GSM Channel concept and SDCCH

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SDCCH configration

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GSM Channel concept and SDCCH

  1. 1. Know More - SDCCHNov 17, 2003 S. Rajshekhar Deshraj
  2. 2. Contents• Channel Concepts• Call Setup• Burst & Multi Frames• Mapping of Logical Channels• Definitions of SDCCH• Usage of SDCCH in the GSM network (BSC)• Possible SDCCH Configuration• SDCCH Holding Time Nov 17, 2003 S. Rajshekhar Deshraj
  3. 3. Contents• SDCCH Traffic Estimations• SDCCH Congestion• Reasons for SDCCH congestion• How to detect SDCCH congestions• Preventive actions to avoid SDCCH congestions• SDCCH Dimensioning• Parameters for SDCCH Dimensioning• Counters & Report Analysis Nov 17, 2003 S. Rajshekhar Deshraj
  4. 4. Logical ChannelsNov 17, 2003 S. Rajshekhar Deshraj
  5. 5. Broadcast Channels (BCH)Frequency Correction Channel (FCCH)•Downlink Channel•BTS: Transmits a carrier frequency (Pure sine wave of 67.7 KHz) This Solve 2 purpose : a> Make sure that this is BCCH Carrier b> To allow the MS to synchronize to the frequency•MS: After Switch on MS Scan for this channel, since it has noinformation to which frequency to use. FCCH carrier enables a mobile totune its frequency to that being broadcast by the BTS. Nov 17, 2003
  6. 6. Broadcast Channels (BCH)Syncronization Channel (SCH)•Downlink Channels•BTS: Transmits TDMA Frame number + Base Station Identity Code (BSIC= NCC + BCC )•MS: MS decodes the BSIC if the chosen BTS is GSM Base station within a cell Nov 17, 2003
  7. 7. Broadcast Channels (BCH)•Broadcast Control Channel (BCCH)•Downlink Channels•BCCH contains the detailed Network and cell specific information such as : •Frequency used by Cell and its Neighboring cells. •Frequency HSN •Paging Groups •LAI •Max output power allowed in the cell Nov 17, 2003
  8. 8. Common Control Channels (CCCH)Paging Channel (PCH)•Downlink Channels• BTS: Broadcast the paging message to indicate the Incoming Calls or Incoming SMS. Paging message also includes the MS’s identity number IMSI/TMSI• MS: MS listens to the PCH. If it identifies its own mobile subscriber identity number on the PCH, it will respond. Nov 17, 2003
  9. 9. Common Control Channels (CCCH)Random Access Channel (RACH)•RACH is transmitted Uplink only•When mobile is paged , it replies on RACH requesting a signaling channel.•RACH can also used if the MS wants to make a contact the NW/Originating calls Nov 17, 2003
  10. 10. Common Control Channels (CCCH)Access Grant Channel (AGCH)•Downlink channel•AGCH is answer to the RACH•NW assigns a signaling channel (SDCCH) to the MS. Thisassignment is performed on the AGCH Nov 17, 2003
  11. 11. Dedicated Control Channels (DCCH)Stand Alone Dedicated Control Channel (SDCCH)•SDCCH is bi-directional Channel•System Signaling•Call Setup•Authentication•Location Update•Assignment of Traffic channels and•Transmission of Short messages Nov 17, 2003
  12. 12. Dedicated Control Channels (DCCH)Slow Associated Control Channel (SACCH)•SACCH is transmitted in both Uplink and Downlink directions•SACCH is associated with each SDCCH and also with TCH•Uplink : MS Sends the averaged measurement on its own BTS andneighboring BTS’s•Downlink: MS receives information regarding informationconcerning •Transmit power to use •Instructions on Timing Advance Nov 17, 2003
