Controller In Wireless Sensor Network
Now a days wireless sensor networks have been gaining interact with physically in world. Whereas these can be used in different applications in medical, military, roadside, industrial etc .In the wireless sensor network reducing power is the main approach. In this paper we are explaining about the S-MAC (Sensor-Medium Access Controller) protocol which is new MAC protocol designed for wireless sensor network. It provides a machinery to go around ideal listening, collision and overhearing avoidances'.
In this listen period is divided into three different phases they are SYNCH, RTS(Ready To Send) and CTS(Clear To Send).S-MAC is absolutely equivalent to IEEE 802.11 protocol.Wireless sensor network is a raising technology which has a wide range application they are environment monitoring, spaces, medical systems etc...So these networks have the number of nodes which are distributed and they con form themselves into a number of hop wireless network. Medium Access Controller is also a one of the important protocol in the wireless sensor network which operates successfully. The main theme of this protocol is to avoid the collision, due to this the one against other nodes that do not transmit the data at the same time.This paper presents S-MAC which is new MAC protocol designed for WSN .This S-MAC protocol has a collision avoidance and good subject.
Reducing energy consumption is the primary goal for this design. This protocol has an ability of collision avoidance with the use of procedure. This protocol provides a machinery to go around ideal listening, collision and overhearing to hear without the speakers.By comparing S-MAC with STEM ,it doesn't need two different channel.S-MAC chooses a periodic wake up scheme because each node in this protocol have the interchange repeatedly between a stationary length of listen period and stationary length of wake up period according to the proposed objective.
In S-MAC the listen period has both received and transmit packet which can be used. When S-MAC start to coordinate with the proposed objective of the neighbouring nodes, the listen period starts at the same time. The listen period is divided into three different phases they are SYNCH, RTS and CTS.
The wireless sensor network operation largely depends upon low-level medium access control (MAC) effectiveness. In wireless sensor network MAC goals to secure that no two nodes are meddling to one other transmission.S-MAC is nothing but a sensor MAC protocol which is specially designed for a wireless sensor networks. S-MAC is similar to IEEE which is built on connection based protocol. In a multi hope network while enhancing the efficiency of energy, it preserves the compliance of connection based protocols.
It executes a way for the reduction of energy consumption from all the factors.
3. S-MAC PROTOCOL DESIGN:
The main theme of this protocol is to decrease the energy consumption, when supporting good scheme and avoiding collisions. It tries to reduce the energy consumption. It finds the causes of energy waste i.e. idle listening, collision, overhearing and control overhead.
To achieve this they designed S-MAC protocol they are Periodic listen and sleep, collision and over hearing avoidance and message passing.
3.1. PERIODIC LISTEN AND SLEEP:
If there is no sensing issue occurs between the nodes in the wireless sensor application then these nodes goes to idle position. Due to this the data rate is very low during this time and there is no necessary to keep the nodes to be listening period in all the time. So S-MAC protocol reduces the listens time by knowing the nodes in a periodic sleep.
In a sensor network each and every nodes goes to a sleep mode and wake up and cheeks if there is another node is to talk to it .when a node goes to a sleep mode in that mean it used to off the radio and itself sets the timer to wakeup. The plan is to synchronize between neighbouring nodes to tolerance their clock drift. In this sensor network each and every node has there individual choice to choose their own listen and sleep modes.
To decrease the control overhead, we first give priority for neighbouring nodes to synchronize between them that is at the same time the nodes will go to sleep mode and listen period.In a network, nodes interchange the data by their plan to produce by transmitting it to all it's occurring without delay to neighbours. This to make sure that all the neighbouring nodes will contact with each other. If suppose in a network A wants to talk with B then A waits until B listens.
If the number of neighbours wants to talk with node they should be connected with the medium when the node is ready to listen. This connection mechanism is same as the IEEE 802.11 that is by using Request To Send(RTS) and Clear To Send(CTS) packets.So,if suppose A wants to send a data to B node then fist A sends the RTS packet to B node and if the receiver B node receives the it reply A node with CTS packet. Then the data is started to transmitted, due to this they do not fallow the sleep schedule until the data is transmitted.
3.2. CHOOSING AND MAINTAINING SCHEDULE:
3.2.1. CHOOSING SCHEDULE:
It should need the schedule and exchange to the neighbour before starting its periodic listen and periodic sleep. In a network a node listen for a schedule for a certain time if it doesn't listen from any other node it goes to a sleep mode or if it listens it will be in a wake up period. In a network a node listen for a schedule in a certain period of time if it doesn't listen from any other node it goes to a sleep mode and then it sends or transmit its procedure in SYNCH message, to indicate that node is going to sleep mode after t-seconds.
