Mobile Signaling Overview

GSM Signaling Overview
] GSM signaling defines the communications between the mobile and
the network
] Signaling has to be carried through the network and across the air-
interface to the mobile
] Different protocols are used across different interfaces
] All GSM signaling is based on the Open Systems Interconnect (OSI)
model used for computer systems
] The MSC uses ITU’s Signaling System No:7, (SS7 or CCS7) for all its
signaling; to the BSC, HLR, VLR and to other networks
] The Air-interface and A-bis signaling is based on ISDN Link Access
Protocol (LAP-D and LAP-Dm)
] Signaling channels are integrated into the air-interface as the BCCH,
PCH, AGCH, SDCCH, SACCH and FACCH
] Signaling across all interfaces is specified in the standards to allow
different equipment manufacturers for each unit

TWS Proprietary - www.tws -inc.com - (770) 752-7033

Mobile Signaling
] When the mobile is first switched on it is under
the control of its’ own internal algorithms.
] It performs the following sequence:
c Search for GSM frequencies
c Find a FCCH and synchronize frequency
c Find a SCH and synchronize time
c Listen for a BCCH and download information
about the system
c Download idle neighbor list and make
measurements
c Select a “best server” and camp on it
c If the user wants to make a call, the mobile has to
signal to the network.
c It does this by sending a “service request” to the
network on the RACH.


GSM SIGNALLING
Switching
System
VLR AC NSS
MAP MAP
MAP MAP
VLR HLR EIR
MAP MAP
MSC ISUP
GMSC PSTN
TUP
BSSAP

Base Station
BSC System (BSS) PLMN
LAPD (GSM) ISDN

BTS SS7 User Parts:
•MAP: SS7, Mobile Application Part
LAPDm •BSSAP: SS7, Base Station Sub-System Application Part
MS •ISUP: SS7, International Subscriber User Part
•TUP: SS7, Telephone User Part
LAPD: ISDN, Link Access Protocol Version “D”


GSM Signaling
Open Systems Interconnect uses “layers” where only layer 1, the physical
layer is actually physically connected between devices. Messages are sent
between devices by handing them down to lower layers from transmission
across the physical interface.

OSI - Model GSM Equivalent
7 APPLICATION USER
6 PRESENTATION TASKS

5 SESSION

4 TRANSPORT

3 NETWORK
NETWORK Network Messages
GSM
2 DATA LINK
DATA LINK Framing / Addressing NETWORK
PHYSICAL Coding / Modulation TASKS
1 PHYSICAL


OSI Layers

Layer 3 Network Layer :
Carries signaling messages, for getting the message to
Layer 3 Layer 3 its destination. Provides connection oriented
(dedicated signaling link) or connectionless services
(packet-type signaling). Example: Radio Resource
message sent from MSC to BSC.

Layer 2 Layer 2 Layer 2 Data Link Layer :
Transfers frames error free between nodes. Concerned
with error detection, framing, re-transmission Example:
LAPD protocol on A-bis between BSC and BTS.

Layer 1 Layer 1 Layer 1 Physical Layer:
Transmits all information across the physical medium.
Specifies the physical medium used: mechanical,
Information Flow electrical, functional and procedural characteristics.
Example: GMSK modulation on an RF carrier for the
Air-interface between the BTS and the MS


Signaling Layers for the Air Interface
Layer 1: Functions required to transfer bit steams over physical
TDMA / FDMA channels:
j Ciphering
j Setting of timing advance & TX power
j Channel Coding
j Mapping of logical channels onto physical channels

Layer 2: Provides a reliable signaling link between MS and the
network. Protocol is based on the LAPDm of ISDN
j Framing
j Addressing
j Error correction

Layer 3: Takes care of the main control of the MS -network
procedures. It is split into 3 sublayers:
j Radio Resource Management
j Mobility Management
j Connection Management


Speech
Air-interface Layers Speech
User Data
User Data

Signaling OSI layer 3 Network Functions
Signaling

OSI layer 2 Data link functions

Builds frames, requests
acknowledgement Reconstruct frames,
acknowledges

Channel coding,
error protection, Error correction,
interleaving deinterleaving
OSI layer 1 Physical layer

