Download Moodle-5 - Willingdon College, Sangli

5
Moodle
WILLINGDON COLLEGE SANGLI
(B. SC.-II)
Digital Electronics
NETWORKING TECHNOLOGY
Moodle developed
By
Dr. S. R. Kumbhar
Department of Electronics
Willingdon College Sangli
1
NETWORKING TECHNOLOGY
Transmission Media
Various intities must communicate through some form of media on the network, whether it is
technologically based simply uses sensors to detect sound waves propagating through the air. In the similar
way computer communicates through the cables, light as well as radio waves. The transmission media enable
to establish the communication.
Transmission media can be divided into two types.
1) Bonded media or cable media.
This includes coaxial cable, shielded twisted pair cable, unshielded twisted pair cable and their optic
cable.
2) Boundless media
Which includes wireless media. Transmission media uses some important frequencies to transmit the data.
Transmission media characteristics
The important characteristics of transmission media are
1) Cost 2) Installation requirement
3) Bandwidth
4) Band usage
5) Attenuation 6) Immunity from
Electromagnetic Interference (EMI).
1) Cost : The one of the main factor in the purchase is network components cost. We often require faster and
robust transmission media which limits the speed of the maintenance, so cost must be low and new
technology must be maintained.
2) Installation requirement : It requires skilled labours, so it gets delay and cost increases while bringing the
skilled labours.
3) Bandwidth : Bandwidth refers to measure of the capacity of medium to transmit data. A media that has
high capacity has high bandwidth. The bandwidth that cable can accommodate is determined in part by
cable's length. A short cable generally accommodate greater bandwidth than long cable, which specifies
the restriction of cable run. Beyond specified length the signal may distort and error occurs.
4) Band usage : There are two ways to allocate the capacity of transmission media are base band and broad
band transmission. Base band denotes entire capacity of medium to one channel. Broad band enables two
or more communication channels to share the bandwidth of communication media. Fig. 1 shows the base
band and broad band transmission modes.
BW
Base band
Broad band
Fig. 1 Base and broad band transmission modes
Attenuation : It is a measure of how much the signal weakens as it travels through the medium. If the signal
strength falls below certain level then false triggering will take place therefore designer must specify limits in
the length of cable run.
2
5) EMI : It consists of outside electromagnetic noise that distorts the signal in a medium. EMI is received
over the transmission in the form of noise caused by nearby motors, lightening, cross talk occurs due to
EMI.
Cable Media
The cable media is divided in to 3 types
1) Coaxial cable
2) Twisted pair cable. 3) Fiber optic cable.
1) Coaxial cable: This type of cable was first cable type used in LANs. Fig. 2 shows the cross section
coaxial cable.
Outer conductor
Insulator
Jacket
Center conductor
Fig. 2coaxial Cable
The name coaxial got as the two conductors share a common axis which are mainly used in TV cable.
1) A center conductor : It is a solid stranded wire.
Outer conductor : It forms a tube surrounding conductor. It consists of braided wires, metallic foils or both.
Outer conductor is always called shield which protect the inner conductor from EMI.
Coaxial characteristics :
1) Installation : It is installed in daisy chain and star type network. Coaxial cable is easy to install because
cable is robust and difficult to damage.
2) Cost :When thinnet is used its cost is less than that of the Thicknet.
3) Capacity : The coaxial LAN typically have bandwidth between 2.5 Mbps to 10 Mbps. Thicker cables
always offers high bandwidth.
EMI characteristics : All copper media are sensitive to EMI though the shield makes the cable fairly resistant.
Coaxial cable however, do radiate a portion of signal.
Types of Coaxial cables :
1) Thinnet :
1) It is light and flexible cabling medium,
2) Easier to install and inexpensive.
3) It transmit a signal reliably up to 185 meters.
Thicknet :
1) Thicknet is thicker than thinnet.
5) It has approximately 0.5 inches in diameter.
2) Thicknet cable is harder to work with it.
6) It can carry more signals at longer distance.
3) It can transmit a signal up to 500 meter.
7) It is also called standard Ethernet.
4) Because of greater size it is more expensive than thinnet.
Classification of thinnet cables :
Cable
RG - 58 / U
RG - 58 A / U
RG - 58 C/ U
RG - 59
RG - 62
Classification
Solid copper center
Wire strand center
Military version
TV cable
ARC Net
3
Impedance
50 
50 
50 
75 
93 
Twisted Pair Cable
Twisted pair cable has dominant cable type for all new network designers that employ copper cables.
