UNIT III
MAC PROTOCOLS
DESIGN ISSUES OF MAC PROTOCOLS
Ad hoc wireless networks are included portable nodes that trade packets by sharing a
typical communicate radio channel. Because of the constraints of this channel, the
data transmission to be shared among the nodes is constrained.
In this manner, the point in these networks is to have the option to use the
transmission capacity effectively, and ensure decency to all nodes. As we probably
are aware, wireless networks contrast gigantically from wired networks moreover, ad
hoc wireless networks have significantly progressively explicit attributes, for example,
node versatility, power requirements.
Thus, new protocols are required for controlling access to the physical medium. The
special properties of the ad hoc network make the structure of a medium access
control (MAC) protocol all the more testing.
RESPONSIBILITIES OF MAC PROTOCOL :
Network overhead should be low.
Efficiently allocate the bandwidth.
Distributed MAC operation.
Power control mechanism should be present.
Maximum utilization of channel.
Hidden and Exposed problem should be removed.
Nodes should be sync with time.
DESIGN ISSUES OF MAC PROTOCOLS
Bandwidth Efficiency –
The shortage of data transfer capacity assets in these networks requires its
proficient use. To evaluate this, we could state that
bandwidth capacity is the proportion of the bandwidth used for data
transmission to the complete accessible bandwidth capacity.
Quality of Service Support –
Quality of service support is difficult due to the mobility of the nodes. Once a
node moves out of reach, the reservation in it is lost. In these networks, QoS
is extremely important because if it is being used in military environments, the
, service support needed time to time.
Synchronization –
Some instruments must be found so as to give synchronization among the
nodes. Synchronization is significant for directing the bandwidth reservation.
Hidden Terminal Problem –
When there are two nodes, both are outside of each other’s range and try to
communicate with same node within their range at the same time, then there
must be packet collision.
Exposed Terminal Problem –
Uncovered nodes might be denied channel access pointlessly, which implies
under usage of the bandwidth resources.
GOALS AND CLASSIFICATION OF MAC
PROTOCOLS:-
MAC layers are above the physical layer, it transmits the frames over the medium and
transmits the data by resolving if any issues occur regarding the source and
destination address. It will specify the channel through which the frames will travel or
access the resources, it supports more than one frame at a time. Collision-free
transmission has happened here when in any situation collision occurs then it will
retransmit the frame again to the destination. It also prevents transmission errors
while transmitting the data and for every frame, it checks for the sequence to
maintain the correct sequent order so that the users will receive the correct
information. It will transfer frames over NIC. The reachability of remote channels
which are sharable is restricted. It also assures the flow control mechanism.
CLASSIFICATION OF MAC PROTOCOLS
The MAC protocols specify the influence of different protocols on nodes to access the
remote channels.
MAC protocols have been divided into 4 types −
Contention-based MAC protocol
Channel polling-based MAC protocol
Scheduling-based MAC protocol
Hybrid MAC protocol
The description of four types of MAC protocols is listed below −
1. CONTENTION-BASED MAC PROTOCOL
, It is used for accessibility purposes. To transmit the data from one node to
another node, before initiation it will check for the nearest nodes and their
positions and also examine the carrier status. The accessibility of the channel
is specified by the carrier status. If the value is ideal, then it can start the
transmission of data. If it is not then the node has to wait for a while. This
mechanism will reduce the collision and simultaneous accessing of resources.
It is flexible even the network grows or shrinks. There is no guarantee of
transmission of data and it is solely dependent on the sender. Under
contention-based, there are sender-based and receiver-based sender-based
transmissions that can start by the sender. The receiver initiates the
Connection.
Contention-based MAC Used in Wireless Sensor Networks:-
Sensor MAC (SMAC) is a contention-based MAC protocol that is specifically
designed for wireless sensor networks. The primary objective of SMAC is to
minimize idle listening, over-hearing, and collisions of data packets. To
achieve this goal, SMAC adopts a duty-cycle approach, also known as a
sleep-wakeup cycle. In this approach, each node alternates between a fixed
length of active and sleeping periods based on its schedule.
To prevent collisions among packets, SMAC utilizes the Request to Send
(RTS) and Clear to Send (CTS) packets before transmitting data packets. This
helps to ensure that only one node is transmitting data at a time, reducing the
likelihood of collisions and improving overall network efficiency.
2. CHANNEL POLLING-BASED MAC PROTOCOL
Under channel polling-based MAC protocol, there is the keyword “preamble
sampling”. Like the above before transmission, the sender will check for the
receiver’s availability by sending a preamble. A preamble is a byte that is
added with the data packet prefix value. It will help the sender to activate the
receiver when it is in sleep mode. If the receiver is active then it will take the
packet otherwise this preamble will be in sleep mode. The receiver is in sleep
mode until no more activation signals are sent by the sender. This happens on
an interval basis. For this scheduling is not needed. All nodes are
synchronized. This channel polling is also represented as LPL in BMAC
protocol.
