| Summary: | The popular Internet protocol stack, TCP/IP, is not suitable for low bandwidth, high
latency wireless channels. Problems associated with TCP's throughput in wireless
conditions has necessitated the development of alternative protocols that can provide
efficient means of transmitting Internet content over a wireless network. Wireless
Applications Protocol (WAP) is one such alternative to using TCP/IP for accessing
Internet services over wireless channels.
In this thesis, the performance of two different WAP network configurations, one
being more secure than the other is evaluated and compared under varying Internet and
wireless conditions. Effect of asymmetric conditions is also studied. Possibility of
providing WAP services over wireless bearers with no error recovery Link Layer is also
evaluated experimentally.
Simulations indicate that the secure configuration, termed as the alternate
configuration (AC), has a better performance than non-secure standard configuration
(SC) for good (1% FER) and average (6% FER) wireless conditions. SC has better
performance on bad wireless conditions (44% FER, <1000 bps throughput). Performance
of AC is affected primarily by wireless conditions whereas performance of SC is affected
primarily by Internet conditions. Primary factor that degrades AC's performance is
flooding of the wireless channel by redundant reply packets from the server end causing
long waiting times on the wireless channel queues. Additionally, under bad wireless
conditions, if there is asymmetry present on the channel, AC is unusable. SC's
performance degrades under degraded (congested) Internet conditions because TCP's
employs congestion avoidance mechanisms and reduces its throughput on detecting congestion on the Internet. Another result of consequence is that under good and average
wireless and Internet conditions, presence of the error recovery Link Layer has minimal
effect on performance of AC and SC.
Some solutions to cushion effect of bad wireless conditions on AC's performance are
proposed and tested. The solutions proposed are the use of duplicate packet filtering at
link layer level and use of larger reply timers and gradually increasing timers at the WAP
gateway. First solution is not employable if data decryption is used. The other two
gateway end solutions improve AC's performance under bad wireless conditions but
decrease its performance under good and average wireless conditions. This leads to the
conclusion that better flow control mechanisms are needed in WTP such that the traffic
generation (of retransmissions) at the server is sensitive to conditions on the wireless
channel. === Applied Science, Faculty of === Electrical and Computer Engineering, Department of === Graduate
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