A Generic Event Notification System Using XML and SIP Knarig Arabshian and Henning Schulzrinne Department of Computer Science Columbia University September 12, 2003 NYMAN Workshop

Event Notification Event notification can be applied to many different systems SIP has been extended to support event notification Various types of event notification systems using subscribe/notify Presence/Instant Messaging Emergency Notification Conference control

Overview What is SIP (Session Initiation Protocol)? Details of SIP event notification architecture Incorporating XML Benefits Conclusions

What is SIP? The Session Initiation Protocol (SIP) is a signaling protocol used for establishing sessions in an IP network. SIP is part of the IETF standards and is modeled upon other Internet protocols such as SMTP (Simple Mail Transfer Protocol for ) and HTTP (Hypertext Transfer Protocol for www) SIP is also being used in Microsoft Messenger in Windows XP A session could be a simple two-way telephone call or it could be a collaborative multimedia conference session. Different services are possible Internet telephony Event notification Device control

What is SIP? Two Components within SIP: User Agent and the SIP Network Server. User Agent end system component for the call can be both a User Agent Client (UAC) and a User Agent Server (UAS) client element initiates the calls and the server element answers the calls.

What is SIP? SIP Network Server Network device that handles the signaling associated with multiple calls. Main function of the SIP servers is to provide name resolution and user location Caller is unlikely to know the IP address or host name of the called party Caller will dial an -like address or a telephone number associated with the called party. Receives requests, determines where to send these, and passes them onto the next server (using next hop routing principals).

home.com office.com alice bob m2.home.com Basic call setup like identifier: Alice’s phone registers with home.com Bob dials Local server does DNS Registrar => REGISTER home.com SIP/2.0 To: Contact: … DNS lookup sip.udp.home.com Resolve to m2.home.com

home.com office.com alice bob m2.home.com Basic call setup Phone sends INVITE; acts as User Agent Client Server can proxy the call to current location INVITE … To: From: “Bob” … c=IN IP m=audio 8000 RTP/AVP User agent client INVITE … To: From: “Bob” … Proxy

home.com office.com alice bob m2.home.com Basic call setup Alice’s phone rings; acts as a User Agent Server When Alice picks up, call is accepted and Bob’s phone sends ACK to complete the setup pc4.home.com SIP/ Ringing Proxy User agent server SIP/ OK … c=IN IP m=audio 9000 RTP/AVP 0 8

home.com office.com alice bob Basic call setup Encoded audio packets sent over RTP

home.com office.com alice bob Basic call setup When either party hangs up BYE is sent BYE

Columbia SIP user agent (sipc) Media Audio, video, text, white board Screen sharing Shared web browsing Advanced Presence, instant messaging Conference control Emergency notification and handling Device control

Subscribe/Notify SIP has also been extended to generate event notifications and instant messages Users subscribe to an event with the SUBSCRIBE method and receive notifications via NOTIFY This feature can be used for various event notification systems

Subscribe Request Resembles that of a SIP INVITE Must have one “Event” header in the header field which will specify the type of event it is subscribing to Must also contain an “Expires” header which defines the duration of the subscription Subscriptions to multiple events requires multiple subscribe messages to be sent to the notifier To unsubscribe, it sends a SUBSCRIBE message with the ”Expires” field set to zero

Subscribe Request Can contain optional message body in SUBSCRIBE request Further details of notification Standardized grammar to automate the processing of the SUBSCRIBE request in the Notification Server If message body is not present then Subscriber will expect the default method of alert

Notify Request Notification server receives the subscription, adds the subscriber to the particular event list and then generates NOTIFY requests accordingly The “Event” header will indicate the type of notification it is The message body of the NOTIFY message may include a remote procedure call or other details of notification.

CLIENT (SUBSCRIBER) SUBSCRIBE SIP/2.0 Event: sos Expires: From: To: SERVER (NOTIFIER) SIP/ Accepted From: Expires: NOTIFY SIP/2.0 Event: sos To: From:

Incorporating XML XML (Extensible Markup Language) is “metalanguage”, which is a language used for describing other languages An XML schema is an XML language that defines various data types found in the XML document Popular in web-related programming Good choice for interoperability within many different types of institutional systems.

XML Messages and SIP XML messages may be used for representing schemas used for automatic GUI generation and configuration of sub-events a filter for events subscribed to

performing remote procedure calls (SOAP) Flushing, NY severe

Message Flow Runs on separate host 1) SIP SUBSCRIBE message requesting possible events 2) 302 Redirect message with body listing all the events 3) SUBSCRIBE message with body containing an XML filter for event (ie. Fire) 4) 200 OK 5) 302 Redirect message with a reference to the XML Schema for event Fire 6) GUI generated with XML Schema and user selects the filtered values. Updated SUBSCRIBE sent to server with filtered values in XML format in SIP message body 7) 200 OK SIPCSIPD

GUI Screens Generated

Detailed overview of architecture 2) Generic emergency address: is added to sipc Fire Earthquake Notification server (sipd) 3) Sipc contacts notification server and gets list of emergency events user can subscribe to 4) User subscribes to event it wants to be notified of 1) Event generators publish their events to notification server 5) Sipc gets XML schema reference from notification server that will generate a form which queries for the event’s properties. Sipc then updates its subscription to the notification server with the filtered expressions

Detailed overview of architecture 3)Sipc will process SOAP body and invoke the procedure call—such as flashing of lights Fire Earthquake Notification server (sipd) 2) Sipd will process parameters of the fire and send a NOTIFY to sipc including SOAP body 1) Fire occurs and event generator notifies sipd

Benefits: Why SIP and XML? Device Neutrality SIP-based end systems, ranging from IP telephones to 3G wireless handsets More Information Video conferencing, text messaging Automated Action Device control using the SIP “DO” method Generic in its Application Using XML schemas and messages allows for variety of event notification systems

Conclusion and Future Work SIP is a signaling protocol that supports SUBSCRIBE/NOTIFY methods Incorporating XML in SIP event notification allows the system to be generic in its application Currently implementing emergency notification Future work includes incorporating all the different types of events supported in sipc in one generic event notification module