GSM Overview

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					Layered Architectures Tutorial

Postal Service Communications Example
Simplified Layered Architecture User User-Network interface Network Network-Carrier interface Physical Carrier Physical layer protocols Physical Carrier Network layer protocols Network User layer protocols User

Layered Architectures for Data Communications
Virtual

Layer N
Data from Layer N (N-1) Services

Layer N

Layer N Receives Data

Layer N-1

Virtual

Layer N-1

Layer N-1 Peels Off Its Data

Layer N-1 Add Its Info

(N-2) Services

Layer N-2

Virtual

Layer N-2

Layer N-2 Peels Off Its Data

Layer N-2 Add Its Info

Layer 1 Service

Layer 1
Machine A

Physical

Layer 1
Machine B

• Onion analogy: each layer’s data forms a ‘skin’ around previous data • Protocol: communication between equal layers • Interface: communication between adjacent layers

The Open Systems Interconnection (OSI) Reference Model
• Goal: to establish a universally accepted structured approach for communication between open systems • Initiated by the ISO in 1977 • Adopted by the CCITT (X.200) • OSI reference model - basic architecture - layer service definitions - protocol specifications

Communication across a Packet-Switched Network (OSI Model)
User Process User Process

Application Presentation Session

Transport
Network

Data Link
Physical Physical Media Physical Media

End System

Intermediate Node

End System

An OSI Data Transfer
User Process User Process

User Data
User Data

Application Presentation Session Transport Network Data Link Physical LH NH TH SH PH

AH

Application Presentation Session Transport Network LT Data Link Physical

Data Unit Data Unit

Data Unit Data Unit Data Unit Bit stream Physical Media

Overview of GSM Interfaces and Signalling Protocols

GSM Signalling and Transport Layers
Signalling Layer D HLR VLR C E SSP SS7 Network Fixed Station Fixed Exchange Transport Layer MSC Trunk Network MSC PSTN/ISDN PLMN A BSS MS Local SS7 Network A SSP SSP Um SSP SSP B F EIR VLR G

MSC BSS HLR VLR -

Mobile Services Switching Centre Base Station System Home Location Register Visitor Location Register

EIR - Equipment Identity Register MS - Mobile Station SSP - Service Signalling Point in SS7 Network

Signalling System 7 (SS7)
SSP - Service Signalling Point STP - Signal Transfer Point SCP - Service Control Point

STP

STP

SCP

SSP

STP

STP

SSP

The SS7 Architecture
OMAP Operations Maintenance and Administration Part Application Service Element

OSI Model

SS7 Protocol Model Non-Circuit related Circuit related

ASE

-

OMAP Application TCAP

ASEs

TCAP

-

Transaction Capabilities Application Part
ISDN User Part Signalling Connection Control Part Message Transfer Part

ISDN-UP SCCP -

ISDN-UP Presentation Null Session Transport User Parts

MTP

-

SCCP
Network MTP Level 3 Data Link Physical MTP Level 2 MTP Level 1 Transport Services Parts

Mobile Application Part (MAP)
• Location registration and cancellation • Handover procedures • Handling of supplementary services • Retrieval of subscriber parameters during call set-up • Authentication procedures • OA&M TCAP Mobile Application Part

MAP
Mobile Application Entity (AE)

OMAP

ASEs

SCCP MTP L3 MTP L2 MTP L1

Intelligent Networks - CAMEL
IN Implementation in a GSM Network SCP - Service Control Point SSF - Service Switching Function INAP - Intelligent Network Application Part of C7 MAP - Mobile Application Part of C7 SCP Manages service aspects Eg. Pre-paid accounts

SCP

SSF

VLR

MAP HLR

MAP

VLR

SSF

MSC

MSC

BSS

BSS

HLR/VLR’s Manage Mobility

BSS

BSS

The Intelligent Network

• Charging options – Freephone – Local rates – Premium rates • Routing options – Group calls • Network call centre options • Virtual Private Networks – Personal calls • one number • configurable routing

The IN adds a computer and voice system to the fixed network

Service Control Point

Intelligent Peripheral

CAMEL
• Customised Applications for Mobile Network Enhanced Logic • Designed to support operator specific services whilst roaming – E.g. keying your usual number to recover voice mail • Allows a mobile network to offer IN facilities • Specific CAMEL subscription info is transferred when mobile registers in foreign network • All calls to and from Camel customers are referred back to home network.

BSS/MSC Interface (A)
BSSAP - BSS Application Part DTAP - Direct Transfer Application Part BSSMAP - BSS Management Application Part BSSOMAP- Operations and Maintenance Application Part SCCP - Signalling Connection Control Part MTP - Message Transfer Part

BSSAP
DTAP BSSMAP

Distribution

BSSOMAP

A MSC BSS

SCCP

MTP Level 3
MTP Level 2 MTP Level 1

32-Channel E1 Digital Facilities
A-Interface to MSC
One PCM 30 Frame 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 SIGNALING SYNC

Voice and/or Data

Voice and/or Data

GSM A-Interface Signalling Protocol Stack

Connectivity Management Mobility Management BSS Application Part Signalling Connect Control Part Message Transport Part – Layer 3 Message Transport Part – Layer 2 Message Transport Part – Layer 1

BSC/BTS Interface (A-bis)
Abis
BTS BSC

Radio Link Distribution Traffic Management Procedures L3 Transport Non Transport

Other Processes

Distribution

Network Management

L2 Management
L2 L1 LAPD Physical Layer

Mobile Station/Base Station Interface (Um)
CC - Call Control entity SS - Supplementary Services support entity SMS - Short Message Service support entity LAPDm - Link Access Procedures on Dm channel (Similar to ISDN LAPD) Um

MS

Connection Management (CM) CC L3 SS Mobility Management (MM) Radio Resource Management (RR) SMS

L2

LAPDm Physical Layer (RADIO SUBSYSTEM)

L1

Protocol Summary
MS–BTS–BSC–MSC Signalling Protocol Model

MS

BTS

BSC

MSC

Um MS MM

A-bis

A CM MM BSSAP

RR

RR

BSSAP SCCP MTP SCCP MTP

RR’
LAPDm Phys. LAPDm Phys.

BTSM LAPDm Phys.

BTSM LAPD Phys.

Mobile Station Functional Models
Mobile Data Terminal MT0 MT0 Speech-only Mobiles MT0

ISDN Speech and Data Terminal (TE1)

ISDN Equipment Interface S

MT1

Non-ISDN Data Terminal (TE2) R

Phone ISDN Equipment MT1 Interface S ISDN TA

Data Terminal (TE2)

X- or V- Series Terminal Equipment Interface R

MT2


				
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