WAP Downlink Performance Evaluation in UMTS Network

1. WAP Downlink Performance Evaluation in UMTS Network Author: Pertti Hakkarainen Supervisor: Prof. Jorma Virtamo Instructors: MSc Jani Kokkonen, Dr Samuli Aalto Work was carried out: Nokia Networks, Espoo Thesis number: 1033 – 2004 Presentation date: November 9, 2004

2. Table of contents • Introduction • Research Problem • WAP • Wireless TCP/IP • Measurement Setup • Measurement Results • Conclusion

3. Introduction • The study is the downlink performance measurement in the Universal Mobile Telecommunication Services (UMTS) network • Technical specification of the network is based on 3rd Generation Partnership Project (3GPP) Release 99

4. Research Problem • The object of this study is to compare the download performance of the Wireless Application Protocol (WAP) and TCP/IP protocol WAP applications in the 3G network. • The protocols are designed for different network domains • WAP protocol stack for circuit switched networks where the bandwidth is relatively low • TCP/IP protocols for packet switched networks where the bandwidth is considerably higher • The aim of this work is to study how well different protocols can utilize the performance of the 3G network.

5. WAP 1/2 Why WAP? • The WAP specification is designed to bring Internet access to the wireless environment. • Wireless data networks present a more constrained communication environment compared to wired networks. • Handheld wireless devices present a more constrained computing environment compared to desktop computers (CPU, memory, power supply, display, keypad etc.). • WAP-compatible component communicate with all other components in the solution network by using the standard methods and protocols defined in the WAP specification

6. WAP 2/2 WAP version 2.0 • WAP 2.0 is based on TCP/IP • WAP Gateway is acting as a WAP 2.0 proxy • No security gap, security is comparable to the Internet model – transaction all the way from WAP Device to the Web server will be secured WAP version 1.2 • WAP 1.2 is based on WAP protocols • WAP gateway makes the conversion from text to binary and vice versa • The plain text headers of HTTP are translated into binary code that significantly reduces the amount of data that must be transmitted over the air interface. • Complete end-to-end security cannot be guaranteed due to a security gap in the GW

7. Wireless TCP/IP • The Transmission Control Protocol/Internet Protocol (TCP/IP) forms the basis of the Internet. Originally it is designed and optimized to provide reliable byte transfer with retransmission in a terrestrial environment where conditions are relatively stable compared to the wireless environment. The assumption is that a packet loss is due to congestion in the network. • The wireless networks have brought new aspects to the packet loss. • More narrow and variable bandwidth • Higher bit error rate • More latency • More transmission delay • Less connection stability • Less predictable availability • Since TCP/IP operates over different kinds of link conditions, from stable and fast wireline links to delay sensitive wireless links, there may be situations that performance degrades due to the fact that the optimization is done in a different way on different parts of the network and packet delays that are treated as congestion • wireless TCP/IP provides the same functions as the “normal” TCP/IP with some optimization in the protocols • The round-trip time (RTT) is one of the most essential issues that has affected to wireless TCP optimization.

8. Measurement setup 1/2 • The target of the measurement has been to measure WAP throughput with different WAP versions, WAP 1.2 and WAP 2.0, to the download direction and evaluate that network is capable to carry traffic with nominal throughputs. • Tools • Ostrich is a trace interface adapter device that provides mechanisms for buffering the tracing and debugging data sent by the phone. • EARP is a PC application for decoding and logging trace data during the testing and debugging of user equipment. • Measurement is carried out in the Nokia WCDMA test network. • During the measurement there were not other traffic in the network UE Test network setup Gateway Iub Iu-PS Gn Gi BS RNC 3G SGSN 3G GGSN Firewall Switch Ostrich EARP RTT Content Server

9. Measurement setup 2/2 • Measurement was conducted with 13 different file sizes, ranging from 2 kilobytes to 160 kilobytes • Downlink rates are 64 kbps, 128 kbps and 384 kbps, for uplink 3G Partnership Project Release 99 defines 64 kbps • Used phones • Nokia 6650 for WAP protocol measurement • Nokia 7600 for TCP/IP measurement Nokia 6650 Nokia 7600

10. Handshake packets Measurement results 1/4 • WAP 1.2 used segmentation and reassembly (SAR) value of 5 • SAR defines a method for a WAP gateway to break a large message into small chunks (the segmentation) and for the phone to piece it back together (the reassembly) • SAR requires the UE to acknowledge to the WAP gateway after every fifth packet • Operator controlled value and optional • The measurement starts when the user has selected the file for download and presses the button on the phone in order to receive it. The connection for the download is already created. • The measurement stops at the reception of the last octet of the file.

11. Steady transfer part of the connection Handshake packets Measurement results 2/4 • Calculation for average and maximum download throughput • Average throughput is the download period from the very first octet of the file until the last octet of a particular file is received including the slow start • The maximum throughput calculation is done over the stabilized transfer part of the download (figure) • WAP protocol has the segment size of 1412 bytes => 7060 bytes requires ACK • In TCP/IP the Maximum Segment Size (MSS) is 1460 bytes and UE allows 20 segments per window

12. Measurement results 3/4 • WAP 1.2 shows quite poor download utilization in 3G network • The reason is SAR value that requires UE to acknowledge to the gateway • If SAR is not used and there is failure in transmission, the whole file must be retransmitted, the bigger the file is the more retransmission deteriorates the throughput • WAP 1.2 designed for circuit switched environment and hence it can not utilize the packet switched environment features

13. Measurement results 4/4 • Wireless TCP/IP utilizes the link connection pretty well, the ’pipe’ fill is optimal • Wireless TCP/IP is designed for the packet switched environment • For small packets the WAP 1.2 throughput is better than WAP 2.0 throughput • When using the SAR value five in WAP 1.2, the better throughput in favor of WAP 2.0 happens between 7 and 10 kilobytes

14. Average throughputs WAP 1.2 average throughputs for different bearer rates • Average throughput remains below the maximum throughput WAP 2.0 average throughputs for different bearer rates

15. Conclusion • What we found out in our measurement? • The WAP protocol is beneficial when a small amount of data is downloaded, less than 10 kilobytes • For larger file size wireless TCP gains better performance • The proportion of the slow start from whole downloaded data on the time scale decreases as the file size grows • The transition in favor of wireless TCP depends on the algorithms and parameters used in both protocols • In our measurement, the wireless TCP gained better download performance around 10 kilobytes file • The 3G network is mature to achieve and maintain nominal transfer rates with WAP applications when using WAP 2.0 in stable environment