HDLC-Frame Protocol User's Guide (February 2004)

Using HDLC.FRAME Protocol
Link State Indications
Chapter 320
Link State Indications
If the “DSIG” configuration bit is set then the UP/DOWN state of the
HDLC.FRAME terminal is dependent on the state of the CTS and DCD
signals. When CTS and DCD are both asserted, the HDLC.FRAME
terminal is UP.
• If the “DSIG” configuration bit is clear then the state of the
HDLC.FRAME terminal is not dependent on the state of the CTS
and DCD signals. In this case the HDLC.FRAME terminal is always
UP.
• If the “qdown” option is set then the port is set DOWN whenever the
hardware detects a loss of synchronization. It is possible for the
hardware to alternately re-establish and lose synchronization
extremely rapidly with a poor quality line, making it difficult for
higher layer protocols to operate. The “qdown” bit should be used
only where line quality is known to be very good and with upper
layer protocols that need immediate notification of any line problems
(SS7 for example).