1. Prof.PoonamK. 1
Ch 1. Overview of Networking Concepts
• Basics of communication systems
• Transmission Media
• Topology and Types of Networks
• TCP/IP protocolStacks
• Wireless Networks
• The Internet
2. Prof.PoonamK. 2
Data Communication
• In data communication data refers to facts, concepts and instructions presented in
various form and communicationrefers to actuallyexchange or share theinformation.
• Communication is local: face to face or remote: takes place over distance.
• Data communication is the exchange of data between two devices via some
transmissionmedium.
• Three fundamental Characteristics: Delivery,Accuracy and Timeliness.
3. Prof.PoonamK. 3
Components of Data Communication
• Message
Is the information to be communicated.
• Sender
which sends the data message.
• Receiver
Which receives the message.
• Medium
Physical path by which message travels from sender to receiver.
• Protocol
set of rules govern data communication. Its agreement betweenvarious communication devices.
4. Computer Networks
Prof.PoonamK. 4
• Computer Network means an interconnected
collectionof computers.
• Two computers are said to be interconnected if theyare able to exchange
information.
• Connections are through copper wire, fiber optic,microwaves or satellite.
• Here the model and software is absent. User aredirectly exposed to machine.
5. Goals of Network
Prof.PoonamK. 5
• Resource Sharing
• High reliability
• Distribution of workload
• Saving money
• Expandability
• Powerful communication
• Protectinginformation (Security)
• Preserving information
6. Prof.PoonamK. 6
Computer Network Application
• Business Application
– Company point of view
• Home Application
– Access to remote information
– Person-to-person communication
– Interactive entertainment
7. Prof.PoonamK. 7
Transmission Mode
• Used to define direction of signal flow between twolinked devices.
• Three modes are supported
– Simplex
– Half Duplex
– Full Duplex
8. Prof.PoonamK. 8
Transmission Mode – Three Modes
• Simplex
– Communication is unidirectional. Only one of the twodevices on a link can
transmit; the other can only receive.
– Example: keyboards and traditional Monitors
Mainframe Monitor
Direction of Data
9. Transmission Mode
Prof.PoonamK. 9
• Half Duplex
– Each station can both transmit and receive, but not at the same time. When one device is
sending, the other can only receive and vice versa.
– Example: Walkie-talkies
Workstation Workstation
Direction of Data at time 1
Direction of Data at time 2
10. Transmission Mode
Prof.PoonamK. 10
• Full Duplex
– Both stations can send and receive simultaneously.
– Signals going in either direction share the capacity of the link
– Sharing occur in two ways: either link must contain two physically separate transmission
paths, one for sending and the other for receiving or the capacity of the channel is divided
between signals traveling in both directions.
– Example: communication in telephone networks, bothcan talk and listen simultaneously.
12. Prof.PoonamK. 12
Transmission Technology (Line Configuration)
• It is mainly related to handle the technical issues.
• Two types of transmission technologies are used
– Broadcast Networks
– Point-to-point networks
13. Broadcast Networks
Prof.PoonamK. 13
• Single communication channel shared by all machines on the network.
• Packets with address are sent by any machine are received by all others.
• Upon receiving packet machine checks address field. If it is for itself, it processes the packet
otherwise simply ignore.
• It allows the possibility of addressing a packet to all destinations by using special code in
address field. When packet with this code is transmitted it is received and processed by every
machine hence mode is broadcasting.
• Geographical localized networks tend to use broadcast networks.
14. Broadcast Networks
Prof.PoonamK. 14
• Broadcast networks are classified depending on channel allocation
• Static allocation
Each machine is allocated a discrete time interval in which machine can transmit the
packet.
• Dynamic allocation
Centralized: here central or single entity decides which machine is going to transmit next.
It may accept request and takes decision according to algorithm define.
Decentralized: no central entity each machine decides whether to transmit or receive.
16. Prof.PoonamK. 16
Point-to-Point
• It consist of many connections between individual pairs of machines.
• To go from onesourceto destination, packet first visit oneormore intermediate nodes
(machines).
• Packet is sometime stored on intermediate machine till required line is free.
Mechanism is called store- and-forward.
• Routing algorithms: multiple routes are present and of different length.
• Larger networks are usually point to point.
17. Topology
Prof.PoonamK. 17
• Topology refers to the way a network is laid out,physicallyor logically.
• Two or more links forms a topology.
