RRC Setup Report

Presentation TimetablePilotMethodology wk5Net. IssuesServicesCountersAlarmsDrive DataNeighbours wk5Performance wk5RRC Access wk7SHO wk6ISHO wk6RRC Stp wk7Access wk4Common Alarms wk4Common Failures wk4Analysis wk3CM Service wk2Test Nos wk3Script bugs wk3CC Disc wk1Power Spikes wk1HC Failures EOC6650 ISHO wk3RRC Active wk7Inter RNC HO wk2TCH/BCH wk2

Table of Contents

Introduction

Detailed DescriptionsHandover ControlAdmission ControlSetup Fail BTSSetup Fail TransSetup Fail Frozen BTS/Internal RNC

Conclusion

Introduction

RRC Setup PhaseThe RRC Setup phase starts when the UE sends the RRC CONNECTION REQUEST message and it is completed when the RNC, after reserving all the necessary resources for the RRC Connection (RNC, BTS, Radio and Transmission), replies with DL RRC CONNECTION SETUP message.

During this phase, there are several processes happening between the Node B and the RNC. If any of these processes fail, the Ue will either try again or will fail. In either case the relevant counter will be triggered, giving the Network Analyst clues as to why calls are failing on a particular cell.

A schematic of the Setup phase can be seen on the RHS.

RRC Setup Failures

RRC Setup Failure due to Handover Control (HC)RRC Setup Failure due to Admission Control (AC)RRC Setup Failure due to BTSRRC Setup Failure due to TransmissionRRC Setup Failure due to BTS frozenRRC Setup Failure due to RNC internal reason

Detailed Descriptions

Handover Control

Handover Control is the algorithm that is used to allow a Ue connect to two or more cells simultaneously

Handover Control appears to start in the HA3 Program Block during RRC Setup ProcedureRRC Setup Fail due to HC

HC Setup Procedure in RNCHC Setup appears to reside in the Interface Control and Signalling Unit (ICSU)ICSU board resides in RNCICSU board has redundancy where the redundancy unit is only employed if the active unit fails.Checked RNC alarms and there were older alarms on ICSU boards

Admission Control

Admission Control (AC) is the algorithm that decides whether a request to establish a RAB is admitted or not. It is also involved during the handover procedure.

RRC Setup Failure due to AC

RRC Setup Failure for AC:AC can block the call at RRC level if there is too much noise on a cell. (i.e. Target + Offset is exceeded)AC also blocks calls if UL or DL is blocking. Check Cell Resource counters (Prx/Ptx total)In general its possible to check the AC blocking in RRC setup phase by checking the Traffic counters(M1002):DCH_REQ_LINK_REJ_UL_SRNCDCH_REQ_LINK_REJ_DL_SRNCMain failure reasons for ACRRC_conn_req_nack (Cell overload on UL or DL)No response from BRM - timer expired (indicates a cell availability problem)

RRC Setup failure AC for cell availability

A high number of RRC failures for Admission Control does not necessary mean a high traffic or an interference problem but it might reflect a cell availability problem.Typical detection through counters and KPIs: High RRC Setup Failure AC Rate : There may also be a huge number of RRC attempts (see example). This indicates that the problem is continuous.Traffic counters may or may not reflect the full extent of the problem: in some cases the traffic counters are not incremented because the request is not even received by the Admission Control.(e.g. MHA Faulty)Cell Availability

Cell Availability ExampleSite GLN0395 shows high number of RRC Setup Failures for Admission Control on March 15.From Service Level counters huge number of RRC attemptsRRC repetitions.From Cell Resource counters:Average PrxTotal shows nearly no traffic nor interferenceCell Availability problem from 17:30Alarm in the cell

RRC Setup Failure BTS

RRC Setup Failure for BTS:main failure reasons can be:RL_setup_failure (not enough resources) might be a WSP problemRL_setup_failure (hardware overload): might be some internal BTS issueThese fails can be seen in the counters :SETUP_FAIL_RL_NOT_ENOUGH_RESSETUP_FAIL_FIRST_RL_HW_RES

BTS Resource Issue may occur hereRRC Setup Failure BTS

RRC Setup Failure TransRRC Setup Failure due to Transmission: main failure reasons is:serv_req_nack_from_nrm meaning some problem in setting up AAL2 transmission resources in Iub

NRM (Network Resource Model) is in-charge of Iub capacityAfter capacity check, AAL2 signalling startsCounter RRC_CONN_STP_FAIL_TRANS is incremented if:Not enough Iub capacityAAL2 setup fails

RRC Setup Failures TransIt appears that the problem may be in this part of the setup protocolReason for fail is usually:Not enough Iub capacityAAL2 setup fails

AAL2 Setup over IubIub resource reservation is performed in order such that all CAC reservations for RNC internal and external (AAL2 path) resources are done before signaling. If the CAC actions are successfully completed, the signaling is started and the RNC asks the BTS to arrange its resources accordingly. If the CAC actions fail, the signaling phase is not started at all and the signaling counters are not aware of the connections rejected due to RNC AAL2 layer CAC.

* NOKIA

AAL2 user plane setup over Iub (MOC)

RNC

BTS (WAM)

UE

AAL2 SIG

CAC

CAC

AAL2SIG

ATM RM

RRC: connection request

resource reservation

AAL2 connection establishement

ERQ (SUGR)

resource reservation

ECF

AAL2 conn. estab. confirmation

RRC:connection setup

RRC

Transport res. reserv. req.

Possible NACK

Possible NACK

Others RRC Setup FailuresRRC Setup Failure Frozen BTS: the AC blocks RL establishment to allow the setup of an emergency call(in case of pre-emption, when BTS is frozen no new RRC connection are allowed)

RRC Setup Failure for RNC internal reason: all other failure reasons (e.g. parameter mismatch, timer expiry)

RRC Setup Fail RNCProblem should affect the entire RNC (ALL THE CELLS)Reasons are due to RNC Software/Hardware

RRC Setup Fails on Croydon RNCAC, BTS and TRANS are the most common fails on Croydon RNC

Numbers of fails can be huge but this does not indicate that the issue is necessarily RNC wide. It is probably 1 site with a huge number of fails, possibly due to repeated registration attempts.

The other fails should be at or near 0.

ConclusionSetup Fails generally occur due to hardware issues in a low traffic situation. They are the first counters triggered by any attempt to access the network

The counters give us clues where to look

Some Setup Fails will occur repeatedly in response to a single issue causing the counter appear worse than the problem really is. Conversely, in some cases, the counters may not trigger when a fault is occurring but this can be seen by a drop in traffic.

Overview of the Operational Optimisation environment and process.

Subscriber Service ManagementSubscriber Service management layer define the services offered and the target service QoS.Responsible for handling customer reported faults and customer accounts.

Responsible for steering network quality and efficiency by defining performance targets.

Network management and EngineeringThe aim is to maintain the network to achieve the Performance Targets and resolve customer faults.

Network management operate within a continuous cycle of:-

MeasurementsAnalysisReportingModellingReconfigure

Operational Optimisation! This is Aircoms arena!