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15 Jan. 2001 LM/ERA/LVG/TD Hans Andersson/Thomas Walldeen

Characteristics. C. C. BSC. BSC. BSC Overload Handling. 15 Jan. 2001 LM/ERA/LVG/TD Hans Andersson/Thomas Walldeen. BSC Overload Handling. C. BSC. Overload Handling, Concepts. OVERLOAD: “The system is offered more jobs per time unit than it can handle”.

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15 Jan. 2001 LM/ERA/LVG/TD Hans Andersson/Thomas Walldeen

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  1. Characteristics C C BSC BSC BSC Overload Handling 15 Jan. 2001 LM/ERA/LVG/TD Hans Andersson/Thomas Walldeen BSC Overload Handling

  2. C BSC Overload Handling, Concepts OVERLOAD: “The system is offered more jobs per time unit than it can handle” LOAD CONTROL: “Control delays and throughput by rejecting excessive amount of jobs” OVERLOAD PROTECTION: “Do whatever needed to survive (i e, avoid restart)” 15 Jan 2001 LM/ERA/LVG/TD Hans Andersson BSC Overload Handling

  3. C BSC Load Control (according to ITU-T) Traffic throughput Ideal With Load Control Blind load Without Load Control Overload Engineeredcapacity Offered traffic 17 Dec. 1999 LM/ERA/LVG/TD Hans Andersson BSC Overload Handling

  4. C BSC Load Regulation Due to a Traffic Load Peak PROCESSOR LOAD 95 % TIME CALMAX CALIM ACTUAL NO. OF SERVED JOBS CALMIN TIME Load Peak 17 Dec. 1999 LM/ERA/LVG/TD Hans Andersson BSC Overload Handling

  5. C BSC Load Regulation Due to an O&M Load Peak PROCESSOR LOAD 95 % TIME CALMAX CALIM O&M Jobs ACTUAL NO. OF SERVED TRAFFIC CALMIN TIME Load Peak 17 Dec. 1999 LM/ERA/LVG/TD Hans Andersson / Thomas Walldeen BSC Overload Handling

  6. C BSC The PLLDP Printout (R7) PLLDP; PROCESSOR LOAD DATA INT. PLOAD CALIM OFFDO OFFDI FTCHDO FTCHDI OFFMPH OFFMPL FTCHMPH FTCHMPL 1 94 3000 335 43 335 43 0 5 0 5 INTERVAL One interval equals 5 seconds PLOAD Average processor load (%) during this interval CALIM Max. number of served jobs during interval OFFDO All mobile originating capacity requests (call, SMS, registration attempts) OFFDI All mobile terminating capacity requests (paging) FTCHDO The number of OFFDO that are served during interval FTCHDI The number of OFFDI that are served during interval OFFMPH Offered high priority maintenance tasks (currently not used in BSC) OFFMPL Offered low priority maintenance tasks (BALREG and printouts) FTCHMPH Fetched OFFMPH FTCHMPL Fetched OFFMPL 17 Dec. 1999 LM/ERA/LVG/TD Hans Andersson / Thomas Walldeen BSC Overload Handling

  7. C BSC The LOAS block Once every 20 ms Once every second Picture from UAB BSC in R7: Buff. 10 for MT (= paging) {highest prio.} Buff. 11 for MO accesses {16 pos. LIFO} Buff. 12 for printouts + high prio O&M Buff. 13 for normal O&M 17 Dec. 1999 LM/ERA/LVG/TD Hans Andersson / Thomas Walldeen BSC Overload Handling

  8. C BSC Traffic Loss due to Disturbances A B Traffic (Erlang) Catch-up Traffic loss = A - B Disturbance Time 17 Dec. 1999 LM/ERA/LVG/TD Hans Andersson BSC Overload Handling

  9. C BSC Load Graph Depends on Averaging Time “Hour” “Seconds” “CPU cycle” 17 Dec. 1999 LM/ERA/LVG/TD Hans Andersson BSC Overload Handling

  10. C BSC Priority: Two Dimensions Importance Recovery of base station TAS One access for mobile terminated SMS/ptp Urgency (real-time requirement) 17 Dec. 1999 LM/ERA/LVG/TD Hans Andersson BSC Overload Handling

