BLF implementation using XML

Goals

• Align BLF and Extension behavior for PFKs on Snom desk phones by using XML definitions instead 
  • Improve user experience
  • Improve performance

Background and strategic fit

BLF is a valuable feature for Snom customers, like enterprises who are looking to assist in connecting their customers to a live, available person as well as save business phone use time. Overall, it enables businesses to streamline their communication and better serve customers. BLF aka Extension monitoring has been utilized in numerous ways by businesses using Snom phone systems with multiple extensions. The current implementation appears to be kind of duplicated, but with a few little differences and erroneous behaviour.

Assumptions

• Use case#1: A secretary's phone shall display the call status of the boss's line, allowing the secretary to know whether the boss is on a phone call or not. This will enable the secretary to make the decision to put the new caller on hold or let them through to the boss.
• Use case#2: Call centers and customer support groups have also a need for BLF: it enables employees to see if their colleagues are free to take a support call or if their supervisor is on another line and unable to help another customer.
• Use case#3: BLF is needed by teams working on a specific project: supervisors can monitor team members' extensions and vice versa so all team members are aware of each other's current status.

Requirements

#	Requirement title	Functionality	Importance	Notes
1	D8XX_BLF-XML_FR-1	On D8xx IP phones, any PFK (programmable function key - physical or virtual) can be assigned to a function, which allows monitoring state changes of the configured SIP extension on another IP phone. This function shall be called "BLF-XML". The following state changes shall be visualized: monitored SIP extension is in idle mode => idle monitored SIP extension seizes a line => busy monitored SIP extension receives an incoming call => ringing monitored SIP extension places an outgoing call => busy monitored SIP extension dials or accepts an incoming call => busy	Must Have	This means, that the D8xx phone acts as a User Agent Client (UAC) and the IP phone of the monitored extension acts as User Agent Server (UAS).
2	D8XX_BLF-XML_FR-2	On Snom IP phones acting as UAS, any SIP extension having an active subscription of its state changes, shall sent a notification SIP message (NOTIFY) to the UAC, at least when one of the following state changes occur: from any state => idle from any state => trying from any state => early from any state => busy	Must Have	Fully implemented
3	D8XX_BLF-XML_FR-3	The assignment shall be configured either manually via web user interface (WUI) and/or phone user interface (PUI), and automatically via auto-provisioning (HTTP/TFTP setting server), SRAPS, or remote management (TR-069).	Must Have	Fully implemented
4	D8XX_BLF-XML_FR-1-1	On D8xx series, during an active subscription, state changes of the monitored SIP extension shall be visualized on both, PFK LED and PFK label.	Must Have	Fully implemented
5	D8XX_BLF-XML_FR-1-1-1	The PFK LED behaviour and colour shall be according to this table state idle ringing busy LED behaviour off blinking on LED colour - red red	Must Have	Fully implemented
6	D8XX_BLF-XML_FR-1-1-2	The PFK label shall be composed of 3 areas: Label area Screenshot (A) icon area (B) name area (C) state area	Must Have	Fully implemented
7	D8XX_BLF-XML_FR-1-1-2-1	The label icon area (A) shall contain the following distinguishable graphical symbol, representing the state State idle ringing busy Description person with a handset person with a handset plus an arrow (pointing towards the handset) person with a handset and 2 sound waves (heading away from the handset) Graphical symbol Idle Ringing Busy Colour white red red	Must Have	Fully implemented
8	D8XX_BLF-XML_FR-1-1-2-2	The label name area (B) shall contain the following text representing the display name or number (configurable) of the monitored / calling party state idle ringing busy roles Monitored party Calling party > monitored party Calling party <> monitored party text 101 or Alex 102 > 101 or Alice > Alex 102 <> 101 or Alice <> Alex text colour white white white	Must Have	Partly implemented
9	D8XX_BLF-XML_FR-1-1-2-3	The label state area (C) shall contain the following text representing the state state idle ringing busy text idle ringing busy colour white white white	Must Have	Fully implemented

User interaction and design

NOTIFY
...
<?xml version="1.0"?>
<dialog-info
	xmlns="urn:ietf:params:xml:ns:dialog-info"
	version="12"
	state="full"
	entity="sip:101@...">
	<dialog id="..." >
		<state>trying</state>
	</dialog>
</dialog-info>

NOTIFY
...
<?xml version="1.0"?>
<dialog-info
	xmlns="urn:ietf:params:xml:ns:dialog-info"
	version="4"
	state="full"
	entity="sip:101@192.168.245.1">
	<dialog id="0204e48c15abcbfc72bfc6d57ad7d36e"
		direction='initiator'
		call-id='f6bb00647f9d-tq2si6sz97bz'
		local-tag=""
		remote-tag="">
		<state>terminated</state>
		<local>
			<identity display="B">sip:101@...</identity>
			<target uri="sip:101@...;line=caioqij3">
				<param pname="x-line-id" pval="0" />
			</target>
		</local>
	</dialog>
</dialog-info>

NOTIFY
...
<?xml version="1.0"?>
<dialog-info
	xmlns="urn:ietf:params:xml:ns:dialog-info"
	version="20"
	state="full" entity="...">
	<dialog
		id="..."
		direction='recipient'
		call-id='...'
		local-tag="..."
		remote-tag="...">
		<state>early</state>
		<local>
			<identity display="B">
				sip:101@...
			</identity>
			<target uri="sip:101@...;line=...">
				<param pname="x-line-id" pval="0" />
			</target>
		</local>
		<remote>
			<identity display="C">
				sip:102@...
			</identity>
			<target uri="sip:102@..."/>
		</remote>
	</dialog>
</dialog-info>

Questions

Below is a list of questions to be addressed as a result of this requirements document:

Not Doing