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About GSM Network
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Telecommunication Basics(GSM Network)
Software Engineering Lab - 김영기 책임
Remember Again !!!
1G 2G 3G 3.5G 4G
음성 통화 통화, 문자, 이메일 통화, 문자, 멀티미디어, 무선인터넷 초고속 인터넷 초고속 무선 인터넷유,무선간 연동
IS-95 A IS-95 B
GSM GPRS
CDMA-1X
EV-DV
CDMA-1XEV-DO r0
W-CDMA R3
W-CDMA R5
(HSCPA)
CDMA-1XEV-DO rA
W-CDMA R6
(HSUPA)
CDMA-1XEV-DO rB
W-CDMAR7
(HSPA+)
LTEEDGE
UMB
W-CDMAHSPA+Phase2
AMPS
NMT
LTE Advanced
802.15e Wave1(Mobile WiMAX)
802.15e Wave2(Mobile WiMAX)
802.16eWiMAX R1.5
802.16nWiMAX R2.0
GSM track
CDMA track
WiMAX track
GSM Characteristics
F1 F2 F1' F2'
Frequency
1
2
3
4
5
6
7
8
45 MHz
BS Transmission Band : 935 – 960 MHZ
MS Transmission Band : 890 – 915 MHZ
Year Introduced 1990
Access method TDMA
Channel Bandwidth
200 kHz
Number of duplex channels
125
Users per channel 8
Speech coding bit rate
13 kbps
Data coding bit rate
12 kbps
Frame size 4.6 ms
GSM Nework Architecture
MS
SIM
MEPSTN
ISDN, PSPDNCSPDN
SIM : Subscriber Identity Module
ME : Mobile Equipment
MS : Mobile Station
BTS : Base Transceiver Station
BSC : Base Station Controller
HLR : Home Location Register
VLR : Visitor Location Register
EIR : Equipment Identify Register
MSC : Mobile Service Switching Station
AuC : Authentication Center
UM : Radio Link
NMS : Network Management System
Mobile Station
Base Station Subsystem Network Subsystem
UM
A
BTS
BTS
BSC
BSC
MSC
VLRHLR
EIR AuC
Network Management Subsystem
O&M
DataCommunication
Network
Abis
DatabaseSever
Network PlanningSystem
Network MeasurementSystem
GSM Interface (1/2)
Interface Description
Um Interface The "air" or radio interface standard that is used for exchanges between a mobile (ME) and a
base station (BTS / BSC). For signaling, a modified version of the ISDN LAPD, known as LAPDm is used
Abis Interface This is a BSS internal interface linking the BSC and a BTS, and it has not been totally
standardized. The Abis interface allows control of the radio equipment and radio frequency allocation in the BTS
A Interface
The A interface is used to provide communication between the BSS and the MSC. The interface carries information to enable the channels, timeslots and the like to be allocated to the mobile equipment being serviced by the BSSs. The messaging required within the network to enable handover etc to be undertaken is carried over the interface
B Interface
The B interface exists between the MSC and the VLR . It uses a protocol known as the MAP/B protocol. As most VLRs are collocated with an MSC, this makes the interface purely an "internal" interface. The interface is used whenever the MSC needs access to data regarding a MS located in its area
C Interface
The C interface is located between the HLR and a GMSC or a SMS-G. When a call originates from outside the network, i.e. from the PSTN or another mobile network it ahs to pass through the gateway so that routing information required to complete the call may be gained. The protocol used for communication is MAP/C, the letter "C" indicating that the protocol is used for the "C" interface. In addition to this, the MSC may optionally forward billing information to the HLR after the call is completed and cleared down
D Interface The D interface is situated between the VLR and HLR. It uses the MAP/D protocol to
exchange the data related to the location of the ME and to the management of the subscriber
E Interface The E interface provides communication between two MSCs. The E interface exchanges data
related to handover between the anchor and relay MSCs using the MAP/E protocol
GSM Interface (1/2)
The layered model of the GSM architecture integrates and links the peer-to-peer communications between two different systems
UM Abis A
GSM RF MTP 1GSM RF Layer 1 Layer 1 MTP 1
LAPDm MTP 2LAPDm LAPD LAPD MTP 2
MTP 3RR BTSM BTSM
MTP 3
SCCPSCCP
BSSMAP/DTAPRRDTAP
BSSMAP
RR
MM MM
CM CM
Interface Description
