Wireless Networks and 2G Sowjanya Talasila Kalpana Uppalapati Karthik Dhoopati Sudheer Adumulla

Wireless Networks and 2G

Sowjanya TalasilaKalpana Uppalapati

Karthik DhoopatiSudheer Adumulla

Agenda

Introduction to Wireless Networks 2G Architecture SS7 and IS-95 protocols Connection Management Radio resource management MSC-MSC interfaces and protocols

Advantages of Wireless

Reduced Cost Accuracy of data User mobility( Stay connected to the network) Flexible Return on investment and increased

productivity

Limitations

Energy constraints

Variability in network performance

Wireless media

Fading

Interference

Types of wireless networks

Centralized

User terminals communicate with access points only

Non-centralized

Communication not limited between user terminals and access points

Comparision

Services Coverage area

Limitation

Examples

Cellular Handheld phones

Continuous

Limited bandwidth

AMPS, IS-95

WLAN Extended LAN

Local environments

Limited range

IEEE 802.11a,b,g

GPS 3D position,

velocity

Anyplace on earth

Cost GNSS,

NAVSTAR

Wireless Network

Mobile Data Set

PSTN

PacketNetwork

MobileVoice Unit

Base Transceiver System (BTS)

Base Station Controller

(BSC)

Mobile Switching

Center (MSC)

Packet Inter-Working Function

Challenge is to keep connection and not loose any data during handoff operation

Components

Base Transceiver System (BTS)

Consists of one or more transceivers at a single location

Base Station Controller (BSC)

Provides allocation and management of radio resources

Mobile Switching Center (MSC)

Provides and controls mobile access to PSTN

Contd..

Public Switching Telephone Network (PSTN)

Landline calls initiated from cell get connected via this network

Handoff

The technique of handing over a call from one access point to another (as the user moves from one cell to another) without the call getting terminated is handoff

Contd..

Types of handoff

Soft handoff

Hard handoff

Contd..

Access Techniques

Time Division Multiple Access (TDMA)

Frequency Division Multiple Access (FDMA)

Code Division Multiple Access (CDMA)

Contd..

FREQUENCY

TIME

FDMA

1 2 3

FREQUENCY

TIME

User 3

User 2

User 1

TDMA

TIME

FREQUENCY

CODE

CDMAo r “Spread Spectrum”

User 3

User 2

User 1

Mobile Systems

Single high powered transmitters

High coverage

Limited number of subscribers

Cellular Concept

Number of low power transmitters

Large number of subscribers

Increased system capacity without adding more spectrum

Frequency reuse

Frequency reuse refers to the use of same radio channels on the same carrier frequency to cover different areas which are seperated by a significant distance

Contd..

Different generations

1G – Analog, only voice communication 2G – Digital, only voice communication, SMS 2.5G – Digital, voice communication, simple

web browsing 3G – Digital, data, voice communication ,

Multimedia

Interfaces and Protocols

Bsc-msc interface and protocols. Msc-msc interface and protocols.

IS-95 Interfaces

A Interface (BSC-MSC) .. This interface is between the BSC and the MSC. It supports both the control plane and user plane

Abis Interface (BTS-BSC)—This is the interface between the BSC and BTS. This is internal interface and generally proprietary

B Interface (MSC-VLR) This interface is defined by TIA IS-41

IS-95 interface (cont..)

C Interface (MSC-HLR) This interface uses IS-41 messaging as well

D Interface (HLR-VLR) – HLR-VLR signaling is based on IS-41 as well. It sits on top of SS7

E Interface (MSC-MSC)– Inter MSC signaling is defined in IS-41

L interface (MSC-IWF) This interface allows the ability for circuit switched data in second generation networks

Um Interface (BS-MS) – This is the air interface between the mobile and the network

Multiple Access

CDMA unique digital codes are used to differentiate

subscribers codes are shared by both MS and BS all users share the same range of radio spectrum

Benefits of CDMA: Capacity increases: 4 to 5 times (GSM) Improved call quality Simplified system planning Enhanced privacy Improved coverage characteristics Increased talk time for portables Bandwidth on demand

CDMA

There are two CDMA common air interface standards: Cellular (824-894 MHz) - TIA/EIA/IS-95A PCS (1850-1990 MHz) - ANSI J-STD-008

They are very similar in their features, with exceptions of the frequency plan, mobile identities, and related message fields.

