Gsm
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GSM • Example of a PLMN (Public Land Mobile Network) • At present most successful cellular mobile system (over 200 million subscribers worldwide) • Digital (2nd Generation) cellular mobile system operating in several frequency bands (GSM 900, GSM 1800 = DCS 1800, GSM 1900 = PCS 900) • ETSI Specifications ( www.etsi.org ) • Future evolution ?
GSM Course requirements: ”Understanding Telecommunications” book by Ericsson (Part D – PLMN) + supporting material (= these slides)
GPRS Course requirements: ”GPRS: Architecture, Protocols, and Air Interface” article available at www.comsoc.org/pubs/surveys/3q99issue/bettstetter.html If you have problems obtaining this article, please contact the course assistant (Mika Nupponen)
Digital PLMN systems (status 2000) 2nd Generation
3rd Generation IMT-2000 UMTS WCDMA
GSM GPRS EDGE
TDD
IS-136 USA IS-95
CDMA 2000
4th Generation
Digital PLMN systems GSM – Global System for Mobile communications: (FDMA/)TDMA-based system specified by ETSI Several evolution steps towards 3rd generation systems: HSCSD – High Speed Circuit Switched Data (possibility of combining up to 4 time slots for a data connection) GPRS – General Packet Radio Service (packet switching overlay on TDMA radio access network) EDGE – Enhanced Data rates for GSM Evolution (change at the air interface: 8 PSK modulation as in UMTS) IS-95 – American CDMA system IS-136 – American TDMA system
UMTS – Universal Mobile Telecommunications System UTRA FDD mode (UMTS Terrestrial Radio Access, Frequency Division Duplex mode) Ø W-CDMA UTRA TDD mode CDMA2000 – American 3rd Generation CDMA system
IMT-2000 – International Mobile Telecommunications (ITU) Other wireless systems & networks: DECT (no roaming), TETRA (not public), HIPERLAN et al., UPT concept, GPS, mobile satellite systems …
GSM system architecture BSS
NSS MS
GMSC
BSC MSC
SIM
VLR BTS MS HLR
NMS BTS
MS
OMC
AC EIR
MS
database
GSM: circuit switched connections BSS
NSS GMSC
BSC MSC MS
VLR HLR
MS
BTS
AC EIR
GPRS: packet switched connections BSS
NSS GMSC
BSC PCU MS
MSC VLR SGSN
BTS
HLR AC EIR
MS GGSN
UMTS network architecture Radio access network UTRAN RNC
MS Uu
Iu CS VLR
Iur Iub BS
GMSC
MSC
BS
MS
MS
Core network (GSM/GPRS-based)
HLR RNC
SGSN
AC
Iu PS Gn
GGSN
EIR
IMT-2000 / UMTS: RNS (access network)
Core network (GSM-based) RNC
MS
MSC
BS
GMSC
VLR HLR
MS BS
RNC
SGSN
AC EIR
MS
GGSN MS
Radio interface aspects • • • • •
Radio access techniques (FDMA / TDMA / CDMA) Physical / logical channel structure / GSM ”burst” Modulation method (GMSK, 8-PSK) Source coding / channel coding / interleaving Radio channel estimation & equalization techniques (constructive use of the multipath channel) • Diversity techniques • Circuit vs. packet switched access • Protocols: random access, power control, handover (with associated measurement procedures)
Radio interface – access techniques frequency
Time division time
code nr.
