This document discusses medium access control (MAC) protocols, which regulate access to a shared wireless medium between nodes. It covers key requirements for MAC protocols including throughput efficiency, fairness, and low overhead. It also describes challenges like the hidden terminal problem, exposed terminal problem, and sources of overhead from collisions, overhearing, and idle listening. Finally, it categorizes common MAC protocols as fixed assignment, demand assignment, and random access and notes additional energy conservation requirements for wireless sensor networks.

1. PRESENTED BY,
M. JUNO ISABEL SUSINTHRA

2.  Medium Access Control (MAC) protocols is the first
protocol layer above the Physical Layer (PHY) .
 The fundamental task of any MAC protocol is to regulate
the access of a number of nodes to a shared medium in
such a way that certain application-dependent performance
requirements are satisfied.

3.  Requirements and design constraints for wireless MAC
protocols
 Important classes of MAC protocols
 MAC protocols for wireless sensor networks

4.  The most important performance requirements for MAC
protocols are throughput efficiency, stability, fairness, low
access delay, and low transmission delay, as well as a low
overhead.
 Overhead of MAC protocols:
Per packet overhead
Collision-Multiple sender wants to talk.
Collisions can happen if the MAC
protocol allows two or more nodes to send packets at the same
time.

5.  Hidden-terminal problem
The hidden-terminal problem occurs specifically for
the class of Carrier Sense Multiple Access (CSMA) protocols,
where a node senses the medium before starting to transmit a
packet.
 Exposed-terminal scenario
In wireless networks, when a node is prevented
from sending packets to other nodes because of a neighbouring
transmitter is known as the exposed node problem.

7. The exposed terminal analogy is described as follows:
 B sends to A, C wants to send to another terminal D not A or B
 C senses the carrier and detects that the carrier is busy.
 C postpones its transmission until it detects the medium as
being idle again
 But A is outside radio range of C, waiting is not necessary
 C is “exposed” to B
Tip: Hidden terminals cause collisions, where as Exposed
terminals causes unnecessary delay.

8.  A huge number of (wireless) MAC protocols have been devised
during the last thirty years. They can be roughly classified into
the following classes.
 fixed assignment protocols
 Demand assignment protocols
 Random access protocols.

9.  fixed assignment protocols
-In fixed-assignment schemes, each
communicating node is assigned a frequency band in FDMA
systems or a time slot in TDMA systems.
 Demand assignment protocols
-Demand Assigned Multiple Access (DAMA) is
a protocol used in satellite communications, particularly Very
Small Aperture Terminal (VSAT) systems.

10.  Random access protocols
- In random access or contention methods,
no station is superior to another station and none is assigned
the control over another.
-Transmission is random among the
stations.
-That is why these methods are
called random access.

11.  Balance of requirements
 Energy problems on the MAC layer

12.  Balance of requirements
-The balance of requirements is different
from traditional (wireless) networks. Additional requirements
come up, first and foremost, the need to conserve energy.
Important requirements for MAC protocols
-scalability
-The need for scalability is evident
when considering very dense sensor networks with dozens or
hundreds of nodes in mutual range.

13.  Energy problems on the MAC layer
 Collisions -Multiple sender wants to talk.
 Overhearing-The wireless medium is a broadcast medium
and all the source’s neighbours that are in receive state
hear a packet and drop it when it is not destined to them;
these nodes overhear the packet.
 Protocol overhead -RTS and CTS packets or request
packets in demand assignment protocols, and furthermore
by per-packet overhead like packet headers and trailers.
 Idle listening –active listening to an redundant channel.
A node being in idle state is ready to receive a packet but
is not currently receiving anything.

14. THANK YOU