zte ps-data service optimization

Data Service Optimization

ZTE University

PS and HSDPA Service Overview

HSDPA Service Optimization

Content

PS Data Transmission Channel

PS data reaches UE after running through Internet service server, GGSN, SGSN, RNC, and NodeB via Gi, Gn, IuPS, Iub, and Uu interfaces in turn. Any faults occurred during this process may bring impacts on PS services.

HSDPA Service Data Analysis

In terms of throughput, HSDPA service transmission rate is not only high, but also unstable with large fluctuations; In terms of service quality, stream images is not clear, buffering is required, FTP download takes a long time, and a slow responding occurs in browsing websites.PS data reaches UE after running through Internet service server, GGSN, SGSN, RNC, and NodeB via Gi, Gn, IuPS, Iub, and Uu interfaces in turn. During this process, the data transmission between the Internet server and GGSN abides by the IP protocol. There are a or multiple routers and firewall just in between of the Internet server and GGSN.

HSDPA Service Data Analysis

PS services use the AM mode of RLC and thus support the re-transmission function. For services like FTP and HTTP, the TCP protocol is followed. As to service monitoring, UE is often regarded as an application run by the computer of the MODEM to judge the service quality.

PS and HSDPA Service Overview

HSDPA Service Optimization

Content

HSPA Service Call Process I

Direction=UE -> RNC, rrcConnectionRequest, Direction=NODEB <- RNC, RadioLinkSetupRequestFDDMsg, Direction=NODEB -> RNC, RadioLinkSetupResponseFDDMsg, process of setting up RRC connectionDirection=UE <- RNC, rrcConnectionSetup, Direction=NODEB -> RNC, RadioLinkRestoreIndicationMsg, Direction=UE -> RNC, rrcConnectionSetupComplete, Direction=UE -> RNC, initialDirectTransfer, Direction=RNC -> CN, InitialUE_MessageMsg, Direction=RNC <- CN, DirectTransferMsg, process of authentication and encryptionDirection=UE <- RNC, downlinkDirectTransfer, Direction=UE -> RNC, uplinkDirectTransfer, Direction=RNC -> CN, DirectTransferMsg, Direction=RNC <- CN, SecurityModeCommandMsg, Direction=UE <- RNC, securityModeCommand, security mode partDirection=UE -> RNC, securityModeComplete, Direction=RNC -> CN, SecurityModeCompleteMsg,

HSPA Service Call Process IIDirection=RNC <- CN, CommonIDMsg, Direction=UE -> RNC, uplinkDirectTransfer, -- PDP activation requestDirection=RNC -> CN, DirectTransferMsg, Direction=RNC <- CN, RAB_AssignmentRequestMsg, Direction=NODEB <- RNC, RadioLinkReconfigurationPrepareFDDMsg, Direction=NODEB -> RNC, RadioLinkReconfigurationReadyMsg, Direction=UE <- RNC, radioBearerSetup, Direction=NODEB <- RNC, RadioLinkReconfigurationCommitMsg, process of RAB assignmentDirection=UE -> RNC, radioBearerSetupComplete, Direction=UE <- RNC, measurementControl, Direction=UE <- RNC, measurementControl, Direction=UE <- RNC, measurementControl, Direction=RNC -> CN, RAB_AssignmentResponseMsg, Direction=RNC <- CN, DirectTransferMsg, Direction=UE <- RNC, downlinkDirectTransfer, -- acceptance of PDP activation

HSPA Service Call Process III

Direction=UE -> RNC, uplinkDirectTransfer, Direction=RNC -> CN, DirectTransferMsg, process of deactivating PDPDirection=RNC <- CN, DirectTransferMsg, Direction=UE <- RNC, downlinkDirectTransfer, Direction=RNC <- CN, RAB_AssignmentRequestMsg, Direction=NODEB <- RNC, RadioLinkReconfigurationPrepareFDDMsg, Direction=NODEB -> RNC, RadioLinkReconfigurationReadyMsg, Direction=UE <- RNC, radioBearerRelease, Direction=NODEB <- RNC, RadioLinkReconfigurationCommitMsg, process of