Frequency division
Code division
Radio interface - physical channels TS0
Typically used for signaling
TS1
Carrier 0
T S S T T T T T T S S T
Carrier 1
T T T T T T T T T T T T TS2
TS2
Carrier 2
T T T T T T T T T T T T
Carrier 3
T T T T T T T T T T T T Frame of length 8 time slots
Radio interface – logical channels Traffic channels
TCH/F TCH/H
Control channels (for signaling)
Broadcast SCH
Common control PCH
Dedicated SDCCH
AGCH bidirectional downlink uplink
FCCH BCCH
SACCH RACH
FACCH
GPRS channel structure TS0 Carrier 0
Carrier 1
Used for GSM signaling
TS1
T S S T T T T T T S S T T T T T
T T T
PDCH:s for GPRS use (for example) Carrier 2
T T T T
T T T
PBCCH – Packet Broadcast Control Channel (optional) PCCCH – Packet Common Control Channel (optional) PDTCH – Packet Data Traffic Channel Also, PACCH and PTCCH possible
GSM/GPRS channel allocation example TS7
Only for GPRS Dynamical allocation (circuit switched GSM channels are given higher priority)
TS0 time (observation intervals)
Allocation schemes are network operator dependent
GSM radio interface GSM normal burst: 156.25 bits (0.577 ms) 3
57 encrypted bits
1 26 training bits
1
57 encrypted bits
3
8.25
TDMA frame (4.615 ms): TS7 TS0 TS1 TS2 TS3 TS4 TS5 TS6 TS7 TS0 TS1
TDMA multiframe: 1
2
3
4
5
SACCH 6
7
8
9
10 11 12 13 14 15
Idle = 26 TDMA frames / 51 TDMA frames
23 24 25 26
GSM speech encoding Voice coding: 260 bits in 20 ms blocks (13 kbit/s) 260 bits
MS - BSC
260 bits
Channel coding: 456 coded bits (22.8 kbit/s)
MS - BTS
456 bits
Interleaving: 8 x 57 bits (22.8 kbit/s) 57 bits
57 bits
57 bits
bits 4, 12, 20, 28, 36, 44, etc. from the 456 bit frame
GSM signaling message encoding Signalling message in (split into) block(s) of 184 bits: 184 bits
Each block is coded into 456 bits (22.8 kbit/s) 456 bits
Interleaving: 8 x 57 bits (22.8 kbit/s) 57 bits
57 bits
57 bits
bits 4, 12, 20, 28, 36, 44, etc. from the 456 bit frame
GPRS packet encoding FH
For instance, segment of IP packet
Segment BH
Segment Info
Segment BCS
….
T
Interleaving: 8 x 57 bits (22.8 kbit/s) 57 bits
LLC frame
Segment
RLC block
Convolutional encoding into 456 bits
57 bits
FCS
57 bits
bits 4, 12, 20, 28, 36, 44, etc. from the 456 bit frame
GSM protocols (MS Ø MSC) Um
Abis
A
CM
CM
MM
MM DTAP
RR
RR RR
BTSM
BTSM
LAPDm
LAPDm
LAPD
Radio
Radio
64 kb/s
MS
BTS
BSSMAP BSSAP BSSAP
LAPD
SCCP MTP
SCCP MTP
64 kb/s
64 kb/s
64 kb/s
BSC
MSC
GPRS protocols (user plane) Um
Gb
Gn
IP/X.25
IP/X.25
SNDCP
SNDCP
GTP
GTP
LLC
LLC
TCP
TCP
RLC
RLC
BSSGP
BSSGP
IP
IP
MAC
MAC
NS
NS
L2
L2
Radio
Radio
L1bis
L1bis
L1
L1
MS
BSS
SGSN
GGSN
GSM signaling at ”layer 3” RR (Radio Resource management) • Access and initial assignment (reserving a SDCCH) • Handover management MM (Mobility Management) • Registration (MS power switch on) • Location updating (MS moves to another location area) • Authentication CM (Call control Management) • Signaling for setting up and releasing circuit switched connections (very similar to DSS 1 in N-ISDN)
Connectivity ”modes” in GSM and GPRS GSM: Disconnected Idle Connected
MS is switched off (circuit mode) location updates are performed handovers in c.s. connection
GPRS: Idle Standby Ready
MS is switched off (packet mode) location updates on a larger basis location updates on cell-by-cell basis
Random access in GSM / GPRS No communication between MS and network can be started without first using the random access procedure in • network originated activity (paging, e.g. for MTC) • MS originated activity (MOC, location updating, registration, de-registration at power switch-off) 1) MS sends a short access burst over the RACH (uplink), (Slotted Aloha, collision possibility Ø retransmission) 2) Network (BSC) returns ”permission” message including: - allocated channel (frequency, time slot) - timing advance for correct time slot alignment
Important identifiers in GSM IMSI – International Mobile Subscriber Identity (global) TMSI – Temporary Mobile Subscriber Identity (local and temporary) LAI – Location Area Identity (global) MSISDN – Mobile Subscriber ISDN number (address of subscriber HLR database) PIN – Personal Identification Number (only within MS) IMEI – International Mobile Equipment Identity (global) Temporary, local numbers for routing (MSRN, HON …)
Case study: location updating (1) MS SIM LAI TMSI
VLR 2 LAI
VLR 1 LAI TMSI Ø IMSI
HLR IMSI LAI => VLR 1
Last LAI and TMSI stored in SIM. MS monitors broadcast LAI. LAI matching => everything ok !
Case study: location updating (2) VLR 1 MS SIM LAI TMSI
LAI TMSI Ø IMSI
HLR IMSI LAI => VLR 1
VLR 2 LAI
LAI different => location update needed !
