CONVENTION: Raw counters are marked in BLUE Formulas are marked in GRAY Parameters are marked in RED MML commands are marked in GREEN LOW TROUGHPUT Analysis process: 1.Low throughput may be due to problems across the packet service transmission path. Thorough checks should be done in Gb, Abis, Um interfaces. Also in SGSN, PCU, BSC systems. 2.Gb interface: - Check usage of Gb links. Expand Gb capacity if congestion appears. Gb usage can be checked through Real Time Monitoring function of BSC LMT: On the Trace & Monitor tab page, choose : Monitor Monitor GPRS Flux. . Also Gb utilization can be checked through following counters: RL9608:BC_TRAN_UP_UTILIZATION_RATE: Uplink Utilization Rate on BC (%) RL9610:BC_TRAN_DOWN_UTILIZATION_RATE: Downlink Utilization Rate on BC (%) Both counters above provide the ratio of actually used bandwidth over configured bandwidth on a BC of Gb. - Check alarms on GDPUP board (BSC6000) or DPUd board (BSC6900) which are the boards that provide PCU functionality in BSC (internal PCU). 3. Abis interface: - Check for congestion on Abis interface. Congestion will lower the throughput. - Higher CS and MCS coding schemes will occupy higher number of Abis timeslots. Check relative parameters for CS transition: - UPTHDCSUPGRADE1: Uplink TBF Threshold from CS1 to CS2 - UPTHDCSUPGRADE2: Uplink TBF Threshold from CS2 to CS3 - UPTHDCSUPGRADE3: Uplink TBF Threshold from CS3 to CS4 - UPTHDCSDEGRADE1: Uplink TBF Threshold from CS2 to CS1 - UPTHDCSDEGRADE2: Uplink TBF Threshold from CS3 to CS2 - UPTHDCSDEGRADE3: Uplink TBF Threshold from CS4 to CS3 - DNTHDCSUPGRADE1: Downlink TBF Threshold from CS1 to CS2 - DNTHDCSUPGRADE2: Downlink TBF Threshold from CS2 to CS3 - DNTHDCSUPGRADE3: Downlink TBF Threshold from CS3 to CS4 - DNTHDCSDEGRADE1: Downlink TBF Threshold from CS2 to CS1 - DNTHDCSDEGRADE2: Downlink TBF Threshold from CS3 to CS2 - DNTHDCSDEGRADE3: Downlink TBF Threshold from CS4 to CS3 Note: For more details on how to cope with Abis interface congestion refer to “ HUA_2G_Capacity_Optimization_v1.0.pptx ” document from Multivendor Team in IMS. 4.Um interface:
- Check if TCH congestion exists on air interface. High CS usage will leave less dynamic PDCHs free for PS service. Refer to Case 4 of present document for handling suggestions on TCH blocking. - Check Radio quality in the cell. Bad quality will negatively affect throughput. Refer to Case 7 of present document for more details on RxQual measurements. - Check UL interference in the cell. High interference will negatively affect UL throughput. Refer to Case 8 of present document for more details on UL interference measurements. High SDCCH Blocking - KPI formula: SDCCH Congestion Rate (Overflow) = ([Failed SDCCH Seizures due to Busy SDCCH]/[SDCCH Seizure Requests])*{100} Analysis process: 1.High SDCCH blocking is due to congestion on the SDCCH channel. Check what causes the high SDCCH usage. Then appropriate actions can be taken: •Check Call Setups: - CELL_ESTB_IND_MOC_NONSMS_SD: Number of Call Setup Indications for MOC on SDCCH - CELL_ESTB_IND_MTC_SD: Number of Call Setup Indications for MTC on SDCCH •Check amount of SMS. Check and verify with Core engineers SMS Center parameterization. - A3030B: CELL_ESTB_IND_MOC_SMS_SD: Number of Call Setup Indications for SMS on SDCCH - CA3340: CELL_Pt_to_Pt_SMS_SD: Number of Point-to-Point Short Messages on SDCCH (includes UL+DL) •Check LAU/RAU requests: - A300F: CELL_CH_REQ_LOC_UPDATE: Number of Channel Requests for Location Update - A3030F: CELL_ESTB_IND_LOC_UPDATE_SD: Number of Call Setup Indications on SDCCH for Location Update. 2.If high SCDDH usage is due to LAU then: • Check if the problem is caused by roamers that do not have access to the network, thus causing big amount of failed LAUs/RAUs. • Check if cell is in LA border: if yes, then we can increase CRH parameter value - CRH: Cell Reselect Hysteresis Parameters (Cell reselection hysteresis. This is one of the parameters used for deciding whether to reselect cells in different location areas.) • Check LA border planning. Verify LA borders by checking HO statistics between cells in LA border: - H380:CELLCELL_INCELL_HO_REQ: Incoming Inter-Cell Handover Requests between 2 cells