Equalization
Transmitter Receiver

RF RF
Modulation Demodulation


Network Layer
] The network layer is split into three sub-layers Network Layer
c RR - radio resource management: Layer 3
c routes messages to the correct channels
CM CC SS SMS
c establishes and maintains physical
connections for control and traffic channels.
c MM - mobility management: Mobility Management MM
c controls authentication and security
management. Radio Resources RR
c provides services for the CM layer.
c CM - connection management: Data Link Layer
c CC: call control: responsible for establishing,
maintaining and releasing calls
Layer 1: Physical Layer
c SS: supplementary services: data etc
c SMS: short message services


Signaling Protocol Reference Model

BSS NSS
To other processes Other applications,
within the BSS A - Interface ie. call control

BSSAP BSSAP Operation &
maintenance info. to
BSS BSS
To air interface DTAP DTAP OA&M center
MAP
MAP
transmission
equip.
BSS BSS
Distribution function
Distribution function OMAP OMAP

SCCP SCCP To other
users
MTP MTP of the SCCP
and MTP
Physical Layer

Terminology:
DTAP (direct transfer application part)
BSSMAP (BSS management application part)
BSS OMAP (operation & maintenance application part) Note: X.25 can be used
SCCP (signaling connection control part) for transferring O & M
MTP (message transfer part) information


GSM Network Protocol Model
The MSC and the mobile always control all the network signaling.

MS BTS BSC MSC
CM

Layer 3 CM MM
“Network”
MM BSSAP BSSAP
BSSAP

RR RR BTSM BTSM SCCP SCCP
Layer 2
“Data Link” LAPDm LAPDm LAPD LAPD
MTP MTP
Layer 1 Radio
Radio 64 kbit/s 64 kbit/s 64 kbit/s 64 kbit/s
“Physical”

Air - Interface A - bis A - Interface


Example “Page Jim”
Mobile recognizes
Layer 3 message Layer 3 message
“Page Jim” and “Page Jim”
sends “response to
page” MSC
BSC
Layer 2 Layer 2
Layer 2 recognizes a Layer 2 recognizes a Layer 2
frames message for selects message for the selects
Layer 2 message the mobile and BTS mobile and correct BSC
decodes converts to converts to
message LAPDm LAPD

BTS Layer 1 sends
MS Layer 1 BSC Layer 1 Layer 1 sends
Layer 1 message
receives BTS Layer 1 receives 64 kbit message across
sends across A-bis:
PCH receives A-bis signaling from 64 kbit signaling
message T1 or
message MSC channel
on PCH microwave


Radio Resource Messages

] Radio resource functions are controlled by the BSC and include:
c SACCH measurement reporting on the uplink
c System Information messages 5&6 transmitted on the downlink
c Immediate assignment (assignment of SDCCH)
c Assignment command (from SDCCH to TCH)
c Control of the mobile during handover
c Intra-BSC handovers
c Frequency hopping
c Channel mode changes
c Ciphering
c Channel release procedures
c Radio link failure


Radio Resource Messages
] Assignment request ] Handover Request
] Assignment complete ] Handover candidate inquiry
] Assignment failure ] Handover request acknowledge
] Handover required
] Block ] Handover required reject
] Overload ] Handover command
] Unblock ] Handover complete
] Handover failure
] Clear command
] Clear complete ] Paging
] Clear request
] Reset
] Cipher Mode Command ] Queuing
] Cipher Mode Complete ] Trace Invocation


System Information Messages
] The System Information ] System Information Messages 1 to
Messages are sent to the 4 are sent on the BCCH and rotated
mobile from the network on the with PCH, AGCH, SCH and FCCH,
BCCH in Idle mode and on the and maybe the SDCCH.
SACCH in active mode. ] System Information Messages 5 &
] The Physical Information 6 are transmitted continuously on
Messages are very similar and the SACCH to active mobiles on the
are sent on the FACCH after a downlink while the measurement
handover. report is being sent on the uplink.
] They contain the basic ] The contents of the System
information that the mobile Information Messages are given in
needs to gain access to the the following slides:
network.


] System Information Type 1: ] System Information Type 2:
1) Cell Channel description (CA) 1) Neighbour cells description which
which gives the ARFCNs used in gives the ARFCNs of the
the cell neighbour cells to be monitored
2) RACH control parameters which by the mobile. Note that this is an
includes: offset and a bit map listing up to
c the maximum number of 124 ARFCNs.
retransmissions on the RACH 2) PLMN permitted which lists: the
c the number of slots to spread the network colour codes (NCCs)
transmissions which the mobile can use.
c the cell barred for access 3) the RACH control parameters as
parameter System Information Type 1.
c call re - establishment allowed
c emergency call allowed
c control class allowed.