Among the several reasons for the popularity of twisted pair cable the most significant cable is low cost per
foot of any cable. Example is telephone cable. The basic twisted-pair cable consists of copper wire twisted
together as shown in Fig. 3
Fig. 3 Twisted pair cable
The twisting reduces the sensitivity of the cable to EMI and also reduces the tendency of cable to
radiate radio frequency noise that interfere with nearby cables and electromagnetic components be in case the
radiated signal from the twist wires tend to cancel each other out. Twisting also reduces the cross talk.
Twisting pair cable is used in most cables to connect PC to either HUB or AAU.
Shielded Twisted Pair (STP) Cable
Shielded twisted-pair cabling consists of one or more twisted pairs of enclosed in a foil wrap and woven
copper shielding.
Coaxial and STP cables use shields for the same purpose. The shield is connected to the
ground portion of the electronic device to which the cable the cable is connected. A ground is a portion of the
device that serves as an electrical reference point, and usually, it is literally connected to a metal stake driven
into the ground. A properly grounded shield prevents signals from getting into or out of the cable.
The STP cable, and includes two twisted pairs of wire within a single shield.
Because so many
different types of STP cable exist, describing precise characteristics is difficult. The following section,
however, offer some general guidelines.
Cost: STP cable costs more than thin coaxial or unshielded twisted-pair cable. STP is less costly than thick
coax or fiber-optic cable.
Installation:
Naturally, different network types have different installation requirements. One major
difference is the connector used. Apple Local Talk connector generally must be soldered during
installation, a process that requires some practice and skill on the part the installer.
Capacity : The capacity of STP cable is 500 Mbps. Although few implementations exceed 155 Mbps with 100
meter cable run. The common data rate for Token Ring networks.
Attenuation : All twisted pair cable offer attenuation that limits the length of cable runs. The 100 meter length
is more common.
EMI characteristics : The shielded STP cable results in good EMI characteristics for copper cable, as
compared to coaxial cable. This is the reason STP may be preferred to unshielded twisted pair cable in
same situations.
4
Unshielded Twisted Pair (UTP) cable :
This cable is not having any shield on its structure. But the characteristics are similar in many respects to
that of STP. Only difference is attenuation and EMI. Telephone systems commonly uses UTP cables.
UTP cable has following 5 grades.
Category 1 and 2 : These are voice grade cables are suitable only for voice and for low data rates.
Category 3: This cable is suitable up to data rate of 10 Mbps.
Category 4 : This data grade cable consists of 4 twisted pairs which is suitable for rates up to 16 Mbps.
Category 5: It consists of 4 twisted pairs and suitable for data rates up to 100 Mbps. Almost all few cabling
systems and designed with category 5. Price of the grades increase as you move from 1 category to 5.
Cost : UTP is least costly of any cable type, although properly installed category 5 tends to be fairly
expensive.
Installation : UTP cable is easy to install, so special equipment’s may be required.
Capacity : The data rates possible with UTP is 100 Mbps.
Attenuation : UTP cable share similar attenuation characteristics with other copper cables. UTP cable runs are
limited to a few hundred meters with 100 meters.
EMI : Because UTP cable lacks a shield, it is more sensitive to EMI for noisy environments.
Optical Fiber Cable:
Today almost every where fiber-optic cable is ideally used for data transmission. This optical fiber
cable has a capability to accommodate extremely high bandwidths. The optical fiber cable also presents no
problems with EMI and supports durable cable, which runs several kilometers long. There are two
disadvantages of optical fiber cable are cost and installation difficulty.
Jacket
Cladding
Fiber Core
Fig. 4 Fiber Optic Cable
The center conductor of fiber-optic cable is a fiber consisting of highly purified glass or plastic
designed to transmit light signals with little loss. The fiber optic cable is made up of glass or mixture of glass
and plastic. It consists of central part called core having n1 refractive index and outer covering of core is called
cladding having n2 refractive index. The fiber is coated with a cladding or a gel that reflects the signal back
into the fiber to reduce signal loss. Optical fiber cable can’t transmit electrical signals. The data signals are
converted into light signals. Light source includes LASERS and LED’s. The light is made to pass at one end to
5
make total internal reflection and light travels through fiber and at receiver light signals are converted back in
electrical form by using photodiodes.
CHARACTERSTICS OF OPTICAL FIBER
1) Cost: The cost of optical fiber instrument is very high but is significantly reduced in these days.
2) Installation: Greater skill is required to install fiber-optic cable than simple copper cables. Improved tools
and techniques are required for installation. Cables must be handled gently during installation. Every cable
has minimum bend radius. The cable may damage if it bend sharply during installation.