• Check the value of T3212; if too low, increase - T3212: T3212 (This parameter specifies the length of the timer for periodic location update). Recommended value: as high as possible, usually 4h. • Check whether moving LA borders (if possible to move) could help relieving the congestion. • Check the pattern of LAU requests. Check hours and duration of high number of such requests. Check whether the problem is constant throughout the day or it occurs only during 1 hour for example. If the problem occurs only on specific hour of day check if it is worth acting to solve it (costs vs. benefits). 3.Check if TCH Immediate Assignment is allowed: - IMMASSEN: TCH Immediate Assignment (Whether to allow immediate TCH assignment. If this parameter is set to YES, the BSC can assign a TCH immediately when there is no available SDCCH for a channel request.) Note: It is not recommended to activate this in congested LA borders. 4. Activate SDCCH dynamic conversion feature: Dynamic SDCCH conversion can be triggered if the SDCCH resource is insufficient or the SDCCH allocation fails during the channel assignment - SDDYN: SDCCH Dynamic Allocation Allowed (Whether to allow SDCCH dynamic allocation, that is, whether to allow dynamic conversion between TCHs and SDCCHs.) - IDLESDTHRES: Idle SDCCH Threshold N1 (When the number of idle SDCCH channels in a cell is smaller than this parameter, the system searches for available TCHs and transforms them into SDCCH channels) - CELLMAXSD: Cell SDCCH Channel Maximum (Maximum number of SDCCHs in the cell. Before converting a TCH into an SDCCH, the BSC compares the number of SDCCHs after the conversion in the cell with "Cell SDCCH Channel Maximum". If the number of SDCCHs after the conversion in the cell exceeds this parameter, the BSC does not convert the TCH into an SDCCH.) 5. Add SDCCH/8 channel 6. Add TRX Note: for more details on SDCCH capacity optimisation check “HUA_2G_Capacity_Optimization_v1.0.pptx ”document from Multivendor Team in IMS. 2. High SDCCH Drop Rate (1) - KPI formula: SDCCH Drop Rate = ([Call Drops on SDCCH]/[Successful SDCCH Seizures])*{100}
Analysis process: 1.Identify the route cause of SDCHH drops by checking the following counters. The total number of SDCCH drops is given by: Call Drops on SDCCH = [Call Drops on Radio Interface (SDCCH)]+[Call Drops due to No MRs from MS for a Long Time (SDCCH)]+[Call Drops due to Abis Terrestrial Link Failure (SDCCH)]+[Call Drops Due to Equipment Failure (SDCCH)]+[Call Drops due to Forced Handover (SDCCH)]: •Call Drops on Radio Interface (SDCCH): the drop is due to radio. Check for missing neighbours. Check radio environment/signal strength at drop points. Adjust antenna parameters appropriately to improve coverage if this is the problem. Check whether the drops are during handover. Check interference. •Call Drops due to No MRs from MS for a Long Time (SDCCH): After seizing an SDCCH, the MS sends a measurement report to the BSC every 470 ms. When the BSC does not receive a measurement report within a certain period of time, the BSC sends a CLEAR REQUEST message to the MSC to release the call, and this counter is incremented by one. Check UL coverage and quality (interference). Check for possible MS problem. •Call Drops due to Abis Terrestrial Link Failure (SDCCH): transmission problem on Abis. Check relative alarms. •Call Drops Due to Equipment Failure (SDCCH): BSC hardware or software failure. Check alarms to discover the exact cause. • Call Drops due to Forced Handover (SDCCH): After an MS seizes a channel, if the system initiates a forced handover and the handover fails, the BSC may initiate a call release procedure. Check why the handover failed: Timer expired? Check whether the emergency handover is due to preemption, or blocking of cell/TRX/channel. 3. CSSR (1) - KPI formula: BSS Call Setup Success Rate = (([Immediate Assignment Success Rate]*[TCH Assignment Success Rate])*(1-[SDCCH Drop Rate]))*{100} The CSSR combines 3 other KPIs: - Immediate Assignment Success Rate = ([Call Setup Indications (Circuit Service)]/[Channel Requests (Circuit Service)])*{100} - TCH Assignment Success Rate = ([Successful Assignments]/[Assignment Requests])*{100} - SDCCH Drop Rate = ([Call Drops on SDCCH]/[Successful SDCCH Seizures])*{100}
