TCP Analysis over wireless local area networks

The TCP analysis is studied under the influence of IEEE 802.11b protocol used in the Access Point (AP) and the network interface card (NIC) in the LINUX and MAC operating systems. The experimental setup is shown below

The server and access point (Belkin or Airport) are connected across a Ethernet distribution system and the wireless client is either a MAC OS X or a LINUX wireless client and the channel is a laboratory space with the non line of sight (NLOS) and the line of sight (LOS) is shown. The NLOS is positioned behind a metal obstruction, and the dimensions are as shown.

The experiment is performed for a block transfer of 100000 IP packets and the packet headers are collected at the AP and server using a monitoring utility called tcpdump.

        ----------------------------------------------------------------------------------------------------------------------------------------------------------

Analysis

----------------------------------------------------------------------------------------------------------------------------------------------------------

CONCLUSIONS

           - TCP throughputs of 5 - 6 Mbps observed in LOS and NLOS time invariant conditions

           - Throughput reduction induced when channel is time varying

                    * Due to channel fades and loss at signal level

           - Throughput reduction also induced by specific AP functions

                    * Apple Airport : Interference of polling frames with data frames

                    * Belkin BS : Inability to capture signal at receiver during fades

           - TCP Error Recovery

                    * Fast Retransmit predominant for airport induced errors

                    * RTO expiry and backoff predominant in Belkin base stations

 

Other links:

TCP and IEEE 802.11b Protocol Performance in Indoor Wireless Channels - Proceedings of Sarnoff Technical Symposium March 2003 - Paper/Presentation

Performance on DS-CDMA Protocol in Wireless LAN's - SPIE 2002 Conference - Paper/Presentation

Installing ORINOCO wireless card in a LINUX - README