SIP Servlets

1
SIP Servlets

• DynamicSoft Technology Compatibility Kit

2

• Brief overview of SIP
• What is SIP?
• SIP Concepts
• SIP Typical Architecture and Call Flow
• SIP Servlet Description
• Specification
• Components
• Examples
• SIP Servlets CallC

3
What is SIP?

• SIP Session Initiation Protocol
• Application-layer protocol approved by the IETF
  (Internet Engineering Task Force)
• Creation and management of communication sessions
  between devices
• No concern about nature or content of calls
• Any type of media can be exchanged
• Other protocols used with SIP
• SDP (Session Description Protocol)
• RTP (Real Time Protocol)

4
SIP Concepts

• User Agent end point to create and manage a
  communication session (either SIP phone or
  software application)
• SIP Proxy Server primary task is to ensure a
  request is sent to another entity closer to the
  target user.
• SIP Registrar and Redirect Servers usually
  combined with Proxy Server
• SIP Message either a request or a response
• SIP Address uniquely identifies a user looks
  like an email address with sip prefix

5
SIP Messages

• Requests
• REGISTER ? BYE
• INVITE ? CANCEL
• ACK ? OPTIONS
• Responses
• 1xx progress ? 4xx request failure
• 2xx success ? 5xx server failure
• 3xx redirect ? 6xx global failure
• Format
• Request or status line headers body
• Mandatory headers To, From, Cseq, Call-Id, Via,
  Contact

6
SIP Typical architecture
7
SIP Basic Proxy Call Flow
Proxy
UA Caller
UA Callee
(1) INVITE
(2) INVITE
(3) 200 OK
(4) 200 OK
(5) ACK
(6) BYE
(7) 200 OK
8
SIP Servlet Specification

• SIP Servlet API developed under the JCP (Java
  Community Process) as JSR 116 (Java Specification
  Request), as a set of neutral interfaces
• Goal to deliver a consistent, open platform on
  which to develop and deploy portable services

9
SIP Servlets vs. HTTP Servlets

• Common concepts
• Service method
• JAR based deployment file
• Deployment descriptors
• Differences
• SIP has proxy concept that can initiate new
  requests
• SIP is asynchronous
• SIP supports composition

10
SIP Servlet Components

• Servlet Container
• Environment in which a servlet can exist
• Loads and initializes a servlet
• Invokes the appropriate methods when SIP messages
  arrive
• Servlets
• Class with a service method, compiled into a
  Servlet Archive File (SAR)
• Deployment descriptors
• XML based file with configuration information and
  message matching rules

11
DynamicSoft implementation

• Compliant with the JCP specification
• Provided with a testing framework
• Specification Restriction
• The SIP Servlet API does not currently let you
  create an initial request in response to a
  non-SIP event (need to obtain the
  SipApplicationSession from an existing request to
  create a new request)
• Implementation Restrictions
• Application composition is not implmented
• Transport is only TCP (not UDP)

12
Example 1 Simple Servlet

• Servlet listens to INVITE requests, and forwards
  the INVITE to the desctination UA

• public class SampleServlet extends SipServlet
• public void doInvite(SipServletRequest
  a_Request)
• throws ServletException, java.io.IOException
• try
• a_Request.send()
• catch (IOException e)
• throw new ServletException("Could not send
  request", e)

13
Example 2 Proxy behavior

• Servlet acts as a proxy and sends the request
  downstream
• Supervised mode will allow it to see responses
• RecordRoute will allow it to see ACK and BYE

• public void doInvite(SipServletRequest a_Request)
  
• throws ServletException, IOException
• Proxy p a_Request.getProxy(true)
• p.setSupervised(true)
• p.setRecordRoute(true)
• System.out.println("Proxying request "
  a_Request.getRequestURI())
• p.proxyTo(a_Request.getRequestURI())

14
SIP Servlets CallC

• Initial background work
• Validate through a set of examples that we can
  implement all the CallC features in the SIP
  Servlet platform
• Identify issues related to deployment, robustness
  and security
• Goal
• Modify the CallC compiler to generate java code
  for the SIP Servlet Platform

15
Example CallC Code

• To redirect a call towards several addresses

• sip Adr 'siplatry_at_enseirb.fr',
• 'sipfabien.latry_at_wanadoo.fr',
• 'siplatry_at_inria.fr',
• 'siplatry_at_compose.fr'
• sip THIRD_PART 'sipPHILISTIN_at_enseirb.fr'
• response incoming(call c)
• response x
• c.subject "call redirection "
• foreach(sip s in Adr)
• x forward(c,s)
• if (x.code 200)
• response y
• c.subject "successfull redirection "
  ((string)s)
• y forward(c,THIRD_PART)
• return x
• return x

16
Example Servlet Code

• private void doInvite(SipServletRequest req)
• throws ServletException, IOException
• ArrayList dest new ArrayList()
• dest.add(sipFactory.createAddress("siplatry_at_ense
  irb.fr").getURI())
• dest.add(sipFactory.createAddress("sipfabien.lat
  ry_at_wanadoo.fr").getURI())
• dest.add(sipFactory.createAddress("siplatry_at_inri
  a.fr").getURI())
• dest.add(sipFactory.createAddress("siplatry_at_comp
  ose.fr").getURI())
• req.setHeader("Subject", "call redirection")
• Proxy p req.getProxy(true)
• p.setSupervised(true)
• p.setRecordRoute(true)
• log("proxying to " dest)
• p.proxyTo(dest)