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Thursday, November 22, 2007

The Difference of CSMA/CD and CSMA/CA

CSMA/CD - Ethernet (wired) networks Carrier Sensing Multiple Access / Collidision Detection, this is the full acronym of the well-known medium accessprotocol that made Ethernet based LAN'S so spread and efficient. While CSMA/CA - 802.11 Wireless LAN Collision Detection cannot be used for wireless environments for 3 main reasons:- Wireless communications are in half-duplex. If we had an antenna to listen and another to transmit we should be able to detect a collision while we transmit. This time the medium is the air and the power of the transmitting antenna willconfuse the receiving one thus making detection almost impossible.

CSMA/CD vs CSMA/CA
CSMA/CD
is used on Ethernet networks (or similar). We can detect any collisions because all the receivers are on the same wire as the transmitters.
CSMA/CA cannot do this as the receivers may suffer a collision due to the hidden terminal problem.
CSMA/CD senses the medium and then immediately transmits. If it detects a collision, it backs off for a random period.
CSMA/CA senses the medium, then waits a random number of slots, then senses again. This avoids the problem of all stations waiting until the medium is free, and then immediately all transmitting (i.e. colliding).
CSMA/CA therefore introduces slight delays, because of this extra random wait time.
We can detect collisions on both by means of listening CSMA/CD, and by the lack of an ACK in CSMA/CA.


Difference of Client and Server

A Servers are often dedicated, meaning that they perform no other tasks besides their server tasks. A computer or device on a network that manages network resources. Typically, a client is an application that runs on a personal computer or workstation and relies on a server to perform some operations.


Characteristics of a client
Request sender is known as client
Initiates requests
Waits for and receives replies.
Usually connects to a small number of servers at one time
Typically interacts directly with end-users using a
graphical user interface

Characteristics of a server
Receiver of request which is send by client is known as server
Passive (
slave)
Waits for requests from clients
Upon receipt of requests, processes them and then serves replies
Usually accepts connections from a large number of clients
Typically does not interact directly with end-users