Overview of GSM Architecture
GSM/DCS1800 System
•
•
•
•
•
•
•
•
•
Some Histories & Some Background
GSM/DCS1800 System Architecture
High-Level View of Some Scenarios
GSM Time Slot Structure
GSM Logical Channels
GSM Frame Structure
Low-Level View of Some Scenarios
GSM System Diagram& Protocol Stack
Different Between GSM and DCS 1800
Page-2
Milestones of the GSM
1982
1984
1985
1987
1988/89~1991/92
1990
• CEPT decides to establish a Groupe Speciale
• Discussion & adoption of a list of
• GSM becomes a technical committee within
Mobile (GSM) to develop a set of common
recommendations to be generated by the group > ETSI & splits up into GSM group 1-4, later
standards for a future pan-European cellular
100 recommendations in series of 12 volumes
called Special Mobile Group (SMG) 1-4
mobile network
• Establishment of 3 work parties to define &
• Initial Memorandum of Understanding (MoU)• The GSM specifications for the 900
describe the services offered in a GSM (radio
signed by telecommunication network operator MHz are also applied at 1800 MHz
interface, signaling protocol, interfaces,…...)
organizations
band (DCS1800), a PCN applications
initiated in the UK
1991
1992
1993
1997
1995
• July:: Planned GSM commercial launch of GSM
service in Europe (MoU plan) delayed to 1992
because of non-availability of type-approved
terminals
• The GSM-MoU has 62 members (signatories) in
•Over 64 million subscribers
39 countries worldwide; in addtion 32 potential
member (observers/applicants) in 19 other
GSM
countries
Global System for Mobile
• GSM networks operational or under
• Official commercial launch of GSM service in
development in 60 countries worldwide,
Communication
Europe
with over 5.4 million subscribers
Page-3
GSM/DCS1800 System (1)
GSM Services
Service Category
Tele-services
Service
y Telephony (Speech)
Comments
y Full rate (13Kbps)
y Emergency calls (speech)
Bearer Services
y Short Message services: point-to-point
y Alphanumeric information: user
& point-to-multi-point (cell broadcast)
y Tele-fax
y Group 3
y Asynchronous data
y 300-9600 bps
y Synchronous data
y 300-9600 bps
y Asynchronous PAD (packet switched,
y 300-9600 bps
to user & network to all users
packet assembler/disassembler) access
y Alternate speech & data
y 300-9600 bps
Supplementary
Services
y Call forwarding
Phase 1
Services
y Call barring
GSM/DCS1800 System (2)
Page-4
GSM Services
Service Category
Tele-services
Service
y Telephony (Speech)
Comments
y Half rate (6.5 Kbps)
y Short Message services:
y General Improvements
dedicated packet data y 2400-9600 bps
Bearer Services
y Synchronous
Supplementary
Services
y Calling/connected
access
line
identity
presentation
y Calling/connected
line
identity
restriction
y Call waiting
y Call hold
y Multiparty communication closed user
group
Online charge information
y Advice of charge
GSM/DCS1800 System (3)
Phase 2
Services
Page-5
GSM/DCS1800 System
)
•
•
•
•
•
•
•
•
•
Some Histories & Some Background
GSM/DCS1800 System Architecture
High-Level View of Some Scenarios
GSM Time Slot Structure
GSM Logical Channels
GSM Frame Structure
Low-Level View of Some Scenarios
GSM System Diagram& Protocol Stack
Different Between GSM and DCS 1800
Page-6
GSM System Architecture
HLR
BTS
BTS
MS
VLR
AUC
BSC
PSTN
BTS
MSC
ISDN
BTS
BTS
Data
Network
BSC
OMC
BTS
Base Station Subsystem
Operation &
Maintenance Subsystem
Network Switching Subsystem
Public Network
MS
Page-7
GSM/DCS1800 System (4)
GSM System Architecture
• Functional Entities of GSM
AUC
HLR
D
OMC
VLR
B
C
GMSC
F
PSTN
EIR
A
E
MSC
BSC
Abis (through ISDN protocol)
BSC
BTS
š
š
š
š
š
BTS
AUC Authentication Center
BTS Base Transceiver Station
BSC Base Station Controller
EIR Equipment Identity Register
GMSC Gateway Mobile Switching Center
Um
MS
š
š
š
š
HLR Home Location Register
MSC Mobile Switching Center
OMC Operation and Maintenance Center
VLR Visited Location Register
GSM/DCS1800 System (5)
Page-8
Mobile Station
• Mobile Station Types
– Vehicle-mounted stations
– portable stations
– handheld stations
• Mobile Station Power Classes
– Vehicular & portable units can be either class I or class II
– Handheld units can be class III, IV, & V
Class
Class
II
IIII
III
III
IV
IV
VV
Max.
