Collision-Free Protocols
• In computer networks, when more than one station tries to transmit
simultaneously via a shared channel, the transmitted data is garbled. This event
is called collision.
• The Medium Access Control (MAC) layer of the OSI model is responsible for
handling collision of frames.
• Collision – free protocols are devised so that collisions do not occur. Protocols like
CSMA/CD and CSMA/CA nullifies the possibility of collisions once the transmission
channel is acquired by any station.
• However, collision can still occur during the contention period if more than one
stations starts to transmit at the same time.
• Collision – free protocols resolves collision in the contention period and so the
possibilities of collisions are eliminated.
What is MLMA protocol?
Multi-Level Multi-Access (MLMA): The problem with BRAP is the delay
when the channel is lightly loaded. When there is no frame to be
transmitted, the N-bit headers just go on and on until a station inserts a
1 into its mini slot. On average, the waiting time would be N=2. MLAM
scheme [41] is nearly as efficient under high channel load, but has
shorter delay under low channel load. In MLAM, a station wants to
transmit a frame sends its identification in a particular format. A group of
10 bits (called decade) is used to represent a digit of the station number
[48].
What are IEEE 802 wireless standards?
• IEEE 802 is a collection of networking standards that cover the physical and
data link layer specifications for technologies such as Ethernet and wireless.
The user layer in IEEE 802 is serviced by the two layers- the data link layer and
the physical layer.
• These specifications apply to local area networks (LANs) and metropolitan
area networks (MANs). IEEE standards 802 are used for controlling the
Local Area Network and Metropolitan Area Network.
• Essentially, the IEEE 802 standards help make sure internet services and
technologies follow a set of recommended practices so that network devices
can all work together smoothly.
• IEEE 802 is divided into different parts that cover the physical and data
link aspects of networking.
• The family of standards is developed and maintained by the Institute of
Electrical and Electronics Engineers (IEEE) 802 LAN/MAN Standards
Committee, also called the LMSC.
The generally uses specifications of IEEE 802 are:
• IEEE 802.3 The IEEE 802.3 standard determines the
CSMA/CD access control protocol. The best known scheme
for controlling a local area network on a bus structure is
carrier sense multiple action with collision
detection(CSMA/CD).
• IEEE 802.4 IEEE 802.4 describes a token bus LAN standards.
In token passing methods, stations connected on a bus are
arranged in a logical ring. In this method only the station
having token(token holder)is being permitted to transmit
frames.
• IEEE 802.5 IEEE 802.5 describes the token ring standards. In
a token ring a special bit pattern, called the token, circulates
around the ring whenever all stations are idle. The sequence
of token is determined by the physical locations of the
stations on the ring.
Let’s see the difference between IEEE 802.3, 802.4 and 802.5 :-
S.No. IEEE 802.3 IEEE 802.4 IEEE 802.5
Topology used in IEEE Topology used in IEEE
Topology used in IEEE
1. 802.4 is Bus or Tree 802.5 is Ring
802.3 is Bus Topology.
Topology. Topology.
Size of the frame Size of the frame
Frame format in IEEE
format in IEEE 802.3 format in IEEE
2. 802.5 standard is of the
standard is 1572 802.4 standard is
variable size.
bytes. 8202 bytes.
It supports
There is no priority In IEEE 802.5 priorities
3. priorities to
given in this standard. are possible
stations.
Size of the data
Size of the data field is No limit is on the size of
4. field is 0 to 8182
0 to 1500 bytes. the data field.
bytes.
It can handle
Minimum frame It supports both short
5. short minimum
required is 64 bytes. and large frames.
frames.
Efficiency decreases
Throughput &
when speed increases Throughput & efficiency
efficiency at very
6. and throughput is at very high loads are
high loads are
affected by the outstanding.
outstanding.
collision.
Modems are
Modems are not Like IEEE 802.4, modems
7. required in this
required. are also required in it.
standard.
Protocol is
Protocol is very Protocol is moderately
8. extremely
simple. complex.
complex.
It is not applicable on It can be applied for Real
Real time applications, time applications and
interactive It is applicable to interactive applications
9.
Applications and Real time traffic. because there is no
Client-Server limitation on the size of
applications. data.
