Subject: Advanced Network Technologies

Topic: Emerging Wireless Technologies

Difficulty: High

Fig shows the Sensor Network Protocol Stack

Physical Layer

The physical layer addresses the needs of simple but robust modulation, transmission, and receiving techniques. It is responsible for frequency selection,carrier frequency generation, signal detection, modulation, and data encryption.The 915 MHz ISM band has been widely suggested for sensor networks.

Data Link Layer

The data link layer is responsible for multiplexing data streams, data frame detection, medium access, and error control. It ensures reliable point-to-point and point-to-multipoint connections in a communication network. The MAC protocol in a wireless multihop self-organizing sensor network should achieve two goals. The first is the creation of the network infrastructure. The second objective is to fairly and effi ciently share communication resources between sensor nodes.

Network Layer The network layer takes care of routing the data supplied by the transport layer. The network layer of a sensor network is usually designed according to the following principles:

1.Power efficiency is always an important consideration.

2.Sensor networks are mostly data-centric.

3.Data aggregation is useful only when it does not hinder the collaborative effort of the sensor nodes.

4.An ideal sensor network has attribute-based addressing and location awareness.

Data aggregation combines data from many sensor nodes into a more compact form before forwarding to a location for processing. Data aggregation is needed to handle the large amount of data generated in sensor networks.

Another important issue is that routing may be based on the data-centric approach. In data-centric routing, interest dissemination is performed to assign the sensing tasks to the sensor nodes.

Transport Layer

The transport layer helps to maintain the fl ow of data if the sensor network application requires it. The transport layer is needed when a system is planned to be accessed through the Internet or other external networks. Transmission control protocol (TCP) with its current transmission window mechanisms matches the extreme characteristics of the sensor network environment

Application Layer

Depending on the sensing tasks, different types of application software can be built and used on the application layer. Three possible application layer protocols for sensor networks are sensor management protocol (SMP), task assignment and data advertisement protocol (TADAP), and sensor query and data dissemination protocol (SQDDP). An application layer management protocol makes the hardware and software of the lower layers transparent to the sensor network management applications. System administrators interact with sensor networks by using SMP, which provides the software operations needed to perform the tasks.