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

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. 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. Logical Channels
Nov 17, 2003 S. Rajshekhar Deshraj

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 no
information to which frequency to use. FCCH carrier enables a mobile to
tune its frequency to that being broadcast by the BTS.
Nov 17, 2003

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. 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. 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. 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. 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. This
assignment is performed on the AGCH
Nov 17, 2003

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. 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 and
neighboring BTS’s
•Downlink: MS receives information regarding information
concerning
•Transmit power to use
•Instructions on Timing Advance
Nov 17, 2003

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 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
Nov 17, 2003

14. Traffic Channels (TCH)
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.
Nov 17, 2003

15. Call to an MS
More..
Nov 17, 2003 S. Rajshekhar Deshraj

16. Relationship Between Burst & Frame
Burst : 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
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. TDMA frames with Common and Dedicated Channels
Nov 17, 2003

18. 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
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. Bursts
Frequency 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
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. Bursts
Synchronization 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. 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.
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. 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.
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. Mapping of Logical Channel
Method 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
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. 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
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. 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.
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. 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

27. Possible Configurations
SDCCH/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
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. 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. 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. SDCCH Congestion
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.
Nov 17, 2003

31. 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

32. SDCCH Traffic Estimations
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/Sub
IC : No Location updating at all =1000X(0 X 3.5)/3600=0 mE/Sub
BC: 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
Nov 17, 2003

33. Reasons for SDCCH congestion
Increased 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. 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. How to detect SDCCH congestion in the BSC
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!)
Nov 17, 2003

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. SDCCH Dimensioning
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 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. SDCCH Dimensioning
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%
Nov 17, 2003

39. SDCCH Dimensioning
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.
Nov 17, 2003

40. SDCCH Dimensioning
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’s
21TCH’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 %=0.12Erlang
1SDCCH/8 => TCH=(3TRX*8TS) –(1BCCH)-(1SDCH/8)=22TCH’s
22TCH’s with 2 % GOS => 14.9 Erlang
Actual TCH Capacity=14.9 – 0.12 = 14.7 Erlang
TCH Capacity in the cell is increased with 0.7 Erlang
Nov 17, 2003

41. SDCCH Dimensioning
Immediate Assignment on TCH not used
Nov 17, 2003

42. SDCCH Dimensioning
Recommended SDCCH Configurations
Nov 17, 2003

43. SDCCH Dimensioning
HALF RATE CAPACITY CALCULATION
Half 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 Subscriber
Penetration 10% of 14 is 1.4 = 2 Subscribers (Req’d 2 Half Rate TCH/H)
Total 13 TCH/F+2TCH/H = 15 TCH required
Capacity :
Erlang B Table: 15 TCH @ 2% GOS => 9.0096 Erlang
Nov 17, 2003

44. SDCCH Dimensioning
Max Allowed SDCCH/TCH Load Ratio (Half Rate)
AC : Average Cells
BC : Border Cells
IC : Inner Cells
Nov 17, 2003

45. SDCCH Dimensioning
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
Nov 17, 2003

46. Parameters
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).
Nov 17, 2003

47. Parameters for SDCCH Dimensioning
Nov 17, 2003

48. STS Counters
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)
Nov 17, 2003

49. Formulas
No. of SDCCH Attempts CCALLS
SDCCH Congestion (%) 100 X { CCONGS / CCALLS }
No. of SDCCH Connections CMSESTAB
SDCCH 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 / CNSCAN
SDCCH/TCH Ratio (CTRALACC/CNSCAN) / ((TFTRALACC/TFNSCAN)+
(THTRALACC/THNSCAN))
Nov 17, 2003

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 72Cells
22Sep-29Sep 127 Cells 295 Cells 192 Cells 378 Cells 98 Cells 174 Cells 116Cells
29Sep-5Oct 112 Cells 309 Cells 187 Cells 400 Cells 71 Cells 135 Cells 97Cells
06Oct-12Oct 25 Cells 154 Cells 178 Cells 382 Cells 55 Cells 109 Cells 81Cells
03Nov-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 SDCCH's ALL SDCCH Drop Rate %
SCSR SDCCH Call Success Rate % SDCCH Estab Success Rate %
CONR SDCCH Congestion rate % SDCCH Congestion rate %
Nov 17, 2003

51. Know More - SDCCH
Thank you
Nov 17, 2003 S. Rajshekhar Deshraj

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+TN
RACH
4>Channel Req(On RACH) 5>Channel Reqd (Access Delay)
6>Channel Actn (MSPwr,BSPwr,TA)
7>Channel Activation Ack
AGCH
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 Channel
SDCCH 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. 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 Ack
SDCCH 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