Essential of Computer Network

8/12/2019 Essential of Computer Network

1/93

Essential of Computer Network

Network Types ; LAN MAN WAN Physical Topology: Bus Star Ring Mesh

Cellular Logical Topology(Channel access Topology):

CSMA/CD and CSMA/CA, Token Ring andpolling

Transmission media(TP-STP, UTP, Coax, OF,Terrestrial Microwave Link, Sat.Comm, IRTx,Radio wave Propag.)


2/93


Tx Modes: Simplex, Duplex, Full DuplexTx Types: ATM and Synchronous Mode.OSI Layer: Appln Layer, Presentation Layer N/wLayer , data link layer Phy Layer, Transport Layer

etcSwitching Technique: Circuit Switching, MessageSwitching , Packet SwitchingInternet working Devices: Repeater, Router,gateways, and bridgesN/W services: File services,Message services,Database services,


3/93


N/W Management: Configurationmanagement, Performance managementFault management, Security management etc

N/W protocol: TCP/IP, IEEE 802.X N/W connectivity Hardware:

Connectors,(Hub, Switches), N/W interfacecard, Modem etc

N/W Operating System: Novel Netware, Unix

Ware, Windows XP, Windows 2000, etc


4/93

Computer N/W Types

It is classified according to thegeographical area over whichthe computer N/W can spanand accordingly we have gotthe following classification ofCOMP N/W.


5/93


6/93

LAN

It is a combination of variouscomputer hardware and various

Tx media which span over adiameter of less than or equal 2KM or so,. LAN can span within abuilding within an organization.


7/93

Features of LAN

Covers a small areasuch as building

BW is Expensive

Consist of

Computers thatare connected

using cable

Owned Bycompany ororganisation

Suit Businessorganisation

situated in singlelocation


8/93

MAN

It is a combination of variouscomputer hardware and various Txmedia which span over around ametropolitan city e nodesconnected within the city

MAN= Interconnection of severalLAN on a city


9/93

Features of MAN

It span over adiameter of 10 KM

to 100 KM

Owned by single ormultiple organisation

BW is moreExpensive than LAN

Microwave or OFC istypically used as

transmission media

Connects two or

more LANS


10/93

WAN

It is a combination of variouscomputer hardware and variousTx media which span overaround and across the globe.


11/93

Features of WAN

Connects Compter N/Wlocated in differentcountries

Offices are connectedthrough Satt of under

sea.

BW is much moreExpensive than LAN &

MAN

Data rate; 1.5 mbps

transmission mediais typically hiredfrom third party

service provider

Owned by multipleorganization


12/93

TOPOLOGY

Phy Topology

LogicalTOPOLOGY


13/93

Phy Topology

P2P connection

Multiple Connection:Bus, Star, Mesh, Ring, Etc


14/93

Logical Topology

It means actual movement ofdata on the N/W.

It describes the operation of theN/W

It is linked with OSI data link


15/93

Logical Topology

Logical Topology provides somespecific rules that controls the

timings of the transmission ofDATA from the N/W devices.

The rules are Media access Rules(MAR)


16/93

Why we need MAR

If there is no MAR, then each N/Wdevice can transmit the data wheneverhe feels to do so

There will a collision of data and asaresult the message will be hold off orthe message will be corrupted.

MAR reduces this and control collisionon the N/W


17/93

Media access control


18/93

CONTENTION A N/W will transmit the data on

first come first serve basis Contention will surely result into

collision To avoid collision we have to use

CSMA/CA and CSMA/CD


19/93

CONTENTION

Channel access is allowed on FCFS basis.CSMA/CD protocols not only sense the data but

detects the collision and initiate re-

transmissionIn CSMA/CA protocols , collision is avoided

totally, each and every N/W device on the

N/W is given a time slot and whenever anydevice wants to transmit data it can transmitdata during that allotted time slot.

Example: Local Talk in apple computer.


20/93

Benefits of CONTENTION

I. When the traffic is low, the N/Wworks fast

II. Software required used are verysimple and produce very little overhead

III.Immediate control over media aslong as no other N/W device has

access.