• There are basic five topologies
– Mesh
– Ring
– Bus
– Tree
– Star
• Hybrid topology
18. Mesh Topology
Prof.PoonamK. 18
• Every device has dedicated point-to-point link toevery device.
• Dedicated means links carries traffic between twodevices if connected.
• Fully connected network has n(n-1)/2 physical
channelsto link ‘n’ devices and n-1 ports.
19. Prof.PoonamK. 19
Advantages
• Dedicated links guarantees that connection carry its owndata thus eliminating traffic
problem
• Privacy and security since every message sent along
dedicated line
• Fault isolation and identification is easy
Disadvantages
• Since every device must be connected to each other
installation is difficult.
• Bulk of wires can be greater than available space.
• The hardware requirement is expensive.
21. Star Topology
Prof.PoonamK. 21
• Each device has dedicated point-to-point look to centralcontroller, usually called HUB.
• Devices not connected directly hence no direct traffic
• Controller acts as exchange: data->controller-
>other device
Advantages
• Only one link and one I/O to connect it to many device.
• Easy to install and configure. Less expensive.
• Additions, deletion involves only one connection.
• Robust, only one link is affected.
23. Tree Topology
Prof.PoonamK. 23
• Variation over star. Every device is not connected to centralhub directly but through
secondary hub.
• The central hub is active hub having repeaters to regeneratesignal before sending out.
• Secondary hubs can be active or passive. Passive hubssimply provides physical connection
between device.
• Secondary hub adds two additional advantages to star.
– Allow more device connected to central hub.
– Allows network isolation and priority communication
• Example Cable TV
25. BUS Topology
Prof.PoonamK. 25
• It is multipoint. One long cable acts as backbone tolink all devices in network.
• Drop lines: connection running between device andmain cable.
• Tap:punctures the sheathing of cable to create acontactwith metallic core.
• Limitation on number of taps.
26. Advantages
Prof.PoonamK. 26
• Backbonecable can laid along most efficient path and then connectedto node,
hence less cabling than other topologies. Redundancyof cable is eliminated.
Disadvantages
• Difficult to add new device
• Signal reflection at taps can cause degradation inquality.
• The fault or break in cable stops all transmission
28. Ring Topology
Prof.PoonamK. 28
• Here each device has dedicated point-to-point linewith two devices either side
of it.
• Signal reaches to destination through device to
device in one direction.
• Repeateris present.
• To add or remove device only one connection tomove.
• Signal is circulating all the time. If destination isunreachable it issues alarm.
• Break in cablecan affect entire network.
30. Types of Networks - LAN
Prof.PoonamK. 30
• LAN usually privately owned and links devices in single office, building or campus.
LANs are limited to few KM.
• It allows sharing of resources between computers. Resources includes hardware,
software or data.
• One computer with large disk acts as server to other client
• Mostly LAN uses one transmission media and most common topologies: bus, mesh,
ring,star etc.
• Single building LAN or Multiple building LAN
32. Types of Networks - MAN
Prof.PoonamK. 32
• To extend over an entire city.
• It may be single network as television network or means of connecting number of
LANs into larger network to share resources LAN-LAN
• MAN can be wholly owned and operated by private company or may be service
provided by public company such as telephone company.
• There is broadcast medium to which all computers are connected.
34. Types of Networks - WAN
Prof.PoonamK. 34
• Provides long-distance transmission of data, voice, image and video information over large
geographical area.
• WANs may utilize private, public or leased communication devices in combinations and can
span unlimited number of miles.
• Irregular topology. E.g satellite or ground radio system
• Hosts are connected by subnet which carry data from host- to-host.
• Two components: transmission line: moves bits betweenmachines and switching elements: to
connect two or more transmission lines.
37. Protocols and Standards
Prof.PoonamK. 37
• Protocols
– Define it as set of rules that govern data communication.
– An entity which is capable of sending or receiving information will not send any bit stream to other place till both
not agreed on set of rules.
– A protocol defines what is communicated, how it is communicatedand when it is communicated.
– The key elements of protocol
• Syntax : refers to the structure or format of the data, meaning the order in which they are presented.
• Semantics : refers to the meaning of each section of bits. How is a particularpattern to be interpreted, and what action is to be taken based
on thatinterpretation
• Timing : refers to two characteristics: when data should be sent and howfast can be sent.
38. Protocols and Standards
Prof.PoonamK. 38
• Standards
– Are agreed upon rules
– Essential in creating and maintaining an open and competitive market for equipment manufacturers and in
guaranteeing national and international interoperability of data and telecommunications technology and process.