  13. 13. Dedicated Control Channels (DCCH)Fast Associated Control Channel (FACCH)•While Calls in progress and HO is required FACCH is used•FACCH works in Stealing mode meaning that one 20ms segment of speech is exchanged for signaling information necessary for the HOCell Broadcast Channel (CBCH)•CBCH is used in Downlink only•It is used to carry Short Message Service Cell Broadcast(SMSCB) and uses the same physical channel as the SDCCH Nov 17, 2003
  14. 14. Traffic Channels (TCH)Traffic channels are Bi-directional logical channel that transfer the userspeech or data.•Full Rate TCH ( TCH/F) : •This channel carries information at a gross rate at 13Kbit/s * * Now it is 22.8 Kbit/s with latest R9.1•Half Rate TCH (TCH/H) : •This Channel carried information at a gross rate at 6.5Kbit/s* * Now it is 11.4 Kbit/s with latest R9.1•Enhance Full Rate : •The speech coding in EFR is still done at 13Kbit/s, but the coding mechanism is different that is used for normal FR. EFR gives better speech quality at the same bit rate than normal FR. Nov 17, 2003
  15. 15. Call to an MS More..Nov 17, 2003 S. Rajshekhar Deshraj
  16. 16. Relationship Between Burst & FrameBurst : Physical content of a TS is called Burst.There are 5 types of Bursts each having 15/26 ms duration and 156.25 Bits.Hyperframe: In GSM system every TDMA frame is assigned a fixed number, which repeats itself in a time period of 3 HOURS 28 MINUTES 53 SECONDS 760 MILLISECONDS. This time period is referred to as Hyperframe.Superframe : =51x26 Multiframes. So, Duration =51x26x8x15/26=6Sec 120msMultiframe :There are two types of multiframe. 26 TDMA Frame Multiframe :Used to carry TCH, SACCH and FACCH Duration =26 x 8 x 15/26 =120ms 51 TDMA Frame Multiframe : Used to carry BCCH,CCCH,SDCCH and SACCH. Duration =51 x 8 x 15/26 =235.38ms Nov 17, 2003 S. Rajshekhar Deshraj
  17. 17. TDMA frames with Common and Dedicated Channels Nov 17, 2003
  18. 18. BurstsNormal Bursts: This burst is used to carry information on : •Traffic channel •SDCCH Channel •Broadcast Control Channel •Paging Channel •Access Grant Channel •SACCH & FACCH Channel 1 Time slot = 156.25 bits durations (15/26 = 0.577 ms ) TB Encrypted bits Training Sequence Encrypted bits TB GP F F 3 57 26 57 3 8.25 F : One Stealing Bit:=0 Indicates 57bit packet contains user data or speech :=1 Indicates burst stolen for FACCH Signalling RxQual derived from the 26 bit midable from the TDMA frame Nov 17, 2003
  19. 19. BurstsFrequency Bursts:All 148 bits(142+6) are coded with 0. The output of GMSK Modulator is a fixedfrequency signal exactly 67.7 Khz above the BCCH carrier frequency.Thus the MS on receiving this fixed frequency signal fine tunes to the BCCHfrequency and waits for the Sync burst to arrive after 1 TDMA Frame .i.e=15/26*8=4.615ms 1 Time slot = 156.25 bits durations (15/26 = 0.577 ms ) TB TB GP ALL ZERO 142 BITS 3 3 8.25 Nov 17, 2003
  20. 20. BurstsSynchronization Bursts:This burst is used for time synchronization of the MS 1 Time slot = 156.25 bits durations (15/26 = 0.577 ms ) TB SCH DATA Extended Training Sequence SCH DATA TB GP 3 39 Bits 64 Bits 39 Bits 3 8.25 39Bit x 2=78 Bits :Are decoded to arrive 25-SCH control bits and that contains the information of the NCC ,BCC & TDMA FN 64 Bits : Long training seq. of 64 Bits are identical for all BTS Nov 17, 2003
  21. 21. BurstsAccess Bursts:This burst is used only for initial access by the MS to the BTS which applies 2 cases :•For connection setup when idle state where a CHAN_REQ message is sent usingaccess burst•For HO when MS send HND_ACC message. 1 Time slot = 156.25 bits durations (15/26 = 0.577 ms ) TB SCH Sequence RACH Data TB Guard Band 8 41 Bits 36 Bits 3 68.25 Bits 36Bit Contains : BSIC+CHAN_REQ or HND_ACC 41Bit Contains : Fixed bit sequence allow BTS to recognize it is Access Burst 86.25 bits GP: Long GP enables BTS to get Propagation delay information. Nov 17, 2003