Max.RF
RFPower
Power(W)
(W)
20
20
88
55
22
0.8
0.8
GSM/DCS1800 System (6)
Page-9
Identities of Mobile Station
• Mobile station has three identities
– International Mobile Subscriber Identity (IMSI)
– International Mobile Equipment Identity (IMEI)
– Temporary Mobile Subscriber Identity (TMSI)
GSM/DCS1800 System (7)
Page-10
Identities of Mobile Station
• International Mobile Subscriber Identity
– IMSI is assigned to an MS at subscription time
– It uniquely identifies a given MS
– It contains 15 digits
• Mobile Country Code (MCC)
– 3 digits (home country)
• Mobile Network Code (MNC)
– 2 digits (home GSM PLMN)
• Mobile Subscriber Identification(MSIN)
• National Mobile Subscriber Identity(NMSI)
– 262
02
MCC = Germany
Mobile Subscriber
Identification Number (MSIC)
454 275 1010
NMC = private operator D3 private
GSM/DCS1800 System (8)
Page-11
Identities of Mobile Station
• International Mobile Equipment Identity (*#06#)
– IMEI uniquely identifies the MS equipment
– It is assigned by the equipment manufacturer
– It contains 15 digits
• Type Approval Code (ATC)
– 6 digits
• Final Assembly Code (FAC)
– 2 digits
• Serial Number (SNR)
– 6 digits
• Spare (SP)
– 1 digit
GSM/DCS1800 System (9)
Page-12
Identities of Mobile Station
• Temporary Mobile Subscriber Identity
– TMSI is assigned to MS by the Visitor Location Register (VLR)
– TMSI uniquely identifies an MS within the area controlled by a given
VLR
– A maximum of 32 bits can be used for TMSI
GSM/DCS1800 System (10)
Page-13
Identities of Mobile Station
• Subscriber Identity Module Card (SIM card)
–
–
–
–
–
–
–
–
IMSI
Authentication Key
Subscriber information
Access control class
Cipher key
Additional GSM services
Location Area Identity
Forbidden PLMN
GSM/DCS1800 System (11)
Page-14
Base Station Subsystem
• Base Station Subsystem (BSS) contains 2 Parts
– Base Station Controller (BSC)
– Base Transceiver System (BTS)
• It contains the Transcoder Rate Adopter Unit (TRAU)
– GSM-specific speed encoding & decoding is carried out, as well as the rate
adaptation function for data
• Power class are also classified in a similar way to MS with 8 classes in 3 dB
steps from 2.5 W to 320 W
GSM/DCS1800 System (12)
Page-15
Network and Switching Subsystem
• Network and Switching Subsystem contains
– Switching functions of the GSM
• MSC & GMSC
– Database required for the subscriber
– Mobility management
GSM/DCS1800 System (13)
Page-16
Operational & Maintenance
Subsystem
• Operational and Maintenance Subsystem
– Responsibility
• The OMS is responsible for handling system security based on validation of
identities of various telecommunication entities.
– Performed by
• Authentication Center (AUC): The AUC is accessed by HLR to determine whether an
MS will be granted services
• Equipment Identity Register (EIR): The EIR provides MS information used by the
MSC. The EIR maintain a list of legitimate, fraudulent or faulty MSs.
• In charge of remote operation and maintenance of PLMN.
• Operational and Maintenance Center (OMC)
– The functional entity through which the service provider monitors and controls
the system.
GSM/DCS1800 System (14)
Page-17
GSM QoS Requirements
• GSM Service Quality Requirements
QoS
QoS
Required
RequiredTime
Time
Time
Timefrom
fromswitching
switchingtotoservice
serviceready
ready
Connect
time
to
called
network
Connect time to called network
44sec
secininthe
thehome
homesystem
systemand
and10
10sec
secininthe
thevisiting
visitingsystem
system
44sec
sec
Release
Releasetime
timetotocalled
callednetwork
network
Time
Timetotoalert
alertmobile
mobileofofinbound
inboundcall
call
22sec
sec
44sec
secininfirst
firstattempt
attemptand
and15
15sec
secininfinal
finalattempt
attempt
Maximum
Maximumgap
gapdue
duetotohandoff
handoff
Maximum
one-way
Maximum one-wayspeech
speechdelay
delay
150
150ms
msififintercell
intercelland
and100
100ms
msififitracell
itracell
90ms
90ms
Intelligibility
Intelligibilityofofspeech
speech
90%
90%
GSM/DCS1800 System (15)
Page-18
GSM/DCS1800 System
)
•
•
•
•
•
•
•
•
•
Some Histories & Some Background
GSM/DCS1800 System Architecture
High-Level View of Some Scenarios
GSM Time Slot Structure
GSM Logical Channels
GSM Frame Structure
Low-Level View of Some Scenarios
GSM System Diagram& Protocol Stack
Different Between GSM and DCS 1800
Page-19
High-Level View of Some Scenarios
• GSM Registration Scenarios
MS
BTS
BSC
MSC
VLR
HLR
Channel Request
Channel activation command
Channel activation acknowledge
Channel Assignment
Location Update Request
Authentication Request
Authentication Response
Comparison of the Authentication
parameters
Assignment of the new area & TMSI
Acknowledgement of new area & TMSI
Entry of the new area & identity
into VLR & HLR
Channel Release
GSM/DCS1800 System (16)
Page-20
GSM Call Flow Scenarios
• Call Setup with a Mobile to Land Call
– Part I
Um
MS
1
2
3
A
B
BSS
MSC
SETUP_REQ
Access Subscriber Data
Call Proceeding
4
7
8
SUB_DATA_RESP
Assign Truck &
Radio Channel
5
6
VLR
Assign Radio
Channel
Radio Assignment
Complete
Truck & Radio
Assignment complete
Page-21
GSM/DCS1800 System (17)
GSM Call Flow Scenarios
• Call Setup with a Mobile to Land Call
– Part II
MS
MSC
1
2
3
PSTN
NET_SETUP
NET_ALERT
Alerting
Connect (Answer)
4
5
6
Connect
Connect
Acknowledgement
GSM/DCS1800 System (18)
Page-22
GSM Call Flow Scenarios
• Call Release With Mobile to Land Call
– Mobile Initiated
Um
MS
A
BSS
MSC
PSTN
CALL_DISC
1
2
3
NET_REL
CALL_REL
REL_COMP
4
CLR_COMM
5
CHH_REL
6
CLR_COMP
7
Page-23
GSM/DCS1800 System (19)
GSM Call Flow Scenarios
• Land to Mobile Call
– Part I
– Assumption
• MS is registered with the system & has been assigned a TMSI
• MS is in its home system
C
PSTN
1
2
3
4
5
MSC
HLR
VLR
INC_CALL
GET_ROUT
ROUT_INF
INCO_CALL
PERM_PAGE
GSM/DCS1800 System (20)
Page-24
GSM Call Flow Scenarios
• Land to Mobile Call (Paging)
– Part II
Um
MS
1
2
5
B
MSC
VLR
PERM_PAGE
PAGE_MESS
CH_REQ
3
4
A
BSS
DSCH_ASS
PAGE_RESP
PAGE_RESP
6
PAGE_RESP
7
GSM/DCS1800 System (21)
Page-25
GSM Call Flow Scenarios
• Handoff
– MS scans transmission from surrounding BSs in the spare timeslots
• It then reports the measured results back to the fixed network via BS, where
the handoff decision is made
– Classifications
• Internal Handoff
– Inter-BSS Handoff
• External
– Intra-MSC Handoff
– Inter-MSC Handoff
GSM/DCS1800 System (22)
Page-26
GSM Call Flow Scenarios
• Handoff
– Intra-MSC Handoff
GSM/DCS1800 System (22)
Page-27
GSM/DCS1800 System
)
•
•
•
•
•
•
•
•
•
Some Histories & Some Background
GSM/DCS1800 System Architecture
High-Level View of Some Scenarios
GSM Time Slot Structure
GSM Logical Channels
GSM Frame Structure
Low-Level View of Some Scenarios
GSM System Diagram& Protocol Stack
Different Between GSM and DCS 1800
Page-28
GSM Time Slot Structure
• Frequency Bands and Bandwidth
GSM 900
Down-link (BS to MS)
• 935 MHz ~ 960 MHz (25 MHz Bandwidth)
Up-link (MS to BS)
• 890 MHz ~ 915 MHz (25 MHz Bandwidth)
Carriers or Channels
• Each up-link or down-link has 124 Carriers with a bandwidth of 200 KHz, excluding 2×100
KHz edges of the band
• The use of carrier 1 and 124 are optional for operators.
