Shared (Bridged) line appearance

I love Asterisk and it is just about exactly what I want. The only problem is it can’t seem to do the one thing I and most small businesses want. That is shared call appearance. Most small businesses are familiar with KSU’s and Hybrid PBX’s which have multiline phones where every PSTN line is associated with a specific button on each phone.

This simplifies things because there is no need to do transfers or memorize any key sequence or who is on what extension etc… Just place the call on hold on one phone and pick it up at another. It also gives an instant visual representation of which lines and extensions are busy.

I see that some IP phones such as Polycom and Aastra support this feature but it also needs to be supported on the server end. I have not been able to find any info on Asterisk being able to support this feature. Is there any current or planned way of doing this. A modification or hack. Anything?

I see there is an internet draft describing this support in SIP. They are calling it "bridged line appearance: … bla-02.txt

bump :blush:

Been studying the same thing myself. Only thing ive found was this … 69164.html

Seems the snom is the only sip phone capable so far. I am now thinking maybe a windows program to show the status of the phones.

[quote=“rusty”]Been studying the same thing myself. Only thing ive found was this … 69164.html

Seems the snom is the only sip phone capable so far. I am now thinking maybe a windows program to show the status of the phones.[/quote]


Thanks for the “hint” :wink: rusty.

The Asterisk Wiki is saying that Polycom and Sayson/Aastra phones also support this. Since I have an Aastra 9133i phone I’m going to give it a try. Will post and update wiki if I can acomplish anything.

I may be wrong but seems I read it was an option that would be in future firmware

I think your right. Sayson responded that the feature is not in their firmware. They also said that the Broadsoft firmware is identical. At least for the 9133i. Not sure about the 480i.

Can anyone help me with the requirements specification to submit a request for this feature in future firmware from Sayson. I emailed them the info at the Asterisk Wiki about the “hint” using the Subscribe/Modify mechanism of RFC3265 but the engineer responded that it was not enough information for them.

Sayson Firmware Engineer response to “hint” Asterisk Feature

RFC 3265 is just an application frame and doesn’t define any SIP flow.
To implement an application based on RFC 3265, we need more details. For example, message-summary is an application based on RFC 3265, and defined in RFC 3842. I don’t think we support
Asterisk+standard+extensions unless it’s something same as Broadsoft
Shared Call Appearance.<<

Add me to the list of people interested in this - we are using Polycom IP501 phones, and I think I know how to program them to display SCA (Shared Call) and BLA (Bridged Line) Appearances.

Problem is, I can’t find any information on how to get * to do the same - and believe me, I have looked.

Does anyone have any insight?

Looking for same feature… this would be very usefull @ home and small business…

Hey all,

Well as far as I know the Grandstream 2000 series telephones will shortly have a feature called “hint” inbuilt to the firmware…

What this means is the capability of showing an extensions status ergo Busy Lamp Field (BLF).

I represent a small Telco that installs maintains the major supplier hardwired telephone systems in Australia… ie Aria, Nex, Panasonic Samsung etc…

I have been requesting that this feature be active within a SIP telephone. The representatives for Digium Australia are talking direct with the Grandstream 2000 series manufacturer as far as i am aware and are hoping to include this very sought after feature within their code.

Stay tuned to the Grandstream 2000 series because it will be within it shortly ( so im told )


Gooood, we are looking to use this feature as soon as it is available. We just bought 4 gxp2000 without knowing about SCA. Now that we want to test the phones in a business environement we rapidly got knocked by the lack of SLA support in Asterisk and on phones. Anyone knows when this feature will be available exactly? The gxp2000 current firmware is and i found the next one that will be with the release note. It contains no information about supporting SCA/SLA yet. I’m waiting on some info from a dealer about that. I’ll post the results.

Anyone knows how this will work exactly? They say through HINT sip feature whatever that means. Anyone’s got a detailed explanation?


I know this is not what your looking for but it is what i am using at the present. … ator+Panel

I have mine setup where they can only see if someone is on the phone they cant do anything

Yeah that s a cool software. We want to be able to install phones where there will be no computer.


I understand completly

Here is what Snom answers about shared line appearence:

Thank you for your request.

snom phones do support shared line appearance. SIP lines are registered as normal on the registrar but if its known to be a shared line, a programmable key with ‘Shared Line’ can be assigned to it to get the exact status of other same registrations on the led. Its something short of Bridged Line Appearance, which we’ll be providing in the future when its standardized. For info about *, please try

And here is Grandstream:

This is called presence and we will support it via future firmware upgrade.

I’m waiting for Sipura now.

Anyone have any luck with this and a Polycom phone?

Was anyone able to get this to work with any Aastra/Sayson phones or even at all?

keep in mind, BLF (busy lamp field) and SCA/BCA (shared call appearance/bridged call appearance) are very different.

As of right now, Asterisk supports BLF only, no SCA. This means it will (if you set stuff up correctly) NOTIFY any SUBSCRIBEd phones about extension states (free/busy/ringing) if you setup the hint priority in extensions.conf. On a Grandstream GXP2000, this makes the light next to the speed dial key light up when the user is on the phone and flash when that extension is ringing. On an Aastra 480, this makes little icons next to the speed dials change. On an Aastra 9133, i’m told it makes the lights next to speed dials light up (like GXP2000) and the lights will flash quickly when the line is ringing

What this will NOT do is let you push that button to a. answer a ringing phone; or b. barge into the active conversation that person is on turning it into a 3way call. That functionality is SCA. Asterisk does not currently support it at all, either natively or with an addon. It might (in theory) be possible to write an AGI that might do this, but it would have to be worked into most of the dialplan.

It IS possible to answer another ringing phone- using *8 and pickupgroup and features.conf.

mustard’s link is a draft for a standard that would allow this. I have also referred to what i think is the same document/standard as SIP-B.

I agree that this is a missing feature, however while it would be very useful in the SOHO space there is not much developer interest in it. Asterisk is by nature a PBX- NOT a key system. Adding KSU functionality would make a bunch of people happy though… any dev’s interested?

I’m not sure if what I want and what you guys are talking about is the same thing - but I had assumed it was from what I read earlier.

My setup is as follows:

1 secretary, 1 voIP phone which allows viewing multiple line appearances
1 worker, 1 VoIP phone which allows viewing multiple line appearances
1 asterisk PBX which is connected via an IAX2 trunk to a VoIP provider

What I need is the ability for my secretary to answer a call, put it on hold, and notify me of this. I want to be able to look at my phone and see that there is now a call on hold on ‘line x’, pick it up and be talking to that person. There is no need for any 3-way conferencing type functionality. Is this sort of thing possible with the ‘hinting’?

no, its not. If you are using zap channels (which allows you to actually have the concept of a ‘line-x’) you can see the zap channel is active but you can’t actually grab it.

what you can do is parking- she answers the call, parks it in extension xxx, tells you theres a call waiting on xxx. You then pick up the phone and dial xxx to get the call. If you are even in a large department store and hear something like ‘bob, you have a call on 8502’ on the speaker, that’s what they’re talking about

ok, thank you