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Below is some additional info on its capabilities:
Q: What is the difference between a "Shared" line and any other line on the phone?
A: The shared line is like any other line on the phone (in the sense that you can make and receive calls on it), except that others see the status of that line. The big difference is that calls can be handed back and forth between sets with an appearance of the shared line just by putting the call on hold on one set and taking it off hold (by pressing the button with the flashing light) on another - no transfer required.
Q: How are Shared or Bridged Lines different from BLF?
A: A Busy Lamp Field (BLF) allows a set to display the status of another user (busy or ringing), but a BLF button is not an appearance of that user. It is not possible to answer calls on that button. In the sipx implementation, pressing a BLF button initiates a speed dial call to that user, rather than dialing a call "as" that user, which is the case for SAA.
Q: Can I join a call in progress at another set?
A: Not directly. One of the parties on the active call can conference in other sets (including other sets with appearances of the shared line), but it is not possible to conference in several users by pressing the "busy" line button.
Q: Is there a limit on how many other users can add this shared line to their phone and have it function like a BLA line?
A: A somewhat artificial limit of 20 subscriptions per shared line is enforced (i.e. 20 sets with an appearance of the same shared line). This was inherited from the RLS and can be modified or removed if we so decide.
Q: Let's assume the user w/ extension 250 wants a BLA appearance of line 200 on his phone. Both user 200 and user 250 have several phones registered, all Polycom. Will BLA function between any of the phones of users 200 and 250 provided the shared line 200 is registered on all phones?
A: Yes. Once we get the configuration for the shared line feature integrated into sipXconfig, then all appearances of the shared line (200 in this case) will be made shared, and calls can be shared between any set with an appearance of it. (After some discussion on the list, we agreed that in the first implementation anyway, a simple "all appearances of this line are shared" was preferred to a per-device setting).
Q: Is the number of phones each user can register to line 200 limited in any way?
A: There are no limits enforced on how many phones can be registered to a single address. For SLA the limit mentioned above would apply.
Q: User 250 registered line 200 on his phone as a BLA line. Line 250 itself is 'Shared' and user 300 registered line 250 as a BLA line on his phone. Does this work? In particular can user 250 put calls on hold on both lines 200 and 300 (and not get confused)?
A: Yes, subject to the physical limitations of the set. Lights will be flashing beside the lines labelled 200 and 300 (or, on the smaller set e.g. IP330, phone icon 1 for Line 1 and 2 for Line 2 - this might be confusing but if users are stuck with this set there is no labelling capability except for a bit of tape).
Q: On an attendant console (Polycom with up to 3 sidecars) the admin would like to configure as many different shared lines as there are line keys (the UI says I can have max 34 lines). This allows the attendant to use the BLA function with all the contacts registered on the attendant console phone instead of just using speed dial and BLF. Does this work?
A: I don't think there is any reason that it would not work, provided that the phone can process all the required subscriptions for all the different lines.
Q: If shared line 200 rings on the assistants phone (extension 250) while user 200 (the boss) is on the phone (i.e. using line 200 on his phone), is the assistant able to see the 'On the phone status' while line 200 rings? The assistant needs to take a decision whether to pickup the shared ringing line 200.
A: As soon as one appearance of the shared line goes off-hook (even to dial), all other appearances of it will show that the line is in use. When another call comes in, the phone presents it depending on its capabilities... if the phone has only one button assigned to the line, it changes from solid red (indicating line in use) to flashing green. So the assistant would not know that the line was in use somewhere else unless they saw it before it started flashing. If the set has more than one button assigned to the line, the incoming call is presented on another button, and you can see that one call is in progress on the line, while another is ringing.