[email protected] types of computer networks lan ( local area network ) wan (wide area...
TRANSCRIPT
Types of computer networks
• LAN ( LOCAL AREA NETWORK )
• WAN (WIDE AREA NETWROK )
LAN (Local Area Network)• It covers small area• Most LANs are used to connect computer in a single building or group
of buildings• LANs can be found in industrial plants , office buildings ,colleges or
universities• Capable of transmitting data at very fast rate • It is much faster than data transmission over a telephone line
LAN CHARACTERISTICS
Size Transmission Technology Topology
Restricted in Size
Single Cable
10 to 100 Mbps
Low delay (ms)
Very few Errors
Megabits/Sec. (Unit)
BUS (Ethernet) Ring (Token ring)
Uses of LAN
• Sharing of one copy by all users
• System resources can be share like printer
• Easy to manage data store • Data is more secure from
being copied or destroyed • It may be in form of • Peer-to-peer Network • Client Server Network
WAN (Wide Area Network )• It covers the large area • WAN connects computer in different cities and countries• When devices are speared by more than a few hundred yards. • Normally a WAN consists of two or more interconnected LANs • Connected through telephone lines or satellites • WAN is expensive than LAN • Speed depends on the speed provided by the company• Communication may be via microwave, satellite link or telephone
line. • Use in banks or in air ticketing system• Alternative technologies
– Circuit switching– Packet switching– Frame relay– Asynchronous transfer mode (ATM)
•
Transmission Rate • Baud rate: The speed at which data is transmitted serially is known as the
baud rate.• The 'Baud Rate' is the number of symbols transmitted per second. A
'symbol' is one chunk of information. • Note that 'baud rate' is not the same as bit-rate. One symbol (a chunk of
information) can be carried by many bits.• Difference between Baud and bit rate• The difference between the two is complicated and intertwining. They are
dependent and inter-related. • But the simplest explanation is that a Bit Rate is how many data bits are
transmitted per second. • A baud Rate is the measurement of the number of times per second a
signal in a communications channel changes. • Engineers use more than one bit per symbol because it helps detect errors. •
Modes of operation
• Baseband mode:• One channel system – whole bandwidth
dedicated to one data channel, e.g. Ethernet. • Used for data communication over short
distances for example, LAN’s.• LANs typically operate in baseband mode,
which means that a given cable is carrying a single data signal at any one time.
• Computers connected to this LAN must take turns using the medium.
BroadBand Mode• Multi-channel system - several channels are combined onto a
carrier signal – the bandwidth is shared by several data channels.• Used for long distance data communication. Using the analogy of
SKY TV, all channels are broadcast to your receiver at once but on different frequencies.
• The receiver then decodes the channel you wish to watch and displays it on the TV.
• Long-distance communications media, on the other hand, are expensive to install and maintain.
• It would be wasteful if each media path could support only a single data stream. WANs, therefore tend to use broadband media.
• Broadband media allow two or more data streams to be carried at the same time.
Network Topologies
• The physical layout or the way in which network connections connection are made is called topology
• It refers especially to the locations of the computer and how the cable runs between them
• It may be • Bus or Line Topology • Star Topology• Ring Topology • Tree Topology
Bus or Line Topology • All computers or network nodes are connected to a common
communication medium • In a local network this medium is often a central wire called
bus• Information can be transmitted in either direction from any
PC to any other • Working• If a computer wants to send data to the other computer in
the network ,it sends the data via the bus• The data and address move from one computer to other and
checks the address if it matches then it goes to other computer
Advantages
• Simple easy and suitable for small network • Least amount of cable is required• Easy to extend a bus
Disadvantages • Heavy network traffic can slow a network • A cable breaks or loose connector will
disconnect the entire network • No of computer increase then speed of network
will be slow • Cable failure is difficult to isolate.
Star Topology
• Is one in which all the cables run from the computers to a central location
• Connected with the device called hub
• Used in client server network
• Working • If two computers want to share
data the sender computer sends data to the hub and hub sends it to the receiving computer
Advantages • Hub can accommodate multiple cable types• Easy to modify • Reliable market proven system• Finding faults becomes easy• No problem with collisions of data since each stations
has its own cable to the server.• Single computer failure cannot break the network• Message passing from one workstation to other is more
secure• Variable transmission rates are possible between the file
server.• Disadvantages• If central hubs fails the entire network fails • It is more expensive because all network cables must be
pulled to a central point
Ring Topology
• Each computer is connected to the next computer with the last one connected to the first
• Data flow around the circle from device to device in one direction only
• Working • Each computer
retransmits what it receives from the previous computer
• The message flow in one direction
Advantages • There is no signal loss problem • Every computer has a equal access to the token• Transmission of messages around the ring is
relatively simple• Transmission rate is higher.
Disadvantages • Failure of one computer on ring effect the whole
network• Difficult to troubleshoot • Adding or removing computers disrupts the
network
Protocols• Used for communications between entities in a
system• An agreed-upon format or set of rules for transmitting
data between two devices. • Must speak the same language• Entities
– User applications– E-mail facilities– Terminals
• Systems– Computer– Terminal– Remote sensor
Design Issues • Addressing.• Data transfer.
– Simplex communication.– Half-duplex communication.– Full-duplex communication.
• Number and priorities of the logical connection channels. Many networks provide at least two logical channels per connection, one for normal data and one for urgent data.
• Error control.– Error detecting code.– Error correcting code.
• How to receive data in order (sequence no.).• How to keep a fast sender from swamping a slow receiver with data (flow
control).• Size of the message: disassembling >transmitting >reassembling
messages.• Routing: multiple paths between source and destination.
Protocol Architecture• Task of communication broken up into modules• For example file transfer could use three
modules– File transfer application– Communication service module– Network access module
Standard Protocol
Protocol stack: A list of protocol used by a certain system, one
protocol per layer.Examples of Protocol:TCP/IP :Whereas the IP protocol deals only with
packets, TCP enables two hosts to establish a connection and exchange streams of data.
X25A: popular standard for packet-switching networks.
The X.25 standard was approved by the CCITT (now the ITU) in 1976.
Problems in protocols
• It is also possible to link equipment using a special translation device called a protocol converter to link then there is a compatibility problem for example
• PC to Mainframe communication Protocol • Different types of transmission: PC may use
asynchronous transmission, and the mainframe synchronous transmission.
• Different character representation: PC use ASCII whereas Mainframe use EBCDIC
• Different Error detection and Correction methods
Handshaking• Handshaking is the exchange of signals
between devices to establish their readiness to send or receive data.
• E.g. Between Computer and Printer• It is one method of ensuring that both the sender
and receiver are ready before transmission begins.
• The conversation between the two devices is along the lines of following
• Device 1 Device 2 • Are you ready to receive data Yes go ahead• Sends data Message received
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