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A Gateway For SIP Event Interworking - Sasu Tarkoma & Thalainayar Balasubramanian Ramya MOTIVATION • Interworking of SIP event framework with the generic publish/subscribe system Challenges: • SIP Event Framework does not support anonymous one-to-many event dissemination • SIP Event Framework does not support expressive filtering Proposed Solution: • Implementation of a gateway component enabling interworking between the SIP event framework, and publish/subscribe system Application of the proposed Gateway: • Universal Data Access BACKGROUND INFORMATION Session Initiation Protocol (SIP) : a standard, text-based, application layer, signaling protocol developed by the Internet Engineering Task Force (IETF). Described in RFC 3261 Purpose of SIP: To establish, modify and terminate multimedia sessions over the IP network Acceptance as standard: Selected by the 3rd Generation Partnership Project (3GPP), as the session establishment protocol for the 3GPP IP Multimedia Core Network Subsystem (IMS) BACKGROUND INFORMATION SIP Application Areas: • Internet Telephony • Control Applications • E-Commerce • Multimedia Conferences • Instant Messaging SIP EVENT FRAMEWORK SIP Event Framework: An extension of Session Initiation Protocol, described in RFC 3265 Methods supported: SUBSCRIBE, NOTIFY SUBSCRIBER NOTIFIER SUBSCRIBE 200 NOTIFY 200 NOTIFY 200 Fig 1. SIP Event Subscription and Notification SIP DOMAIN Forward notification to subscriber proxy DNS Forward SUBSCRIBE Forward notification to subscriber SIP Proxy1 (Redirect mode) Proxy Update location server query Registrar register UAC1 Location Server register UAC2 Forward SUBSCRIBE to notifier Forward subscription to notifier proxy DNS lookup SIP Proxy2 (Redirect mode) UAC3 Fig 2. Working of SIP Domain COMPONENTS IN SIP DOMAIN SIP Proxy: Receives SIP requests/responses from clients/ proxies, processes, and forwards it to the next hop or final destination SIP Client: Receives/Sends SIP requests/responses Registrar: Maintains registered clients information, queries and gets recent updates from Location Server Redirect Server (Redirect Mode): Provides the contacted client’s current address to the contacting client Location Server: Stores updated client information APPLICATION AREAS OF CONTENT BASED PUB/SUB EVENT MODEL • Active Badge Systems • Proximity Sensors • Information and Multimedia Delivery Services • Positioning Systems WORKING OF PUBLISH/SUBSCRIBE EVENT MODEL Publishers P1 P2 Consumers Event Service Subscribe() Subscribe S2 Publish() Pn Unsubscribe() S1 Unsubscribe Fig 3. Publish/Subscribe Event model Sn GATEWAY DESIGN Gateway SIP Domain I I Pub/Sub Domain O O Conversion, Mapping, State Fig 4. Gateway Design IMPLEMENTATION ARCHITECTURE G subscribe/ A SIP clients notify T subscribe/ E Fuego JAIN-SIP publish W Clients Proxy A NIST-SIP Fuego Event Y STACK Service Fig 5. Implementation Architecture GATEWAY FUNCTIONALITIES • Receive SIP messages (requests/responses) • Convert SIP message to pub/sub messages. Forward the converted messages to Fuego domain • Receive pub/sub messages • Convert pub/sub messages to SIP messages (requests/ responses). Forward the converted messages to the SIP domain • Associate the received messages using unique identifiers. Call Identifier of the SIP and subscription identifier of the Fuego message are used for association. • Generate and send SIP provisional responses to the SIP domain SIP AND FUEGO SUBSCRIPTIONS/NOTIFICATIONS SIP DOMAIN GATEWAY FUEGO SYSTEM SUBSCRIBE Mapping, reformat SUBSCRIBE Forward SUBSCRIBE Process subscription Forward SIP response Forward NOTIFY Subscription status Create SIP response PUBLISH Mapping, reformat PUBLISH OK Fig 6. SIP SUBSCRIBE and Fuego PUBLISH SIP AND FUEGO SUBSCRIPTIONS/NOTIFICATIONS SIP Domain Gateway Fuego System SUBSCRIBE Forward SUBSCRIBE Process subscription OK Mapping, reformat SUBSCRIBE NOTIFY Mapping, reformat NOTIFY OK Forward NOTIFY Fig 7. FUEGO SUBSCRIBE and SIP NOTIFY MOBILITY IN THE INTERWORKING ARCHITECTURE Intradomain mobility: • Intradomain terminal mobility is possible in both the SIP and Fuego domains • Disconnected operation should be supported for user mobility Interdomain mobility: • Need buffering of messages at the gateway • Roaming clients can send a signal to the gateway informing their location update, and get the buffered messages ADVANTAGES OF THE GATEWAY COMPONENT Advantages: + No modifications in the API of the interworked domains + Supports extensibe implementation + Transparent architecture Experimentatal observation: • Performed scalability and performance test for the gateway • Used the presence event package Conclusion • Under heterogenous environments interworking of different event standards is essential Future Work: • Enhancing gateway functionality by providing filtering support, and load balancing • Investigate the possibilities to provide various mobility support such as session mobility REFERENCES • Java APIs for Integrated Network (JAIN) – Session Initiation Protocol (SIP) API: http://www.jcp.org/aboutJava/communityprocess/final/jsr032/ • National Institute of Standards and Technology (NIST) – SIP (Session Initiation Protocol) Stack and Proxy: http://snad.ncsl.nist.gov/proj/iptel/ QUESTIONS ? 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