  22. 22. BurstsDummy Bursts:To enable the BCCH frequency to be transmitted with a constant power level, dummyburst are inserted.This burst is transmitted on CHGR=0 when no other type of burst is to be sent.Thus it makes possible for MS to perform the power measurement on the BTS in orderto determine which BTS to use for initial access or which to use for HOCCCH is replaced by the dummy page, when there is no paging message to transmit. 1 Time slot = 156.25 bits durations (15/26 = 0.577 ms ) TB Mixed Bits Training Sequence Mixed Bits TB Guard Band 3 58 26 58 3 8.25 58Bits: Coded with pseudo random bit seq. to prevent confusion with Freq correction burst Nov 17, 2003
  23. 23. Mapping of Logical ChannelMethod of transmitting logical channels onto physical channel is called MappingFCCH+SCH+BCCH+CCCH: An idle MS search for the FCH. When MS findsthe frequency correction burst it knows that this is TS 0 on CHGR=0The cycle means F,S,B repeats after the Idle frame I.e. at Frame no 50. Cycle=51TS TS=0 / CHGR=0 DOWNLINK 0 1 7 0 1 7 0 1 7 F0 F1 F2-F5 F6-9 F10 F11 F12-F15 F16-19 F20-23 F24 F25 F26-29 F30 F31 F32-F35 F36-F39 F40 F41 F42-F45 F46-49 F50 TS-0 F S BCCH CCCH F S BCCH CCCH CCCH F S CCCH F S CCCH CCCH F S CCCH CCCH I F: FCCH 1 TS ( Use 4 Slots in each 51 TDMA Frame) S: SCH 1 TS ( Use 4 Slots in each 51 TDMA Frame) I: IDLE 1 TS BCCH 4 TS CCCH 4 TS (PCH or AGCH) Paging Block 51 TDMA Frame = 9 Paging Blocks TS=0 / CHGR=0 UPLINK F0 F1 F3 F3 F4 F5 F6 F7 F8 F9 F10 F46 F47 F48 F49 F50 TS-0 R R R R R R R R R R R R R R R R R: RACH 1 TS Nov 17, 2003
  24. 24. Mapping of Logical ChannelSDCCH+SACCH: Cycle=102 TS This sequence is repeated after last idle frame.The Uplink & Downlink pattern are time shifted, so SDCCH sub channel is sent in frame 0-3 on downlinkand in frame 15-18 on uplink. The reason for this is to achieve efficient communication, by giving MS time tocalculate its answer to the request received on down link SDCCH TS=2 / CHGR=0 DOWNLINK 1 2 3 1 2 3 1 2 3 7 F0-F3 F4-F7 F8-F11 F12-F15 F16-F19 F20-F23 F24-F27 F28-F31 F32-F35 F36-F39 F40-F43 F44-F47 F48 F49 F50 SDCCH0 SDCCH1 SDCCH2 SDCCH3 SDCCH4 SDCCH5 SDCCH6 SDCCH7 SACCH0 SACCH1 SACCH2 SACCH3 I I I SDCCH0 SDCCH1 SDCCH2 SDCCH3 SDCCH4 SDCCH5 SDCCH6 SDCCH7 SACCH4 SACCH5 SACCH6 SACCH7 I I I TS=2 / CHGR=0 UPLINK I: IDLE 1 TS 1 2 3 SDCCH 4 TS 1 2 3 1 2 3 7 SACCH 4 TS F0-F3 F4-F7 F8-F11 F12 F13 F14 F15-F18 F19-F22 F23-F26 F27-F30 F31-F34 F35-F38 F39-F42 F43-F46 F47-F50 SACCH5 SACCH6 SACCH7 I I I SDCCH0 SDCCH1 SDCCH2 SDCCH3 SDCCH4 SDCCH5 SDCCH6 SDCCH7 SACCH0 SACCH1 SACCH2 SACCH3 I I I SDCCH0 SDCCH1 SDCCH2 SDCCH3 SDCCH4 SDCCH5 SDCCH6 SDCCH7 SACCH4 I: IDLE 1 TS SDCCH 4 TS SACCH 4 TS Nov 17, 2003
  25. 25. Mapping of Logical ChannelTCH+SACCH: 0&2 used by control channels. This leaves TS-1and 3-7 free for theuse by TCHs.Repetition time (Cycle) =26 Frames .i.e. =26*8*(15/26)=120msEvery 13th TS contains SACCH. Downlink contains TA value and Uplink containsmeasuring report. TS=1 / CHGR=0 DOWNLINK 0 1 2 7 0 1 0 1 2 7 F0 F1 F2 F3 F4 F5 F6 F7 F8 F9 F10 F11 F12 F13 F14 F15 F16 F17 F18 F19 F20 F21 F22 F23 F24 F25 F26 T T T T T T T T T T T T A T T T T T T T T T T T T T I T: TCH 1 TS A: SACCH Nov 17, 2003
