Connection and non-connection

Can it be said: "circuit switching is equivalent to connection orientation, while group switching and connectionless are equivalent "?

A: No. This is quite different in concept. The following is an example.

Circuit Switching is the start of communication between A and B. A connection from A to B must be established first (there may be many exchange nodes in the middle ). After the connection between A and B is established, the communication proceeds along this path. A and B always use this channel during communication (full usage), even if the communication signal is temporarily not in the communication path (for example, when both parties stop talking ), it also occupies the same channel. When the communication is complete, the occupied channel is released, that is, the connection is disconnected, and the communication resources are returned to the network for other users to use. Therefore, circuit switching uses connection-oriented services.

However, the connection-oriented service can also be used for group switching. For example, the X.25 network, the frame relay network, or the ATM network belong to the group exchange network. However, this connection-oriented group exchange network must establish a connection before transmitting user data. The connection must be released after data transmission is completed.

Therefore, connection-oriented services can be circuit switching or group switching.

When grouping and switching is used, the channel resources of the link are occupied by the link on which the group is transmitted, but the link that the Group has not yet reached does not occupy this part of network resources (in this case, these resources can be used by other users ). Therefore, group exchange uses resources for a period of time instead of occupying resources. It can be seen that the group exchange method is flexible.

The current Internet uses the IP protocol, which uses a connectionless IP datagram to transmit data, that is, data can be sent immediately without establishing a connection. After the data is sent, the connection is released. Therefore, it is simple and flexible to use connectionless data packets for communication.

Connection-oriented and connectionless scenarios emphasize the stages of communication. Connection orientation must go through three phases: "establish connection> transmit data> release connection", while no connection has only one phase: "Transfer Data ".

Circuit Switching and group switching emphasize the way users occupy network resources during communication. A circuit switch occupies channel resources throughout the process after the connection is established and before the connection is released, in contrast, group switching uses channel resources intermittently during data transmission (the channel resources of the link are used when the group is transmitted on any link ).

connection-oriented and connectionless methods can be discussed at different levels. For example, on the data link layer, HDLC and PPP protocols are connection-oriented, while CSMA/CD for Ethernet is connectionless (see section 4.2.1 ). At the network layer, the X.25 protocol is connection-oriented, while the IP protocol is connectionless. In the transport layer, TCP is connection-oriented, while UDP is connectionless. However, we cannot say that "TCP is a circuit switch". Instead, we should say: "TCP can provide connection-oriented services to the application layer ".