Analysis process: (CSSR) 1.Each of the 3 component-KPIs will affect CSSR: - Low Immediate Assignment Success Rate will decrease CSSR - Low TCH Assignment Success Rate will decrease CSSR - High SDCCH Drop Rate will decrease CSSR 2.Examine at which point most of the failures appear by checking thoroughly the 3 componentKPIs. Find out the corresponding failure causes for Immediate Assignment, Assignment and SDCCH Drops. 3.Low Immediate Assignment Success Rate • If Immediate Assignment failures are due to no channel available (point A in Figure 2), this means that there is SDCCH congestion. Refer to Case 1 of present document for handling. • If Immediate Assignment failures are due to channel activation failure or channel activation timeout (points B, C in Figure 2) check hardware/software alarms. 4.Low TCH Assignment Success Rate
• Check following counters to identify the reason for Assignment failure: (1) Failures due to mismatch between the state machine of the BSC and the ASS REQ message or due to the abnormality of the ASS REQ message:
- A3129I: CELL_ASS_FAIL_INVALID_STATE: This counter provides the number of ASS FAIL messages sent by the BSC to the MSC when the BSC receives an ASS REQ message that is not expected by the internal state machine of the BSC (for example, the state machine is in release status). - A3129J: CELL_ASS_FAIL_INVALID_MSG_CONTENTS: This counter provides the number of ASS FAIL messages sent by the BSC to the MSC when the BSC receives an ASS REQ message but the ASS REQ message fails to be decoded (for example, an error occurs during the decoding of an IE, such as CHANNEL TYPE, CIC, or Layer 3 header information). - A3129E: CELL_ASS_FAIL_NO_CIC: This counter provides the number of ASS FAIL messages sent by the BSC to the MSC when the BSC receives an ASS REQ message that carries an unavailable A interface CIC. - A3129F: CELL_ASS_FAIL_CIC_ALLOC: This counter provides the number of ASS FAIL messages sent by the BSC to the MSC when the BSC receives an ASS REQ message that carries an A interface CIC that is already occupied by another call. (2) Failures due to abnormal radio resource allocation: - A312A: CELL_ASS_FAIL_Frst_ASS_NO_CH: This counter provides the number of ASS FAIL messages sent by the BSC to the MSC when the cell does not have available channels and the directed retry procedure fails to be initiated or the directed retry is prohibited by the data configuration in the first air interface assignment procedure. - A312L: CELL_ASS_FAIL_RECONN_SUCC_ASS_NO_CH: This counter provides the number of ASS FAIL messages sent by the BSC to the MSC when the cell does not have available channels and the directed retry procedure fails to be initiated or the directed retry is prohibited by the data configuration in the air interface assignment procedure except for the first air interface assignment procedure. - A312K: CELL_ASS_FAIL_Frst_DR_NO_CH: This counter provides the number of ASS FAIL messages sent by the BSC to the MSC when the cell does not have available channels and the directed retry procedure is successfully initiated but failed due to no available channel in the first air interface assignment procedure. - A312M: CELL_ASS_FAIL_RECONN_SUCC_DR_NO_CH: This counter provides the number of ASS FAIL messages sent by the BSC to the MSC when the BSC attempts to make a directed retry but the directed retry failed because the target cell does not have available channels in the air interface assignment procedure except for the first air interface assignment procedure. - A312F: CELL_ASS_FAIL_NO_IDLE_ABIS: This counter provides the number of ASS FAIL messages sent by the BSC to the MSC when the dynamic allocation of Abis resources is enabled on the BSC but the assignment fails due to no available Abis resources.
