Wireless Networking

Smart triggering mechanisms for 802.11 handover

The handoff algorithms in the current generation of 802.11 networks are primarily reactive in nature, because they wait until the link quality degrades substantially to trigger a handoff. They further rely on instantaneous signal strength measurements when choosing the best AP. This approach leads to handoff delays on the order of 1-2 seconds that are unacceptable for delay sensitive applications such as VoIP. We propose a fundamentally new approach to handoffs that is based on continuous monitoring of wireless links. In our approach, a client measures the beacon strengths of all the APs operating on the current, and the overlapping channels, and makes its handoff decisions based on the long-term, and short-term trends in these signals. We show through experiments in a campus wireless network that our proposed algorithms result in more than 50 reduction in average handoff delays, while having the potential to improve overall user performance. Our algorithms have been implemented in today's hardware, and need no infrastructure support.

• V. Mhatre, and K. Papagiannaki.
  Using Smart Triggers for Improved User Performance in 802.11 Wireless Networks
  To appear in ACM Mobisys, Uppsala, Sweden, June, 2006.
  Download: (pdf)

Home Networking

Anecdotal evidence suggests that home wireless networks may be unpredictable despite their limited size. In this work, we deploy six-node wireless testbeds in three houses in the United States and the United Kingdom. We examine the quality of links in home wireless networks and the effect of (i) transmission rate, (ii) transmission power, (iii) node location, (iv) type of house, (v) external interference, and (vi) 802.11 physical layer technology. We provide empirical evidence suggesting that homes are challenging environments for wireless communication. Wireless links in the home are highly asymmetric and heavily influenced by precise node location, transmission power, and encoding rate, rather than physical distance between nodes or local interference. Our findings have implications on the design of future home wireless networks and the capabilities that may need to be supported by wifi-enabled consumer electronics. Our measurements demonstrate that not all wireless devices inside the house will be able to communicate with each other, while a large number of pairs of nodes will not be able to make use of the maximum rate supported by the deployed 802.11 technology. We show that such shortcomings can be alleviated using the multi-hopping paradigm, implying that mesh capabilities may actually be needed in consumer electronics for seamless connectivity across the home.

• K. Papagiannaki, M. Yarvis, and W. S. Conner.
  Experimental Characterization of Home Wireless Networks and Design Implications
  In IEEE Infocom, Barcelona, Spain, April, 2006.
  Download: (pdf)
• M. Yarvis, K. Papagiannaki, and W.S. Conner.
  Characterization of 802.11 Wireless Networks in the Home.
  In 1st workshop on Wireless Network Measurements (Winmee), Riva del Garda, Italy, April, 2005.
  Download: (pdf), Intel Research Technical Report, IRC-TR-05-35 (pdf).

Mesh networking

Infrastructure wireless networks based on the IEEE 802.11b protocol have become a popular choice as a network access technology. The fact that they require no wires thus allowing for increased mobility has led to their widespread acceptance in home and office environments. Within this context a wireless access point (AP) attaches a multitude of wireless devices to an infrastructure network through a single wired connection. Potential disadvantages of this environment are i) the fact that each AP needs to feature one wired connection that constitutes the most significant part of the network cost, and ii) the range of the access network is limited by the range of the wireless medium. These limitations gave birth to a new area of wireless communication referred to as mesh networking. Within this area each AP no longer needs to feature its own wired connection and may relay traffic generated by other APs. The benefits of the proposed solution are i) the network can now extend beyond the range of a single access point, and ii) the expensive wired connection attaching the wireless network to the Internet now serves more traffic than that of a single AP. The objective of our project is to study the performance of multi-radio multi-hop wireless networks. This evaluation is performed both in terms of simulations as well as actual experimental testbeds. We are interested in understanding the fundamental behaviors guiding the performance of multi-hop wireless networks and ways in which such a network should be designed to offer good performance. As a result, we are currently looking into algorithms for the self-configuration of multi-hop wireless nodes so that they perform as good as possible within their surrounding environment.

• J. Robinson, K. Papagiannaki, C. Diot, X. Guo, and L. Krishnamurthy.
  Experimenting with a Multi-Radio Mesh Networking Testbed.
  In 1st workshop on Wireless Network Measurements (Winmee), Riva del Garda, Italy, April, 2005.
  Download: (pdf)

Intelligent Access Point Selection Mechanisms

In this work we explore the fundamental requirements in the problem of AP selection. We identify potential MAC-layer throughput as the metric of interest in such a process, and define it as the throughput that the client is likely to receive after affiliating with a particular AP. We further limit ourselves to passive measurement mechanisms that do not necessitate previous affiliation with the AP and can thus allow for the simultaneous evaluation of the throughput to multiple APs; a requirement that can also facili tate more informed roaming decisions. We propose a methodology for the estimation of upstream and downstream throughput between client and AP which operates on measurements of delay as incurred by 802.11 Beacon frames. Preliminary experiments conducted in a controlled environment demonstrate that the proposed methodology looks promising yielding fairly accurate results under varying conditions.

• K. Sundaresan and K. Papagiannaki.
  The Need for Cross-Layer Information in Access Point Selection Algorithms
  To appear in ACM Internet Measurement Conference, Rio de Janeiro, Brasil, October, 2006.
  
• S. Vasudevan, K. Papagiannaki, C. Diot, J. Kurose, and D. Towsley.
  Facilitating Access Point Selection in IEEE 802.11 Wireless Networks.
  In ACM Internet Measurement Conference, New Orleans, LA, October, 2005.
  Download: (pdf)