MAC PROTOCOLS
DESIGN ISSUES OF MAC PROTOCOLS
Ad hoc wireless networks are included portable nodes that trade packets by sharing a
typical communicate radio channel. Because of the constraints of this channel, the
data transmission to be shared among the nodes is constrained.
In this manner, the point in these networks is to have the option to use the
transmission capacity effectively, and ensure decency to all nodes. As we probably
are aware, wireless networks contrast gigantically from wired networks moreover, ad
hoc wireless networks have significantly progressively explicit attributes, for example,
node versatility, power requirements.
Thus, new protocols are required for controlling access to the physical medium. The
special properties of the ad hoc network make the structure of a medium access
control (MAC) protocol all the more testing.
RESPONSIBILITIES OF MAC PROTOCOL :
Network overhead should be low.
Efficiently allocate the bandwidth.
Distributed MAC operation.
Power control mechanism should be present.
Maximum utilization of channel.
Hidden and Exposed problem should be removed.
Nodes should be sync with time.
DESIGN ISSUES OF MAC PROTOCOLS
Bandwidth Efficiency –
The shortage of data transfer capacity assets in these networks requires its
proficient use. To evaluate this, we could state that
bandwidth capacity is the proportion of the bandwidth used for data
transmission to the complete accessible bandwidth capacity.
Quality of Service Support –
Quality of service support is difficult due to the mobility of the nodes. Once a
node moves out of reach, the reservation in it is lost. In these networks, QoS
is extremely important because if it is being used in military environments, the
, service support needed time to time.
Synchronization –
Some instruments must be found so as to give synchronization among the
nodes. Synchronization is significant for directing the bandwidth reservation.
Hidden Terminal Problem –
When there are two nodes, both are outside of each other’s range and try to
communicate with same node within their range at the same time, then there
must be packet collision.
Exposed Terminal Problem –
Uncovered nodes might be denied channel access pointlessly, which implies
under usage of the bandwidth resources.
GOALS AND CLASSIFICATION OF MAC
PROTOCOLS:-
MAC layers are above the physical layer, it transmits the frames over the medium and
transmits the data by resolving if any issues occur regarding the source and
destination address. It will specify the channel through which the frames will travel or
access the resources, it supports more than one frame at a time. Collision-free
transmission has happened here when in any situation collision occurs then it will
retransmit the frame again to the destination. It also prevents transmission errors
while transmitting the data and for every frame, it checks for the sequence to
maintain the correct sequent order so that the users will receive the correct
information. It will transfer frames over NIC. The reachability of remote channels
which are sharable is restricted. It also assures the flow control mechanism.
CLASSIFICATION OF MAC PROTOCOLS
The MAC protocols specify the influence of different protocols on nodes to access the
remote channels.
MAC protocols have been divided into 4 types −
Contention-based MAC protocol
Channel polling-based MAC protocol
Scheduling-based MAC protocol
Hybrid MAC protocol
The description of four types of MAC protocols is listed below −
1. CONTENTION-BASED MAC PROTOCOL
, It is used for accessibility purposes. To transmit the data from one node to
another node, before initiation it will check for the nearest nodes and their
positions and also examine the carrier status. The accessibility of the channel
is specified by the carrier status. If the value is ideal, then it can start the
transmission of data. If it is not then the node has to wait for a while. This
mechanism will reduce the collision and simultaneous accessing of resources.
It is flexible even the network grows or shrinks. There is no guarantee of
transmission of data and it is solely dependent on the sender. Under
contention-based, there are sender-based and receiver-based sender-based
transmissions that can start by the sender. The receiver initiates the
Connection.
Contention-based MAC Used in Wireless Sensor Networks:-
Sensor MAC (SMAC) is a contention-based MAC protocol that is specifically
designed for wireless sensor networks. The primary objective of SMAC is to
minimize idle listening, over-hearing, and collisions of data packets. To
achieve this goal, SMAC adopts a duty-cycle approach, also known as a
sleep-wakeup cycle. In this approach, each node alternates between a fixed
length of active and sleeping periods based on its schedule.
To prevent collisions among packets, SMAC utilizes the Request to Send
(RTS) and Clear to Send (CTS) packets before transmitting data packets. This
helps to ensure that only one node is transmitting data at a time, reducing the
likelihood of collisions and improving overall network efficiency.
2. CHANNEL POLLING-BASED MAC PROTOCOL
Under channel polling-based MAC protocol, there is the keyword “preamble
sampling”. Like the above before transmission, the sender will check for the
receiver’s availability by sending a preamble. A preamble is a byte that is
added with the data packet prefix value. It will help the sender to activate the
receiver when it is in sleep mode. If the receiver is active then it will take the
packet otherwise this preamble will be in sleep mode. The receiver is in sleep
mode until no more activation signals are sent by the sender. This happens on
an interval basis. For this scheduling is not needed. All nodes are
synchronized. This channel polling is also represented as LPL in BMAC
protocol.
