How does "dual-line" feature work on Cisco/Avaya IP phones for VOIP?

Question

For below CME configuration which I configured on UC500 where ephones are not configured with dual-line feature and in button command separator 'c'(call waiting) is used.

CME_VOICE(config)#ephone-dn 10
CME_VOICE(config-ephone-dn)#number 1010
CME_VOICE(config-ephone-dn)#no huntstop

CME_VOICE(config)#ephone-dn 11
CME_VOICE(config-ephone-dn)#number 1010
CME_VOICE(config-ephone-dn)#preference 1
CME_VOICE(config-ephone-dn)#no huntstop

CME_VOICE(config)#ephone 8
CME_VOICE(config-ephone)#button 1c10,11

CME_VOICE(config)#ephone 9
CME_VOICE(config-ephone)#button 1c10,11

what will happen if a guy is already busy on ephone 8 and at the same time second call to '1010' comes in? Would call ring on ephone 8? If YES, then please explain why? In my opinion since I haven't configured ephone with dual-line feature, receiving second call on that ephone is not possible even when we have configured it for call waiting. Another question is what will happen for below configuration:

CME_VOICE(config)#ephone-dn 10 dual-line
CME_VOICE(config-ephone-dn)#number 1010
CME_VOICE(config-ephone-dn)#no huntstop

CME_VOICE(config)#ephone-dn 11 dual-line
CME_VOICE(config-ephone-dn)#number 1010
CME_VOICE(config-ephone-dn)#preference 1
CME_VOICE(config-ephone-dn)#no huntstop

CME_VOICE(config)#ephone 8
CME_VOICE(config-ephone)#button 1o10,11

CME_VOICE(config)#ephone 9
CME_VOICE(config-ephone)#button 1o10,11

Answer 1

If the huntstop attribute is set, an incoming call does not roll over (hunt) to another ephone-dn when the called ephone-dn is busy or does not answer and a hunting strategy has been established that includes this ephone-dn.

When the no huntstop command is used on the ephone-dn, the call would ring on the first ephone-dn and go through any hunting defined on the two channels in a dual-line ephone-dn before being sent to the next most preferred ephone-dn that also has a matching destination pattern. This will continue until an ephone-dn with huntstop configured is reached or no more dial peers (ephone-dns) have matching destinations patterns.

The difference in configuration between overlaid ephone-dns with call waiting and overlaid ephone-dns without call waiting is that overlaid ephone-dns with call waiting use the c keyword in the button command and overlaid ephone-dns without call waiting use the o keyword.

Call waiting allows phone users to know that another person is calling them while they are talking on the phone. Phone users hear a call-waiting tone indicating that another party is trying to reach them. Calls to IP phones with soft keys can be answered with the Answer soft key.

Example-

A Cisco Unified IP Phone 7910 (maximum two call-waiting calls) has a button configured with a set of overlaid ephone-dns with call waiting (button 1c1,2,3,4). A call to ephone-dn 1 is answered. A call to ephone-dn 2 generates call-waiting notification. Calls to ephone-dn 3 and ephone-dn 4 will wait in line and remain invisible to the phone user until one of the two original calls ends. When the call to ephone-dn 1 ends, the phone user can then talk to the person who called ephone-dn 2. The call to ephone-dn 3 issues call-waiting notification while the call to ephone-dn 4 waits in line

The following example demonstrates call waiting for overlaid ephone-dns that are shared on two phones:

ephone 1

button 1c1,2,3,4

!

ephone 2

button 1c1,2,3,4

1. A call to ephone-dn 1 rings on ephone 1 and on ephone 2. Ephone 1 answers, and the call is no longer visible to ephone 2.

2. A call to ephone-dn 2 issues a call-waiting notification to ephone 1 and rings on ephone 2, which answers. The second call is no longer visible to ephone 1.

3. A call to ephone-dn 3 issues a call-waiting notification to ephone 1 and ephone 2. Ephone 1 puts the call to ephone-dn 1 on hold and answers the call to ephone-dn 3. The call to ephone-dn 3 is no longer visible to ephone 2.

4. A call to ephone-dn 4 is issues a call-waiting notification on ephone 2. The call is not visible on ephone 1 because it has met the two-call maximum by handling the calls to ephone-dn 1 and ephone-dn 3. (Note that the call maximum is six for those phones that are able to handle six call-waiting calls, as previously described.)

There are a few more differences between seperator o and c. For further explanation you can check SRND for CME. If there is still some confusion, please leave a comment. I can explain it to you.