GSM Signaling Matrix PSTN MAP ISUP RIL3 RSM RSM TUP BSSAP

GSM Signaling Matrix PSTN MAP ISUP RIL3 RSM 08.58 RSM 08.58 TUP BSSAP
Company Confidential 3/23/2018 GSM Signaling Matrix Databases PSTN BSSMAP BSS MAP MAP DTAP DTAP ISUP RR RIL3 RSM 08.58 RSM 08.58 TUP BSSAP BSSAP TCAP RIL3 SCCP SCCP The fig above gives an overview of GSM Protocol Matrix. The MSC uses ISUP/TUP protocols for PSTN signaling. It has MAP for signaling to database applications like HLR,VLR,EIR,AUC,SMSSC,GMSC. On the A interface it has GSM specific protocol as BSSAP. The BSSAP comprises of DTAP and BSSMAP. DTAP signaling is direct signaling between mobile and MSC, whereas BSSMAP is mobile related signaling between MSC and BSC. The BSC also uses the BSSAP but only the BSSMAP part of it for MSC. On the BTS side GSM has defined its own set of protocols in which has no official name but we term it as RSM ( Radio Subsystem Management. The BSC on layer 2 uses Lapd ( Link Access Procedures on D - Channel ) which is an ISDN protocol and includes functions for error correction and detection and frame delimitation by insertion of flags. The BTS on the mobile has again set of GSM protocols for physical layer which is the Radio Air Interface and uses Lapdm for Layer 2 signaling . This is a modified Lapd protocol with one difference being some Lapd functions like error correction are removed and used at Layer 1, and second major difference being the Lapdm messages cannot be lengthy due limitation of burst length. The BTS on the Mobile user part uses RIL3 which is again a GSM protocol for Radio Resource Management. The Mobile on the other hand in RIL3 has DTAP for MSC signaling and RR for Radio Resource signaling. MTP Level 2 ,3 MTP Level 2 & 3 LAPDm LAPDm LAPD LAPD MTP Level 1 MTP Level 1 Rad Int G.703 G.703 Rad Int MS BTS BSC MSC Air Abis A Company Confidential Author: Arif R.

Map Interfaces VLR HLR/ VLR AUC EIR A,B,C,D,E,F,G,H,I = SS7
Company Confidential 3/23/2018 Map Interfaces A,B,C,D,E,F,G,H,I = SS7 Abis = LAPD OML = X.25 VLR G HLR/ AUC VLR MSC D BSC B HLR/AUC C Abis A F EIR BTS I OML OMC E SUPP H PSTN SS7/R2 GSMSC GMSC IWMSC Company Confidential Author: Arif R.

MAP Messages - Points to be noted
Company Confidential 3/23/2018 MAP Messages - Points to be noted MAP messages are between Switching and Database interfaces MAP messages are not present on the Air Interface Not much significance related to Drive Testing Can be useful in analyzing some Protocol failures experienced on the air interface during drive testing. Company Confidential Author: Arif R.

Base Station Application Part ( BSSAP )
Company Confidential 3/23/2018 Base Station Application Part ( BSSAP ) DTAP BTS BSC MSC BSSMAP DTAP BSSMAP DTAP BSSMAP Distribution Layer Distribution Layer BSSAP is used between BSC and MSC on A interface. It uses the services of MTP and SCCP and hence it is based on C7. BSSAP deals with signaling between MSC and BSC and also MSC and Mobile . BSSAP has two subsets the DTAP and the BSSMAP. DTAP deals with the signaling messages directly between the MSC and Mobile. The BSC and/or BTS just routes theses messages. DTAP messages are all connection oriented messaged.BSSMAP messages are MS related messages but originate and terminate at the BSC,from where BSC modifies the message and sends it across in different message ( RSM ,08.58 messages ). The distribution layer does the function of distribution of message to DTAP and BSSMAP. It does this by identifying certain parameter in the BSSAP message which is explained on next message. BSSAP supports both connectionless and connection-oriented signaling. Messages like paging, reset are sent in CL mode, ( Message lists are give further ). BSSAP BSSAP SCCP SCCP MTP MTP Company Confidential Author: Arif R.

Company Confidential 3/23/2018 BSSMAP & DTAP message BSSMAP ( Base Station Subsystem Mobile Application Part) Between BSC and MSC Linked to certain messages on the Air Interface Useful in troubleshooting certain Blocked Calls and Dropped Calls problems in conjunction with Drive Testing DTAP (Direct Transfer Application Part) Transparent Messages between MSC and MS Further divided into sub-categories ( MM ,CC,SMS,SS) Company Confidential Author: Arif R.

BSSMAP Messages Connection Oriented Messages Connectionless Messages
Company Confidential 3/23/2018 BSSMAP Messages Connection Oriented Messages Assignment Complete Assignment Failure Assignment Request Candidate Response Cipher Mode Command Cipher Mode Complete Classmark Update Complete Layer 3 Information Handover Candidate Enquiry Handover Command Handover Complete Handover Detect Handover Failure Handover Performed Handover Request Handover Request Acknowledge Handover Required Reject Trace Invocation Queuing Indication Connectionless Messages Block Block Acknowledge Paging Reset Reset Acknowledge Reset Circuit Reset Circuit Acknowledge Resource Indication Resource Request Unblock Unblocking Acknowledge Company Confidential Author: Arif R.

DTAP Messages Types of DTAP Messages*
Company Confidential 3/23/2018 DTAP Messages Types of DTAP Messages* CC : Call control and call related SS Messages -- related to call setup and activation/deactivation of SS between . MM : Mobility Management Messages --- location updates, security procedures and connection management . SS : Non-Call related Supplementary Messages --- like call barring, call forwarding etc. SMS : Short Message Service Messages --- related of transmission and reception of SMS. Company Confidential Author: Arif R.

DTAP Messages CC Messages SS Messages MM Message Alerting Hold
Company Confidential 3/23/2018 DTAP Messages SS Messages Hold Hold Acknowledge Hold Reject Retrieve Retrieve Acknowledge Retrieve Reject Facility Register MM Message Authentication Request Authentication Response CM Re-Establishment Request CM Service Accept CM Service Reject CM Service Request Identity Request Identity Response IMSI Detach Location Updating Accept Location Updating Reject Location Updating Request TMSI Reallocation Command TMSI Reallocation Complete CC Messages Alerting Call Confirmed Call Proceeding Connect Connect Acknowledge Disconnect Emergency Setup Facility Hold Hold Acknowledge Modify Modify Complete Notify Progress Release Release Complete Retrieve Retrieve Acknowledge Setup SMS Messages CP-Ack CP-Data CP-Error RP-Ack RP-Data RP-Error DTAP messages are divided into two categories, the CM ( connection management) messages and the MM ( Mobility Management ) Messages. The CM messages deals the establishment , release and maintenance of calls. The MM messages deals with the security,mobility ( location updating ) and CM establishment messages. Company Confidential Author: Arif R.

Air Interface 04.08/ 04.10 04.08/ 04.10 RIL3 RIL3 04.04 Rad Int
Company Confidential 3/23/2018 Air Interface DTAP 04.08/ 04.10 04.08/ 04.10 RIL3 RR RIL3 The Interface between the MS and BTS is the Air Interface. On the Physical Layer it uses thew GSM specified Radio Interface characteristics which is as per GSM recommendations. The data link layer uses the LAPDm ( Link access procedure on Dm channel i.e. control channel.) LAPDm is a variant of LAPD and explained in further sessions. The Layer 3 is again controlled by GSM recommendations and LAPDm LAPDm Rad Int 04.04 Rad Int 04.04 MS BTS Company Confidential Author: Arif R.

Radio Interface ( Layer 1 )
Company Confidential 3/23/2018 Radio Interface ( Layer 1 ) --- The Physical Layer on the Air interface is Radio --- Messages are sent on Radio Interface through appropriate logical channels Functions of Layer 1 --- Mapping of Logical Channels to Physical Channel --- Channel Coding --- Ciphering --- Cell Selection and Reselection --- Connection Establishment on Logical Channels --- Measurement of serving and neighbouring cells signal level --- Setting of Timing Advance --- Transmit Power Control as commanded by BTS. The Physical Layer on the air Interface is the Radio Medium which is a 200Khz channel in the 900Mhz GSM specified band with 8 timeslots on which messages sent on appropriate logical channels. The various functions of Layer1 are listed above. Company Confidential Author: Arif R.

Radio Interface (Layer 3)
Company Confidential 3/23/2018 Radio Interface (Layer 3) Air Interface L3 Message categories DTAP Messages : transparent to BTS -- CC -- MM -- SS -- SMS RR : Radio Resource messages specific to MS and BTS Test Messages : Related to testing procedures ( like loopback etc.) Company Confidential Author: Arif R.

RIL3 Messages DTAP Message Type CC Messages SS Messages MM Message
Company Confidential 3/23/2018 RIL3 Messages Message Type DTAP CC Messages Alerting Call Confirmed Call Proceeding Connect Connect Acknowledge Disconnect Emergency Setup Facility Hold Hold Acknowledge Modify Modify Complete Notify Progress Release Release Complete Retrieve Retrieve Acknowledge Setup SS Messages Hold Hold Acknowledge Hold Reject Retrieve Retrieve Acknowledge Retrieve Reject Facility Register MM Message Authentication Request Authentication Response CM Re-Establishment Request CM Service Accept CM Service Reject CM Service Request Identity Request Identity Response IMSI Detach Location Updating Accept Location Updating Reject Location Updating Request TMSI Reallocation Command TMSI Reallocation Complete SMS Messages CP-Ack CP-Data CP-Error RP-Ack RP-Data RP-Error Company Confidential Author: Arif R.

RIL3 Messages RR Message Type Assignment Command Immediate Assignment
Company Confidential 3/23/2018 RIL3 Messages Message Type RR Assignment Command Assignment Complete Assignment Failure Channel Mode Modify Channel Mode Modify Acknowledge Channel Release Channel Request Ciphering Mode Command Ciphering Mode Complete Classmark Change Frequency Redefinition Handover Access Handover Command Handover Complete Handover Failure Immediate Assignment Immediate Assignment Extended Immediate Assignment Reject Measurement Report Paging Request Type 1 Paging Request Type 2 Paging Request Type 3 System Information Type 1 System Information Type 2 System Information Type 3 System Information Type 4 System Information Type 5 System Information Type 6 System Information Type 2bis Company Confidential Author: Arif R.

Mobile Phone Mode CC Release MM Release RR Release RR Idle Mode
Company Confidential 3/23/2018 Mobile Phone Mode BCCH & PCH RR Idle Mode RACH & AGCH RR Connection Establishment Mode SDCCH RR Connected Mode Initial Message MM Connection Establishment Mode Initial Message Ack MM Connected Mode Call Control Process CC Release MM Release RR Release Company Confidential Author: Arif R.

Air Interface Communication Procedures
Company Confidential 3/23/2018 Air Interface Communication Procedures Non-call Related Call Related Access Procedure ( RACH/AGCH) MM CM Procedure ( SDDCH) MM Common Procedures MM Specific Procedures Release Procedures Access Procedure ( RACH/AGCH) MM CM Procedure ( SDDCH) MM Common Procedures ( SDDCH) CC Procedures ( SDDCH) RR Procedures ( TCH ) (TCH) Release Procedures ( SDDCH) Company Confidential Author: Arif R.

