Group Network and user access for Frame Relay

User Access Procedures
Frame Relay Service is a kind of bearer service which provides two-way transparent transmission of user information through standard interface between user device and Frame relay network, and keeps its order unchanged. The interface between the user and the network is called the User----network interface (UNI), as shown in the figure. In the user----the user side of the network interface is a Frame relay access device, which is used to connect the local user device to the Frame relay network.

Frame Relay access devices can be standard frame relay terminals, Frame Relay mounting/disassembling devices, and network bridges or routers that provide LAN access, and so on. In the user----network interface network side is the Frame relay network device, Frame Relay network device can be circuit switching, can also be frame exchange or letter along the exchange.
The user access code refers to the protocol that the Frame relay access device should have or implement when it is connected to the Frame Relay network device. When a user device accesses a Frame relay network, it should conform to one of the following three protocols and be compatible with the standard supported by the Frame Relay network device. They are the FRF.1/FRF.4 developed by the ITU-T q.922/q.933, ANSI-developed t1.617/t1.618 and Frame Relay forum.
User Access Circuit
At present, users can connect to the frame relay network by means of a direct user circuit, or they can use a telephone switching circuit or an ISDN dial-up switching circuit to access the Frame relay network. As shown in the figure:

1, second line or four lines of modulation and demodulation transmission mode:
The user rate supported by this mode of transmission is determined by the line length, line characteristics, and the type of modem used, with a maximum speed of up to 38.4Kbps. The working mode is Full-duplex, some high-speed modems have multiplex tap function, which can provide network for multiple users. This approach is suitable for users with a lower rate and farther away from the frame relay network device.
2, Baseband transmission mode:
This mode of transmission using the second line or four-wire full-duplex work, the user rate is usually 16Kbps, 32Kbps, 64Kbps. This baseband transmission device can also have time division multiplexing (TDM) function, can be lower than 64KBPS sub-rate multiplexing to 64KBPS digital access, for a number of users access to the network to provide connectivity, in the reuse of a portion of the capacity to be used for network management control.
3, 2b+d line terminal (LT) transmission mode:
This mode of transmission using ISDN digital subscriber loop technology, two-way digital transmission on a pair of lines, can provide a network for multiple users, used in the Frame relay network equipment near (6KM) users.
4, ISDN dial-up access mode:
ISDN dial-up access means that the ISDN subscriber terminal is connected to the frame relay network via an ISDN network. In this way, many users can share the interface, which can reduce the cost of access, on the other hand, can improve the user's flexibility, simplify the network, expand the role of the FR market. The ISDN dial-up access method can be applied in the following situations:
A backup of a leased circuit or a backup of an important user;
Provide broadband replenishment when additional bandwidth is required;
Provides a possibility for remote users to access Frame Relay networks.
5, PCM digital transmission mode:
With the development of digital technology, users can use new digital transmission devices, such as high-speed digital subscriber loop (HDSL) devices or asymmetric data subscriber Loop (ADSL) devices to connect to the Frame relay network.