53
Nov 17, 2003 Know More - SDCCH S. Rajshekhar Deshraj

GSM Channel concept and SDCCH

Embed Size (px)

DESCRIPTION

SDCCH configration

Citation preview

Page 1: GSM Channel concept and SDCCH

Nov 17, 2003

Know More - SDCCH

S. Rajshekhar Deshraj

Page 2: GSM Channel concept and SDCCH

Contents

Nov 17, 2003

• 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

S. Rajshekhar Deshraj

Page 3: GSM Channel concept and SDCCH

Contents

Nov 17, 2003

• 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

S. Rajshekhar Deshraj

Page 4: GSM Channel concept and SDCCH

Nov 17, 2003 S. Rajshekhar Deshraj

Logical Channels

Page 5: GSM Channel concept and SDCCH

Broadcast Channels (BCH)

Nov 17, 2003

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 Carrierb> To allow the MS to synchronize to the frequency

•MS: After Switch on MS Scan for this channel, since it has no

information to which frequency to use. FCCH carrier enables a mobile to

tune its frequency to that being broadcast by the BTS.

Page 6: GSM Channel concept and SDCCH

Broadcast Channels (BCH)

Nov 17, 2003

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

Page 7: GSM Channel concept and SDCCH

Broadcast Channels (BCH)

Nov 17, 2003

•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

Page 8: GSM Channel concept and SDCCH

Common Control Channels (CCCH)

Nov 17, 2003

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.

Page 9: GSM Channel concept and SDCCH

Common Control Channels (CCCH)

Nov 17, 2003

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

Page 10: GSM Channel concept and SDCCH

Common Control Channels (CCCH)

Nov 17, 2003

Access Grant Channel (AGCH)

•Downlink channel

•AGCH is answer to the RACH

•NW assigns a signaling channel (SDCCH) to the MS. This assignment is performed on the AGCH

Page 11: GSM Channel concept and SDCCH

Dedicated Control Channels (DCCH)

Nov 17, 2003

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

Page 12: GSM Channel concept and SDCCH

Dedicated Control Channels (DCCH)

Nov 17, 2003

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 and

neighboring BTS’s

•Downlink: MS receives information regarding information concerning

•Transmit power to use•Instructions on Timing Advance

Page 13: GSM Channel concept and SDCCH

Dedicated Control Channels (DCCH)

Nov 17, 2003

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 HO

Cell 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

Page 14: GSM Channel concept and SDCCH

Traffic Channels (TCH)

Nov 17, 2003

Traffic channels are Bi-directional logical channel that transfer the user speech 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.

Page 15: GSM Channel concept and SDCCH

Nov 17, 2003 S. Rajshekhar Deshraj

Call to an MS

More..

Page 16: GSM Channel concept and SDCCH

Nov 17, 2003 S. Rajshekhar Deshraj

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 120ms

Multiframe :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 TDMA Frame Multiframe : Used to carry BCCH,CCCH,SDCCH and SACCH.Duration =51 x 8 x 15/26 =235.38ms

Page 17: GSM Channel concept and SDCCH

TDMA frames with Common and Dedicated Channels

Nov 17, 2003

Page 18: GSM Channel concept and SDCCH

Bursts

Normal Bursts: This burst is used to carry information on :

•Traffic channel

•SDCCH Channel

•Broadcast Control Channel

•Paging Channel

•Access Grant Channel

•SACCH & FACCH Channel

Nov 17, 2003

1 Time slot = 156.25 bits durations (15/26 = 0.577 ms )

TB Encrypted bits Training Sequence Encrypted bits TB GP3 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

F F

Page 19: GSM Channel concept and SDCCH

BurstsFrequency Bursts:

All 148 bits(142+6) are coded with 0. The output of GMSK Modulator is a fixed frequency signal exactly 67.7 Khz above the BCCH carrier frequency.

