Explain CSMA with collision detection?

- CSMA with collision detection is abbreviated as CSMA/CD. 

- CSMA in itself makes use of the LBT technology i.e., listen or sense before talk. 

- But when incorporated with the ability of collision detection, it gets much better. 

- If the channel is sensed to be idle the data packets or frames are transmitted immediately but if not, the transmitter is bound to wait for some time before it can re-transmit. 

- Sensing the channels prior to transmission is absolutely necessary if the collisions are to be avoided. 

- Sensing the channel is the most effective way of avoiding the collisions. 

- There are two types of CSMA protocols namely persistent and the non-persistent CSMA.

- In CSMA/CD protocol all the hosts have freedom for transmitting and receiving the data frames on one and the same channel. 

- Also, the size of the packets is variable.

CSMA/CD comprises of two processes:

Carrier Sense: In this process the transmitter or the host checks if the channel or the line is not occupied before starting the transmission.

Collision Detection: CSMA/CD tries to detect the collisions in the shortest possible time. If it happens to detect a collision, it stops the transmission then and there and waits for a random amount of time which is equal to the binary exponential back-off. It then again senses the channel.

- For ensuring there occurs no collision during the transmission of a packet, a host must have the capability of detecting the collision before the transmission process is complete. 

- What happens is that the host A sensing the line to be idle starts transmitting a frame. 

- Just before the first unit of this frame reaches host B, it also senses the line to be idle and starts its transmission. 

- Now the host B receives data while its transmission is still in progress and so it detects that a collision is about to occur. 

- A collision occurs close to the host B. the host A also receives data in midst of its transmission and therefore detects the collision. 

- For making the hosts detect collision before transmission, a minimum length has to be decided for the packets that are transmitted via CSMA/CD networks. 

There are 3 states for a CSMA/ CD channel namely:

1. Contention
2. Transmission
3. Idle

- Ethernet is the most popular example of the CSMA/CD networks. 

- A minimum slot time is required for collision detection between the stations.

- This slot time must equal twice the maximum value of the propagation delay. - The host acquires the channel on the basis of the 1 – persistence. 

- Also, a jam signal is transmitted if a case of collision detection occurs. 

- CSMA/CD make use of the binary exponential back-off algorithm. 

- It is obvious that the idle time of the channel will be small if the load is heavy. 

- It normalizes all the packets with respect to the time of the packet transmission.

- CSMA/CD represents a very effective method for media access control. 

- There are different methods available for detecting the collisions. 

- Which method is to be followed depends largely on the transmission medium that exists between the two stations. 

- For example, if the two stations are connected via electrical buses, the collision can be detected by making comparison between the transmitted and the received data. 

- Some other way involves recognition of a signal of higher amplitude than the normal one. 

- The jam signal used in the CSMA/CD networks is constituted of 32 bit binary pattern.

What are different principles of communication?

Effective communication forms the most important part of the human interaction. Its importance can be hardly over looked. Each and every individual who forms a part of a team ought to know the principles of effetive communication in order to work and talk with the rest of the members of the organization and be listened to.

Here communication principles have been explained from different view poiints including litening and speaking.

Communication as we all know is a 2- way process of giving and receiving information through any channel.

The following basic principles apply everywhere irrespective of who the speaker or the listener are:

- Know your topic
- Know your purpose
- Know your audience
- Anticipate objections
- Present a clear picture
- Follow through on what you say in regard to your topic.
- Achieve credibility with your audience.
- Present what you want to say in different catchy ways
- Communicate a little at a time
- Develop a practical way to get feedback from your audience
- Use multiple and effective communication techniques

Communication is a complex process and sometimes even our own thoughts and opinions prove to be a major barrier in the way of effective communication.

Communication between different team members can be influenced by various environmental factors that actually don’t have anything to do with the content of the message.

Some of those factors have been listed below:

- Nature of the place or the room i.e., how cold or warm it is etc.
- Distractions like what is going on at that place.
- Reputation of the speaker.
- Appearance or the personality of the speaker.
- Knowledge of the listener about the topic.
- Language used.

According to a research, people remember most of what they hear and see rather reading or only seeing. To deal effectively with the decision makers, it is important to know and understand their opinions and interests.

Asking following questions will prove to be a great help:
- Whom to persuade?
- Who will make decisions about the change?
- What are the past experiences of the decision makers?
- What is current attitude of the decision maker?
- What is the most effective way to approach decision maker?
- What are the work styles of other team members?
- What programs will the new decision improve?
- How will the decision benefit the decision maker?

While making a formal presentation to the rest of the organization, the following principles hold good:

- Do not over state your case.
- Make appropriate use of understatement.
- Persuasion should be clear and simple.
- Be ready to back up facts or claims.
- Incorporate most anticipated objections.
- Use visuals aids appropriately.
- Try to find out what the other members think about your opinion.

Importance of Idea
- A good idea must always be recognized.
- The idea should be sold to those who can use it effectively.
- Organization must be convinced that the idea has enough merit to be acted upon. - Getting and giving feedback is also another important part of the communication process.
- Be patient and listen to the complete message.
- Don’t ever prejudge the incoming message.
- It’s well said that if you listen then you will be the most listened to!
- Good listeners demonstrate alertness.
- Always keep your attention directed towards the message and judge the content of the message.
- Distractions seriously impair listening.
- Always think critically and efficiently.
- Message should be conveyed in such a way that it discourages rejection and encourages retention.