F Interface The F interface is used between an MSC and EIR. It uses the MAP/F protocol. The
communications along this interface are used to confirm the status of the IMEI of the ME gaining access to the network
G Interface The G interface interconnects two VLRs of different MSCs and uses the MAP/G protocol to
transfer subscriber information, during e.g. a location update procedure
H Interface The H interface exists between the MSC the SMS-G. It transfers short messages and uses the
MAP/H protocol
I Interface The I interface can be found between the MSC and the ME. Messages exchanged over the I
interface are relayed transparently through the BSS
Mobile Station
GSM MSs consist of
Mobile Equipment
SIM (Subscriber Identity Module)
Functions of Mobile Station
Voice and data transmission & receipt
Can receive, store, send SMS up to 160 charactors
Frequency and time synchronization
Monitoring of power and signal quality of the surrounding cells
Power levels of 20W, 8W, 5W, 2W and .8W
Provision of location updates even during inactive state
MS identified by unique IMEI shown on pressing “*#06#”
MS
SIM
ME
Mobile Station
SIM (Subscriber Identity Module) (1/2)
SIM has microprocessor and memory
Fixed data stored for the subscription
IMSI
Authentication Key , Ki
Security Algorithms : Kc, A3, A8
PIN & PUK
Network Identities
IMEI (International Mobile Equipment Identity)
Unique Code and is checked in the EIR
White List, Grey List, Black List
MSISDN (Mobile Station ISDN Number)
Is register in the telephone directory and used by the calling party for dialing
Shall not exceed 15 digits
White list : IMEI, assigned to valid ME.Black list : IMEI reported stolenGray list : IMEI having problems like faulty
software, wrong make of equipment etc.
CC NDC SN
1 to 3 digits Variable Variable
NDC : National Destination CodeSN : Subscriber Number
SIM (Subscriber Identity Module) (2/2)
Network Identities (cont.)
IMSI (International Mobile Subscriber Identity)
An unique identity which is used internationally and
used within the network to identify the mobile subscribers
Stored in the SIM, the HLR, VLR database
TMSI (Temporary Mobile Subscriber Identity)
Is a temporary IMSI No. made known to an MS at registration
The VLR assigns a TMSI to each mobile subscribers entering the VLR area
Assigned only after successful authentication
MSRN (Mobile Station Roaming Number)
Used in the GMSC to setup a connection to the visited MSC/VLR
Is a temporary identity which is assigned during the establishment of a call to a roaming
subs
NSS (Network Subsystem)
Network Subsystem contains
MSC, VLR, HLR, AC and EIR
Main Functions
Call control
Identifies the subscriber, establish a call, and clear connection
Charging
Collect the charging information about a call and transferers it to the Billing Center
Mobility management
Maintain information about subscriber’s location
Signaling
Interface with the BSS and PSTN
Subscriber data handling
Permanent data HLR
Temporary data VLR
NSS Entities
Entity Functionality
MSC(Mobile service Switching Center)
Call control (Switching and call routing)
Initiation of paging
Charging data collection
Service provisioning
Communication with other NEs (HLR, VLR, MSCs, BSCs)
VLR(Visitor Location Register)
Temporary data (data valid when subscriber is within its service area)
Identification numbers of the subscribers
Security information for authentication of the SIM card and for ciphering
Services that the subscriber can use
Data in VLR : IMSI & TMSI, MSISDN, MSRN, Location Area,
Supplementary service parameters, MS category, Authentication Key
HLR(Home Location Register)
Permanent data
Keeps track of the current location of its customers
Same functionality the VLR
AC(Authentication Center)
Provides security information to the network (for verify the SIM cards)
- TRIPLET : RAND, SRES, Kc
EIR(Equipment Identity Register)
Responsible for IMSI checking (for verify the mobile equipment)
Only one EIR per PLMN
