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 In computing, a client is a system that accesses a (remote) service on another computer by some kind of network.

The client-server model is used on the Internet, where a user may connect to a service operating on a remote system through the internet protocol suite. Typically, a client is a software program, such as a web browser, that runs on a user's local computer or workstation and connects to a server as necessary and retrieve web pages for display. Most people use e-mail clients to retrieve their e-mail from their ISP's mail storage servers. Online chat uses a variety of clients, which vary depending on the chat protocol being used.
 
  
 In geometry, coaxial means that two or more forms share a common axis; it is the three-dimensional analog of "concentric".

Coaxial cable, for example, has a conducting wire in the center and a second conducting layer running all the way around the exterior circumference, under the insulation. Coaxial cable is used primarily for wideband, video, or rf applications.
 
  
 In a data transmission system, the situation that occurs when two or more demands are made simultaneously on equipment that can handle only one at any given instant.
 
  
 A mathematical technique used to check for errors when sending data by modem. It is a type of hash function used to produce a checksum which is a small integer from a large block of data, such as network traffic or computer files, in order to detect errors in transmission or duplication. CRCs are calculated before and after transmission or duplication, and compared to confirm that they are the same. The most widely used CRC calculations are constructed in ways such that certain types of errors, such as those due to noise in transmission channels, are almost always detected.
 
  
 CSMA is a Media Access Control (MAC) protocol in which a node verifies the absence of other traffic before transmitting on a shared physical medium, such as an electrical bus, or a band of electromagnetic spectrum.

"Carrier Sense" describes the fact that a transmitter listens for carrier wave before trying to send. That is, it tries to detect the presence of an encoded signal from another station before attempting to transmit.
"Multiple Access" describes the fact that multiple nodes may concurrently send and receive on the medium.

In pure CSMA a transmitter does not detect collisions, and a receiver cannot distinguish between collisions and other sources of frame errors. Collision recovery relies on the ability of the receiver to detect frame error and invoke an error recovery procedure. For example, it may not send a required ACK, causing transmitters to time out and retry.

Two common modifications to CSMA, Collision Detection and Collision Avoidance, attempt to improve performance by addressing these problems.
 
  
 Carrier Sense Multiple Access with Collision Avoidance is a network control protocol in which a data station that intends to transmit sends a jam signal. After waiting a sufficient time for all stations to receive the jam signal, the data station transmits a frame, and while transmitting, if the data station detects a jam signal from another station, it stops transmitting for a random time and then tries again.
 
  
 Carrier Sense Multiple Access with Collision Detection is a network control protocol in which a carrier sensing scheme is used and a transmitting data station that detects another signal while transmitting a frame, stops transmitting that frame, transmits a jam signal, and then waits for a random time interval before trying to send that frame again.