] System Information Type 3: 4) Cell Options including
1) Cell Identity (CI) to identify any cell c Power Control enabled
in a given location area c DTX enabled
c the value of the radio link timeout
2) Location Area Identification counter
including: 5) Cell selection parameters
c the Mobile Country Code (MCC)
including:
c the Mobile Network Code (MNC)
c the Cell Reselect Hysteresis parameter
c the location area code (LAC)
c the maximum mobile power on the
3) Control channel description control channel MsTxPwrMaxCCH
including: c the minimum access threshold
c the attach / detach parameter (ATT) RXLEVMin.
c the number of blocks reserved for 6) the RACH control parameters as
access grant (AG) System Information Type 1.
c the common control channel
configuration, ie whether it is combined
with an SDCCH etc.


] System Information Type 4:
1) Location area identification as in
System Information Type 3 ] System Information Type 5:
2) Cell selection parameters as in System 1) Neighbour cells description which
Information Type 3 gives the ARFCNs of the
3) RACH control parameters as in neighbour cells to be monitored
System Information Type 1 and reported on by the mobile.
4) Cell Broadcast Control Channel Note that this is also an offset
(CBCH) description which gives the and a bit map listing up to 124
description of the channel used for ARFCNs.
cell broadcast
5) Cell Broadcast Control Channel mobile
allocation to give the mobile the
ARFCN used for the CBCH


] System Information Type 6:
1) Cell Identity (CI) to identify any cell in ] Physical Information
a given location area. Message:
2) Location Area Identification including 1) Contains the timing advance
c the Mobile Country Code (MCC) for the mobile and is sent on
c the Mobile Network Code (MNC) the FACCH after a handover
c the location area code (LAC). if the handover is to another
3) Cell Options including site, ie a non - synchronous
c Power Control enabled handover. It is not sent for a
c DTX enabled intra-site synchronous
c the value of the radio link timeout counter handover. (Either between
4) PLMN permitted which lists the sectors of the same site or a
network colour codes (NCCs) which timeslot shuffle)
the mobile can use. .


Call Control Messages
] Call Establishment Messages ] Call Information Phase Messages
c Alerting c Modify
c Call confirmed c Modify Complete
c Call proceeding c Modify Reject
c Connect c User Information
c Connect Acknowledge
c Emergency Setup ] Connection Management Messages
c Progress c CM Service Accept
c Setup c CM Service Reject
c CM Service Request
] Call Clearing c CM Re-establishment Request
c Disconnect
c Release ] Miscellaneous Messages
c Release Complete c Start / Stop DTMF Tones
c Notify
c Status


Mobility Management Messages
] Registration Messages
c IMSI Detach
c Location Updating Request
c Location Updating Accept
c Location Updating Reject LAC 1 LAC 2

] Security Messages
c Authentication Request
c Authentication Response
c Authentication Reject
c Identity Request
c Identity Response
c TMSI Reallocation Command
c TMSI Reallocation Complete


GSM Cause Codes Rec 2:10
Cause Tone 47 Resources unavailable, unspecified 6
(see Table 1) 49 Quality of Service Unavailable 3
1 Unassigned number 6 50 Requested facility not subscribed 6
3 No Route to Destination 6 57 Bearer Capability not authorised 6
58 Bearer Capability not available 3
6 Channel Unacceptable 6
63 Service or option not available, unspecified 6
16 Normal Clearing 1
65 Bearer Service not implemented 6
17 User Busy 2 69 Requested Facility not implemented 6
18 No User Responding 6 79 Service or option not implemented, unspecified 6
19 User Alerting, No Answer 6 81 Invalid Call Reference Value 6
21 Call Rejected 6 88 Incompatible Destination 6
22 Number Changed - 91 Invalid Transit Network Selection 6
27 Destination out of order 6 95 Invalid Message, unspecified 6
28 Invalid Number Format 6 96 Mandatory Information Element error 3
30 Response to STATUS ENQUIRY - 97 Message Type non-existent or not implemented 6
31 Normal, unspecified - 98 Message not compatible with calls state or
Message Type non-existent or not implemented 6
34 No circuit/channel available 3
99 Information Element non-existent or not implemented 6
38 Network out of order 6
100 Invalid Information Element contents 6
41 Temporary Failure 3 101 Message not compatible with call state 6
42 Switching Equipment Congestion 3 102 Recovery on timer expiry 6
43 Access Information Discarded 6 111 Protocol error, unspecified 6
44 Requested circuit/channel not available 3 127 Interworking, unspecified 6


