I did some more research, and it looks like Grandstream's UCM which is based on Asterisk supports this as well! They call it Event List BLF or BLF resource list. Its RFC4662 which is what I am looking for: Although SIP protocol (RFC3261) was not provide the semantics to support the Busy Lamp Field (BLF) but there?s a way around to make the Busy Lamp Field function works on our phone by using the proper instantiation and the appropriate extension of the SIP Specific Event Notification framework (RFC3265). RFC4235 - Dialog Event Package is the instantiation RFC3265 which defined the mechanism of how the endpoint can subscribes for the status of any dialog including another endpoint. Busy Lamp Field feature is useful but can create a lot of overhead when trying to subscribe for the status of a large number of the resources. Event List BLF or BLF resource list is the solution to solve the overhead problem by reducing the number of request. Instead of generating an individual SUBSCRIBE request for each resource status, the concept of the Event List is combining all of those requests into a single request that query the resources status from the Event List. RFC4662 ? Resource List defines an aggregating mechanism that allows for subscribing and notifying for a list of resources. This mechanism is useful when the device needs to subscribe to a large number of resources. The overhead of generating individual SUBSCRIBE requests and the overhead of processing individual NOTIFY requests can be reduce by aggregating resources using a resource list concept. The above is from this PDF. It shows how you could configue this on their UCM IP PBX as well as their phones : http://www.grandstream.com/sites/default/files/Resources/GXP21x0_Eventlist_B... So anyone else support RFC4662 besides grandstream and Broadsoft? On Sat, Sep 2, 2017 at 11:37 AM, Colton Conor <colton.conor at gmail.com> wrote:
I asked this question in 2015, so I am wondering if anyone has an update.
Is the the way that Broadsoft implements Busy Lamp Field (BLF) using list URI unique only to Broadsoft, or have any other softswitch providers now implemented this method?
With a Broadsoft switch and a Polycom or Yealink phone, all that needs to be done on the phones config is to enter the BLF list URI server address. Then on the Broadsoft server you select the users you want to monitor, and the BLF list instantly updates on the phone. I think this reduces overall signaling too which is a big issue with BLF status updates. There is no rebooting or going into the phones configuration file once the BLF List URI is set.
For an example on how easy BLF is setup on Yealink phones with Broadsoft see this http://www.yealink.com/Upload/UCOne/features/Quick_ Setup_BLF_List_on_Yealink_IP_Phones_with_BroadSoft_UC_ONE_v1.0.pdf
Compare this to most other platforms I have seen based on Asterisk and Freeswitch. I think 3CX and Metaswitch are the same. In all these platforms, on the phones confige its self, you have to manually create a key on the phone to monitor a user. That might be done through the provisioning interface itself, but it still static adds a BLF line key to the phones configuration. Any updates to BLFs are usually not dynamic, and adding or removing a BLF requires a reboot to the phone as you have to change the config file.
Example of this method on a Yealink using a Asterisk based service like Virtual PBX see this https://www.virtualpbx.com/ support/dash/topics/t48g-blf/
Anyone have BLF List URI working on a non Broadsoft switch?