Routing in Mobile Hosts - Computer Network Routing for...

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Computer Network Routing for Mobile Hosts Prof. d-r Aksenti Grnarov
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Introduction The integration of mobile hosts into the existing internetwork gives rise to some peculiar problems because of the special requirements of the small low power mobile hosts and also because of the special characteristics of the wireless link. Several Mobile-IP proposals have addressed the problem of delivering IP packets to mobile hosts regardless of their location. In theory one can use existing fixed network transport protocols such as UDP and TCP on the mobile. An Indirect model for mobile hosts allows the development and use of specialized transport protocols that address the performance issues on the comparatively low bandwidth and unreliable wireless link. Protocols developed based on this model can also mitigate the effects of disconnections and moves while maintaining interoperability with existing protocols. In this job I presented the design and implementation of I-TCP which allows a mobile host to communicate over a transport layer connection with the fixed network via its current Mobile Support Router (MSR). The TCP connection with the fixed host is actually established by the MSR on behalf of the mobile host (MH). If the MH moves to another cell during the lifetime of the TCP connection, the new MSR takes over the connection from the old MSR. Experiments with I-TCP on our testbed show substantial throughput improvement over regular TCP when one of the end points is mobile. TCP/IP in Mobile Field The main reasons for throughput falling is the loss of TCP segments during cell crossovers especially with non-overlapped cells. Lost segments trigger exponential back off and congestion control at the transmitting host and the congestion recovery phase may last for several seconds even after network layer communication is reestablished in the new wireless cell. Fast retransmission coupled with modification of the TCP software on the mobile hosts solves only part of the problem because the transmitting host still performs a slow start if more than one 2
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segment is lost per window, thus limiting the effective throughput. Other proxy-based approaches have been suggested for mobile hosts but they do not pertain to the transport layer. Indirect Protocol Model for Mobile Hosts The indirect model for MH suggests that any interaction from a mobile host (MH) to a machine on the fixed network (FH) should be split into two separate interactions — 1) Between the MH and its mobile support router (MSR) over the wireless medium and 2) Between the MSR and the FH over the fixed network. This provides an elegant method for accommodating the special requirements of mobile hosts in a way that is backward compatible with the existing fixed network. All the specialized support that is needed for mobile applications and for the low speed and
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This note was uploaded on 10/20/2008 for the course COMPUTER S 2212 taught by Professor Grnarov during the Spring '08 term at St. Augustine IL.

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Routing in Mobile Hosts - Computer Network Routing for...

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