Cell Selection & Reselection
Company Confidential 3/23/2018 Cell Selection & Reselection Criteria for Camp on to a cell Reliably decode downlink data High probability of communications on the uplink Company Confidential Author: Arif R.

Cell Selection and Reselection
Company Confidential 3/23/2018 Cell Selection and Reselection Definitions Available PLMN -- one for which at least 1 cell is unbarred and C1>0 Suitable Cell -- part of selected PLMN -- unbarred -- C1 > 0 The MS uses BA list for camp on Company Confidential Author: Arif R.

WHAT IS CELL BARRING ? BTS Every Mobile has an access class on the SIM
Company Confidential 3/23/2018 WHAT IS CELL BARRING ? Cell barring is a GSM Feature by which certain Mobiles could be barred access to certain cells. BTS Every Mobile has an access class on the SIM Every cell defines the Mobile classes which are barred access. Company Confidential Author: Arif R.

USE OF CELL BARRING Reserving Cells for Handovers.
Company Confidential 3/23/2018 USE OF CELL BARRING Reserving Cells for Handovers. Reserving Cells for a certain Mobile Class. Company Confidential Author: Arif R.

Cell Selection & Reselection
Company Confidential 3/23/2018 Cell Selection & Reselection In the camp on process, mobile checks for ' C 1 ’ ' C1 ' is the path loss criteria. ' C1' calculations are done by mobile while camping On and for cell reselection. Cell reselection means leaving the existing cell and selecting a new cell in the idle mode. Company Confidential Author: Arif R.

Path Loss Criterion ' C1 ' C1 = A - max ( B,0 )
Company Confidential 3/23/2018 Path Loss Criterion ' C1 ' C1 = A - max ( B,0 ) A = Average Received signal Level - Min Receive Level B = Access Power - Max power of Mobile ( Classmark ) A = + = Good Downlink Path B = -- = Good Uplink Path The mobile calculates the C! parameter on the BCCH it is attempting to camp on during cell selection process. If C1 is positive camps on. Mobile in active mode monitors the Received Signal strength of neighboring cells. From the received level, it computes the C1 for these neighboring cells, and if the value of C1 for any of the neighboring cells is greater than the existing cell, mobile switches over to that BCCH. For Cell selection C1 > 0 For Cell Reselection C1 of new cell > C1 of current cell or C1 falls below 0, both for a period of 5 seconds. Company Confidential Author: Arif R.

Company Confidential 3/23/2018 Mobile Camp On A Mobile Subscriber is issued with a SIM to access the network. The SIM card has the preferred list which contains 8 PLMN codes. This list can be updated by the user The Mobile also has forbidden list , which is dynamically updated by the mobile. It has 4 PLMN codes. Company Confidential Author: Arif R.

Camp on with preferred list
Company Confidential 3/23/2018 Camp on with preferred list 5 samples/ARFCN spread over 3 to 5 secs Scans 124 ARFCN's Locks on to best A Searches for FCH Locks on to next best in BA list Lock on to next best Yes Cell IF barred Found No Yes No Read BCCH Info If the SIM is programmed with Preferred List, the mobile turns in and scans all the 124 ARFCNs. The MS takes readings of RXLEV of each channel, and calculates the RXLEV average for each. The averaging is based on at least 5 samples per RF carrier spread over 3 to 5s, the measurement samples from the different RF carriers being spread evenly during this period. MS locks on to the ARFCN having the highest signal level.After locking on it searches for the frequency correction burst to check whether it is BCCH carrier or not . If it is BCCH carrier, it reads the BCCH info and checks for the network code , if the network code matches with that on SIM. If it matches , it checks for cell barring, if it is not barred, it calculates the C1 to see if is positive. If it is it camps ON. No C1 > 0 NC No matches Yes Yes CAMP ON A Company Confidential Author: Arif R.

No preferred list Scans 124 ARFCN's A Lock on to next best
Company Confidential 3/23/2018 No preferred list Scans 124 ARFCN's A Lock on to next best Locks on to best Location Update Searches for FCH Puts PLMN in forbidden list No IF No Found Successful Yes Yes Read BCCH Info If there is no preferred list on SIM , the mobile locks on to the best ARFCN, reads BCCH , and goes in for the Location Update . The Network does Authentication/Identity check for the mobile. If the BCCH belongs to other network, mobile will fail authentication. If it is successful it writes this NC in its preferred list and checks for cell barring and C1 and then camps on Stores the BA list Next in BA list Yes Cell barred No C1 > 0 A Company Confidential Author: Arif R.

Abnormal Cases Invalid Network Response
Company Confidential 3/23/2018 Abnormal Cases Invalid Network Response PLMN not allowed. IMSI unknown or illegal MS Does Cell Reselection, if still PLMN not allowed Search 30 strongest RF channels Camps on to determine next PLMN availability If 30 RF channels are scanned and no suitable PLMN is found (provided 1 of 30 is BCCH ), Mobile goes to No SIM state . Company Confidential Author: Arif R.

Abnormal Case No suitable cell found Cell reselection as per BA
Company Confidential 3/23/2018 Abnormal Case No suitable cell found Cell reselection as per BA If no suitable cell found, then No SIM sate Company Confidential Author: Arif R.

Abnormal Case No SIM State Only Emergency Calls allowed
Company Confidential 3/23/2018 Abnormal Case No SIM State Only Emergency Calls allowed Will do Cell Reselection Company Confidential Author: Arif R.

Mobile Frame Synchronization
Company Confidential 3/23/2018 Mobile Frame Synchronization The purpose of Synchronizing is to read the BCCH message Mobile gets Synchronized with the cell by SCH Mobile locates SCH with the help of FCCH FCCH Burst Fixed Bits ( all zeros ) 142 How does a mobile get synchronized with the cell, so that it can read the remaining channels. Mobile gets it synchronization Information from the SCH.But how does the mobile find SCH. This is done with the help of FCCH which has very easily recognizable structure of 142 fixed bits which are also zeros. The Mobile after locating FCCH knows that SCH follows FCCH ( after 7 slots ). One more function of FCCH is that mobile corrects it internal time base so that it can ease the process of demodulation , this is so because with a pattern all zero's the FCCH looks like a unmodulated wave with a drift of 67Hz above the carrier. TB3 TB3 GP FCCH has a easily recognizable structure with all zeros Mobile knows that SCH follows FCCH The maximum time allowed for synchronization is 0.5s, and the maximum time allowed to read the BCCH data, when being synchronized with the BCCH carrier, is 1.9 secs. Company Confidential Author: Arif R.

Mobile Frame Synchronization
Company Confidential 3/23/2018 Mobile Frame Synchronization SCH Burst Contains the TDMA Frame No and BSIC Information 39 Midamble 64 TB3 SCH Burst Frame Number (19 Bits) BSIC (6 Bits) Actual Information in SCH Superframe No 11 Bits Multiframe No 5 Bits SCH Frame No 3 Bits Frame No = 11bits ( To point Superframe No out of 2048 Superframes ) 5bits ( To point Multiframe No out of 26 Mulitframes ) 3bits ( To Point out the SCH Frame No out of 5 in 1 Multiframe ) MS calculates the TDMA Frame no from this information The Mobile must know the TDMA frame on which it is sending information ( access only). This is required in the random access procedures . The SCH informs the mobile about BSIC and TDMA Frame No. The SCH has actual 19 bits for TDMA frame no. The TDMA frame is one out of Frames ( within 1 Hyperframe ). This requires 22 bits, but what is informed to the mobile in SCH is the Superframe No ( which has max value of 2048 ) this requires 11 bits, then it informs the Muliframe No ( which are 26 in one superframe ) this will require 5 bits, and the remaining three bits inform the SCH Frame to which the mobile is tuned on . Once the MS gets the SCH number as 1/2/3/4/5, It calculates the TDMA frame No, since it is known standard that SC1 falls on 2nd Frame of the Multiframe and so on for others. 1 11 21 31 41 50 S1 S2 S3 S4 S5 1 Multiframe Company Confidential Author: Arif R.

Company Confidential 3/23/2018 Cell Reselection Primarily based on comparison of C1 of serving and neighbor cells. In order to optimize cell reselection, C2 calculations can be optionally implemented , for which additional parameters are broadcasted on the BCCH of each cell. Company Confidential Author: Arif R.

C2 Calculations - Parameters
Company Confidential 3/23/2018 C2 Calculations - Parameters CELL_RESELECT_OFFSET : ( dB // 2 dB steps ) Used to achieve cell prioritization, i.e to encourage MS's to select some suitable cells in the presence of others. More useful for Multiband and Umbrella cells architecture. Applies a positive or a negative offset to each cell TEMPORARY_OFFSET : ( dB // 10 dB steps) For a neighbor cell , when placed on the list of the strongest carriers by the MS, it starts a timer and applies a negative offset to the C1 of that neighbor for the duration of this timer. The offset can also be infinite, which means the cell never be selected in the reselection process. PENALTY_TIME : ( 20s to 620s // 20secs steps) The duration for which the Temporary_Offset is applied. Company Confidential Author: Arif R.

"C2" Calculations C2 = C1 + CELL_RESELECT_OFFSET
Company Confidential 3/23/2018 "C2" Calculations For Serving Cell, C2 = C1 + CELL_RESELECT_OFFSET If Penalty Time = 620 secs, then C2 = C1 - CELL_RESELECT_OFFSET Company Confidential Author: Arif R.

"C2" Calculations For Neighbor Cells,
Company Confidential 3/23/2018 "C2" Calculations For Neighbor Cells, C2 = C1 + CELL_RESELECT_OFFSET - TEMPORARY_OFFSET(t) t = 1 , till the Penalty timer equals the set value t = 0 , after the Penalty timer has expired If Penalty Time = 620 secs, then C2 = C1 - CELL_RESELECT_OFFSET Company Confidential Author: Arif R.

Measurements for Cell Reselection
Company Confidential 3/23/2018 Measurements for Cell Reselection F S B "ON" B Measurements (optional to MS) B B P0 Measurements P0 "ON" P0 P0 Company Confidential Author: Arif R.

Measurements for Cell Reselection
Company Confidential 3/23/2018 Measurements for Cell Reselection Serving Cell A running average of 5 measurement samples are required per receive level average value. Measurement samples should be collected over a period of : 5 secs to Max ( 5s, five consecutive paging blocks of that MS) Neighbor Cells A running average of 5 measurement samples are required per receive level average value of each neighbor cell. Measurement samples should be collected over a period of : 5 secs to Max [ 5s, (5*N + 6) DIV 7) * BS_PA_MFRMS / 4 ] N is the number of non-serving cell BCCH carriers in the BA list Company Confidential Author: Arif R.

Cell Reselection - Measurements and BCCH decode
Company Confidential 3/23/2018 Cell Reselection - Measurements and BCCH decode MS shall calculate the C1 and C2 for serving and non-serving cells every 5 secs. MS shall attempt to decode the full BCH data of the serving cell at least every 30 seconds. MS shall attempt to decode the BCCH data block that contains the parameters affecting cell reselection for each of the 6 strongest neighbor cell BCCH carriers at least every 5 minutes. When MS recognizes a new BCCH carrier has become one of the 6 strongest, the BCCH data for the new carrier within 30 seconds. MS shall attempt to decode the BSIC for each of the 6 strongest carriers at least 20 seconds, to confirm that it is monitoring the same cell. If the change in BSIC is detected,then the carrier would be treated as a new carrier. Company Confidential Author: Arif R.

