Wcn Unit_ii Wireless Introduction to Wireless Networking Dec-11

8/3/2019 Wcn Unit_ii Wireless Introduction to Wireless Networking Dec-11

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WIRELESS COMMUNICATION AND NETWORKSB.TECH IV , II SEM

UNIT IIINTRODUCTION

TO

WIRELESS NETWORKING

(REF. BOOK WIRELESS COMMUNICATION

BY RAPPAPORT-CHAP-10)

BY

PROF. K.S. VERMA

2011-2012


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UNIT II Syllabus

Introduction

Difference between wireless and fixed telephone

networks

Development of wireless networks

Traffic routing in wireless networks


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INTRODUCTION TO WIRELESS NETWORKS

Demand of personal communication is driving the development of newnetworking techniques to accommodate mobile voice and data users

globally.

Cellular telephone system is responsible for coverage of a particularregion or territory.

Interconnection of many systems defines wireless Network which iscapable of providing service through out the country.

To provide wireless communications within a particular geographicregion, an integrated network of base stations, connected to MSC isrequired

MSC provides connectivity between the PSTN.

PSTN forms the global communication grid.


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Air Interface

Mobile Subscribers are connected to base stations via a radio link.

These Radio Links work on a carefully defined communication protocolcalled COMMON AIR INTERFASCE(CAI), Which is in essence is aprecisely defined HANDSHAKE communication protocol.

The CAI must provide a great deal of channel reliability to ensure thatdata is properly transmitted and received .

The basic concepts and standards used in todays wireless networksare covered in a manner which first address the mobile-to-base link,followed by the connection of the base station to MSC, the connectionof the MSC to PSTN, and interconnections of MSCs throughout theworld.


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Limitations of the mobile environment

y Limitations of the Wireless Networky limited communication bandwidth

y frequent disconnections

y heterogeneity of fragmented networks

y Limitations Imposed by Mobility

y route breakages

y lack of mobility awareness by system/applications

y Limitations of the Mobile Device

y short battery lifetime

y limited capacities


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Difference Between Wireless and Fixed Telephone

Networks In PSTN transmission of information takes place over land lines and

trunked lines

Medium of communication could be fiber cables, copper cables,microwave links and satellite links.

PSTN network is virtually static and stable.

Wireless networks are highly dynamic, with the network configurationbeing rearranged every time subscriber crossed the cell boundary.

The reconfiguration process is very fast ( fraction of a seconds) tosupport Roaming.


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Structure of PSTN In the PSTN, each city or a geographical grouping of towns is called a

LOCAL ACCESS and TRANSPORT AREA (LATA)

Surrounding LATAs are connected by a company called LOCALEXCHANGE CARRIER ( LEC).

A LEC is a company that provides intra-lata telephone service, andmay be a local telephone company, or a Telephone company that isregional in scope.

A Long distance Telephone Company collects Toll Fee to provideconnections between different LATAs over its long distance network.These companies are referred as INTER-EXCHANGE CARRIERS (IXCs).

IXC companies own and operate large fiber optic and microwave radionetworks which are connected to LECs throughout a country orcontinent.


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LIMITATIONS IN WIRELESS NETWORKING

As compared to the local fixed telephone network, where all end users are static, a wireless communication system is extremely

complex.

1: The wireless network requires an air interface between base stationand subscribers to provide telephone grade communication underwide range of propagation conditions and for any possible location.

2:Large no of BSs are required to provide coverage of an area and areconnected to MSCs.

3:MSCs must eventually provide connection for each mobile user tothe PSTN. This requires simultaneous connections to the LEC , one or

more IXCs, and to other MSCs via a separate cellular signalingnetwork.

5:An MSC can handle around 100,000 to 200,000 simultaneous cellularTelephone subscribers, While a TELEPHONE Switch can handlemillions of land line subscribers.


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LIMITATIONS IN WIRELESS NETWORKING (Cont..)

6: A problem unique to wireless network is extremely hostile andrandom nature of the radio channel.

7: Issue of Handover and consequent load on MSC.

8: Very limited Radio Spectrum for various services as compared to

demand and rise in demand over time.