- A3129S: CELL_ASS_FAIL_NO_SPEECH_VER: This counter provides the number of ASS FAIL messages sent by the BSC to the MSC when the assignment fails because the intersection between the speech version set carried in the ASS REQ message from the MSC and the speech version set supported by the current cell of the MS does not have available speech versions. (3) Failures due to abnormal air interface access: - A3129C: CELL_ASS_FAIL_Frst_ASS_EXP: This counter provides the number of ASS FAIL messages sent by the BSC to the MSC when the timer for the BSC to wait for an ASS CMP message expires after the BSC sends an ASS CMD message to the MS in the first air interface assignment procedure. - A3129P: CELL_ASS_FAIL_RECONN_SUCC_ASS_EXP: This counter provides the number of ASS FAIL messages sent by the BSC to the MSC when the timer for the BSC to wait for an ASS CMP message expires after the BSC sends an ASS CMD message to the MS in the air interface assignment procedure except for the first air interface assignment procedure. - A3129O: CELL_ASS_FAIL_Frst_DR_EXP: This counter provides the number of ASS FAIL messages sent by the BSC to the MSC when the cell does not have available channels and the directed retry procedure is successfully initiated but failed due to the expiry of the timer for waiting for an HO CMP message in the first air interface assignment procedure. - A3129Q: CELL_ASS_FAIL_RECONN_SUCC_DR_EXP: This counter provides the number of ASS FAIL messages sent by the BSC to the MSC when the timer for waiting for an ASS CMP message expires after the BSC sends an HO CMD message to the MS in the air interface assignment procedure except for the first air interface assignment procedure. - A3129D: CELL_ASS_FAIL_RECONN_SUCC_ASS_RECONN_SUCC: This counter provides the number of ASS FAIL or RR STATUS messages reported by the MS to the BSC when the MS attempts but fails to access the new channel and then successfully reconnects to the old channel after receiving an ASS CMD message. - A3129R: CELL_ASS_FAIL_RECONN_SUCC_DR_RECONN_SUCC: This counter provides the number of HO FAIL or RR STATUS messages reported by the MS to the BSC when the MS attempts but fails to access the new channel and then successfully reconnects to the old channel after receiving an HO CMD message. (4) Failures due to the abnormality of terrestrial resources or the call clearing performed by the MSC. - A3129B: CELL_ASS_FAIL_Frst_APPLY_TRSL_FAIL: This counter provides the number of ASS FAIL messages sent by the BSC to the MSC when the MS drops from the connection to the air interface, or a circuit fails to be obtained for the call, or the obtained circuit is faulty during the circuit connection of the BSC in the first air interface assignment procedure.
- A3129N: CELL_ASS_FAIL_RECONN_SUCC_APPLY_TRSL_FAIL: This counter provides the number of ASS FAIL messages sent by the BSC to the MSC when the MS drops from the connection to the air interface, or a circuit fails to be obtained for the call, or the obtained circuit is faulty during the circuit connection of the BSC in the air interface assignment procedure except for the first air interface assignment procedure. - A3129G: CELL_ASS_FAIL_A_INTERF_FAIL: This counter provides the number of times that the BSC locally releases the call when the BSC receives an SS7 link abnormality indication in the assignment procedure. - A3129H: CELL_ASS_FAIL_MSC_CLR_CMD: This counter provides the number of times that the BSC releases the call after receiving a CLEAR CMD message from the MSC in the assignment procedure. 5.High SDCCH Drop Rate In case high SDCHH Drop Rate causes deterioration of CSSR, refer to Case 2 of present document for handling. 6.Parameters that affect CSSR - RACHACCLEV: RACH Min. Access Level This parameter affects the coverage area. If this parameter is set to a higher value, the actual coverage area of the network becomes small; if this parameter is set to a lower value, call drops are likely to occur because of invalid access or too weak access signals, thus decreasing the success rate of BSS call setup. - RACHBUSYTHRED: RACH Busy Threshold This parameter affects the coverage area. If this parameter is set to a higher value, the actual coverage area of the network becomes small; if this parameter is set to a lower value, call drops are likely to occur because of invalid access or too weak access signals, thus decreasing the success rate of BSS call setup. - RANERRTHRED: Random Access Error Threshold This parameter affects the coverage area. If this parameter is set to a higher value, the actual coverage area of the network becomes small; if this parameter is set to a lower value, call drops are likely to occur because of invalid access or too weak access signals, thus decreasing the success rate of BSS call setup. - CIC No. The values of CICs must be consistent with that on the MSC side. 7.Network functions that affect CSSR - Directed retry When TCHs in a cell are insufficient, TCHs in other cells can be assigned through directed retry, thus increasing the BSS CSSR. By default, this function is enabled. - SDCCH dynamic adjustment When SDCCHs are insufficient, this function can be enabled to convert some TCHs into SDCCHs to increase the success rate of immediate assignment, thus increasing the BSS CSSR. By default, this function is enabled.