Thus the MS on receiving this fixed frequency signal fine tunes to the BCCH frequency and waits for the Sync burst to arrive after 1 TDMA Frame .i.e =15/26*8=4.615ms

Nov 17, 2003

1 Time slot = 156.25 bits durations (15/26 = 0.577 ms )

TB TB GP3 3 8.25

ALL ZERO 142 BITS

Page 20: GSM Channel concept and SDCCH

Bursts

Synchronization Bursts:

This burst is used for time synchronization of the MS

Nov 17, 2003

1 Time slot = 156.25 bits durations (15/26 = 0.577 ms )

TB TB GP3 3 8.25

SCH DATA39 Bits

SCH DATA39 Bits

Extended Training Sequence64 Bits

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

Page 21: GSM Channel concept and SDCCH

Bursts

Access 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 using access burst

•For HO when MS send HND_ACC message.

Nov 17, 2003

1 Time slot = 156.25 bits durations (15/26 = 0.577 ms )

TB8

SCH Sequence RACH Data TB41 Bits 36 Bits 3

Guard Band68.25 Bits

36Bit Contains : BSIC+CHAN_REQ or HND_ACC41Bit Contains : Fixed bit sequence allow BTS to recognize it is Access Burst86.25 bits GP: Long GP enables BTS to get Propagation delay information.

Page 22: GSM Channel concept and SDCCH

Bursts

Dummy Bursts:

To enable the BCCH frequency to be transmitted with a constant power level, dummy burst 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 order to determine which BTS to use for initial access or which to use for HO

CCCH is replaced by the dummy page, when there is no paging message to transmit.

Nov 17, 2003

1 Time slot = 156.25 bits durations (15/26 = 0.577 ms )

TB3

Mixed Bits Training Sequence TB Guard BandMixed Bits58 26 3 8.2558

58Bits: Coded with pseudo random bit seq. to prevent confusion with Freq correction burst

Page 23: GSM Channel concept and SDCCH

Mapping of Logical ChannelMethod of transmitting logical channels onto physical channel is called Mapping

FCCH+SCH+BCCH+CCCH: An idle MS search for the FCH. When MS finds the frequency correction burst it knows that this is TS 0 on CHGR=0

The cycle means F,S,B repeats after the Idle frame I.e. at Frame no 50. Cycle=51TS

Nov 17, 2003

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 F50TS-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 TSCCCH 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

Page 24: GSM Channel concept and SDCCH

Mapping of Logical Channel

SDCCH+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 downlink and in frame 15-18 on uplink. The reason for this is to achieve efficient communication, by giving MS time to calculate its answer to the request received on down link SDCCH

Nov 17, 2003

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

I: IDLE 1 TSSDCCH 4 TSSACCH 4 TS

TS=2 / CHGR=0 UPLINK

1 2 3 1 2 3 1 2 3 7

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 TSSDCCH 4 TSSACCH 4 TS

Page 25: GSM Channel concept and SDCCH

Mapping of Logical Channel

TCH+SACCH: 0&2 used by control channels. This leaves TS-1and 3-7 free for the use by TCHs.

Repetition time (Cycle) =26 Frames .i.e. =26*8*(15/26)=120ms

Every 13th TS contains SACCH. Downlink contains TA value and Uplink contains measuring report.

Nov 17, 2003

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 TSA: SACCH

Page 26: GSM Channel concept and SDCCH

Usage of SDCCH

The 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

Page 27: GSM Channel concept and SDCCH

Possible ConfigurationsSDCCH/8 : 8 Sub channels for signaling are mapped on 1 TS, this results 1 less TCH for the cell.