9: New techniques like Spectrally Efficient modulation techniques,frequency reuse techniques and geographically distributed radioAccess Points ( AP) are vital components of wireless networks.

10: This Geographical distribution of users and consequent mobilityrequires extra overhead load and software on MSC to provideseamless connection.


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MERGING WIRELESS NETWORKS AND THE PSTNRoaming/ global connectivity

Telephone signaling initially was through the same trunk as thevoice, making it very in-efficient utilization ofLECs and long

distance voice circuits.

C

ommon channeling signaling developed for better utilizationresources. All modern telephone networks have adopted

common channel signaling now.

Most recently , dedicated signaling channels have been used

by cellular MSCs throughout the world to pass the subscriber

information.

Nowadays signaling networks are separated from Voice

networks.


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DEVELOPMENT OF WIRELESS NETWORKS

FIRST GENERATION WIRELESS NETWORKS

1: First generation (1G) Cellular and cordless telephone networks arebased on analog technology

2: All Cellular Systems use FM modulation. Example AMPS

3: Cordless telephones use a single base station to communicate withsingle portable terminal.

4: 1G systems use the transport architecture shown below.


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FIRST GENERATION CELLULAR NETWORK IS SHOWN BELOW

The MSC is interconnected with PSTN via land trunked line and a Tandemswitch

MSCs are also connected with other MSCs via dedicated signaling channels


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Home MSCs are connected with other Visitor MSCs viadedicated signaling channels for exchange of

i) Location

ii) validation and iii) Call signaling information


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1G technology

First Generation Analog wireless network. Narrow band

Can have the voice calls and

can send text messages.These services are provided with circuitswitching

1G is that with this we could contact with inthe premises of that particular nation

Speech

AMPS, TACS


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IS-41PROTOCOL STANDARD ROAMING FEATURE IN 1G

NETWORKS

INTER-OPERATOR ROAMING :In early 1990, US cellular carrierimplemented the network protocol standard IS-41 to allow differentcellular systems to automatically accommodate subscribers who roaminto their region.

IS-41 allows MSCs of different service providers to pass informationabout their subscribers to other MScs on demand.

IS-41 Relies on a feature of AMP calledAutonomous Registration.Autonomous Registration is a process by which a mobile notifies aserving MSC of its presence.

MSC constantly updates its customer list based on Mobile autonomousregistration requests.


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SECOND GENERATION WIRELESS NETWORKS

Second generation wireless systems employ digital modulation, digital

voice coding and advanced call processing capabilities.

GSM, TDMA, CDMA Based systems are 2nd generation wirelessnetworks.

Similarly CT2- Second generation Cordless telephone system , Britishstandard PACS- Personal Access Communication system and DECT-DIGITAL European Cordless Telephone are examples of 2nd Generationwireless systems.

Architecture of 2nd GEN Wireless networks is also different from 1stGen architecture. Base Station Controller (BSC) introduced in 2nd Genreduced computational load of Main processor.


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2G Technology

Second Generation Digital Systems

Narrow Band Wireless Digital Network.

It brings more clarity to the conversation.

circuit-switching model

Enhanced Capacity

In 2G the roaming facility- a semi-global facilityis available.

CDMA, D-AMPS, TDMA, GSM, DECT, PDC


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2.5G Technology

Firstly, this mid generation was introduced

mainly for involving latest bandwidth

technology with addition to the existing 2G

generation.

2.5 Generation Systems

Low Speed Data

GPRS, EDGE


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3G Technology To overcome the limitations of2G and 2.5G the 3G had

been introduced.

In this 3G Wide Brand Wireless Network is used withwhich the clarity increases and gives the perfection aslike that of a real conversation.

The data are sent through the technology called PacketSwitching .

Voice calls are interpreted through Circuit Switching.

Third Generation Systems

INTERNET on Wireless

WiFi / HyperL AN , WiMAX/ HyperWANCDMA2000/WCDMA

Evolution to All IP Network including VoIP


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Main 3G Services GLOBALROAMING.

Wide Band Voice Channel. Messaging in any part of the world. 3G gives

clarity of voice as well can talk with out anydisturbance.

