Synchronous+Networks

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 * Asynchronous** means "not synchronous". A **Synchronous Network** is basically a network in which clocks are controlled to run, ideally, at identical rates, meaning that the transmit and recieve sides of a circuit synchronise their signal, in order for thr transfer of bits to occur. On the other hand, **Asynchronous** simply means "not synchronous".

Each device uses a clock to measure out the 'length' of a bit. The transmitting device simply transmits. The receiving device has to look at the incoming signal and figure out what it is receiving and coordinate and retime its clock to match the incoming signal.

Synchronous
Synchronous systems decide how to communicate, and check things like information before communication begins. Basic synchronous systems will synchronize the signal clocks on both sides before transmission begins, reset their numeric counters and take other steps. Usually, there is a process to decide which end should be in control (sending/receiving). Once a connection is established, the transmitter sends out a signal, and the receiver sends back data regarding that transmission, and what it received. This connection negotiation process takes longer than asynchronous data transfer, but is more reliable.

Asynchronous
Asynchronous communication utilizes a transmitter, a receiver and a wire without coordination about the timing of individual bits. There is no coordination between the two end points on just how long the transmiter leaves the signal at a certain level to represent a single digital bit. Sending data encoded into your signal requires that the sender and receiver are both using the same encoding/decoding method, and know where to look in the signal to find data. Asynchronous systems do not send separate information to indicate the encoding or clocking information. The receiver must decide the clocking of the signal on it's own. This means that the receiver must decide where to look in the signal stream to find ones and zeroes, and decide for itself where each individual bit stops and starts.

When the receiver of a signal carrying information has to derive how that signal is organized without consulting the transmitting device, it is called asynchronous communication. Asynchronous transmission is sometimes more efficient than sychronous, because no time is spent setting negotiating the connection parameters at the beginning of transmission. Asynchronous systems just transmit and let the far end station figure it out. It's important to note that Asynchronous transmission is sometimes called "best effort" transmission because one side simply transmits, and the other does it's best to receive most of the data. So basically, asynchronous is used as a faster means of connecting, but less reliable when transmitting.

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