GSM Supervisory Tones
Tone Frequency Type

1 Dial Tone (optional) 425 Hz Continuous

2 Subscriber Busy 425 Hz Tone on 500ms
* (Called Number) Silence 500ms

3 Congestion 425 Hz Tone on 200ms
* Silence 500ms

4 Radio Path Acknowledgement 425 Hz Single Tone
(Mobile originated only) 200ms
(optional)

5 {Radio Path Not Available 425 Hz 200ms} On/off for
{Call dropped - Mobile originated only 200ms} 3 bursts

6 Error/Special Information} 950 Hz {Triple Tone
* Number Unobtainable } 1400 Hz {Tones on 330ms
Authentication Failure } 1800 Hz {Silence 1.0s

7 Call Waiting Tone 425 Hz, on for 400 ms, 8 s silence
followed by (425 Hz, on for 150 ms
off for 150 ms, on for 150 ms, 8 s
silence and repeated as necessary)


GSM Signaling Recommendations

Air Interface A - bis A - Interface

Layer 1 protocol Radio GMSK 64 kbit/s E1, T1, CCS7
“Physical layer” microwave 64 kbit/s MTP
GSM Recs Rec 4:04 Rec 8:54 Rec 8:04

Layer 2 protocol LAPDm LAPD CCS7 / MTP
“Data link layer”

Layer 3 protocol CM/ MM/ RR CM/ MM/ RR MTP / SCCP
“Network layer” DTAP BSSMAP BSSAP


GSM Timers
] Timers are used to supervise ] Usually, when a timer times out,
messages sent across the network. the message is re-transmitted.
] The network entity sending the ] If the timer times out again, the
message starts and stops the channels will be released and a
supervisory timer. failure will be recorded by the
] The mobile uses timers to control its MSC or BSC.
behavior when not under the direct ] Timers are classified as:
control of the network, for example, c Radio Resource Timers
when idle, during a handover or during c Mobility Management Timers
channel disconnect. c BSSAP Timers
] Various messages are used to trigger c A-bis Timers
the start and stop of each timer. c Call control Timers
] The timers allow the MS and BTS time ] There are timers for both Layer 3
to respond to requests for functions and Layer 2 functions.
resources or to send information.


GSM Timers

Sue Smith TWS
GSM Timers - Radio Resource Timers
4th February '97
Name Range Default Comments

Network
T3101 1-5s 1s Supervision of network access. Started when IMMEDIATE_ASSIGNMENT is sent to MS. Stops when MS successfully seizes
SDCCH. On expiry, newly allocated channels are released and the access request is forgotten.

T3107 3.5 - 10 s 6s Supervision of assignment procedure. Started when ASSIGNMENT_CMD is sent to the mobile. Stopped when
ASSIGNMENT_COMplete message is received on the new channel or ASSIGNMENT_FAILURE is received on the old channel.
On expiry, all resources are released and the connection with the mobile is released.

T3109 5 - 15 s 8s Releases channels in case of a loss of communication. Started when a lower layer failure is detected by the network when not
engaged in a RF procedure. Also used during the channel release procedure. On expiry channels are released. Default is 9 s.

T3111 0.5 s Supervision of channel disconnection. Started when CHANNEL_RELEASE message is sent. On expiry, disconnects the main
signalling link. Allows for possible repetition of the disconnection command.

T3113 Supervision of paging procedure. Started when PAGING_REQUEST is sent to the mobile and stopped when
PAGING_RESPONSE message is received from the MS. This timer must be longer than T3102 plus T3101. If timer times out,
network may allow PAGING_REQUEST to be sent again and the T3113 is re-started.

Mobile
T3110 0.5 s Used to delay channel deactivation after receipt of the CHANNEL_RELEASE message. Allows some time for disconnection of
main signalling link. Must be short enough to prevent T3109 timing out.

T3120 nRACCH+T1 Supervision of network access attempts. Started when CHANNEL_REQUEST message is sent on the RACCH. Stops on receipt
of an IMMEDIATE_ASSIGNMENT on the AGCH. On expiry, if the mobile has not exceeded the maximum number of
retransmissions allowed (RET = 4) then the MS sends another CHANNEL_REQUEST and T3120 is loaded with a new value.
The value is obtained from T3120 = n RACCH slots + T1 where n = 1..N and N=8 initially and the valaue of "Tx-integer"
subsequently, and T1 = 350 ms.

