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ProblemStatement

Introduction

Melbourne wireless aims to set up a community network. Unlike many other wireless groups, our focus is not on free internet connection sharing, but on actually establishing a large network of wide area links with little emphasis on Internet connectivity. This places us in a distinct niche (well, a slightly cramped niche along with Brisbane, Madrid & Seattle wireless).

Scope

To provide a routing architecture and deployment specification for community wireless netwoorks. Scope includes both internal routing within a regional mesh, as well as peering via a smaller set of wireless links, Internet tunnels or other mechanisms to other regional meshes and Internet Protocol based internetworks.

Requirements

Mesh routing principles

(1) Nodes within a region _must_ cooperate in order to forward packets to the ultimate destination on behalf of peers.
(2) Any solution must be scalable to thousands of nodes within an individual regional mesh
(3) Nodes must be able to support host networks attached via fixed or wireless technologies.
(4) The mesh must be able to be inter-connected to other regional meshes and Internet Protocol based internetworks.

Issues

(1) This is mostly straight-forward. The nodes in the mesh must either switch or route packets towards their destination. Switching is largely impractical except for bridging in special circumstances (such as a repeater). In order to route, the node must support an operating system with routing functionality, e.g. *NIX, Win2K, Cisco IOS. Merely having 802.11 IBSS implementation is not enough as 802.11 does not (contrary to some beliefs) specify any mechanism for forwarding frames.

(2) There are a large number of difficulties to achieving the scalability critieria. Firstly, scalable networks rely upon hierarchy. Secondly in order to grow a network to this size requires minimal management.

Management

Addition of a new node to the mesh should be achieved with minimum or zero configuration changes on adjacent nodes. This implies a number of things, but foremost, it requires that a dynamic routing protocal is needed.

Hierarchy

Hierarchy is difficult to achieve. Community wireless mesh networks exhibit a graph structure that is approximately related to geographical positioning of the nodes. Nodes that are in geographic proximity are more likely to be linked than nodes that are distant. This feature of the network topology makes the imposition of hierarchy extremely difficult. Secondly, wireless technology is such that most links will have the same order of magnitude of bandwidth. This makes aggregation, a key principle of hierarchies, even more difficult. The inability to easily impose hierarchy will limit the scalability of the mesh. A good technical reference on scalability issues of routing protocols is available from a North American Network Operators' Group - nanog - External linktalk.

(3) This is another relatively simple issue, easily solved again through the use of a dynamic routing protocol that can advertise reachability information into the mesh.

(4) This is where it starts to look a little more like an enterprise network. Techniques from the Internet and enterprise networking worlds are readily applicable.


Version 1 (current) modified Tue, 03 Jul 2007 23:12:18 +1000 by graybeard
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