Cell Reselection Cell in the same LA Cell in the different LA
Company Confidential 3/23/2018 Cell Reselection Cell in the same LA C2 for new cell should exceed C2 of current cell and should remain high for a period of 5 secs. C1 of current cell falls below zero. Cell reselection occurring within 15 secs, C2 of the new cell shall exceed the C2 of the serving cell by at least 5 dB for a period of 5 secs. The left cell on reselection shall not be returned within 5 secs if another suitable cell can be found. Cell in the different LA Depends on Reselect hysteresis. Company Confidential Author: Arif R.

Reselect Hysterisis Reselect Hysterisis Value is broadcasted on BCCH
Company Confidential 3/23/2018 Reselect Hysterisis Reselect Hysterisis Value is broadcasted on BCCH For the new cell in different Location Area, the value for C1 for new cell > the C1 for serving cell by the hysterisis value broadcasts on the serving cell BCCH for a period of 5 secs. This hysterisis is to avoid exorbitant Location Updates when the mobile is on border of two location areas. The mobile is monitoring the neighboring cells. It calculates the values for C1 of the neighboring cells, and reselects the new cell if its C1 is greater than the C1 of existing for 5 secs. If the new cell belongs to a different Location Area the mobile has to do Location Update. So in order to avoid this there is hysterisis value broadcasted , The C1 of new cell ( of different LA ) has to be more than the existing C1 by this hysterisis value . The value of hysteresis can be set between db in steps of 2 db. Company Confidential Author: Arif R.

Reselect Hysterisis Location Area 1 C1 = 13 dB Location Area 2
Company Confidential 3/23/2018 Reselect Hysterisis Location Area 1 C1 = 13 dB As seen in the figure, the mobile is on the boundaries of two Location Areas, where the new Location Area 1 Cell has a C1 better then the current cell by 3 db's, but since the hysterisis is kept at 5 db, the mobile will not go for Cell Reselection. Location Area 2 Hysterisis = 5 db C1 = 10 dB Company Confidential Author: Arif R.

Mobile - Cell Access Location Update Signaling Diagram BTS MSC BSC
Company Confidential 3/23/2018 Mobile - Cell Access Location Update Signaling Diagram BTS BSC MSC Channel Req Channel Reqd Channel Activation Chan Actvn Ack Imm Assgn Cmd Immediate Assgn Loc Upd Req ( SABM ) Establish Ind Complete Layer 3 Info Authentication Request Data Request Auth Req Auth Resp Data Ind Authentication Response Loc Upd Accept Data Request Loc Upd Accept Clear Command Clear Complete Company Confidential Author: Arif R.

Mobile Cell Access RACH T3120 Re-transmission T3120 AGCH T3101
Company Confidential 3/23/2018 Mobile Cell Access Channel Request RACH T3120 Re-transmission The mobile sends a RACH to access the cell with an establishment cause which could be response to page, call originating, emerg call, supplementary service. In response to RACH the mobile expects an AGCH to get details of SDCCH. The moment the mobile sends a RACH it starts an internal timer T3120 and waits for AGCH. If it does not get any response till the expiry of this timer, it retransmits the RACH. The network on sending an AGCH starts Timer T3101 and waits for mobile to tune to SDCCH. On expiry of this timer, if does not responds it discards the establishment request. T3120 AGCH Immediate Assignment Reserves SDCCH T3101 Response Company Confidential Author: Arif R.

Immediate Assignment Procedure
Company Confidential 3/23/2018 Immediate Assignment Procedure BTS BSC Channel Request Channel Required T3120 Channel Activation Channel Activation Ack Immediate Assign Command Immediate Assignment T3101 Company Confidential Author: Arif R.

BSIC (coded in parity bits)
Company Confidential 3/23/2018 Message Contents Channel Request Random Access TB8 SYNCH 41 TB3 G P Information 36 5 bits 3 bits 6 bits Random Reference No. Establishment Cause BSIC (coded in parity bits) Establishment Cause Answer to paging Emergency Call Call re-establishment Originating Call Location Update IMSI Detach, SMS, SS Management 011 - Reserved for future use Company Confidential Author: Arif R.

Message Contents Channel Required
Company Confidential 3/23/2018 Message Contents Channel Required Channel Number Indicates on which channel the message was received ( RACH ) Request Reference --- Contains RACH info ( Random No, Cause ), Frame No Access Delay Delay in terms of bit period ( ) Physical Context --- Optional for manufacturer to add more information ( RxLev etc, ) Immediate Assignment Command Channel Number --- channel on which the message is to be sent ( AGCH ) Message type --- Immediate Assignment Channel Description --- SDCCH/4 or SDCCH/8. Sub-channel Number TSC, ARFCN, Single or Hopping, HSN Mobile Allocation Table Request Reference --- Contains RACH info ( Random No, Cause ), Frame No Timing Advance Timing Advance value ( ) Mobile Allocation --- MAI table if hopping is used Starting time --- TDMA Frame No if frequency for new channel changes ( NC - case ) Company Confidential Author: Arif R.

Message Contents BTS BSC Immediate Assignment Extended
Company Confidential 3/23/2018 Message Contents Channel Request Immediate Assign Command Immediate Assign Extended BTS BSC Immediate Assignment Command Immediate Assignment Extended Channel Number -- AGCH Message type -- Immediate Assign Extended Channel Description 1 Request Reference 1 Timing Advance 1 Channel Description 2 Request Reference 2 Timing Advance 2 Mobile Allocation Starting time Channel Description 1 Request Reference 1 Timing Advance 1 Channel Description 2 Request Reference 2 Timing Advance 2 Mobile Allocation Starting time Company Confidential Author: Arif R.

Immediate Assignment Procedure Completion
Company Confidential 3/23/2018 Immediate Assignment Procedure Completion BTS Channel Request RACH Immediate Assign Command AGCH Stops T3120 Initial MS message SDCCH (Location Update Request CM Service Request Paging Response CM Reestablishment Request IMSI Detach) Company Confidential Author: Arif R.

Abnormal Cases No Channel ( SDCCH ) available BTS BSC Channel Request
Company Confidential 3/23/2018 Abnormal Cases No Channel ( SDCCH ) available BTS BSC Channel Request Channel Required Immediate Assign Command Immediate Assignment Reject Stops T3120 Starts T3122 Immediate Assignment Reject Immediate Assignment Command One Immd Assgn Reject message can have information for up to five mobiles. The purpose of the Wait Indication Element is to provide the time the mobile station should wait before attempting another channel request. On receipt of this message the MS stops T3120 , starts timer T3122 ( with the value indicated ) and returns to the idle mode ( listens to paging ) . The MS is not allowed to make a RR -Connection in the same cell until the T3122 expires. Request Reference 1 -- EC, Ref no, Fr.No Wait Indication -- T3122 Request Reference 5 -- EC, Ref no, Fr.No Channel Number -- AGCH Message type -- Immd Assgn Reject Request Reference 1 -- EC, Ref no, Fr.No Wait Indication -- T3122 Request Reference 5 -- EC, Ref no, Fr.No Company Confidential Author: Arif R.

Abnormal Cases Lower Layer Failure on MS before establishment on SDCCH
Company Confidential 3/23/2018 Abnormal Cases Lower Layer Failure on MS before establishment on SDCCH -- Allocated Channels are released -- MS returns to Idle Mode -- Transaction is process are aborted -- Cell reselection may take place Timer T3101 on Network expires before MS responses -- Allocated Channels are released -- Request Forgotten Company Confidential Author: Arif R.

RACH Collisions TWO Mobiles Send RACH at same Frame No
Company Confidential 3/23/2018 RACH Collisions TWO Mobiles Send RACH at same Frame No with same Reference No and EC If YES A both strong No One may reach and one may not reach Both rejected and follow the Re-transmission Process RACH's are differentiated by the network with reference to Random Reference Number, Establishment Cause and the Frame Number. If two RACHs are sent identically, and if one reaches the network , then AGCH will be assigned and both will tune to SDCCH and one will release during Call Setup, If both are strong, then both are rejected and they follow the retransmission process. Network assigns AGCH with the same RRN Both will tune to SDCCH B One will release the channel during setup Company Confidential Author: Arif R.

ALOHA Process Rejected AGCH AGCH
Company Confidential 3/23/2018 ALOHA Process RACH RACH T3120 Rejected T3120 Re-transmission The Mobile sends a RACH and starts an internal timer T3120. The maximum value of this timer is broadcasted on the System Information Messages..The possible values for this Timer in term s of RACH Slots is mentioned above.If RACH collision occurs, the mobile if it does not get an AGCH till the expiry of T3120, it transmits the RACH again and starts this timer again, but this time the value is different, this value is randomly generated by the mobile. So in case of RACH Collision, there are very less chances that both mobiles will generate the same timer value for every retransmission. AGCH AGCH T3120 = ,14,16,20,25,32,50 RACH Slots Maximum Re-transmission = 1,2,4,7 For every Re-transmission T3120 is randomly generated Company Confidential Author: Arif R.

RACH Collision ( B ) -- One RACH reaches one does not RACH RACH
Company Confidential 3/23/2018 RACH Collision ( B ) -- One RACH reaches one does not RACH RACH Both Wait for AGCH Immediate Assignment Both tune to SDCCH SABM ( Initial Message ) SABM ( Loc Upd Req ) Initial Message = IMSI UA ( Initial Message ) UA ( Initial Message ) DROPS ( since IMSI mismatches ) Company Confidential Author: Arif R.

MM - Common Procedures TMSI Reallocation Procedure
Company Confidential 3/23/2018 MM - Common Procedures TMSI Reallocation Procedure Authentication Procedure Identification Procedure Ciphering * IMSI Detach Procedure * Ciphering is not a MM procedure, but since it is linked with other procedures discussed here , it is covered in this section Company Confidential Author: Arif R.

TMSI Reallocation Loc Upd ( IMSI ) TMSI Allocation Call Setup ( TMSI )
Company Confidential 3/23/2018 TMSI Reallocation Loc Upd ( IMSI ) TMSI Allocation Call Setup ( TMSI ) TMSI Reallocation TMSI : Temporary Mobile Subscriber Identity Company Confidential Author: Arif R.

TMSI REALLOCATION Purpose Operational Requirements
Company Confidential 3/23/2018 TMSI REALLOCATION Purpose Provide identity confidentiality Operational Requirements TMSI is an unambiguous identity associated with LAI Must be performed at change of Location Areas Initiated in ciphered mode Can also be associated with some other procedure The purpose of TMSI reallocation is to provide identity confidentiality, i.e. to protect a user against being identified and located by an intruder. The TMSI has only local significance within a location area. Outside the location area it has to combined with the LAI to provide for an unambiguous identity. TMSI reallocation must be done at least at each change of LA. Reallocation in other cases is left o the operators choice. If the TMSI provided by the MS is unknown to the network ( could be due to database failure ), the MS has to provide its IMSI on request from the network ( i.e by the Identification procedure ) This can also be a part of some other procedure like LOcation Update, Call Setup. Company Confidential Author: Arif R.

