The connection between Cisco DTE and DCE equipment
In the CISCO remote access server, use three pairs of lines to connect DTE and DCE. In each pair of lines, one sends and one receives:
1. TX/RX data transmission line
Send: DTE->TX->DCE
Receive: DTE<-RX<-DCE
The DCE device (MODEM) sends data to DTE through RX, and receives data from DTE through TX. The rate of sending and receiving is set on the MODEM. The speed of the MODEM connected by RS232 and the router must be the same.
2. RTS/CTS hardware flow control
DTE->RTS->DCE
DTE<-CTS<-DCE
When the DTE data buffer is full, the RTS signal will be lowered to notify the DCE not to send data. Similarly, the DCE will lower the CTS signal to notify the DTE not to send data. MODEM and access server must be set to hardware flow control.
3. DTR/DCD MODEM control
DTE->RTS->DCE
DTE<-DCD<-DCE
When the remote access server (DTE) is READY, the DTR output signal is high, by lowering the DTR signal, the remote access server hangs up the line. The MODEM informs the DTE through the DCD signal, indicating that there is a dial-in dial-in, and the remote access server is required to provide services, and the DCD signal of the MODEM disappears, indicating that the MODEM has lost the dial-up.
How to judge DTE DCE
The distinction between DTE and DCE is actually only for serial ports, and routers usually connect to WANs through serial ports.
The serial V.24 port (25 pins) usually stipulates that the second pin of DTE is used as TXD (transmit data line), and the third pin is RXD (receive data line), (the remaining pins are: 7 is the signal ground line, 4 It is DTS, 5 is RTS, 6 is DTR, 8 is DCD, and includes sending clock, receiving clock, etc., all have specific pins), serial V.35 (34 pins) is the communication interface standard commonly used by routers , but V.35 uses differential signals for transmission, and the sending and receiving are undertaken by two signal lines. The DCE device is usually docked with the router, so the pin assignments are reversed, that is, 2 is receive (but also called TXD), and 3 is transmit. Therefore, routers are usually DTE devices, and transmission devices such as modems, GV converters, etc. are usually specified as DCEs. In fact, for a standard serial port, it is usually possible to judge whether it is DTE or DCE from the appearance, DTE is a needle (commonly known as a male header), and DCE is a hole header (commonly known as a female header), so that the two interfaces can be connected together.
It is generally used to distinguish interfaces. For example, a router is at the edge of the network. It has an S0 port that needs to learn some parameters from another router. When implementing it, we do not need to configure it on this S0 port." clock rate", which it learns from the other side. At this time it is the DTE, and the other party is the DCE.
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