SDCCH/4 (Combining BCCH and SDCCH) :4 Sub channels for signaling are mapped on 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

Nov 17, 2003

SDCCH TCH SDCCH TCHSDCCH/4 4 7 4 15SDCCH/4+CBCH 3 7 3 15SDCCH/8 8 6 8 14SDCCH/8+CBCH 7 6 7 14SDCCH/4+SDCCH/8 12 6 12 14SDCCH/4+SDCCH/8+CBCH 11 6 11 14SDCCH/4+SDCCH/8+SDCCH/8 X X 20 13SDCCH/4+SDCCH/8+SDCCH/8+CBCH X X 19 13

CONFIGURATIONS1 TRX 2 TRX

HYD006AHYD007A

Page 28: GSM Channel concept and SDCCH

Possible Configurations -BCCH COMBC+CBCH

Nov 17, 2003

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

Page 29: GSM Channel concept and SDCCH

Possible Configurations -BCCH NCOMB+CBCH

Nov 17, 2003

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

Page 30: GSM Channel concept and SDCCH

SDCCH Congestion

Nov 17, 2003

SDCCH congestion: All SDCCH in a cell are at the same time busy for a period 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.

Page 31: GSM Channel concept and SDCCH

SDCCH Holding Time

Normal Location Updating = 3.5 Sec

Periodic Registration = 3.5 Sec

IMSI Attach = 3.5 Sec

IMSI 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

Page 32: GSM Channel concept and SDCCH

SDCCH Traffic Estimations

Nov 17, 2003

Normal Location Update: Mean Holding time =3.5 Sec No of Location update =1.0 per sub and BH

AC: 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/Sub

SMS: Mean Holding time =6.2 Sec No of SMS submitted =1.0 per Sub and BH

Traffic : 1000 X (1.0 X 6.2) / 3600 =1.7 mE/sub

Call 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 BHCA

Traffic : 1000 X {(0.8 X 2.7)+(0.4 X 2.9)} / 3600 =0.9 mE/sub

Page 33: GSM Channel concept and SDCCH

Reasons for SDCCH congestion

Nov 17, 2003

Increased mean hold time of SDCCH can be caused by:

• Too low signal strength at access to the systemDue 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 SDCCHHandover on SDCCH will in itself increase mean hold time on SDCCH. However minor increase is expected.

Page 34: GSM Channel concept and SDCCH

Reasons for SDCCH congestion

Nov 17, 2003

• Congestion on Air-interfaceCongestion 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-interfaceCongestion on the A-interface will lead to increased mean hold time on SDCCH. Increase is unknown.

• High load in MSC/VLR or HLRHigh load in MSC/VLR and/or HLR will lead to increased mean hold time on SDCCH. Increase is unknown.

Page 35: GSM Channel concept and SDCCH

How to detect SDCCH congestion in the BSC

Nov 17, 2003

There is no good way to detect SDCCH congestion in real time in the

BSC!

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!)

Page 36: GSM Channel concept and SDCCH

Preventive actions to avoid SDCCH congestion

Nov 17, 2003

• 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

Page 37: GSM Channel concept and SDCCH

SDCCH Dimensioning

Nov 17, 2003

SDCCH Dimensioning is a compromise between SDCCH blocking rate and TCH Capacity. In order to have a successful call setup there has to be an available SDCCH as well as available TCH.

Basic SDCCH configuration:

It is recommended to choose1 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)

Page 38: GSM Channel concept and SDCCH

SDCCH Dimensioning

Nov 17, 2003

Automatic SDCCH dimensioning: This can be done with optional Adaptive Configuration of Logical Channel feature.This feature will add extra SDCCH/8 by reconfiguring idle TCH when SDCCH load is high, and revert back to TCH if SDCCH load goes 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%

Page 39: GSM Channel concept and SDCCH

SDCCH Dimensioning

Nov 17, 2003

Immediate Assignment on TCH:In case of this feature on the channel administration assigns TCH for signaling instead of an SDCCH, based on 7 different channels allocation 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.

