network
DESCRIPTION
TRANSCRIPT
NETWORKA computer network is a network of geographically distributed multiple computers connected in a manner to enable meaningful transmission and exchange of information among them.
Its main objectives are:
•Sharing of resources •Sharing of information
•Sharing of processing load
BASIC ELEMENTS OF COMMUNICATION SYSTEM
It is a process of transferring information from one point to another
The three basic elements of a computer system are:
•A sender•A medium
•A receiver
SENDER RECEIVER
DATA TRANSMISSION MODES
• There are 3 modes of data transmission:
1. SIMPLEX:
2. HALF DUPLEX
3. FULL DUPLEX
SENDER RECEIVER
SENDER(or RECEIVER)
RECEIVER(OR SENDER)OR
SENDER(AND RECEIVER)
RECEIVER(AND SENDER)AND
DATA TRANSMISSION SPEED
• The data handling capacity of a communication system is bandwidth
• The range of frequencies that is available for the transmission of data
• Wider bandwidth permits more rapid information flow. Wider the bandwidth of a communication system, the more data it can transmit in a given period.
• The communication data transfer rate is measured in BAUD
• In general a baud is identical to bits/sec
• Depending upon their transmission speeds, communication channels are grouped into 3 basic categories:
1. Narrow band: speed in the range of 45 to 300 baud
2. Voice band: speed up to 9600 baud
3. Broad band: speed up to 1 million baud or more
DATA TRANSMISSION MEDIA
1. Twisted pair wire or unshielded twisted pair(UTP) used in local telephone communication and short distance up to 1 km for digital data transmission
• Normally used to connect terminals to the main computer
• Data transmission speed of up to 9600 bits/sec , if the distance is not more than 100 meters
• Inexpensive medium
• Easy to install and use
• Easily pick up noise signals when length extends 100 meters
2. Coaxial cable: capable of transmitting digital signals at rates of 10 mbps
• They are extensively used in long distance telephone lines and as cables for cable TV
• Higher noise immunity
3. Microwave system: data transmission rates of about 16 gbps
Transmitting station Receiving station
In between repeaters
Line of sight
4.Communication satellite
Transmitting station receiving station on Earth
on earth
satellite in space
5. Optical fibers
Electrical signal
Electric to light wave converter
Light to electrical wave converter
Optical fiber Electrical signal
amplifier
Light waves
MODEMS
• The process of modulation and demodulation is carried out by a special device called a modem
• Modulation: conversion of digital data to analog
• Demodulation: conversion of analog to digital
TerminalModulator
Demodulator
Demodulator
ModulatorComputer0 1 1 0
0 010
01 1
0
0 010
Digital signals
Analog signals on telephone lines
Digital signals
A modem at terminal end
A modem at computer end
Analog versus digital transmission
• If data is sent over long distances the analog signal can become weak and distorted. To avoid this amplifiers are used. Amplifier strengthens a weak signal
• When digital mode of transmission is used over long distances a repeater is used to receive and then transmit the signal
• Its purpose is to strengthen a weak digital signal over long distances
DATA TRANSMISSION SERVICES
• Dial‐up line
• Leased line
• Integrated services digital network
• Value added network
TRANSMISSION MODES
1. ASYNCHRONOUS TRANSMISSION: data is transmitted character by character at regular intervals i.e A sender can send a character at any time and the receiver will accept it.
• In order to enable the receiver to recognize a character when it arrives a transmitter frames each character: Preceding a character a start bit and following a character one or two stop bits
• The time between transmitting any two characters can be zero or of any length.
• Best suited to key board type terminals, printers
• Advantage is this does not require any local storage at the terminal ,because transmission takes place character by character. So it is cheaper to implement
• Since the transmission line is idle during the time intervals between transmitting characters , the idle time of transmitting line may be a matter of concern, if the line cost is high
character character character
Irregular time intervals between two characters
Each character framed by start bit and stop bits
2. SYNCHRONOUS TRANSMISSION
• It involves blocking a group of characters .
• Each block is framed by header and trailer information
• Header contains synchronization information and information to identify the sender and receiver
• Following the header is a block of characters which contains actual message to be transmitted
• The message characters in the block are terminated by a trailer
• The trailer contains an end of message followed by a check character to aid detection of any transmission error
• Its advantage is its efficiency.
