Internet Telephony

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Internet Telephony

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• 88321050 

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Part I

• Internet Telephony Architecture and Protocols
• an IETF Perspective
• Henning Schulzrinne, Jonathan Rosenberg
• Computer Networks and ISDN Systems, February 11,
  1999, vol 31/3, pp. 237-255.

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OUTLINE

• Introduction
• Features of IPTelephony
• Protocols RTP, RTCP, SIP, WASRV, RTSP
• Protocol Integration
• How does IPTel differ from GSTN
• Conclusion

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Some Terms

• POTS
• Short for plain old telephone service, which
  refers to the standard telephone service that
  most homes use. In contrast, telephone services
  based on high-speed, digital communications
  lines, such as ISDN and FDDI, are not POTS. The
  main distinctions between POTS and non-POTS
  services are speed and bandwidth. POTS is
  generally restricted to about 52 Kbps (52,000
  bits per second).
• The POTS network is also called the public
  switched telephone network (PSTN).

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Some Terms

• PBX
• Short for private branch exchange, a private
  telephone network used within an enterprise.
  Users of the PBX share a certain number of
  outside lines for making telephone calls external
  to the PBX.
• Most medium-sized and larger companies use a
  PBX because it's much less expensive than
  connecting an external telephone line to every
  telephone in the organization. In addition, it's
  easier to call someone within a PBX because the
  number you need to dial is typically just 3 or 4
  digits.

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Some Terms

• ISDN
• Abbreviation of integrated services digital
  network, an international communications standard
  for sending voice, video, and data over digital
  telephone lines or normal telephone wires. ISDN
  supports data transfer rates of 64 Kbps (64,000
  bits per second).

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Internet Telephony

• Internet telephony products are sometimes called
  IP telephony, Voice over the Internet (VOI),
  Voice over IP (VOIP) or IP telephony (IPtel)
  products.
• Enables people to use the Internet as the
  transmission medium for telephone calls.
• Real time delivery of voice between two or more
  parties, across the network using IP and the
  exchange of the information required to control
  this delivery.
• CoolTalk, Netmeeting, Net2Phone, MediaRing.

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Introduction

• Global multimedia communication system.
• Differs from multimedia streaming protocols.
• Uses SIP as a signaling protocol and RTP to
  transmit the packets.

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Internet protocol stack
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Internet protocol stack
Real-Time Transport Protocol, an Internet
protocol for transmitting real-time data such as
audio and video. RTP itself does not guarantee
real-time delivery of data, but it does provide
mechanisms for the sending and receiving
applications to support streaming data.
Typically, RTP runs on top of the UDP protocol,
although the specification is general enough to
support other transport protocols. RTP has
received wide industry support. Netscape intends
to base its LiveMedia technology on RTP, and
Microsoft claims that its NetMeeting product
support RTP.
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Internet protocol stack
A standard approved by the International
Telecommunication Union (ITU) that defines how
audiovisual conferencing data is transmitted
across networks.
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Internet protocol stack
Session Initiation Protocol, a signaling protocol
for Internet conferencing, telephony, presence,
events notification and instant messaging. The
protocol initiates call setup, routing,
authentication and other feature messages to
endpoints within an IP domain.
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Internet protocol stack
Short for Real Time Streaming Protocol, a
proposed standard for controlling streaming data
over the WWW. RTSP grew out of work done by
Columbia University, Netscape and RealNetworks
and has been submitted to the IETF for
standardization. Like H.323, RTSP uses RTP
(Real-Time Transport Protocol) to format packets
of multimedia content. But whereas H.323 is
designed for videoconferencing of
moderately-sized groups, RTSP is designed to
efficiently broadcast audio-visual data to large
groups.
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Internet protocol stack
Resource Reservation Setup Protocol, a new
Internet protocol being developed to enable the
Internet to support specified Qualities-of-Service
(QoS's). Using RSVP, an application will be able
to reserve resources along a route from source to
destination. RSVP-enabled routers will then
schedule and prioritize packets to fulfill the
QoS. RSVP is a chief component of a new type of
Internet being developed, known broadly as an
integrated services Internet. The general idea is
to enhance the Internet to support transmission
of real-time data.
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Internet protocol stack
Transmission Control Protocol, is one of the main
protocols in TCP/IP networks. Whereas the IP
protocol deals only with packets, TCP enables two
hosts to establish a connection and exchange
streams of data. TCP guarantees delivery of data
and also guarantees that packets will be
delivered in the same order in which they were
sent.
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Internet protocol stack
User Datagram Protocol, a connectionless protocol
that, like TCP, runs on top of IP networks.
Unlike TCP/IP, UDP/IP provides very few error
recovery services, offering instead a direct way
to send and receive datagrams over an IP network.
It's used primarily for broadcasting messages
over a network.
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Internet protocol stack
Point-to-Point Protocol, a method of connecting a
computer to the Internet. PPP is more stable than
the older SLIP protocol and provides error
checking features. Working in the data link layer
of the OSI model, PPP sends the computer's TCP/IP
packets to a server that puts them onto the
Internet.
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Internet protocol stack
Synchronous Optical Network, a standard for
connecting fiber-optic transmission systems.
SONET defines interface standards at the
physical layer of the OSI seven-layer model.
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Internet protocol stack
Asynchronous Transfer Mode, a network technology
based on transferring data in cells or packets of
a fixed size.
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Internet protocol stack
The standard for full-duplex modems sending and
receiving data across phone lines at up to 28,800
bps. V.34 modems automatically adjust their
transmission speeds based on the quality of the
lines.
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Features of IP Telephony

