GRP Series - Eventlist BLF Guide

  • Updated on May 9, 2024

Although SIP protocol (RFC3261) was not providing 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 subscribe 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. Eventlist BLF or BLF resource list is the solution to solve the overhead problem by reducing the number of requests. Instead of generating an individual SUBSCRIBE request for each resource status, the concept of the Eventlist is combining all of those requests into a single request that query the resources status from the Eventlist. 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 reduced by aggregating resources using a resource list concept.

This document serves as an end user guide on how to configure Grandstream GRP26XX Carrier-Grade IP Phones for the UCM Eventlist BLF feature. How to configure BLF list on Grandstream UCM and apply them on the GRP26xx phones.


Grandstream GRP26XX Carrier-Grade IP Phones support both Grandstream UCM Busy Lamp Field and EventList BLF features and allows end users, such as attendant, to monitor the call status of users in the list. GRP26XX support this feature by sending out the subscription request to the UCM and changing the indicator status of the Line keys, MPKs, or VPKs that associated with the monitored users. Additionally, the phone is also able to pick up the calls to the monitored extensions by using a pre-defined feature code called BLF- Call-pickup Prefix.

Available Programmable Keys on each Model


Line Keys



Extension Board Keys

Virtual Extension


GRP2602/GRP2602P/ GRP2602W/GRP2602G















According to the RFC4662 – Resource List, UCM must allow no more than 20 endpoints to subscribe on the single resource list. However, in practical, only a single endpoint will subscribe on a particular EventList.

In the first step, the endpoint will send a SUBSCRIBE request to the configured Eventlist URI as per RFC3265. The main goal of this subscription is to obtain the state information of all endpoints that are associated with the Eventlist.

In order to subscribe for the Eventlist, it is necessary that phone includes the “eventlist” tag in the supported header and in most cases, Authorization header also required.

Via: SIP/2.0/UDP;branch=z9hG4bK341324999;rport
From: <sip:5000@>;tag=1620181217
To: <sip:170BLF@>
Call-ID: 1469406960-5060-2@BJC.BGI.EA.BBJ
Contact: <sip:5000@>
Authorization: Digest username="5000", realm="Grandstream", nonce="509e9f25", uri="sip:170BLF@", response="47c40eb60804fff79e3478e327145432", algorithm=MD5
X-Grandstream-PBX: true
Max-Forwards: 70
User-Agent: Grandstream GRP2614
Expires: 3600
Supported: replaces, path, timer, eventlist
Event: dialog
Accept: application/dialog-info+xml,multipart/related,application/rlmi+xml
Content-Length: 0


Upon the successful subscription, the UCM will reply back the Eventlist initial status information in form of the NOTIFY message that contains the state and other information of each endpoint on the Eventlist in the XML format. In normal cases, each NOTIFY will contains the information of 3 endpoints. Therefore, it is normal to have a set of NOTIFYs from the UCM even if the user only subscribes for a single Eventlist.

Content-Transfer-Encoding: binary
Content-ID: <5000@>
Content-Type: application/dialog-info+xml;charset="UTF-8"

<?xml version="1.0" encoding="UTF-8"?>
<dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info" version="2" state="full" entity="sip:5000@">
<dialog id="5000">
<identity display="John Smith">sip:5000@</identity>

Content-Transfer-Encoding: binary
Content-ID: <5001@>
Content-Type: application/dialog-info+xml;charset="UTF-8"

<?xml version="1.0" encoding="UTF-8"?>
<dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info" version="2" state="full" entity="sip:5001@">
<dialog id="5001">
<identity display="David Jackson">sip:5001@</identity>

Content-Transfer-Encoding: binary
Content-ID: <5002@>
Content-Type: application/dialog-info+xml;charset="UTF-8"

<?xml version="1.0" encoding="UTF-8"?>
<dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info" version="3" state="full" entity="sip:5002@">
<dialog id="5002">
<identity display="William Thompson">sip:5002@</identity>

Endpoint States


When there is no active call for a specific endpoint or when a call to or from a subscribed endpoint is just being released, then the endpoint is considered idle/terminated.

  • If applicable, the LED for the associated endpoint should be solid green or background should be solid green for the related VMPKs.


When an incoming call arrives for a subscribed endpoint, the endpoint is considered ringing/in the early state.

  • If applicable, the LED for the associated endpoint should be blinking red or background should be solid red for the related VMPK.


When a call is originated from a subscribed endpoint or a subscribed endpoint answered the call, then the resource is said to be in the “active” state.

  • If applicable, the LED for the associated endpoint should be solid red or background should be solid red for the related VMPK.