T3122 2 - 255 s 6s Delays network access. Started on receipt of an IMMEDIATE_ASSIGNMENT_REJECT message from the network. On expiry, the
mobile may attempt to access the network again.

TWS Proprietary - www.tws-inc.com - (770) 752-7033

GSM Timers

Handover
T3103 4 - 10 s 6s Supervises the handover in the BSC. Started when the HANDOVER command is sent to the MS. Stopped when the
HANDOVER_COMPLETE message is received via the new BTS on the new channel or HANDOVER_FAILURE message
received via the old BTS on the old channel. On expiry ALL RF channels are released and the mobile is assumed to be lost
during the handover procedure.

T3105 100 ms Supervision of repetition frequency of the PHYSICAL INFO message. Started when the network sends the PHYSICAL INFO
message to the MS and stopped when any correct frames are received from the MS. On expiry, the PHYSICAL INFO message is
sent again up to the number of repetitions (NY1 = 8) and the timer is re-started. If NY1 is reached, the handover is aborted.
T3105_F = 100 ms and T3105_D = 280 ms.

T3124 320 ms Supervision of handover in the MS. Started when the MS receives a HANDOVER_CMD and stops when the
HANDOVER_COMPLETE message is sent. If the handover fails due to the BTS failing to receive the HANDOVER_ ACCESS
message, or the mobile fails to receive the PHYSICAL INFO message, then the Timer expires and a HANDOVER_FAILURE is
recorded. The mobile the deactivates the new channels, reactivates the old channels and continues as if no handover attempt
had occurred.


GSM Timers

Sue Smith TWS
GSM Timers - Mobility Management Timers
4th February 1997

Mobile
T3210 20 s Started when LOC_UPD_REQ sent. Stopped if LOC_UPD_ACK or LOC_UPD_REJ received from network, or on AUTH_REJ. On
expiry start Timer 3211.

T3211 15 s Started on receipt of LOC_UPD_REJ with cause = network failure. Causes a delay before the mobile attempts access to the
network again. On expiry restart location update procedure.

T3212 Time between periodic updates. Started on termination of MM service signalling. Stopped on initiation of MM service signalling.
On expiry, initiate location update procedure.

T3213 4s Started on location update failure. Delays network access attempt. On expiry, generate a new random access attempt.

T3220 5s Allows time to receive network messages on IMSI Detatach. Started on IMSI_DETACH sent to network. Stopped on release from
Radio Management sub-layer. Enter NULL or IDLE into HLR/VLR, not updated.

T3230 15 s Cipher mode supervision. Started on CIPHER_REQUEST sent to BTS. Stopped on CIPHERMODE_SETTING. On expiry, provide
RELEASE indication to network.

T3240 10 s Allows time to disconnect from network. Start on normal end of location update procedure. Stop on receipt of any message from
the network. On expiry, release RR connection.

Network
T3250 5s Start on TMSI_REAL_CMD or LOC_UPD_ACK with new TMSI sent to MS. Stop on TMSI_REAL_COM received. On first expiry,
retransmit AUTH_REQ; on second expiry, release RR connections.

T3260 5s Supervision of authentication procedure. Start on AUTHentication_REQuest sent to MS. Stop on AUTH_RESP received. On first
expiry, retransmit AUTH_REQ; on second expiry, release RR connections.

T3270 5s Supervision of identity procedure. Start on IDENTITY_REQUEST sent to MS. Stop on IDENTITY_RESPONSE received. On first
expiry, re-transmit IDENTITY_REQUEST; on second expiry, release RR connections.


GSM Timers

Sue Smith TWS
GSM Timers - BSSAP Timers
4th February 1997

T4 10 - 120 s 60 s Supervision of sending RESET to MSC. Started whenever BSC RESET occurs. Stopped when RESET Acknowledge is received
from MSC. On expiry procedure is repeated until RESET ACK is received.

T5 1 - 10 s 4s Supervision of OVERLOAD procedure. Started when OVERLOAD message is received from MSC. On expiry new OVERLOAD
messages are taken into account.

T6 3 - 20 s 10 s Supervision of OVERLOAD procedure. Started with T5 when OVERLOAD message is received from MSC. On expiry traffic is
increased to next level.

