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TCP Performance and Packet Aggregation in Wireless Mesh Networks under low link quality
Karlstad University, Faculty of Economic Sciences, Communication and IT, Centre for HumanIT. Karlstad University, Faculty of Economic Sciences, Communication and IT, Department of Computer Science.
Karlstad University, Faculty of Economic Sciences, Communication and IT, Department of Computer Science. Karlstad University, Faculty of Economic Sciences, Communication and IT, Centre for HumanIT.
2008 (English)In: Second ERCIM Workshop on eMobility / [ed] Torsten Braun, Geert Heenk, Dimitri Konstantas, Markus Wulff, 2008Conference paper (Refereed)
Abstract [en]

Recently, Wireless Mesh Networks (WMNs) have attracted attention as means to provide alternative internet connectivity to rural areas or communities. In WMNs, wireless access points communicate with each other wirelessly forming a true wireless, mesh based access network of mesh relay nodes (MRN). Mesh gateways (MG) provide internet connectivity and standard mobile clients attach to MRNs, which forward packets via other MRNs to other meshed clients or through MGs to the internet. Therefore, the wireless backbone comprised of MRNs and MGs is similar to static, internet connected Ad Hoc networks. A major problem is however scalability of WMNs as well as MAC and PHY layer overhead for packet transmission. Capacity of WMNs can be increased significantly by aggregating (combining) several smaller packets into larger ones [1][2]. This is in particular beneficial to VoIP flows where packet sizes are small. The overall number of packets is reduced, average packet size increased and contention will take place only once for the larger packets. A relay node will then process fewer large packets instead of many small ones. While such aggregation mechanisms have been proposed for single-hop infrastructure WLAN, designing an aggregation strategy for multi-hop WMNs is a hard problem because in this multi-hop environment, signal quality and congestion for each link is different. When mesh relay nodes aggregate small packets, there is an inherent trade-off regarding packet size. Aggregating more packets leads to larger packets, which reduces the overall number of packets in the mesh and thus reduces multi-hop contention and packet loss due to collisions. However, such larger (aggregated) packets can lead to higher packet loss for a link that operates at low signal quality [3]. To find the optimum frame size for packet aggregation is therefore not trivial and depends on traffic and link quality which can vary over time and might be different for each link in a multi hop path. In this paper, we will evaluate if packet aggregation is beneficial when applied to standard TCP in a WMN environment with low quality links. For integration of Mesh Networks into 4G environment, the transport layer needs to be compatible and interoperable with already deployed transport protocols. We will therefore compare end-to-end performance of standard TCP (with Selective and Delayed ACKs) using different MSS sizes in a mesh environment, both with and without deploying packet aggregation. Delayed ACKs and Selective ACKs has shown to be beneficial in multihop environments as the number of packets is reduced leading to less contention [4]

Place, publisher, year, edition, pages
2008.
Keyword [en]
MESH packet aggregation TCP
National Category
Computer Science
Research subject
Computer Science
Identifiers
URN: urn:nbn:se:kau:diva-24156ISBN: 9789521519727OAI: oai:DiVA.org:kau-24156DiVA: diva2:597923
Conference
Second ERCIM workshop on emobility, Tampere, May 30 2008
Available from: 2013-01-22 Created: 2013-01-22 Last updated: 2013-11-05Bibliographically approved

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