1
100 kHz
200 kHz
2
124
3
F u = 890 . 2 + 0 . 2 × ( N − 1 ) MHz
F d = 935 . 2 + 0 . 2 × ( N − 1 ) MHz
N = 1, 2 ,
100 kHz
,124
Page-29
GSM/DCS1800 System (23)
Frequency Bands and Bandwidth
Down-link (BS to MS)
• 1805 MHz ~ 1880 MHz (75 MHz Bandwidth)
DCS-1800
Up-link (MS to BS)
• 1710 MHz ~ 1785 MHz (75 MHz Bandwidth)
Carriers or Channels
• Each up-link or down-link has 374 Carriers with a bandwidth of 200 KHz, excluding
F u = 1710 + 0 . 2 × ( N − 1 ) MHz
F d = 1805 + 0 . 2 × ( N − 1 ) MHz
512 ≤ N ≤ 885
GSM/DCS1800 System (24)
Page-30
Frequency Bands and Bandwidth
• FDMA/TDMA Structure
• The total bandwidth is divided into 124×200 kHz bands (FDMA)
• Each 200 kHz band can support maximum 8 users (TDMA)
• The GSM can support up to 992 (124×8) simultaneous users with the fullrate speech coder.
TS1
TS2
TS3
TS5
TS6
TS7
Freq. #1
Channel #1
TS0
Channel #2
Channel #3
Channel #4
Channel #5
TS4
Channel #6
Channel #7
Channel #8
Freq. #2
Channel #1
Channel #2
Channel #3
Channel #4
Channel #5
Channel #6
Channel #7
Channel #8
Freq. #124
Channel #1
Channel #2
Channel #3
Channel #4
Channel #5
Channel #6
Channel #7
Channel #8
Page-31
GSM/DCS1800 System (24)
Frequency Bands and Bandwidth
Time-Division Duplex (TDD)
• No need for a dedicated duplex stage (duplexer); the
only requirements are to have a fast switching
synthesizer, RF filter paths & fast antenna switches
available
• Increased battery life or reduced battery weight
0
1
2
3
4
5
6
7
BS Transmits
5
6
7
0
1
2
3
4
MS Transmits
GSM/DCS1800 System (25)
Page-32
Frequency Bands and Bandwidth
Pulsed Transmission
• The tendency for a pulsed radio to disturb neighboring
frequency channels is called AM splash.
4 dB
-1 dB
-6 dB
-30 dB
-70 dB
10µ s 8µ s 10µ s
542.8µ s (147 bits)
GSM/DCS1800 System (26)
10µ s 8µ s 10µ s
Page-33
GSM Time Slot Structure
• Time Slot Structure or Burst types in GSM
–
–
–
–
Normal Bursts
Random Access Burst
Frequency Correction Bursts
Synchronization Bursts
GSM/DCS1800 System (27)
Page-34
GSM Time Slot Structure
Tail Bits (TB)
• Used as a guard time.& this time covers the periods of uncertainty during the ramping up & down of
the power bursts form the MS in accordance with the power-versus-time template
Stealing Flag
• Used as an indication to the decoder of whether the incoming burst is
carrying signaling data or user data
TB
(3 bits)
Normal
Burst
Coded Data
(57 bits)
Stealing
Flag
(1 bits)
Training
Sequence
(26 bits)
Stealing
Flag
(1 bits)
Coded Data
(57 bits)
TB
(3 bits)
Guard Time
(8.25 bits)
148 bits = 546.12 µ s
Training Sequence
• Used to compensate for the effects of multi-path fading.
There are 8 different sequences defined in GSM.
