paging blocking rate analysis

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Customer Confidential

1 © Nokia Siemens Networks NMI / Paging – 07/05/2009

Paging Blocking Rate AnalysisTunisiana

Sadok Ben Ali




2 © Nokia Siemens Networks

• RNC Capacity & paginging discarding options

• Buffer therory and cases study

• LAC Re-design

• Recomendation DRX Cycle lenght

• Recomendation 24Kbps feature• Recomendation Timers adjusting

NMI / Paging – 07/05/2009

Agenda





• RRC Master capacity is limited by ISCU load

• The “100 paging unhandled messages” is an intrinsic limit for RNC.

• So the minimum RNC paging capacity could be 360000msg/hour assuming instantaneous incoming of the 100 messages .

Buffer

RRC Master Capacity





RRC-c Buffering & MAC-c Scheduling

• The first discarding option in RRC Master is due to processing load reason.

• The second one in MAC-c happens during scheduling and recovery actionare possible.

• The paging messages stored in buffer can be rescheduled in the nextpaging occasion (SFN)

• Paging buffers are 1 each SFN up to the maximum possible number related

to DrxCycleLenght.

• If the bottleneck becomes the MAC-c entity, to avoid collision duringthe scheduling activity a reduction of DrxCycleLength can beproposed.

• A smaller DrxCycle returns more occasion for UE and more bufferingcapacity as described in the following.





• The gain obtained using buffering has its reason in blockingprobability model.

• It can be estimated that without buffering the blocking probability is:

• where the Pn(t) is the probability that n paging messages arrive in10 ms frame (=> t =10ms)

Buffering Theory (1)

• The paging messages arrive with Poisson distribution the





Buffering Theory (2)

0%

1%

2%

3%

4%

5%

6%

7%

8%

9%

10%

11%

12%

13%

14%

15%

16%

17%

18%

19%

20%

21%22%

23%

24%

25%

26%

27%

3 6 8 11 1 4 1 7 19 2 2 2 5 2 8 3 1 33 3 6 3 9 4 2 44 47 5 0 5 3 56 5 8 6 1 6 4 67 6 9 7 2 75 7 8 8 1 83

paging messages per s

p a g i n g b l c o k i n g [ % ]

buffering M=2

no buffering

Using the formula in the previous slide following chart can be made to show the paging blocking % for nobuffering case as well as M=2 and M=4 (2,4 paging messages can be buffered) -> paging bufferingincreases the paging message delay but reduces the paging message blocking

Case staudy 2 After LAC reduction :

DRX lenfgth 7 (1280ms)

M=2Number of pagings/s = 27 msg/s

Lac 2101

Paging Blocking Rate % = 1%

Case staudy 3 After LAC reduction :

DRX lenfgth 6 (640ms) M=4

Number of pagings/s = 21 msg/s

LAC 2101

Paging Blocking Rate % = 0.3%

Case staudy 1 before LAC reduction :

DRX lenfgth 7 (1280ms) M=2Number of pagings/s = 9 msg/s(32000 msg/h)

LAC 2147

Paging Blocking Rate % = 0.1%

Those are theoretical results, real blocking rate depend in the instantaneous incoming paging which

could reach higher value (26 msg/s is on hour avreage )





Buffering – RNCHR01 Actual blocking Rate

LAC re-design DRX Change

Roll Back






Reduce by 60 % of RRC

cause registration

After the LAC fusion in RNCCHR from 6 LACs toone LAC 2101, paging drop at RNC MAC layer level is increased from 0.2% to 0.7%. Thecounters are PAGING_DROP_LOW_PRIORITY(M1006C251)/PAGING_DROP_HIGH_PRIORITY(M1006C252).

DRX cycle length changed from 1280ms to

640ms PAGING_DROP_HIGH_PRIORITY isback to his previous values butPAGING_DROP_LOW_PRIORITY still high.

Gain: huge decrese on RRC registration by60% which will deacrease the processing loadon the RNC and will improve KPIs

LAC Re-design





group 1 group 2 group 128 group 1

10 ms

10ms * DRX cycle length

1

2


10 ms


10ms * DRX cycle length = 1280ms


Bufering size M= 4

Buffering time=M *DRXcycle shouldbe shorter than theCN repetationTimer

Bufering size M= 2

Buffering time=M *DRXcycle shouldbe shorter than theCN repetationTimer

1

2

1

2

3

4

1

2

3

4

A smaller DrxCycle returns more occasion for UE and more buffering capacity asdescribed in the following.

1 paging records can beprocessed by frame 10msin case of 8 Kbps

First Recomedation (1) – Decrease DRX Length






First Recomedation (1) – Results

DRX cycle length changed from 1280ms to 640ms PAGING_DROP_HIGH_PRIORITY

is back to his previous values but PAGING_DROP_LOW_PRIORITY still high.





NMI / Paging – 07/05/2009


10 ms



Bufering size M= 4

Buffering time=M *DRXcycle should beshorter than the CNrepetation Timer

1

2

3

4

1

2

3

4

Up to 5 paging records canbe processed by frame10ms in case of 24 Kbps

Up to 20 paging recordscan be processed by frame10ms in case of 24 Kbps

24 kbps PCH (240 bit TB per every 10ms) has almost 5 times more capacity than8kbps PCH (80 bit TB per every 10ms). Activation this feature allows RNC toschedule up to 5 paging records per Frame 10ms.

Second Recomendation (1) – Activate 24 Kbps feature





Activation threshold NSN recomendation is :

• PCH throughput greater than 4Kbps (50%)

• M1006C25+M1006C26 at busy hour exceeds 50 msg/s

MAX PCH throyugput 2Kbps (25%) LAC 2101

MAX 26 pages/s

Based on therecomendation we arebelow the tresholds to

activate 24Kbps feature

Second Recomendation (2) – Activation thresholds





• PageRep1stInterv default value was/is 700ms. That is too short time, especially

if DRXcycleLength=1280ms.

- When DRXcycleLength = 0640ms (coefficient 6) -> Recommended PageRep1stInterv := 1100ms.

- When DRXcycleLength = 1280ms (coefficient 7) -> Recommended PageRep1stInterv := 1800ms.

• Adjust CN paging Timers- Repaging timer in SGSN, is chaged from 3.5s to to 5.5s

NMI / Paging – 07/05/2009

Third Recomendation

Timer Change





Conclusion

• Paging analysis should include PCH point view and buffer handling analysis

• Buffer Blocking is not hardware limitation but it is related to UMTS buffer paginghandling

• Buffer Blocking Rate of 0.6% is acceptable for Low Priority paging is tolerate up to5%.

• First Recommendation is implemented and it improved High Priority Paging drop

• Second Recomendatiom :Feature 24 Kbps will help to improve the Buffer Blocking Rate

• After changing repaging timer is paging drop is decreased significantly.

NMI / Paging – 07/05/2009

Conclusion

paging blocking rate analysis

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