• No need of individual start and stop bits and gives higher data rates
• Its disadvantage is need of local storage at the two ends of line and need of synchronized clock at both ends
char trailerchar char charT
indefinite time interval between two blocks of data
Trailer containing end of character
Header containing synchronizing and other information
SWITCHING TECHNIQUES
CIRCUIT SWITCHING:
ADVANTAGES:1. Once the circuit is established data is transmitted with no delay
2. It is suitable for low speed communication between a terminal and a computers the method is simple and requires no special facilities
3. Because of a dedicated path ,it is suitable for long continuous transmission
4. Full capacity of the circuit is available for exclusive use by the connected pair of nodes, the transmission time required to send a message can be known
DISADVANTAGES1. Since the physical link is dedicated one ,the channel capacity is dedicated to one
source for the entire duration of a connection. So network resources are not properly used
2. Is very uneconomical since communication between computers occur in short fast bursts with long silent periods
3. Before actual data transfer the time required to establish a physical link between the two stations is of the order 10 secs or more, depending on the distance. For many computer applications this time elapse is too large and unsuitable
MESSAGE SWITCHING:
ADVANTAGES:
1. No physical connection is established
2. As channels are used only when messages are transmitted, this method uses the channels very effectively
DISADVANTAGES:
1. Each switching node must have a sufficient storage to buffer messages
2. A message is delayed at each node for the time required to receive the message, plus a queuing delay while waiting for an opportunity to retransmit the message to the next node
3. Method is too slow for real/interactive applications.
1
5
4
23
A
D
B
C
Store and forward method
1 2 3 N
message
Broadcast channel
Broadcast method
--------
Packet switching
ADVANTAGES
1. Packets are of small and fixed size. Hence the storage requirement for buffering the packets at intermediate nodes is minimal
2. Since the routing is done on packet basis, the intermediate nodes do not have to wait for the entire message. Hence the transmission is very fast
3. The method is fast enough for interactive/real time applications
4. Is used in wide area networks
DISADVANTAGES
1. Due to the need to buffer each packet at every at intermediate node , and to reassemble the packet at the destination node ,the overhead incurred per packet is large
2. There is no guarantee of how long it takes a message to go from its source to its destination node, because the time taken for each packet depends on the route chosen for that packet ,along with the volume of data being transferred along that route
How networks are structured• Server based networks
• Client/server networks
• Peer‐to‐peer networks
NETWORKING TOPOLOGIES
• The term topology refers to the way in which the nodes of a network are linked together
• It determines the data paths which may be used between any pair of nodes in the network
The four major topologies are:
1. STAR NETWORK:
Multiple computers are connected to the
host computer
The computers in the network are not linked
directly to each other and can communicate only via host
computer
The routing function is performed by the host
computer , which centrally controls communication
between any two other computers by establishing a logical path between
them
Host computer
2.RING NETWORK
• Each computer has communicating subordinates, but there is no master computer for controlling other computers
• A node receives data from one of its two adjacent nodes
• The only decision a node has to take is whether
the data is for its own use. If it is addressed
to it, it utilizes it else passes it on to the
next node
• More reliable than star network as communication
is not dependent on a single host
3.MESH NETWORK
• It has a separate physical link for connecting
each node to any other node
• Each computer has a point‐to‐point link with
all other computers
BUS NETWORK
• A single transmission media is shared by all nodes
• When a computer wants to send a message to another computer
it appends destination address to the message and checks
whether the communication line is free or not
• As soon as the line gets free it
broadcasts the message on the line
• As the message travels the line
each computer checks whether it is
addressed to it
• The message is picked up by
the addressee computer which sends an
acknowledgement to the source
computer and frees the line.
• Also known as multidrop or multipoint
or broadcasting network
• It is appropriate for use in LAN where a high speed communication channel is used and when satellite communication is used (one satellite channel may be shared by many computers at a time)
Single communication line shared by all nodes
HYBRID NETWORK
• The exact configuration of the network depends on the needs and overall organization structure of the company involved
ringstar
mesh
NETWORK TYPES
1. GEOGRAPHIC DISTIBUTION:
LAN –few kms
WAN‐may extend up to several thousands kms
2. DATA RATE:
LAN: transmission rates usually range from 10 Mbps‐1 Gbps
WAN: transmission rates usually range from 122 bits/sec‐2Mbps
3. ERROR RATE: LANs experience fewer transmission errors than WANs
LAN: In the range of 10‐8 to 10‐12
WAN: In the range of 10‐5 to 10‐7
4. COMMUNICATION LINK:
LAN; twisted pair, coaxial cable, fiber optics
WAN: telephone lines, microwave links, satellite channels
5. OWNERSHIP:
LAN: single organization
WAN: different organizations
6. COMMUNICATION COST:
LAN has negligible cost
Network linking devices• Hubs: not a fast connection because it broadcasts the packets it receives
to all nodes attached to its ports.
• Bridges : it is used to connect two LANS or two segments of the same LAN.
• It looks at the information in each packet header and forwards data that is travelling from one LAN to another
• Switches: it is a device that learns which machine is connected to its port by using the PC, printer or other devices
• It reduces the amount of broadcast traffic and is currently the most popular network linking device
• Modern switches can even function as routers , allowing multiple LANs to be interconnected by linking each LAN ‘s switches together. This is called an UPLINK
• Routers: it is a complicated device that stores the routing information for networks
• It determines the best routes for the packet
• These are located as gateways, the places where two or more networks connect
• It include security options, filters data