TMSI REALLOCATION MSC T3250 Stops TMSI Reallocation Command
Company Confidential 3/23/2018 TMSI REALLOCATION MSC T3250 Stops TMSI Reallocation Command TMSI Realacation Complete TMSI Reallocation Command Location Area Identification Mobile Identity : TMSI / IMSI TMSI Reallocation Complete No Elements Company Confidential Author: Arif R.

MM - Common Procedures Authentication Purpose
Company Confidential 3/23/2018 MM - Common Procedures Authentication Purpose -- To verify Subscriber Identity ( IMSI and SIM ) -- To provide a new ciphering key to the Mobile Station Operational Requirement -- at each registration -- at every call attempt ( MOC & MTC ) ( left to operators , but should be done for visiting subscribers ) -- before performing some supplementary services activation, de-activation, registration or erasure -- required for Location Updating for roaming -- not mandatory prior to IMSI Attach and Detach Authentication process is always initiated and controlled by the network Company Confidential Author: Arif R.

MM - Common Procedures A3 A3 = Authentication Ki Ki RAND RAND SRES
Company Confidential 3/23/2018 MM - Common Procedures Authentication Ki Ki RAND RAND A3 A3 The Network sends the Random Number to the Mobile. The Mobile has the Subscriber Identity Key Ki stored in its SIM. The Mobile uses an algorithm A3 and sends the signed response to the AUC/VLR. On the other side the network also knows the subscriber key, which is either stored in the HLR, or most probably in the AuC it also calculates the SRES and compares it with the one sent by the Mobile. IF matches then Authentication is Successful. SRES SRES = Company Confidential Author: Arif R.

MM - Common Procedures Authentication MSC T3260 Stops
Company Confidential 3/23/2018 MM - Common Procedures Authentication MSC T3260 Stops Authentication Request Authentication Response Authentication Request Ciphering Key Sequence No -- Values ( 0-6 ) , 7 = No key Authentication Parameter RAND bits Random Number Authentication Response Authentication Parameter SRES bits Signed Response Company Confidential Author: Arif R.

MM - Common Procedures Unsuccessful Authentication
Company Confidential 3/23/2018 MM - Common Procedures Unsuccessful Authentication Authentication Reject MSC BTS BSC Authentication Req Data Request T3260 Authentication Req Authentication Resp Data Indication Authentication Resp Invalid SRES Stops T3260 Authentication Rej Data Request Authentication Rej RR- Connection Release procedure initiated All MM-Connections Released Sets Authentication Failure Flag Waits for Connections to be released Delete its TMSI,LAI,Ciphering Key, CKSN Return to IDLE no IMSI state Authentication Reject No elements Company Confidential Author: Arif R.

MM - Common Procedures Abnormal Cases Expiry of timer T3260 MSC
Company Confidential 3/23/2018 MM - Common Procedures Abnormal Cases Expiry of timer T3260 MSC Authentication Request Starts T3260 T3260 Expires Re-Starts Authentication Reject RR - Connection Release Procedure initiated Company Confidential Author: Arif R.

MM - Common Procedures Identity Check EIR
Company Confidential 3/23/2018 MM - Common Procedures Identity Check Identity Check ( IMEI ) Sends IMEI White listed / Grey listed / Black listed ????? EIR Company Confidential Author: Arif R.

MM - Common Procedures Identification
Company Confidential 3/23/2018 MM - Common Procedures Identification MSC requests the Mobile to send its identity , for verification Identity could be IMSI, TMSI,IMEI IMEI shall only be sent in ciphered mode MSC T3270 Stops Identity Request Identity Response Identity Request Identity Response Identity type : IMSI / IMEI / TMSI Mobile Identity Company Confidential Author: Arif R.

MM - Common Procedures Identification Abnormal Case
Company Confidential 3/23/2018 MM - Common Procedures Identification Abnormal Case Expiry of timer T3270 MSC Identification Request Starts T3270 T3270 Expires Identification Request Re-Starts T3260 T3270 Expires Releases RR - Connection Company Confidential Author: Arif R.

MM - Common Procedures Ciphering Purpose -- privacy of speech and data
Company Confidential 3/23/2018 MM - Common Procedures Ciphering Purpose -- privacy of speech and data -- privacy of signaling information Operational Requirements -- Implementation dependent -- Ciphering should be done before confidential signaling information is passed ( Called Number, Calling Number, TMSI ) * Note : IMSI and IMEI are also confidential signaling information ,but they require physical protection Company Confidential Author: Arif R.

MM - Common Procedures A8 A5 RAND Ki Ciphering Frame No Kc XOR
30 Company Confidential 3/23/2018 MM - Common Procedures RAND Ki Ciphering A8 Frame No Kc The same RAND ( 128bits ) and the Ki is used to generate the Ciphering Key ( Kc ) of 64 bits by using algorithm A8 , which is then passed through Algorithm A5 with the TDMA Frame No to produce a Ciphering stream of 114bits which is then Exported with the speech bits ( 114 ) and send across. XOR A5 Ciphering Stream Ciphered Bits Information Bits ( 114 ) Company Confidential Author: Arif R.

MM - Common Procedures Ciphering MSC BTS BSC Cipher Mode Command
Company Confidential 3/23/2018 MM - Common Procedures Ciphering MSC BTS BSC Cipher Mod Cmd Encryption Cmd Cipher Mod Cmd start deciphering Start ciphering & deciphering correct L2 frame start ciphering Ciph Mod Comp Data Indication The MSC sends a cipher mode command to the BSC, which contains the algorithm to be used or no ciphering, and the Kc. The BSS forwards this information to the BTS along with the Layer 3 information to be forwarded to the MS. This information has only an indication to the MS, whether it should use ciphering or not. The key and other Algorithm are utilized by the BTS for other ciphering and deciphering purpose. The BTS then sends a cipher mode command which indicates to the Mobile to start ciphering. Cipher Mode Comp Cipher Mode Command Cipher Mode setting : No Ciphering Start Ciphering Encryption Command Cipher Mode Command Channel Number Encryption Information : Algorithm Identifier Key L 3 Information Layer 3 Header Information Algorithm Identifier : No encryption/ A5 / 1 Key : Ciphering key Cipher Mode Complete No Elements Company Confidential Author: Arif R.

MM - Common Procedures Network Network
Company Confidential 3/23/2018 MM - Common Procedures Ciphering Key Sequence No ( CKSN ) Authentication Request ( RAND + CKSN ) Network Ki Authentication Response ( SRES ) A3/A8 FNo ( CKSN ) ( stored in MSC/VLR ) ( Kc + CKSN ) ( stored in SIM ) Channel Request Immediate Assignment Network Initial Message ( CKSN ) If CKSN Checked , No authentication Company Confidential Author: Arif R.

IMSI Detach Procedure Purpose Conditions Operation
Company Confidential 3/23/2018 IMSI Detach Procedure Purpose To mark the Mobile as inactive in the network Conditions Mobile Station Power down SIM is removed Operation If no RR-connection exists, RR-connection will be first established If RR-connection exists, then all MM - connections will be first released If Location Update procedure is On, than it will be finished, then this procedure will be started Company Confidential Author: Arif R.

IMSI Detach Procedure Abnormal Case MSC Starts T3220
Company Confidential 3/23/2018 IMSI Detach Procedure MSC IMSI Detach Indication Starts T3220 Marks MS as detached in VLR Will not sent any page Wait for RR-Connection Release If T3220 expires, MS will localy release RR-Connection IMSI Detach Indication Abnormal Case PD : MM TI : 0 MT : IDI Mobile Station Classmark 1 Mobile Identity RR-Connection cannot be established or RR-Connection is lost before message is sent, then the IMSI detach is aborted by the MS Company Confidential Author: Arif R.

Importance of Location Area
Company Confidential 3/23/2018 Importance of Location Area L.Area = 1 L.Area = 2 L.Area = 3 By dividing a PLMN area into various location areas,paging load reduce since whenever there is page for a mobile it is send by the MSC to those BSC's which have cells with location areas same as that of the current location area of the Mobile If entire PLMN area is termed as one location area then the MSC has to page for every mobile in every BSC which increases Paging load and as a result signaling load and hence wastage of resources. Reduce Paging Load Resource Planning Company Confidential Author: Arif R.

What is Location Update ?
Company Confidential 3/23/2018 What is Location Update ? MSC should know the Location of the Mobile for paging. Mobile is continuously changing Location Area. Mobile when changes Location Area informs the MSC about its new L.A Process of informing MSC about new Location Area is Location Update L.Area = 1 L.Area = 2 L.Area = 3 Location Update Company Confidential Author: Arif R.

Location Updating Procedure
Company Confidential 3/23/2018 Location Updating Procedure IMSI Attach -- Power on in same LAI -- Compliment to Explicit IMSI Detach Normal Location Update -- Change in LAI due to mobility -- Power on in new LAI -- MS unknown in VLR as a response to Connection establishment request Periodic Updating -- Expiry of Periodic Update Timer ( T3212 ) -- In the event of MS out of Service , on exit, MSC will mark it as Implicit Detach in the VLR -- Timer is reset to "0" on any Loc Update, first MM message recd , MS responded to page, on expiry of timer Company Confidential Author: Arif R.

Location Update Procedure
Company Confidential 3/23/2018 Location Update Procedure Location Update is done at VLR or VLR and HLR Update at VLR -- When MS roams into a new Location Area -- Periodically Update at HLR -- When MS registers in a new VLR -- When MS registers in the same VLR, but MSC Location Area has changed and HLR requires new routing information -- On HLR or VLR Restoration Company Confidential Author: Arif R.

Location Update Signaling Diagram
Company Confidential 3/23/2018 Location Update Signaling Diagram BTS BSC MSC Channel Req Channel Reqd Channel Activation Chan Actvn Ack Imm Assgn Cmd Immediate Assgn Loc Upd Req ( SABM ) Establish Ind Complete Layer 3 Info Authentication Request Data Request Auth Req Auth Resp The Mobile sends a RACh which states the cause as Location Update. The BSC performs the Channel Activation and the BTS assigns a SDCCH to the MS . The mobiles tuns to it sends a Location Update Request ( piggybacked on SABM ) which contains the type of update ( Attach,Periodic, Normal ) , the CKSN, The old LAI, and the Mobile Classmark, IMSI or TMSI. This is a initial MS message to which the BSC adds the new LAI and sends a Complete Layer 3 message to the MSC. The MSC then starts the authentication process if required and then ciphering . After the success of these , it sends a Location update accept message to the MS which may also contain the TMSI or TMSI Reallocation Command may be send separately as shown. If TMSI was included in Location Upd Accept then the MS will send the TMSI Reallocation Complete, after which the resources are cleared. Data Ind Authentication Response Loc Upd Accept Data Request Loc Upd Accept Clear Command Clear Complete Company Confidential Author: Arif R.

Company Confidential 3/23/2018 Location Update Procedure ( SABM ) Loc Upd Req Establish Indication ( CR )Comp Layer 3 Info BTS BSC MSC Starts T3210 ( UA ) Loc Upd Req MM - Security Procedures Loc Upd Accept Data Request Stops Loc Upd Request : MS Identity(IMSI/TMSI), Classmark, and OLD LAI Company Confidential Author: Arif R.

