UNIT-4 PART-2

CONTENTSIntroductionBlock Diagram of Cellular SystemDifference between Wireless& PSTNPublic Switched Telephone NetworkLimitations of Wireless NetworkingMerging Wireless Networks &PSTNDevelopment of Wireless Networks

INTRODUCTIONWireless network is an interconnection of many systems capable of providing service to mobile users within a particular geographic region (country or continent)

Components

Base stationMobile Switching Center (MSC)PSTN

Block Diagram of Cellular System

Differences

Wireless PSTN (fixed)

Highly Dynamic.Often Reconfigure

for roaming and Handoffs.

BW constrain ( RF cellular BW).

No cables required.

Virtually Static.Difficult to change

N/W.Channel BW can be

increased.Comprises of Trunks

(cables).

Local Landline Telephone Network (PSTN)

Residential customer

Business customer

Residential customer

Business customer

Class 1: regional centers

Class 2: sectional centers

Class 3: primary centers

Class 4: toll centers

Class 5: local central office

Local loops

Tandem office

Local loops

Local Carrier's Domain of Influence, Intra-LATA

Class 1: regional centers

Class 2: sectional centers

Class 3: primary centers

Class 4: toll centers

Class 5: local central office

GOLDMAN & RAWLES: ADC3e FIG. 02-04

Limitations of Wireless Networking

Extremely complex (100’s BS connected to MSC’s).

Extremely hostile and Random in nature (MSC –Handoff strategy – Limited BW spectrum).

MSC required extra overhead.Capacity-MSC = 1 lac – 2 lacs users.CO ( central office) =10 lacs users.

Merging Wireless Networks &PSTN

Common channel signaling.MSC = User Traffic ChannelPSTN = Signal Channel

In Wireless 1 Gen = One channel for voice and signal.2 Gen = Simultaneous parallel channels for voice and signal.

Wire Line PSTN = Wireless + PSTN.

Development of Wireless NetworksFirst Generation Wireless NetworksSecond Generation Wireless NetworksThird Generation Wireless NetworksFixed Network transmission HierarchyTraffic Routing in Wireless Networks

Circuit SwitchingPacket SwitchingX.25 Protocol

First Generation Wireless Networks

Mobile User

Base

Station

MSC

fixed network

BSC

BSC

MSC MSC

GMSC

OMC, EIR, AUC

VLR

HLR

NSSwith OSS

RSS

4.11.1

VLR

Second Generation Wireless Networks

Employs digital modulation and advanced call processing capabilitiesEx: GSM, TDMA ,CDMA, Cordless Phones.

Dedicated control channel for voice, signal data.

Provides paging and other data services.High data rate (N/W access.)Uses MAHO (Mobile Assisted Hand Off)

where mobile units performs the following functions: reporting received power. scanning adjacent base station. data encoding and encryption.

Third Generation Wireless NetworksAim: to provide single set of standards that

can meet wide range of applications and provide universal access thru out the world.

Distinction between cordless and cellular phones disappear as personal handset provides access to voice, data and video services.

It uses broadband integrated service digital N/W (ISDN) to provide internet for both fixed or mobile users.

Provides reliable transfer of information.

Signal level Digital bit rate Equivalent voice ckts.

Carrier system

North America and Japan

DS-0 64.0 Kbps 1 -

DS-1 1.544 Mbps 24 T-1

DS-1c 3.152 Mbps 48 T-1c

DS-2 6.312 Mbps 96 T-2

DS-3 44.736 Mbps 672 T-3

DS-4 274.176 Mbps 4032 T-4

CEPT( Europe and more other PTTs)

0 64.0 Kbps 1 -

1 2.048 Mbps 30 E-1

2 8.448 Mbps 120 E-1c

3 34.368 Mbps 480 E-2

4 139.264 Mbps 1920 E-3

5 565.148 Mbps 7680 E-4

Fixed Network transmission Hierarchy

Traffic Routing in Wireless Networks

1. Circuit Switching2. Packet Switching3. X.25 Protocol

Circuit SwitchingThere are three phases in

circuit switching:EstablishTransferDisconnect

The telephone message is sent in one go, it is not broken up. The message arrives in the same order that it was originally sent.

Packet SwitchingIn packet-based networks, the

message gets broken into small data packets. These packets are sent out from the computer and they travel around the network seeking out the most efficient route to travel as circuits become available. This does not necessarily mean that they seek out the shortest route.

Each packet may go a different route from the others.

