DCN Unit 3 Ppt

8/13/2019 DCN Unit 3 Ppt

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UNIT-3


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Types of Networks..

Local Area Networkor LAN

Metropolitan Area Network orMAN

Wide Area Network orWAN


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Other networks include.

WLAN - Wireless LAN

SAN - Storage Area Network, System Area

Network, Server Area Network, or sometimes

Small Area Network

CAN - Campus Area Network, Controller

Area Network, or sometimes Cluster Area

Network

PAN - Personal Area Network DAN - Desk Area Network


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LAN (Local Area Network)

A LAN is generally a privately ownednetwork within a office, building or campus

covering a distance of a few kilometers.

A LAN is a computer network that covers asmall area.

Ownership by a single organization

Transmission speed of at least several Mbps(tens to hundreds are economical)

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Features of LAN..

The main purpose for designing a LAN is toshare resources such as printers, programs anddata.

Speed at a maximum of several 100s of

Megabits per second (Mbps) i.e., like 10 Gbps.Previously LAN had speed of around 4-16 Mbps,later 100 Mbps was developed.

Relatively low cost

Limited to short distance

Often rely onshared media.


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Topologies in LAN..

Topology refers to the way in which the

stations attached to the network are

interconnected.

Different topologies are

- Bus

- Tree

- Star

- Ring


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Bus Topology

Stations attach to linear medium (bus) Via a tap - allows for transmission and reception

Transmission propagates in medium in both directions(Full-duplex).

Data is transmitted in frames with addressing. Received by all other stations

Not addressed stations ignore

Need to identify target station

Each station has unique address Destination address included in frame header

Terminator absorbs frames at the end of medium


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Since a single cable is used to connect

all the stations, it is inexpensive i.e., lowcost to implement this topology.

Easy to design

Easy to implement

The disadvantage is, if the cable breaks

down, entire network will not work.

The other disadvantage is, it requires

termination.


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Tree Topology


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Star Topology

In star topology, each station is connected to a centralhub with a point-to-point connection.

Each station connected directly to central node usinga full-duplex (bi-directional) link.

Central node or hub can broadcast

Physical star, but logically like bustopology

Only one station can transmit at a time


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Star Topology


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Star topology advantages

Break in one cable does not affect other devices

Easy to locate problems Easy to install

Does not require termination like bus topology

Star topology disadvantages Center of star topology device (hub) can be

expensive

Hub failure can affect entire topology

Amount of cable is expensive


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Ring Topology A network topology that is set up in a circular

fashion in which data travels around the ring inone direction and each device on the right acts asa repeater to keep the signal strong as it travels.Each device incorporates a receiver for theincoming signal and a transmitter to send thedata on to the next device in the ring.

Repeaters joined by point-to-point links in closedloop Links unidirectional Receive data on one link and retransmit on another

Stations act like repeaters Data transmitted in frames

Frame passes all stations in a circular manner Destination recognizes address and copies frame Frame circulates back to source where it is terminated.


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Frame Transmission in Ring LAN


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Ring topology advantages

Prevents network collisions Each station acts like a repeater

Ring topology disadvantages

Cable break can affect all devices Temporarily shut down network to add a

new station

Maintenance and monitoring is difficult


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For building networks of different

topologies, stations are required, along

with hubs, repeaters and cables.


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Fiber-Optic cable Advantages of fiber-optic cabling

Transmit data over long distances

Not susceptible to EMI

High transmission rates Not susceptible to eavesdropping

Small cable size

Disadvantages of fiber-optic cabling Expensive

Cable can be easily damaged during install makinginstallations more difficult

Manual termination of ends is time consuming


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Metropolitan Area Network

A metropolitan area network(MAN) is a computernetwork that usually spans a city or a large campus. A

MAN usually interconnects a number of local area

networks (LANs).

A MAN is optimized for a larger geographical area thana LAN, ranging from several blocks of buildings to entire

cities.

A MANis a collection of LANs within the same

geographical area, for instance a city. Distances between 5 and 50 kms

Data rate above 1 Mbps

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Wide Area Network

A Wide Area Network ( WAN) is a computer

network covering multiple distance areas, which

may spread across the entire world.

WANs often connect multiple smaller networks,

such as local area networks (LANs) or metro

area networks (MANs).

A WAN is a computer network that spans arelatively large geographical area.

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IEEE Standards

IEEE stands for

Institute for Electrical and ElectronicEngineers.

IEEE has produced several standardfor LANs collectively known as

IEEE 802 standards for LANs andMANs.


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802.1: This standard gives an introduction to the set ofstandards and defines internetworking. This provides forcompatibility of different LANs and MANs across

protocol. 802.2:This standard describes the upper part of the DLL,

which uses Logical Link Control Protocol.

802.3: Describes the LAN Standard

802.4: Describes the LAN Standard Token Bus

802.5: Describes the LAN Standard Token Ring

802.6:Describes the LAN Standard Distributed QueueDual Bus (DQDB)

802.11:Wireless LAN

802.15: Bluetooth


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According to IEEE 802 reference model the

data link layer is divided into two sub-

layers.

