HDLC-Frame Protocol User's Guide (April 2000)

Chapter 3 23
Using HDLC.FRAME Protocol
Link State Indications
• 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 t o 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).
If an E1/T1 port is configured for external clock, and has no cable
connected,itispossibleforthehardwaretodetectframingdueto
crosstalk from other E1/T1 lines, so HDLC.FRAME terminals on the port
may be indicated as UP.