Case study: location updating (3) VLR 1 MS SIM LAI TMSI
LAI TMSI Ø IMSI
HLR IMSI LAI => VLR 1
VLR 2 LAI LAI TMSI
SIM sends old LAI and TMSI to VLR 2 But, VLR 2 does not know IMSI!
Case study: location updating (4) VLR 1 MS SIM LAI TMSI
LAI TMSI Ø IMSI LAI => VLR 2
HLR IMSI LAI => VLR 1 LAI => VLR 2 TMSI
VLR 2 LAI LAI TMSI
VLR 2 sends new LAI to VLR 1 which in turn updates the HLR
Case study: location updating (5) VLR 1 MS SIM LAI TMSI
LAI
HLR IMSI LAI => VLR 2
VLR 2 LAI LAI TMSI Ø IMSI
HLR sends IMSI to VLR 2 and cancels subscriber data in VLR 1
Case study: location updating (6) VLR 1 MS SIM LAI TMSI
VLR 2 LAI TMSI Ø IMSI
LAI
HLR IMSI LAI – VLR 2 Important information for MTC (see below)
VLR 2 sends new TMSI to MS (SIM). MS also updates LAI. Compare with slide (1). Location update successful!
Case study: mobile terminated call (1) (mobile terminated call = MTC) GMSC MS
MSC
SIM
VLR 2
LAI TMSI
LAI TMSI => IMSI
MSISDN HLR MSISDN => IMSI LAI => VLR 2
MTC directed through PSTN to GMSC using MSISDN. GMSC contacts HLR (MSISDN is in fact the address of the register location of the subscriber with given IMSI)
Case study: mobile terminated call (2) GMSC MS
MSC
SIM
VLR 2
LAI TMSI
LAI TMSI => IMSI
MSISDN LAI => VLR 2 HLR MSISDN => IMSI LAI => VLR 2
HLR returns to GMSC the current LAI of called mobile subscriber. The GMSC can now route the call to the MSC serving the subscriber
Case study: mobile terminated call (3) GMSC MS
MSC
SIM
VLR 2
LAI TMSI
LAI TMSI => IMSI
HLR IMSI LAI => VLR 2
The MSC broadcasts a paging message (including TMSI) within the location area defined by LAI
Case study: mobile terminated call (4) GMSC MS
MSC
SIM
VLR 2
LAI TMSI
LAI TMSI => IMSI
HLR IMSI LAI => VLR 2
Only the mobile subscriber with the correct TMSI reacts to the paging. A connection between MS and MSC is established and the call set-up is completed.
GSM Course requirements: ”Understanding Telecommunications” book by Ericsson (Part D – PLMN) + supporting material (= these slides)
GPRS Course requirements: ”GPRS: Architecture, Protocols, and Air Interface” article available at www.comsoc.org/pubs/surveys/3q99issue/bettstetter.html If you have problems obtaining this article, please contact the course assistant (Mika Nupponen)
Digital PLMN systems (status 2000) 2nd Generation
3rd Generation IMT-2000 UMTS WCDMA
GSM GPRS EDGE
TDD
IS-136 USA IS-95
CDMA 2000
4th Generation
Digital PLMN systems GSM – Global System for Mobile communications: (FDMA/)TDMA-based system specified by ETSI Several evolution steps towards 3rd generation systems: HSCSD – High Speed Circuit Switched Data (possibility of combining up to 4 time slots for a data connection) GPRS – General Packet Radio Service (packet switching overlay on TDMA radio access network) EDGE – Enhanced Data rates for GSM Evolution (change at the air interface: 8 PSK modulation as in UMTS) IS-95 – American CDMA system IS-136 – American TDMA system
UMTS – Universal Mobile Telecommunications System UTRA FDD mode (UMTS Terrestrial Radio Access, Frequency Division Duplex mode) Ø W-CDMA UTRA TDD mode CDMA2000 – American 3rd Generation CDMA system
IMT-2000 – International Mobile Telecommunications (ITU) Other wireless systems & networks: DECT (no roaming), TETRA (not public), HIPERLAN et al., UPT concept, GPS, mobile satellite systems …
GSM system architecture BSS
NSS MS
GMSC
BSC MSC
SIM
VLR BTS MS HLR
NMS BTS
MS
OMC
AC EIR
MS
database
GSM: circuit switched connections BSS
NSS GMSC
BSC MSC MS
VLR HLR
MS
BTS
AC EIR
GPRS: packet switched connections BSS
NSS GMSC
BSC PCU MS
MSC VLR SGSN
BTS
HLR AC EIR
MS GGSN
UMTS network architecture Radio access network UTRAN RNC
MS Uu
Iu CS VLR
Iur Iub BS
GMSC
MSC
BS
MS
MS
Core network (GSM/GPRS-based)
HLR RNC
SGSN
AC
Iu PS Gn
GGSN
EIR
IMT-2000 / UMTS: RNS (access network)
Core network (GSM-based) RNC
MS
MSC
BS
GMSC
VLR HLR
MS BS
RNC
SGSN
AC EIR
MS
GGSN MS
Radio interface aspects • • • • •
Radio access techniques (FDMA / TDMA / CDMA) Physical / logical channel structure / GSM ”burst” Modulation method (GMSK, 8-PSK) Source coding / channel coding / interleaving Radio channel estimation & equalization techniques (constructive use of the multipath channel) • Diversity techniques • Circuit vs. packet switched access • Protocols: random access, power control, handover (with associated measurement procedures)
Radio interface – access techniques frequency
Time division time
code nr.
