SIP Servlets. SIP Summit 2001 5.01.01 SIP Servlets Problem Statement Want to enable construction of...

SIP Servlets

www.dynamicsoft.comSIP Summit 2001 5.01.01SIP Servlets

Problem Statement Want to enable construction of a wide variety of IP telephony

applications Traditional voice features IN features Converged applications – integration with IM, Web, Presence

Generic call model based APIs not sufficient! Don’t expose features of SIP needed for converged services Call model not central – other events drive apps!

API should appeal to a wide developer community

Want to support hosting model Developer is not the deployer

Carrier grade applications


Appealing to the Web Development Community

Number of web developers to telecom developers is on order of :1

Most CS graduates today know servlets, CGI, XML, and web development servers

Goal is to create lots of services by appealing to the masses Great ideas will come from two hackers in a garage

Therefore, Want a SIP services API that is familiar to web developers Leverage the HTTP servlet model


HTTP Servlets HTTP Java Servlets Widely Used in Web

Application Development

Applications Consist of Sets of HTTP Servlets, Each of Which Processes a Single Web Request in the Application

HTTP Servlets Return Web Pages to Display

HTTP Servlets Can Create “Session Data” e.g., shopping cart, that spans multiple

requests

“Container” Manages HTTP Servlet Lifecycles, Fault Tolerance, Session State

HTTP Servlets Collected into a War File – Web Archive

HTTP Servlets

Web Server

Developer

Deployer

War File


SIP Servlets Direct Application of HTTP

Servlet Model to SIP

Java-based API

Telecommunications application is a set of SIP (and HTTP!) servlets

SIP servlets process a particular SIP request or response

Lifecycle managed by container

SIP servlets can create and access session data, call data, transaction data

SIP servlet container provides same functions as http container

CAR file equivalent of WAR file

SIP Servlets Car File

SIP Server

Developer


What is a SIP Servlet? Java interface

Defines methods that are callbacks when certain events occur

doInvte() doBYE() doResponse()

Application writer implements servlet class, fills in methods with own code

Servlets don’t store state – domain objects are used (later)

Servlet can instruction container to Proxy a request Initiate a new request Forward a response Generate a response

Servlet engine handles the messy details of SIP Call-Ids, tags, retransmissions,

record-routes, vias…

Servlet has access to important fields of SIP messages To, From, Request-URI, Contact,

body


Example SIP Servlet

public class MyServlet implements SipServlet{ public void doInvite(SipServletRequest req, SipServletResponse res) { req.getProxy(true).proxy(“sip:user@host”); }}


Definition of Servlet Mappings Single server supports many

applications

When a SIP INVITE arrives, which one (or ones) process the request??

Servlet mappings are rules that create bindings from SIP messages to servlet classes Based on expression matching in

fields of message

Servlet mappings can be Set up by application deployer Set by application writer

RuleMatch

Class 1

Class 2

Class 3

Class 4

Rule DB

INVITE


Deployment Descriptors Third party model requires

information to be conveyed from writer to deployer beyond just code

Deployment descriptor fills this need Descriptive names and usage of

classes Name and usage of entire

application Servlet mappings Context parameters References to resources needed

by applications EJB Homes JNDI contexts

Session timeouts

Converged Archive (CAR) File JAR file with specific structure Used to package entire

application into one bundle Contains

Servlet classes Deployment descriptor Static content

HTTP Servlets use WAR file (Web Archive)

CAR file is superset of WAR


Storing application state In most applications, state is

distributed throughout the objects it uses

Troublesome for fault tolerance The data must be replicated Data might need to be distributed

across a set of homogeneous servers

The data might need to be stored on reliable media to ensure recovery

If data is distributed, container has no easy way to store and manage it for the application

Result: application needs to handle its own data management. Bad.

Alternative: container provides domain objects in which application can place all state All state in one place Container can easily manage fault

tolerance, reliability, etc.

In HTTP Servlets, the domain objects are Session and ServletContext Session are things like shopping

carts, span multiple HTTP requests


ApplicationSession

SIP Domain Objects

ServletContext

HttpSession

Unification

SipSessionSipTransaction


Relationship to JAIN SIP JAIN SIP is a generic, low-level

interface for accessing SIP services Can be used in

Clients Servers Gateways

Focuses purely on the protocol Complete access to SIP

capabilities Supports transactions only

SIP Servlet Container is a particular application of JAIN SIP

SIP Protocol

SIP ServletContainer

Ser

vlet

JAIN SIP

SIP Servlet API

Ser

vlet


Relationship to JAIN SIP Servlets focus on high volume

carrier grade servers

Add significant, non-SIP protocol functions Lifecycle management Domain objects Context and configuration Deployment descriptors Archive files Synchronization primitives Security

Add significant SIP protocol functions Construction of requests and

responses from domain objects

Hide many parts of JAIN SIP Direct access to many headers is

not provided Write access to most everything is

often restricted

Servlets should be defined to allow a SIP container to be built using JAIN SIP SIP Objects in Servlet API defined

with interfaces that match JAIN SIP signatures

Cannot directly expose JAIN SIP objects, though

Information Resource Jonathan [email protected]

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