3) Capacity: Fiber-optic cable can support high data rates (200,000 Mbps) even with long cable runs.
Although UTP cable runs are limited to less than 100 meters with 100 Mbps data rates. Fiber-optic cable
can transmit 100 Mbps signals for several kilometers.
4) EMI :
As fiber-optic doesn’t use electrical signal to transmit data, they are totally immune to
electromagnetic interference. These cables are also immune to variety of electrical effects that must be
taken into account. Because fiber-optic cable is immune to electrical effects which is best way to connect
networks in different buildings.
5) Attenuation: It offers very less attenuation than the copper cables.
COMPARISON OF CABLE MEDIA
S.
No
Cable type
Cost
Installation
Capacity
Range
EMI
1
Coaxial Thinnet
Less than STP
Easy
10 Mbps
185 M
2
Coaxial Thicknet
10 Mbps
500 M
10 Mbps
100 M
/ 10 Mbps
100 M
Less sensitive
than UTP
Less sensitive
than UTP
Less sensitive
than UTP
Most sensitive
/ 100 Mbps
10’s
Km.
3
4
5
Greater than STP, Easy
less than fiber
Shields twisted pair Greater than UTP, Fairly easy
(STP)
less than Thicknet
UTP
Lowest
Inexpensive
easy
Optic- fiber
Lowest
Expensive
difficult
of Insensitive.
WIRELESS MEDIA.
Wireless media is an extraordinary convenience of wireless communications has placed an increased emphasis
on wireless networks in recent years. The wireless media is divided into three basic types.
1) Local area network (LAN)
2) Extended local network
3) Mobile computing in which the mobile machine connects to the home network using cellular or satellite
technology
The usefulness of the wireless network.
1) A space where cabling would be impossible or inconvenient. These include open lobbies, old buildings
historical buildings, etc.
2) People who move around the world like doctors, managers, police, etc they use a wireless communication.
6
3) Temporary installation: It is costlier to provide a temporary installation, but using the wireless it is easy to
provide temporary installation.
4) People who travel outside the work environment and need instantaneous access to network resources.
5) Satellite offices, branches, ships in ocean, or streams in remote field location.
WIRELESS COMMUNICATION WITH LANs
An access point is a stationary transreceiver to the cable based LAN that enables the cordless PC to
communicate with the network. LAN communication can be classified according to the transmission method.
The most common 4 methods are
1) Infrared
2) LASER
3) Narrow band Radio 4) Microwave 5) Spread Spectrum Radio.
1) INFRARED TRANSMISSION :
The use of infrared communication system every time control TV with remote control. The remote
control transmits pulses of infrared light that carry coded instructions to a receiver on the TV. Infrared
transmissions are limited to 100 feet. Its speed is about 10 Mbps. Infrared devices are insensitive to radio
frequency interference.
2) LASER TRANSMISSION
High power laser transmitters can transmit data for several thousand yards. When line – of – sight
communication is possible. Laser light technique is similar to infrared technology is employed in both LAN
and WAN transmissions through WAN.
3) NARROW BAND TRANSMISSIONS
It is called frequency radio transmission The range of narrow band radio is greater then that of infrared
effectively enabling mobile computing over limited area.
4) SPREAD SPECTRUM RADIO TRANSMITTER
This method was originally developed by the military to solve several communications problems. It
improves reliability, reduces sensitive to interference and timing. This method is commonly used for WAN
transmitters.
SATELLITE MICROWAVE
Satellite microwave systems uses communication satellite. Satellites are 22300 miles above the earth.
It remains located at fixed point on the earth, earth satellite stations uses satellite dish antennas to
communicate with satellite. These satellite then transmit signals in narrow band. Satellite always operate with
Gigahertz i.e 11-14 Ghz.
Cost involved is very high and distribute among the many users –
NETWORK TOPOLOGIES
Topology is a map of network it tell the detailed study of the particular area. It is a plan how the.
Cabling will interconnect the nodes or devices and how the nodes function in relation to one another there are
7
several important factors of topology and most important is the access method. Accessing is nothing but it is a
set of rules sharing the transmission medium.
Accessing Methods
There are three important accessing methods.