  26. 26. Usage of SDCCHThe SDCCH are used in some different ways in the GSM network:• Registrations: Periodic Location Updates, IMSI Attach/Detach• Call Setup: Immediate Assignment -> Assignment.• SMS point-to-point: SMS messages to/from MS in Idle mode.• Fax Setup• Optional: USSD (Unstructured Supplementary Service Data) data transfer. MS<->Network. Similar to SMS. Controlled by the MSC. Nov 17, 2003
  27. 27. Possible ConfigurationsSDCCH/8 : 8 Sub channels for signaling are mapped on 1 TS, this results 1 less TCHfor the cell.SDCCH/4 (Combining BCCH and SDCCH) :4 Sub channels for signaling are mappedon BCCH TS. As a result Paging capacity on BCCH is reduced by 1/3.CBCH : If CBCH is active 1 sub channel of SDCCH is replaced by 1 CBCH channel.Limitations : SDCCH/8 in a cell = Number of TRX’s CONFIGURATIONS HYD007A HYD006A 1 TRX 2 TRX SDCCH TCH SDCCH TCH SDCCH/4 4 7 4 15 SDCCH/4+CBCH 3 7 3 15 SDCCH/8 8 6 8 14 SDCCH/8+CBCH 7 6 7 14 SDCCH/4+SDCCH/8 12 6 12 14 SDCCH/4+SDCCH/8+CBCH 11 6 11 14 SDCCH/4+SDCCH/8+SDCCH/8 X X 20 13 SDCCH/4+SDCCH/8+SDCCH/8+CBCH X X 19 13 Nov 17, 2003
  28. 28. Possible Configurations -BCCH COMBC+CBCH CELL BCCH CBCH SDCCH NOOFTCH HYD007A 1 1 3 7 CHGR BPC CHANNEL CHRATE SPV STATE ICMBAND CHBAND 0 4590 SDCCH-28646 BUSY SDCCH-28645 IDLE CBCH-34305 BUSY SDCCH-28644 IDLE BCCH-34797 BUSY 4496 TCH-4629 FR 1,2 IDLE 4497 TCH-4630 FR 1,2 IDLE 4499 TCH-4631 FR 1,2 IDLE 4505 TCH-4654 FR 1,2 IDLE 4506 TCH-4655 FR 1,2 IDLE 4509 TCH-4661 FR 1,2 IDLE 4575 TCH-4670 FR 1,2 IDLE Nov 17, 2003
  29. 29. Possible Configurations -BCCH NCOMB+CBCH CELL BCCH CBCH SDCCH NOOFTCH HYD006A 1 1 7 14 CHGR BPC CHANNEL CHRATE SPV STATE ICMBAND CHBAND 64K 0 6899 SDCCH-27810 IDLE SDCCH-27809 IDLE CBCH-34619 BUSY SDCCH-27808 IDLE SDCCH-27807 IDLE SDCCH-27806 IDLE SDCCH-27805 IDLE SDCCH-27804 IDLE 6900 BCCH-34804 BUSY 6887 TCH-1242 FR 1,2 IDLE NONE 6888 TCH-1243 FR 1,2 IDLE NONE 6891 TCH-1246 FR 1,2 IDLE NONE 6893 TCH-1248 FR 1,2 IDLE NONE 6895 TCH-1250 FR 1,2 BUSY NONE 6897 TCH-1252 FR 1,2 IDLE NONE CHGR BPC CHANNEL CHRATE SPV STATE ICMBAND CHBAND 64K 1 6885 TCH-1240 FR 1,2 BUSY NONE 6886 TCH-1241 FR 1,2 IDLE NONE 6889 TCH-1244 FR 1,2 IDLE NONE 6890 TCH-1245 FR 1,2 IDLE NONE 6892 TCH-1247 FR 1,2 IDLE NONE 6894 TCH-1249 FR 1,2 BUSY NONE 6896 TCH-1251 FR 1,2 IDLE NONE 6898 TCH-1253 FR 1,2 IDLE NONE Nov 17, 2003
  30. 30. SDCCH CongestionSDCCH congestion: All SDCCH in a cell are at the same time busy for aperiod of time which leads to rejection for new MS.Reasons :• Hanging SDCCH: Are SDCCH that are hanging busy and unusable for a long time (many minutes or indefinite). Hanging SDCCH are generally caused by SW faults.• Heavily used SDCCH: SDCCH seen as continuously busy even though they are used by different MS and thus carries traffic. It may cause due to : > Extreme end-user behaviors: Sport event ending, festivals or celebrations. > Increased mean hold time of the SDCCH: Mean hold time increase from 2 to 10 seconds can give SDCCH congestion. Nov 17, 2003
  31. 31. SDCCH Holding TimeNormal Location Updating = 3.5 SecPeriodic Registration = 3.5 SecIMSI Attach = 3.5 SecIMSI Detach = 2.9 Sec (IMSI detach Indication message sent to NW, no authentication is performed (which normally takes 0.6Sec) & no ack is sent to MS.)Call Setup = 2.7 Sec (MOC) = 2.9 Sec (MTC)Short Message Service(SMS) = 6.2 Sec (Vary depending the length of SMS)Fax Transmission = 2.7 Sec (MOC) = 2.9 Sec (MTC)False Access = 1.8 Sec (when Channel req is rec’d by system ,as SDCCH is allocated by sending Imm Ass message, and the system waits a certain time before performing disconnection.) Nov 17, 2003