– Provide guidelines to manufacturers, vendors, and other service providers to ensure the kind of interconnectivity
necessary in today’s market.
– Fall in two categories:
• De facto (by fact or by convention): standards that have not been approved by an organized body but have been adopted as standards through
widespread use. They are established by manufacturers
• De jure (by law or by regulation): standards that have been legalized by an officially recognized body.
39. Protocols and Standards
Prof.PoonamK. 39
• De-facto standardsare divided into two parts
– Proprietary standards are those originally invented by commercial organizations as basis
for the operation of itsproducts. They are called proprietary because they are wholly
owned by the company that invented them. They are also called closed standards
because they close off communication between systems produced by different vendor.
– Non-proprietary standards are those originally developedby groups or committees that
have passed them into the public domain; they are open standards because they open
communications between different systems.
40. What is LAN
Prof.PoonamK. 40
• LAN is combination of computers, LAN cables, Network interface cards, network
operating system and LAN application software.
What LAN can do
• Share Files
• Transfer Files
• Access information and files
• Share Applications
• Printer Sharing
• Electronic Mail
41. Components of LAN
Prof.PoonamK. 41
• Computers
– Server
• File Server
• Print Server
• Database Server
– Workstation
• LAN Cables
• Network Adapter Card
• LAN Software
– Network Operating Software
– Application Software
42. Prof.PoonamK. 42
Server
• Server is computer that serves all the workstations primarilyby storing and retrieving data from
files shared on disk
File Server
• Usually fast computers running at faster speed with large memory.
• Heart of network. Contains monitors and inexpensive keyboards. Have one-or more large, fast, expensive
hard disk.
• Servers must of high quality, heavy duty machines as serves entire network. To serves other machines it
has operating systemcalled network operating system.
43. Workstations
Prof.PoonamK. 43
• These are various PCs or terminals connected toserver.
• Employees can use them as their own or throughnetworksoftware
• Referred as clients, usually intermediate speed
machines sufficient memory.
• Also have good quality colormonitor as well as highquality keyboards and hard
disk.
• Diskless workstation. Characteristics of workstation.
44. Characteristics of Workstation
Prof.PoonamK. 44
• Extra messages: NOS loadingetc.
• User authentication:username and password
• Additional drive letters
• User can use remote printer
45. Network Interface Card
Prof.PoonamK. 45
• Provides the physical connection between the network andthe computer workstation.
• NICs are internal, with card fit into an expansion slot ofmotherboard.
• Now a days, it is on board. Major factor since determinesspeed of network.
• Only two network cards may communicate with each otherat the same time on a LAN.
Wait.
• Such delays are unnoticeable. Gives the appearance as manyworkstations are communicating
simultaneously.
47. Prof.PoonamK. 47
Working of NIC
• It first listens to all traffic on the cable.
• Filters out the messages designated for your workstation.
• Sends signal to your workstation when workstationis ready to attend them.
• When workstation wants to send request to server, the adaptercard waits for break in
cable traffic and then inserts your message.
• Verifies message also handles error.
48. Transmission media
Prof.PoonamK. 48
• Cable is medium through which information usuallymoves from one network
device to othernetwork device.
• Network can be based on one type of cable or manytype of cables.
• Decision depends on topology, protocolsand size.
50. LAN Cables or transmission medium
Prof.PoonamK. 50
• Twisted pair wire categorized as:
– UTP (Unshielded Twisted Pair): like telephone wire
– STP (Shielded Twisted Pair): like the wire that carrieselectricity
51. LAN Cables or transmission medium
Prof.PoonamK. 51
• Coaxial Cable
– Thick coaxial cable (Thicknet)
– Thin coaxial cable (Thinnet)
52. LAN Cables or transmission medium
Prof.PoonamK. 52
• Fiber Optic Cable
53. Prof.PoonamK. 53
LAN Software
• Network Operating System
– DOS: manage applications on standalone machine
– Needs NOS to control the flow of LAN data messagesbetween stations.
– Makes the disk drive of the server appear to be an extradrive on each workstation.
• Application Software
– In order to accelerate speed of LAN well developedapplication software are necessary.
55. Server Based LAN
Prof.PoonamK. 55
• Contains one unattended dedicated computer act as file server and it uses the same
peer LAN NOSproduct to have server-based LAN.
• By managing the computer completely as file server and managing disk in such way
that it gives better performance and increases reliability.