Page-35
GSM/DCS1800 System (28)
GSM Time Slot Structure
TB
(8 bits)
Synchronization Sequence
(41 bits)
Coded Data
(36 bits)
TB
(3 bits)
Guard Time
(68.25 bits)
88 bits = 324.72 µ s
Random Access
Burst
GSM/DCS1800 System (29)
Page-36
GSM Time Slot Structure
TB
(8 bits)
Fixed bit Sequence
(142 bits)
TB
(3 bits)
Guard Time
(8.25 bits)
148 bits = 546.12 µ s
FrequencyCorrection
Burst
Page-37
GSM/DCS1800 System (30)
GSM Time Slot Structure
TB
(3 bits)
Synchronization
Sequence
(264bits)
Coded Data
(39 bits)
Coded Data
(39 bits)
TB
(3 bits)
Guard Time
(8.25 bits)
148 bits = 546.12 µ s
Synchronization
Burst
GSM/DCS1800 System (31)
Page-38
GSM/DCS1800 System
)
•
•
•
•
•
•
•
•
•
Some Histories & Some Background
GSM/DCS1800 System Architecture
High-Level View of Some Scenarios
GSM Time Slot Structure
GSM Logical Channels
GSM Frame Structure
Low-Level View of Some Scenarios
GSM System Diagram& Protocol Stack
Different Between GSM and DCS 1800
Page-39
GSM Logical Channels
• Classifications
Logic Channel
Traffic Channel
(TCH)
TCH/Full
(TCH/F)
TCH/Half
(TCH/H)
Control Channel
(CCH)
Broadcast Channel
(BCH)
Cell Broadcast
Channel (CBCH)
Common Control
Channel (CCCH)
Freq. Correction
Channel (FCCH)
Paging
Channel (PCH)
Synchronization
Channel (SCH)
Access Grant
Channel (AGCH)
Broadcast Control
Channel (BCCH)
Random Access
Channel (RACH)
SACCH/TF
Dedicated Control
Channel (DCCH)
Associated Control
Channel (ACCH)
Slow Associated
Control Channel
(SACCH)
Stand-Alone Dedicated
Control Channel (SDCCH)
Fast Associated
Control Channel
(FACCH)
FACCH/F
SACCH/TH
GSM/DCS1800 System (32)
SACCH/C4
SDCCH/4
SDCCH/8
FACCH/H
SACCH/C8
Page-40
GSM Logical Channels
• Traffic Channel
– Are used to transmit user information (speech or data)
– 2 categories
• TCH/Full (TCH/F)
– Allows the transmission of 13 Kbps of speech
• TCH/Half (TCH/H)
– Allows the speech coded at a half rate
Logic Channel
Traffic Channel
(TCH)
TCH/Full
(TCH/F)
Control Channel
(CCH)
Cell Broadcast
Channel (CBCH)
TCH/Half
(TCH/H)
GSM/DCS1800 System (33)
Page-41
GSM Logical Channels
• Control Channel (CCH)
– Are used to transmit control and signaling information
• Broadcast Channel (BCH)
• Common Control Channel (CCH)
• Dedicated Control Channel (DCCH)
Logic Channel
Broadcast Channel
(BCH)
Control Channel
(CCH)
Traffic Channel
(TCH)
Common Control
Channel (CCCH)
Dedicated Control
Channel (DCCH)
GSM/DCS1800 System (34)
Cell Broadcast
Channel (CBCH)
Page-42
GSM Logical Channels
• Control Channel (CCH)
– Broadcast Channel (BCH)
• Are point-to-multipoint, downlink-only channels
• Classification
– Broadcast Control Channel (BCCH)
– Frequency Correction Channel (FCCH)
– Synchronization Channel (SCH)
Logic Channel
Control Channel
(CCH)
Dedicated Control
Channel (DCCH)
Broadcast Channel
(BCH)
Common Control
Channel (CCCH)
Freq. Correction
Channel (FCCH)
Synchronization
Channel (SCH)
Broadcast Control
Channel (BCCH)
Page-43
GSM/DCS1800 System (35)
GSM Logical Channels
• Control Channel (CCH)
– Common Control Channel (CCH)
• Are point-to-multipoint, downlink-only channels that are used for paging &
access except for RACH.
• Classifications
– Paging Channel (PCH)
– Access Grant Channel (AGCH)
– Random Access Channel (RACH)
Paging
Channel (PCH)
Logic Channel
Control Channel
(CCH)
Common Control
Channel (CCCH)
Broadcast Channel
(BCH)
Access Grant
Channel (AGCH)
Random Access
Channel (RACH)
GSM/DCS1800 System (36)
Dedicated Control
Channel (DCCH)
Page-44
GSM Logical Channels
• Control Channel (CCH)
– Dedicated Control Channel (DCCH)
• Are bidirectional, point-to-point channels
• Classifications
– Stand-Alone Dedicated Control Channel (SDCH)
– Associated Control Channel (ACCH)
• Slow Associated Control Channel (SACCH)
• Fast Associated Control Channel (FACCH)
Dedicated Control
Channel (DCCH)
Associated Control
Channel (ACCH)
Logic Channel
Control Channel
(CCH)
Broadcast Channel
(BCH)
Common Control
Channel (CCCH)
Stand-Alone Dedicated
Control Channel (SDCCH)
GSM/DCS1800 System (37)
Page-45
GSM/DCS1800 System
)
•
•
•
•
•
•
•
•
•
Some Histories & Some Background
GSM/DCS1800 System Architecture
High-Level View of Some Scenarios
GSM Time Slot Structure
GSM Logical Channels
GSM Frame Structure
Low-Level View of Some Scenarios
GSM System Diagram& Protocol Stack
Different Between GSM and DCS 1800
Page-46
GSM Frame Structure
Channel
Combinations
(I)
• I : TCH/FS + FACCH/FS + SACCH/FS
• II : TCH/HS(0,1) + FACCH/HS(0,1) + SACCH/HS(0,1)
• III: TCH/HS(0) + FACCH/HS(0) + SACCH/HS(0) + TCH/HS(1) +
FACCH/HS(1) + SACCH/HS(1)
• IV: FCCH + SCH + CCCH + BCCH
• V : FCCH + SCH + CCCH + BCCH + SDCCH/4 + SACCH/4
• VI : CCCH + BCCH
• VII: SDCCH/8 + SACCH/8
Each channel combination requires one single physical channel
Page-47
GSM/DCS1800 System (38)
GSM Frame Structure
Traffic Channel Frame Structure (26-multi-frame)
Channel
Combinations (II)
• I : TCH/FS + FACCH/FS + SACCH/FS
T=TCH, S=SACCH, I=Idle
T0 T1 T2 T3 T4 T5 T6 T7 T8 T9
T
10
T S
11 12
T
13
T
14
T T
15 16
T T
17 18
T T
19 20
T T
21 22
T T
23 24
I
25
26 Frames = 120 ms
GSM/DCS1800 System (39)
Page-48
GSM Frame Structure
Traffic Channel Frame Structure (26-multi-frame)
Channel
Combinations (III)
• II : TCH/HS(0,1) + FACCH/HS(0,1) + SACCH/HS(0,1)
• III: TCH/HS(0) + FACCH/HS(0) + SACCH/HS(0) +
TCH/HS(1) + FACCH/HS(1) + SACCH/HS(1)
T0
t
1
T2
t
3
T4
t
T6
5
t
T8
7
t
9
T
10
t S
11 12
T
13
t
14
T t
15 16
T t
17 18
T t
19 20
T
t
21 22
T t
23 24
s
25
26 Frames = 120 ms
T=TCH1 , S=SACCH1 , t=TCH2, s=SACCH2
Page-49
GSM/DCS1800 System (40)
GSM Frame Structure
Signaling Channel Frame Structure (51-multi-frame)
Channel
Combinations (IV)
• IV : FCCH + SCH + CCCH + BCCH
F0 S1 T2
BCCH
2~5
CCCH F
6 ~ 9 10
S CCCH
11 12~19
F S
20 21
CCCH
22~29
F S
30 31
CCCH
32~39
F S
40 41
CCCH
42~49
I
50
Down-Link :: F=FCCH, S=SCH, B=BCCH, C=CCCH (PCH,AGCH), I=Idle
R0 R1
R
10
R
11
R R
20 21
R R
30 31
R R
40 41
R
50
Up-Link :: R=RACH
51 Frames = 235.38 ms
GSM/DCS1800 System (41)
Page-50
GSM Frame Structure
Signaling Channel Frame Structure (51-multi-frame)
Channel
Combinations (V)
• V : FCCH + SCJ + CCCH + BCCH + SDCCH/4 + SACCH/4
GSM/DCS1800 System (42)
Page-51
GSM Frame Structure
Signaling Channel Frame Structure (51-multi-frame)
Channel
Combinations (VI)
VI : CCCH + BCCH
• Used as a BS has to manages a huge number of transceiver which means the number of
CCCHs provided by combination IV is not enough to handle the network
• Assign additional control channels in combination IV. While combination IV always
occupies time slot 0, combination VI is assigned to time slot 2, 4, or 6.