IS-95A 45 MHz spacing for forward & reverse channel Permissible frequency assignments are on 30 kHz

increments

Forward CDMA Channel of IS-95A

From BSS to MS It carries traffic, a pilot signal, and overhead

information. Pilot is a spread but unmodulated Pilot and overhead channels establish the

system timing and station identity. Pilot channel is also used in the mobile-

assisted handoff (MAHO) process as a signal strength reference.

Overhead Channels

There are three types of overhead channel in the forward link: pilot, is required in every station sync paging

Pilot channel pure short code with no additional cover or information

content always code channel zero a demodulation reference for the mobile receivers and

for handoff level measurements carries no information all stations use the same short code, distinguished by

the phase

Overhead Channels

Sync Channel sync channel carries timing and system configuration

information data rate is always 1200 bps

Paging channel used to communicate with MSs when they are not

assigned to a traffic channel successful accesses are normally followed by an

assignment to a dedicated traffic channel paging channel may run at either 4800 or 9600 bps each BS must have at least one paging channel per

sector, on at least one of the frequencies in use

Traffic Channel

Traffic channels assigned dynamically, in response to MS accesses, to

specific MS always carries data in 20 ms frames carry variable rate traffic frames, either 1, 1/2, 1/4, or

1/8 of 9600 bps rate is independently variable in each 20 ms frame the 800 bps reverse link power control subchannel is

carried on the traffic channel by puncturing 2 from every 24 symbols transmitted.

Timing all base stations must be synchronized within a few

microseconds

Overhead Messages

System Parameter Message: configuration of the Paging Channel registration parameters parameters to aid pilot acquisition

Access Parameter Message configuration of the Access Channel control parameters used to stabilize the Access Channel

Neighbor List Message time offset of the pilot basic neighbor configuration

CDMA Channel List Message CDMA frequency assignment that contain Paging Channels

Paging Channel Messages

Page Message: contains pages to one or more mobile

stations. Order Message:

a broad class of messages used to control a particular MS.

Channel Assignment Message: let BS to assign a MS to the traffic channel change Paging Channel Assignment

Access Channel

Access Channel provides communications from MS to BS when MS is not using a Traffic Channel.

All Access Channel use 4800 bps mode Access Channel Message:

call origination response to pages orders registrations

Control of Access Channel transmission is accomplished through the Access Parameter Message sent on the Paging Channel

Connection Management

Mobile Origination Mobile Termination Call clearing procedure

Call origination

Call termination

Supplementary services

Call waiting Three way calling Message notification on the paging system Message notification on the traffic channel

Call waiting

Three way calling

MS BS MSCtime comment

a

bFlash with Information

Flash with Information

c

dFlash with Information

Flash with Information (2nd party called address)

e

fFlash with Information


g

hFlash with Information


Call paging on paging/traffic channel

Radio Resource Management

Purpose: Keeps a state of Radio Resources Allocates Physical Radio Resources Allocates Scrambling Codes (UL) Allocates Spreading Codes (DL) Knows Radio Network Configuration and State

Data Informs PS for current resources state

Radio Resource Management

Handles QoS Controls Cell Capacity and Interference in

order to provide an optimal utilization of the wireless interface resources.

Includes RRM Mechanisms: Power Control Handover Call Admission Control Load Control Packet Scheduling Resource Management

Handoff

Based on Signal Quality (thresholds) Traffic Level (maximum cell capacity or

maximum threshold) User Mobility

Faster movements many handovers Types

Softer (BSsection1 BS section2) Soft (BS1 BS2) Hard (lose connectivity, change frequency)

Contd..

2G Access Technologies

Frequency division multiple access (FDMA)

Time division multiple access (TDMA)

Code division multiple access (CDMA)

FDMA

FDMA separates the spectrum into distinct voice channels by splitting it into uniform chunks of bandwidth

Used mainly for analog transmission

TDMA

A narrow band that is 30 kHz wide and 6.7 milliseconds long is split time-wise into time slots

Voice data takes up significantly less transmission space

TDMA has three times the capacity of an analog system

Operates in either 800MHz(IS-54) or 1900MHz(IS-136) frequency bands

CDMA After digitizing data, spreads it out over

the entire available bandwidth Multiple calls are overlaid on each other

on the channel, with each assigned a unique sequence code.