  32. 32. SDCCH Traffic EstimationsNormal Location Update: Mean Holding time =3.5 Sec No of Location update =1.0 per sub and BHAC: Avg No of Location updates =1000X(1 X 3.5)/3600=0.972 mE/SubIC : No Location updating at all =1000X(0 X 3.5)/3600=0 mE/SubBC: 3 times the Avg no of Location updates =1000X(3 X 3.5)/3600=2.916mE/SubSMS: Mean Holding time =6.2 Sec No of SMS submitted =1.0 per Sub and BHTraffic : 1000 X (1.0 X 6.2) / 3600 =1.7 mE/subCall Setup: Mean Holding time =2.7 Sec(MOC) & 2.9 Sec(MTC) Mob Originating Traffic (Incl B Ans) =0.8 BHCA Mob Terminating Traffic (Incl B Ans) =0.4 BHCATraffic : 1000 X {(0.8 X 2.7)+(0.4 X 2.9)} / 3600 =0.9 mE/sub Nov 17, 2003
  33. 33. Reasons for SDCCH congestionIncreased mean hold time of SDCCH can be caused by:• Too low signal strength at access to the system Due to LSS MS will be lost communication with the system, This will lead to timeout in the BSC (RLINKT ), and thus the SDCCH is used until timeout. Increase ACCMIN.• Congestion of TCH/TRA/RALT Will increase CP execution time before rejecting Imm Ass. Minor increase in mean hold time expected.• C7 problems to MSC (or TRC) In case of C7 signalling problems (SCCP) towards MSC (and/or TRC) can lead to timeout on SCCP connection setup. This will lead to more than 2 minutes hold time for SDCCH.• Handover on SDCCH Handover on SDCCH will in itself increase mean hold time on SDCCH. However minor increase is expected. Nov 17, 2003
  34. 34. Reasons for SDCCH congestion• Congestion on Air-interface Congestion on Air-interface leads to delay in communication to the MS. Can give timeout in BSC during Imm Ass.Increases SDCCH mean hold time with more than 2 seconds.• Congestion on Abis (LAPD link) Congestion on Abis leads to delay in communication with BTS and MS. Can give timeout in BSC during channel activation (TCHACTIVE). Increase SDCCH mean hold time with more than 5 seconds..• Congestion on A-interface Congestion on the A-interface will lead to increased mean hold time on SDCCH. Increase is unknown.• High load in MSC/VLR or HLR High load in MSC/VLR and/or HLR will lead to increased mean hold time on SDCCH. Increase is unknown. Nov 17, 2003
  35. 35. How to detect SDCCH congestion in the BSCThere is no good way to detect SDCCH congestion in real time in theBSC!A number of symptoms to look for:• Increased CP Load.• Decreased usage of TRA devices.• Location Updates fails => Mobile terminating calls does not reach the subscriber.• Subscriber complaints. Can not access the system.• STS counters . Object type: CLSDCCH and CLSDCCHO.• Seizure Supervision of LCHs (but only for Hanging SDCCHs!) Nov 17, 2003
  36. 36. Preventive actions to avoid SDCCH congestion• Avoid combined BCCH in cells with many SDCCHs• Use the optional feature Adaptive Configuration of SDCCHs (ACLC)• Use USSD (Unstructured Supplementary Service data) with care, can cause long meanhold time on SDCCH.• Avoid Handover on SDCCH• Proper Dimensioning of the TCHs and TRA devices in the BSC.• Use recommended values for Periodic Location Updates Avoid unnecessary Periodic Location Updates : BSC: T3212 (RLSBC) = 40 (4 hours) MSC: BTDM (MGIDI) = 240 (4 hours) MSC: GTDM (MGIDI) = 6 (6 minutes)• Use Immediate Assignment on TCH.• Increases the no of SDCCH in a Cell where SDCCH load is high Nov 17, 2003
  37. 37. SDCCH DimensioningSDCCH Dimensioning is a compromise between SDCCH blockingrate and TCH Capacity. In order to have a successful call setupthere has to be an available SDCCH as well as available TCH.Basic SDCCH configuration: It is recommended to choose 1 SDCCH/8 as the basic configuration for all the cells, If LA> 2100 Erlang (500 TRX) 1 SDCCH/4 as the basic configuration for all the cells, If LA< 2100 Erlang (500 TRX) Nov 17, 2003
