Overlay lines are ephone-dns that share a single button on a multibutton phone. When more than one incoming call arrives on lines that are set on a single button, the line (ephone-dn) that is the leftmost in the button command list is the primary line and is given the highest priority. If this call is answered by another phone or if the caller hangs up, the phone selects the next line in its overlay set to present as the ringing call. The caller ID display updates to show the caller ID for the currently presented call.
Ephone-dns that are part of an overlay set can be single-line ephone-dns or dual-line ephone-dns, but the set must contain either all single-line ephone-dns or all dual-line ephone-dns, and not a mixture of the two.
The primary ephone-dn on each phone in a shared-line overlay set should be unique to the phone being configured to guarantee that there is a line available for outgoing calls, and to ensure that the phone user can obtain dial-tone even when there are no idle lines available in the rest of the shared-line overlay set. Use a unique ephone-dn in this manner to provide for a unique calling party identity on outbound calls made by the phone so that the called user can see which specific phone is calling.
The name of the first ephone-dn in the overlay set is not displayed because it is the default ephone-dn for calls to the phone, and the name or number is permanently displayed next to the phone's button. For example, if there are ten ephone-dns in an overlay set, only the last nine ephone-dns are displayed when calls are made to them.
Overlay Ephone-dns with Call Waiting (c)
The configuration for the overlaid ephone-dns with call waiting (keyword c) and without call waiting (keyword o) is the same.
Ephone-dns accept call interruptions, such as call waiting, by default. For call waiting to work, the default must be active. To ensure thatthe default is active, remove the no call-waiting beep accept command from the configurations of ephone-dns for which you want to use call waiting.
In Cisco Unified CME 4.0(3), the Cisco Unified IP Phone 7931G cannot support overlays that contain ephone-dn configured for dual-line mode.
call-forward busy 7000
! The next ephone configuration includes the first instance of shared line 1001.
! The next ephone configuration includes the second instance of shared line 1001.
! The next ephone configuration includes the third instance of shared line 1001.
Note: For Cisco CallManager Express versions prior to 3.2.1, ephone-dn overlays disable call waiting. If a phone is using an overlaid ephone-dn on an active call, call waiting is disabled for any incoming calls to any ephone-dn in the overlay set.
For Cisco CallManager Express 3.2.1 and later, call waiting is available for overlaid ephone-dns. Overlaid ephone-dns with call waiting use the c: keyword in the button command and overlaid ephone-dn without call waiting use the o: keyword. To understand the difference in the behavior of overlaid ephone-dns with call waiting and overlaid ephone-dns without call waiting is the same, refer to the Call Waiting section of Cisco Unified CallManager Express: Configuring Call-coverage feature .