Company Confidential 3/23/2018 Location Update Procedure Abnormal Cases Location Update Rejection BTS BSC MSC Loc Upd Reject Data Request Loc Upd Reject Stops T3210 Location Update Reject Reject Cause -- IMSI Unknown -- PLMN not allowed -- LA not allowed -- TMSI not allocated Stores the Reject Cause Starts T3240 Waits for n/w to release RR-Connection Upon release of RR-Connection, take necessary action based on Reject Cause Company Confidential Author: Arif R.

Company Confidential 3/23/2018 Location Update Procedure Abnormal Cases on MS side Random Access Fails No response to RACH after max_retransmissions Timer T3213 is started MS goes for a cell reselection, with return to cell inhibited for 5 secs After 5 secs , the MS returns to the cell where Random access failed On expiry, procedure is initiated again Company Confidential Author: Arif R.

Mobile Originated Call
Company Confidential 3/23/2018 Mobile Originated Call Channel Request Immediate Assign Service Request Authentication Ciphering Set Up Call Proceeding Assignment Alerting Connection Company Confidential Author: Arif R.

CC - Call Establishment Procedures
Company Confidential 3/23/2018 CC - Call Establishment Procedures Mobile Originated Call MS BTS BSC MSC Channel Req Channel Reqd Channel Actvn Chan Actvn Ack Imm Assgn Imm Assgn CM Serv Req Establish ind CL3 Informtn Authentication CM Service Accept Cipher Mode Setting and TMSI Reallocation Set Up Call Proceeding Assgn Req Assgn Cmd Assign Comp Alert Connect Connect Ack Speech Company Confidential Author: Arif R.

CC- Call Establishment Procedure
Company Confidential 3/23/2018 CC- Call Establishment Procedure Service Request MSC CM Service Request Starts T3230 & T303 CM Service Accept Stops T3230 CM Service Accept CM Service Request CM -Service Request : is basically a request for service for the connection management and also the establishment of MM connection . The Mobile sends a CM service request and starts two timers T3230 and T303 . T3230 is the MM establishment timer and stops on the receipt of CM Service Accept (or Reject). T303 has a value higher than T3230 and is the call control timer . CM Service Accept : Sent by the network to the MS to indicate that the requested service has been accepted. PD : MM TI : MT : CSR --- No Information Elements PD : MM TI : MT : CSR CM Service Type : MOC , Emergency Call, SMS transfer, SS activation Ciphering Key Sequence Number : Mobile Station Classmark 2 : Power , Revision , Encryption,Frequency, SMS Mobile Identity : IMSI, TMSI , IMEI Company Confidential Author: Arif R.

Company Confidential 3/23/2018 CC - Call Establishment Procedures Abnormal Case CM Service Rejection MSC CM Serv Reject Stops T3230 CM Service Reject CM Service Reject : Sent by the network to the Ms to indicate that the requested service cannot be provided Network starts RR connection release Reject Cause #4 : IMSI unknown in VLR #17 : Network Failure #22 : Congestion #32 : Service Option not supported #33 : Requested Service option not subscribed #34 : Service option temporarily out of order #38 : Call cannot be identified T3230 Expires -- Mobile aborts the RR connection Company Confidential Author: Arif R.

Company Confidential 3/23/2018 CC - Call Establishment Procedures SETUP Setup MSC Call Proceeding Stops T303 Starts T310 Call Proceeding PD : CC TI : MT : CP Repeat Indicator : Used for in-call modification procedure Bearer Capabilities : Included if the network has to specify the connection element Progress Indicator : * Setup : Sent by the MS to the network to initiate Call establishment Call Proceeding : This message is sent by the network to the calling MS to indicate that the requested call information has been received send no more call establishment will be accepted. Setup PD : CC TI : MT : S Bearer Capabilities : * Mobile Identity : IMSI, TMSI , IMEI Calling Party Sub-Address : X.213 / ISO 8348 AD2 coding , user specifed coding Called Party Sub-Address : X.213 / ISO 8348 AD2 coding , user specifed coding User -User : Convey information between the MS & the remote ISDN user. * * Detailed Information follows Company Confidential Author: Arif R.

Company Confidential 3/23/2018 CC - Call Establishment Procedures Abnormal Cases Invalid Call Information Setup MSC Release Complete Stops T303 Releases the MM connection Returns to Idle Mode Release Complete PD : CC TI : MT : RC Cause : See next page Company Confidential Author: Arif R.

Company Confidential 3/23/2018 CC - Call Establishment Procedures Company Confidential Author: Arif R.

Company Confidential 3/23/2018 CC - Call Establishment Procedures Channel Assignment MSC Assignment Command Assignment Complete TCH ( FACCH ) Company Confidential Author: Arif R.

Company Confidential 3/23/2018 CC - Call Establishment Procedures Assignment Command Channel Mode : signaling only, speech full rate, speech half rate Data- 9.6 / 4.8 / 2.4 kbps full Data- 9.6 / 4.8 / 2.4 kbps half PD : RR TI : 0 MT : AC Channel Description Channel type & TDMA offset Timeslot Number : 0 - 7 TSC : BCC Hopping Channel : Single , Hopping Channel Selector : For single Channel -- Band Number, ARFCN For Hopping Channel -- MAIO ( ), HSN ( 0 - Cyclic = Algorithm ) Power Command : Power Level ( 0 to 31 ) Cell Channel Description : Used to decode the Mobile Allocation table Mobile Allocation table TCH / F T TCH / H 0 0 1 T T SDCCH/ 4 0 1 T T T SDCCH/ 8 T indicates the subchannel Assignment Command : Message is sent to the MS to change the channel configuration to another independent dedicated channel configuration , in this case TCH. Starting Time : Indicates the MS to start the Transmission after an offset of how many TDMA frames. The maximum value is which is equal to a delay of secs. Company Confidential Author: Arif R.

Company Confidential 3/23/2018 CC - Call Establishment Procedures Abnormal Cases MSC Assignment Command Assignment Complete SDCCH ( SDCCH ) In this case the MS is not able to come over to new channel. Assignment Failure : This message is sent by the MS to the network on the SDCCH to indicate that the MS has failed to seize the new channel. Assignment Failure PD : RR TI : 0 MT : AF RR Cause : No cell allocation available Invalid Message Invalid Information element contents Protocol Error Company Confidential Author: Arif R.

Company Confidential 3/23/2018 CC - Call Establishment Procedures Alerting MSC Stops T310 Alerting Alerting Alerting : Sent by the network to the calling MS to indicate that the called user alerting has been initiated. PD : CC TI : MT : A Progress Indicator : Coding standard - Q.931 , GSM Location - connected element ( explained earlier ) Progress Indicator - In band information or appropriate pattern ( RBT,BT ) now available Company Confidential Author: Arif R.

Company Confidential 3/23/2018 CC - Call Establishment Procedures Call Connection MSC Connect Connect Acknowledge Connect : This message is sent by the network to the MS to indicate call acceptance by the called user. The MS on receiving this message will stop any timer if running, attach the user to the radio path and send an acknowledgement Connect Acknowledge : This message is sent by the MS to indicate that the MS has established connection and symmetrical call control procedures are allowed. Connect PD : CC TI : MT : C Progress Indicator : Coding standard - Q.931 , GSM Location - connected element ( explained earlier ) Progress Indicator - In band information or appropriate pattern ( RBT,BT, Connection tone ) now available Connect Acknowledge PD : CC TI : MT : C ---- no information elements Company Confidential Author: Arif R.

Emergency Calls -- GSM Specs define ' 112' as emergency number
Company Confidential 3/23/2018 Emergency Calls -- GSM Specs define ' 112' as emergency number -- '112' is accessible with or without SIM -- Without SIM it is sent on the best channel -- Mobile on sensing '112' sets the establishment cause to emergency call in the RACH -- Routing of this call can be done to a desired location defined in the Switch. Company Confidential Author: Arif R.

Company Confidential 3/23/2018 CC - Call Establishment Procedures Emergency Calls Service Request MSC CM Serv Request CM Service Accept Emergency Setup Call Proceeding CM Serv Request PD : CC TI : MT : CSR Bearer Capability : Only significance is for full rate/ half rate speech coding Emergency Setup PD : MM TI : MT : CSR CM Service Type : Emergency Call CKSN : Mobile Station Classmark 2 : Mobile Identity : IMSI, TMSI , IMEI Company Confidential Author: Arif R.

Company Confidential 3/23/2018 CC - Call Establishment Procedures Call Re-establishment CM Re-estb Request MSC CM Service Accept Assignment Command (TCH) Conditions: Call Re-establishment should be allowed in the cell Occurs only on lower layer failure ( RF Link ) Mobile should be in active mode on TCH New cell should be in the same BSC Re-establishment will occur within 20 secs Company Confidential Author: Arif R.

Paging Paging is process by which Mobile receives incoming calls
Company Confidential 3/23/2018 Paging Paging is process by which Mobile receives incoming calls Mobile has to monitor the paging channel to receive paging messages Mobile will not monitor all paging channels, it will monitor the channel specific to its CCCH_Group and Paging Group CCCH_ GROUP BCCH defines the number of PCHN ( timeslots ) supporting CCCH CCCH can be allocated only to TN 0,2,4,6 CCCH will have the same structure on all allocated timeslots ( 9 blocks ) Each PCHN supporting CCCH is alloted a CCCH_Group No ( range : ) Each CCCH_Group carries its own group of Mobiles. Mobiles will listen to paging messages and send RACH's only in their specific group Company Confidential Author: Arif R.

Company Confidential 3/23/2018 Paging Group Within the CCCH_Group , Mobile listen to paging in specific paging (CCCH) blocks only The block specific to a mobile is its Paging Group Company Confidential Author: Arif R.

Paging How to derive CCCH_Group and Paging Group for a mobile ?
Company Confidential 3/23/2018 Paging How to derive CCCH_Group and Paging Group for a mobile ? Let us understand some parameters required to achieve this . 1. BS_CC_CHANS : Total No of PCHN supporting CCCH ( Sys Info Type 3 ) Range : 2. BS_AG_BLKS_RES : Blocks reserved for AGCH 3. BS_PA_MFRMS : Multiframe Repetition rate 4. IMSI : 15 digit Mobile Identity We will now understand 2 & 3 Company Confidential Author: Arif R.

Paging BS_AG_BLKS _RES Each BCCH and CCCH block = 4 Frames
Company Confidential 3/23/2018 Paging BS_AG_BLKS _RES Each BCCH and CCCH block = 4 Frames CCCH = AGCH + PCH For Non-Combined & B+C, CCCH = 9 For Combined , CCCH = 3 Company Confidential Author: Arif R.

Paging BS_AG_BLKS _RES --- Some CCCH Blocks can be reserved for AGCH
Company Confidential 3/23/2018 Paging BS_AG_BLKS _RES --- Some CCCH Blocks can be reserved for AGCH --- This parameter broadcasted on BCCH informs the Mobile about the number of blocks reserved for AGCH The value for Non-Combined MF structure ranges between For combined MF structure it ranges between 0-2 Example * Each Paging block ( P ) is a paging group Company Confidential Author: Arif R.

