What kind of network is Frame Relay?

Frame Relay network is a wide area network; Frame Relay is a bearer service that provides two-way transmission of user information flow between users and network interfaces and keeps the order of information unchanged; Frame Relay Network It is composed of Frame Relay node machines and transmission links; in the Frame Relay network, it is difficult to connect each Frame Relay node machine in pairs, both economically and in terms of construction.

Frame Relay is a bearer service that provides bidirectional transmission of user information flow between users and network interfaces while keeping the order of information unchanged. The Frame Relay network is composed of Frame Relay node machines and transmission links. A network provides a connection between two or more user terminals for communication. In the Frame Relay network, it is difficult to connect each Frame Relay node machine to each other in terms of economy and construction, so how to build the network reasonably is very important.

Frame relay (frame relay) is a new public data network communication protocol that emerged in 1992 and began to develop rapidly in 1994. Frame Relay is an efficient data transmission technology that can transmit digital information quickly and cheaply in one-to-one or one-to-many applications. It can be used for voice and data communications, and can be used for both local area network (LAN) and wide area network (WAN) communications. Each Frame Relay user will get a dedicated line to the Frame Relay node. For end users, the Frame Relay network handles data transmission with other users through a channel that changes frequently and is invisible to the user.

Main features: User information is transmitted in units of frames. During the transmission process, the network checks the frame structure, transmission errors, etc., and discards error frames directly. At the same time, statistical multiplexing of user information is achieved by identifying the DLCI of the address segment in the frame.

Frame Relay is a packet-switched communication network, generally used in the Data Link Layer in the Open System Interconnection Reference Model (Open System Interconnection). Permanent virtual circuit PVC is used on physical network switched virtual circuits (SVCs) to form an end-to-end logical link, similar to circuit switching in the public switched telephone network, and is also part of the frame relay description, but it is now very Rarely used in practice. In addition, Frame Relay was originally designed for a compact version of the X.25 protocol.

The data link connection identifier DLCI is a numerical value with local meaning used to identify each endpoint. Multiple PVCs can be connected to the same physical terminal. PVCs generally specify the committed information rate CIR and the additional information rate EIR.

Frame Relay is designed to make more efficient use of existing physical resources. Since the vast majority of customers cannot utilize 100% of data services, it allows the provision of more than 100% data services to telecom operators' customers. data service. Frame Relay has gained a bad reputation in some markets because telecom operators overbook bandwidth.

Telecom companies have been selling frame relay services to customers who are looking for a lower cost than dedicated lines, and it is used in a variety of applications according to government and telecom company policies.

Frame Relay is gradually being replaced by ATM, IP and other protocols (including IP virtual private network).

The frame relay network has the following characteristics:

(1) Use public channel signaling. The logical connections carrying call control signaling and user data are separate. For example, Ansi T1.603 and ITU-T Annex A both use DLCI=0 as the signaling channel. The multiplexing and switching of logical connections occurs at the second layer, thus reducing the number of layers of processing.

(2) Simplify the mechanism. Frame Relay streamlines x. 25 protocol, cancels the flow control and error control of the second layer, and is only implemented by end-to-end high-level protocols. The user-network interface and internal network processing functions are greatly simplified, resulting in low latency and high throughput performance. Frame relay simply processes the frame and then forwards it. The processing functions include: checking whether the DLCI in the frame header is valid, transmitting the frame if it is valid, and deleting it if it is invalid; checking whether the frame is correct, transmitting the frame if it is correct, and deleting it if it is incorrect. Therefore, it is a transmission and loss mechanism that detects and does not correct.

(3) Use high-speed virtual circuits. Frame Relay cancels the third layer and transfers multiplexing to the second layer. It establishes multiple layer 2 logical channels on a physical connection and realizes statistical multiplexing and dynamic allocation of bandwidth, thus improving efficiency and throughput. Reduced latency.

(4) Large frame transmission to adapt to bursts. The frame length of FR is much longer than x. 25 The packet length is large, large frames are used for transmission, and the frame length is variable. The information length of the switching unit (frame) is longer than that of packet switching, reaching 1024 to 4096 bytes. The reservation frame length is at least 1600 bytes, which is suitable for encapsulating data in a local area network. unit, suitable for transmitting burst services (such as compressed video services, www services, etc.).

(5)Hardware forwarding, super speed transmission. DLCI is a label with a short and fixed length, which facilitates high-speed forwarding by hardware.

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