Layer 3 Questions/Answers
1] How do you escalate RRC set up failure message in Optimization? RRC Set up failure occurs most widely because of network inaccessibility Optimizer should find out the Network Access level Parameters like RSCP and EcIo On specified SC where UE tries to access N/W. Should recommend new site in genuine coverage hole rather stretching coverage from far site. 2] Why Layer 3 analysis is a must for Optimizer along with Drive data foot print? Because with Drive data foot print, p rint, Optimizer would only know the Coverage /Quality footage of the drive area and can see the locations of failures/Drops by visual developing into MapInfo or other Geomap software’s However one won’t be able to address the exact root cause of Drop like missing NBR, Active set update failure or Soft HO failure, Timer expiry, Over shooting site issue, Uplink coverage issues (High UE TX Power), wrongly assigned SC and wrong Neighbor planning issues etc. 3] How do you escalate “Unspecified Release” from Layer 3? Anything apart from “Normal Release” is said to be “Unspecified or Abnormal release” from network and should be considered as a Drop call. Optimizer should follow the detailed message up to the Cause code and particular Cause code value leads to further reason like Channel busy or SGSN/Core network problem and lots of more. ( Cause code values/3GPP ) 4] What are the prime columns in Layer 3 message structure? Regardless to the Vendor and tool, minimum three columns is a must in Layer structure. a) Message Time b) Message direction/Source (like UL or DL/ MS1 or MS2) c) Message information/Details (Actual message) 5] Can we filter Layer 3 messages? Yes we can filter it. Would be easier for our analysis if filter unnecessary statistical, link supervisory and monitoring measurements. 6] If I send SMS, what are the procedural steps involved in layer 3 messages? The signaling flow is divided into 3 parts: a) The initial connection b) The Security&Signalling and/or SMS transfer Phase c) The call release
7] Can we see the Cell name/Cell ID in Active set of Layer 3 message? No. we can only see Primary Scrambling Code (SC) of specific site if defined in RNC 8] what information is available in Layer 3 messages:”RRC Connection Request” –UL (CCCH) from UE, to Network? -Initial UE identity: T-IMSI or PTIMSI -PLMN Identity: MCC, MNC -Network/Cell level identity: LAC, RAC -Measurement channel-RACH (Mode specific info: FDD or TDD) -Establishment Cause: Originating or Background or Streaming etc. -Cells specific info: SCs and measurement Quality: EcNos 9] The events “Radio link Addition or Deletion” related to which Layer 3 message? Successful Radio link addition and deletion only taken place when you UE reports back to network about its Active set have been updated successfully via Layer 3 message: “Active Set Update complete” from UE to Network.
10] Difference between Layer 3 and Layer 2 messages Layer-3 is messaging is responsible to translate messages related to Logical channels (mapped on transport channels) with respect to signaling, control and user information in a simple transparent directional way (UL/DL), However Layer 2 messaging is addressing all information related to internal transport channels/logical channels and most of them are non transparent (internal) to users, that why first we consider Layer 3 for our analysis 11] Is there any difference in Hand over command for PS and CS domain in layer 3 message? Yes. Both commands are different with respect to PS and CS domain. In CS domain we receive, RRC/ Hand over from UTRAN command (serving RNC to UE) While in PS domain we receive, Cell change Order from UTRAN command (serving RNC to UE)
12] After successful RRC Connection procedure in Packet call (PS), what layer 3 messages we should expect? After successful RRC connection procedure in PS call, UE should send a request for PDP context activation and layer 3 messages will be, “RRC/Initial Direct Transfer (Activate PDP Context request-PS Domain)” From UE to Network 13] After receiving RRC/Cell change Order from UTRAN what should be the next layer 3 message from UE to Network? During PS Domain Hard hand over, Network sends Cell change order from UTRAN command and UE should respond back to Network with layer 3 message: ”GMM/RA update request” to be known at SGSN level in GPRS domain. 14] What are SIB and MIB in layer 3 messages? MIB is the Master Information Block and SIB is System Information Block. System information elements are broadcast in SIBs. SIBs are organised as a tree.MIB gives a reference to a number of SIBs, its functions include scheduling information for those SIBs. UE is always able to find MIB on the BCCH, and to get the scheduling information for other SIBs. SIBs contain all information necessary for UEs to work properly in both idle and connected mode. 15] When you can see MIB on layer 3 message? MIB comes into layer 3 message wheneverUE reading the PLMN Identity on BCCH as PLMN related info is broadcasted via MIB only. 16] Layer 3 message “Pegging type 1” should contain what information? “Pegging type 1” DL message should contain at least below information Specific user identity - IMSI, Type of channel used- Logical Pegging channel (PCCH) Pegging cause – Terminating (Paged by CN)
17] Basic Mobile Originating Call sequence (Layer 3) UE-----------------------------------------------------------------------------RNC RACH/RRC Connection Request (cause) -------> <-----RRC Connection Set up (FACH/CCCH) RRC Connection set up complete (DCCH) ---> Initial Direct Transfer----- > < Authentication/Ciphering/Security procedures > < Radio Bearer Set up procedures> <--------- CC/Alerting <----------CC/Connect Connect ACK--------->
18] What are the possible establishment causes in RRC Connection request message? -Conversational -Background -Streaming -Interactive 19] Which are the channels involved in RAB establishment in layer 3 messages? Below two channels will be involved in RAB established Dedicated control channels (DCCH) and Dedicated traffic channels (DTCH) 20] When you can see SIB3 and/or SIB11 in layer 3 message? Whenever UE is performing Cell Selection/Re-selection in idle mode, using above system information blocks. 21] When you can see SIB1 in layer 3 message? SIB1 comes into picture when -Pegging related information UE receives in idle mode -During LA and/or RA updating -During Start/expiry of Timers/Counter in Idle or Connected mode
22] Which are the two UTRA States, seen in layer 3 during Call set up procedure? Call set up procedure will be taken place in either Cell_DCH state or Cell_FACH state, according supported by UTRAN release and set by Operator 23] What is the advantage of Cell_FACH state in RRC connection set up procedure? The establishment of RRC Connection set up in Cell_FACH state would decrease the Call set up time compared to Cell_DCH state.
