TL Multiplexing

Introduction
Multiplexing is a method of sending multiple streams of information over a communications link at the same time in the form of a single, complex signal.

Time Division Multiplexing [TDM]
Time division multiplexing (often abbreviated to TDM) is where you use time to seperate the streams of data rather than space. It works by sequencing groups of bits/bytes from each individual stream one after the other. This works well for low speed transmissions and is a lot more efficient than getting a certain number of cables per transmitter.

Synchronous TDM
Synchronous TDM is where the timing is the same for every device connected to the multiplexer.

Asynchronous TDM
Asynchronous TDM is where timing is unique depending on what/which device is connected to the multiplexer. Each device is tagged with an ID number in order to distinguish them. This requires more processing by the multiplexer, but overall it is more efficient.

Packet Switching
Packet switching   is a digital networking communications method that groups all transmitted data into suitably sized blocks, called  packets, which are transmitted via a medium that may be shared by multiple simultaneous communication sessions. Packet switching increases network efficiency, robustness and enables technological convergence   of many applications operating on the same network. When transversing network nodes packets are buffered and queued.

There are two types of packet switching. Data Gram and Virtual Circuit.

Data Gram

 * Each packet created individually.


 * Each data gram contains address of its destination.


 * Some have the same address, but don’t necessarily follow the same route.


 * They often arrive out of order with delays in between.


 * It’s the messiest type of data transfer.

Virtual Circuit

 * Data arrives in the correct order.


 * Can get lost on the way.


 * Established route, all packets follow that route then it’s disconnected.


 * <span style="color:rgb(37,37,37);">Data is stored temporarily on the nodes.

<span style="color:rgb(37,37,37);">Advantages and disadvantages of packet switching
<span style="mso-fareast-font-family: "TimesNewRoman";mso-bidi-font-family:Arial;color:black;mso-fareast-language: EN-GB">Advantages of Packet Switching 
 * <span style="mso-fareast-font-family: "TimesNewRoman";mso-bidi-font-family:Arial;color:black;mso-fareast-language: EN-GB">It makes very efficient use of the network - no tied-up lines.


 * <span style="mso-fareast-font-family: "TimesNewRoman";mso-bidi-font-family:Arial;color:black;mso-fareast-language: EN-GB">It can easily get around broken bits of the network.

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 * <span style="mso-fareast-font-family: "TimesNewRoman";mso-bidi-font-family:Arial;color:black;mso-fareast-language: EN-GB">As customers increase, the network only has to expand slowly compared  to circuit switching.

<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto; line-height:normal;mso-outline-level:5">'''<span style="mso-fareast-font-family: "TimesNewRoman";mso-bidi-font-family:Arial;color:black;mso-fareast-language: EN-GB">Disadvantages of Packet Switching '''
 * <span style="mso-fareast-font-family: "TimesNewRoman";mso-bidi-font-family:Arial;color:black;mso-fareast-language: EN-GB">The time it takes to put back the data package changes each time,  which can be a problem for time-critical information such as an emergency  signal. The fancy name is for this is 'latency'.

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 * <span style="mso-fareast-font-family: "TimesNewRoman";mso-bidi-font-family:Arial;color:black;mso-fareast-language: EN-GB">Not very good for small data packages - for example if the data package itself is only 600 bytes long, then two packets of 512 bytes need to  be used, plus the address information.

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