Such types of nodes are called as synchronizer. Due to this, it selects its procedure independent and other nodes will synchronized with it.If suppose node receives a data from the neighbours without choosing it own, then it keeps the schedule to be same. So this type of method is called follower. That is it will wait for a pattern delay tb and then it retransmitted to the node with the t-tb sleep mode.
So the tb pattern delay is used for avoiding the collisions and if we retransmit it also it will not collide.
3.2.2. MAINTAINING SHEDULE:
The both listen and sleep period needs synchronization with neighbouring nodes. In fact if it listen for a long time it can also presence clearly the large clock drift. So the updating procedure is done by transmitting a SYNC pack.
This SYNC packet is having the address of the sender and the sender's time of the nest sleep mode and it is very small. The sender will go to the sleep mode when a SYNC packet is received to the receiver. Whenever the receiver received the SYNC packet it automatically adjusts the timer.In this the listen period is divided into two packets SYNC and data packets. The first part is for SYNC and the remaining part is for data packets.
When the receiver is ready to listen then the carrier sense will be begins for receive the SYNC packets. It selects the time slots one by one to complete its carrier sence.If the carrier sense has not discovered and transmission by the end of the time slot then it starts the sending SYNC packet at that time. From the fig 3 sender one transmits the SYN packet, sender 2 transmits the data and sender 3 sends both SYNC and RTS packet.
3.3. COLLISION AVOIDENCE:
Collision avoidance is the major part in the SYNC protocol. In a network the number of nodes that is sender wants to send a data to the receiver at a same time. If there are connected in a medium then the collision can be avoid. The collision avoidance is done by 802.11 protocols. S-Mac protocol also follows the common produce by combining virtual and carrier sense and RTS/CTS exchange.
For each and every transmitted packet has a duration time that shows the how much time it will take for remaining transmission. The packet can understand that hoe much time to keep in a sleep mode whenever the received packet is received from the sender. The received value is stored in a variable and this is called as network allocation vector (NAV) and also sets a timer to it. For each and every time, when the NAV, then it decreases until it reaches to zero. If the node has data send to the receiver it first looks for the NAV and checker whether the NAV value is zero or not .if the value is not equal to zero then it understands that the medium is busy.
This type is called as virtual carrier sense. Before transmitting the data the sender performs the carrier sence.The node goes to the sleep mode when it fails to receive the medium and then wake up when the receiver is ready to listen.
3.4. OVERHEARING AVOIDANCE:
S-MAC protocol avoids the overhearing by known's that whenever the node receives the RTS/CTS then it goes to the sleep mode. Let us consider multi hop-network containing A, B, C, D, E and F nodes. Each and every node hears the transmission from the neighbouring node. Suppose node A sending the data to node B and in the multi hope network.
We have to decide that which should goes to sleep mode. So according to the figure node D wants to go to sleep mode because there will be a transmission interference with B reception. In this node E and F are no need to go to sleep mode because there are two far from the transmission. Node C is a two -hop away from B and C do not interference with the transmission. So the C node is free to transmit to the neighbour node E but the node C doesn't get any reply from the E. In this all the sender and receiver will goes to the sleep mode whenever they received the RTS or CTS packet.
If the NAV is not zero then the overhearing avoidance is decreased. It can wake up whenever the NAV becomes zero.FIG 4: Which node should goes to sleep mode when A node transmission
3.5. MESSAGE PASSING:
Message is to gather the information and units of data. It can be a long series or small or short packets. There is one disadvantage of sending a long message as a single packet, if we retransmission this packet it will be high cost, there will be a few bits that will be corrupted for the first transmission. Whereas RTS and CTS are connected for each every independent packets. In this protocol the long message is cut into small fragment and transmitting them into break.
So, first the sender sends the RTS to the receiver and receiver sends the CTS to the sender after receiving that sender sends the data to the receiver. Then the sender waits for the ACK from the receiver .if the ACK fails to receive by the sender then it will be extended the reserved transmission time for the one more fragment and then retransmit the present fragment immediately.
By concluding this sensor-Medium Access Controller, it is a contention based protocol. By using this protocol in wireless sensor network it can avoid the collision and overhearing. It is simplicity to design; there is need of time synchronization. It supports all common pattern supports.
It has a good adaptively to change.
Article name: Controller In Wireless Sensor Network essay, research paper, dissertation