releasing RABDirection=NODEB -> RNC, DedicatedMeasurementReportMsg, Direction=NODEB -> RNC, DedicatedMeasurementReportMsg, Direction=UE -> RNC, radioBearerReleaseComplete, Direction=RNC -> CN, RAB_AssignmentResponseMsg, Direction=RNC <- CN, Iu_ReleaseCommandMsg, Direction=RNC -> CN, Iu_ReleaseCompleteMsg, Direction=UE <- RNC, rrcConnectionRelease, process of releasing RRCDirection=UE -> RNC, rrcConnectionReleaseComplete, Direction=NODEB <- RNC, RadioLinkDeletionRequestMsg, Direction=NODEB -> RNC, RadioLinkDeletionResponseMsg,

Faults Occurred in Signaling Process

1: Configuration of H channel can be viewed in the re-configuration of wireless links:hSPDSCH_RL_IDPresent = 1 hSDSCH_RNTIPresent = 1hSDSCH_FDD_InformationPresent = 1ueCapability_Info.hSDSCH_Physical_Layer_Category = 3 (indicating that UE capability level is 3)2: Subscription type can be viewed in RAB assignment request: trafficClass = 2 (indicating the Interaction class)trafficClass = 3 (indicating the Background class)


Failure to set up RRC connection:If UE failed to initiate RRC Connection Request, it indicates that:

Modem port may not be selected in Hardware Config.There may be configuration errors in test software.

Exceptions may occur on the UE port. If UE cannot receive response or receives RRC Connection Reject after sending RRC Connection Request, it may be caused by poor coverage or access deny due to uplink and downlink overload.


UE failed to send Service Request: This may be caused by that UE has not enabled the PS function or has not completed the PS domain registration yet.

UE failed to enable the PS function:Some UEs can be set to support CS, PS, or CS+PS. If it is set to CS only, then PS services cannot be set up. In this case,check the UE configuration and change the setting to PS or CS+PS.

UE has not completed the PS domain registration: Talking from the perspective of signaling process, Attach Reject is received from the network side after UE sends Attach Request. Ensure that the PS services are supported in the setting of this USIM card account.


PDP activation is rejected:After sending Activate PDP Context Request, UE receives Activate PDP Context Reject. Wrong APN setting at the UE sideWrong transmission rate setting at the UE side

Signaling Works While Service Carrying Does Not

The successful setup of connection indicates that the signaling plane works normally. But the faults caused by TRB reset at the RAN side might cause the fact that the service plane does not work normally.

Signaling path

Service pathCN

UE


Faults occur in authentication and encryption processFaults occur in the process from NAS signaling (Authentication AND Ciphering REQ) to RRC signaling (Security Mode Complete).

Main Indices for Data Services

Access indices (RRC successful setup rate, RAB successful setup rate, PDP successful activation rate, and so on）PS service call drop rateThroughput rateDelay and the like that may affect subscriber using experience

Analysis Process for PoorDownloading Performance

Viewing Alarms

After a fault occurs, check if a corresponding alarm is generated. For RAN side problems, view the alarms about NodeB and RNC; for CN side problems, view the alarms about SGSN, GGSN, LANSWITCH, ROUTER and other network elements (NEs). The alarms about clock exception, transmission error, and device exception may affect the downloading performance.

Viewing Alarms

If the alarms about NEs is not helpful for locating the problem causes, then do the comparison and analysis of operation class, and try to narrow the scope of the causes from the numerous factors. If the causes fall into RAN side problems, then turn to do analysis on RAN side factors that may affect downloading performance; and it is the same for the CN side problems. Otherwise, you need to do analysis from both perspectives previously mentioned.

Operation Class Comparison and Analysis

PurposeTo locate the NEs on which faults occurred through comparison and analysis, and find out if the problem is caused by core network, service software, or access network faults.

Operations need to be compared and analyzed: Change of USIM card, mobile phone card, data card, PCChange of PDN server’s modes (web, gateway, or service)Change of other networks on the common server, such as switch to 2G or other 3G network.

Operation Class Comparison and ConclusionN

o.Operation Operation Results Conclusion

Key Points

Downloading function comes back to normal.

The problem is related with USIM card subscription.

Uplink and downlink subscription

1 Changing USIM card The downloading

function problem insists.

The problem causes cannot be located and the investigation should continue.