1) Contention 2) Polling
3) Token ring
Collision
Fig. 12 Collision of contention based network
1)
Contention : Contention means the computers are contended for use of transmission medium the
system brakes down when the two computers attempt to transmit the data at the same time in which collision
occurs. When the network is busy collision occurs several times. These number of collision are minimized by
using certain mechanics. Carrier sensing is one of the mechanism that listen to the network before transmit its
data. If the required device is busy then computer stops transmitting until the network is free. Here the listen
before talking strategy is employed to reduce the collision
Carrier detection is another contention mechanism. In this method computer listen to the network as they
transmit when computer detects the signal that interferes with other, computer stops sending signal. Then both
computers will wait for some time and then tries to transmit.
Contention is a simple protocol that can operate with simple network software and hardware as the
collision occurs at unpredictable intervals no computers is guaranteed the capacity to transmit at any given
time. These are called probabilistic networks. The number of collisions increases as computers used. When
many computers are used collisions dominate the total traffic lines. All computers on the contention-based
network are equal so there is possibility to greater access to the network.
Polling :
A
B
Controller
C
Fig. 13 Polling of computers
8
Polling based system requires controls or master devices to poll the other devices on the network the
controls or master checks whether device is ready to transmit or receive data polling based access is not used
in common networks because polling itself can create a traffic on the network.
Common example is the computer where interrupt priorities are concerned. Each time computer
checks whether the interrupt signals has appeared or not.
TOKEN PASSING:
Token passing uses a frame called a token, which circulates around the network. A computer that needs
to transmit has to wait until it receives the token. Then it may transmit their required data. When computer
has done transmitting then it passes the token. Frame to the next station on the networks. Fig. 14 shows the
scheme of token passing access.
Token ring is most common standard used by IEEE. FDDI is a 100 Mbps fiber optic network standard
that uses token passing as that of IEEE .Token passing methods can use station priorities and other
methods to prevent only one station from monopolizing the network. Because each computer has chance
to transmit each time and token travels around.
Token passing more appropriate then contention.
1) As the network carries time critical data.
2) When network uses heavy traffic the token ring is not locked, because of large no. of lines.
NETWORK TOPOLOGIES:
A term topology refers to the description of the network. The arrangement of nodes, cables, and connectivity
devices which makes the network. The network consists of two categories.
1) Physical topology : the physical topology describes the actual layout of the network transmission media.
2) Logical topology : It describes the path of signal flow through the network nodes.
9
The physical topology may defines about the network how it looks and logical topology defines the way of
the way passes, along the nods. The topology is the complete network defines the physical as well as logical
topologies, and also the specifications of elements. Such as transmission media.
The physical and logical topologies takes several forms. Ethernet and token ring are the two main
Topologies has following types,
1) Bus topology 2) Star topology 3) Ring topology, 4) Mesh topology.
BUS TOPOLOGY:
A bus is a physical topology in which all devices connected to a common based cables. Fig. 16 shows
the physical bus topology. Bus is nothing but a collection or bundle of wires through which the data flows.
Common bus is shared by the no. of devices. Generally bus type topology is used in LAN and Ethernet. The
Ethernet is the most common contention based. Network architecture typically uses. Physical topology most
bus networks broadcast signals in both directions on the backbone cable, enabling all the devices to directly
receive the signal. A terminator must be kept at the end of the back bone cable to prevent the signal from
reflecting on cable causing interference.
RING TOPOLOGY:
Ring topology is connected in circled each note is connected to neighbors on either side and data
passes around the ring in one direction only.
Each device consists of receiver and transmitter which serves
as a repeater that passes the signal onto the next device in the ring. Ring physical topologies are quite rare.
This ring topology is almost always implemented on logical topology. The main disadvantage of ring topology
is that if one node fails all the network branches stand still and this is also requires larger time.
10
STAR TOPOLOGY
T1
T3
T2
T5
T4
Fig. 10 STAR Topology.
STAR topology is a physical network in which all the nodes are connected to central hub. This hub
receives the signal from the network and routes to proper destination.
It is generally used to implement a bus or ring logical topology.
ADVANTAGES:
1) If one node fails other nodes handles the data.
2) Data transmission is faster.
3) Low cost.
MESH TOPOLOGY
A mesh topology is a hybrid model representing an all channel sort of physical topology. This
topology can incorporate all points so that it is called hybrid topology. It is an around topology in the every
device is directly connected to every other device on the network. Whenever new device is connected then
connection to all the existing devices must be made which provides a great deal of tolerance but involves extra
work. If the network communication is failure then data transfer can find alternative routes. Cabling network
in mesh topology is very expensive and complicated. Fig, 11 shows the mesh topology diagram.
Fig. 11 Mesh Topology.