T7 5 - 30 s 20 s Supervision of periodicity of HANDOVER_REQUIRED message. Started when HANDOVER_REQUIRED message is sent to
MSC. Stopped when HANDOVER_COMMAND message is received from MSC. On expiry, handover procedure is repeated.

T8 8 - 15 s 12 s Supervision of handover procedure in source BSC. Started when HANDOVER_COMMAND message is received from MSC.
Stopped when CLEAR_COMMAND (external handover) is received from MSC. On expiry, ASSIGNMENT_FAILURE message is
sent to MSC.

T10 4 - 14 s 8s Supervision of assignment procedure. Started when ASSIGNMENT_COMMAND message is sent to the MS via the BTS.
Stopped when ASSIGNMENT_COMPLETE or ASSIGNMENT_FAILURE is received from the MS. On expiry,
ASSIGNMENT_FAILURE message is sent to MSC.

T12 5 - 30 s 15 s Serves as a guard period for local call clearing procedure. Started when a RESET message is received from the MSC. Stopped
when a SSP (sub-system prohibited) message is received from SCCP. On expiry RESET_ACKNOWLEDGEMENT sent to MSC.


GSM Timers

Sue Smith TWS
GSM Timers - ABIS Timers
4th February '97

T9101 10 s Non-modifiable

T9103 2s Non-modifiable

T9104 5 - 20 s 15 s Supervision of clear procedure from MSC. Started when CLEAR_REQ is sent to MSC. Stopped when CLEAR_CMD is received
from MSC. On expiry, CHANNEL_REL is sent to mobile, via the BTS.

T9105 2 - 240 s 10 s Supervision of SCCP connection procedure. Started when SCCP_CONNECTION_REQUEST is sent to the MSC. Stopped when
SCCP_CONNECTION_CONFIRM or _REFUSED is received from MSC. On expiry, CHANNEL_RELEASE is sent to MS via BTS.
Set to 31 s.

T9108 2s Non-modifiable

T9113 8 - 15 s 12 s Supervision of external handover in target BSC. Started when HANDOVER_REQUEST_ACK is sent to MSC. Stopped when
HANDOVER_COMplete is received from MS or when CLEAR_CMD is received from MSC. On expiry CLEAR_REQUEST is sent
to MSC.

T200 240 ms Layer 2 repeat timer. Values depend on timers used to supervise message flow between the MS and the network. For proper
operation T200 should be greater than the maximum time between re-transmission of command frames and the reception of
their corresponding response or acknowledgement frames but should be shorter than the corresponding Layer 3 timer
supervising this message flow.


GSM Timers

Sue Smith TWS
GSM Timers - MSC Timers
4th February '97

TNT1 60 - 300 s 300 s Timer deployed to ensure release of SCCP resources. Internal SCCP Integrity Timer

TNT2 1 - 30 s 5s ASSIGNMENT_REQUEST message sent, awaiting for ASSIGNMENT_COMPLETE reply from BSS. On expiry channels are
released. Value of TNT2 should be greater than BSS timer T10.

TNT3 1 - 30 s 5s CLEAR_COMMAND message sent, awaiting CLEAR_COMPLETE reply from BSS. On expiry resources are released and mobile
is assumed lost during call clear. Value of TNT3 + T102 should be greater than T8 at the BSS.

TNT4 1 - 30 s 5s CIPHER_MODE_COMMAND message sent, awaiting CIPHER_MODE_COMPLETE reply from BSS. On expiry the connection is
released and a cipher failure is logged (GMSC601 log).

T101 1 - 10 s 5s At MSC-A, HANDOVER_REQUEST message sent, awaiting HANDOVER_REQUEST_ACKNOWLEDGEMENT from BSS. If T101
expires, the MSC tries to use another cell from the list of preferred cells. (see NPC parameter)

T201 1 - 30 s 5s At MSC-B, HANDOVER_REQUEST message sent, awaiting HANDOVER_REQUEST_ACKNOWLEDGEMENT message at MSC-
B after inter-MSC handover. If T201 expires the MSC attempts to use another cell from the preferred cell list if available.

T102 1 - 30 s 5s With T103, T104, T202, T204, T210 these supervise the sending of messages between two MSCs for an inter-MSC handover.
On expiry resources are released (similar to inter-BSC handover supervisory timers)

T3250 1 - 20 s 5s TMSI_REALLOCATE_COMMAND or LOCATION_UPDATE_ACCEPT message sent, awaiting TMSI_REALLOCATE command
from mobile station. On initial expiry message re-sent, on second expiry release connection.

