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Seminar on Electronic Commerce 24-28 September 2001 Overview of User Terminal Interfaces Edoardo Berera University of Nice Sophia Antipolis Telelinea 26 September 2001 Objectives • A common understanding of – Variety of user terminals – Underlying networks and their interconnections – Servers and protocols • Non goals – To describe any specific e-commerce application – To be exhaustive E. Berera UNSA / Telelinea 2 Which “things” do we use to communicate ? • Terminals – Telephones, PCs – but also …? • Networks – Phone net, Internet – but also … ? • Languages, protocols – English, HTML, SMS… ? – HTTP, WAP, … ? • Servers – Yellow Pages, Yahoo,…? E. Berera UNSA / Telelinea 3 Information Utility • Information system developers must – understand how to interconnect all the components • terminals, switches, routers, gateways, satellites, servers – using a variety of • languages, programs, protocols and tools E. Berera UNSA / Telelinea 4 Keep it simple please: Tin Can Telephones • Did you ever build tin can telephones when you were children ? • Simple device that allows you to talk at one end and get someone to listen at some distance at the other end • Can you analyze this communication system ? E. Berera UNSA / Telelinea 5 Basic Service 01 23 45 67 89 01 23 45 67 89 • Local and long-distance calls • Usage – Voice – Fax – Internet access • Tariffs – Duration – Distance • Circuit Switched Network E. Berera UNSA / Telelinea 6 Intelligent Services • Emergency calls – 112 in Europe – 911 in USA • Where is the number translation done ? 112 • Where is the “intelligence” ? 04 12 34 56 78 E. Berera – “800” numbers – Services • Toll free (callee pays !) • Special rates • Location / time dependent UNSA / Telelinea 7 Intelligent Network (IN) SS7 112 E. Berera • Network servers provide service intelligence (e.g. number translations) • Separation between – Voice transport network • Circuit switched network – Signaling network (call control) • Packet switched network • SS7 Signaling System n°7 UNSA / Telelinea 8 IN Components SCP STP Modem/Fax SSP Answering machine E. Berera Intelligent Peripheral • Service Control Point (SCP) • Signaling Transfer Point (STP) • Service Switching Point (SSP) usually integrated in the telephone switches • Intelligent Peripherals – Interactive Voice Response (IVR) – Media Gateways UNSA / Telelinea 9 Modern Telephone Network Structure • Dumb terminals (little or no intelligence in normal telephones) • Advanced services provided by network servers • Packet switched signaling network (call control messages) • Circuit switched voice transport network E. Berera UNSA / Telelinea 10 Internet and the Intelligent Network • Internet structure: – Application servers – Network routers – Intelligent terminals • Workstations, PC, PDA • IN programmable components – Service Control Points – Intelligent Peripherals – Dumb (?) terminals • Phone • PC and a modem E. Berera UNSA / Telelinea 11 Integrated IP Telephony Example • Distance education • Tutor works on a computer at the university connected to the Internet OSI stack application presentation session transport network data link physical E. Berera Internet stack HTTP, SMTP TCP,UDP IPv4, IPv6 IEEE802.x UNSA / Telelinea 12 IP Telephony Protocols • Tutor receives an audio and video call from Bruno • SIP – Session Initiation Protocol SDP H.323 RTSP SIP • SDP Media RTP RTCP TCP – Session Description Prot. RSVP • RTP – Real-time Transport Prot. UDP IPv4, IPv6 E. Berera UNSA / Telelinea 13 Signaling Protocols • User Location – Where is the callee ? Which (dynamic) IP address ? • Session Establishment – Accept, reject, redirect (voicemail, web page) • Session Negotiation – Multimedia session, capabilities exchange • Call Participation Mgmt – Add new participants; participants may leave session • Feature Invocation – Hold, transfer, mute, ... E. Berera UNSA / Telelinea 14 SIP Operation • Example – sip:[email protected] • • • • • SIP User Agent Client SIP Proxy Server SIP Redirect Server SIP Registration Server SIP User Agent Server © IEEE Network, Henning Schulzrinne, Columbia University, Jonathan Rosenberg, Bell Labs-Lucent Technologies, May/June 1999 E. Berera UNSA / Telelinea 15 SIP Message Structure • sip:[email protected] • Signaling message INVITE – similar to e-mail • Message content (payload) – Session Description (SDP) • c: caller’s address • m: media • a: attribute – May contain more info © GMD FOKUS, SIP Tutorial, 2001 E. Berera UNSA / Telelinea 16 SIP Methods • INVITE – initiates sessions – session description included in message body • ACK – confirms session establishment • BYE – terminates sessions • CANCEL – cancels a pending INVITE E. Berera UNSA / Telelinea 17 SIP Methods (cont.) • OPTIONS – capability inquiry • REGISTER – binds a permanent address to current location – may convey user data (CPL scripts) E. Berera UNSA / Telelinea 18 Model for Programming SIP • SIP server augmented with service logic (programs) – SIP Common Gateway Interface (CGI) • flexible for trusted users • operators, administrators – similar to HTTP CGI © IEEE Network, Henning Schulzrinne, Jonathan Lennox, Columbia University, Jonathan Rosenberg, Bell Labs-Lucent Technologies, May/June 1999 E. Berera – Call Processing Language (CPL) • simpler, more restricted • for untrusted users • consumers UNSA / Telelinea – based on XML 19 Example CPL Decision Graph • Directed acyclic graph © IEEE Network, Henning Schulzrinne, Jonathan Lennox, Columbia University, Jonathan Rosenberg, Bell Labs-Lucent Technologies, May/June 1999 E. Berera – Decision (switch) nodes – Location nodes – Signaling actions nodes • proxy • redirect • response – Non-signaling actions nodes • log • send an e-mail • send an instant message UNSA / Telelinea 20 CPL Example <call> <!-- Proxy the call to jones --> <location url="sip:[email protected]"> <proxy timeout="8s"> <!-- When busy, forward to voicemail --> <busy> <location url="sip:[email protected]" merge="clear" id="voicemail" > <proxy /> </location> </busy> <!-- When there is no answer, jump to the voicemail link above and also forward to voicemail --> <noanswer> <link ref="voicemail" /> </noanswer> </proxy> </location> © IEEE Network, Henning Schulzrinne, Jonathan Lennox, Columbia University, Jonathan Rosenberg, Bell Labs-Lucent Technologies, May/June 1999 </call> E. Berera UNSA / Telelinea 21 IP Telephony and Agent Software • Tutor and Bruno need to talk to Clara • Clara works at home and at the university M Clara ? Home PC University Workstation – Personal agent software will ring Clara • at home – sip:[email protected] • at the university – sip:[email protected] • on her cellular phone – sip:[email protected] E. Berera UNSA / Telelinea Source: Mampaey, Alcatel (© IEEE Communications, Oct. 2000, p. 105) 22 Cellular Telephony • Clara in on the train she answers the call – WAP enabled GSM cellular phone • How did the cellular network find Clara ? – In which cell is she actually in ? • And the train is moving fast – TGV, ICE, Pendolino – cell handover problem • redirection E. Berera UNSA / Telelinea 23 Global System for Mobile (GSM) Source: Oliphant, IFR (© IEEE Spectrum, Aug. 1999, p. 21) E. Berera UNSA / Telelinea 24 Streaming Media – Tutor recalls a tutorial stored on the university video server and decides to play it – Bruno receives both audio and video SDP H.323 Clara will receive the audio and only text… for the moment ! E. Berera RTSP SIP Media RTCP TCP RTP RSVP UDP IPv4, IPv6 UNSA / Telelinea 25 References • Henning Schulzrinne, Columbia University, Jonathan Rosenberg, Bell Laboratories-Lucent Technologies, “The IETF Internet Telephony Architecture and Protocols”, IEEE Internet Computing, May/June 1999 • Jonathan Rosenberg, Bell Laboratories, Jonathan Lennox, Henning Schulzrinne, Columbia University, “Programming Internet Telephony Services”, IEEE Internet Computing, May/June 1999 • Dorgham Sisalem, Jiri Kuthan, Mobile Integrated Services, GMD Fokus, “Understanding SIP”, 2001 E. Berera UNSA / Telelinea 26 RFCs and Internet Drafts • • • • SIP: RFC 2543 SDP: RFC 2327 SIP call flows: draft-ietf-sip-call-flows SIP services call flows: draft-ietf-sip-serviceexamples • SIP-CGI: RFC 3050 • CPL: draft-iptel-cpl E. Berera UNSA / Telelinea 27 Online Resources • IEEE – http://computer.org/internet/telephony • GMD Fokus – http://www.fokus.gmd.de/glone/projects/ipt/ • Columbia University – http://www.cs.columbia.edu/~hgs/sip • Free World Dialup – http://www.pulver.com E. Berera UNSA / Telelinea 28