There are five main WAN connection technologies!

1. DDN

DDN is the abbreviation of Digital Data Network. It consists of digital transmission channels such as optical fiber, digital microwave or satellite and digital cross-multiplexing equipment. It provides users with high-quality data transmission channels and transmits various data services.

Features of DDN:

The transmission delay is small, the quality is high, the route is automatically detour, and the fully transparent transmission is realized. It can support multimedia services such as data, images, and voice, and the optional rate is 2400bps~2048kbps. DDN digital data network has been widely used in my country, covering a wide area and with relatively complete supporting facilities. It is very suitable for fixed interconnection between remote LANs, but the rental fee is relatively high.

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2. X.25 packet switching data network

Packet switching is also called packet switching. It divides the data to be transmitted by the user into several data segments of a certain length, called "packets" or "packets", and then transmits them in the network in a "store-and-forward" manner. X.25 packet switching is suitable for communication between computers of different types and speeds.

The X.25 packet switching network features can realize multi-party communication, greatly improve line utilization, and transmit information safely, reliably, and at a high transmission rate. By applying for an account and password (NUI), nationwide roaming can be achieved, providing a rate of 2,400bps to 64kbps. X.25 lines have been widely used in my country, covering a wide area, with low line rental fees, and are very suitable for low-speed interconnection between remote nodes.

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3. PSTN Public Telephone Network

PSTN public telephone network is the most widely used network system at present. Its advantages are wide coverage, easy to use and low price. Its disadvantages are poor network line quality and low transmission rate. PSTN is suitable for occasions with low communication quality requirements or as a backup network connection.

4. ISDN Integrated Services Data Network

ISDN Integrated Services Digital Network realizes the digitization of user line transmission based on IDN, and provides a set of standard user/network interfaces, so that users can use an existing pair of telephone lines to connect various terminal devices to carry out various business communications such as telephone, fax, data, image, etc., or carry out comprehensive business (multimedia business) communications including voice, data and image at the same time.

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ISDN terminal equipment accesses the ISDN network through a standard user-network interface. Narrowband ISDN has two standard interfaces with different rates: one is Basic Access, which has a rate of 144kbps and supports two 64kbps user channels and a 16kbps signaling channel; the other is Primary Rate Access, which has the same rate as the PCM primary rate (2 048kbps or 1 544kbps), and supports 31 or 24 64kbps user channels and a 64kbps signaling channel. Both interfaces can use twisted pair cables as transmission media. The transmission rate on the user-network interface of broadband ISDN is higher than the PCM primary rate, which can reach several hundred Mbps, and optical fiber must be used for transmission.

5. Frame Relay

Frame relay is a bearer service that provides two-way transmission of user information flows between user-network interfaces and keeps the information sequence unchanged. User information is transmitted in frames, and user information flows are statistically multiplexed. Frame relay is an important technology produced during the standardization process of the Integrated Services Digital Network (ISDN). It is a transmission technology developed from the X.25 packet switching technology as digital optical fiber transmission lines gradually replace the original analog lines and user terminals become increasingly intelligent.