What’s Up with Shared Line Appearance and Polycom Phones?

Recently, VoIP Supply had a technical support case dealing with SLA or Shared Line Appearance functionality. More specifically, the case dealt with a Polycom Soundpoint IP Phone. When I first opened the case, I was aware that the “shared” line option was available on the Polycom phones. This option is “plain as day” on the Web GUI Line tabs. Simply select the “shared” radio button on the two Polycom phones you would like to share and voila, right?…wrong!!!! SLA is considered a “server side” or IP PBX function, the phones can support only what is being pushed to them.

Hmm, ok, let’s try SLA on a couple of platforms with a variety of phones. I’ll try trixbox CE, Switchvox SMB, and Elastix running Free PBX for platforms and Polycom, Grandstream, and Linksys phones for endpoints. Here are my findings per platform and endpoint, wait actually we can simplify this to one statement: Polycom SLA didn’t work on any of these platforms while Grandstream and Linksys worked flawlessly. Polycom phones would register and display the “shared” icon look on the phone display, but all I got was busy signal when attempting to make a call.

Here is what I don’t understand, what’s the trick to get these Polycom phones to share a line on any of these platforms? I even engaged Polycom tech support, (not bashing these guys, they do one heck of a job) but they claim their phones have been tested with SLA to work on BroadSoft and Sylantro systems. What if I’m not using these systems? Do I turn to the IP PBX manufacturer? Trixbox? Switchvox? Elastix? Will they modify their systems to get this to work? I know plenty of others are having the same issues, I’ve read about them on the forums out there. What needs to be done about this?

I’m not calling out Polycom, in my mind their phones are “top of the line,” but when I first took this case, I thought to myself “hmm this will be an easy one,” I’ll never think those thoughts again. What is portrayed to be an easy one-button click in reality is causing nightmares for users who would like to take advantage of this feature.

I’d first like to ask anyone who has read this post, to comment on whether or not they have performed this function, desiring to explore this functionality, or simply gave up because you couldn’t get it to work. Share your thoughts on the topic as well what system you are using, and what you have done to your Polycom phones to get this function to work.

Maybe something needs to be done? When I have a problem, I first dig myself deep into hands-on testing, and if I can’t solve it, then I turn to assistance from the manufacturer, but what happens when you don’t get an answer that solves the problem?

Please share your thoughts, feelings, and experience with this subject. It has been weighing on me for two weeks now. Phew.

Garrett Smith

Garrett is the former VoIP Supply CMO.

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View Comments

Joseph says:

August 11, 2008 at 8:38 PM

I want to do SLA with FreePBX and SPA 941, where you able to fo that? If you did, can you give me some pointers? Thanks
Dan Wagoner says:

August 14, 2008 at 11:44 AM

SLA on SPA is not supported. Sorry...I found this out the hard way as well. Spent 2 days muddling through documentation, forum threads and how-to articles. I guess there are some lines of modified code out there, but it was released as "at your own risk"...and required jumping through some major hoops if I remember right. From what I've found on the web Aastras are the way to go if you need SLA on Asterisk. I have a few on the way that I'm going to test this theory out on. I will let you know how that turns out. In the meantime, here's a link to the patch for SPA's I was talking about: http://bugs.digium.com/bug_view_advanced_page.php?bug_id=11688
Rory Daulton says:

August 14, 2008 at 12:49 PM

I am trying to do SLA on Evolution PBX and Polycom SoundPoint IP650. Intuitive Voice (maker of Evolution PBX) insists that they do not support SLA, even though the underlying Asterix does. This supports your point, Chris. It's a shame Polycom does not make this more clear.
Joseph says:

August 25, 2008 at 3:12 PM

Any more news to getting SLA on any phone to work with Elastix or FreePBX?
Andreas vandem Helge says:

January 8, 2009 at 11:19 PM

Further information is to be found here:

http://bugs.digium.com/bug_view_advanced_page.php?bug_id=11688

Currently it is not officially supported in Asterisk.
Andreas vandem Helge says:

January 8, 2009 at 11:20 PM

RE: Rory's comment... yes Asterisk does "support" SLA (see sla.conf file for details) but IMO it is a horrible implementation. In my testing it did not even pass callerid data. Maybe for sharing analog lines it could work "ok."
Matthew Kaufman says:

January 26, 2009 at 11:13 PM

There's several different ways of supporting SLA/BLA, none of them a real standard (eg., Broadsoft's call-info/line-seize event approach, the draft-anil-sipping-bla approach with dialog;sla, the Linksys notify dialog without subscription approach). Polycom phones do one of the first two, depending how they're configured.

I've been working on adding support for draft-anil-sipping-bla-style SLA/BLA to FreeSWITCH for the last couple of weeks and have some prototype code working.

But you're right, unless you're using the SPA9000 and Linksys phones or you're using Broadsoft or Sylantro with phones that support that (including Polycom), you're not going to have much luck getting the behavior you want.

(And the behavior Asterisk provides for SLA is far from that)
dennis says:

February 2, 2009 at 9:58 PM

I've got switchvox smb, two polycom IP330 and a linksys spa962. I have exactly the same experience as you with trying to get SLA working on the polycoms. If I buy a second spa962, will i be able to get one extension appear on both spa962 by just configuring the spa962's through the spa962 gui?

I'm at the end of my rope on this one...very frustrated.

Thanks!
Chadwick says:

March 2, 2009 at 3:20 PM

Just an FYI SLA is a server side feature, meaning the phone is told what to do and is updated by the server. Each phone updates the server individually and the server is responsible for updating the phones. The phones don't keep track of each other, how could they? They would have to keep track of all the registrations and bindings as well. It is not as easy as turning on a switch.

I guess the trick is knowing that SLA/BLA requires server side interop and is a very complex feature.
Anthony Minessale says:

January 7, 2010 at 3:40 PM

We managed to get SLA working on FreeSWITCH with the help of a patch from
Matthew Kaufman. We finished what he started and can get it working using the Sylantro method on polycom. Now we added support for it on cisco/snom/aastra by using the broadsoft method. Polycom claims to support this method in several documents but it does not seem to work whatsoever. So either they are lying or it's broken or there is another secret config option we can't find.