Page 40: GSM Channel concept and SDCCH

SDCCH Dimensioning

Nov 17, 2003

Example :ASSUME: CELL=3TRX ,SDCCH Traffic =4 Erlang, Bcchtype=NCOMB.No CBCH GOS: SDCCH/4 = 1%, SDCCH/8 =0.5% & TCH % =2%

1> When Immediate Assignment on TCH not used Erlang B Table :To maintain 0.5 % GOS & 4 Erlang min 13 Subchannels reqd 2SDCCH/8 => TCH=(3TRX*8TS) –(1BCCH)-(2SDCCH/8)=21TCH’s21TCH’s with 2 % GOS => 14.04 Erlang

2> When Immediate Assignment on TCH used If 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 Erlang

TCH Capacity in the cell is increased with 0.7 Erlang

Page 41: GSM Channel concept and SDCCH

SDCCH Dimensioning

Nov 17, 2003

Immediate Assignment on TCH not used

Page 42: GSM Channel concept and SDCCH

SDCCH Dimensioning

Nov 17, 2003

Recommended SDCCH Configurations

Page 43: GSM Channel concept and SDCCH

SDCCH Dimensioning

Nov 17, 2003

HALF RATE CAPACITY CALCULATIONHalf rate will affect SDCCH dimensioning since more signaling will be req’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/8

TCH/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

Page 44: GSM Channel concept and SDCCH

SDCCH Dimensioning

Nov 17, 2003

Max Allowed SDCCH/TCH Load Ratio (Half Rate)

AC : Average CellsBC : Border CellsIC : Inner Cells

Page 45: GSM Channel concept and SDCCH

SDCCH Dimensioning

Nov 17, 2003

Dimensioning based on STS data More accurate dimensioning is achieved by using cell statistics .i.e. STS counters

•SDCCH Traffic•TCH Traffic•SDCCH/TCH Load Ratio %•SDCCH Congestion•TCH Congestion•SDCCH Mean Holding Time•Availability of SDCCH Channels•Availability of TCH Channels

Page 46: GSM Channel concept and SDCCH

Parameters

Nov 17, 2003

MFRMS :This parameter defines period of transmission for PAGING REQUEST messages to the same paging subgroup.

T3212 : Is the periodic registration timer

ACCSTATE : Activate/Deactivate the Adaptive config of logical channel feature per cell basis

CHAP :Selecting Channel Allocation profile per cell.

SLEVEL: The attempt to increase the number of SDCCH/8 will take place when allocation of an SDCCH has failed due to congestion.

STIME :Parameter STIME determines how long the system waits before the number of SDCCH/8 added by this function is decreased when the demand for signalling channels has returned to a low level

BTDM :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 failure in decoding SACCH messages. The parameter is given as number of SACCH periods (480ms).

Page 47: GSM Channel concept and SDCCH

Parameters for SDCCH Dimensioning

Nov 17, 2003

Page 48: GSM Channel concept and SDCCH

STS Counters

Nov 17, 2003

CCALLS : Call attempt counter

CCONGS : Congestion counter

CTRALACC : 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)

Page 49: GSM Channel concept and SDCCH

Formulas

Nov 17, 2003

No. of SDCCH Attempts CCALLS

SDCCH Congestion (%) 100 X { CCONGS / CCALLS } 

No. of SDCCH Connections CMSESTAB

SDCCH Establishments No Congestion (%)

100 X {CMSESTAB / (CCALLS - CCONGS)}

SDCCH Time Congestion (%) 100 X { CTCONGS / (RPL * 60)}

SDCCH Drop (%) 100 X { CNDROP / CMSESTAB }

SDCCH Mean Holding Time (Sec.)