T3260 1 - 20 s 5s AUTHENTIATION_REQUEST message sent, awaiting AUTHENTICATION_RESPONSE message from mobile. On initial expiry
message re-sent, on second expiry release connection.

T3270 1 - 20 s 5s IDENTITY_REQUEST message sent, awaiting IDENTITY_RESPONSE message from mobile. On initial expiry message re-
sent, on second expiry release connection.

T2_DTAP 30 - 120 s 30 s Call initiated to mobile station and no response message is received. Incoming call timer for network side integrity. On expiry,
release connection.

T301 45 - 300 s 180 s ALERT message is received for the mobile, awaiting sending of CALL_CONFIRMED message. On expiry, release connection.


GSM Timers

T303 1 - 60 s 30 s SETUP message is received for the mobile station, awaiting sending of CALL_CONFIRMED message. On expiry, release
connection.

T305 1 - 60 s 30 s DISCONNECT message sent to mobile, awaiting RELEASE_COMPLETE from the mobile. On expiry RELEASE message sent.

T308 1 - 60 s 30 s RELEASE message sent to the mobile. Awaiting ALERT, CONNECT or DISCONNECT message from the network. On expiry,
DISCONNECT sent.

T310 1 - 60 s 30 s CALL_CONFIRMED message is sent to the mobile, awaiting ALERT, CONNECT or DISCONNECT message from the network.
On expiry, DISCONNECT sent.

T313 1 - 60 s 30 s CONNECT message has been sent to the mobile, awaiting reply of CONNECT_ACKNOWLEDGEMENT. On expiry,
DISCONNECT sent.

TC1N 1 - 60 s 20 s CP_DATA_INDICATION sent to the mobile, awaiting reply of CP_ACKNOWLEDGEMENT. Error indication on second expiry.


CALL SET-UP - Mobile Terminate
MS BTS BSC MSC
RR MM BSS MAP
CM

PAGING REQUEST (PCH) PAGING COMMAND CM PAGING COMMAND CM

CHANNEL REQUEST (RACH) T3113
CHANNEL REQUIRED
T3120
(RR)
CHANNEL ACTIVATION (IMMEDIATE ASSIGNMENT)
RR nRACCH >T3101 + T3120
+ T1 (350ms)
CHANNEL ACTIVATION ACK

IMM ASSIGN RES IMMEDIATE ASSIGNMENT (AGCH)
IMMEDIATE ASSIGN COMMAND RR
T3122 (6s)

SABM (PAGING RESPONSE) (SDCCH) PAGE RESPONSE CM
T3101
UA (PAGING RESPONSE) (SDCCH)
(RR) 1s
ESTABLISH INDICATION RR

AUTHENTICATE AUTHENTICATE REQUEST (RAND)

AUTHENTICATE REQPONSE AUTHENTICATE RESPONSE (SRES)

CIPHER MODE CMD CIPHER MODE COMMAND

TNT4
CIPHER MODE COMPLETE CIPHER MODE COMPLETE

SETUP PHYSICAL CONTEXT REQUEST SETUP

T303
CALL PROCEEDING PHYSICAL CONTEXT CONFIRM CALL PROCEEDING

LAYER 2 TIMERS
CHANNEL ACTIVATION (TCH ASSIGN)
T200 240ms x 4 rep. T310
THEN T3109 (8s)
CHANNEL ACT. ACK RELEASES LOWER
LAYER.

ASSIGNMENT COMMAND (SDCCH) DATA REQUEST (CM) ASSIGNMENT REQUEST COMMAND CM

(FACCH on TCH) SABM (FACCH) call confirmed TNT TNT2 should be
T10
T3107 2
greater than T10
6s 8s
UA call proc. (5s)
ESTABLISH INDICATION

DATA INDICATION CM
ASSIGNMENT COMPLETE (CM) ASSIGNMENT COMPLETE

RF CHANNEL RELEASE (SDCCH) RR

RF CHANNEL RELEASE ACK RR

ALERTING (FACCH) DATA REQUEST ALERTING

T301
CONNECT DATA REQUEST CONNECT

CONNECT ACK DATA INDICATION CONNECT ACKNOWLEDGE T313

MOBILE DISCONNECT

DISCONNECT DATA INDICATION CLEAR REQUEST

RELEASE DATA REQUEST CLEAR COMMAND

TNT3
RELEASE COMPLETE DATA INDICATION CLEAR COMPLETE (5s)