- TCH reassignment When this function is enabled, the BSC initiates a re-assignment procedure after receiving the failure indication of the TCH assignment on the Um interface. This function can be used to increase the success rate of TCH assignment, thus increasing the BSS CSSR. By default, this function is enabled. - Flex Abis This function is implemented in the BSC6000V900R003 and later versions. This function enables dynamic assignment of Abis timeslots to more efficiently utilize the Abis link resources; however, assignment may fail because of congestion on the Abis links. This function may decrease the BSS CSSR.
High TCH Blocking Analysis process: 1.High TCH blocking means congestion on the Traffic Channel: there are not enough free TCHs to accept new service requests. 2.Check cell traffic channel availability in order to verify that congestion is not due to availability issue. Check cell alarms. 3.Check availability of neighboring sites. If neighboring cells are unavailable this will cause big amount of HOs directed to our current cell thus leading to congestion. 4.Check cell traffic channel configuration. Check if all HR resources are in use before TCH congestion occurs. Verify that HR is enabled. In case AMR is supported by the operator, verify that is enabled. 5.Load balancing between cells: certain features can be activated to manage the traffic sharing between cells: - Enable LO handover algorithm: LoadHoEn: Load Handover Support - Enable Directed Retry due to load: DIRECTRYEN: Directed Retry 6.Load balancing between cells: - Concentric Cells: check relative parameters so as to implement optimal traffic sharing between underlaid-overlaid cells. - Enhanced Dual Band Network: check relative parameters so as to implement optimal traffic sharing between underlaid-overlaid cells. 7.Check if additional capacity related features can be activated in the network in order to improve the utilisation of TCH resources:
- BCCH Dense Frequency Multiplexing: enables the BCCHs to reuse frequencies more tightly to free more frequencies for non-BCCH TRXs, thus increasing the system capacity. TIGHTBCCHSWITCH: TIGHT BCCH Switch (Whether to enable the BCCH aggressive frequency reuse algorithm) - Interference Based Channel Allocation (IBCA): The IBCA algorithm requires the BSC to estimate the C/I ratio of the new call in every channel assignment procedure; it also requires the BSC to estimate the interference caused to the established calls on the network when an idle channel is assigned to a new call. In this way, the optimal channel, that is, the one that meets the C/I ratio requirement of the new call and causes the least interference to the established calls after being occupied, is assigned to the new call to alleviate the interference and ensure the full use of the frequency resources. IBCAALLOWED: IBCA Allowed (Whether to enable the IBCA algorithm) - Flex MAIO: BSC dynamically adjusts the MAIO according to the current interference level of a channel when assigning an MAIO to the channel . FLEXMAIO: Start Flex MAIO Switch (Whether to enable the function of Flex Mobile Allocation Index Offset) 8.If congestion is still present although the previous described fine tuning and features activation, then: - Check Interference in the network (C/I); check frequency plan - Check coverage: maybe network layout should be changed in traffic hot spots - We can use TA distribution in order to identify traffic distribution among cells. In some cases overshooting can be detected, so we can check the possibility to reduce service area of the overshooting cell. Before doing so, we need, of course, to make sure that there is clear dominance in the area that we are going to shrink serving cell’s coverage. - Implement physical network changes where necessary and feasible: tilt, azimuth, antenna type, etc. - Add TRX - Long term monitoring (e.g. one month) can be used to identify whether we have constant growth in traffic in a site and area close by. If traffic increases in area level and we have already high HR/AMR HR utilization then there are not too many other options than implement a new site. - Add Site Note: for more details on TCH capacity optimisation check “HUA_2G_Capacity_Optimization_v1.0.pptx ”document from Multivendor Team in IMS.