RPL X 60 X {(CTRALACC/CNSCAN) / CMSESTAB }

SDCCH Traffic (Erlang) CTRALACC / CNSCAN

SDCCH/TCH Ratio (CTRALACC/CNSCAN) / ((TFTRALACC/TFNSCAN)+(THTRALACC/THNSCAN))

Page 50: GSM Channel concept and SDCCH

Quality Report : Call Setup Analysis Report

Nov 17, 2003

23.09.03ALL

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 (S)

CELL >0.5% NOC CT (S)

Worst Cells

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

W-6QUALITY REPORT :Call Setup Analysis Report ( W-6)

CONR% (HYD) CONR% (ROAP)S DRP(HYD) S DRP (ROAP) SCSR %(HYD) SCSR % (ROAP)

Measuring Period : 03 Nov 2003 to 09 Nov 2003 (7Days) (Weekly Avg Stats)

SDRPNOD

SCSRCONR SDCCH Congestion rate %

LEGENDSSDCCH Drop Rate %

Week Total Dropped SDCCH'sSDCCH Call Success Rate %

NOCCT(S)

SDCCH Congestion CounterCong. Time in Secs (Week Tot)

ALL SDCCH Drop Rate %SDCCH Estab Success Rate %

SDCCH Congestion rate %

Page 51: GSM Channel concept and SDCCH

Nov 17, 2003

Thank you

S. Rajshekhar Deshraj

Know More - SDCCH

Page 52: GSM Channel concept and SDCCH

Call Setup-Mobile Terminating Call

Nov 17, 2003

MS BTS BSC MSC1>Paging(LAI+IMSI/TMSI)

2>Paging Command Imsi/Tmsi+PG+TRX+CG+TN3>Paging Req(Imsi on PCH)

4>Channel Req(On RACH) 5>Channel Reqd (Access Delay)

6>Channel Actn (MSPwr,BSPwr,TA)

7>Channel Activation Ack

8>Imm Assign Cmd(On AGCH , Freq +TS+ SDCCH SubChannel No+TA

8>Immediate Assign

9>Estblish Ind (Paging Resp) IMSI+MS Class

9>Conn Req (Paging Resp: BSC add CGI)

10>Auth Req (128 bit RAND+ 3bit CKSN)10>Auth Req (128 bit RAND+3bitCKSN)10>Auth Req (128 bit

RAND+3bitCKSN)

11>Auth Response (MS Calculate SRES & Kc with its own Ki stored in SIM by appling algorithm A3&A8)

11>Auth Response (SRES) 11>Auth Response (SRES)

SABM (Paging Resp:IMSI/MS Class)

UA(Paging Resp) Unnumbered Ack Frame which confirms only 1 MS is using Sig Channel

PCH

RACH

AGCH

SDCCH

SDCCH

Next..

Page 53: GSM Channel concept and SDCCH

Call Setup-Mobile Terminating Call

Nov 17, 2003

MS BTS BSC MSC14>Setup (Req for Services I.e.Speech/Data/Fax etc)

15>Call Confirmed

17>Channel Activation(BSC Allocated Idle TS for Traffic)

20>Assign Comp (MS tune to TCH and send Ind that Chan is Seized)

14>Setup14>Setup

15>Call Confirmed 15>Call Confirmed

16>Assignment Req (MSC send CIC to BSC)

18>Channel Activation Ack

19>Assignment Cmnd (BSC send message on SDCCH to MS telling to go TCH)

19>Assignment Cmnd (BSC send message on SDCCH to MS telling to go TCH)

20>Assign Comp (MS tune to TCH and send Ind that Chan is Seized)

20>Assign Comp (MS tune to TCH and send Ind that Chan is Seized)

21>RF Chann Realease

21>RF Chann Realease Ack22>Alert (MS Send Alert to MSC as soon as the ringing is started in MS)

22>Alert (MS Send Alert to MSC as soon as the ringing is started in MS)

22>Alert (MS Send Alert to MSC as soon as the ringing is started in MS)

23>Connect (When MS Sub Answer the Conn message sent to MSC)

23>Connect (When MS Sub Answer the Conn message sent to MSC)

23>Connect (When MS Sub Answer the Conn message sent to MSC)

24>Connect Ack24>Connect Ack24>Connect Ack

SDCCHSDCCH

SDCCH

TCH

TCH

TCH

TCH Exit..