学习笔记：高级信息网络Ch6.Multiplexing

(来源：notes of course Advanced IT Network.Ch6.Multiplexing )

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Multiplexing

• Capacity of physical links does not necessarily match the throughput requirement of the application. i.e. the capacity may be wasted because of the lowly use of link. So some link could be designed to be available to carry several data flows together, which is called Multiplexing.
• 简单来说，在一条链接上能传输多个数据流

Two approaches to the Multiplexing

• Circuit switching ( 电路交换 )

• Frequency domain multiplexing

• Synchronous time domain multiplexing

• Packet switching ( 分组交换 )

• Connectionless

• Connection oriented

Circuit switching

-traditionally used in telephone network system.

• the capacity of the share links could be subdivided in predefined parts which are called Circuit
• once requested, a circuit will be reserved for the certain conversation
• unless requesting to release, the circuit is still available.
• if charge, the circuit is duration based charging.

Frequency domain multiplexing

-spliting the signal to different frequency entities, maybe Fourier Transform, every different frequency could transmitt different data flow.

example.

• GSM Radio Slot

• wave domain multiplexing

Synchronous time domain multiplexing

-in digital field

• combine two or more bit flows synchronously

How to demultiplex?

• often use a unique bit pattern, put this bit pattern in the end for marking.

Packet switching

-preferred technique in data world

• the data streams are separated in data packets, rather than bits.
• if charge, it will depend on the data size.
• user will be able to use all the capacity of link in a certain time( the packet delivery time) !

Connectionless

-IP protocol

• no guarantee to successful delivery and delay
• each packet is an independent message
• no error correction by retransmission

-–can do fragmentation to long, low priority data to reduce delay for high priority data

Connection oriented

-have state variables

• Virtual Circuit Number is use to identify the data flow
• sliding window error correction is used
• throughput is committed
• have a defined upper limit for delay

Circuit switching vs Packet switching?

• the data rate is stable and low, please choose the Circuit switching
• the data rate is not stable or peak is extremely high, packet switching!

Network coding

eg.