Paging Available Paging Blocks on 1 CCCH_Group
Company Confidential 3/23/2018 Paging Available Paging Blocks on 1 CCCH_Group Available Paging Blocks = CCCH Blocks -- bs_ag_blks_res Maximum AGCH Reservation for Non-Combined = 7 Available Paging Blocks = 2 Maximum AGCH Reservation for Combined = 2 Available Paging Blocks = 1 Mimimum AGCH Reservartion for Non-Combined = 0 Available Paging Blocks = 9 Minimum AGCH Reservation for Combined = 0 Available Paging Blocks = 3 No of Paging Blocks will have a range of Company Confidential Author: Arif R.

Company Confidential 3/23/2018 Paging BS_PA_MFRMS -- No of Multiframes after which Same Paging Group is repeated -- This Parameter is broadcasted on BCCH -- Ranges between Multiframes Mobile belonging to Paging Group P0 will remain idle during P1 ,P2,P3 Mobile utilizes power only during PO. This is known as DRX Company Confidential Author: Arif R.

Paging Total No of Paging Groups on 1 CCCH_Group ( N )
Company Confidential 3/23/2018 Paging Total No of Paging Groups on 1 CCCH_Group ( N ) No of Paging Groups = Paging Blocks x Repitition of Paging BLock N = [ CCCH - bs_ag_blks_res ] x bs_pa_mfrms Range of Paging Groups on 1 CCCH_Group Minimum Available Paging Groups = Min Pag blocks x Min bs_pa_mfrms = x 1 = 1 Maximum Available Paging Groups = Max Pag blocks x Max bs_pa_mfrms = x 9 = 81 Company Confidential Author: Arif R.

Paging How does a Mobile knows it CCCH_Group Paging Group No ?
Company Confidential 3/23/2018 Paging How does a Mobile knows it CCCH_Group Paging Group No ? CCCH_Group = [ ( IMSI mod 1000 ) mod ( BS_CC_CHANS x N ) ] div N Pag Grp No = [ ( IMSI mod 1000 ) mod ( BS_CC_CHANS x N ) ] mod N N = Total Paging Groups = No of Paging Blocks x bs_pa_mfrms Company Confidential Author: Arif R.

Would you like to do an exercise ?
Company Confidential 3/23/2018 Would you like to do an exercise ? Calculate the CCCH_Group & Paging group for a Mobile with IMSI in a cell with 2 PCHN's for CCCH and 7 blocks reserved for AGCH, and paging group repetition is after 5 multiframes ? C=1 & P=8 Company Confidential Author: Arif R.

Paging Paging Procedures
Company Confidential 3/23/2018 Paging Paging Procedures BTS packs some paging requests and sends them together in Paging Requests messages on Air Interface. The Mobile on the other hand listens to it corresponding Paging Group On getting a Paging Message belonging to its IMSI/TMSI it sends a response * Detailed Paging Procedure will be explained with Mobile Terminated Calls Company Confidential Author: Arif R.

Paging Packing of Paging Requests
Company Confidential 3/23/2018 Paging Packing of Paging Requests Paging Request Type > IMSI or 2 TMSI Paging Request Type > TMSI and 1 IMSI or TMSI Paging Request Type > TMSI Paging Mode Normal mode : Paging Message is specific Paging Group only Full Mode : Paging Message for that group can occur in any Paging Block Extended : If paging message has more data, it follows in next block Company Confidential Author: Arif R.

Mobile Terminated Call
Company Confidential 3/23/2018 Mobile Terminated Call Company Confidential Author: Arif R.

Mobile Terminated Call
Company Confidential 3/23/2018 Mobile Terminated Call MS BTS BSC MSC Paging Paging Command Paging Request Channel Req Channel Reqd Channel Actvn Chan Actvn Ack Imm Assgn Imm Assgn Paging Response Establish ind CL3 Informant CM Service Accept Security Procedures Set Up Call Proceeding TCH Assignment Alert Connect Connect Ack Speech Company Confidential Author: Arif R.

Paging BTS BSC MSC Starts T3113 Paging Request 1 Paging Command
Company Confidential 3/23/2018 Paging BTS BSC MSC Paging Paging Command Starts T3113 Paging Request 1/2/3 Paging Request 1 Paging Message Type : P IMSI : 15 digits TMSI : ( omitted if not used ) Cell Identifier List : Cell Id Discrimtr - CGI,LAC & CI, CI,LAC, All cells PD : RR TI : 0 MT : PR Page Mode : Normal, Extended Re-organization, Same as before Mobile Identity : IMSI, TMSI Mobile Identity : IMSI, TMS Paging Request Paging Request 3 TMSI TMSI TMSI TMSI Mobile Identity : IMSI, TMSI TMSI TMSI The MSC sends the paging message to the BSC and starts the Timer T3113. This message contains the IMSI and TMSI if it is used and the Cell Identifier list which contains either the LAI or the Cell Id of the cells in which the BSC should forward the paging message.The IMSI is used by the BSC to calculate the paging group. Paging Command Channel Number : PAGCH Paging Group : Company Confidential Author: Arif R.

Paging Response BTS BSC MSC Starts T3113 Stops T3113 Paging Response
Company Confidential 3/23/2018 Paging Response BTS BSC MSC Paging Request 1/2/3 Paging Channel Request Starts T3113 Immd Assign ( SABM )Paging Response Establish Indication ( UA )Paging Response Complete L3 Info Stops T3113 Paging Response PD : RR TI : 0 MT : PR Ciphering Key Sequence Number : Mobile Station Classmark 2 : Power , Revision , Encryption,Frequency, SMS Mobile Identity : IMSI, TMSI , IMEI Abnormal Case T3113 Expires : Paging message is retransmitted --- No of retransmission and the value of T3113 are implementation dependent Company Confidential Author: Arif R.

Company Confidential 3/23/2018 CC - Call Establishment Procedures SETUP MSC Setup Call Confirmed Setup PD : CC TI : MT : S Bearer Capabilities : * Mobile Identity : IMSI, TMSI , IMEI Calling Party BCD Number : Number of the calling party User -User : Convey information between the MS & the remote ISDN user. * Setup : Sent by the MS to the network to initiate Call establishment Call Proceeding : This message is sent by the network to the calling MS to indicate that the requested call information has been received snd no more call establishment will be accepted. Call Confirmed PD : CC TI : MT : CP Repeat Indicator : Used for in-call modification procedure Bearer Capabilities : Included if the network has to specify the connection element * Detailed explained earlier in MOC Company Confidential Author: Arif R.

Alerting Alerting MSC Alerting Connect Connect Acknowledge
Company Confidential 3/23/2018 Alerting MSC Alerting Connect Connect Acknowledge Alerting Alerting : Sent by the MS to the network to indicate that the called user alerting has been initiated. PD : CC TI : MT : A Progress Indicator : Coding standard - Q.931 , GSM Location - connected element ( explained earlier ) Progress Indicator - In band information or appropriate pattern now available Company Confidential Author: Arif R.

Active Mode Procedures
Company Confidential 3/23/2018 Active Mode Procedures Mobile in Active Mode -- Mobile receives the signal strength of the serving cell -- Mobile transmits -- During the Idle timeslots measures signal strength of neighbor Mobile receives speech on allotted timelsot and at the same instance measures the signal strength of the serving cell and during the remaining seven idle timeslot measures the signal strength of at least one neighbor. The Period available to the mobile for neighbor cells measurement is as shown above. In the first case the mobile has to tune its frequency hence these 2 TS cannot be used for measurements and hence only the next two cases are applicable for measurements Measurement Period Available to Mobile End of Reception to start of Transmission is = 2 Timelsots End of Transmission to start of Reception is = 4 Timeslots End of Transmisson in 25th frame to start = 12 Timelsots of reception in 1st frame in next MF --- Mobile does measurement of neighbors in last two cases only Company Confidential Author: Arif R.

Measurements in Active Mode
Company Confidential 3/23/2018 Measurements in Active Mode Measurements are made over each SACCH multiframe . SACCH multiframe is 104 TDMA frames(480ms) for TCH and 102 TDMA frames (470.8ms) for a SDCCH. MS shall make a RxLev measurement in every TDMA frame on at least one of the BCCH carriers indicated in the BA one after another . Measurements on the frame preceding the idle frame may be optionally omitted to allow more time to MS for BCCH synchronization. If frequency hopping is used and if BCCH carrier is in the hopping sequence and PWRC indicator is set , then the BCCH carrier bursts will not be used in the averaging process for RxLev, but for RxQual it will be used. Measurements made during the previous recording period are to be discarded. Company Confidential Author: Arif R.

Measurements in Active Mode
Company Confidential 3/23/2018 Measurements in Active Mode Full and Sub Rxlev_Full & RxQual_Full : Measurements taken over full set of TDMA frames Full set of TDMA frames : 102 for SDCCH Full set of TDMA frames : 104 TCH Rxlev_Sub & RxQual_Sub : Measurements taken over subset of TDMA frames If even one frame is not transmitted in the measurement period, then it is considered as subset of TDMA frames. When are sub measurements done practically ? When DTX used, and the receiver enters the DTX mode , then the measurement is done over all the frames is not valid. With DTX, if there is completely no speech for 480ms, then still there will be 8 frames of SID and 4 frames of SACCH, these 12 subset frames will be used for sub measurements . DTX is not used on BCCH carrier (all timeslots) , hence if the call is on a TCH which is on a BCH carrier, then it will always be FULL, and in the measurement report both Sub and Full values will be same. DTX is not used on the SDCCH also , hence the above clause applies to this also. On a TCH carrier, when DTX was used by the BTS in the previous 480ms period, measurement is Sub, else it is full. If Frequency Hopping was used, and BCH carrier was a part of it, and dowlink power control is used, then the measurements for Rx_Lev will always be sub ( since BCH carrier frames are not included in the measurement averaging) Company Confidential Author: Arif R.

Company Confidential 3/23/2018 Mobile in Active Mode --- Mobile also has to verify Neighbor ARFCN by decoding BSIC --- BSIC can be decoded by getting SCH of neighboring cells which is on its TS 0 --- Mobile uses the Idle time slot to locate TS0 of neighbor Will the mobile hit SCH on TS0 of neighbor ? --- TCH MF is 26 and CCH MF is 51 ( non-divisible ) --- Sliding Multiframe Cycles helps mobile in getting SCH ( next pg ) --- As seen, Within 11 cycle, idle TS will align with SCH ( about 1.2 seconds ) --- Within 10 secs mobile will be able to decode BSIC of 6 neighbors --- MS shall keep on decoding the BSIC for each carrier at least one in 10s Mobile also has to verify the neighbor by decoding the BSIC. to read the BSIC mobile has to tune to the BCCH of the neighbor which is on TS 0 , so mobile has to synchronize to TS0 of the neighbor. This may not come in the remaining seven slots, so the mobile makes use of the idle timeslot in the multiframe to locate TS0 of neighbor. Company Confidential Author: Arif R.

Sliding Multiframe Cycle
3 Company Confidential 3/23/2018 Sliding Multiframe Cycle Company Confidential Author: Arif R.

Measurement Reporting
Company Confidential 3/23/2018 Measurement Reporting --- Mobile sends the measurement report to the BTS in every SACCH Frame --- Measurement Report is of 18 octets and takes 4 SACCH bursts --- It takes 480ms to send 1 Measurement Report Company Confidential Author: Arif R.