• Dedicated concept helps in expandability of LAN and do more work.
57. Peer-to-Peer LAN
Prof.PoonamK. 57
• To connect small group of computers permanently.
• You need simple file transfer utility
• Every computer needs to act as file server as well as workstation at the same time
hence peer-to-peer LAN.
• Disk space and files on your computer becomes communal property.
59. Network Model
Prof.PoonamK. 59
• ISO-OSI Reference Model:Function of each layer
• Internet (TCP/IP)Model:All Layers, Ports, ProtocolStack
60. Network Model
Prof.PoonamK. 60
Network Model is conceptual structure which shows how various parts are fit together
and work together to transmit data.
Network Model
ISO-OSI Reference Model TCP/IP Refernce Model/
Internet Model
61. ISO-OSI Reference Model
Prof.PoonamK. 61
• ISO is International Standards Organization developed in 1947. It is multinational
bodydedicated to worldwide agreement on international standards
• An ISO standard develop themodel that covers all aspectsof networkcommunication
called as Open System Interconnection (OSI) model.
• The designing of the OSI model is based on theproposal developed by ISO as first
step towards international standardization of protocol used in various layers.
62. ISO-OSI Reference Model
Prof.PoonamK. 62
7
6
5
4
3
2
1
Physical Layer
Data Link Layer
Network Layer
Transport Layer
Session Layer
Presentation Layer
Application Layer
63. Organization of Layer
Prof.PoonamK. 63
• In 7 layered OSI model layers 1, 2 and 3 are the network support layers. They deals with
physical aspects of moving data from one device to other.
• Layers 5,6,7 are acts as user support layers. They allows interoperability between unrelated
software system.
• Layer 4 ensures the end to end reliable data transmissions. While layer 2 ensures reliable
transmission on single link.
• Upper layer OSI layers are almost software dependent. Lower layer models are combination of
hardware and software except for the physical layer which is mostly hardware related.
64. Physical Layer
Prof.PoonamK. 64
• To transmit a bit stream over a physical medium.
• Deals with mechanical and electrical specification of interfaces andtransmission medium.
• Defines procedure and function for physical devices
• Physical characteristics of Interfaces
– Characteristics of interface between device and transmissionmedium.
Type of transmission medium.
• Representation of bits
– Sequence of 0s and 1s. To be transmit bits must be encoded intosignals- electrical or optical
• Data rate
– Transmission rate- the number of bits per second
65. Physical Layer
Prof.PoonamK. 65
• Synchronization of bits
– Sender and receiver clock must be synchronized.
• Line Configuration
– Point-to-point or multipoint line configuration
• Physical Topology
– How to connect devices in network
• Transmission mode
– Simplex, Half Duplex, Full Duplex
66. Physical Layer
Prof.PoonamK. 66
From data link lay er To data link lay er
L2 data L2 data
Physical
Layer
Physical
Layer
Transmission Medium
10101000010
10101000010
67. Data Link Layer
Prof.PoonamK. 67
• Responsible for node-to-node delivery of frames. It makes physicallayer appear error free to the upper layer.
• Framing
– Divides stream of bits received form network layer into
manageable data units called Frames.
• Physical Addressing
– When frames are send over a network it is required to add headercontaining source and destination address.
• Flow Control
– The rate at which data is absorbed bythe receiver.
• Error Control (Trailer)
– Adding mechanism to detect and retransmit damaged or lost frame
• Access Control
– To determine which device has controlover link at any given time.
68. Data Link Layer
Prof.PoonamK. 68
From netw orklayer To netw orklayer
To Physical Layer From Physical Layer
T2
Data
10 87
Trailer Source Address Destination Address
Data
Link
Layer
Frame
H2
T2
Data
Link
Layer
Frame
H2
T2
10101000010 10101000010
L3 data L3 data
69. Network Layer
Prof.PoonamK. 69
• Responsible for the source-to-destination delivery of packetacross multiple networks.
• If two systems are connected to same link, no need ofnetwork layer.
• If systems in different networks then need to implementnetwork layer to accomplish
source-to-destination delivery.
• Logical Addressing
– To handle addressing problems over network logical addressingscheme is used.
• Routing
– When independent networks or link are connected properpathselection should be achieved.