--


The problem is related with UE, such as compatibility or the performance of UE itself.

Capability difference between terminals (they may be based on different chips and thus have capability difference)

2

Changing mobile phone/data card

The downloading function problem insists.


--

Operation Class Comparison and Conclusion


The problem is related with driver installation, APN setting of PCs, rate limit setting, or firewall.

Drivers, APN setting of PCs, rate limit setting, firewall and so on



--


The problem is related with CN side faults, such as server performance, TCP/IP parameters, or service software.

Server processing capability, TCP/IP settings, and compatibility of service software



--4

Changing PDN/website (downloading from other PDN/websites)

3 Changing PCs

RAN Side Fault Analysis

Alarms About NEs

When the problem of poor downloading performance for PS data occurs, do the analysis on alarms about NodeB and RNC. Alarms about clock, and transmission error may also cause PS data transmission rate fluctuation.

UE Category

HS-DSCH categoryMaximum number of HS-DSCH codes received

Minimum inter-TTI interval

Maximum number of bits of an HS-DSCH transport block received withinan HS-DSCH TTI

Category 1 5 3 7298Category 2 5 3 7298Category 3 5 2 7298Category 4 5 2 7298Category 5 5 1 7298Category 6 5 1 7298Category 7 10 1 14411Category 8 10 1 14411Category 9 15 1 20251Category 10 15 1 27952Category 11 5 2 3630Category 12 5 1 3630

In this table, category 11 and 12 support QPSK only; while other terminalsall support QPSK and 16QAM. Now category 6, 8, and 12 are mainstreamterminals in commercialization.

Code Resources Configuration

HSDPA Channel Code Assignment

In configuration of HSDPA cells, HS-SCCH and HS-PDSCH that are the same as that for R99 should be configured. Besides, code resources should also be reserved for HS-SCCH and HS-PDSCH (in static code resources assignment). SF of HS-SCCH should be set to 128 while SF of HS-PDSCH set to 16. The number of channels for HS-SCCH and HS-PDSCH in cells can be set as per actual service throughput requirement, or other factors.

Channel SF

HS-SCCH 128

HS-PDSCH 16

HSDPA A-DCH Code Resources Assignment

When a subscriber requests for a high-speed PS service, the system has HSDPA carries the service. Thus, the subscriber not only takes HS-SCCH and HS-PDSCH, but also takes a downlink A-DCH to transmit signaling when the service is set up. In the case that the rate of signaling channel is 3.4 kbps, each subscriber should be assigned a dedicated downlink channel whose spreading factor is SF256.

HSDPA Power Configuration

HSDPA power can be configured in a dynamic or static mode. In dynamic configuration, the available HSDPA power = total power of a cell x (1-remaining power) – power for R99 service channel and public channelIn static configuration, the available HSDPA power is just the power you configured.

HS-SCCH Power Control

HS-SCCH power can be configured in a dynamic or static mode. But the transmission power is fixed in the static configuration without consideration of channel condition changes. Therefore the flexibility of static configuration is poor. Besides, it may lead to waste of power when channel conditions are good and shortage of power when channel conditions are poor. The dynamic power configuration features a high flexibility. In dynamic power configuration, transmission power changes according to channel conditions.

Consideration of Scheduling Algorithm

There are three traditional scheduling methods, namely, RR, PF and MAX_C/I algorithm. From the perspective of fairness, RR is the fairest, PF followed, and MAX_C / I most unfair; from the perspective of cell throughput rate, MAX_C / I is the most optimal, PF followed, and RR worst; from the perspective of the actual commercial networks, in order to take into account of fairness, ZTE recommends the PF algorithm, because it takes into account of subscriber history throughput and channel conditions. Of course, operators can use special configuration according to actual situations.

