Experts, please! Why is a virtual circuit also packet switched?

Packet switching, also known as packet switching, divides the data transmitted by a user into a certain length, and each part is called a packet. Add a packet header in front of each packet to indicate which address the packet is sent to, and then the switch will send them to the destination according to the address flag of each packet, this process is called packet switching. The communication network that performs packet switching is called a packet switched network.

From the perspective of the development history of switching technology, data exchange has gone through the development process of circuit switching, message switching, packet switching and integrated service digital switching. Packet switching is essentially developed on the basis of "storage-**". It has the advantages of both circuit switching and message switching.

Dynamic multiplexing technology is used on packet switching** to transmit data that is divided into many small segments according to a certain length - packets. After each packet is identified, the technology of dynamic multiplexing is used on a physical line to transmit multiple data packets at the same time. Data from the user is temporarily stored in the switch's memory and then in the network**.

When it arrives at the receiving end, the packet header is removed and the data fields are reassembled into a complete packet in order. Packet switching has higher circuit utilization, smaller transmission delay than packet switching, and better interactivity.

Virtual circuit switching is a combination of circuit switching and packet switching.

Packet switching divides a large packet into sub-packets.

The virtual circuit also uses the mechanism of storing **, and its data is exchanged in the form of packets one by one.

1. Virtual circuit packet switching is transmitted and exchanged in packets, it is a storage-** switching mode, that is, the packets that arrive at the switch are sent to the memory for temporary storage and processing, and then sent out when the corresponding output circuit is free.

2. The basic principle of virtual circuit packet switching is to use the "storage-**" technology, when sending packets from the origin station, the packets are divided into packets with a fixed format, and the destination address is added to the packet, and then the switch in the network temporarily stores the packet of the origin station in the memory after receiving it, and then continuously selects the idle path ** through other switches in the network according to the destination address provided, and finally sends it to the destination address.

Circuit switching.

The switching device finds an actual physical line on both sides of the communication (the earliest circuit switching connections were established by the operator through the plug, and now the computerized program-controlled switch. )

Features: An end-to-end channel needs to be established before data transmission.

Call – Establish connection – Transmit – Hang up.

Pros and cons: It takes a long time to establish a connection;

Once the connection is established, the line is monopolized, and the line utilization rate is low;

No error correction mechanism;

Once the connection is established, the transmission delay is small.

Packet switching (packet switching).

Divide packets into packets of equal size for storage**.

Advantages: 1) The storage amount is small, and the memory can be used to buffer the grouping - fast speed;

2) Low latency – suitable for interactive communication;

3) When an error occurs in a group, only the group is retransmitted, which is highly efficient;

4) Each packet can be transmitted through different paths, with high reliability.

Features: 1) There is no need to establish an end-to-end channel before data transmission.

2) There is a powerful error correction mechanism, flow control and routing function.

Advantages: The storage requirements are small, and the memory can be used to buffer the grouping - fast;

**Low latency – suitable for interactive communication;

When an error occurs in a group, only the group is resent - high efficiency;

Each packet can be transmitted through different paths, which has high reliability.

Cons: Long time to establish a connection;

Once the connection is established, the line is monopolized, and the line utilization rate is low;

No error correction mechanism;

Once the connection is established, the transmission delay is small.

1. The definitions are different.

Circuit switching is the earliest exchange mode in the communication network, and it is also the most widely used exchange mode, which is mainly used in the communication network to complete the exchange and has a history of more than 100 years.

In the process of communication, the communication mode in which the two parties of the communication use the storage-** mechanism to realize data interaction in packets is called packet switching. Packet switching, also known as packet switching, divides the data communicated by the user into a number of smaller equal-length data segments, and adds the necessary control information in front of each data segment as the head of the data segment, and each data segment with the header constitutes a packet.

2. The structure is different.

The basic structure of circuit switching is formed by the expansion of switching units according to a certain topology, and the switching network formed by it is also called the interconnection network. The network structure of packet switching is generally composed of basic equipment such as packet switching, network management center, remote concentrator, disassembly equipment, packet terminals, non-packet terminals and transmission lines.

3. The advantages and disadvantages are different.

The advantages of the circuit-switched method are that the data is transmitted reliably and quickly, the data is not lost, and the original sequence is maintained. The disadvantage is that in some cases, the channel capacity is wasted when the circuit is idle.

The advantage of packet switching mode is that different data packets can be transmitted in dynamic sharing and multiplexing mode on the same link, and the utilization rate of communication resources is high, which greatly improves the capacity and throughput of the channel. The disadvantage is that sometimes the delay jitter and the overhead is large.

Circuit switching: Because circuit switching establishes a physical path between the two parties that is exclusive to both parties before communication, it is formed by the switching equipment and links between the two parties to communicate one by one.

Differences: 1. Circuit switching is an exchange method for the purpose of circuits, that is, the two sides of the communication should establish contact through the circuit, and the circuit has been maintained without hanging up after establishment, with high real-time performance.

Packet switching is to divide the information into several packets, and each packet has a packet header containing routing and control information, which can reach the receiver, but cannot communicate instantly.

2. The two sides of packet switching communication do not occupy a communication line fixedly, but partially occupy this physical path at different times and periods of time, thus greatly improving the utilization rate of communication lines.

When the circuit is exchanged, the data is direct, and it is difficult for terminals of different types, specifications and rates to communicate with each other, and it is also difficult to control errors in the communication process. Once the physical channel between the two parties is established, the two parties can communicate at any time with strong real-time performance.

3. Packet switching due to the fact that the data enters the exchange node to go through the process of storage, which causes the first delay (including receiving messages, checking the correctness, queuing, sending time, etc.), and the larger the communication volume of the network, the greater the delay caused, so the real-time nature of the message exchange is poor, and it is not suitable for transmitting the data of real-time or interactive services.

After the circuit switching connection is established, the physical path is monopolized by both parties, and even if the communication line is idle, it cannot be used by other users, so the channel utilization is low.