Implementation and Evaluation of TCP Retransmission Algorithm For Wireless Packet Channel with Delay Variation

Proceedings ofInternational Conference on Mobile Computing and Ubiquitous Networking (ICMU2008)In this paper, we propose the TCP retransmission timeout method for 3G/3.5G wireless packet access systems. TCP sender calculates RTO timer according to the value of RTT. However, the transmission characteristic of wireless packet channel is fluctuated randomly by fading, shadowing of radio signal, and radio channel controls of wireless packet system. When the variation of propagation delay of the channel increases, RTO timer is not calculated appropriately, that leads to a spurious timeout or an idle time of transmission that degrades TCP performance. The proposal RTO method consists from TS-RTO and improvement of exponential backoff. TS-RTO is an algorithm that calculates RTO timer in proportion to the value of difference between RTO timer and RTT. And we modify the exponential backoff to avoid expanding RTO interval. We implemented proposal RTO method on Linux, and evaluated the performance on the W-CMDA network emulator and on the 3G/3.5G commercial network