BSS (Base Station Subsystem)
Base Satation Subsystem contains
BSC, BTS and TC (Transcoder)
Main Functions
Radio path control
Taking care of radio resources (channel allocation and quality of the radio connection)
Synchronisation
It is a critical issue in the GSM network due to the nature of the information transferred
Air-and A-interface signalling
Connection establishment between the MS and the NSS
May be either Signalling connection or a traffic(speech, data) connection
Mobile management and speech transcoding
Handover and transcoding
BSS Entities
Entity Functionality
BSC(Base Station Controller)
Connection establishment between the MS and the NSS
Mobility management (Handling of MS connections)
Statistical raw data collection (Internal BSC O&M)
Air-and A-interface signaling support (Radio Resource Management)
BTS and TC control
BTS(Base Transceiver Station)
Air interface signaling (Radio resource, Signaling link management)
Ciphering (Synchronization)
Speech processing (Signal processing)
TC(SM)(Transcoder (SubMultiplexer))
To enable an efficient transmission, the digital speech signal is
compressed
SM2M
TC
TC
TC
TC
BSCMSC
TCSM(Transcoder and Submultiplexer)
A ter Interface A ter’ Interface A Interface
TC is a device that takes 13 KBPS speech data and multiplexes four of them into standard 64 Kbps data
NMS (Network Management Subsystem)
Network Management Subsystem contains
Workstation, Servers, and router, etc
Main Functions
Fault management
Ensure the smooth operation of the network
Rapid correction of any kind of problems that are detected
Configuration management
Maintain up-to-date information about operation and configuration status of NE
Including management of the radio network, S/W and H/W , time synchronization,
security operation
Performance management
Collects measurement data from individual network elements and stores it in a database
Network operator is able to compare the actual performance of the network with the
planned performance
OMC (Operations and Maintenance Centre)
Dynamic monitoring & Controlling of the network
The centralized operation of the various units in the system and
functions needed to maintain the subsystems
Functions
O&M data function
Configuration management
Fault report and alarm handling
Performance supervision/management
Storage of system software and data
GSM Frame Structure
Superframe = 51 Traffic MultiframeOr 26 Control Multififrame
Traffic Multifame= 26 Frames
Control Multiframes= 51 Frames
Hyperframe = 2048 Superframes
Frame = 8 Slots
Slot = 577µs
120ms
0 1 2 3 4 5 6 7 0
5 6 7 0 1 2 3 4 5
Slot numbers
Time
Base station receive
Base station transmit
Correspondingreceive frame
235.4ms
Traffic multiframe: The Traffic Channel frames are organised into multiframesconsisting of 26 bursts and taking 120 ms. In a traffic multiframe, 24 bursts are used for traffic. These are numbered 0 to 11 and 13 to 24. One of the remaining bursts is then used to accommodate the SACCH, the remaining frame remaining free. The actual position used alternates between position 12 and 25.
Control multiframe: the Control Channel multiframe that comprises 51 bursts and occupies 235.4 ms. This always occurs on the beacon frequency in time slot zero and it may also occur within slots 2, 4 and 6 of the beacon frequency as well. This multiframe is subdivided into logical channels which are time-scheduled- Frequency correction burst, Synchronization burst- Broadcast channel (BCH), Paging and Access Grant Channel (PACCH), Stand Alone Dedicated Control Channel (SDCCH)
GSM Channels
GSM Channels
Traffic Channels Signaling Channels
Full-rate Half-rate
Broadcast Channels Common Control Channels Dedicate Control Channels
TCH/F TCH/H BCCH FCCH SCH PCH AGCH RACH TCH/H TCH/H TCH/H
downlink uplink fastslow
Common Channel
The forward common channels are used for paging to inform a mobile of an incoming call, responding to channel requests, and broadcasting bulletin board information.
