Providing Solutions For Mobile Adhoc Networking 

  • Background
  • Protocols
  • Software
  • Requirements
  • Download
  • License
  • Documentation
  • Mail List
  • Background

    Mobile adhoc networking allows users to exchange information in a wireless environment without the need for a fixed infrastructure. Each user (or node), equipped with one or more radios, is free to roam about while communicating with others. The path between any pair of users can traverse multiple wireless links and the radios themselves can be heterogeneous, thus enabling an assortment of different types of links to be part of the same adhoc network.

    The mobility of the nodes results in a network whose topology is dynamic.  The job of the network is to discover the links between the mobile nodes and to build paths so that any user can communicate with any other user, as long as each has a link to the adhoc network. Within the adhoc network, each node acts as a router and forwards packets on behalf of others.

    Discovering links and building paths across the mobile adhoc network are challenging problems. As part of our Mobile Mesh research project, we have developed a suite of non-proprietary protocols  and Open Source software tools that we believe provide robust, scalable, and efficient solutions.

    Protocols

    We have developed three separate protocols, each addressing a specific function, namely:
    1. link discovery
    2. routing
    3. border discovery
    An aesthetically pleasing aspect of these protocols is that they each contain only a single message type. This form of simplicity, we believe, will enable others to easily understand and implement the protocols. Also, by keeping each function separate, we enable flexibility and extensibility. For example, if a radio is able to discover links at the link layer, then there's no need to run our link discovery protocol, yet we will still want to utilize the routing protocol.

    Link Discovery

    Our Mobile Mesh Link Discovery Protocol (MMLDP) is based upon a traditional "Hello" protocol. Each interface running the protocol periodically broadcasts a Hello message containing its interface address and the addresses of the interfaces that it has heard Hello messages from in the previous period. This is sufficient for a node's interface to discover all links incident to it as well as bidirectional links.

    Routing

    Our Mobile Mesh Routing Protocol (MMRP) is based upon the link state approach and allows us to build least cost paths between any source and destination.   Each "Link State Packet" (LSP) contains various information including a unique router id and a list of lists that contains each local interface address and a list of the neighbor interface addresses which have links to it and their corresponding costs. Also in the LSP are a list of "External RouteAdvertisements" which enable the node to advertise routes into the mobile cloud. One use of this is to allow routers that have a wired connection to a fixed network to advertise a default route for the mobile nodes. Thus, we provide a mechanism for allowing mobile nodes to gain external connectivity. Also, this mechanism can be used by a wireless router to advertise a route for a collection of hosts which are directly connected to it.

    To enhance scalability, we perform a technique called fish-eye routing where the resolution of a node's map of the network is a function of distance. This enables us to decrease the overhead associated with the flooding of LSP's.

    Border Discovery

    Our Mobile Mesh Border Discovery Protocol (MMBDP) is a novel mechanism that enables flow existing outside the mobile cloud to be utilized Other approaches to mobile adhoc networking ignore this possibility. If two or more nodes in the mobile cloud each have a connection into a fixed network (let's call these nodes "border" routers), then the opportunity exists for mobile nodes to communicate with other mobile nodes across the fixed network. This is accomplished by setting up tunnels between the "border" routers across the fixed network. Our border discovery protocol enables a "border" router to discover other "border" routers and then setup tunnels with them. We believe the ability to leverage flow across fixed networks is an important capability that will someday be commonplace.

    Software

    The Mobile Mesh software includes separate Linux based programs that implement each of the above protocols. These tools are loosely coupled and communicate with each other through Unix sockets. This software architecture enables any piece to be easily swapped out and replaced, just as long as it speaks the right messages across the Unix socket. Our goal was to build flexible and extensible pieces so that they could evolve independently of each other. This is a key requirement for building future-proof networks.

    No set of tools would be complete without a visualization tool and Mobile Mesh has one. "mmrpviz"graphically displays all nodes, their interfaces, and links in the network. Links can optionally be labeled with their costs and nodes can be labeled with various useful information from LSP's like sequence number and age. Newly discovered links are drawn in green, links that have recently broken are drawn in red. A screenshot is available here.The visualization tool has proved quite valuable in our development of the routing protocol and we think it will benefit others as well. When you wonder why your mobile router can't communicate with another, the visualization tool let's you know where the links in the network really are.

    Requirements

    The Mobile Mesh software was developed for a Linux  2.2.X kernel. It's quite possible that it may run under 2.3.X kernels as well, but, the author has not tested this. The Mobile Mesh software is comprised of user space code and does not contain any kernel modules or modifications.

    The Mobile Mesh tools require additional software packages:

    Download

    The latest version as well as archived versions of the source code is available here.

    License

    Mobile Mesh is covered by this license agreement.

    Documentation

    The Mobile Mesh protocols are documented in the following Internet Drafts: The Mobile Mesh distribution contains man pages of the various software tools: Also, a brief FAQ is available here.

    Mail List

    A Mobile Mesh mail list exists for users and developers to discuss issues related to the software distribution. The discussion includes questions about using the software, bug reports, and announcements of updates to the distribution. To subscribe to the discussion, send an email to listserv@mitre.org with a body containing the line "subscribe mobilemesh-list YourFirstName YourLastName".  To unsubscribe, send an email to listserv@mitre.org with a body containing the line "unsubscribe mobilemesh-list YourFirstName YourLastName". After subscribing , you may post emails to the discussion by sending them to mobilemesh-list@lists.mitre.org.


    Last update: 11 October 2000
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