70. Network Layer
Prof.PoonamK. 70
From Transport lay er To Transport lay er
To Data Link Lay er From Data Link Lay er
T2
Data
A B 10 87
Trailer Source Physical Address Destination Physical Address Source LogicalAddress Destination Logical Address
Network Layer
Packet
L3 data
H3
Network
Layer
Packet
L3 data
H3
L4 data L4 data
71. Transport Layer
Prof.PoonamK. 71
• Responsible for source-to-destination delivery of entire message. Treats each
message independently.
• Ensures whole message arrived in order and an errorfree
• Security: implements connection between source and destination. Connection
implementation involves: connection establishment, data transfer and connection
release.
• Other issues are:
72. Transport Layer
Prof.PoonamK. 72
• Service Point Addressing
– Computer runs several processes (running program) at same time. So transport layer makes delivery
from one runningprocess to other running process. So it adds service point address (Port Address) to
header.
• Segmentation and reassembly
– A message is divided into transmittable segments. Sequence number is with segment, which helps to
reassemble segments.
73. Transport Layer
Prof.PoonamK. 73
• Connection Control
– Connectionless or connection oriented. Connectionless: segment is treated independently and deliver
to transport layer of destination
– Connection oriented: after establishing connection, data istransfer and then connection is terminated.
• Flow Control
– Here flow control is done end-to-end rather across a single link.
• Error Control
– Here error control is done end-to-end rather across a single link.
74. Transport Layer
Prof.PoonamK. 74
From Session lay er To Session lay er
To Network Lay er From Network Lay er
L5 data
Transport
Layer
H4
H4
H4
L4 data
L5 data
Transport
Layer
L4 data
H4
H4
H4
L4 data L4 data
L4 data L4 data
75. Session Layer
Prof.PoonamK. 75
• It is a network dialog controller. It establishes, maintains and synchronizes the
interaction between communicating system.
• Dialog Control
– Allows two systems to enter into a dialog. Allows communication between two processes
to take place either half or full duplex.
• Synchronization
– Allows a process to add checkpoints into a stream of data
– E.g. 2000 pages
76. Session Layer
Prof.PoonamK. 76
Session Layer
Syn
L5 data
L6 data
Session Layer
Syn
L5 data
L6 data
From Presentation lay er To Presentation Lay er
To Transport Lay er From Transport Lay er
H5 H5
77. Presentation Layer
Prof.PoonamK. 77
• Concerned with the syntax and semantics of the information exchanged between two
systems.
• Translation
– Exchange information: characters, numbers and so on.
– Information must be changed to bit streams before transmitting using encoding techniques.
– Different encoding schemes are used. So presentationlayer changes sender information in
sender-dependentformat whereas on receiver side in receiver-dependent format.
78. Presentation Layer
Prof.PoonamK. 78
• Encryption and Decryption
– To carry sensitive information, privacy is important.
• Compression
– Reduces the number of bits contained in the information. It is required in case of
transmission of multimedia such as text, audio and video.
79. Presentation Layer
Prof.PoonamK. 79
From Application lay er To Application lay er
To Session Lay er From Session Lay er
Presentation
Layer
H6
Encoded, Encrypted, and
compressed data
L7 data
Presentation
Layer
H6
Decoded, decrypted, and
decompressed data
L7 data
L6 data L6 data
80. Application Layer
Prof.PoonamK. 80
• Enablesuser to access the network.
• Provides user interfaces and support or services likeelectronicmail, remote file
access and transfer, shared DBMS and otherdistributed type of
applications.applications.
• Other Issues
81. Application Layer
Prof.PoonamK. 81
• Network Virtual Terminal
– Is software version of physical terminal which allowsuser to log on to a remote host.
– The user’s computer talks to software terminal, which in turns, talks to host, and vice versa.
• File Transfer, access and Management (FTAM)
– Allows user to access files in remote host (to make changes or read data), to retrieve files
from remote computer for use in local computer and to manage or control other issues.
82. Application Layer
Prof.PoonamK. 82
• Mail Services
– Provides the basis for email forwarding and storage.
• Directory Services
– Provides distributed database sources and access for
global information about various objects and services.
83. Application Layer
Prof.PoonamK. 83
User User
From Presentation Lay er To Presentation Lay er
X.500 FTAM X.400
Application
Layer
L7 data
X.500 FTAM X.400
Application
Layer
L7 data
84. Internet Model (TCP/IP)
Prof.PoonamK. 84
• ARPANET: Grandparent of computer networks andworldwideInternet.
• ARPANET was research network sponsored by
DOD (Department of Defense).
• It eventually connected universities and governmentinstallationsusing leased
telephone lines.