• The combination VI multi-frame structure is similar to combination IV.
GSM/DCS1800 System (43)
Page-52
GSM Frame Structure
Signaling Channel Frame Structure (51-multi-frame)
Channel
Combinations (VII)
• VII : SDCCH/8 + SACCH/8
Page-53
GSM/DCS1800 System (44)
GSM Frame Structure
• Frame Hierarchical Structure
– Hyper-frame,super-frame,multi-frame,frame,time slot
– A time slot carries 156.25 bits
156.25 bits
GSM Time-Slot
(Normal Burst)
Tail
Data
3
Training
Stealing
Bit
1
26
1
57
0
GSM Frame (4.615 ms)
1 Multi-frame=26 frame
(120 ms)
0
1 Multi-frame=51 frame
(3060/13 ms)
GSM Super-frame
(26×51=1326 frame
=6.12 sec)
GSM hyper-frame
0
(3.48 hours)
Stealing
Bit
0
0
1
1
2
2
2
3
57
4
……
……
2
1
1
1
2
Data
……
……
GSM/DCS1800 System (45)
5
6
Tail
Guard
3
8.25
7
23
24
47
47
48
25
49
48
2045
50
49
2046
2047
Page-54
GSM Frame Structure
• T1, T2 & T3 Counters
– T1 counter counts the super-frames
• Whenever a super-frame is completed, T1 is incremented by 1 & 0 ≤ T1 ≤
2047
– T2 counter counts the speech frames, which only occur in 26 multi-frame
structure & 0 ≤ T2 ≤ 25
– .T3 counter counts the signaling frames, which are 51-multi-frame
structure & 0 ≤ T3 ≤ 50
Page-55
GSM/DCS1800 System (46)
GSM Frame Structure
T
B
S
TDMA Frame
0
1
2
3
0
1
0
1
21
22
23
24
1 2
3
2
46 47 48 49 50
46
3
2
3
21
T
Example of How a
MS Behaves
0
25
T
47
22
T
48 49
23 24
T
50
25
T
26
multi-frame
51
multi-frame
B
S
B
S
B
GSM/DCS1800 System (47)
S
B
S
B
S
Page-56
GSM Frame Structure
When a MS is turned on, it has to orient itself within the network
1. It synchronizes itself in frequency
2. It synchronizes itself in time
3. It reads the system & cell data from base channel or more specifically from BCCH
To find the frequency where the FCCH, SCH & BCCH are being
transmitted
Synchronization
With the Network
The MS uses the SCH for this purpose. Since it has found the
FCCH, so it already knows that SCH will be follow in the next
TDMA frame
GSM/DCS1800 System (48)
Page-57
GSM/DCS1800 System
)
•
•
•
•
•
•
•
•
•
Some Histories & Some Background
GSM/DCS1800 System Architecture
High-Level View of Some Scenarios
GSM Time Slot Structure
GSM Logical Channels
GSM Frame Structure
Low-Level View of Some Scenarios
GSM System Diagram& Protocol Stack
Different Between GSM and DCS 1800
Page-58
GSM
Location Updating Scenarios
Logical Channel
MS
BS
RACH
Channel Request
AGCH
Channel Assignment
Request for location updating. This is already
transmitted on the assigned channel
Authentication Request from the network
SDCCH
SDCCH
SDCCH
Authentication Response from the MS
SDCCH
Request to transmit in the ciphered mode
SDCCH
SDCCH
Acknowledgement of the ciphered mode
Confirmation of the location updating
including the optional assignment TMSI
Acknowledgement of the new location & the temporary identity
SDCCH
Channel Release from the network
SDCCH
Page-59
GSM/DCS1800 System (49)
GSM
Call Establishment Scenarios
Mobile Terminated Call
Logical Channel
PCH
RACH
AGCH
SDCCH
SDCCH
SDCCH
SDCCH
SDCCH
SDCCH
SDCCH
SDCCH
FACCH
FACCH
FACCH
FACCH
TCH
MS
BS
Paging of the MS
Channel Request
Channel Assignment
Answer to the paging from the network
Authentication Request from the network
Authentication Response from the MS
Request to transmit in the ciphered mode
Acknowledgement of the ciphered mode
Set up message for the incoming call
Confirmation
Assignment of a traffic channel
Acknowledgement of the traffic channel
Alerting (now the caller gets the ringing sound)
Connect message when the MS is off-hook
Acceptance of the connect message
Exchange of user data (speech)
GSM/DCS1800 System (50)
Page-60
GSM Logical Channels
• Logic Control Channel Structure
– Classify by call setup
BCH
(Broadcast Channel)
(Before Call Set-up)
CAC
(Common Access Channel)
CCCH
(Common Control Channel)
(During Call Set-up)
CCH
SDCCH
USC
SACCH
(User Specific Channel)
(After call set-up)
FACCH
BCCH
FCCH
SCH
PCH
RACH
AGCH
GSM/DCS1800 System (51)
Page-61
GSM/DCS1800 System
)
•
•
•
•
•
•
•
•
•
Some Histories & Some Background
GSM/DCS1800 System Architecture
High-Level View of Some Scenarios
GSM Time Slot Structure
GSM Logical Channels
GSM Frame Structure
Low-Level View of Some Scenarios
GSM System Diagram& Protocol Stack
Different Between GSM and DCS 1800
Page-62
GSM System Diagram
• GSM System Block Diagram
– Information Processing
– RF Baseband Processing
Speech
MS
Digitizing &
source coding
Source deconding
& D/A
Channel coding
Channel decoding
Interleaving
De-interleaving
Encryption
