ITC 254

ITC 254: Assessment 2

ITC 254: Assessment 2

Question 1: Compare the applications of Zigbee with those of IEEE 802.11?

ZigBee is a unique communication standard developed for wireless of low rates for use in personal area network. It has extremely low usage difficulty, cost and energy requirement for connectivity in wireless which is not expensive, is portable and mobile devices (Bartz, 2009). Among the well-known ZigBee topology, ZigBee cluster-tree is especially suitable for low power and low-cost wireless sensor networks because it supports power saving operations and light-weight routing. In a constructed wireless sensor network, the information about some area of interest may require further investigation such that more traffic will be generated. The ZigBee Network layer forms a mesh network capable of routing data around failed nodes. A two-tier ZigBee network is tested in the lab and various failures induced in sensor and router nodes, simulating realistic fault conditions. A ZigBee network analyzer is used to view the packet traffic and measure the response to these induced faults at the Network layer (Albert & Xavier, 2002).

ZigBee, which is based on the IEEE 802.15.4 standard, defines the network (NWK) layer and the application layer (APL) in the protocol stack. There are three types of device in a ZigBee network: a coordinator, a router, and an end device. A ZigBee network is comprised of a ZigBee coordinator and multiple ZigBee routers/end-devices. The coordinator provides the initialization, maintenance, and control functions for the network. The router has a forwarding capability to route sensed data to a sink node. The end device lacks such a forwarding capability. ZigBee supports three kinds of network topology, namely, star, cluster-tree, and mesh topology. In a star network, multiple ZigBee end devices connect directly to the ZigBee coordinator.

The standard of 802.15.4 in IEEE explains the physical layer and medium access control sub layer for low-rate wireless personal area network (LR-WPANs). IEEE 802.15.4 defines a super-frame structure that begins by transmitting a beacon issued by a PAN coordinator. The process consists of an active portion and an inactive portion. The coordinator and devices can communicate with each other during the operative period and enter a low-power phase during the inactive period. The active portion consists of sixteen time slots which are divided into three parts. The three parts are beacon, contention access period (CAP) and contention free period (CFP). Coordinator transmits the beacon at the beginning of the slot 0, and then transmission is followed by CAP (Albert & Xavier, 2002).

Existing WLAN applications are mainly data centric; there is growing demand for real-time services over WLAN. Now days it is nevertheless, to use WLAN for multimedia servers allocated in a wired network. WLAN is a no-blocking system: new users entering into the system try to access the shared medium for transmitting and receiving data. Consequently, throughput decreases with increasing number of users. This is particularly true for 802.11 MAC based on DCF access method. The 802.11 MAC protocol was carefully designed for the wireless LAN environment and, numerous of the ...