Overview of User Terminal Interfaces Edoardo Berera University of Nice Sophia Antipolis Telelinea 26 September 2001 Seminar on Electronic Commerce 24-28

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


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,…?


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


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 ?


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


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


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


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


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


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


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


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


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, ...


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


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


SIP Methods

• INVITE– initiates sessions– session description included in message body

• ACK– confirms session establishment

• BYE– terminates sessions

• CANCEL– cancels a pending INVITE


SIP Methods (cont.)

• OPTIONS– capability inquiry

• REGISTER– binds a permanent address to current location– may convey user data (CPL scripts)


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


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


CPL Example

<call>  <location url="sip:[email protected]"> <proxy timeout="8s">

 <busy> <location url="sip:[email protected]" merge="clear" id="voicemail" > <proxy /> </location> </busy>

 <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


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:[email protected]

• at the university– sip:[email protected]

• on her cellular phone– sip:[email protected]

Home PC

University Workstation

Clara ?

M

Source: Mampaey, Alcatel (© IEEE Communications, Oct. 2000, p. 105)


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


Global System for Mobile (GSM)

Source: Oliphant, IFR (© IEEE Spectrum, Aug. 1999, p. 21)


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 !


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


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


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

Documents

Overview of User Terminal Interfaces Edoardo Berera University of Nice Sophia Antipolis Telelinea 26 September 2001 Seminar on Electronic Commerce 24-28