  38. 38. SDCCH DimensioningAutomatic SDCCH dimensioning:This can be done with optional Adaptive Configuration of LogicalChannel feature.This feature will add extra SDCCH/8 by reconfiguring idle TCHwhen SDCCH load is high, and revert back to TCH if SDCCH loadgoes down.Manual SDCCH Dimensioning :•Monitoring SDCCH / TCH Traffic in a cell•SDCCH/TCH load ratio•SDCCH Grade of Service:- Max allowed TCH GOS % = 2 % The rule of Thumb says: SDCCH/4 : Max. SDCCH GOS =1/2 * 2= 1 % SDCCH/8 : Max. SDCCH GOS =1/4 * 2= 0.5% Nov 17, 2003
  39. 39. SDCCH DimensioningImmediate Assignment on TCH:In case of this feature on the channel administration assigns TCH forsignaling instead of an SDCCH, based on 7 different channelsallocation strategies (CHAPs)TCH first strategy : Decreases the SDCCH load and enable to use SDCCH/4 in all the cells Traffic load on TCH will in this case increases substantially so this strategy is not recommended.SDCCH first strategy : SDCCH is always allocated first if available, otherwise signaling is performed on TCH. Nov 17, 2003
  40. 40. SDCCH DimensioningExample :ASSUME: CELL=3TRX ,SDCCH Traffic =4 Erlang, Bcchtype=NCOMB.No CBCHGOS: SDCCH/4 = 1%, SDCCH/8 =0.5% & TCH % =2%1> When Immediate Assignment on TCH not usedErlang B Table :To maintain 0.5 % GOS & 4 Erlang min 13 Subchannels reqd2SDCCH/8 => TCH=(3TRX*8TS) –(1BCCH)-(2SDCCH/8)=21TCH’s21TCH’s with 2 % GOS => 14.04 Erlang2> When Immediate Assignment on TCH usedIf we use 1SDCCH/8 only than 4 Erlangs with 8 sub channels GOS=>3 %Congested Erlang will be =4 Erlang x 3 %=0.12Erlang1SDCCH/8 => TCH=(3TRX*8TS) –(1BCCH)-(1SDCH/8)=22TCH’s22TCH’s with 2 % GOS => 14.9 ErlangActual TCH Capacity=14.9 – 0.12 = 14.7 ErlangTCH Capacity in the cell is increased with 0.7 Erlang Nov 17, 2003
  41. 41. SDCCH DimensioningImmediate Assignment on TCH not used Nov 17, 2003
  42. 42. SDCCH DimensioningRecommended SDCCH Configurations Nov 17, 2003
  43. 43. SDCCH DimensioningHALF RATE CAPACITY CALCULATIONHalf rate will affect SDCCH dimensioning since more signaling will bereq’d when no of TCH is increased.Important dimensioning factor is therefore the Half rate penetration.i.e.the % of Half rate mobile in a NW.Example: 2 TRX Cell, Half Rate Penetration =10 %, 1 SDCCH/8TCH/F =14 support 14 SubscriberPenetration 10% of 14 is 1.4 = 2 Subscribers (Req’d 2 Half Rate TCH/H)Total 13 TCH/F+2TCH/H = 15 TCH requiredCapacity :Erlang B Table: 15 TCH @ 2% GOS => 9.0096 Erlang Nov 17, 2003
  44. 44. SDCCH DimensioningMax Allowed SDCCH/TCH Load Ratio (Half Rate) AC : Average Cells BC : Border Cells IC : Inner Cells Nov 17, 2003
  45. 45. SDCCH DimensioningDimensioning based on STS dataMore accurate dimensioning is achieved by using cell statistics .i.e. STScounters •SDCCH Traffic •TCH Traffic •SDCCH/TCH Load Ratio % •SDCCH Congestion •TCH Congestion •SDCCH Mean Holding Time •Availability of SDCCH Channels •Availability of TCH Channels Nov 17, 2003