Frequency division
Code division
Radio interface - physical channels TS0
Typically used for signaling
TS1
Carrier 0
T S S T T T T T T S S T
Carrier 1
T T T T T T T T T T T T TS2
TS2
Carrier 2
T T T T T T T T T T T T
Carrier 3
T T T T T T T T T T T T Frame of length 8 time slots
Radio interface – logical channels Traffic channels
TCH/F TCH/H
Control channels (for signaling)
Broadcast SCH
Common control PCH
Dedicated SDCCH
AGCH bidirectional downlink uplink
FCCH BCCH
SACCH RACH
FACCH
GPRS channel structure TS0 Carrier 0
Carrier 1
Used for GSM signaling
TS1
T S S T T T T T T S S T T T T T
T T T
PDCH:s for GPRS use (for example) Carrier 2
T T T T
T T T
PBCCH – Packet Broadcast Control Channel (optional) PCCCH – Packet Common Control Channel (optional) PDTCH – Packet Data Traffic Channel Also, PACCH and PTCCH possible
GSM/GPRS channel allocation example TS7
Only for GPRS Dynamical allocation (circuit switched GSM channels are given higher priority)
TS0 time (observation intervals)
Allocation schemes are network operator dependent
GSM radio interface GSM normal burst: 156.25 bits (0.577 ms) 3
57 encrypted bits
1 26 training bits
1
57 encrypted bits
3
8.25
TDMA frame (4.615 ms): TS7 TS0 TS1 TS2 TS3 TS4 TS5 TS6 TS7 TS0 TS1
TDMA multiframe: 1
2
3
4
5
SACCH 6
7
8
9
10 11 12 13 14 15
Idle = 26 TDMA frames / 51 TDMA frames
23 24 25 26
GSM speech encoding Voice coding: 260 bits in 20 ms blocks (13 kbit/s) 260 bits
MS - BSC
260 bits
Channel coding: 456 coded bits (22.8 kbit/s)
MS - BTS
456 bits
Interleaving: 8 x 57 bits (22.8 kbit/s) 57 bits
57 bits
57 bits
bits 4, 12, 20, 28, 36, 44, etc. from the 456 bit frame
GSM signaling message encoding Signalling message in (split into) block(s) of 184 bits: 184 bits
Each block is coded into 456 bits (22.8 kbit/s) 456 bits
Interleaving: 8 x 57 bits (22.8 kbit/s) 57 bits
57 bits
57 bits
bits 4, 12, 20, 28, 36, 44, etc. from the 456 bit frame
GPRS packet encoding FH
For instance, segment of IP packet
Segment BH
Segment Info
Segment BCS
….