Uu Interface Bit Error

The bit errors occurred on uplink and downlink Uu interface directly affect HSDPA download rate. If the averages of UL BLER and DL BLER in a specified duration are close to or better than BLER Target and CQI, it indicates that the bit error rate of the Uu interface is within the normal range; otherwise, you need to analyze the causes of bit errors on the Uu interface.Measuring DL BLER: to obtain data via drive test softwareMeasuring UL BLER: to obtain data at the RNS side, and specific monitoring points are decided by the implementation output of different vendorMeasuring CQI: to obtain data via drive test software or background at the RNS side

Uu Interface Bit Error

Power control and coverage are two main factors that affect uplink and downlink BLER: 1. InterferenceCheck if there is severe external interference (uplink/downlink)in the area with poor UL BLER, DL BLER and CQI2. CoverageCheck if there is uplink limit or downlink limit in the area with poor UL BLER, DL BLER and CQI3. UE performance differenceThe demodulation capability and CQI submission capability of UEs may be different due to UE classification and individual differences. You can change UEs or compare the results of using other models of UEs.

Iub Interface FactorsAffecting Downloading

1. Transmission bit error, delay variation, and packet lossStart your check from alarms about transmission and clock exception.2. Iub bandwidthCheck if there is Iub congestion, according to specific monitoring points provided by each vendor3. Throughput in typical Iub interface transmission

Other Factors

If throughput rate at APP layer and RLC layer is lower than theoretical normal range, it indicates that the overhead for TCP/IP re-transmission is too large. Check and modify the TCP Receive Window and MTU setting.

Peak Traffic in Typical E1 Configuration

典型E1配置峰值流量典型E1配置峰值流量

Numberof E1s

Total Bandwidth (Kbps)

AAL5 Bandwidth (Kbps)

AAL2 Bandwidth (Kbps)

Theoretical Maximum Transmission Rate(Kbps)

1 1920 384 1536 11522 3840 384 3456 25923 5760 384 5376 40324 7680 384 7296 54725 9600 384 9216 69126 11520 384 11136 83527 13440 384 13056 97928 15360 384 14976 11232

The bandwidth of E1 is 2,048 Kbps, equal to 30 standard DS0 channels for data transmission. Besides, it has two 64 Kbps non –standard DS0 channels for signaling control and synchronization. The effective bandwidth of E1 for data transmission is 30 / 32 x 2,048 = 1,920 Kbps.

CN Side Fault Analysis

Analysis of alarms about each NEFor the core network side, pay attention to the alarms about SGSN, GGSN, and so on (mainly focus on the alarms about SGSN and GGSN. Alarms about clock, transmission error, and so on may also cause PS data fluctuation.

TCP receive windowFor services depend on TCP (such as FTP), the TCP receive window at the client and server side affect service performance a lot.

Maximum transmission unit (MTU)If there is a datagram needs to be transmitted at the IP layer, and the datagram is larger than MTU, then the IP layer needs t o segment the datagram into smaller fragments that are smaller than MTU. To improve efficiency, it is necessary to avoid IP segmentation and reassembly, as well as to set MTU to a value as large as possible. Usually, MTU should not be greater than 1,450 bytes.

Modifying TCP Receive Window

For services depend on TCP (such as FTP), the TCP receive window at the client and server side affect service performance a lot. To ensure a better performance, set the receive window to a value as large as possible. Beside, ensure that the size at the client is the same as that at the server side, for example, set both of them to 168,000.Operation method:Modify the registry in Windows as follows:

Choose HKEY_LOCAL_MACHINE > SYSTEM > CurrentControlSet > Services > Tcpip > Parameters, and then add a 2-byte key value TcpWindowSize. Set its value to 168,000 (decimal) or 29,040 (hexadecimal).

Modifying MTU

If there is a datagram needs to be transmitted at the IP layer, and the datagram is larger than MTU, then the IP layer needs t o segment the datagram into smaller fragments that are smaller than MTU. To improve efficiency, it is necessary to avoid IP segmentation and reassembly, as well as to set MTU to a value as large as possible. Usually, MTU should not be greater than 1,450 bytes. Both of the server and client sides have MTU setting. After a PS service is set up, the server side will negotiate with the client side about the using whose MTU setting. Usually the MTU whose size is smaller prevails.

Modifying MTU

To modify MTU setting, do changes to the registry as follows:Modify MTU setting of the server/client side interface:

Choose HKEY_LOCAL_MACHINE > SYSTEM > CurrentControlSet > Services > Tcpip > Parameters > Interfaces > {.........}, and then add a 2-byte key value mtu. Usually set its value to 1,420.

You can find out corresponding interfaces through IP addresses under Interfaces.Restart Windows after modification.

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