IM 2000 -- May 24, 2000 Introduction to SIP Jonathan Rosenberg Chief Scientist.

www.dynamicsoft.comIM 2000 -- May 24, 2000Introduction to SIP

Introduction to SIP

Jonathan Rosenberg

Chief Scientist


Talk Outline Brief Introduction on SIP

SIP As a Platform for Presence Requirements of a presence protocol Requirements of an IM protocol Components SIP already provides What else is needed in SIP


Introducing - 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 Invitation of users to sessions

Find the users current location, match will their capabilities and preferences, in order to deliver invitation

Carry opaque session descriptions

Modification of sessions Termination of sessions


Introducing - Session Initiation Protocol (SIP) cont. Main Features

Personal mobility services Wide area operation Session independence

voice, video, games, chat, virtual reality, etc.

Leverages other Internet protocols


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 + UAS


Protocol Components cont. Redirect Server

“Network” server; redirects users to try other server

Proxy Server “Network Server” Proxies request to another server can “fork” request to

multiple servers, creating a search tree

Registrar Receives registrations regarding current user locations


SIP ArchitectureRequest

Response

Media

1

2

3

45

67

8

9

1011

12

SIP Client

SIP Redirect Server

SIP ProxySIP Proxy

SIP Client(User Agent Server)

Location Service

13

14


Benefits of SIP Scalability

Proxy servers can be stateless Features pushed to the periphery of the network UDP

Extensibility Numerous capabilities built in for extensibility

New headers New methods New bodies

Protocol mechanics exist to determine common operating sets


Benefits of SIP cont. Modularity

SIP based on a component model for systems Complete solution built by piecing together independent but

cooperative protocols SIP provides a general purpose mechanism for rendezvous to

enables communications


Components of a Presence Solution Subscription

Means to subscribe to some entity Requires huge scalability

Distributed subscription state Lightweight transactions

Authentication of subscribers Ability to convey complex subscription rules Routing and namespace partitioning


Components of a Presence Solution cont. Publication

Enables a user to send information to server for distribution Must be possible to have multiple entities publish for a single address

My cell phone My IM client

Describes communications means, state, capabilities and characteristics


Components of a Presence Solution cont. Notification

Rapid delivery of published data to subscribers Makes use of distributed subscription state Highly scalable

Presence data changes often Many subscribers

Must be able to convey a variety of presence data formats Ideally, push notifications to the client


SIP and Presence/IM are Closely Related SIP Requires Presence State to Route Calls from A to B

SIP and presence protocol use same data But SIP is asynchronous; presence protocol is synchronous

SIP and Presence Share Similar Scalability Requirements SIP can handle more than phone calls - supports all types of sessions Namespace partitioning for scale Stateless/UDP operation for scale “Fast in the core, smart at the edge” model needed in both cases


SIP and Presence/IM are Closely Related cont. SIP and Presence Share Similar Security Requirements

End-to-end authentication of messages and responses Not mandatory

Hop by Hop encryption and authentication for privacy and authentication

transitivity to achieve scale


SIP and Presence/IM are Closely Related cont.

SIP and Presence/IM Both Require Routing Difficult part of IM is finding user to deliver IM Difficult part of SIP is finding user to deliver session invitation Presence also requires same routing - finding presence server for user

SIP and presence/IM share similar extensibility requirements Core communications services Broad uses Wide area services


SIP and Presence/IM are Cousins cont.

SIP and presence/IM share similar content carriage requirements SIP and presence will need to carry a common data format

SIP carries SDP Presence carries presence data format

IM needs to support MIME SIP provides MIME


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

Client

Client


Requirements for SIP to Support Presence Define New Entity -- Presence Server

Possibly co-located with registrar

Extend with New SUBSCRIBE Method SIP’s Routing, naming, security, content, transaction labeling and

sequencing capabilities are all required Define distributed subscription state

Similar to mailing lists


Requirements for SIP to Support Presence cont.

Extend with New NOTIFY Method

Create Mechanism to Fetch Friend Lists REGISTER response? Need not be a SIP mechanism

Define Presence URL


Requirements for SIP to Support IM cont.

Possible Approaches IM is a session, established with INVITE IM is a messaging service Would need new SIP method

IM as a Session Supportable with SIP now New RTP payload format for text Allows tight synchronization with voice and video One character at a time readily supported Similar to chat


Requirements for SIP to Support IM cont. IM as a Messaging Service

No session setup needed Ordering not important Simplifies storage for later delivery All messages need to travel through servers, rather than be sent

directly to user No notion of session over which lifetime of an address exists

Can be easily done using new method, MESSAGE


Advantages of Using SIP for Presence and IM Unifies Major Communications Services

Voice/video IM Presence

Shared Databases

Shared Proxies

Shared Servers


Advantages of Using SIP For Presence and IM cont.

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, email These new services will be “killer app” for communications on the Internet Delivery of combined services is greatly facilitated by alignment of

presence and communication signaling protocols


Information Resource Jonathan Rosenberg

[email protected] +1 732.741.7244

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IM 2000 -- May 24, 2000 Introduction to SIP Jonathan Rosenberg Chief Scientist.

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