CHANNEL RELEASE DATA REQUEST CHANNEL RELEASE
T3110
0.5s DEACTIVATE SACCH
T3111 T308
DISC
RELEASE INDICATION 0.5s
RELEASE COMPLETE

UA
RF CHANNEL RELEASE on RF channel
release
RF CHANNEL RELEASE ACK or T3111 expiry
Air Interface A-Interface
A-bis

INTER - BSC HANDOVER
Mobile BTS 1 BSC 1 MSC BSC 2 BTS 2 Mobile
RR MM CM BSS MAP RR MM CM BSS MAP

SYS INFO 5 & 6 BTS MEAS. RESULT

(SACCH)
MEASUREMENT REPORT MS MEAS. RESULT T7 20s
HANDOVER REQUIRED
HANDOVER REQUEST
CHANNEL ACTIVATION
T101
ACT. ACK.
Def:
5s
H/O REQ. ACK. (FACCH)
Note: Handover
Access
HANDOVER DETECT HANDOVER ACCESS on FACCH
HANDOVER COMMAND DATA REQUEST HANDOVER COMMAND
using
T9113 RACCH burst
(FACCH) PHYSICAL INFO structure
RELEASE REQUEST
T8 12s

T3113 T3105
12s 100ms PHYSICAL INFO
6s T102 No Phys Info
ESTABLISH INDICATION on Synchronised
SABM Handovers
T8 +T102 + Def: 5s
TNT3 T3124
UA
320ms

HANDOVER
H/O COMPLETE DATA INDICATION COMPLETE

CLEAR COMMAND

TNT3
CLEAR COMPLETE

RF CHAN. RELEASE
RELEASE

RF CHAN. REL. ACK
Air Interface
RELEASE COMPLETE

H/O
FAILS
T3124 TIMES OUT

HANDOVER ACCESS

(FACCH)

SABM

UA

DATA INDICATION HANDOVER FAILURE
OLD BSC
H/O FAILURE

Return to Old CLEAR COMMAND
channel
TNT3
NEW BSC
(5s) CLEAR COMPLETE

RELEASE RELEASE RF CHANNEL

RELEASE COMPLETE RF CH. REL. ACK.

Air Interface
A-bis A-Interface A-Interface A-bis

LOCATION UPDATE
Mobile BTS BSC MSC
RR / CM / MM BSSMAP
CHANNEL REQUEST (RACH) CHANNEL REQUIRED

CHANNEL ACTIVATION

CHANNEL ACTIVATION ACK

IMMEDIATE ASSIGNMENT (AGCH) IMMEDIATE ASSIGNMENT

CM SERVICE REQUEST (LOC UPDATE)
LOCATION UPDATE REQUEST CM

(SDCCH) VLR
( SDCCH) UPDATE LOCATION AREA

IDENTITY REQUEST
IDENTITY REQUEST
T
T3270
3
T3230 5s T3270
2 IDENTITY RESPONSE IDENTITY RESPONSE
15s
3 VLR
TMSI
0
ACKNOWLEDGE

1
5
s AUTHENTICATION REQUEST AUTH. REQUEST (RAND)

T T3260
T3260
3
SRES 5s
2 AUTHENTICATION RESPONSE AUTH. RESPONSE (SRES) VLR
1
0 TMSI, LOC AREA
ACCEPTED

2
0 CIPHER MODE COMMAND CIPHER MODE CMD (Key)
s
TNT
4
CIPHER MODE COMPLETE CIPHER MODE COMPLETE (5S)

T3210
20s

LOC UPDATE ACCEPTED T LOC UPDATE ACCEPTED (TMSI)
3
T3250 2
5 T3250
TMSI REALLOCATION COMPLETE 5S TMSI REALLOCATION COMPLETE
0

5 TMSI
RELEASE CHANNEL RELEASE S CLEAR COMMAND
T3240
T3240 ACKNOWLEDGE

10s
10s TNT 3
RELEASE COMPLETE CLEAR COMPLETE
RELEASE COMPLETE (5S)

CHANNEL RELEASE RELEASED

DEACTIVATE SDCCH T3111

DISC

UA
RELEASE INDICATION
RELEASE COMPLETE

RELEASE RF CHANNEL

RF CHANNEL RELEASE ACK.

S.Smith Dec ‘94

Air Interface
A-bis
A-Interface

Mobile Signaling Overview

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