  11. CP TRH Interaction C BSC TRH RPH CP JBC ChanReq 8 pos RMHBIthrottle JBB 512+ pos LOASbuffers .... APT APZ SDCCHs? Very simplified! RPbus RPSB (JBR) 17 Dec. 1999 LM/ERA/LVG/TD Hans Andersson BSC Overload Handling

  12. 2.Paging < 4 s C BSC Real-Time Challenges BTS BSC MSC 1.Immediate Assignment TRH CP ChanRqd < 250 ms 17 Dec. 1999 LM/ERA/LVG/TD Hans Andersson BSC Overload Handling

  13. C BSC Faster Recovery With R7 (and more robust ...) Load Load 95% 60% 95% O&M O&M Traffic Traffic R7 Time Time 17 Dec. 1999 LM/ERA/LVG/TD Hans Andersson / Thomas Walldeen BSC Overload Handling

  14. 1. Capacityrequest Feature 1 3. More freecapacitybelow 95%? LOAS Priority Feature 2 O&M:High prio.Low prio. BALREG Feature N 2. 10+3% guaranteed C BSC Adaptive Base Level Regulation 22 Aug. 2000 LM/ERA/LVG/TD Hans Andersson BSC Overload Handling

  15. CP Load Short peak 95% 10% Traffic limitation O&MLOAD TRAFFIC LOAD IDLE LOAD Time C BSC Adaptive Base Level Regulation 22 Aug. 2000 LM/ERA/LVG/TD Hans Andersson BSC Overload Handling

  16. C BSC Short Load Peaks at Occasions (such as major link outages) Control algorithm Input Output 17 Dec. 1999 LM/ERA/LVG/TD Hans Andersson BSC Overload Handling

  17. C BSC “ Call rejects ...? ” F Actually, most accesses are for registrations, not calls F We don’t really reject, we say ‘welcome back later’ F Accesses may be one of many from the same mobile (due to repetition/retrial mechanisms) 17 Dec. 1999 LM/ERA/LVG/TD Hans Andersson BSC Overload Handling

  18. C BSC Causes of Overload • SRS congestion • Over dimensioning of TRA • Increase TALLOC timer (~10-20 seconds) • TRA congestion • Increase TALLOC timer • Huge amount of traffic • Problems in Core network (MSC, HLR, C7 networks etc.) • BSC problems (e.g. Restart at busy hour) 17 Dec. 1999 LM/ERA/LVG/TD Thomas Walldeen BSC Overload Handling

  19. C BSC Problems at overload • Massive paging -> TRHs go ABL • Correction to limit paging • RMPAGR CNI with overload control • SRS RPs goes ABL • Corrections available (monitor situation) • R8 will have a complete solution 17 Dec. 1999 LM/ERA/LVG/TD Thomas Walldeen BSC Overload Handling

  20. C BSC Handling • Access class baring • Manual (R7 AC-A7, R7.1 AC-A4) ACs available. • Automatic (Future) • Set print priority (PLSUC:PRPRY=ON) (R7) • Stops ‘hanging IO at high load’. • Define an Emergency terminal (special use) • IORLC:IO=AT-x,PRI=EMERGENCY; • False ‘Exchange Input Load Supervision’ alarms • PLSVC:ACL=A3,REJCLLS=255,TDMI=1,TASK=NOMISC; 17 Dec. 1999 LM/ERA/LVG/TD Thomas Walldeen BSC Overload Handling

  21. C BSC Load Regulation in R8, Simplified! MSC BSC/TRC BSC CP O&Mtasks BALREG AterFlowCtrl Paging Processor Load ControlLOAS • Send capacity request to LOAS • Continue call setup immediately • Decrement counter for job type • Upon capacity ACC: Incr. counter • Upon capacity REJ: Decr. Counter • If counter 0: Send neg. reply to RP SGSN Pre-seize Throttle PSDownlinkAssign-ment • Max. 45 (APZ21211) sent uplink per 100 ms • If OK, send pos. reply to RP • If NOK, send neg. reply to RP Flow Ctrl &Radio Resource Ctrl FlowControl • Send access to CP, decrement window • Pos. reply from CP: Increment window • Neg. reply from CP: Close window; timeout • Full queue or too old: Send reject to MS • Window size = 1 RPPinPCU TRH IfMPDCH If no MPDCH PS Uplink Access CS Uplink Access 2 March 2000 LM/ERA/LVG/TD Hans Andersson BSC Overload Handling

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