Category:HowTo:Extension Monitoring:RFC4235

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Contents

Terminology

  1. Ext 1: Monitoring Extension
  2. PBX: SIP Proxy (no subscription management required) or SIP Back-To- Back User Agent (B2BUA)
  3. Ext 2...Ext n: Monitored Extensions

Configuration

1 Navigate to the Free Function Keys Section of the Web User Interface page of the monitoring phone (e.g.Ext 1 = 484)


2 Choose one of the free function keys Px and select the "Context", i.e. the SIP identity Ext 1 = 484 which is supposed to monitor Ext 2


3 Choose the "Type":

 

4 Enter the monitored extension Ext 2 = 485 in the "Number" field


5 After pressing "Save" the extension entered in the "Number" field will be converted into a valid SIP URI:


SIP Flow (Subscription)

1) After pressing the "Save" button Ext 1 = 484 sends the following SIP message to Ext 2 = 485:

Sent to ... 16:15:11:491 ..:

SUBSCRIBE sip:Ext 2
Via: ...
From: <sip:Ext 1...
To: <sip:Ext 2...
Call-ID: ...
CSeq: 122 SUBSCRIBE
Max-Forwards: 70
Contact: ...
Event: dialog
Accept: application/dialog-info+xml
User-Agent: snom370/7.1.33
Expires: 3600
Content-Length: 0
  • The "Event" header specifies the dialog event for the subscription
  • The "Expires" header contains the proposed expiration time for the dialog subscription (by default 1 hour). This value can be configured via the Web User Interface:

2) Ext 2 = 485 confirms the SUBSCRIBE message as follows:

Received from ...:

SIP/2.0 200 Ok
Via: ...
From: <sip:Ext 1...
To: <sip:Ext 2...
Call-ID: ...
CSeq: 122 SUBSCRIBE
Contact: ...
Expires: 180
Content-Length: 0

3) If the expiration time was changed by the PBX the snom phone will sent a new subscription message after half the expiration time (180/2) :

Sent to ...16:16:40:519 :

SUBSCRIBE sip:Ext 2...
Via: ...
...
CSeq: 123 SUBSCRIBE
Max-Forwards: 70
Contact: ...
Event: dialog
Accept: application/dialog-info+xml
User-Agent: snom370/7.1.33
Expires: 3600
Content-Length: 0

4) When the state of one of the monitored extension the server sends a new NOTIFY, such as:

(in this example 405 calls 404, and the call is in state Ringing)

NOTIFY sip:402@192.168.168.174:1025;line=5kuxyuka SIP/2.0
Via: SIP/2.0/UDP 192.168.168.254:5060;branch=z9hG4bK-344c521499d7b20690e6b76412a404cb;rport
From: <sip:402@lab.test.local;user=phone>;tag=833971b3f6
To: <sip:402@lab.test.local>;tag=ia16559l89
Call-ID: 3c26706ac50e-68u035pyaapf
CSeq: 14870 NOTIFY
Max-Forwards: 70
Contact: <sip:192.168.168.254:5060;transport=udp>
Event: dialog
Subscription-State: active;expires=325
Content-Type: application/dialog-info+xml
Content-Length: 490

<?xml version="1.0"?>
<dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info" version="16" state="full" entity="sip:404@lab.test.local"><dialog
id="3c268f0cc248-7paj5csqwvfw" call-id="3c268f0cc248-7paj5csqwvfw" direction="recipient"><state>early</state><remote>
<identity>sip:405@lab.test.local</identity><target uri="sip:405@lab.test.local"/></remote><local>
<identity>sip:404@lab.test.local</identity><target uri="sip:404@lab.test.local"/></local></dialog>
</dialog-info>

Status

In firmware version Image:Fw-version-7.gif and Image:Fw-version-8.gif the status of the outgoing subscription can be monitored in the "Status --> Subscriptions" Web User Interface page

Result

"Dialog" state changes of the monitored extension (Ext 2 = 485) cause the monitored phone (Ext 2) to send SIP NOTIFY messages to Ext 1 = 484:

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