Decryption
Burst formatting
Burst deformatting
Modulation
Demodulation
Speech
MSC
Page-63
GSM/DCS1800 System (52)
GSM System Diagram
• Source (Speech) Coding
– Mobile Station (Analog Signal)
• Low-pass filter, then A/D converter, then RPE-LTP speech encoder
– MSC (Base Station) (Digital Signal)
• 8-bit A-law to 13-bit Uniform converter, then RPE-LTP speech encoder
Mobile Station
Analog Signal
Low-Pass Filter
13 kbps
A/D Converter
RPE-LTP Encoder
To
Channel Encoder
13 kbps
MSC
Digital Signal
13×8000=104 kbps
8bit A-law to 13bit
Uniform Converter
13 ×8000=104 kbps
GSM/DCS1800 System (53)
RPE-LTP Encoder
To
Channel Encoder
Page-64
GSM System Diagram
• Source (Speech) Coding
– Regular Pulse Excited Long-Term Prediction (RPE-LTP) Encoder
• Input has bit rate of 104 kbps
• Has net bit rate of 13 kbps
• Output from RPE-LTP 260 bits every 20 ms
bits
bitsper
per55ms
ms
Linear
LinearPrediction
PredictionCoding
Coding(LPC)
(LPC)filter
filter
Long
LongTerm
TermPrediction
Prediction(LTP)
(LTP)filter
filter
Excitation
ExcitationSignal
Signal
Total
Total
Class
ClassI I
99
47
47
Class
ClassIIII
Bits
Bitsper
per20
20ms
ms
36
36
36
36
188
188
260
260
182
182
(class
(classIa=50,
Ia=50,class
classIb=132)
Ib=132)
78
78
Page-65
GSM/DCS1800 System (54)
GSM System Diagram
RPE-LTP Speech Encoder
260
bits
50 bits
20 ms
Class I: 182 bits
53 bits
Cyclic Redundancy Encoder
132 bits
4 tail bits all equal to zero
185 bits
189 bits
1/2 Convolutional Encoder
Speech
& Channel
Coding
20 ms
378 bits
Class II: 78 bits
456
GSM/DCS1800 System (55)
bits
Page-66
GSM System Diagram
• Structure of Interleaver
– interleaving speech frames onto TDMA frame
Page-67
GSM/DCS1800 System (56)
GSM System Diagram
TCH/F9.6
• 9.6 Kbps refers to the user’s transmission rate, the actual rate is brought up to 12 Kbps through channel
coding in the terminal equipment; that is, 12 Kbps is the rate delivered to the MS.
User Information
240
bits
Add 4 “0” bits
20 ms
Data
& Channel
Coding (I)
1/2 Convolutional Encoder
488 coded bits
Puncturing of 32 coded bits
20 ms
456
GSM/DCS1800 System (57)
bits
Page-68
GSM System Diagram
Structure of Interleaver
• The blocks are spread over 22 bursts. Even though the interleaving covers 22 bursts, it is
referred to as a 19-bursts interleaving plan.
• 456 bits = 16 parts of 24 bits each (16× 24= 384) + 2 parts of 18 bits each (2×
18=36) + 2 parts of 12 bits each (2× 12=24) + 2 parts of 6 bits each (2× 6=12)
• A burst (time slots) contains information from either 5 or 6 consecutive data blocks;
that is, 4 parts of 24 bits each and 1 part of 18 bits (96 + 18 = 114) or 4 parts of
24 bits each and 1 part of 12 bits each and 1 part of6 bits each (96+12+6=114)
• 1st & 22nd burst contains 6 bits each (12 bits); 2nd & 21st burst contain 12 bits each
(24 bits); 3rd & 20th carry 18 bits each (36 bits) & we have 6 bursts. We need
another 16-burst. We then put 24 bits in each of the 4th~19the bursts (384 bits).
c
d
Data
& Channel
Coding (II)
Page-69
GSM/DCS1800 System (58)
GSM System Diagram
Channel Coding of Signaling Channels
• Signaling information contains a maximum of 184 bits. It does NOT make a difference whether the type of
signaling information to be transmitted is mapped onto a BCCH, PCH, SDCCH or SACCH. The format
always stays the same.
• Special format are reserved for the SCH & RACH
• FCCH requires no coding at all
Signaling Information
184
Signaling
& Channel
Coding (I)
bits
Block Encoder (Fire Code)
Fire coded adds 40 parity bits to the 184 bit
= 224 fire-coded bits, then adds 4 “0” bits
1/2 Convoluational Encoder
456
GSM/DCS1800 System (59)
bits
Page-70
GSM System Diagram
Structure of Interleaver
Bit
BitNumber
Numberofofthe
theCoded
CodedBits
Bits
00
11
22
Signaling
& Channel
Coding (II)
Position
Positionwithin
withinthe
theframe
framestructure
structure
8……448
8……448
9……449
9……449
10……450
10……450
Even
Evenbits
bitsofofburst
burstNN
Even
bit
of
burst
Even bit of burstN+1
N+1
Even
Evenbit
bitofofburst
burstN+2
N+2
33 11……451
11……451
44 12……452
12……452
55 13……453
13……453
66 14……454
14……454
Even
Evenbit
bitofofburst
burstN+3
N+3
Odd
Oddbits
bitsofofburst
burstN+4
N+4
77 15……455
15……455
Odd
Oddbits
bitsofofburst
burstN+7
N+7
Odd
Oddbits
bitsofofburst
burstN+5
N+5
Odd
bits
of
burst
Odd bits of burstN+6
N+6
GSM/DCS1800 System (60)
Page-71
GSM System Diagram
GMSK
• is a constant-envelop variety of modulation & it lacks of AM in the carrier with a
consequent limiting of the occupied bandwidth.
