SIP Programming :

1
SIP Programming

• SIP has texture encoding feature.1
• SIP allows third parties or user to program
• SIP follows HTTP programming model

2
Programming Mechanisms

• In order to develop services programmers needs
  APIs
• Three mechanisms suggested in IETF2
• SIP Call Processing Language ( SIP CPL )
• SIP Common Gateway Interface ( SIP CGI )
• SIP Servlet
• Other efforts
• Parlay
• JAIN

3
Call Processing Language (CPL)

• Designed by the IETF to support sophisticated
  telephony services
• May be used by both SIP or H.323.
• XML based scripting language for describing
  controlling call services3
• Simple Syntax
• Extendible
• Easily edited by GUI tools
• Scripts runs on network SIP signaling server to
  create end user services
• Lightweight CPL interpreter is need to parser
  validate scripts.

4
CPL Example

• A simple script that blocks anonymous callers
  4
• lt?xml version"1.0" ?gtlt!DOCTYPE cpl PUBLIC
  "-//IETF//DTD RFCxxxx CPL 1.0//EN"
  "cpl.dtd"gtltcplgt  ltincominggt    ltaddress-switch
  field"origin" subfield"user"gt      ltaddress
  is"anonymous"gt        ltreject status"reject" 
          reason"I don't accept anonymous calls"
  /gt      lt/addressgt    lt/address-switchgt 
  lt/incominggtlt/cplgt

5
Common Gateway Interface (CGI)

• Almost identical to HTTP CGI 5
• Language independent ( Perl, Tcl, C, C, ... )
• Any binary may be executed as a separate program
• Suitable for services that contains substantial
  web content
• Passes message parameters through environmental
  variables to a separate program.
• More flexible but more risky
• Feb. 1, 2001 RFC 3050 (Common Gateway Interface
  for SIP) published 6

6
Java Servlets

• Similar to HTTP servlets
• Instead of using a separate process, messages are
  passed to a class
• The class runs within a JVM (Java Virtual
  Machine) on server
• Security provided by Java
• Portable between OSs servers

7
JAIN SIP API

• Low level API that maps to IETF - RFC 2543
• Interfaces for services across circuit switched
  and packet networks
• Three major objectives
• Service Portability Write Once Run Anywhere
• Network Converges Any underlying network
  architecture IP, ATM,Wireless,...
• Service Provider Access by Anyone

8
JAIN SIP API ( Cont.)

• Three SIP APIs under JAIN initiative
• JAIN SIP API (JSR 32)
• Low level API for almost any signaling protocol (
  SIP, H.323, ... )
• Requires extensive knowledge of SIP.
• Avaliable at Final Release, http//jcp.org/jsr/sta
  ge/final.jsp
• JAIN SIP Lite
• High Level API for rapid application development
• Especially User Agent development
• Under development , http//jcp.org/jsr/detail/125.
  jsp
• SIP Servlets 7
• API for SIP servlets
• Under development, http//jcp.org/jsr/detail/116.j
  sp

9
Conclusion

• As the arena become more more crowded for
  service providers, the choice of the appropriate
  service creation mechanism inherently follows
  HTTP service creation mechanisms and highly
  depends on different scenarios where
  security,portability and performance have
  different roles of importance.

10
References

• 1,5 Sisalem D.,Kuthan J., Understanding SIP ,
  Http//iptel.org/sip/siptutorial.pdf
• 2 Programming SIP, http//www.sipcenter.com/abou
  tsip/progsip.htm
• 3 Rosenberg D.J, Shockey R., The Session
  Initiation Protocol (SIP) , ComputerTelephony ,
  June 2000
• 4 A Spotlight on Call Processing Language,
  http//www.ubiquity.net/cpl.html
• 6 News, http//www.cs.columbia.edu/hgs/sip/
• 7 Java Specification Request,JSR 116,SIP
  Servlet API,http//jcp.org/jsr/detail/116.jsp