Analyzing Poor Performance of Data Transfer at CN Side

Figure 1.1 shows the flow for analyzing poor performance of data transfer at CN side.

Figure 1.1 Flow for analyzing poor performance of data transfer at CN side

NE Alarms

At CN side, analyze the alarms on SGSN, GGSN, LAN switch, router, and firewall (collecting SGSN and GGSN alarms as key task). Clock alarms and transport code error alarms may lead to fluctuation of PS data.

Package lose on CN side result in TCP/IP layer RTT overtime touch off congestion avoidance

TCP apply credible transmit layer. One method is to affirm the data which receive from the other side. But data and affirmance may lose . TCP transit set a timer in the send time to solve the problem. When the timer overflow , it don’t receive affirm message, it will retransmission data.

TCP send point will be a measure to a connect RTT. Maintain a RTT timer.

If it measure RTT overtime , TCP think net congestion , it will start-up congestion avoidance.

Consequently, it will affect data transmit rate.

IP package lose on CN side will make RTT overtime.

Environment Problems

The rate is relevant to PC, OS, and applications. The internal algorithm of software at different application layer and TCP parameters of OS have great impact on performance. If other conditions are the same, the rate of data transfer on Windows 2000 computer is superior to that on Windows 98 computer. Therefore, it is recommended to use Windows 2000 Professional and Windows 2000 server as the OS of PCs and servers.

Now the laptops are installed with Windows XP, so there is no problem concerning perform due to OS. Anyhow, the servers must be installed with Windows 2000 server, because Windows XP will affect the performance of data transfer.

The PC (laptop) for being daemon of UE must be of good performance. Tests prove that IBM laptops have good performance in playing VODs. Now Huawei RNP engineers use the new laptops of D Corporation, which have worst performance in data transfer of HSDPA test than the new ones of H Corporation.

If the utilization CPU being daemon of UE is 100%, the TCP/IP receiver window is full. As a result, the performance of data transfer is affected.

The performance of servers may affect service effect, which must be considered.

TCP Receiving and Sending Window

For the services (such as VOD and FTP) using TCP protocol, the TCP window size of test laptop (client) and server have great impact on performance of services. Set the window as large as possible to guarantee good performance. Set the window of client and server in the same size, such as 64K.

For modification method, see the appendix.

Maximum Transmission Unit

If a data packet at IP layer is to be sent, and the data packet is larger than the maximum transmission unit (MTU), the IP layer will divide the data packet to pieces. Each piece is smaller than MTU.

Using larger MTU and avoiding IP segment and reassembly helps to raise efficiency. MTU is usually smaller than or equal to 1450.

Changing MTU includes changing the MTU of server and changing the MTU of test laptop. After PS service connection setup, the service negotiates with the client. The MTU in use takes the smaller of the two MTUs.

For modification, see the appendix.

Service-related Problems

 FTP

Use the commercial FTP software, because the FTP software embedded in Windows OS is of average performance. Download data with FTP in binary. The multi-thread

downloading software like FlashGet is recommended.

If update rate is low , it can consider process multi-FTP transmission at the same time, or use tools send fixed rate package to make sure whether the bottom has a problem.

 VOD

The software RealPlayer sets the maximum play rate to larger than 384 kbps. The buffer time must not be over long, and 3s is proper. Some computers are installed with qualified video adapter, so the monitor jumps some frames. Change the resolution to 800x600. If

the problem is still present, change the video adapter.

 Net TV

When the rate of down-layer declines, the Net TV is difficult to restore. Note this.

 Video conference

Set the output rate of convergence TV smaller than the rate of down-layer; otherwise, data packets will be dropped. Huawei conference video sets 64 kbps as step from 128 kbps. The recommended configuration is 320 kbps. If the rate is over low, utilization rate of down-layer rate will be over low. Otherwise, using the rate higher than 320 kbps, such as equal to or larger than 384 kbps, leads to dropping data packets because the rate of down-layer cannot meet the requirements by application layer. As a result, the

performance of video conference declines. If a lightning sign appears on the right upper corner of conference TV, there must be code error or packet dropping during

transmission.

HSDPA Subscribed Rate

In test, if the downlink throughput of HSDPA subscriber is only 384 kbps, 128 kbps, or 64kbps. By check the HSDPA cell is set up exactly. After confirmation that the problem is not at RAN side, check the HLR subscribed rate and subscribers' QoS parameters of SGSN and GGSN.

 HLR

The APN and subscribed rate is changed in MOD GRPS of HLR. You can set multiple APNs to a SIM card. Each APN matches a highest rate.

When the maximum rate is not restricted at UE side, the RAB assignment request message sent by CN brings the subscribed rate.

If no resource, such as power resource and code resource, is restricted at RNC side, the Activate PDP content Accept message of NAS signaling brings the assigned rate to UE.

Obtain the rate contained in the Activate PDP content Accept message in Probe or other DT tools.

 GGSN

Modify subscribers'' QoS parameters on GGSN. Set downlink bit rate and downlink guaranteed rate as required. The default configuration is 384 kbps. The commands are as below:

SET QOS: MBRDNLK=2048, GBRDNLK=2048;

The previous command sets the downlink maximum rate to 2048 kbps. As a result, the CN allows the downlink maximum rate of HSDPA to be 2 Mbps.

 SGSN

Modify downlink maximum rate and downlink guaranteed rate of subscriber by executing the command below:

SET 3GSM: MBRDNLK=151, GBRDNLK=151;

Set the maximum bandwidth to 151 (standing for 2 Mbps) by executing the command SET 3GSM.