11
NETWORK ARCHITECTURE
It is a design specification of physical layout of connected devices which includes cable, wireless,
multimedia, the type of network cards being used and the mechanism through which the data is sent on to the
network and passed to each device. There are two types of network architectures;
1) Ethernet
2) Token ring.
1) Ethernet : Ethernet is a very popular local area network (LAN) architecture based on CSMA / CD access
method. The original Ethernet specification was the base of IEEE 802.3 specification. But in the present
Ethernet term is used to represent original + IEEE 802.3 standards. The different types of networks used
are called Ethernet topologies. The different types of top-topologies are listed below.
1) 10 BASE 2
2) 10 BASE 5
3) 10 BASE – T
4) 10 BASE – FL
5)
100
VG-Any
LAN
6) 100 BASE X
Here in the above list of topologies every topology begins with number either ‘10’ or ‘100’ which
specifies the transmission speed of the network.
For example 10 BASE 2 is designed to operate at 10 Mbps and 100 BASE – X operate at 100 Mbps.
The ‘BASE’ specifies that baseband transmission is used.
‘T’ Refers for unshielded twisted pair wiring,
‘FL’ indicate optical cabling,
‘VG AnyLAN’
indicate voice grade, ‘X’ implies multiple media type.
The small unit in which the Ethernet transmit data is called frame. The size of the Ethernet can be
anywhere between 64 to 1,518 bytes, which contain source and destination addresses, protocol information
and error checking information.
Ethernet is generally used on light to medium traffic networks and performs best when network data
traffic transmits in short bursts. Ethernet is a standard network used for communication.
10 BASE 2 :
Terminator
with ground
0.5 M minimum
Transceiver
Repeater
Terminator
with ground
Segment
185 M maximum
12 BASE 2 Ethernet Cabling
The 10 BASE 2 cabling topology generally uses the on board transreceiver of the network
interface cord to translate the signal back and forth the other networks. The 10 BASE 2 is a
12
thinnet network, uses BNC T type connectors which are directly attached to the network
through adapter. The end of the cable is connected with a terminator. The cost of the network
is very less. The network has upto 185 M length, which is often cheapest of all the networks.
1] Min. cable distance in two devices is 0.5 meters.
2] Drop cable should not be used to connect BNC connector on adapter.
3] Maximum network length of segment is 185m.
4] Entire network cabling scheme cannot exceed 925 meters.
5] Maximum number of nodes per segment is 30.
6] A 50 ohm terminator must be used having either a grounding wire.
7] One must have more than 5 segments on the network.
10 BASE 5:
The 10 BASE 5 cabling topology (Thickness) uses an external transreceivers to attach to network. An
attachment Universal Interface cable runs from the transreceivers to a fix connected on the back of the
network.
The network must be terminated at both ends by using ground terminator, devices are connected through
transreceiver cable. The thicknet network is shown in fig.13
1] Its capacity is more than 10 BASE 2.
2] Minimum cabling distance must be 2.5 meters (8Pt).
3] Maximum segment lengths 500 mts
4] Entire cabling should not exceed 2500 meters.
5] One end of the terminator must grounded.
6] Drop cables can be as short as required but can’t be longer than 50 meters from transrecieivers to
computers.
7] Maximum number of nodes per network segment is 100 including repeaters.
Transceiver cable
Terminator
with ground
8 Feet minimum
Transceiver
Repeater
Segment
Terminator
with ground
1640 Feet maximum
Fig. 13 10 BASE 5 Ethernet Cabling
13
10 BASE T:
This uses unshilded pair cable. It is based on the IEEE 802.3 standard. This supports data rate of 10mbps.
Using baseband 10 BASE T is a cabling of star topology. The nodes are connected by wires to central hub
which supports multiport repeater. The hub repeats the signal to all nodes and nodes will access the data. This
uses RJ-45 cable connectors.
The network has the following advantages:
1] Easier to manage and repair.
2] Central hub can detect defecting cable segments.
3] One bad cable does not affect entire network.
The following are the rules for 10 BASE T network.
1] Maximum numbers of devices on a LAN is 1024.
2] UTP should be used for category 3,4 or 5, twisted pair can be used in place of (UTP).
3] Maximum unshilded cable segment length is 100 m.
4] Cable minimum distance between computers is 2.5 meters.
5] Minimum distance between a hub and a computer or between two hubs is 0.5 meters.
Fig. 22 10 BASE – T Cabling
10 BASE-FL
10BASE-FL is a specification for ethernet of optical fiber cable. This uses 10 Mbps data scale using base
band.