  46. 46. ParametersMFRMS :This parameter defines period of transmission for PAGING REQUEST messages to the samepaging subgroup.T3212 : Is the periodic registration timerACCSTATE : Activate/Deactivate the Adaptive config of logical channel feature per cell basisCHAP :Selecting Channel Allocation profile per cell.SLEVEL: The attempt to increase the number of SDCCH/8 will take place when allocation of anSDCCH has failed due to congestion.STIME :Parameter STIME determines how long the system waits before the number of SDCCH/8added by this function is decreased when the demand for signalling channels has returned to a lowlevelBTDM :Implicit detach supervision should be equal or longer than T3212 in BSC.GTDM : is an extra Gurad time in minutes before the subscriber is set to detach.RLINKT: Radio link time-out This parameter defines the time before an MS disconnects a call due to failurein decoding SACCH messages. The parameter is given as number of SACCH periods (480ms). Nov 17, 2003
  47. 47. Parameters for SDCCH DimensioningNov 17, 2003
  48. 48. STS CountersCCALLS : Call attempt counterCCONGS : Congestion counterCTRALACC : Traffic level accumulator.CNSCAN : Number of accumulations of SDCCH traffic level counter.CNDROP : Dropped connections due to Failure.CNUCHCNT : Number of defined channels.CAVAACC : Available channels accumulator.CMSESTAB : Successful MS channel establishment on SDCCHs.CTCONGS : SDCCH congestion time ( Sec) Nov 17, 2003
  49. 49. FormulasNo. of SDCCH Attempts CCALLSSDCCH Congestion (%) 100 X { CCONGS / CCALLS }No. of SDCCH Connections CMSESTABSDCCH Establishments No 100 X {CMSESTAB / (CCALLS - CCONGS)}Congestion (%)SDCCH Time Congestion (%) 100 X { CTCONGS / (RPL * 60)}SDCCH Drop (%) 100 X { CNDROP / CMSESTAB }SDCCH Mean Holding Time RPL X 60 X {(CTRALACC/CNSCAN) / CMSESTAB }(Sec.)SDCCH Traffic (Erlang) CTRALACC / CNSCANSDCCH/TCH Ratio (CTRALACC/CNSCAN) / ((TFTRALACC/TFNSCAN)+ (THTRALACC/THNSCAN)) Nov 17, 2003
  50. 50. Quality Report : Call Setup Analysis Report Measuring Period : 03 Nov 2003 to 09 Nov 2003 (7Days) (Weekly Avg Stats) W-6 QUALITY REPORT :Call Setup Analysis Report ( W-6) 23.09.03 S DRP(HYD) S DRP (ROAP) SCSR %(HYD) SCSR % (ROAP) CONR% (HYD) CONR% (ROAP) ALL SDRP>1% SER <96% CONR >0.5 %15Sep-21Sep 134 Cells 275 Cells 175 Cells 357 Cells 68 Cells 109 Cells 72Cells22Sep-29Sep 127 Cells 295 Cells 192 Cells 378 Cells 98 Cells 174 Cells 116Cells29Sep-5Oct 112 Cells 309 Cells 187 Cells 400 Cells 71 Cells 135 Cells 97Cells06Oct-12Oct 25 Cells 154 Cells 178 Cells 382 Cells 55 Cells 109 Cells 81Cells03Nov-09Nov 89 Cells 295 Cells 206 Cells 372 Cells 59 Cells 78 Cells 60Cells Sr No CELL NOD >1% CELL NOD >1% CELL < 96 % CELL < 96 % CELL >0.5% NOC CT CELL >0.5% NOC CT Worst Cells (S) (S) 1 HYD001B 633 1.08 ADO001B 109 1.52 HYD012C 73.35 KOL001B 65.95 HYD201A 3.31 3081 1952 HIN002C 2.37 90 326 NIZ001A 2 HYD004B 305 1.03 ADO002B 54 1.33 HYD117C 78.45 JGP001C 72.07 HYD176A 3.19 2862 8177 KAD001B 2.35 602 1989 NIZ001B 3 HYD005A 359 1.54 AKI001A 29 1.04 HYD155B 81.57 HIN002C 73.01 HYD176C 2.98 1695 4397 GUN009B 2.19 641 2410 CHL001A 4 HYD007B 79 1.34 AKI001B 21 1.04 HYD161B 82.57 RAJ001B 73.06 HYD176B 2.3 942 3095 VIZ027C 1.91 267 638 BHI001A 5 HYD012C 432 6.51 AKI001C 37 2.15 HYD168A 83.77 VIZ020C 73.67 HYD137C 1.94 559 1423 KAD001C 1.72 392 1702 MAH002B 6 HYD018A 433 1.18 AMA001A 3 1.54 HYD058A 83.99 JGP001A 75.2 HYD168A 1.75 207 656 HIN001B 1.59 183 664 KHA001B 7 HYD018B 653 1.13 AMA001A 82 2.66 HYD124B 84 VJA018B 75.81 HYD005B 1.6 725 2465 ANA001B 1.42 275 1084 TEN002C 8 HYD020B 298 1.02 AMA001B 37 1.08 HYD146B 86.41 CHI001C 77.68 HYD155A 1.39 152 403 TEN002C 1.4 372 1434 TIR008A 9 HYD025C 481 1.28 AMA001C 5 2.94 HYD012A 86.52 EMG001C 78.01 HYD161B 1.36 138 262 KAD001A 1.33 268 1127 AKI001A 10 HYD026C 653 1.7 AMA001C 72 2.94 HYD093B 86.86 RAZ001B 78.98 HYD137B 1.3 257 993 VIZ023C 1.32 183 790 BPL001B 11 HYD028A 413 1.03 ANK001B 144 