It802 d mobilecommunicationspart3

IT 802DMobile Communications

Part 3Debasis Das

04/12/2023 Debasis Das Mallabhum Institute of Technology

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GSMGSM 900

890-915 uplink, 935-960 downlinkGSM 1800 (DCS 1800)

1700-1785 uplink, 1805-1880 downlinkGSM 1900 (PCS 1900)

1850-1910 uplink, 1930-1990 downlink

GSM 400450.4-457.6/478.8-486 uplink, 460.4-

467.6/488.8-496 for downlinkGSM Rail


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Mobile ServicesBearer Services

Tele services

Supplementary Services


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Services

TE

MT

GSMPLM

N

Transit networ

k

Source/Destination Network

TE

R,S UmU,S,R

Bearer Services

Tele Services

MS


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Services Stacks

Application

Presentation

Session

Transport

Network

DLC

Physical

Bearer ServicesAll services that EnableTransparent Transmission ofData(connection Oriented, circuit Switched.

Tele servicesEnd to end


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Bearer ServicesTransparent

Uses functions of the physical layer only. Data transmission has constant delay and throughput if no errors occur. FEC is possible. Depending on FEC 2.4, 4.8 or 9.6 kbps speeds are supported, no lost data recovery due to shadowing or handover

Non-transparentUses protocols of layer 2 & 3 to implement error

correction & flow control, A radio link protocol or RLP(similar to HDLC) is used, error rates 10^-7 is possible, but delays could be variable


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Bear ServicesSeveral bearer services are specified that use

transparent and non transparent services

PSTN, ISDN and PSPDN (X.25) are used for

internetworking

Data transmission can be full duplex 1.2, 2.4, 4.8 and

9.6 kbps and asynchronous full duplex 300 to 9.6 kbps


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Tele ServicesMainly voice oriented

Encrypted voice, message services, Emergency number, highest priority, to nearest

emergency centerSMS, up to 160 characters, uses unused

capacity of the signaling channels, all kinds of content, updating of software

EMS(760 characters) and MMS(video clips, images)

Group 3 Fax


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Supplementary Services

May vary with provider

User id, call redirection, call forwarding

Closed user group, multi party

communication


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System Architecture

Radio subsystem(RSS)

Network and switching subsystem(NSS)

Operation subsystem(OSS)


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System ArchitectureOMCAUC

BTS

MSC

BSC

MSC

GMSC

BSC IWF

BTS

EIR

VLR

HLR

VLR

MSBSS

ISDNPSTN

Signaling

PDN

OSS

NSS

RSS


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Radio Subsystem(RSS)Radio specific entities

Mobile stationBase station subsystem(BSS)“A” interface connects the RSS to NSS“O” interface for connection to OSSA interface is circuit switched, PCM 30 systems30x 64 kbps connectionsO interface is SS7, management data to/fro

RSS


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Base Station SubsystemA base station controller controls(BSC)

multiple base station subsystems(BSS)BSS contains several base transceiver

stations(BTS)All functions required to maintain radio

communication to MS is carried out by BSSCoding/decoding of voice, rate adaptation

to/fro wireless network part, etc.


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Base Transceiver StationsBTS contains all radio equipmentAntenna, signal processing, amplifiersConnects to MS through a Um interface.

The ISDN U interface for mobile useConnects to BSC through Abis interfaceUm contains all the mechanisms for

wireless transmission such as TDMA, FDMA etc.

The Abis interface contains 16 or 64 kbps connections


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BTS & BSC FunctionsFunction BTS BSC

Management of radio channels yes

Frequency hopping Yes yes

Management terrestrial channels yes

Mapping of terrestrial onto radio channels yes

Channel coding & decoding yes

Rate adaptation yes

Encryption and decryption yes yes

Paging yes yes

Uplink signal management yes

Traffic management yes

Authentication yes

Location registry, location update yes

Handover management yes


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Mobile Station(MS)All user equipment and software needed for communicationHardware, software , subscriber identity module(SIM), stores

user specific data relevant to GSMSIM contains an International mobile equipment

identity(IMEI)Usually contains card type, serial number, ,subscribed

services, PIN, PIN unblocking key, authentication key ki, international mobile subscriber identity(IMSI)

Dynamic information when logged into GSM system, such as cipher key Kc and TMSI or temporary mobile subscriber identity(TMSI) and location area identification(LAI) are stored

The MS can have many other interfaces and vendor specific features.


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Network & Switching Subsystem(NSS)Connects RSS with standard public networksPerforms handovers between different BSSsHas functions for localization of usersSupports charging, accounting, and roaming

of users between different providers in different countries

Subsystems includeMobile services switching center(MSC)Home location register(HLR)Visitor location register(VLR)


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MSCThe fixed backbone network nodes. Connections to other MSCs and BSCs are set

up through theseManages several BSC in a particular

geographic locationA gateway MSC(GMSC) has connections to

other public networks such as PSTN, ISDNCan also connect to public data

networks(PDN) through inter working functions (IWF)


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More on MSCUses the standard signaling system 7 or the

SS7 for all aspects of control signaling for digital networks that includesReliable routing and delivery of control messages

for establishing and monitoring of callsSS7 provides

Number portability, free phone, tool/collect calls, credit calls, call forwarding, 3-way calling etc.

MSC also provides functionality for supplementary services like call forwarding, multi-party calls, reverse charging etc.


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Home Location register(HLR)Database for all user relevant data

Static information like mobile subscriber ISDN number(MSISDN), services subscribed and IMSI

Dynamic information like current location area(LA), mobile subscriber roaming number(MSRN), current VLR and MSC, when a MS leaves LA, the info is updated

Only one set of user home information is maintained in for any user for any user worldwide

Some information may need to meet real time criteria


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Visitor Location Register(VLR)Dynamic database for relevant information

for the MS user in LA associated with the

MSC

Typically, MSISDN, IMSI, HLR address etc.

VLR copies the information from the HLR


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Operation Subsystem(OSS)Consists of the following subsystems

Operation and maintenance center(OMC)

Authentication center (AuC)

Equipment identity center(EIR)


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OMCMonitors and controls all other entities via O

interface (SS7 & X.25). Typical functions include

Traffic monitoring, status reports, subscriber and

security management, accounting and billing

Uses “telecommunication management network”

as standardized by ITU-T


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Authentication center(AuC)Contains algorithms for authentication, as

well as keys for encryption and generates the

values needed for user authentication in HLR

AuC may actually be located in a special

protected part of HLR

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