Logical Link Control(LLC)

Medium Access Control (MAC)


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Generally, the functions of data-link layer are

framing,

flow control &

error control.

Therefore in IEEE 802, the above functions aredivided among LLC and MAC sub-layers.

Flow control, error control and part of framing aredone by LLC.

The remaining part of framing is done in MAC sub-

layer along with other functionalities.


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The main difference between LLC and

MAC is that.LLC sub-layer provides single protocol for

all networks

MAC sub-layer is different for differentnetworks depending on the topology of thenetwork.

Eg: MAC sub-layer provides different

protocol for Bus topology and anotherprotocol for Ring topology.


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IEEE Standard 802.2=Logic Link Control

Interface Between Network layer & MAC sub-layer

Specifies method of addressing and controls exchange of

data.

Independent of topology, medium, and medium access

control.

Assemble data into a frame with address and error-detection

fields.

Interface to higher levels and performs flow and error control.


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IEEE 802.2 frame format.

M di A C t l


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Medium Access Control

(MAC) MAC is a protocol used in networks to

facilitate the flow of frames in the medium. Main concern: interference from users.

Uses some mechanisms to coordinate the access of channel.

From the name itself it suggests that thisprotocol looks into the control of how the

medium is accessed.

MAC provides a means of controlling access

to the transmission medium in an efficient and

orderly manner.


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Medium Access Control Sublayer

Coordinate access to medium

Connectionless frame transfer service Machines identified by MAC/physical address

Broadcast frames with MAC addresses

Prepare data for transmission

Error detection

Address recognition

Governs access to transmission medium


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To know the MAC address of a system.

Applicable to windows 7, 98, 2000, XP. ipconfig /all

or

ipconfig /all > %UserProfile%\Desktop\IP.txt(to save as a file on desktop)


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IEEE 802.6=Distributed Queue Dual Bus (DQDB)

DQDB protocol is a dual bus configuration.

DQDB architecture has two unidirectional buses

A and B.

It facilitates traffic in the opposite directions.

Bus A allows data flow from station 5 to 1 and

bus B allows data flow from station 1 to 5.


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Consider an example where data has to sent fromstation 4 to station 2.

The head of Bus A i.e., station 5 will create an

empty transmission slot. When the transmission slot reaches station 4, it

fills the slot with data along with destinationaddress (i.e., station 2).

Next the data frame moves to station 3, where itchecks for the address and realizes that the datais not meant for it.

The data slot reaches station 2, where theaddress is checked, data is copied and makes anindicator on the slot to acknowledge the receipt ofdata.

The slot next moves to station 1 wherein it getsabsorbed.


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If in case station 1 has to send data to station

3, then the same process follows but here

Bus Bwill be used.


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IEEE Standard 802.4=Token Bus

Physically the Token bus is a linear cable to which the stations

are attached.

Logically , the stations are arranged in a ring with each station

knowing the address of the station to its left or right.

When the ring is initialized the highest numbered station may

send the first frame.

After it does, it passes the permission to its immediate neighbor

by sending the neighbor a special control frame called Token.

The token propagates around the logical ring, with only the token

holder being permitted to transmit frames.

Since only one station holds the token at a time, collisions do not

occur.


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17 20Broadband

Coaxial cable

Logical Ring

This station isnot currentlyin the logicalring

14

1971113

This station isnot currentlyin the logical

ring

IEEE 802 4 frame format


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IEEE 802.4 frame format

Bytes 1 1 1 6 or 2 6 or 2 4 1

Destn add Source add Data Checksum

Start of

framedelimiter

Preamble

FrameControl

EndDelimiter


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Each time a station acquires the token it transmitsframes for a certain amount of time after which it

passes the token.

If frames are short enough then several frames may betransmitted consecutively.

If the station has no data it passes the tokenimmediately after receiving it.

Token Bus MAC Sub-layer Protocol


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The stations are arranged to form a circular ring.

Any station connected to the ring can transmit dataonly when it possesses the token.

A special 3-byte token frame is used in 802.5

Once a station gets hold of a token, it can transmitdata over the medium.

A station holds the token, till the data frame is

received by the destination station, and returns backto the source station.

The data will be checked for its destination address

by every station connected to the ring topology.

IEEE Standard 802.5=Token Ring


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The destination station, indicates the receipt of the

data by setting a flag bit.

When the data frame gets back to the source, itchecks the flag bit to know data has been received or

not.

After this, the token will be passed on to the next

consecutive station.

In this manner, every station gets a turn to access the

medium in a ring topology.

Only one station can hold a token at a time

This ensures no congestion or collision over the

medium.


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1 2

3

802 5 F F


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802.5 Frame Format..

Bytes 1 1 1 6 6 no limit 4 1 1

SD AC FC Destn add Source add Data Checksum ED FS

Start offramedelimiter

FrameControl

EndDelimiter

SD AC ED

1 1 1

Token format

Data Frame Format

FrameStatus

Access control


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The Access Control Field contains the token bit, active station

bit and priority bits.

The Frame Control distinguishes between data and various

control frames

The Frame Status is used for acknowledgement by the

destination

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DCN Unit 3 Ppt

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