5. High TCH Drop Call Rate 2.Parameters that affect TCH Drop Call Rate: Check and tune appropriately, if needed, the values of the following parameters: - RLT: Radio Link Timeout; recommended value: 52 - SAMULFRM: SACCH Multi-Frames; recommended value: 32
6. High HO fail 2.Check interference in source and target cells. High interference can cause handover failure. 3.Check whether ping-pong handover occurs due to no dominant server in the area. Ping-pong may lead to HO failures. 4.Parameters that affect HO Success Rate: - T3103A: Timer started after the BSC delivers a HANDOVER COMMAND in an intra-BSC inter-cell handover. If the BSC receives a HANDOVER COMPLETE message before this timer expires, the timer stops. If this timer expires, the BSC considers the handover as failed. Recommended value: 10000 ms - T7: Timer is started after the BSC sends the HO RQD to the MSC and waits for the HO CMD command from the MSC in an inter-BSC inter-cell handover procedure. Recommended value: 10000 ms - T8: After sending the HO CMD message to the MS, the BSC starts this timer to wait for the CLEAR CMD message from the MSC in an inter-BSC inter-cell handover procedure. Recommended value: 10000 ms
9. High Signalling Failures Before TBF Establishment - KPI formula: Success Rate of Random Access (Packet Service) = [A301H:CELL_IMM_ASS_CMD_PS]/[A300H:CELL_CH_REQ_PACKET_CALL] AGCH Blocking = ([L3188A:CELL_DEL_IND]/[Channel Requests (all reasons)])*{100} Paging Overload Rate PS = ([PACKET CCCH LOAD IND Messages Sent on Abis Interface])/([Delivered Paging Messages for PS Service])*{100} Analysis process:
1.High signalling failures before TBF establishment refers to failures on the CCCH. During onephase access or two-phase access on the CCCH, the MS fails to proceed to TBF establishment process due to failures on the CCCH channel: AGCH or PCH. The failures most likely will be due to CCCH congestion. 2.Check the above KPIs to identify congestion on the AGCH or PCH. 3.Check relative alarms on the BSC/BTS in order to locate any hardware/software fault. 4.If blocking is the problem, proceed to the following steps in order to relieve congestion on the CCCH. Note: For more details on CCCH capacity optimisation refer to “HUA_2G_Capacity_Optimization_v1.0.ppt ”document from Multivendor team in IMS. 5.Check the values of following parameters: - BSAGBLKSRES: Blocks Reserved for AGCH. Value range: 0-7. Recommended: 2 - BSPAMFRAMS: Multi-Frames in a Cycle on the Paging CH. Value range: 2-9. Value depends on paging load. Increase value when paging load increases. Value should be kept as small as possible. - PAGTIMES: Paging Times. Value range: 1-8 (For the BTS, this parameter is used to determine paging retransmissions. This parameter and the number of paging times configured in the MSC determine the number of paging retransmissions.) 6.Check if Flow Control feature is enabled. Recommendation is that Flow Control is always enabled. Flow Control, controls the arrival of paging messages on the A interface (MSC-BSC) and on the LAPD links (BSC-BTS). 7.Check volume of PS pagings ( A331:CELL_PAGES_PS: Delivered Paging Messages for PS Service). If too high then check if PCCCH is configured. If PCCCH is configured then packet pages can be transmitted through PPCH, thus reducing PCH load. CS pages can also be transmitted through packet control channels (PACCH or PPCH). For this to work, Gs interface needs to be configured between SGSN-MSC. Also Network Mode of Operation should be set to 1. - NMO: Network Operation Mode 8.Check Location Area: re-size might be required (make smaller). 9.Consider splitting cells in the paging overload area. This will grow CCCH capacity. 10. Add CCCH capacity (Extended BCCH).