• The constant amplitude of the GMSK signal makes it suitable for use with high-efficiency
amplifiers.
Modulation (I)
GSM/DCS1800 System (61)
Page-72
GSM Protocol Stack
MS
Layer
3
BTS
BSC
CM
CM
MM
MM
RR
RR
RR
BTSM
BTSM
LAPDm
LAPDm
LAPD
LAPD
Layer 1
Layer 1
Layer 1
Layer 1
Um
Abis
Signaling Architecture
MSC
BSSMAP
DTAP
BSSMAP/
DTAP
SCCP
SCCP
MTP
MTP
General View
of GSM protocol
A
Page-73
GSM/DCS1800 System (62)
GSM Protocol Stack
Responsibilities of LAPD/LAPDm
• Organization of Layer 3 information into frames
• Peer-to-peer transmission of signaling data in defined frame formats
• Recognition of frame formats
• Establishment, maintenance & termination of one or more data links on signaling channels
• (Un)Acknowledgement of transmission & reception of numbered information frames (Iframes)
• Unacknowledge transmission & reception of unnumbered information frames (UI-frames)
GSM protocol
(I)
Layer 2
(Data Link Layer)
GSM/DCS1800 System (63)
Page-74
GSM Protocol Stack
Layer 2 (Data Link Layer)
Format A
Format B
Address Field
(variable length)
Address Field
(variable length)
Control Field
(8 bits)
Control Field
(8 bits)
Length Indication
(variable length)
Fill Field
(variable length)
Length Indication Information Field
Fill Field
(variable length) (variable length) (variable length)
GSM protocol
(II)
Frames Format
• 4 types of formats: A, B, Abis, Bbis
• The bis designation is sometimes written as a prime mark (Abis = A’)
Page-75
GSM/DCS1800 System (64)
GSM Protocol Stack
Layer 2 (Data Link Layer)
Format Abis
Format Bbis
Length Indication (variable length)
Length Indication
(variable length)
Fill Field (variable length)
Information Field
(variable length)
Fill Field
(variable length)
GSM protocol
(III)
Frames Format
• 4 types of formats: A, B, Abis, Bbis
• The bis designation is sometimes written as a prime mark (Abis = A’)
GSM/DCS1800 System (65)
Page-76
GSM Protocol Stack
Network Layer
• Also referred to as the “signaling layer”
• Use a protocol that contains all the functions & details necessary to establish, maintain & then
terminate mobile connections for all the services offered within a GSM.. The network layer also
provides control functions to support additional services such as supplementary services & short
message services
3 sub-layers
• Radio Resource Management (RR)
• Mobility Management (MM)
• Connection Management (CM)
GSM protocol
(IV)
Layer 3 (Network Layer)
Page-77
GSM/DCS1800 System (66)
GSM Protocol Stack
Radio Resource Management sub-layer (RR sub-layer) is responsible for
• The management of the frequency spectrum
• The GSM’s reactions to the changing radio environment
• Everything related to maintaining a clear channel between the system and the MS
• Handoff from one cell to another
Procedures for the RR sub-layer used to cover these tasks
• Channel assignment
• Channel release
• Channel change & handoff procedure
• Change of channel frequencies, hopping sequences (hopping
algorithms) and frequency tables
• Measurement reports from the MS
• Power control and timing advance
• Cipher mode setting
GSM protocol
(V)
Layer 3 (Network Layer)
GSM/DCS1800 System (67)
Page-78
GSM Protocol Stack
Mobility Management sub-layer (MM sub-layer) is responsible for
• cope with all the effects of handling a mobile user that are not directly related to the radio
function such as
• Support of user mobility, registration, and management of mobility data
• Checking the user and equipment identity
• Checking if the user is allowed to use the services and what kind of extra services are
allowed
• Support of user confidentiality (registering the user under a TMSI)
• Provision of user security
• Provision of an MM connection to the CM sublayer
Procedures for the MM sub-layer used to cover these tasks
• Location Update procedure
• Periodic updating
• authentication procedure
• IMSI attach & detach procedure.
• TMSI reallocation procedure
• Identification procedure
GSM protocol
(VI)
Layer 3 (Network Layer)
Page-79
GSM/DCS1800 System (68)
GSM Protocol Stack
Connection Management sub-layer (CM sub-layer) is responsible for
• It manages all the functions necessary for circuit-switched call control & there are other
entities within the CM sub-layer to cope with providing supplementary services & SMS
Procedures for the CM sub-layer used to cover these tasks
• Call establishment procedures for mobile-originated calls
• Call establishment procedure for mobile-terminated call
• Changes of transmission mode during an ongoing call (incall
modification)
• Call reestablishment after interruption of an MM connection
• Dual-tone Multi-frequency (DTMF) control procedure for DTMF
transmission.
GSM protocol
(VII)
Layer 3 (Network Layer)
GSM/DCS1800 System (69)
Page-80
GSM Protocol Stack
Layer 3 (Network Layer) Message Structure
Double Check the frame format ???
