DDN user inbound

According to the requirements of China's DDN technical system, the basic methods of user access such as, in these basic methods can also adopt different combinations.

1. Second-line analog transmission

Allows you to simulate inbound connections. In the exchange mode, you must transmit both the DC loop and the E & M signaling of the PBX trunk line.

2. Two-line or four-line communication with MODEM

The supported user rate depends on the line length and MODEM model.

3. Second-line (or fourth-line) baseband transmission mode

This transmission method adopts the echo cancellation technology and differential binary encoding technology. The second-line baseband device supports full-duplex transmission of 19.2 kbit/s. The baseband transmission device also supports TDM multiplexing to provide connections for multiple users to access the network. Some capacity needs to be set aside for network management during reuse. In addition, two-line or four-line baseband transmission devices with a speed of 16, 32, or 64 kbit/s are available.

4. baseband transmission and TDM multiplexing transmission modes

This transmission mode is actually based on the second-or fourth-line baseband transmission, coupled with TDM multiplexing devices, to provide connections for multiple users to access the network.

5. multiplexing of Voice/Data transmission methods

On the existing offline user line, the telephone/data independent data multiplexing and transmission are implemented by means of frequency division or time division. In the DOV device, TDM can also be used to provide inbound connections for multiple users.

6. 2B + D Rate of DTU Transmission Mode

DTU (data terminal unit) uses the 2B + D Rate and the second-line full duplex transmission mode to provide network access for multiple users.

7. PCM Digital Line Transmission Mode

In this way, when users directly use optical cables or digital microwave high-order group devices, a PCM device can be used with other services, one of which is 2048 kbit/s to enter DDN.

8. DDN node transmission through PCM Device

When the user's business volume is large, the DDN node host can be placed in the user's room to reuse the transmitted data signal to a 2048 kbit/s digital line, one channel through PCM enters the DDN Backbone Node.