Packet Switching HEADER USER DATA TRAILER

FLAG ADDRESS FIELD

CONTROL FIELD INFORMATION FIELD

FRAME CHECK SEQUENCE FIELD

Packet Data Format

Fields in a Typical packet data

X.25 Protocol

Figure 17-3

Format of a Frame in X.25

Layers of X.25 Protocol

UNIT-4 PART -3

WIRELESS SYSTEMS & STANDARDS Global System for Mobile (GSM)GPRSCDMA Digital Cellular Standard

GSM Network Architecture

NSS

MS MS

BTS

BSC

GMSC

IWF

OMC

BTS

BSC

MSC MSC

Abis

Um

EIR

HLR

VLR VLR

A

BSS

PDN

ISDN, PSTN

RSS

radio cell

radio cell

MS

AUCOSS

signaling

O

Um

Abis

ABSS

radiosubsystemMS MS

BTSBSC

BTS

BTSBSC

BTS

network and switching subsystem

MSC

MSC

Fixed partner networks

IWF

ISDNPSTN

PDN

SS

7

EIR

HLR

VLR

ISDNPSTN

GSM Speech Processing

GSM Signaling Protocol

Security in GSMSecurity services

access control/authentication user SIM (Subscriber Identity Module): secret PIN (personal

identification number) SIM network: challenge response method

confidentiality voice and signaling encrypted on the wireless link (after

successful authentication)anonymity

temporary identity TMSI (Temporary Mobile Subscriber Identity)

newly assigned at each new location update (LUP) encrypted transmission

3 algorithms specified in GSMA3 for authentication (“secret”, open interface)A5 for encryption (standardized)A8 for key generation (“secret”, open interface)

“secret”:• A3 and A8 available via the Internet• network providers can use stronger mechanisms

A3

RANDKi

128 bit 128 bit

SRES* 32 bit

A3

RAND Ki

128 bit 128 bit

SRES 32 bit

SRES* =? SRES SRES

RAND

SRES32 bit

mobile network SIM

AC

MSC

SIM

Ki: individual subscriber authentication key SRES: signed response

A8

RANDKi

128 bit 128 bit

Kc

64 bit

A8

RAND Ki

128 bit 128 bit

SRES

RAND

encrypteddata

mobile network (BTS) MS with SIM

AC

BTS

SIM

A5

Kc

64 bit

A5

MSdata data

cipherkey

GPRS

.

What is GPRS?A new bearer service for GSM that greatly

improves and simplifies wireless access to packet data networks,e.g to the internet.

MotivationSpeedImmediacyNew and better applicationsUser friendly billing

GSM Architecture

BTSMS

BTS

BTS

MS

BSC

BSC

MSC

GMSC

MS

EIR

VLR

HLR

AUC

PSTNPDN

ISDN

GPRS Architecture

BTS

BTSMS

BSC Gb

SGSN

Gf

GsGr

DEIR

MSC/VLR

HLR

Gc

Gn

GGSNGi

PDN

Gp GGSN

Other GPRSPLMN

Protocol ArchitechtureTransmission Plane GPRS specifies a tunnel

mechanism to transfer user data packets .

Signalling Plane GTP specifies a tunnel control management

protocol.The signalling is used to create modify and delete tunnels.

Registration of a Mobile NodeA mobile station must register itself with GPRS

network.GPRS attachGPRS detachGPRS detach can be initiated by the MS or the

network.

Session ManagementAfter Successful attach a MS gets one or

more Packet Data Protocol(PDP) address.This address is unique only for a particular session.

It consists of,PDP typePDP address assigned to MSRequested QoSAddress of the corresponding GGSN

Session Management(Contd.)PDP-Address allocation:Static:Assigned by network operator of User’s

home PLMN.Dynamic:Assigned by Corresponding GGSN.

PDP Context Activation MS SGSN

GGSN Activate PDP Context Request

Security Functions

Activate PDP Context Accept

Create PDP Context Request

Create PDP Context Response

PDP type,PDP AddressQoS Requested,Access Point,…

PDP type,PDP AddressQoS Negotiated,Access Point,…

PDP type,QoS Negotiated,…PDP type,PDP AddressQoS Negotiated,…

Routing

PLMN1 PLMN2

MS

BTS

BSC

SGSNGn

Intra-PLMNGPRS Backbone

Gn

Gn

SGSN

GGSNGi

Packet Data Network(PDN)Eg.Internet,Intranet

Border Gateway

Gp

Inter-PLMNGPRS Backbone

Border Gateway

Intra-PLMNGPRS Backbone

GGSN

RouterLANHost

SGSN

BSCBTS

Location ManagementMS frequently sends location update

messages to inform the SGSN where it is.Determining frequency of update messages is

non-trivial.The location update frequency is dependent

on the state of the MS.

Location Management(Contd.)A MS can be in 3 states:IDLEREADYSTANDBY

Transmission Plane The protocols provide

transmission of user data and its associated signalling

Signalling Plane Comprises protocols for the

control and support of functions of the transmission plane

GPRS Backbone:SGSN GGSNGTP tunnels the user packets and related signalling information between the GPRS support nodes.