21/93

Disad. Of Contention

a. As the no. of N/W devices increases,the traffic increases which in turnincreases collision

b. As each and every N/W devices are onthe same level so we can not setpriority to give faster access to somedevice

c. Acess time are not predictable

d. Not suitable for heavy load N/W


22/93


23/93

Token Passing Channel AccessMethod

In this , there is is a specialframe called TOKEN Frame,

which passes from one N/W toanother N/W device in a

unidirectional fashion eitherClockwise or anticlockwise.

T k P i Ch l A


24/93


As the token passes from one device to anotherdevice , the device which wants to pass or transmitdata will have to hold the token and send the dataframe to the Rx.

Once the Rx receives the data frame it will copythe data into its memory and release the dataframe, the data frame will come back to the sender

and once the sender receives it, it will release thetoken in the N/W again.The same procedure is repeated for for any N/Wdevice that wants to pass or transmits the data.


25/93


A. The device holding the token gets temporary mediacontrol . IEEE802.4 token Bus( Phy Topology)and logical Topology is token Passing and IEEE802.5Token Ring ie Phy topology is Ring Whereas logicalTopology is Token Passing.

B. A token is a short message that specifies thestation currently using the N/W and the

next station, which gain access to the N/Wafter the current station has finished usingit, when a stn or device passes the token itcan send message out in the N/Wand read

the message already present.

T k P i g Ch l A


26/93


Benefit:

Eliminates collisiontotally

Best for heavy loadN/W

Ability to assignpriority levels to

the data

transmission

Token passingproduces predictable

load and delay


27/93

Disadvantages

Softwarereqd israther

complicated

Additioncentralcontroller for

faultdetection

and recovery

The N/Wspeeds slowdown withincrease ofload on the

N/W


28/93

Token passing Vs Contention

Token passingThis system is highlydeterministic

Complicated software isrequiredIt can be used efficiently inautomati

system(bank/drug shop)Suitable for heavy loadN/WIBM Token Ring & FDDI

Contention This system is highlyprobablisticSimple software arerequiredCan not be usedefficientlyNot suitable for heavyload

Ethernet and IEEE 802.3


29/93

Polling

In this method , one device isdesignated as media access

administrator and it querieseach of the other devices(the

secondaries) to see whetherthey have information to

transmit


30/93

Polling Central device in the N/W holds the queries

or request to each of the secondary N/Wdevice in a predetermined fashion which isset by some protocol and then queries each

of the devices whether it is interested insending the data or not.Protocol can also limit the time of data

transfer ie can set the timing limitation fordata transfer by each N/W device.


31/93

Polling

Benefits:Centralizes the channel for greater N/Wcontrol

Max and Min access time and data onthe channel predictable and fixedPriority can be assigned to assure fasteraccessAllows complete use of medias capacity

by eliminating collision.


32/93

Polling

Drawbacks:o Delays, when the devices are being

polled ie if the N/W devices want totransmit it has to wait before themaster ask him to transmit

o High BW usage not possibleo high Overheads


33/93

Access N/W

The Local loop refers to the comm N/Wb/w the local telephone Exchange and the

customers.

Since this forms most pervasive part of anycomm system, it is important that the localloop technology be capable of broadbanddelivery and the transport.


34/93

Access N/W

If every Tx of WDMA is made totransmit on a distinct wavelength and each Rx uses onefilter out of a set of N filters to

tune in.


35/93

Access N/W

The Existing telephone N/W consisting of apair of a pair loaded UTP upto 7 KM lengthof transporting analog signal with a BW of 4KHz.By removing a loading PAD and by usingsophisticated signal processing techniques, A

digital subscriber line (DSL) can be createdwhich can carry data at much rate.


36/93

Access N/W

The cable TV N/W represents the mostpervasive access N/W.

In Traditional analog cable N/W the cable isexactly equivalent to the TV antenna withsignal of freq. upto 400-500 MHz present.