Entertainments such as Fast Communication,

Internet,

Mobile T.V,

VideoC

onferencing, Video Calls,

Multi Media Messaging Service (MMS),

3D gaming,

Multi-Gaming etc


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4G Technology

In 4G in addition to that of the services of

3G some additional features such as

Multi-Media Newspapers, Facility to watch T.V programs with the

clarity as to that of an ordinary T.V.

We can send Data much faster.


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Interaction characteristics

Human-Human: voice, text, multimedia conversation and

messaging

3D video

Human-Machine:

web access, remote operation

virtual reality

Machine-Machine:

Tele-metering, sensor/actuator networks

ubiquitous computing


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Traffic characteristics

Voice

Multimedia

50 %

50 %

70 80 %

20 30 %

2000 20102005

RelativeTra

ffic


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Wireless generations: Users view (1/2)

Attribute 1G 2G 3G 4G

Cost

Initial High Low Low Flexible

Per-min Very high High Affordable Flexible

Installation Inconvenient Quick orinstant

Instant Instant

Handset Clunky,heavy

Reasonablefor voice,

poor fordata

Good forvoice,

poor fordata

Many,

app-

specific

Battery life Very Low Low Low 1 weekuse


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Wireless generations: Users view (2/2)

Attribute 1G 2G 3G 4G

Voice quality Poor Reasonable Good Excellent

Coverage Poor Reasonable Good Excellent

Roaming None or Inconvenient

Reasonable Good for voice Seamless forall apps

Voice

services

Few Basic telephony Reasonable Many

Data None Limited Limited Many

WWW N/A Poor Limited Convenient

Other user

issues

Decreasing $/

MoU butIncreasingtotal $/month

Security:

w-spam,privacy, etc

Tradeoff

security/QoSfor price.

Low

Environment

Impact


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4G: An evolvable, programmable, multi-tier multi-device network

Bluetooth,

Infrared

CellularSatellite

Wireless

LAN, Home

RF, etc


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Fixed Network Transmission Hierarchy


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Traffic Routing in Wireless Networks The amount of traffic capacity required in a wireless network is highly

dependent upon the type of traffic carried.

For example, Voice traffic is real time and requires dedicated networkaddress where as control and signaling traffic may be bursty in natureand can share resources with other networks.

Two routing services are provided by networks

i) Connection oriented services (virtual circuit routing) and

ii) Connectionless services (Datagram services)

In Connection oriented services call set up procedure is required todedicate network resources for both parties for the duration of Call.

A connection oriented service relies heavily on error control coding.

In Connectionless services is based on packet switching offering

flexibility of paths for packets. But frame overhead becomes large.


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CIRCUIT SWITCHING

First Gen Cellular systems provided connection oriented

services. MSC dedicates a voice channel connection betweenBS and PSTN.

When used in conjunction with radio channel, connection-

oriented services are provided by a technique called circuit

switching.

Wireless data networks are not well supported by circuit

switching, due to their short, bursty transmission which are

often followed by periods of inactivity.

Circuit switching will suit in those data links where data is sent

continuously over a long period of time.


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SWITCHING TECHNIQUES FOR DATATRANSMISSION

So far we saw how telephone networks are used to carry data.Telephone networks are designed for voice communication.

There are significant differences in the nature of voice anddata traffic. When a user sits in a computer he spends time in

thinking, Keying the query or command the computer, andwaiting for the response before proceeding further.

Thinking, keying and waiting consume lot of time where nodata transmission takes place. T o reduce these timescomputer should be fast processing type and medium should

be of wide band.


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SWITCHING TECHNIQUES

Diverse characteristics of voice and Data traffic led todevelopment different switching techniques other than the oneused for voice communication.

Two switching techniques are prevalent for data transmission.

1: Circuit switching

2:Store and forward (S&F) switching

Circuit switching is entirely analogous to the telephonicswitching.

S&F switching is analogous to the postal or telegraph system.


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CIRCUIT SWITCHING

Electrical path is established between source and thedestination before any data transfer takes place.

It remains dedicated to the communication pair for the entireduration of the transmission irrespective of whether data isactually being transferred or not.

The connection is released only when specifically signalled soby either of the communicating entities.

Data transmission through PSTN connection is typicalexample of a circuit switched data transfer.

There are three explicit phases involved in circuit switched datatransfer.