SACCH Report From Mobile
Company Confidential 3/23/2018 SACCH Report From Mobile Layer 1 Header --- MS Tx Power Level --- Timing Advance Serving Cell ---- BCCH Indicator ---- DTX( indicates whether DTX was used by the MS in measurement period) ---- RXLEV ( ) = ( -110dbm to -48dbm ) ---- RXQUAL ( ) = ( > 0.2 % to % ) Neighbouring Cells ( 6 ) ---- No of cells measured ---- RXLEV of each cell ( ) = ( dbm to -48dbm ) ---- ARFCN of each cell ---- BSIC of each ARFCN The MS has to take at least 32 samples for each measurement Company Confidential Author: Arif R.

Measurement on BTS Measurement Result from BTS --- BS Power
Company Confidential 3/23/2018 Measurement on BTS Measurement Result from BTS --- BS Power --- Received Signal Strength on Uplink ( --110dbm to -48dbm ) --- Receive Quality on Uplink ( BER >0.2 % to 12.8 % ) --- Layer 3 MS Info ( Measurement Report send by MS ) --- Layer 1 MS Info ( MS Power & Timing Advance ) The BTS performs the following measurements as shown above. The BTS has to take at least 32 samples for each measurement of RxLev and RxQual Company Confidential Author: Arif R.

Measurement Averaging
Company Confidential 3/23/2018 Measurement Averaging --- The BSC Averages the Measurement received after a set period ( Hreqave ) --- The averaging could be following types : Unweighted Average Weighted Average Modified Median Unweighted Average --- Average of all samples Weighted A average --- More emphasis on certain samples Modified Median --- Remove exceptional values ( very high or low ) Hreqave : Averaging Period for Rxlev,Rxqual & Timing Advance ( In terms of SACCH Frames ( 480ms ). Range : ( 1, 31 ) Company Confidential Author: Arif R.

Exercise !!! Company Confidential 3/23/2018 Author: Arif R.

Answer Company Confidential 3/23/2018 Author: Arif R.

Power Control Procedure
Company Confidential 3/23/2018 Power Control Procedure MS Power Control BTS BSC MS Power Control SACCH MS Channel Number : MS Power : Power step 1 to 31 BS Power Control ( optional ) MS BTS BSC BS Power Control Channel Number : BS Power : Power step 1 to 31 BS Power Control Company Confidential Author: Arif R.

Company Confidential 3/23/2018 Handover Cell 2 Cell 1 Handover is a GSM feature by which the control and communication of a mobile is transferred from one cell to another if certain criteria's are met. Handover is a process by which the control/communication of a Mobile is transferred from one cell to another Company Confidential Author: Arif R.

Company Confidential 3/23/2018 Criteria for Handover --- Receive Quality (RXQUAL) on Uplink & Downlink. --- Receive Signal Strength (RXLEV) on Uplink & Downlink. --- Distance ( Timing Advance ). --- Interference Level. --- Power Budget. Company Confidential Author: Arif R.

Internal Inter-Cell Handover
Company Confidential 3/23/2018 Internal Inter-Cell Handover SYNCHRONISED BTS C0 C0 Handover between cells of same BTS Company Confidential Author: Arif R.

Internal Inter-Cell Handover
Company Confidential 3/23/2018 Internal Inter-Cell Handover Non-synchronized MSC BSC BTS --- This type of Handover takes place if the cell to which which handover is to be done belongs to the same BSC. --- In this the BSC handles everything without involving MSC. --- The MSC will be informed by the BSC after Handover. Company Confidential Author: Arif R.

Inter-Cell Handover Procedure
Company Confidential 3/23/2018 Inter-Cell Handover Procedure Inter-Cell Handover CH Actvn CH Actvn Ack DR ( Hand Cmd ) Hand CMD Hand Access Hand Detec Phys Info Hand Complete RF CH Release RF CH Release Ack Hand Performed MS BTS (Old) BSC (New) MSC DI ( Hand Comp ) Starts T3103 T3124 Stops T3105 Any Correct Frame Handover decision is taken by BSC. Once a BSC decides upon a handover, the following signaling takes place Channel Activation : BSC sends this message to the target BTS which contains the handover reference number, power step , ciphering info and timing advance details. Channel Actvn ACk : The BTS allocated a channel and waits for reception and then sends this acknowledgment. Handover Command : The mobile is now commanded to tune to the new channel by this message which contains channel description & reference no. Handover Access : On receiving the previous message, mobile sends this access message to the new BTS which is a short burst containing ref no. Handover Detection : This message is sent to the BSC to inform that the Mobile has tuned to the channel. BSC on receiving this message switches the circuits. Handover Complete : The Mobile on synchronizing to the new channel sends this message to the BSC. CH Release : The BSC then sends this message to the old BTS to release the radio channel which is acknowledged by the BTS. Company Confidential Author: Arif R.

Inter-Cell handover Procedure
Company Confidential 3/23/2018 Inter-Cell handover Procedure BTS (Old) BTS (New) BSC MS CH Actvn CH Actvn Ack DR ( Hand Cmd ) Hand CMD Starts T3103 Handover Command Synchronization Indication : Non Synchronized / Synchronized Cell Channel Description : CA - table ( ARFCN's ) for hopping Channel Mode : Signaling,Speech F/H,Date : 9.6,4.8 f/h, 2.4f/h Mobile Allocation : MA Table Starting Time : Starting TDMA Frame No , FN Module 42432 PD : RR TI : 0 MT : HC Cell Description : BA-NO : Band 0 or 1 NCC & BCC : BSIC value ARFCN No: Channel Description --- SDCCH/4,SDCCH/8 or TCH, TN Number or Subchannel No ( SDCCH ) TSC, ARFCN, Single or Hopping, HSN Mobile Allocation Index Offset Handover Reference Power Command --- Power Level ( ) Handover Command Company Confidential Author: Arif R.

Inter-cell Handover Procedure
Company Confidential 3/23/2018 Inter-cell Handover Procedure Synchronous BTS(Old) BSC BTS(New) MS Hand CMD MS Handover Access Handover Detection BTS starts transmission on the activated channel with ciphering BTS starts transmission on SACCH also MS sends Handover Access burst in four successive slots, immediately starts ciphering & starts sending and receiving information. BTS on receiving the correct Handover Access Burst starts reception on the activated channel Asynchronous BTS(Old) BSC BTS(New) MS Hand CMD Handover Access Handover Detection Physical Info Starts T3124 Correct Frame T3105 Stops Synchronous Handover takes place between cells in the same BTS This is because the timing advance of the Mobile from both cells in the same BTS will be same. The value for T3105 should be as low as possible so that the Phy Info message is almost continuously Broadcasted. No of times this Timer is restarted ( or the message is repeated ) is implementation settable). The value for T3124 is set to 320ms . Stops T3124 BTS starts transmission on the activated channel with ciphering,but not on SACCH MS starts T3124,sends Handover Access burst continously, activates deciphering, starts reception BTS sends a Physical Information Message, starts T3105, starts transmission on SACCH , also starts reception on main ch. MS stops T3124 and starts the normal transmission and reception on the main channel Company Confidential Author: Arif R.

Company Confidential 3/23/2018 Inter-Cell Handover Procedure BTS(Old) BSC BTS(New) MS Handover Access MS Hand CMD Handover Detection Starts T3124 Physical Info Starts T3105 Correct Frame Stops T3105 Handover Access Physical Information Handover Detection PD : RR TI : 0 MT : HC Timing Advance : bits Channel Number : TCH ,SDCCH/4,SDCCH/8 TN No ,Subchannel No (SDCCH ) Company Confidential Author: Arif R.

Company Confidential 3/23/2018 Inter-Cell Handover Procedure BTS(Old) BSC BTS(New) MS Handover Complete DI (Handover Complete) RF Channel Release Stops T3103 Handover Performed MSC Handover Performed Message Type : HP Cause : Uplink Quality,Uplink Strength Uplink Strength,Downlink strength Distance, O & M Intervention, Call Control, Better Cell, Equipment Failure,No Resource Cell Indentifier : * Cell identification discriminator : -- Whole CGI/ LAC&CI / CI only Cell identification 1 : MCC + MNC + LAC + CI Radio Channel Identity : * Channel Description, MA table, Starting time Handover Complete PD : RR TI : 0 MT : HC RR Cause : Normal Release ( of old channels ) * Optional Company Confidential Author: Arif R.

Company Confidential 3/23/2018 Inter-Cell Handover Procedure Abnormal Cases BTS(Old) BSC BTS(New) MS MS Handover Access Hand CMD Handover Detection Starts T3124 T3124 Expires ( asynchronous ) Lower layer failure occurs MS Deactivates new channels Activates Old Channels, & sends Handover Failure Stops T3103 DI (Handover Failure) MS resumes normal operation ( as no handover attempt had occurred ) Handover Failure PD : RR TI : 0 MT : HC RR Cause : Abnormal Release ( unspecified ), Channel Unacceptable, timer expired, Invalid Message( unspecified ), No CA available, Protocol errors Company Confidential Author: Arif R.

External Inter-Cell Handover
Company Confidential 3/23/2018 External Inter-Cell Handover MSC BSC BTS --- In this type of Handover,the Mobile is handed over to a cell which belongs to another BSC. --- The MSC is completely involved in this Handover Company Confidential Author: Arif R.

External Inter-Cell Handover Procedure
Company Confidential 3/23/2018 External Inter-Cell Handover Procedure MS BTS BSC(Old) MSC BSC(New) BTS Hand Reqd Starts T 7 Hand Reqst CH Actvn CH Actvn Ack Hand Reqst Ack Hand CMD DI(Hand CMD) Hand CMD Stops T 7 Hand Access Hand Detection Hand Detect The above diagram illustrates the signaling process of an Inter-BSC handover. BSC decides the need for handover and sends a Handover Required message to the MSC which contains the handover reference number and target cell identity. The MSC then sends a Handover Request message to the target BSC to activate a channel in that cell.The BSC on activating the channel sends an acknowledgment to the MSC. On getting an Ack the MSC sends the Handover Command to the Mobile through the BSC which contains the reference number and details of target channel. The mobile tunes to the channel and sends the short bursts of Handover Access burst. The BSC then on getting an indication of this burst sends a Handover Detection Message to the MSC . The MSC on receiving this does the group switching . The MS on proper synchronization with the new BTS sends the Handover Complete message which is forwarded to the MSC. The MSC on receiving this message sends the Clear Command to the old BSC to release all resources. Phy Info Hand Comp DI(Hand Comp) Hand Comp Clear CMD INTER - BSC Handover Company Confidential Author: Arif R.

Company Confidential 3/23/2018 External Inter-Cell Handover Procedure MS BSC(Old) BSC(New) MSC BTS Hand Access Hand Detect Hand Comp Hand Detection DI(Hand Comp) Phy Info Handover Command Message Type : HC Handover Command Message Type : HC RR Cause : Normal Release ( old channels ) - Optional Company Confidential Author: Arif R.

Company Confidential 3/23/2018 External Inter-Cell Handover Procedure Abnormal Case Failure at MS BSC(Old) BSC(New) MSC Handover Failure MS Clear Command Handover Failure PD : RR TI : 0 MT : HC RR Cause : Abnormal Release ( unspecified ), Channel Unacceptable, timer expired, Invalid Message( unspecified ), No CA available, Protocol errors Cause : Radio Interface Failure , reversion to old channel Company Confidential Author: Arif R.