The return common channel is a random access channel used by the mobile to request channel resources before timing information is conveyed by the BSS
Dedicate Channel The signaling channels are used for maintenance of the call and for enabling call set up, providing
facilities such as handover when the call is in progress, and finally terminating the call. The traffic channels handle the actual payload
TCHf : Full rate traffic channel.TCH h : Half rate traffic channel. BCCH : Broadcast Network information, SCH : Synchronisation of the MSs.FCHMS : frequency correction. AGCH : Acknowledge channel requests from MS and allocate
a SDCCH. PCHMS : terminating call announcement.
RACHMS : access requests, response to call announcement, location update, etc.
FACCHt : For time critical signalling over the TCH (e.g. for handover signalling)
SACCHt : TCH in-band signalling, (e.g. for link monitoring) SDCCH : For signalling exchanges,
(e.g. during call setup, registration / location updates)FACCHs : FACCH for the SDCCH. SACCHs : SDCCH in-band signalling (e.g. for link monitoring)
GSM Call Scenario 1
Location update
BSS MSC/VLR HLR/AuC
Channel Request
Immediate Assignment
Complete L3 Info(location updating request)
Send Authentication Info
PreviousMSC/VLR
Location Update Request
Send Authentication Info RR
Authentication Request
Authentication Response
Update Location
Cancel Location
Cancel Location RR
Insert Subscriber Data RR
Update Location RR
Insert Subscriber Data
Location Updating Accept
Clear Complete
Clear Command
Channel Release
GSM Call Scenario 2
Mobile to Network
Cell Site MSC
CM Service Request(Service type = mobile originated call) Complete Layer3 Info
(CM Service Request)
PSTN
Authentication Request
Authentication Response
Cipher Mode Command
Cipher Mode Command
Cipher Mode Complete
Cipher Mode Complete
Setup
Calling Proceeding
Assignment Request
Assignment Command
Assignment CompleteAssignment Complete
IAM
ACM
ANM
Alerting
Connect
Connect Acknowledge
GSM Call Scenario 3
Network to Mobile
BSS MSC/VLR HLR GMSC PSTN
IAMSRI (MSISDN)
PRN (IMSI)
PRN RR (MSRN)PRI RR (MSRN)
IAM (MSRN)Paging
Paging Request
Channel Request
Immediate Assignment
Paging ResponseComplete Layer 3 info (Paging Response)
Cipher Mode CommandCiphering Mode Command
Ciphering Mode Complete
Ciphering Mode Complete
Setup
Call Confirmed
Assignment Request
Assignment Command
Assignment CompleteAssignment Complete
Alerting
Connect
Connect Acknowledge
ACM
ANM
ACM
ANM
GSM Handover Scenario
Handover between BSCs
Serving BSS MSC/VLR Target BSS
Measurement Report
Measurement Report
Handover Required
Handover Request
Handover Request Ack
Handover Command
Handover Command
MS tunes toNew channel
Handover Access
Handover Detect
Handover Complete
Handover Complete
Clear Command
Clear Complete
Measurement Report
Measurement Report
Measurement Report
Appendix : Mobility Management
In-session mobility management
Move during an active call
Hand-off management
Out-of-session mobility management
Move in standby mode
Location management : Update (Registration) and Paging
LA-1
LA-2
Appendix : Hand-off
Hand-off = Handover
Transfer of a MS from one cell to another
Each BS constantly monitors the received power from each MS
When power drops below given threshold
BS asks neighbor station (with stronger received power) to pic up the MS, on a
new channel
Hand-off Types
Intra-Cell Inter-Cell
Soft Hand-off Hard Hand-off
x
Appendix : Hand-off Problem
Hand-off is
the process of switching from one frequency channel to another by the user in
midst of a communication
Normally induced by …
Received Signal Strength (RSS)
Signal-to-Noise Ration (SNR)
Bit Error Rate (BER)
Triggered either by the BS or the mobile station
In GSM, MAHO (Mobile-Assisted HandOver)
Base Station 1 Base Station 2
Ratio of powerReceived From current BS To next BS
time
Handover Threshold
Receiver Threshold
t0 t1