Contention Based Protocol
November 1, 2016
Categorised in: Data Communicaiton & Wireless Sensor Networks
Random Access-Based Protocols
Traditional random access MAC-layer protocols, also known as contention-based protocols, require no coordination among the nodes accessing the channel.
Colliding nodes back off for a random duration of time before again attempting to access the channel.
The enhancement of these protocols with collision avoidance and request-to-send (RTS) and clear-to- send (CTS) mechanisms improves their performance and makes them more robust to the hidden terminal problem
The energy efficiency of contention-based MAC-layer protocols, however, remains low due to collisions, idle listening, overhearing, and excessive control overhead.
The power aware multicast protocol
The power aware multi access protocol with signaling (PAMAS) avoids overhearing among neighboring nodes by using a separate signaling channel
The protocol combines the use of a busy tone with RTS and CTS packets to allow nodes currently not actively transmitting or receiving packets to turn off their radio transceivers.
The protocol does not, however, provide mechanisms to reduce energy waste caused by idle listening.
Sparse topology and energy management (STEM) protocol
The STEM protocol trades efficiency for energy efficiency. This is achieved using two radio channels: a data radio channel and a wake-up radio channel.
A variant of STEM uses a busy tone instead of encoded data for the wake-up signal. STEM is known as a pseudo asynchronous scheduled scheme. Based on this scheme, a node turns off its data radio channel until communication with another node is desired. When a node has data to transmit, it begins transmitting on the wake-up radio channel. The wake-up signal channel acts like a paging signal. The transmission of this signal lasts long enough to ensure that all neighboring nodes are paged. When a node is awakened from its sleeping mode, it may remain awake long enough to receive a ‘‘session’’ of packets.
A node can also be awakened to receive all of its pending packets before going into the sleep mode again. The STEM protocol is general and can be used in conjunction with other MAC-layer scheduling protocols.
IEEE 802.11-inspired Contention based protocol
A variety of IEEE 802.11 inspired contention based protocols prevent overhearing by using RTS and CTS packets.
A common feature of these protocols is to use the overhearing of RTS and CTS packet exchange between two other contending nodes to force a contending node to go into sleep mode.
These protocols also rely on synchronized schedules between neighboring nodes to avoid idle listening.
These protocols differ in the way they maintain low duty cycles and the way they achieve energy.
Time out MAC
The timeout-MAC (T-MAC) is a contention-based MAC- layer protocol designed for applications characterized by low message rate and low sensitivity to latency.
To avoid collision and ensure reliable transmission, T- MAC nodes use RTS, CTS, and acknowledgment packets to communicate with each other. Furthermore, the protocol uses an adaptive duty cycle to reduce energy consumption and adapt to traffic load variations.
The basic idea of the T-MAC protocol is to reduce idle listening by transmitting all messages in bursts of variable length.
Nodes are allowed to sleep between bursts. Furthermore, the protocol dynamically determines the optimal length of the active time, based on current load
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