Subnetwork dependent convergence protocol

It is used to transfer packets between SGSN and MS

Data link layerLLC(MS-SGSN) RLC/MAC(MS-BSS)

Physical layerPLL:channel coding,detection of errors, forward error correction, interleaving, detection of physical link congestionRFL:modulation and demodulation

PLL RFL Phy Layer

MAC Network Service

RelayRLC BSSP

Phy Layer Phy Layer

Network Data Link Service Service

BSSGP IP

LLC TCP/UDP

RelaySNDCP GTP

Phy layer

Data Link Layer

IP

TCP/UDP

Network Layer(IP or X.25)

GTP

RLC :Radio link control BSSGP:BSS GPRS Application protocolPLL :Physical link layer GTP :GPRS tunneling protocolRFL :Physical RF layer TCP :Transmission control protocolMAC:Medium access control UDP :user datagram protocol IP :Internet Protocol

Transmission Plane

BSS SGSN GGSNGm Gb Gi

PLL

RFL

RLC

MAC

LLC

SNDCP

Network Layer

Application

PLL PHY RFL Layer

MAC Network Service

RelayRLC BSSGP

MSBSS

SNDCP:Subnetwork dependent convergence protocolLLC :Logical link controlRLC :Radio link control

Um

Application

Application

LLC

RLC

MAC

GSM/RF

GMM/SM

GSM RF Physical layer

MAC Network service

Relay RLC BSSGP

Phy Layer

Networklayer

BSSGP

LLC

GMM/SM

MS BSS SGSN

GMM/SM:GPRS Mobilty Management and session Management ProtocolGSM/RF:GSM physical layer(radio interface) I.e.PLL and RFL

Signalling Plane:MSSGSN

Um Gb

BSSAP

SCCP

MTP3

MTP2

Phy Layer Phy Layer

MTP2

MTP3

SCCP

BSSAP

Signalling Plane SGSN MSC/VLR

SGSN MSC/VLR

Gs

MAP

TCAP

SCCP

MTP3

MTP2

Phy Layer Phy Layer

MTP2

MTP3

SCCP

TCAP

MAP

MAP :Mobile Application PartTCAP :Transaction capabilities and application partSCCP :Signalling connection control partMTP :Message transfer part

SGSN HLR(and EIR)

Signalling Plane SGSNHLR/SGSNEIR

Gr

1

123

2

1

124

. . .

. . .

935 MHz

935.2 MHz

960 MHz

959.8 MHz

200 KHz

1

123

2

124

. . .

. . .

890 MHz

890.2 MHz

915 MHz

914.8 MHz

200 KHz

1 2 3 4 5 6 7 8

Data Burst = 156.25 bit periods

11 2 3 4 5 6 7 8

TDMA Frame

TDMA Frame

Uplink

Downlink

Time Slot

0 1 2 43 5 6 7 0 1 2 3 40 1 2 43 5 6 7 0 1 2 3 4

0 1 2 43 5 6 7 0 1 2 3 40 1 2 43 5 6 7 0 1 2 3 4

Uplink

Downlink

Voice User1

Voice User2

GPRS User1

GPRS User2

GPRS User3

F1

F2

F3

F4

F1F2F3F4

Time Slot Number

CarrierFrequency

GPRS Air InterfaceMaster slave concept

One PDCH acts as Master Master holds all PCCCH channels The rest of channels act as Slaves

Capacity on demand PDCH(s) are increased or decreased according to

demand Load supervision is done in MAC Layer

Group Channel Function Direction

Packet data Traffic channel

PDTCH Data Traffic MS BSS

Packet broadcast control channel

PBCCH Broadcast Control MS BSS

Packet commonControl Channel(PCCCH)

PRACH

PAGCH

PPCH

PNCH

Random Access

Access Grant

Paging

Notification

MS BSS

MS BSS

MS BSS

MS BSS

Packet DedicatedControl Channels

PACCH

PTCCH

Associated Control

Timing Advance Control

MS BSS

MS BSS

MS BSS

PRACH or RACH

PAGCH or AGCH

Random Access

Transmission

Packet channel Request

PACCH

PACCH

PDTCH

PACCH

PDTCH

PACCH

Packet Immediate assignment

Packet resource Request

Packet resource assignment

Frame Transmission

Negative Acknowledgement

Retransmission of blocks in error

Acknowledgement

PRACH or RACH

PAGCH or AGCH

Paging

Transmission

Packet channel Request

PACCH

PACCH or PAGCH

PDTCH

PACCH

PDTCH

PACCH

Packet Immediate assignment

Packet paging response

Packet resource assignment

Frame Transmission

Negative Acknowledgement

Retransmission of blocks in error

Acknowledgement

Packet paging requestPPCH or PCH

MS BSS

Multi Slot OperationGPRS allows a mobile to transmit data in

up to 8 PDCHs (eight-slot operation)3-bit USF at beginning of each radio block

in downlink points to next uplink radio block

Comparison with single-slot GSM Higher delay at higher load Low blocking rate Improved Throughput

ConclusionGPRS provides efficient access to Packet

Data Networks.Multislot operation in GPRS leads to efficient

channel utilization.GPRS is more effective for long data packet

transmission than short ones.

References“General Packet Radio Service in GSM”, Jian Cai

and David J. Goodman, Rutgers University, IEEE Communications Magazine, Oct 1997

http://www.comsoc.org/pubs/surveys/3q99issue/bettstetter.html

http://www.wsdmag.com/2000/aug2200/38-45.html

“Wireless Internet Access based on GPRS”, IEEE Personal Comm. April 2000.

CDMA Digital Cellular Standard