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Page Revision: 2007/05/25 17:28

A prioritized Medium Access Control (MAC) grants the right to access to the computer node with the highest priority. Such a protocol was originally created for wireline networks; Controller Area Networks (CAN) is the most known one and it is currently deployed in 700 million units. We are tranferring this idea to the wireless domain and exploring this idea to solve problems in real-time communication and collaborative distributed computing (wireless/line sensor networks and cyber-physical systems).

The study a prioritized MAC protocols has triggered a number of research activities, namely:

• A prioritized MAC protocol for single broadcast domains (SBD), named WiDOM-SBD;
• A prioritized MAC protocol for multiple broadcast domains (SBD), named WiDOM-MBD;
• A prioritized MAC protocol for wireless networks that that offers several channels;
• Efficient computation of aggregated quantities (such as MIN, MAX) of sensor readings;
• Dissimination of data when the topology is unknown;
• Exploiting the multi-channel capability together with a prioritized MAC protocol.

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WiDOM-SBD

WiDom is a prioritized MAC protocol for wireless networks. It is an adaptation of the dominance protocols (used in the CAN bus) to a wireless channel and perform a schedulability analysis. The main idea of our dominance protocol is that a message stream is assigned a static priority and when message streams contend for the channel, they perform a tournament such that the highest-priority message is granted access to the channel.







Protocol Basics
In the starting state, the protocol waits until the transmission queue is non-empty. Next, the protocol waits for a long idle time and then it transmits a pulse of the carrier wave. The beginning of the pulse represents a common reference point in time for all nodes. A node dequeues the highest priority message and then nodes perform a tournament. If a node wins the tournament, it transmits the message. If a node loses the tournament, it continues to listen on the channel to figure out which priority was the winner and receives the















The Tournament
The tournament is performed bit-by-bit, starting with the most significant bit. A bit is assigned a time interval. If a node contends with a dominant bit then a carrier wave is transmitted in this time interval; if the node contends with a recessive bit, it transmits nothing but listens. This makes it possible for a node with a recessive bit to detect that another node has transmitted a dominant bit, and hence the node with the recessive bit withdraws.











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WiDOM-MBD

WiDom is a prioritized MAC protocol for wireless networks where a single broadcast does not reach all computer nodes.

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WiDOM-MC

We are exploring a prioritized MAC protocol for wireless networks that that offers several channels.

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Data Aggregation

Prioritized MAC protocol can be used to efficiently compute aggregated quantities (such as MIN, MAX) of sensor readings.

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Data Dissemination

Prioritized MAC protocol can be used to efficiently disseminate data when the topology is unknown.

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WISHES

We are exploring how to use multi-channel capability together with a prioritized MAC protocol to deal with the well-known hidden node problem.