The subscription for that particular endpoint is failed or unreachable.

  • If applicable, the LED for the associated endpoint should be off or background should be solid grey for the related VPK.


Grandstream UCM supports and allows creating an Eventlist for Busy Lamp Field (BLF) monitoring purpose. To create a list, login into the UCM and follow the below steps:

  1. Go to Call Features 🡪 Eventlist.
  2. Click “Add Eventlist” to start creating a new list.
Create new Eventlist
  1. Enter the unique URI of the Eventlist in the URI field followed by choosing either “dialog” or “presence” eventlist (subscribers must carry the same value in Event header).
Eventlist URI
  1. Select the accounts (endpoint) to be monitored from the both available local and remote extensions. then click on the right arrow head to move them to the “selected” column.
Eventlist Account selection
  1. You can add extensions which are not in the list under the “Special Extensions” field.
Special Extensions
  1. Click “Save” to complete the Eventlist BLF creation.

If the new Eventlist is successfully created, it should be showing on the Eventlist table:

Eventlist Table
  1. Apply Changes

  • Click on to edit the Eventlist configuration.
  • Click on to delete the Eventlist.
  • Once properly configuring the Eventlist on a GRP261X a new section will appear, labeled “Member of Subscribers”. Where users can select one Eventlist to show its subscribers.
Member of Subscribers


Configuring the GRP26xx Carrier-Grade IP Phones to work with Grandstream UCM Eventlist BLF feature is straightforward.

  1. First configure your SIP account settings.
Configure the SIP Account Settings
  1. Choose the provisioning method under Programmable Keys 🡪 Advanced Settings: “Auto Provision List Starting Point”.
Auto Provision List Starting Point
  • The default setting is “VPK”.
  1. Fill in the BLF URI under Account X 🡪 Advanced Settings 🡪 BLF (Busy Lamp Field).
  • Enter the URI (name) of the Eventlist BLF that you just created on the Grandstream UCM.
  • Enable Auto Provision Eventlists by selecting “BLF Eventlist” to automatically assign the BLF extensions into the available MPKs/VMPKs slots.
Eventlist BLF Settings
  1. In the case that Auto Provision Eventlist BLF was disabled:
    • Users can manually configure the MPKs to monitor the BLF extension. Under Settings 🡪 Programmable Keys 🡪 Multi-Purpose Keys: For each MPK, the user needs to select “Eventlist BLF” as Mode, choose the specified Account, and enter the Value of each extension in the list. After saving and rebooting, the UCM extensions will be logged on the extension board, and the phone will start to monitor the extensions status.
MPK Settings
  • To configure the Eventlist BLF on VPKs:
    Go to Settings 🡪 Programmable Keys 🡪 Virtual Multi-Purpose Keys: Select the “Mode”, the “Account” and enter the “Value”. Then “Save”.
Configure Eventlist on VPKs


Grandstream GRP261x Carrier Grade IP Phones are able to notify the end user of the call status of the monitored extension by turning on the LEDs or changing the background colors.

For example, if the monitored extension is ringing, the BLF indicator status will be changed from solid green to blinking red; and if the monitored extension answers the call, the BLF indicator status will be changed from blinking red to solid red.

The following table shows the BLF indicator status in different scenarios:

Monitored Extension Behavior

VPK Icon Background Status

VPK LED Indicator Status


Solid Green

Solid Green

Placing a call

Solid Red

Solid Red


Solid Red

Blinking Red

During a call

Solid Red

Solid Red

Hold the call

Solid Red

Solid Red

Call Park

Solid Red

Solid Red

Monitored extension not registered/BLF subscription failed

Solid Grey


While the following figure shows the BLF LED Pattern Explanation Form, which can be found through accessing the phone Web GUI and navigating to System Settings🡪Preferences🡪BLF LED Pattern Explanation Form.

BLF LED Pattern Explanation Form


Directed call pickup feature allows the GRP26xx phone system to answer the calls to the monitored users. This feature is very useful for the attendant to be able to answer calls if the callees are not available.

For the Grandstream UCM system, it requires to dial the specified prefix ahead of the monitored extension to direct pick up the call. Thus, the end user has to configure the BLF Call-pickup Prefix for GRP phones in order to use this feature.

The following screenshot shows that (**) is configured as the prefix under the Account X 🡪 SIP Settings 🡪 Advanced Features 🡪 BLF Call-pickup Prefix.

Configure BLF Call Pickup Prefix

When the monitored user’s indicator shows an incoming call signal, the GRP26xx phones user can press the BLF button to answer/pick up the call.

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