On a Linux implementation of mobile IP and its effects on TCP performance

Abstract

This article describes the implementation of mobile Internet Protocol (IP) within the Linux kernel and presents results of some experiments that quantify the effects of overheads introduced by mobile IP to the transmission of Transmission Control Protocol (TCP) segments. The mobile IP implementation is designed to support overlapping wireless cells, dynamic routing and multiple wireless interfaces. It has a socket interface that users can use to monitor the kernel stack. To reduce complexity, improve robustness and reduce bandwidth wastage, a few soft states are used. To solve a problem with gratuitous Address Resolution Protocol (ARP) in the Linux operating system used, the implementation introduces the use of vendor-specific extensions; these extensions also provide flexibility for system management and security. The experiments to quantify the transmission overheads involve File Transfer Protocol (FTP) file transfers to and from a mobile node. The results show that a file transfer can take 90% more time to complete as a result of the overheads that mobile IP introduces. In addition, mobile IP also causes a TCP connection to stall for some 2.5 s whenever a handoff event occurs. These effects on the performance of a TCP connection are observed in an internetwork setup in which both signal propagation and mobile IP registration processing delays are negligible. Hence, the impact of mobile IP on TCP performance is expected to be worse in the global Internet.