It supports the max distance of about 2000 meters. The number of nodes a segment can handle is greater than
10BASE 2 and 10 BASE T.
14
100 VG-Any LAN:
This is a standard IEEE 802.3 transmitting ethernet at the rate of 100 Mbps. Here VG stands for voice grade.
This has demanded priority.
The max length for the two longest cables attached to a 100 VG-AnyLAN hub is 250 meters. The cabling
specifications are in category 3,4,5 twisted pair or fiber-optic.
100VG-Any LAN is compatible with 10 BASE-T cabling.
100 BASE-X:
100BASE-X uses star bus topology similar to 10 BASE-T. It provides a data transmission speed of 100 Mbps
using base band. In 100 BASE-X stands for any cabling method i.e. twisted pair. (100 BASE-TX), fiber optic
cabling (BASE-FX) and four twisted pairs (100 BASE-T4).
This is a fast Ethernet like 100 VG-Any LAN. 100 BASE-X, provides capability with existing 10 BASE-T
system.
TOKEN RING
Token ring uses a token-passing arithmetic that uses IEEE 802.5 standard. The topology is physically
a star, but the
logical ring uses to pass the token from station to station. Each node must be attached to a
concentrator called a multistation access unit. Token passing will be takes place. If one computer crushes, the
others will be left waiting forever for the token. Token ring network interface cards can run at 4mbps.All the
given network must have the same speed. Fig. 23 shows the operation of token ring.
In the fig. Each node acts as a repeater that receives tokens and frames from it's nearest active
upstream neighbour. After the node processes a frame, the frame transmits downstream to next attached node.
Each token make's at least one trip around the entire ring and then returns to original node.
Token
R
T
T
RR
R
T
R
T
Fig. 23 Token Ring Passing
15
TOKEN RING CABLING
Generally token ring method's uses twisted pair cable. The types of cables are :
1) Type1:-A braided shield surrounds two twisted pairs of solid wire. This type of wires are used to connect
different wiring closet that are located in the same building. Max. cabling distance is 101meters.
2) Type 2 :-This uses a total 6 twisted pairs. Out of which 4 are of STP. The purpose of this cable is same as
that of type1. The max. cabling distance is 100 meters.
3) Type 3:- Type 3 has unshielded twisted pairs copper wire minimum of two twists per inch. This can not be
used for long, low data grade transmissions within walls max. cable distance is 45 meters.
Type 3 cabling is most popular transmission media for token ring which supports up to 72
computers. A token ring network using STP cabling can support up to 260 computers. The
min. distance between the computers is 250 meters.
PASSING DATA ON TOKEN RING.
The computer that holds the token has control of transmission media. It works in the following sequence.
1. A computer in the ring captures the token.
2. If the computers has data to transmit, it holds the token transmits a data frame.
3. Each computers checks whether it is the intended recipient of the frame.
4. When the frame reaches the destination address, the destination PC copies the frames to receives buffer,
updates the frame. Status field of data frame and puts frame back on the ring.
5. When computers that originally sent the frame receives it from the ring . It acknowledges a successful
transmission, takes the frame or ring and places the token back on the ring.
The sequence of token ring frame:
Start eliminator
:- makes start of frame .
Access control
:- specifies the priority of frames.
Frame control
:- media access control.
Destination address :- address of receiving computer.
Source address
:- Address of sending computers.
Data address
:- Data being transmitted.
Frame check sequence :- Errors checking information.
End deliminator
:- makes the end of frame.
Frame status
:- Whether frame is recognized or not .
Protocols
Protocols are rules by which the computers communicates, when number of computers &
terminal equipment’s are to be connected together to form integrated system, a well understood
standard method of communication & Physical interconnection should be established. This become
particularly critical when equipment supplied by different venders are to be connected since each vender
would have his own standards. If computer is different countries are to be connected together common agreed
rules followed to interconnects & communicate between computers are known as protocols.
Network data is encapsulated in packets at source. It is sent via the network to a destination. At
destination it is reconstructed into the appropriated route.
16
The packet contains the following:
1. Header :- This gives the start of packet, which contains sense & destination.
2. Data
:-This consists of data transmission.
3. Trailer :-It ends the packet, if has error checking information.
When the packet of information reaches the transmission medium the adapts checks the packets. If checks the
packets destination address. If the destination address matches the computer address then microprocessor &
protocol layers of destination PC process the incoming packets.
INTERNET PROTOCOLS (I.P.)
