Cisco 4G-LTE-ANTM-O-3 Installation Guide download pdf (Page 189)

After the DCE transmits the last frame, it transitions to the wait transmit finish state, where it waits for

transmit FIFO to empty and the last frame to transmit to the wire. Then DCE starts a delay timer by

specifying the value using the dcd-drop-delay command. (This timer has the default value of 100 ms;

use the half-duplex timer dcd-drop-delay interface configuration command to specify a delay value.)

The DCE transitions to the wait DCD drop delay state. This state causes a time delay between the

transmission of the last frame and the deassertion of DCD in the controlled-carrier mode for DCE transmits.

When the timer expires, the DCE deasserts DCD and transitions back to the ready state and stays there

until there is a frame to transmit on that interface.

As shown in the figure below, the half-duplex DCE receive state machine idles in the ready state when it is

quiescent. It transitions out of this state when the DTE asserts RTS. In response, the DCE starts a timer based

on the value specified using the cts-delay command. This timer delays the assertion of CTS because some

DTE interfaces expect this delay. (The default value of this timer is 0 ms; use the half-duplex timer cts-delay

interface configuration command to specify a delay value.)

Figure 11: Half-Duplex DCE Receive State Machine

When the timer expires, the DCE state machine asserts CTS and transitions to the receive state. It stays in the

receive state until there is a frame to receive. If the beginning of a giant frame is received, it transitions to the

in giant state and keeps discarding all the fragments of the giant frame and transitions back to the receive

state.

Transitions back to the ready state occur when RTS is deasserted by the DTE. The response of the DCE to

the deassertion of RTS is to deassert CTS and go back to the ready state.

Placing a Low-Speed Serial Interface in Constant-Carrier Mode

To return a low-speed serial interface to constant-carrier mode from controlled-carrier mode, use the following

command in interface configuration mode.

SUMMARY STEPS

no half-duplex controlled-carrier

Cisco 800 Series Integrated Services Routers Software Configuration Guide

OL-31704-02 161

Configuring the Serial Interface

Configuring Low-Speed Serial Interfaces

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Cisco 4G-LTE-ANTM-O-3 Installation Guide Page 189