1.11 HYD170B 87 NID001C 79.41 HYD054B 1.28 386 1654 ADO001C 1.32 190 860 TVR001C 12 HYD028C 601 1.23 ANN001A 14 3.29 HYD155A 87.29 CHL004C 79.47 HYD170B 1.27 139 375 GOD001B 1.31 372 1099 DHA001C 13 HYD030C 373 1.26 ANN001B 30 2.15 HYD161C 87.59 RJM007B 80.13 HYD171B 1.23 323 1219 SUL001A 1.3 71 169 MAH002A 14 HYD031C 581 1.35 ANN001C 96 5.64 HYD089B 87.82 VJA020A 81.21 HYD168C 1.22 82 320 MAH002A 1.23 104 390 HIN001B 15 HYD038A 327 1.11 ANP001A 18 1.06 HYD011B 87.85 ONG004B 81.78 HYD137A 1.1 129 346 STP001B 1.05 374 1865 BPL001C 16 HYD040A 279 1.07 ANP001B 29 2.19 HYD121B 87.97 ANN001A 81.92 HYD177B 1.05 206 791 VSP001C 1.03 135 270 TAD001C 17 HYD040B 522 1.3 ANP001C 20 1.7 HYD146C 88.01 CHI003B 82.55 HYD142A 1.02 147 701 STP001A 1.01 329 1542 CHL002C 18 HYD042A 505 1.14 AVA001A 49 1.95 HYD145B 88.23 VSP001B 82.8 HYD053C 1.01 161 496 TVR001C 1.01 258 924 MAC001A 19 HYD045B 1632 1.28 AVA001B 26 1.13 HYD108C 88.49 ANN001C 83.19 HYD161C 1 95 147 RJM008B 0.98 15 65 DHA001B 20 HYD051C 229 1.01 BHI001A 258 1.45 HYD101C 88.71 VJA019B 83.22 HYD153C 0.99 191 541 SAN001B 0.98 134 318 ADO001B LEGENDS NOC SDCCH Congestion Counter SDRP SDCCH Drop Rate % CT(S) Cong. Time in Secs (Week Tot) NOD Week Total Dropped SDCCHs ALL SDCCH Drop Rate % SCSR SDCCH Call Success Rate % SDCCH Estab Success Rate % CONR SDCCH Congestion rate % SDCCH Congestion rate % Nov 17, 2003
  51. 51. Know More - SDCCH Thank youNov 17, 2003 S. Rajshekhar Deshraj
  52. 52. Call Setup-Mobile Terminating Call MS BTS BSC MSC 1>Paging(LAI+IMSI/TMSI) PCH 2>Paging Command 3>Paging Req(Imsi on PCH) Imsi/Tmsi+PG+TRX+CG+TNRACH 4>Channel Req(On RACH) 5>Channel Reqd (Access Delay) 6>Channel Actn (MSPwr,BSPwr,TA) 7>Channel Activation AckAGCH 8>Imm Assign Cmd(On AGCH , Freq 8>Immediate Assign +TS+ SDCCH SubChannel No+TA SABM (Paging Resp:IMSI/MS Class) UA(Paging Resp) Unnumbered Ack 9>Estblish Ind (Paging Resp) 9>Conn Req (Paging Resp: BSC Frame which confirms only 1 MS is IMSI+MS Class add CGI) using Sig ChannelSDCCH 10>Auth Req (128 bit RAND+ 10>Auth Req (128 bit 10>Auth Req (128 bit RAND+3bitCKSN) 3bit CKSN) RAND+3bitCKSN)SDCCH 11>Auth Response (MS Calculate 11>Auth Response (SRES) SRES & Kc with its own Ki stored in 11>Auth Response (SRES) SIM by appling algorithm A3&A8) Next.. Nov 17, 2003
  53. 53. Call Setup-Mobile Terminating Call MS BTS BSC MSC 14>Setup (Req for Services I.e.SDCCH 14>Setup 14>Setup Speech/Data/Fax etc)SDCCH 15>Call Confirmed 15>Call Confirmed 15>Call Confirmed 17>Channel Activation 16>Assignment Req (BSC Allocated Idle TS for Traffic) (MSC send CIC to BSC) 18>Channel Activation AckSDCCH 19>Assignment Cmnd (BSC send 19>Assignment Cmnd (BSC send message on SDCCH to MS telling to message on SDCCH to MS telling to go go TCH) TCH) TCH 20>Assign Comp (MS tune to TCH 20>Assign Comp (MS tune to TCH 20>Assign Comp (MS tune to TCH and send Ind that Chan is Seized) and send Ind that Chan is Seized) and send Ind that Chan is Seized) 21>RF Chann Realease TCH 21>RF Chann Realease Ack 22>Alert (MS Send Alert to MSC as 22>Alert (MS Send Alert to MSC as 22>Alert (MS Send Alert to MSC as soon as the ringing is started in MS) soon as the ringing is started in MS) TCH soon as the ringing is started in MS) 23>Connect (When MS Sub Answer 23>Connect (When MS Sub Answer the Conn message sent to MSC) 23>Connect (When MS Sub Answer the Conn message sent to MSC) the Conn message sent to MSC) TCH 24>Connect Ack 24>Connect Ack 24>Connect Ack Exit.. Nov 17, 2003

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