The Internet protocols suite was originally developed by United State Departments of defense, to
provide robust service on large Internet works. That incorporate a variety of computers types. Transmission
control protocols/ Internet protocols(TCP/IP) is required to communication over the Internet.
One of the main advantage of TCP/IP i.e. TCP/IP is required for communication over the Internet can be used
as communication backbone.
The disadvantage is that size of the protocol stack makes TCP/IP difficult to implement on some old
machines.
A large number of protocols are associated with TCP/IP. These different protocols are grouped into the
following categories:
1) General TCP/IP Transport protocols.
2) TCP/IP series.
3) TCP/IP Routing
1) General TCP/IP Transport Protocols
This covers general protocols dealing with the addressing and transportation of protocols across the LAN
using TCP/IP.
There are two types of address of TCP/IP; a node address &a typical address. A node is an address of
the device on the network. But logical address is the segment on the network which the node is attached. An IP
address is a set of four numbers or octets that can range in the value between zero &255.Each octet is
separated by a period.
e.g. 200.200.20.20, 2.5.200.15
These address is broken down into three distinct classes . These known as class A, Class B ,class C
addresses. Class A IP address contain a number between 1&127 before the first dot .e.g. 3.3.6.9 In class A
address, first octet represents the network address and last three octets represents the node or host number.
Class B& C follows the similar principle. In class C, the first numbers can range in form 192 to223. The first 3
numbers makes the address of the network and last numbers forms host ID.
17
Internet Protocols (IP)
It is a connectionless protocol that provides data program service and IP packets are most commonly referred
to as datagrams. IP is a packet switching protocol that has capability to perform, addressing and route
selection, IP performs packet deassembly
And reassemble as required by packet size, limitations defined for data link and physical layers, being
implemented. It also provides error checking and checksum.
Transmission control protocol (TCP)
TCP is an internetwork connection oriented protocol that corresponds to the OSI transport layer. It
provides duplex, end
to end connections. TCP maintains logical connection between the sending and
receiving computer systems and integrity of the transmission is maintained. TCP detects error in the
transmission quickly and takes caution to correct them.
TCP provides message fragmentation and reassemble. If above multiplex conversions with Upper
Layer Protocols and can improve. Use of network bandwidth
By combining multiple messages into the same segment.
Modems
Usually standard telephone lines can transmit only analog signals. But computers stores and transmit
data digitally. Modem can transmit digital signal over telephone lines by covering then to analog form.
Converting one signal form to another (digital to analog ) is called modulation. Recovering the original signal
is called demodulation, the modem means modulation/demodulation.
Modems are classified into 2
categories.
1)Asynchronous modems 2) Synchronous modems
1)Asynchronous transmission
It does not use a clocking mechanism to keep the sending and receiving devices synchronized. It transmits one
after another. Here each frame begins with start bit that helps to adjust the timing of transmitted signal.
Messages are short so they are drafted during the transmission of message.
Fig.24b shows the structure of asynchronous frame having four bits .
Start Bit
1) Start bit:
Data Bits
Parity Bit Stop Bit
This states that signal is starting and enabling the receiving device to synchronize itself with massage.
2) Data bit: This consists of group of 7or 8 bits when character is being transmitted.
3) A parity bit: This is used for detecting errors.
4) A stop bit:
This signals end of data frame .
A synchronous transmission is simple; inexpensive, which is practically suitable for transmitting small
frames at irregular intervals. This type of transmission is generally used in PC
18
SYNCHRONOUS
TRANSMISSION
Synchronous transmission eliminates the need for start and stop bit by synchronizing clocks
on the transmitting and receiving devices.
Synchronizing can be achieved in two ways.
1] By transmitting synchronization signals in the data.
2] By using a separate communication channel to carry clock signals.
Under the synchronous transmission, multiple characters or long series of bits can be transmitted
in the single data frame. When frames are long, parity is no longer a suitable method for detecting
errors. If error occurs multiple bits are more likely to be affected and parity techniques are less
likely to report errors.
Synchronous transmission offers many advantages over asynchronous transmission. The overhead
bit compares a smaller portion of overall data frame. which provides more efficient use of available
bandwidth. Synchronization improves the error detection and the device is operated at higher speeds.
Disadvantage of synchronous transmission is that more complex circuitry is necessary and expensive.