Since the cable N/W are not designed forhigh QoS, carrying other forms of data suchas POTS on them is a risky proposition


37/93

Access N/W

Hybrid Fiber coax N/W : In HFC N/W the media is coax of fiber.

While the coax is used to connect thesubscriber in a traditional manner, it isthe op. fiber that carries the signal

The analog signal are sub-carriermultiplexed on to the Optical carrierfreq.


38/93

Access N/W

The BW of copper cable is greatly

enhanced upto 750 MHz freq .The end user uses a cable MODEM (With TDMA as a access Scheme) toaccess the BW of the Copper cable.


39/93

Other Access N/W

TDMA:In TDMA, each node sends the

synchronous data ---either bit-synchronised or block based so thatcollision are automatically avoided.


40/93

Other Access N/W

In bit based TDMA, each node contributes asingle bit , collected in round robin fashion .

This method is impracticable becoz it requiresall the nodes to be bit synchronized.

In block- based TDMA a block of data ismultiplexed on to the medium with pre-determined time-gap separating it from thenext block of data.


41/93


42/93


43/93

Other Access N/W

Three issue related to the theimplementation of the TDMA

1. Distance Equalisation(Ranging)

2. Synchronisation b/w theNodes

3. Optical Power control


44/93

Other Access N/W

Optical Power control:Since the nodes maytransmit the packet or frames with largepower variation, the Rx must have large

dynamic variation, the Rx must have a largedynamic range and must be able to decisionthreshold quickly.

Optical Rx that implements these threecharacteristics are called BRUST Mode Trans-

Rx.


45/93


46/93


47/93


48/93


49/93

The Telephone over passive N/W

The system operates with bi-direction linerate of 20.48 mbps with max of 128 tapingline

The TDMA is frame based with 294x64channels supporting digital Telephony


50/93

Multiple access customer N/W

It is a TDMA PON system with data rate of8.192 Mbps. And max splitting factor of 16.It allows 20 chanells of 160 kbps one ch 2 Mbps

and one ch for broadcast of 2 Mbps.Duplexer can be obtained using the scheme of

WDM . The main frame is of 1 ms. Long with

10 microsecond inter frame gap .Max distance b/w nearest and farthest node is1 KM.


51/93


52/93


53/93

SONET/SDH

Digital TDM schemeevolved as a standardsignal format calledSONET in N. America andSDH in other part of theworld


54/93

S ynchronous Optical NET workDesigned for opt ica l transport (high bitrate)

Direct mapping of lower levels into higherones

ITU version = S ynchronous DigitalHierarchydifferent terminology but interoperable

Overhead doesnt increase with rate

Shannon (Bell Labs) proved that


55/93

Shannon (Bell Labs) proved thatDigital communications

is always better than Analog communicationsBetter means:

More efficient use of resources (e.g. morechannels on trunks)Higher voice quality (less noise, lessdistortion)Added features


56/93

SONET/SDH

1 byte per sample 8000 samplesper second

T1 = 24 conversations per trunk


57/93


58/93

Y(

SONET STS-1 frame

Each STS-1 frame is 90 columns * 9 rows = 810 bytesThere are 8000 STS-1 frames per second so each byterepresents 64 kbps (each column is 576 kbps) Thusthe basic STS-1 rate is 51.840 Mbps.

90 columns

9

r o w s

framing

Layers


59/93

LayersSONET was designed with definite layering concepts

Physical layer optical fiber (linear or ring) when exceed fiber reach regenerators regenerators are not mere amplifiers, regenerators use their own overhead

fiber between regenerators called section (regeneratorsection)Line layer link between SONET muxes ( Add/ Drop

Multiplexers) input and output at this level are Virtual Tributaries ( VCs) actually 2 layers

lower order VC (for low bitrate payloads) higher order VC (for high bitrate payloads)

Path layer end-to-end path of client data


60/93

SONET architecture

The fundamental SONET frame has a 125 s.

