Mrigendra Pratap Singh
Department of Computer Science
Sri Ramswaroop Memorial Group Of Professional Colleges
This paper presents an energy efficient protocol for medium access control layer for single hop ad hoc networks . This protocol is more energy efficient than distributed co-ordination function (DCF) mechanism with RTS/CTS approach given by IEEE 802.11 specification for wireless LAN’S. In contrast to a single node accessing channel and sending data at a time in the original DCF mechanism of IEEE 802.11 ,our protocol consists of a Controller node which can send data of more than one node over the channel at a time . This way the overall energy consumed in the transaction is less than that consumed by a network IEEE 802.11 specification.
IEEE 802.11 ,data link layer, medium access control layer, single hop ad hoc networks, distributed co-ordinated function.
IEEE 802.11 is a specification given by IEEE for wireless local area networks . This standard deals with physical and MAC layers in wireless local area networks. Physical and Data Link Layer are layers in OSI (open system interconnection) model. OSI is a layered framework for the design of network systems that allow communication between all types of computer systems.It consists of seven separate layers but related layers , each of which defines a part of the process of moving information across a network. The OSI model is composed of seven ordered layers : physical(layer 1),data link(layer 2), network(layer3), transport(layer4), session(layer 5),presentation(layer 6) and application(layer 7). The function of Physical layer is to co-ordinate the functions required to carry a bit stream over a physical medium. The Data Link Layer is responsible for moving frames from one node to the next . This layer has two sublayers- a) Logical Link Control Layer:-
b) Medium Access Layer:-
CSMA/CA (carrier sense with multiple access and collision avoidance) is the MAC layer machanism used by IEEE 802.11 instead of CSMA/CD (carrier sense with multiple access and collision detection). The reasons include :- a) The signals loose the strength after certain distance. b) In wireless networks the problems like Hidden Terminal Problem and Exposed Terminal Problems Exist .
The access mechanism of IEEE 802.11 is of two types:-
1) DCF(distributed co-ordination function):- This mechanism is for wireless ad-hoc networks which are networks without any infrastructure.
2) PCF(point co-ordination function):- This mechanism is for wireless networks with some infrastructure attached.
RTS/CTS approach (request to send / clear to send) :- this approach is introduced in wireless local area networks to remove hidden terminal problem and exposed terminal problem.
In our research work we have worked on Single Hop Ad-Hoc Networks which are fully connected networks. This means that each node in the network is connected to every other node in the network. In such networks we face no Hidden Terminal Problem nor Exposed Terminal Problem.
DCF Mechanism with RTS(request to send)/CTS(clear to send) approach for channel access in MAC layer for single hop ad-hoc networks
1) To access the channel in MAC layer any node has to wait for DIFS(distributed interframe space)time period . During this time period a node continuously senses the channel and if it finds it free for this time period it can access the channel and broadcast the RTS(request to send) message to all nodes in the network. 2) If there is a collision detection then the nodes in collision increase their backoff timer value within the contension window window range and start their back-off period. 1) If...