HUB
Hub is central part of the network attachment to connect the no. of devices . It is also called as wiring
connections .The no. of network cables are attached the hub . The hub contains either passive or active
elements which combines the signal from several networks . There are three types of hubs:
1) Passive hub
2) Active hub
2) Switching or intelligent hub
HUB
Fig. 25 Network wiring to central HUB
PASSIVE HUB:
The passive hub does not contain any electronic components and they do not process data
signals in any way. The unique purpose of passive hub is to combine various
signals from several network cable segments. The central passive hub receives all
the packets of data that passes through the hub. As the hub does not amplify the
signals, in fact the hub absorbs small part of the signal, the distance between the
computers and the hub is maximum of the half of the permissible distance between
the two components. For example, if the network is design whose maximum
distance is 100 m; the maximum distance between computer and hub must be 50
m.
19
ADVANTAGES:
1] limited functionality of passive hubs makes inexpensive.
2] easy to configure.
DISADVANTAGES:
1] Passive hub is generally used in small networks.
2] hub follows the 5-4-3 rule where not more than 5 networks segments can be connected to 4 hubs. With only
3 of them being used to connect to the terminals as shown in fig. 26
Fig. 26
5 – 4 – 3 Rule segments
5-4-3 rule, 5 segments connected to 4 hubs & only 3 segments connected to the devices
ACTIVE HUB :
The active hub uses electronic component that amplifies or filter out electronic signals that flow between
devices on the network. The filtering up process is called as signal regeneration. The network is less sensitive
to errors & distance between devices can be increased are the two benefits of signal regeneration .The cost of
active hub is more than that of the passive hub.
INTELLIGENT BUS
These are advanced devices of the active hubs, which adds intelligence to a hub. The hubs supports the
network management protocols that enable the hubs to send packets to a central network console. These
protocols helps to control the hub.
Switching hubs are the latest development in the hubs. This includes the circuits that quickly rotates the
signals between hub & various devices. In switching hub the packet of data is repeated only to the
destination computer rather than other computer. Now-a-days hubs are replaced by bridges. The bridge is
nothing but extended maximum size network.
REPEATERS
As seen from the transmission media that signal get attenuation so maximum range is limited. So in order to
increase the range of networks the repeaters are used. The repeaters extend only service range of signal. it is
the device that repeats the signal from one part to other part.fig.3 shows the regeneration of weak signals by
using repeaters. In repeater the signal does not get filtered or interrupted. It only regenerates signals in all
directions. The length of the network can be increased by using repeaters. This device is simple & cheaper in
20
cost. Repeaters does not require addressing information because it only repeats the bits of data. If the data is
corrupted then repeater will regenerate the signal in any way.
Weak Signal
Repeater
Strong signal
SSS
SSS
Fig. 27Repeater showing regeneration of weak signal
Some repeaters just amplify the signal along with the noise in the network. Repeater does not cleanup the
signal rather it adds the distortion in the original signal. But perfect repeaters can be used to extend the signals
to infinite distance, but size may limit the length. The most important phenomenon that puts the limits is
signal propagation. The propagation delay is the time required to reach the end point of the network. If the
maximum propagation delay expires so no signal encounters, therefore maximum allowed propagation delay
helps to calculate the maximum permissible cable length of the network. Though the repeaters enables signal
to travel further the maximum delay limits the size of network. Therefore repeaters follow 5-4-3 rule.
ROUTERS
Routers are internetwork connecting devices. This may consists of two or more physical connected
independent networks. The network may be Ethernet of token ring network. As each network is internetwork
and assigned to an address, which is considered logically separate, which functions independently of the other
internetwork. Routers uses network address information to assist the delivery of messages.
Delivering the packets according to the logical network address information is called routing. Some routers
can determine the best path for a packet based on routing algorithm. Bridges are suitable for relatively simple
networks. Routers organize the large network in terms of logical network segments. Routers are more
intelligent than bridges. Routers can build tables and also uses logarithms to determine most efficient path for
sending a packet to any given network. If the particular network is not attached to the router, intelligent router
knows the best way to send a packet to a device on the network.
Router A
NET A
Router B
Router
A
NET B
Router C
NET C
NET D
Router E
Router D
NET E
NODE = B
21
Fig. 29 Internetwork Router
In fig. If router A fails, Router B provides back up message path, which make network rough. As
routers determine routes efficiently, so they are usually employed to connect LAN to WAN.
There are two types of Routers;
1) Static routers
2) Dynamic routers
1) Static routers : In static routers paths are not determined by the routers. One has to provide routing table,
potential routers for packets.
2) Dynamic routers: They have a capacity to determine routes based on the packet information and also
other routes. The alternative routes are given in case of failure of one route.
Brouters : It is a router that can act as bridge. It tries to deliver packets on the protocol information. If
protocol is absent then brouter bridges the packet using device address.
22