STS-1 =[ (90bytes/row)x(9 rows/frame)x(8bits/byte)]/ 125 s. = 51.84 Mbps

STS -- Synchronous Transport SignalAll other SONET are integer of multiples of this

A SONET signal is called a


61/93

A SONET signal is called aSynchronous Transport Signal

The basic STS is STS-1, all others are

multiples of it - STS-N

The (optical) physical layer signalcorresponding to an STS-N is an

OC-N SONET O i l


62/93

SONET Optical rate

STS-1 OC-1 51.84MSTS-3 OC-3 155.52M

STS-12 OC-12 622.080M

STS-48 OC-48 2488.32M

STS-192 OC-192 9953.28M


63/93

SDH STM-1 frame

270 columns

9 r o w s


64/93

SONET SDH columns rate

STS-1 90 51.84M

STS-3 STM-1 270 155.52M

STS-12 STM-4 1080 622.080M

STS-48 STM-16 4320 2488.32M

STS-192 STM-64 17280 9953.28M


65/93

STS-N has 90N columnsSTM-M corresponds to STS-N with N = 3MSDH rates increase byfactors of 4 each time


66/93


67/93

Synchronous Payload

Envelope

STS-1 frame structure

9 r o w s

TransportOverhead

TOH

6 r o w s

3 r o w s

90 columns

9 r o w s

Section overhead is 3 rows * 3 columns = 9 bytes =


68/93

Section overhead is 3 rows 3 columns = 9 bytes =576 kbps framing, performance monitoring,management

Line overhead is 6 rows * 3 columns = 18 bytes

=1152 kbps protection switching, line maintenance,

mux/concat, SPE pointer

SPE is 9 rows * 87 columns = 783 bytes = 50.112

Mbps

Similarly, STM-1 has 9 (different) columns of

section+line overhead !


69/93


70/93

STM-1 frame structure

SectionOverhead

SOH

270 columns

RSOH

MSOH


71/93

O ti l i t f


72/93

Optical interface

To ensure interconnection compatibility b/wequipment from different manufacture, theSONET and SDH specification provide detailsfor optical source characteristicsThe Rx sensitivityThe Tx distance for various types of fiber


73/93


74/93


75/93


76/93


77/93


78/93


79/93


80/93


81/93


82/93

Optical Transport N/W ( OTN)

ITU defines a three layer optical Transport N/Wmodel (ITU T Rec . G.709) also referred as

Digital WrappingJust as the SONET/SDH standard enabled themanagement of single-wavelength optical N/Wusing equipment from many different vendor, theG.709 standard enables the board adaptationTechnology for managing multi wave- lengthTechnology optical N/W.


83/93


It is just parallel ( closelyparallel ) the path, linesection sub layers ofSONET



84/93

The model is based on a client /server concept.The exchange of information b/w processesrunning in two different devices connectedthrough a N/W may characterized by aClient/Server interactionThe Term Client and Server describe the functionroles of elements in the N/WThe process or Element that request or receivesthe information is called client and the process orelement that supplies the information is calledSERVER


85/93

O i l T N/W ( OTN)


86/93


Client Signal such as IP, Ethernet, or OC-N/STM-N are mapped from an Electricalsignal format into digital format in anoptical channel (Och) layer.

Ochs deals with single wavelength

channels as end to end paths or as subnetwork connection b/w routine nodes


87/93

O i l T N/W ( OTN)


88/93


OMS layer represents a linkcarrying group of wavelengthsb/w multiplexing equipments orOADMs.

OTS layer relates to link b/wtwo optical amplifier.


89/93


90/93

O i l h l d i (ODU)


91/93

Optical channel data unit(ODU)

It is the structure used to transport the OPU.The ODU consist of the OPU and theassociated ODU overhead and provides path

layer connection monitoring fn

It also helps the maintenance and operation

of optical channels

Optical channel Transport


92/93

p punit(OTU)

This OUT contains the ODU frame structure ,the OTU over head, appended forward errorcorrection.

The OUT changes the digital format into alight signal for transport over an optical

channel. It also provides errors detection and

correction monitoring fn


93/93

Documents

Essential of Computer Network