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Overview of User Terminal Interfaces
Edoardo BereraUniversity of Nice Sophia Antipolis
Telelinea
26 September 2001
Seminar on Electronic Commerce24-28 September 2001
E. Berera UNSA / Telelinea 2
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 3
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 4
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 5
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 6
Basic Service
• Local and long-distance calls• Usage
– Voice – Fax– Internet access
• Tariffs– Duration– Distance
• Circuit Switched Network
01 23 45 67 89
01 23 45 67 89
E. Berera UNSA / Telelinea 7
112
Intelligent Services
• Emergency calls– 112 in Europe– 911 in USA
• Where is the number translation done ?
• Where is the “intelligence” ?– “800” numbers– Services
• Toll free (callee pays !)• Special rates• Location / time dependent
04 12 34 56 78
E. Berera UNSA / Telelinea 8
Intelligent Network (IN)
• 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
112
SS7
E. Berera UNSA / Telelinea 9
IN Components
• 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
SCP
STP
SSP Intelligent PeripheralModem/Fax
Answering machine
E. Berera UNSA / Telelinea 10
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 11
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 12
Integrated IP Telephony Example
• Distance education• Tutor works on a computer
at the university connected to the Internet
applicationpresentation
sessiontransportnetwork
physical
OSI stack Internet stack
HTTP, SMTP
TCP,UDP
IPv4, IPv6
IEEE802.xdata link
E. Berera UNSA / Telelinea 13
IP Telephony Protocols
• Tutor receives an audio and video call from Bruno
• SIP– Session Initiation Protocol
• SDP– Session Description Prot.
• RTP– Real-time Transport Prot.
IPv4, IPv6
H.323 RTSP SIP RTCP RSVP
TCP UDP
SDP Media
RTP
E. Berera UNSA / Telelinea 14
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 15
SIP Operation
• Example– sip:joe@company.com
• 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 16
SIP Message Structure
• sip:UserB@there.com• 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 17
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 18
SIP Methods (cont.)
• OPTIONS– capability inquiry
• REGISTER– binds a permanent address to current location– may convey user data (CPL scripts)
E. Berera UNSA / Telelinea 19
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
– Call Processing Language (CPL)• simpler, more restricted• for untrusted users• consumers
– based on XML© IEEE Network, Henning Schulzrinne, Jonathan Lennox, Columbia University, Jonathan Rosenberg, Bell Labs-Lucent Technologies, May/June 1999
E. Berera UNSA / Telelinea 20
Example CPL Decision Graph
• Directed acyclic graph– Decision (switch) nodes– Location nodes– Signaling actions nodes
• proxy• redirect• response
– Non-signaling actions nodes• log• send an e-mail• send an instant message
© IEEE Network, Henning Schulzrinne, Jonathan Lennox, Columbia University, Jonathan Rosenberg, Bell Labs-Lucent Technologies, May/June 1999
E. Berera UNSA / Telelinea 21
CPL Example
<call> <!-- Proxy the call to jones --> <location url="sip:jones@jonespc.example.com"> <proxy timeout="8s">
<!-- When busy, forward to voicemail --> <busy> <location url="sip:jones@voicemail.example.com" 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> </call>
© IEEE Network, Henning Schulzrinne, Jonathan Lennox, Columbia University, Jonathan Rosenberg, Bell Labs-Lucent Technologies, May/June 1999
E. Berera UNSA / Telelinea 22
IP Telephony and Agent Software
• Tutor and Bruno need to talk to Clara
• Clara works at home and at the university– Personal agent software
will ring Clara• at home
– sip:0123456789@gateway.ft.com
• at the university– sip:clara@university.fr
• on her cellular phone– sip:0612345678@g-way.sfr.com
Home PC
University Workstation
Clara ?
M
Source: Mampaey, Alcatel (© IEEE Communications, Oct. 2000, p. 105)
E. Berera UNSA / Telelinea 23
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 24
Global System for Mobile (GSM)
Source: Oliphant, IFR (© IEEE Spectrum, Aug. 1999, p. 21)
E. Berera UNSA / Telelinea 25
Streaming Media
– Tutor recalls a tutorial stored on the university video server and decides to play it
– Bruno receives both audio and video
Media
IPv4, IPv6
H.323 RTSP SIP RTCP RSVP
TCP UDP
SDP
RTP
Clara will receive the audio and only text… for the moment !
E. Berera UNSA / Telelinea 26
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 27
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-service-
examples• SIP-CGI: RFC 3050• CPL: draft-iptel-cpl
E. Berera UNSA / Telelinea 28
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
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