Transcript Internet Telephony

Internet Telephony
 Introduction
 What is it?
 History
 IP Telephony v. PSTN
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IP Telephony v PSTN
Data Packet Switched
Circuit Switched
 Calls broken to pieces
and sent to
 Dedicated circuit for
destination
 Better use of network
capacity
 Data Network 80%
reliable
 Downtime is 4 hours
per month (Data
Communications)
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each call
 Telephone Network
99.999% reliable
 Downtime measured
in seconds per year
 Regulation
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Voice Gateways
 Physical interface
 Placed between PSTN and IP
Network
 Handles
 signaling to and from telephone network
 reception of telephone numbers
 conversion of tel nos to IP addresses
 voice processing
 reception of voice signal
 compression(to reduce bandwidth and
delay impact from Network) and
packetization
 echo cancellation
 silence suppression
 No of gateways crucial - around 500 in
existence
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IP Telephony
Network
Gatekeeper
IP
Network
R
T
ISDN
PSTN
PSTN
R
T
Gateway
R
T
R
T
Gateway
Gateway
Gateway : Bridge between PSTN & IP Networks
Gatekeeper : Admission control for network
Bandwidth control and management
Address translation (E.164 <-> IP address)
Call Management
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IP Telephony
Services
 Encompasses
phone-to-phone
phone-to-PC
PC-to-PC
fax-to-fax
video conferencing
desktop collaboration
 Software such as
Microsoft NetMeeting
DeltaThree’s DotDialer
IDT’s Net2Phone
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Standards
 Why do we need them?
 The benefits of standardisation
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Interoperability
billing, settlement and reconciliation
uniformity for carriers
marketability
 Currently
• no standards for signaling
• no standard agreement on accounting
records or billing
 These issues being handled through
maturing standards such as ITU’s
• H.323
• Tiphon
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H.323-The Vendors
Choice?
 H.323 recommends G.723
• compresses voice to 5.3 or 6.3 kbit/s
 Some using GSM algorithm
• compresses to 13.3 kbit/s, appears to
provide superior quality to G.723
 Tiphon
• based on H.323
• specifies network architecture,
numbering, supplementary services
integration
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Security
 Initially somewhat overlooked, now being
raised by carriers and business users
 Security Issues
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User and data authentication
Data privacy (integrity, confidentiality)
Access control
Policy management
 Security Measures
• Encryption
– SSL (secure sockets layer)
– TLS (transport layer security)
• Tunnelling
– Layer 2 Tunnelling Protocol (L2TP)
– establish a secure tunnel between
gateways or gatekeepers
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Encryption
 SSL, TLS on transport level, suitable for
Gatekeeper-to-gatekeeper, but not if unreliable,
connectionless UDP transports the voice
 IETF IPsec working group describes security
architecture for IP protocol that makes it suitable
for secure VPN
authenticates users
encrypts payload
tracks who has changed packet
 Incorporated in H.323 V2 via H.235 also called H
Secure
 Encryption Problems
Political/military issues (limits on keys etc)
Hardware issues (processing power)
 Dealing with security issues
 US Chamber of commerce announced automatic
approvals for financial institutions
 Therefore encryption more readily available??
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Effect on the Traditional
Communications
Companies
 Telecommunications or
information service?
 Telecommunications Act 1996
promote competition
facilitate new
telecommunications technologies
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Economics
 Cost savings dependent on the
provider and location
 Calls between London and
Tokyo around 30 cents per
minute ($1 per minute for
POTS)
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The Future
 Market predicted to grow to $560 million
by end of 1999
 By 2002, 3% of US long-distance traffic,
5% of European long-distance traffic,
14% of US international traffic and 11%
of European international traffic
 Not economic but service benefit
 Used with video and data sharing for
multi-media communications
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