Intra-Cell Handover BTS
Company Confidential 3/23/2018 Intra-Cell Handover BTS Handover between channels / timeslots of same cell Company Confidential Author: Arif R.

Interference Handover on Interference is based on RXQUAL & RXLEV
Company Confidential 3/23/2018 Interference Handover on Interference is based on RXQUAL & RXLEV If RXQUAL is poor and RXLEV is good , then Handover takes place Interference Handover is an Intra-cell Handover Company Confidential Author: Arif R.

Intra-Cell Handover BTS BSC MS Channel Activation Channel Actvn Ack
Company Confidential 3/23/2018 Intra-Cell Handover Channel Activation BTS BSC DR ( Assgn Command) Assignment Command Assignment Complete DI ( Assgn Complete ) Starts T10 Channel Actvn Ack Stops Old Channel New Channel MS RF Channel Release RF Channel Release Ack Channel Number : Activation Type : intra cell handover Channel Mode : Channel Identification : Encryption Information : BS Power, MS Power , Timing Advance: BS & MS Power Parameter : Channel Activation Company Confidential Author: Arif R.

CC - Call Clearing Release of Call MSC TCH Disconnect F A Starts C
Company Confidential 3/23/2018 CC - Call Clearing Release of Call TCH Disconnect Release Release Comp F A C H MSC Starts T305 Stops The Mobile sends a Disconnect Message to request the network to clear an end-to-end connection or is sent by the network to the indicate that an end-to-end connection is cleared. The Network responds back with Release message which indicates that it intends to release the TI and the Mobile should also do so.The Release message has only local significance and does not imply an acknowledgement of clearing from the remote user. The MS responds with Rel Comp indicating that it has released the TI and the Network can now release the TI. Channel Release Channel Release Disconnect Release PD : RR TI : 0 MT : CR Cause : - Normal Release - Abnormal Release, unspecified - No activity on radio path - Preemptive release - No CA available ( handover ) - PD : CC TI:1 -7 MT : R Cause : Not reqd PD : CC TI:1 -7 MT : D Cause : #16 - Normal Clearing #38 - Network Out of Order Release Complete PD : CC TI:1 -7 MT : R Cause : Not reqd Company Confidential Author: Arif R.

Radio Link Failure Radio Link Failure is based on SACCH Messages
Company Confidential 3/23/2018 Radio Link Failure Radio Link Failure is based on SACCH Messages It is controlled by the Radio Link Counter ( S ) The max value of ' S ' is broadcasted on BCCH If Mobile is not able to decode SACCH message ' S ' decreases by 1 If Mobile is able to decode SACCH message ' S ' increases by 2 If ' S ' reaches 0 , Radio Link failure is declared As the Receive Quality for the mobile deteriorates, the mobile is not able to decode SACCH messages, which later result into Link failure as mentioned by the process stated above. Company Confidential Author: Arif R.

Radio Link Failure BCCH = ' S ' is 4 SACCH Blocks 4 3 2 1 ' S '
Company Confidential 3/23/2018 Radio Link Failure BCCH = ' S ' is 4 4 3 ' S ' 2 1 SACCH Blocks Company Confidential Author: Arif R.

Radio Link Failure in Idle Mode
Company Confidential 3/23/2018 Radio Link Failure in Idle Mode Idle Mode Link Failure depends on the counter DSC DSC is initialized to the nearest integer of 90 / Bs_pa_mfrms. For every Paging Message non-decode ( BFI=1), DSC is decreased by 4. For every successful decode, it is increased by 1. Once DSC reaches "0", link failure is declared and Mobile does cell reselection. Company Confidential Author: Arif R.

Air Interface - L2 Signaling
Company Confidential 3/23/2018 Air Interface - L2 Signaling 04.08/ 04.10 04.08/ 04.10 DTAP RIL3 RR RIL3 The Interface between the MS and BTS is the Air Interface. On the Physical Layer it uses thew GSM specified Radio Interface characteristics which is as per GSM recommendations. The data link layer uses the LAPDm ( Link access procedure on Dm channel i.e. control channel.) LAPDm is a variant of LAPD and explained in further sessions. The Layer 3 is again controlled by GSM recommendations and LAPDm LAPDm 04.04 Rad Int 04.04 Rad Int MS BTS Company Confidential Author: Arif R.

Link Access Protocol on Dm ( LAPDm)
Company Confidential 3/23/2018 Link Access Protocol on Dm ( LAPDm) LAPDm signaling is done using Frames. LAPDm frames contain Address, Control and L3 information. LAPDm has a window size of 1 ( every frame sent must be acknowledged before next is sent, in acknowledge mode ) Lapdm frame supports maximum 23 octets only Lapdm frame structure has no flags ( since blocks channels available ). Lapdm message has two SAPI's SAPI = for DTAP and RR signaling SAPI = for Short Message Service ** SAPI : Service Access Point Identifier Company Confidential Author: Arif R.

LAPDm Frames Modes of LAPDm Type of LAPDm frames
Company Confidential 3/23/2018 LAPDm Frames Modes of LAPDm Acknowledge : Every frame sent must receive acknowledgement Unacknowledged : No acknowledgement required for the frames sent Type of LAPDm frames Unnumbered Frames ( U - Frame ) : These provide setting up of acknowledge mode and unacknowledged Information ( I - Frame ) transfer. Information Frames ( I - Frames ) : These convey the actual information ( message ) in acknowledge mode. Supervisory Frames ( S- Frame ) : These manages the flow of I-frames by acknowledging or requesting retransmission of I-frames. The data Link of LAPD is based on HDLC and uses two modes of operations , the Acknowledge mode and and Unacknowledged mode . In the acknowledge mode every frame sent must receive acknowledgement whereas for unacknowledged mode no acknowledge is required for the frames sent. There in general 3 types of HDLC and hence LAPD frames U - Frames which set up the acknowledge mode and does unacknowledged mode Information transfer I - Frames which the actual signaling or information data in acknowledge mode S-Frame which maintains the flow of I-frames by acknowledging or requesting retransmission of I-frames. Company Confidential Author: Arif R.

LAPD Frames Unnumbered Frames
Company Confidential 3/23/2018 LAPD Frames Unnumbered Frames SABM ( Set Asynchronous Balance mode ) : This frame is sent to begin acknowledge mode of information transfer ( I -frame ) Disc ( Disconnect Mode ) : This frame is sent to terminate acknowledge mode of Information Transfer UI ( Unnumbered Information ) : This is used for Unacknowledged Information transfer UA (Unnumbered Acknowledge) : This is used to acknowledge the SABM & DISC frames DM ( Disconnect Mode ) : This indicates the disconnection and SABM could be performed These frames don't use sequencing [ N(R) & N(S) ] SABM UA DISC DM ( or UA ) UI UI UI UI Company Confidential Author: Arif R.

LAPD Frames Information Frames Supervisory Frames
Company Confidential 3/23/2018 LAPD Frames Information Frames These frames are used to transfer Layer 3 Information ( RSL,OML,L2M messages ) in sequence,that is is in acknowledged mode. These frames uses Sequencing Supervisory Frames RR ( Receive Ready ) : Positive Acknowledgement. RNR ( Receive Not Ready ) : Stop sending messages ( buffer is full ). REJ ( Reject ) : Negative Acknowledgement These Frames uses Sequencing [ only N ( R ) ] Company Confidential Author: Arif R.

LAPDm Frames Flow Acknowledge Mode SABM Layer 2 UA Layer 2
Company Confidential 3/23/2018 LAPDm Frames Flow Acknowledge Mode SABM UA I - frame ( C ) RR Disc I - frame ( R ) DM ( or UA ) Layer 2 Layer 2 Layer 3 Layer 2 Layer 3 Layer 2 Layer 2 Layer 2 Company Confidential Author: Arif R.

Lapdm Modes Acknowledge Mode ( with window size of 1 )
Company Confidential 3/23/2018 Lapdm Modes Acknowledge Mode ( with window size of 1 ) Unacknowledged mode Lapdm modes vary on the type of logical channel the information is sent For SAPI 0 : BCCH Unacknowledged CCCH Unacknowledged SDCCH Unacknowledged and Acknowledged SACCH Unacknowledged FACCH Unacknowledged and Acknowledged For SAPI 3 : SDCCH Acknowledged SACCH (TCH) Acknowledged Company Confidential Author: Arif R.

LAPDm Frame Structure LAPDm frame for BCCH,RACH,AGCH,PCH
Company Confidential 3/23/2018 LAPDm Frame Structure LAPDm frame for BCCH,RACH,AGCH,PCH Lapdm frame for SDCCH,SACCH,FACCH There are two different frame structures for LAPDm, The structure for BCCH and CCCH is unack mode structure. It has a Length Indicator Field,RIL3 Message and Fill Bits. Fill Bits : If message is short or is not occupying all 20octets , then the left out bits are filled with these bits ( ) in the downlink , this pattern is used to avoid MS mixing this with FACHH..In the Uplink these will be filled with ( ) Length Indicator Field : This is made up of ELI ( Extension Length Indicator ) which is for future if max octets increases. More bit is used to determine if the message continues in next block (frame) or this frame ends the message. The Length Indicator indicates the number of octets of information contained in the frame. The control filed is similar to LAPD, that is N(S) & N(R) sequencing used for I -frames, N(R) used for S frames and these control bits will have different values in case of U-frames Link Protocol Discriminator = 00 ( not used for GSM ) More bit = 1 indicates more information to follow ( in next block ) = 0 indicates end of information ( message ) Company Confidential Author: Arif R.

LAPD Frame Structure - Control Field
Company Confidential 3/23/2018 LAPD Frame Structure - Control Field The LAPD Frame structure is made up of : Flag : This is used to indicate the begin and end of each frame. One Flag at the end indicates the end of one frame and beginning of next frame. Flag has a pattern of ( 7E ). Bit stuffing is used if the information data also has 5 consecutive ones. FCS : Frame Check Sequence : This provides error checking for the frame, all bits between the flags are checked. If errors are found frame will be retransmitted. Control : This filed has two type of structures. In acknowledge mode it has N(S) and N(R). N(S) is the sequence number of frame sent and N(R) is the sequence number of the frame expected to be received next. The sender can transmit a certain number of frames without waiting for acknowledgement of each frame,. These frame which it can transmit without ack is the window size. The window size for RSL is 2 and OML is 1. I C/R : This one bit indicates whether it is command or response. P/F : In the ack mode if it is Command, then this is P,it polls the other end data link layer for response. The other end transmits the response by setting this bit to F. The command / response indicates the type of L3 Information message whether it is command or repose, whereas this is meant for L2. Extended Address : This bit indicates whether there is extension octet for address field. Company Confidential Author: Arif R.

LAPDm Message in a Burst
Company Confidential 3/23/2018 LAPDm Message in a Burst Company Confidential Author: Arif R.

GSM Signaling Matrix PSTN MAP ISUP RIL3 RSM RSM TUP BSSAP

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GSM Signaling Matrix PSTN MAP ISUP RIL3 RSM RSM TUP BSSAP

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