Asterisk SLA

SLA - Shared Line Appearance

Shared Line Appearances: SLAs allow you to place a call on hold at one set and pick it up easily at another set. SLA is also known as SCA: Shared Call Appearance. You can join an existing conversation be pressing the corresponding line button. Typically the phones will have dedicated buttons with LEDs for each of the shared lines.

Bridged Line Appearance: BLA allows multiple devices to share a single directory number (not implemented in Asterisk and not described here).

It appears to be a question of taste - and user expectations based on older phone systems - if you prefer the SLA/BLA approach, or if you would rather go for the BLF/transfer/parking/hint approach that is more typical for Asterisk and SIP devices. In general SLA will only work out well if only a very limited number of lines is available.


June 2007

Q: How can i transfer from SLA to another extension not defined in sla.conf?

A: There is no concept of a transfer in an SLA setup. The traditional way to do this would be to put a call on hold and ask the other person to pick up that line (taken from bug 9459).

Jan. 2007 (Asterisk 1.4.0)

> Kevin - can you give a quick description of what shared lines are
> (as opposed to shared extensions)?

Shared Line Appearance == key system, essentially. Buttons on phones are
mapped to actual trunk lines, and reflect the status of that trunk line,
including being able to barge in (conference), hold and pickup at
another phone, etc.

Shared Extensions are different... although there are a lot of
similarities, and we may end up being able to use our SLA code to
achieve Shared Extensions, it's not currently something we are working on.

> OK, but how do I make that when extension 3 is being used on one phone the
> other one can see its status, and when it is placed on hold then it can be
> picked-up on the other phone by just hitting the line button?

We don't have shared extension support. You can get busy/ringing status
for the other phone by using hints, although that won't work too well if
the line button on the phone has been used for an actual line appearance.

In other words... Asterisk does not currently have what you want.

Vendor implementations


Similar solutions without SLA

Chief - Secretary setup

> We are running a Asterisk (1.2) installation with about 80 snom phones (300,320,360).
> Now we have the demand for a special manager <-> assistant setup for a few extensions.
> Since Shared Line Appearance is not available in 1.2 I´m wondering how to implement this...
> What we need is that the manager can decide whether he wants to get
> calls or not. If not he must have the possibility to redirect all
> incoming calls to his secretary. The secretary itself answers all calls
> and decides if the call is important enough to disturb the manager. If
> so she/he transfers the call to the manager. So the secretary can filter
> the calls for the manager...
> The only way I can imagine so far is via a redirect by AstDB on the
> manager extension. The managers phone has two different lines - the
> official and a secret one only the secretary uses...

The most obvious setup would be

- have SIP accounts, e.g. sip123 for the secretary phone, sip456 and
sip789 for the manager phone.
- the "official"/"public" extension number for the manager might be
"4321", so

exten => 4321,1,Dial(SIP/sip123&SIP/sip456)

would ring both the secretary phone and the manager phone on the
"public" id (which most probably can have a separate ringtone than the
"private" id). You would also want a "private" extension like

exten => 4901,1,Dial(SIP/sip789)

for the secretary to reach the manager. A few thoughts:
- The Callerid setting for both secretary and chief should be "4321", no
matter which line the chief chooses to call out through.
- Do not choose an obvious private number, like 4321 and 4322
- You could even choose a "real long" number, that only is available
from internal phones, and put it to a speed dial button on the secretary

If you want the manager to be able to selectively not be disturbed by
"public number" calls, but only by his secretary, some AstDB logic could
come into the game. This can be highly dynamic, or you just configure a
few extensions by hand to do exactly this:

exten => 770/4321,1,Set(DB(list/4321)=SIP/sip123&SIP/sip456)
exten => 770/4321,2,Playback(feature-donotdisturb-off)
exten => 771/4321,1,Set(DB(list/4321)=SIP/sip123)
exten => 771/4321,2,Playback(feature-donotdisturb-on)
exten => 4321,1,Dial(${DB(list/4321)})

So either the chief or the secretary could activate do-not-disturb by
dialing 771, and deactivate with 770. Just examples; choose those codes
from a range that is not in use as extensions; for my personal setup,
the 2*/3*/4*/5*/6* internal numbering for SIP devices, OOH devices, IAX
devices etc.pp., 8* being applications (like 888 the talking clock), 9*
experimental and 0* PSTN calls (how 80's! :-). A somehow similar
function (divert to VoiceMail delay in seconds can be set from any
phone, between 0 and 60 seconds) is available here as 811x.
Choose whatever suits you best.

Of course one could imagine also that the manager phone number NOT rings
the secretary while the manager is there and ready to take calls - just
edit the 770/771 lines (or add 772 for that function) - in that case,
the secretary could make use of an extension number for him/herself, but
her phone also has several lines, so why not.

Additional feature: Use 'hint' combined with either app_devstate (from bristuff for Asterisk 1.2 and 1.4) or func_devstate (native Asterisk 1.6 or backport to Asterisk 1.4) to light/not light a button's LED for extension 770/771. That way both, manager and assistant, have a direct visual indication of the phone status, i.e. wether all calls are "redirected" to the assistant or not.

See also

Go back to Asterisk

Created by: JustRumours, Last modification: Wed 16 of May, 2012 (13:35 UTC) by feptias
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