Transcript presentation

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
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UNSA / Telelinea
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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,…?
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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
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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 ?
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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
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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
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– “800” numbers
– Services
• Toll free (callee pays !)
• Special rates
• Location / time dependent
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Intelligent Network (IN)
SS7
112
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• 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
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IN Components
SCP
STP
Modem/Fax SSP
Answering
machine
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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
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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
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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
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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
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Internet stack
HTTP, SMTP
TCP,UDP
IPv4, IPv6
IEEE802.x
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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
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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, ...
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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
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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
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SIP Methods
• INVITE
– initiates sessions
– session description included in message body
• ACK
– confirms session establishment
• BYE
– terminates sessions
• CANCEL
– cancels a pending INVITE
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SIP Methods (cont.)
• OPTIONS
– capability inquiry
• REGISTER
– binds a permanent address to current location
– may convey user data (CPL scripts)
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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
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– Call Processing Language
(CPL)
• simpler, more restricted
• for untrusted users
• consumers
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– based on XML
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Example CPL Decision Graph
• Directed acyclic graph
© IEEE Network, Henning Schulzrinne, Jonathan Lennox, Columbia University,
Jonathan Rosenberg, Bell Labs-Lucent Technologies, May/June 1999
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– Decision (switch) nodes
– Location nodes
– Signaling actions nodes
• proxy
• redirect
• response
– Non-signaling actions nodes
• log
• send an e-mail
• send an instant message
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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>
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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]
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Source: Mampaey, Alcatel (© IEEE Communications, Oct.
2000, p. 105)
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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
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Global System for Mobile (GSM)
Source: Oliphant, IFR (© IEEE Spectrum, Aug. 1999, p. 21)
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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 !
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RTSP
SIP
Media
RTCP
TCP
RTP
RSVP
UDP
IPv4, IPv6
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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
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RFCs and Internet Drafts
•
•
•
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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
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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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