Computer Network-Three Exchange Methods
Circuit Switching
- The way telephone switches connect phone lines is called circuit switching
- From the perspective of communication resource allocation, switching is to dynamically allocate transmission line resources in a certain way.
telephone exchange
- In order to solve the problem of excessive connections between telephones, telephone switches were created.
- Simply understood as a switch with multiple switches, the phone lines of any two phones that need to communicate can be connected on demand.
Three steps of circuit switching
- Establish a connection (allocate communication resources)
- Call (always occupying communication resources)
- Release the connection (return communication resources)
- When circuit switching is used to transmit computer data, the transmission efficiency of its lines is often very low.
- The line is continuously occupied and cannot be used by other users, resulting in a waste of resources.
Packet Switching
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Usually we call the entire block of data representing the message a message.
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Before sending a message, the host divides the longer message into smaller data segments of equal length, and adds some necessary control information headers in front of the data segments to form a packet, also called a packet, and the header is also called Baotou
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After receiving a packet, the packet switch first temporarily stores the packet, then checks the packet header, and performs table lookup and forwarding according to the packet destination address in the header.
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After the receiver receives the packet, the host removes the header of the packet and combines each data segment to restore the original message.
Message Switching
- Message switching is similar to packet switching. Switching nodes adopt a store-and-forward method. Message switching has no limit on the size of messages and requires that switching nodes need a large cache space.
- Message switching was mainly used in early telegraph communication networks. It is rarely used now and is usually replaced by packet switching.
Comparison of three exchange methods
Advantages of circuit switching
- Small communication delay
- ordered transfer
- no conflict
- Wide range of use
- Strong real-time performance
- Simple control
Circuit switching disadvantages
- long build time
- Line exclusive, low usage
- Poor flexibility
- Difficult to standardize
Advantages of message exchange
- No connection required
- Dynamically assign lines
- Improve line reliability
- Improve line utilization
- Provide multi-target services
Disadvantages of message exchange
- Caused forwarding delay
- Requires larger storage cache space
- Additional amount of information needs to be transmitted
Packet switching advantages
- No connection required
- High line utilization
- Storage management simplified
- Speed up transmission
- Reduce the probability of errors and the amount of retransmitted data
Packet switching disadvantages
- Caused forwarding delay
- Additional amount of information needs to be transmitted
- For datagram services, there are problems with out-of-order, lost or duplicate packets. For virtual circuit services, there are three processes: call establishment, data transmission and virtual circuit release.