Fall IM 2000 Introduction to SIP Jonathan Rosenberg Chief Scientist

Fall IM 2000 Introduction to SIP Session Initiation Protocol (SIP) Developed in mmusic Group in IETF Proposed standard RFC2543, February 1999 Work began 1995 Part of Internet Multimedia Conferencing Suite Main Functions Invite users to sessions Find the users current location, match with their capabilities and preferences in order to deliver invitation Carry opaque session descriptions Modification of sessions Termination of sessions

Fall IM 2000 Introduction to SIP Protocol Components User Agent Client (UAC) End systems Send SIP requests User Agent Server (UAS) Listens for call requests Prompts user or executes program to determine response User Agent UAC plus UAS

Fall IM 2000 Introduction to SIP Protocol Components cont. Redirect Server Network server - redirects users to try other server Proxy Server Network server - a proxy request to another server can fork request to multiple servers, creating a search tree Registrar Receives registrations regarding current user locations

Fall IM 2000 Introduction to SIP SIP Architecture Request Response Media SIP Client SIP Redirect Server SIP Proxy SIP Client (User Agent Server) Location Service 13 14

Fall IM 2000 Introduction to SIP Requirements for Presence and IM Subscription Ask for notifications of changes in communications state Routing request to server that knows state of a user Notification Propagate state changes to subscribers Publication Tell the network about my changes in state

Fall IM 2000 Introduction to SIP SIP Already Provides Publication Capability REGISTER is a Publication Message for Locations Allows for SIP and Other URL Types Multiple Entities Can Publish for the Same Address SIP Caller Preferences Extension Allows for Attributes for Locations Mobile, landline Home, business Preferences Audio,video - MIME capability Registrar Client Registrar

Fall IM 2000 Introduction to SIP SIP Extension for Presence New Entity: Presence Agent Purely logical entity Knows presence state of user Receives SUBSCRIBE requests Generates NOTIFY requests Co-located with proxy/registrar or User Agent Basic Operation Subscriber send SUBSCRIBE Routed to PA using normal SIP PA authorizes subscriber Acceptance contains presence state NOTIFY sent when state changes Routed using SIP Record-Route REGISTER SUBSCRIBE NOTIFY Presence Agent + Proxy/Registrar = Presence Server Proxy Subscriber Presentity

Fall IM 2000 Introduction to SIP Features of SIP For Presence Extension End Users Can Perform Notifications Scalability Presence Agent Function Can Migrate Network provides service when user is offline When user is online, subscriptions migrate to user Offline Subscriptions Handled Presence server always asks user if a subscription should be accepted

Fall IM 2000 Introduction to SIP Features of SIP For Presence Extension cont. Multiple Entities Can Generate Presence Information for One Presentity Mobile phone, PDA, laptop and desktop PC Multiple Presence Clients Can Be Online at Once Traditional SIP Proxies Route SUBSCRIBE and NOTIFY Presence Data is Orthogonal

Fall IM 2000 Introduction to SIP SIP Extension for Instant Messaging Operation of Extension Messages carried in SIP messages New method - MESSAGE Routed to recipient using normal SIP techniques Simple extension Features Associates an IM with an existing call Any MIME data can be sent TCP for large messages Routed by existing proxies and registrars Possible to have a different client for IM and communications

Fall IM 2000 Introduction to SIP Advantages of Using SIP for Presence and IM Unifies Major Communications Services Voice/video IM Presence Shared Databases Shared Proxies Shared Servers

Fall IM 2000 Introduction to SIP Advantages of Using SIP For Presence and IM Reduces Management Costs One infrastructure instead of two One NOC instead of two One set of managers instead of two Enables New Combined Services Combined services integrate voice, video, IM, presence, web amd These new services will be a killer app for communications on the Internet Delivery of combined services is greatly simplified by alignment of presence and communication signaling protocols

Fall IM 2000 Introduction to SIP Information Resource Jonathan Rosenberg