CDMA is a form of spread spectrum At the receiver, that same unique code is

used to recover the signal

Benefits of CDMA

Capacity increases: 4 to 5 times Improved call quality Simplified system planning Enhanced privacy Improved coverage characteristics Increased talk time for portables

Signaling System #7(SS7)

Signaling in Telecommunications Network Channel Associated Signaling (CAS) Common Channel Signaling (CCS)

Signaling System Number (SS7) is a form of Common Channel Signaling.

SS7 is a communications protocol that provides signaling and control for

various network services and capabilities

Channel Associated Signaling:• Uses In-Band Signaling Signaling is transmitted in the same frequency band as used by voice. Voice path is established when the call setup is complete, using the same path that the

call setup signals used Common Channel Signaling:• Uses Out-of-Band Signaling• Employs dedicated path for signaling• Voice trunks are used only when a connection is established ,not before• Faster call setup

SwitchA

SwitchB

Voice Trunks

Signaling Link

Functions of SS7

Basic call setup, management and tear down Wireless services

Roaming Subscriber Identification

Local Number Portability (LNP) Toll-free services (800) and premium (0907) Advanced call features

Call forwarding Number display Conference/party calls

Properties of SS7

Interconnected network elements exchange messages using standard protocol Uses 56 or 64 kbps bi-directional channels called signalling links All signalling is out-of-band on dedicated channels rather than in-band Three network nodes called signalling points

Service Switching Point

Service Transfer Point

Service Control Point

Each point has a unique number code used in messages

SSP/STP/SCP SSP

Used to originate, terminate and tandem calls Can request routing information from the SCP

STP Packet switching hub Removes need for all Signalling Points to be interconnected May act as a firewall between network operators

SCP Routing databases

SSP’s and SCP’s are also called end points

SS7 Protocol Stack

Physical

Data Link

Network

Transport

Session

Presentation

Application

Message Transfer Part Level 1

OS

I R

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od

el



ISDNUserPart

SCCP

TransactionCapabilitiesApplications

Part

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Message Transfer Part (MTP)




ISDNUserPart

SCCP


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Message Transfer Part (MTP)

Divided into three parts MTP Level 1

Provides an interface to the actual physical channel over which communication takes place

CCITT recommends 64Kbps transmission whereas ANSI recommends 56 Kbps

MTP Level 2 Ensures accurate end-to-end transmission Implements flow control, sequence validation and error

checking MTP Level 3

Provides message routing Detects and reroutes on link failure or congestion

ISDN User Part (ISUP)




ISDNUserPart

SCCP


Part

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ISDN User Part (ISUP)

Defines set-up, management and release of trunk circuits for voice/data traffic Calls that originate and terminate at the same SSP do not use ISUP Messages are sent from a switch, to the switch where the next circuit connection

is required Call circuits are identified using circuit identification code (CIC)

Telephone User Part (TUP)




ISDNUserPart

SCCP


Part

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Telephone User Part (TUP)

Handles analogue circuits only TUP is used to handle call set-up, management, release for the analogue

network Used in countries with less mature networks such as China, South America As digital networks become the norm ISUP is replacing TUP

Signalling Connection Control Part (SCCP)




ISDNUserPart

SCCP


Part

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Signalling Connection Control Part (SCCP)

Provides connection oriented / connectionless services to the network Provides Global Title Translation (GTT)

A GTT may be 800 numbers, Mobile Subscriber ID’s, etc

SCCP translates the GTT into the actual destination SSP point code and subsystem number (SSN)

SSN are codes for applications rather than standard end-points SCCP is used as the transport layer by TCAP

Transaction Capabilities Applications Part (TCAP)




ISDNUserPart

SCCP


Part

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Handles exchange of non-circuit related data between applications on the SS7 network using SCCP messages

For example when a mobile subscriber connects to the network, TCAP carries the

Mobile Application Part (MAP) messages between the mobile switches and their supporting databases used for identifying and authentication the device and subscriber

SCP’s use TCAP to query routing tables in the SCP’s


TCAP has enabled the development of Intelligent Network (IN) services by supporting connectionless non-circuit related data exchange between signalling points

TCAP messages consist of Transaction Portion

Basic packet identifier data (type, ID’s, etc) Component Portion

May be thought of as “function calls” such as invoking, returning, rejecting, etc

References

Few websites found through Google:-

www.intellinet-tech.com/Solutions/wirelessnetworks.htm

www.informit.com/articles/article.asp?p=26330

Few Slides from Dr.Dantu’s 5520 course

uestions?

Documents

Wireless Networks and 2G Sowjanya Talasila Kalpana Uppalapati Karthik Dhoopati Sudheer Adumulla