New version page

SIP_White_Paper

This preview shows page 1-2-20-21 out of 21 pages.

View Full Document
View Full Document

End of preview. Want to read all 21 pages?

Upload your study docs or become a GradeBuddy member to access this document.

View Full Document
Unformatted text preview:

SESSION INITIATION PROTOCOLCOPYRIGHT HEWLETT-PACKARD COMPANY 1999 -1-Next Generation Telephony:A look at Session Initiation ProtocolWhite PaperAuthor: Thomas DoumasVersion: A.00.03Last modified: 04/05/99 9:02 AMFile: SIP_White_Paper.docSESSION INITIATION PROTOCOLCOPYRIGHT HEWLETT-PACKARD COMPANY 1999 -2-Contents1. INTRODUCTION..........................................................................................................................31.1 HISTORICAL PERSPECTIVE.............................................................................................................31.2 IP TELEPHONY BENEFICIARIES......................................................................................................51.3 THE IP TELEPHONY CHALLENGES..................................................................................................51.4 IP TELEPHONY SIGNALING............................................................................................................61.5 VOIP SIGNALING PROTOCOLS.......................................................................................................72. INTRODUCING SIP .....................................................................................................................73. SIP OPERATION..........................................................................................................................83.1 PROXY SERVER OPERATION...........................................................................................................83.2 REDIRECT SERVER OPERATION....................................................................................................103.3 SIP ADDRESSING........................................................................................................................114. SIP MESSAGES ..........................................................................................................................124.1 THE INVITE MESSAGE...............................................................................................................124.2 RESPONSE MESSAGES.................................................................................................................135. SDP...............................................................................................................................................145.1 MEDIA INFORMATION.................................................................................................................146. SIP VS. H.323...............................................................................................................................167. SIP STACK..................................................................................................................................158. TESTING SIP..............................................................................................................................189. VOIP FUTURE............................................................................................................................1910. FURTHER INFORMATION......................................................................................................2011. BIOGRAPHY...............................................................................................................................21SESSION INITIATION PROTOCOLCOPYRIGHT HEWLETT-PACKARD COMPANY 1999 -3-1. INTRODUCTIONNext generation telephony and the role of Session Initiation Protocol is more easilyunderstood with a little background on the telephone industry and the Internet. Thefollowing sections present a brief overview of the current telephone system and theInternet.1.1 Historical perspectiveThe telephone system dates back to 1876 when the Bell Company was formed. This wasthe original public switched telephone network (PSTN). Over the years the telephonesystem evolved to a complex network that provides advanced services in addition tovoice calling. These services include direct dialing, billing options (credit card, callingcard, collect, prepaid minutes, etc), privacy options (caller id, caller id block, etc),convenience options, directory information, etc. The fundamental circuit switchedarchitecture remains, while most everything else has changed. Until recently, thetelephone system in the United States was a monopoly. As is common with monopolies,the innovation is introduced slowly and costs are high. Along with the monopoly camestrict federal regulation of the quality and availability of service.The telephone system of the United States had great influence on the telephone systemsof other countries. Although differences in protocols and physical interfaces exist, theprinciples are the same. Many telephone systems outside of the United States are stillmonopolies under governmental control.The telephone system architecture today makes use of two distinct functional layers, thetransport layer and the control layer. The transport layer consists of a mesh of circuitswitches. The switches on the edge, providing connection to the end-user, are calledClass 5, end office switches (from the AT&T 5ESS). The switches in the core, providingconnection among end office switches, are called Class 4 tandem switches (from theAT&T 4ESS). The control network consists of a mesh of computers and databases thatcontrol the behavior of the circuit switches of the transport layer. The separation betweenthe control layer and the transport layer provides “common channel signaling” withwhich the transport resources are freed from signaling traffic. All signaling traffic travelson the Signaling System 7, or SS7 control network. Figure 1 presents a diagram of thetelephone system that highlights the architecture.SESSION INITIATION PROTOCOLCOPYRIGHT HEWLETT-PACKARD COMPANY 1999 -4-Figure 1 PSTN architectureOn the other hand, the Internet grew out of United States government and universityresearch projects. The intent of these projects was to develop a communications networkthat could survive catastrophes. The Internet does not have nor requires a separate controllayer. The reason for this is that unlike the telephone system, the Internet employs apacket switched transport layer. There is no signaling because circuits do not need to beestablished in advance of data transfer as in a circuit switch transport. Each packetcontains sufficient information so that the packet switches (routers) can forward it to itsultimate


Loading Unlocking...
Login

Join to view SIP_White_Paper and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view SIP_White_Paper and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?