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Paging Blocking Rate AnalysisTunisiana
Sadok Ben Ali
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• 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
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• 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
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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.
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• 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
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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 )
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Buffering – RNCHR01 Actual blocking Rate
LAC re-design DRX Change
Roll Back
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LAC re-design DRX Change
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
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group 1 group 2 group 128 group 1
10 ms
10ms * DRX cycle length
1
2
group 1 group 2 group 64 group 1
10 ms
10ms * DRX cycle length
10ms * DRX cycle length = 1280ms
10ms * DRX cycle length = 640ms
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
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LAC re-design DRX Change
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.
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group 1 group 2 group 64 group 1
10 ms
10ms * DRX cycle length
10ms * DRX cycle length = 640ms
Bufering size M= 4
Buffering time=M *DRXcycle should beshorter than the CNrepetation Timer
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3
4
1
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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
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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
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• 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
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Third Recomendation
Timer Change
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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