1: Connection establishment

2: Data transmission.

3: Connection release.


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DISADVANTAGES OF CIRCUIT SWSITCHING

1:Excessively long path set-up time, typically 20 to 30 s.

Excessive overhead for bursty computer traffic.

The entire line quality is affected if there is one bad link in thecircuit.

Speed of operation of the circuit the link is limited by theslower. This amounts to poor utilization of high quality highcapacity links.

The network provides no error control facilities which are to behandled by the end system.

In circuit switched connections , the required Bandwidth isallocated statistically and the unused band width is wasted.


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STORE AND FORWARD SWITCHING

A store and forward network configuration is given below.

In S&F switching, the switching nodes have the ability to store user

messages and forward the same towards the destination as and whenthe link becomes available.

No end to end link is set up prior to Data tranmission.


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MERITS OF S&F SWITCHING SYSTEM

The user deposits the message to the nearest switching node and thenetwork takes the responsibility for delivering the message.

Network moves the message from node to node and at a time only onelink is active thus line speeds are used efficiently.

S&F switching may be classified as

1: Message switching2: Packet switching

In message switching node processor performs1: Receive the full user message and store the same2: Check the message for data transmission errors and perform error

recovery if required3: Determine the destination address from the message.4: Choose an appropriate link towards destination based on certainrouting criterion5: Forward the message to the next node on the chosen link.


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DRAW BACKS OF MESSAGE SWITCHING ANDADVANTAGES OF PACKET SWITCHING

MESSAGE SWITCHING For long messages it becomes important to ensure thatthere is adequate storage space on the receiving nodebefore transmission is initiated.

If error occurs during transmission, the entire messagemay have to be retransmitted.

If an urgent short message is received duringtransmission of long message, it has to wait untiltransmission of long message is completed.

PACKET SWITCHING

In packet switching messages are split into a number ofpackets (often of fixed sizes) at source and assembledback at the destination.

Packets are transmitted in S&F fashion.

Each packet transmission is independent of others. Theymay travel different path and arrive at destination with

different delays.


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PACKET FORMAT IN PACKET SWITCHING

Every packet need to carry complete address information along

with Actual data,viz1:Destination Identifier

2: Source ID

3: Message ID

4: Packet ID


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PACKET SWITCHING

The control field defines functions such as transfer of

i) Acknowledgements,

ii) Automatic repeat request (ARQ) and

iii) Packet sequencing

The information field contain the user data and may have variablelength.

The final field is CRC check used for Error Detection

Packet switching is also called Packet Radio in wireless links


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TYPES OF DATA PACKET SERVICES

In order to be cost effective, packet networks offer two different forms

of services.1: DATAGRAM service

2: Virtual circuit service

In these services no resequencing is required to be done by thenetwork.

Datagram service is normally used for transmitting short messages ofone or two packet lengths.

In case of virtual circuit service, the route from the source to thedestination is fixed for all packets of a message. Here packetsequencing is maintained. The circuit so chosen is not locked to onemessage only but each node can be fixed for other messages alsosimultaneously. Hence called virtual.


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The X.25 Protocol X.25 was developed by CCITT (now ITU-T) to provide standard connectionless

network access (packet switching) protocols for 1to 3 lowest layers of Open

System Interconnection (OSI Model)

The X.25 protocols provide a standard network interface between originatingand terminating subscriber equipment called DTE, the base station DCE, andMSC.

The X.25 protocols are used in many packet radio air-interface , as well as infixed networks

Layer 1 protocol deals with electrical, mechanical, procedural, and functionalinterface between subscriber( DTE), and the base station (DCE)

Layer 2 protocol defines the data link on the common air-interface between

subscriber and the base station. Layer 3 provides connection between the base station and MSC, and is called

the packet layer protocol.

A packet assembler disassambler (PAD) is used at layer 3 to connect networkusing the X.25 interface with devices that are not equipped with a standardx.25 interface.


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ISO OSI REFERENCE MODEL

OSI reference model proposes a general layered concept, withprovision for adding or deleting layers as demanded by factors

like service complexity, technology options etc.


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THE END

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Wcn Unit_ii Wireless Introduction to Wireless Networking Dec-11

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