvantages of Bus
Topology
• Entire network shuts down if there is a
break in the main cable.
• Terminators are required at both ends of
the backbone cable.
• Difficult to identify the problem if the entire
network shuts down.
• Not meant to be used as a stand-alone
solution in a large building.
Star topology
• A star topology is designed with each node (file
server, workstations, and peripherals) connected
directly to a central network hub.
• Data on a star network passes through the hub
before continuing to its destination.
• The hub manages and controls all functions of
the network.
• It also acts as a repeater for the data flow.
Advantages of Star
Topology
• Easy to install.
• No disruptions to the network other than
connecting or removing devices.
• Easy to detect faults and to remove parts.
Disadvantages of Star
Topology
• Requires more cable length than a bus
topology.
• If the hub fails, nodes attached are
disabled.
• More expensive than bus topology
because of the cost of the hub.
Tree Topology
• A tree topology combines characteristics
of bus and star topologies.
• It consists of groups of star-configured
workstations connected to a bus backbone
cable.
• Tree topologies allow for the expansion of
an existing network.
Advantages of a Tree
Topology
• Point-to-point wiring for individual
segments.
• Supported by several hardware and
software venders.
Disadvantages of Tree
Topology
• Overall length of each segment is limited
by the type of cabling used.
• If the backbone line breaks, the entire
segment goes down.
• More difficult to configure than other
topologies.
Ring topology
• Is a type of computer network configuration
where each network computer and device are
connect to each other forming A large circle.
• Data is divided into packets when transmitted.
• Packet is sent around the ring until it reaches
its final destination.
Advantages of ring
topology
• Requires lesser amount of cable and there are
not much of installation problems
• All stations have equal access
Disadvantages of ring
topology
• Failure of one computer may impact others
• Data transfer is slow
Mesh topology
• It requires that every terminal should be
attached to each other.
• All the computers must have adequate
number of interfaces for the connections to
be made.
• Because of this requirement the
installations is somewhat difficult.
• The length of cable required is quite higher
as compared to other topologies.
Advantages of mesh
topology
• Ease of troubleshooting.
• Data transfer is faster.
Disadvantages of mesh
topology
• uses a lot of cabling.
• Complex
• Most expensive topology
Considerations When
Choosing a Topology
• Money. A linear bus network may be the least
expensive way to install a network; you do not
have to purchase concentrators.
• Length of cable needed. The linear bus
network uses shorter lengths of cable.
• Future growth. With a star topology, expanding
a network is easily done by adding another
concentrator.
• Cable type. The most common cable in schools
is unshielded twisted pair, which is most often
used with star topologies.
Transmission Technology
Two types of transmission technologies are
there:
1. Broadcast Network
Single communication channel is shared by all
the machines in the network.
Transmission Technology
2. Point to Point Network
Data is routed directly from source machine to
destination machine directly.
Dedicated link
Routing
•
When data is to be transmitted between two
remote machines using intermediate machines,
certain routing techniques have to be applied.
• The intermediate machines may be:
1. Gateway
2. Hub
3. Router
4. Repeater
5. Bridge
Gateway
•
•
•
•
•
A gateway is a network point that acts as an
entrance to another network.
Acts as a bridge between two networks so that
data can be transferred between a number of
computers.
In enterprises, the gateway is the computer that
routes the traffic from a workstation to the outside
network that is serving the Web pages.
In homes, the gateway is the ISP that connects
the user to the internet.
For example, when you send an e-mail to a friend
or when you log in to a Web site, there is a
gateway that allows the connection take place.
Hub
•
•
•
•
A common connection point for devices in a
network.
Hubs are commonly used to connect
segments of a LAN.
A hub contains multiple ports.
When a packet arrives at one port, it is
copied to the other ports so that all
segments of the LAN can see all packets
Router
•
•
•
•
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A router is a device that forwards data packets
along networks.
A router is connected to at least two networks.
Routers are located at gateways.
Routers use headers and forwarding tables to
determine the best path for forwarding the
packets.
They use protocols to communicate with each
other and configure the best route between any
two hosts.
Switch
•
•
In networks, a device that filters and
forwards packets between LAN segments.
LANs that use switches to join segments are
called switched LANs.
Repeater
•
•
Repeaters are used in transmission systems
to
regenerate
signals
distorted
by
transmission loss.
Analog repeaters frequently can only amplify
the signal while digital repeaters can
reconstruct a signal to near its original
quality.
Bridge
•
A device that connects two local-area
networks (LANs), or two segments of the
same LAN that use the same protocol is
known as bridge.
More Concepts…
• Network protocols.
• Routing Technology.
Network Protocols
• A communication protocol is a set of rules
that specify the format and meaning of
messages exchanged between computers
across a network.
• A set of related protocols that are designed
for compatibility are called protocol suite.
Routing Technologies
•
Computer Networks may use the
following routing technologies:
1. Circuit Switching
2. Packet Switching
3. Message Switching
Circuit Switching
•
•
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A physical circuit is established between
two machines.
Once the connection is established, the
data transfer takes place and then the
connection is released.
The data transfer rate is high but error
prone.
Packet Switching
•
•
•
•
Data is divided into small, fixed size packets.
Each packet contains the address of destination.
All the intermediate machines inspect the address
and route it to the right machine.
If any packet is missing, the destination machine can
request the source machine to retransmit it.
Message Switching
•
•
•
•
Message as a whole is transmitted.
Each message contains the address of the
destination.
Message switching N/W is “Store and Forward” N/W.
Once the message arrives at the intermediate
machine, it is stored in it completely and transmitted
when the line is free.
Test 1
• This will be done on 21st November 2012
at 1200-1300