• When satellite and radio networks gets added thereis need of new architecture.
• Goal: to connect multiple networks together in
seamless way. Architecture is TCP/IP.
86. TCP/IP Model
Prof.PoonamK. 86
• The model is composed of five ordered layers:
– Physical Layer (Layer 1)
– Data Link Layer (Layer 2)
– Network Layer (Layer 3)
– Transport Layer (Layer 4)
– Application Layer (Layer 5)
• At the time of transmitting messages the messageuses intermediate nodes at
lower layers.
87. Organization of Layers
Prof.PoonamK. 87
• The lower layers physical layer, data link layer and network layer are the network
support layers, deals with physical aspects of moving data from one device to other.
• Layer 5: the upper layer is application –user support layers. Allows interoperability
between unrelated software systems.
• Layer 4: links two subgroups and ensures that what lower layers have transmitted in
the form the upper layer understand.
88. Prof.PoonamK. 88
Internet Layer
• It is connectionless layer.
• Its job is to permit hosts to inject packets into any network and have them travel
independently to destination (on different network)
• They may arrive in different order than they were sent.
• It is job of higher layer to rearrange them in order.
• Internet Layer defines an official packet format (datagram) and protocol called IP
(InternetProtocol).
89. Prof.PoonamK. 89
Transport Layer
• It is designed to allow peer entities on the sourceand destinationhosts to carry
on a conversation
• Transport layer of this model deals with two end-to-endprotocols.
• TCP (Transmission Control Protocol)
• UDP(User Datagram Protocol)
90. Prof.PoonamK. 90
Application Layer
• It consists of all higher-level protocols.
• It uses various protocolslike: TELNET, SMTP, FTPetc.
• TELNET allows user on one machine to log intodistantmachine and work
there.
• FTP provides a way to move data efficiently fromone machine to other.
• SMTP protocol is used for electronic mail facility.
• In addition it provides DNS for mapping hosts,HTTP: World Wide Web.
91. Host-to-Network Layer
Prof.PoonamK. 91
• Layer is developed by combining physical layer and data link layer.
• In addition to OSI model functionalityit adds a special protocol which helps to send
IP packets over it.
92. Protocol Stack
Prof.PoonamK. 92
Data Link Protocols defined by the
Physical underlying protocol
Application
TELNET
Session
RPC
TFTP
NFS
SNMP
DNS
FTP
SMTP
Presentation
Transport UDP
TCP
Network IP
ARP
RARP
IGMP
ICMP
93. IEEE Standards 802.11 Wireless LAN
Prof.PoonamK. 93
• Institute of Electrical and Electronics Engineers (IEEE) defines specification for
wireless LAN, IEEE802.11
• Covers physical and data link layers.
• Architecture – two kind of services
– BSS (Basic Service Set)
– ESS (Extended Service Set)
94. IEEE Standards 802.11 Wireless LAN
Prof.PoonamK. 94
• Basic Service Set
– Building block of wireless LAN
– Made of stationary or mobile wireless stations and
possible centralbase station called access point (AP)
– Two sets: BSS with AP and BSS Without AP
• BSS without an AP is standalone network and can not send datato other BSSs. Called as adhoc architecture in
which stations can form network without an AP, locates each other and agree to be part of BSS
95. IEEE Standards 802.11 Wireless LAN
Prof.PoonamK. 95
• Basic Service Set
BSS without AP BSS with AP
AP
96. IEEE Standards 802.11 Wireless LAN
Prof.PoonamK. 96
• Extended Service Set
– Made of two or more BSSs with APs.
– BSSs are connected through a distribution system usuallya wired LAN.
– Distribution system connects APs in the BSSs
– 802.11 not restrict distribution system, it can be anyIEEE LAN like Ethernet.
– Uses two type of stations: mobile and stationary
– Mobile stations are normal station in BSS.
– Stationary stations are AP stations part of wired LAN.
97. IEEE Standards 802.11 Wireless LAN
Prof.PoonamK. 97
• Extended Service Set
Server or Gateway
BSS BSS
AP AP
Distributed System
98. IEEE Standards 802.11 Wireless LAN
Prof.PoonamK. 98
• Extended Service Set
– When BSSs are connected we have infrastructure
network.
– Stations within each of one another can communicatewithout an AP.
– Communication between two stations in different BSSsoccurs via two APs.
– Idea is similar to communication in cellular network.
– Consider Each BSS to cell and each AP to base station
– Mobile station can belong to more than one BSS at sametime.
