SLA and Cisco SPA509/504

Hello all,

I am trying to setup Shared Line Appearance to emulate Key System functionality. I finally succeeded in getting it to work partially, but each line is requiring two line buttons on the phone; one for the line (extension), and one for the SLAStation. I’m pretty sure I have the Asterisk side of the configuration correct, but I can’t find any documentation on how to make this work (correctly) from the phone side of the configuration. Also, no matter matter what I do, when a call is placed on hold, the indicator LED just shows solid red (In Use).

Does anyone have any experience getting this working correctly with the Cisco SPA50xG or LinkSys SPA942 phones.

Any help is appreciated. Documentation and examples seem scarce on the web.

Best reference site I found on this issue is at

Very well written, and full credit to John Quick at Smartvox Limited in the UK for a very thorough and well written explanation of the various issues.

If anyone is interested in the advancements being made in Shared Line Appearance (SLA) and general Key Telephone System behavior with Asterisk, and happen to be attending the upcoming IT Expo in Miami, be sure to check out the following presentation. … heatre.htm

Topic: Asterisk as a Key Telephone System (KTS) … is there any hope ?

Date: Thursday, January 20, 2010, 2PM
Location: IT Expo East 2010, Miami Beach, FL
Where: Digium Asterisk World Presentation Theatre

I played with this some more before checking out the web site you referenced above. Once I read that write-up it seems that I have the configuration correct it’s just a limitation of the SPA50xG/Asterisk combination.

The whole reason for SLA is becuase the staff was used to this functionality with the current (now old) phone switch (Partner). But as I played with the new phones and tried different configurations I was able to simplify the operation of the phones in combination with Asterisk’s very nice BLF functionality and some training with the staff on how to perform attended and blind tranfers and they are now happy enough with the Asterisk system that they don’t miss the old system or the key system functionality at all. The cutover went live this last Tuesday and with the exception of some of really horrible echo problems, this conversion to Asterisk has been a resounding success.

I think I’ll just give up on the SLA function, which I never really wanted anyway, and work on the echo issues. It’s not exactly a large installation (20 inbound CO lines and 43 extensions distributed across 4 seperate physical locations) but the Asterisk conversion was almost painless.

with 20 co’s have you thought of using a PRI? It may be cheaper than all of those lines… As far as the echo, oslec worked great for the last install I did. For that install the customer also wanted me to use SLA which I got working with Grandstream GXP2000 phones, but it was painfully slow and became annoying to the customer so they had me switch it to just dialing 9 and grabbing a line. It took them no time at all to get used to that. Its working so well they are putting 4 more systems in this year!