• Adjustable quality
• Security
• User Identification
• User Interface
• Computer-Telephony integration
• Feature Ubiquity
• Multimedia
• Silence Suppression and Compression
• Shared Facilities and advanced services
• Separation of voice and control flow

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IPTel Requirements

• Sequencing
• Intra-media synchronization
• Inter-media synchronization
• Payload identification
• Frame indication
• Multicast-friendly
• Media-independent
• Mixers and Translators
• QoS Feedback
• Loose Session control
• Encryption

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Real Time Protocol
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Real-Time Control Protocol

• Companion control protocol for RTP.
• Sender Report, Receiver Report, Source
  Description.
• Participants send RTCP packets periodically.
• Ensures bandwidth used for RTCP reports is fixes
  independent of the group size.
• RTCP provides the following services Q0S
  monitoring and congestion control, source
  identification, inter-media synchronization,
• RTCP can be used for resource reservation also.

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Session Initiation Protocol- SIP

• SIP is the IPTelephony signaling protocol
• Name Translation and User Location
• Feature Negotiation
• Call Participant Negotiation
• Feature Changes

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Overview of SIP

• Client-server text-based protocol used over UDP
  or TCP
• User Agent Server SIP enabled end-system
• Proxy Servers
• Redirect Servers
• SIP Entities Logical connection source, Logical
  connection destination, Media destination, Media
  capabilities
• SIP methods INVITE, BYE, OPTIONS, STATUS, ACK,
  CANCEL, REGISTER

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SIP Proxy Server Operation
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SIP Redirect Server Operation
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Telephony services using SIP

• SIP doesnt explicitly describe the
  implementation of a particular service.
• Uses headers (Ex. Also, Replaces) and methods
  (Ex. STATUS) to construct the services .
• Example of Call Forwarding Service

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Multi-party protocols

• Via network-level multicast
• Via one or more bridges (multipoint control
  units)
• Mesh of unicast connections

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Additional protocols

• IP host communicates with a GSTN endpoint using
  an Internet Telephone Gateway (ITG)
• WASRV Wide Area Service Location server
• Real Time Streaming Protocol (RTSP) establishes
  and controls streams of continuous audio and
  video between the media servers and the clients.

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Protocol Integration
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IPTel versus GSTN

• IPTel - End to end paradigm
• IPTel - Separates call setup from resource
  reservation
• IPTel - Addresses for end-point identification
  and basic service indication
• IPTel - Better scaling for services
  (Authenticated caller ID etc.)
• IPTel - No UNI/NNI distinction both at signaling
  and transport
• IPTel - Components can be provided by different
  vendors.

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Conclusion

• Paper presents the protocols that support IP
  telephony RTP for transport, SIP for signaling,
  RTSP for stored media retrieval.
• IPTel has to overcome unpredictable QoS in the
  wide area, the lack of reliable and cheap end
  systems, Internet and the lack of billing
  infrastructure.

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Internet Telephony Gateway Location
Part II

• Jonathan Rosenberg and Henning Schulzrinne
• Bell Laboratories and Columbia University
• IEEE Infocom 98

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Scenarios
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Problem Statement

• For PC to PSTN case, PC must determine the IP
  address of the remote gateway.
• For PSTN to PSTN case, local gateway must
  determine the IP address of remote gateway
• Need mechanism to assist in such location
• Gateway selection is an application layer
  routing problem

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BMA Architecture
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Conclusions

• Gateway discovery is an important piece of the IP
  telephony puzzle
• Gateway discovery is a multicriteria selection
  problem
• Supporting client based selection is an important
  value-added service
• BMA Architecture is a scalable, fast, efficient,
  and feature rich method for locating gateways

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REFERENCES

• "Internet Telephony, Architecture and Protocols
  an IETF Perspective, H.Schulzrinne, J.
  Rosenberg, Computer Networks and ISDN Systems,
  Febuary 11, 1999, vol 31/3 pp. 237-255.
• " Internet Telephony Gateway Location", H.
  Schulzrinne, J. Rosenberg, Proceedings of IEEE
  Infocom 1998, March 29 - April 2, San
  Francisco,CA, USA.PPT Slides PDF Slides
• Some information for Internet.com
• Other resources