TI flag
(1 bit)
TI
(3 bits)
Protocol
Discriminator
(4 bits)
0
(1 bit)
Message Type
(7 bits)
Information Elements
“Mandatory”
(variable bytes)
Information Elements
“Optional”
(variable bytes)
TI:: Transaction Identifier
GSM protocol
(VIII)
Page-81
GSM/DCS1800 System (70)
GSM Protocol Stack
Layer 3 (Network Layer) Message Structure
TI flag
(1 bit)
TI
(3 bits)
Protocol
Discriminator
(4 bits)
0
(1 bit)
Message Type
(7 bits)
Information Elements
“Mandatory”
(variable bytes)
Information Elements
“Optional”
(variable bytes)
It is used to distinguish between (possible) multiple parallel CM
connections and between the various transactions taking place over
these simultaneous CM connections
GSM protocol
(IX)
GSM/DCS1800 System (71)
Page-82
GSM Protocol Stack
Layer 3 (Network Layer) Message Structure
TI flag
(1 bit)
TI
(3 bits)
Protocol
Discriminator
(4 bits)
PProrototoccool l
RRaaddioioRRees soouurcrceeMMggmmt t
MMoobbility
ilityMMggmmt t
CCaallllCCoonntro
trol l
SShhoortrtMMees ss saaggeeSServ
ervicicee
SSuupppplelemmeenntataryrySSeervrvicicee
Te
Tes st tPProrocceedduurere
AAllllooththeer rvvaalulueeaarereres
reseervrved
ed
0
(1 bit)
Message Type
(7 bits)
Information Elements
“Mandatory”
(variable bytes)
PProrototoccool lDDisisccrim
rimininaatotor r
0011
1100
00110011
000011
11
11000011
110011
11
1111
1111
Information Elements
“Optional”
(variable bytes)
GSM protocol
(X)
Page-83
GSM/DCS1800 System (72)
GSM Protocol Stack
Layer 3 (Network Layer) Message Structure
TI flag
(1 bit)
TI
(3 bits)
Protocol
Discriminator
(4 bits)
0
(1 bit)
Message Type
(7 bits)
Information Elements
“Mandatory”
(variable bytes)
• It indicates the function of the Layer 3 message
• Uses only low 6 bits for addressing 64 different
message in a protocol, another bit is used a send
sequence variable & may be used for MM and CM
messages
GSM/DCS1800 System (73)
Information Elements
“Optional”
(variable bytes)
GSM protocol
(XI)
Page-84
GSM Protocol Stack
Layer 3 (Network Layer) Message Structure
TI flag
(1 bit)
TI
(3 bits)
Protocol
Discriminator
(4 bits)
0
(1 bit)
Message Type
(7 bits)
Information Elements
“Mandatory”
(variable bytes)
There are 4 possible combination of Information Element
• Mandatory fixed length
• Mandatory variable length
• Optional fixed length
• Optional variable length
Information Elements
“Optional”
(variable bytes)
GSM protocol
(XII)
Page-85
GSM/DCS1800 System (74)
GSM Protocol Stack
Layer 3 (Network Layer)
Example of a Call Establishment Sequence
M S Transm its
C hannel R equest
C onnectio n M ana ge m ent
Service R eq uest
A uthentication R esponse
C ip he ring M ode C o m plete
Setup
Assignm ent C om plete
C onnect A cknow led ge
Ö
Õ
Ö
Õ
Ö
Õ
Ö
Ö
Õ
Õ
Ö
Õ
Õ
Ö
N etw ork Transm its
Im m ed iate Assignm ent
A uthentication R eq uest
C ip he ring M ode C o m ma nd
C all proceed ing
Assignm ent com ma nd
GSM protocol
(XIII)
A lerting
C onnect
GSM/DCS1800 System (75)
Page-86
Digital Cellular System (DCS)-1800
• General Description
– As a European ETSI standard for PCN
– Based on GSM technology but configured around a hand-portable
• Based on GSM technology to overcomes the development problems
• Lower power mobile station & smaller cell size
– cell radius ≤ 1 km in a dense urban environment
– cell radius ≤ 5 km in the rural environment
Page-87
GSM/DCS1800 System (76)
Digital Cellular System (DCS)-1800
• Technical Description
– The allocated bandwidth
• 1710~1880 MHz providing 75 MHz duplex bands with a 20 MHz spacing
• The BTS links to the BSC may use 38 GHz radio to avoid laying costly
underground cable links
– Mobile and Base Station Power Class
Class
Class
II
IIII
Max.
Max.RF
RFPower
Power(W)
(W)
11
0.25
0.25
CCl al as ss s
II
I II I
I II II I
IV
IV
Mobile Station
MMa axx. .RRFF PPoowwe er r( W
( W) )
2200~~ ( ≤
( ≤4400) )
1100~~ ( ≤
( ≤2200) )
55~~ ( ≤
( ≤1100) )
22.5.5~~ ( ≤
( ≤55) )
Base Station
GSM/DCS1800 System (77)
Page-88
Digital Cellular System (DCS)-1800
• DCS1800 vs. GSM
– DCS-1800 provides a maximum of 375 radio channels compared to 124
for GSM-900
– DCS-1800 is designed to support hand-portable terminal with a transmit
power not exceeding 1 W
Page-89
GSM/DCS1800 System (78)
GSM/DCS 1800 in Taiwan
@F”@gš
@F”@gš
Äe”Õ
Äe”Õ
ój 拔ò
ój 拔ò
òñ”Õ
òñ”Õ
Քò
Քò
6!”Õ
6!”Õ
6!”Õ
6!”Õ
òñ”Õ
òñ”Õ
6Քò
6Քò
h\”Õ
h\”Õ
í3Kh
í3Kh
»K
»K
»K
»K
»K
»K
»K
»K
»K
»K
>K
>K
ÄK
ÄK
ûK
ûK
>K
>K
ÄK
ÄK
ûK
ûK
݋*„
݋*„
Çï
Çï
AMPS
AMPS
GSM
GSM900
900
090,
090,091
091
0932,
0932,0933
0933
DCS
DCS1800
1800
DCS
DCS1800
1800
0937
0937
0935
0935
DCS
DCS1800
1800
DCS
1800
DCS 1800
0936
0936
09380
09380~~09383
09383
DCS
DCS1800
1800
DCS
DCS1800
1800
09384
09384~~09386
09386
09387
09387~~90389
90389
GSM
GSM900
900
GSM
GSM900
900
09310
09310~~09313
09313
09314
09314~~09316
09316
GSM
GSM900
900
09317
09317~~09319
09319
GSM/DCS1800 System (79)
Page-90