T
Interleaving: 8 x 57 bits (22.8 kbit/s) 57 bits
LLC frame
Segment
RLC block
Convolutional encoding into 456 bits
57 bits
FCS
57 bits
bits 4, 12, 20, 28, 36, 44, etc. from the 456 bit frame
GSM protocols (MS Ø MSC) Um
Abis
A
CM
CM
MM
MM DTAP
RR
RR RR
BTSM
BTSM
LAPDm
LAPDm
LAPD
Radio
Radio
64 kb/s
MS
BTS
BSSMAP BSSAP BSSAP
LAPD
SCCP MTP
SCCP MTP
64 kb/s
64 kb/s
64 kb/s
BSC
MSC
GPRS protocols (user plane) Um
Gb
Gn
IP/X.25
IP/X.25
SNDCP
SNDCP
GTP
GTP
LLC
LLC
TCP
TCP
RLC
RLC
BSSGP
BSSGP
IP
IP
MAC
MAC
NS
NS
L2
L2
Radio
Radio
L1bis
L1bis
L1
L1
MS
BSS
SGSN
GGSN
GSM signaling at ”layer 3” RR (Radio Resource management) • Access and initial assignment (reserving a SDCCH) • Handover management MM (Mobility Management) • Registration (MS power switch on) • Location updating (MS moves to another location area) • Authentication CM (Call control Management) • Signaling for setting up and releasing circuit switched connections (very similar to DSS 1 in N-ISDN)
Connectivity ”modes” in GSM and GPRS GSM: Disconnected Idle Connected
MS is switched off (circuit mode) location updates are performed handovers in c.s. connection
GPRS: Idle Standby Ready
MS is switched off (packet mode) location updates on a larger basis location updates on cell-by-cell basis
Random access in GSM / GPRS No communication between MS and network can be started without first using the random access procedure in • network originated activity (paging, e.g. for MTC) • MS originated activity (MOC, location updating, registration, de-registration at power switch-off) 1) MS sends a short access burst over the RACH (uplink), (Slotted Aloha, collision possibility Ø retransmission) 2) Network (BSC) returns ”permission” message including: - allocated channel (frequency, time slot) - timing advance for correct time slot alignment
Important identifiers in GSM IMSI – International Mobile Subscriber Identity (global) TMSI – Temporary Mobile Subscriber Identity (local and temporary) LAI – Location Area Identity (global) MSISDN – Mobile Subscriber ISDN number (address of subscriber HLR database) PIN – Personal Identification Number (only within MS) IMEI – International Mobile Equipment Identity (global) Temporary, local numbers for routing (MSRN, HON …)
Case study: location updating (1) MS SIM LAI TMSI
VLR 2 LAI
VLR 1 LAI TMSI Ø IMSI
HLR IMSI LAI => VLR 1
Last LAI and TMSI stored in SIM. MS monitors broadcast LAI. LAI matching => everything ok !
Case study: location updating (2) VLR 1 MS SIM LAI TMSI
LAI TMSI Ø IMSI
HLR IMSI LAI => VLR 1
VLR 2 LAI
LAI different => location update needed !
Case study: location updating (3) VLR 1 MS SIM LAI TMSI
LAI TMSI Ø IMSI
HLR IMSI LAI => VLR 1
VLR 2 LAI LAI TMSI
SIM sends old LAI and TMSI to VLR 2 But, VLR 2 does not know IMSI!
Case study: location updating (4) VLR 1 MS SIM LAI TMSI
LAI TMSI Ø IMSI LAI => VLR 2
HLR IMSI LAI => VLR 1 LAI => VLR 2 TMSI
VLR 2 LAI LAI TMSI
VLR 2 sends new LAI to VLR 1 which in turn updates the HLR
Case study: location updating (5) VLR 1 MS SIM LAI TMSI
LAI
HLR IMSI LAI => VLR 2
VLR 2 LAI LAI TMSI Ø IMSI
HLR sends IMSI to VLR 2 and cancels subscriber data in VLR 1
Case study: location updating (6) VLR 1 MS SIM LAI TMSI
VLR 2 LAI TMSI Ø IMSI
LAI
HLR IMSI LAI – VLR 2 Important information for MTC (see below)
VLR 2 sends new TMSI to MS (SIM). MS also updates LAI. Compare with slide (1). Location update successful!
Case study: mobile terminated call (1) (mobile terminated call = MTC) GMSC MS
MSC
SIM
VLR 2
LAI TMSI
LAI TMSI => IMSI
MSISDN HLR MSISDN => IMSI LAI => VLR 2
MTC directed through PSTN to GMSC using MSISDN. GMSC contacts HLR (MSISDN is in fact the address of the register location of the subscriber with given IMSI)
Case study: mobile terminated call (2) GMSC MS
MSC
SIM
VLR 2
LAI TMSI
LAI TMSI => IMSI
MSISDN LAI => VLR 2 HLR MSISDN => IMSI LAI => VLR 2
HLR returns to GMSC the current LAI of called mobile subscriber. The GMSC can now route the call to the MSC serving the subscriber
Case study: mobile terminated call (3) GMSC MS
MSC
SIM
VLR 2
LAI TMSI
LAI TMSI => IMSI
HLR IMSI LAI => VLR 2
The MSC broadcasts a paging message (including TMSI) within the location area defined by LAI
Case study: mobile terminated call (4) GMSC MS
MSC
SIM
VLR 2
LAI TMSI
LAI TMSI => IMSI
HLR IMSI LAI => VLR 2
Only the mobile subscriber with the correct TMSI reacts to the paging. A connection between MS and MSC is established and the call set-up is completed.
