Self-Organizing Neighborhood Wireless Mesh Networks

Researchers in Microsoft Research Redmond, Cambridge, and Silicon Valley are working to create wireless technologies that allow neighbors to connect their home networks together. There are many advantages to enabling such connectivity and forming a community mesh network. For example, when enough neighbors cooperate and forward each others packets, they do not need to individually install an Internet "tap" (gateway) but instead can share faster, cost-effective Internet access via gateways that are distributed in their neighborhood. Packets dynamically find a route, hopping from one neighbor's node to another to reach the Internet through one of these gateways. Another advantage is that neighbors can cooperatively deploy backup technology and never have to worry about losing information due to a catastrophic disk failure. A third advantage is that this technology allows bits created locally to be used locally without having to go through a service provider and the Internet. Neighborhood community networks allow faster and easier dissemination of cached information that is relevant to the local community.

Community-based multi-hop wireless networks is disruptive to the current broadband Internet access paradigm, which relies on cable and DSL being deployed in individual homes. It is important because it allows free flow of information without any moderation or selective rate control. Compared to the large DSL and cable modem systems that are centrally managed, mesh networking is organic -- everyone in the neighborhood contributes network resources and cooperates.

However, to realize the community-based goal, one has to solve many challenging problems including; capacity and range enhancement, privacy and security, self-stablizing and multi-path multi-hop routing, auto-configuration, bandwidth fairness, etc. In addition to solving the tough problems, success also depends on spectrum etiquette, business models, and economics. We are investigating some of the fundamental technical problems that continue to remain challenging despite several decades of research in packet radio networks. We have deployed testbed networks in our office buildings and in a local apartment complex.

Software Artifacts & Support

We implement ad-hoc routing and link quality measurement in a module that we call the Mesh Connectivity Layer (MCL). Architecturally, MCL is a loadable Microsoft Windows driver. It implements a virtual network adapter, so that to the rest of the system the ad-hoc network appears as an additional (virtual) network link. MCL routes using a modified version of DSR (an IETF protocol) that we call Link Quality Source Routing (LQSR). We have modified DSR extensively to improve its behavior, most significantly to support link quality metrics.

The MCL driver implements an interposition layer between layer 2 (the link layer) and layer 3 (the network layer). To higher layer software, MCL appears to be just another Ethernet link, albeit a virtual link. To lower layer software, MCL appears to be just another protocol running over the physical link.

This design has several significant advantages. First, higher layer software runs unmodified over the ad-hoc network. In our testbeds, we run both IPv4 and IPv6 over the ad-hoc network. No modifications to either network stack were required. Network layer functionality (for example ARP, DHCP, and Neighbor Discovery) just works. Second, the ad-hoc routing runs over heterogeneous link layers. Our current implementation supports Ethernet-like physical link layers (e.g. 802.11 and 802.3) but the architecture accommodates link layers with arbitrary addressing and framing conventions. The virtual MCL network adapter can multiplex several physical network adapters, so the ad-hoc network can extend across heterogeneous physical links. Third, the design can support other ad-hoc routing protocols as well.