Voice over IP
Need more gateways that connect IP network to phone
networks
The IP network could be dedicated intra-net or the
Internet.
The phone networks could be intra-company PBXs or
the carrier switches
Phone
Network
Gateway
Voice over IP
IP
Raj Jain
The Ohio State University
Columbus, OH 43210
[email protected]
http://www.cis.ohio-state.edu/~jain/
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Overview
Sample Products and Services
13 Technical Issues
4 Other Issues
H.323 Standard
Session Initiation Protocol (SIP)
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Scenario 1: PC to PC
IP
Network
Need a PC with sound card
IP Telephony software: Cuseeme, Internet Phone, ...
Video optional
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Scenario 2: PC to Phone
IP Phone
Network Network
Gateway
Need a gateway that connects IP network to phone
network (Router to PBX)
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Scenario 3: Phone to Phone
Phone IP Phone
Network Network Network
Gateway Gateway
Need more gateways that connect IP network to phone
networks
The IP network could be dedicated intra-net or the
Internet.
The phone networks could be intra-company PBXs or
the carrier switches
Raj Jain
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Sample Products
VocalTec Internet Phone: PC to PC.
Microsoft NetMeeting: PC to PC. Free.
Internet PhoneJACK: ISA card to connect a standard
phone to PC. Works with NetMeeting, InternetPhone
etc. Provides compression.
Internet LineJACK: Single-line gateway.
Micom V/IP Family:
m Analog and digital voice interface cards
m PC and/or gateway
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Products (Cont)
PBX Gateway
PC w Router IP Network
V/IP S/w
m Features:
q Compression
q Phone number to IP address translation.
q Supports RSVP.
q Limits number of calls.
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Products (Cont)
VocalTec Internet Telephony Gateway:
m Similar to Micom V/IP
m Interactive voice response system for problem
reporting
m Allows WWW plug in
m Can monitor other gateways and use alternate
routes including PSTN
m Sold to Telecom Finland. New Zealand Telecom.
Lucent's Internet Telephony Server: Gateway|
Lucent PathStar Access Server
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Products (Cont)
CISCO 2600 Routers: Voice interface cards (VICs)
Reduces one hop.
Baynetworks, 3COM, and other router vendors have
announced product plans
PBX Router IP Network
PC
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Sample Services
IDT Corporation offers Net2Phone, Carrier2Phone,
Phone2Phone services.
Global Exchange Carrier offers international calls
using VocalTec InternetPhone s/w and gateways
Qwest offers 7.5¢/min VOIP Q.talk service in 16
cities.
ITXC provides infrastructure and management to
'Internet Telephone Service Providers (ITSPs)'
America On-line offers 9¢/min service.
AT&T announced 7.5¢/min VOIP trials in 9 US cities
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Services (Cont)
Other trials: USA Global link, Delta 3, WorldCom,
MCI, U.S. West, Bell Atlantic, Sprint, AT&T/Japan,
KDD/Japan, Dacom/Korea, Deutsche Telekom in
Germany, France Telecom, Telecom Finland, and
New Zealand Telecom.
Level 3 is building a nation wide IP network for
telephony.
Bell Canada has formed 'Emergis' division.
Bellcore has formed 'Soliant Internet Systems' unit
Bell Labs has formed 'Elemedia' division
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Technical Issues
. Large Delay
m Normal Phone: 10 ms/kmile ⇒ 30 ms coast-to-
coast
m G.729: 10 ms to serialize the frame + 5 ms look
ahead + 10 ms computation = 25 ms one way
algorithmic delay
m G.723.1 = 100 ms one-way algorithmic delay
m Jitter buffer = 40-60 ms
m Poor implementations ⇒ 400 ms in the PC
m In a survey, 77% users found delay unacceptable.
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Technical Issues (Cont)
. Delay Jitter: Need priority for voice packets.
Shorter packets? IP precedence (TOS) field.
. Frame length: 9 kB at 64 kbps = 1.125 s
Smaller MTU ⇒ Fragment large packets
. Lost Packets: Replace lost packets by silence,
extrapolate previous waveform
. Echo cancellation: 2-wire to 4-wire.
Some FR and IP systems include echo suppressors.
IP/Phone
PBX Network PBX
Reflection Reflection Raj Jain
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Technical Issues (Cont)
. Silence suppression
. Address translation: Phone # to IP. Directory servers.
. Telephony signaling: Different PBXs may use differen
signaling methods.
. Bandwidth Reservations: Need RSVP.
0. Multiplexing: Subchannel multiplexing
⇒ Multiple voice calls in one packet.
1. Security: Firewalls may not allow incoming IP traffic
2. Insecurity of internet
3. Voice compression: Load reduction
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Other Issues
. Per-minute distance-sensitive charge vs
flat time-insensitive distance-insensitive charge
. Video requires a bulk of bits but costs little.
Voice is expensive. On IP, bits are bits.
. National regulations and government monopolies
⇒ Many countries forbid voice over IP
In Hungary, Portugal, etc., it is illegal to access a web
site with VOIP s/w. In USA, Association of
Telecommunications Carriers (ACTA) petitioned FCC
to levy universal access charges in ISPs
. Modem traffic can’t get more than 2400 bps.
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Telephony/Conferencing Systems
Multiplexing/Demultiplexing
Video I/O Video
Equipment Codec
Audio I/O Audio
Equipment Codec
Network
Interface Network
Data Data
Application Protocol
System Control
Control Protocol
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Conferencing Standards
Network ISDN ATM PSTN LAN POTs
Conf. Std. H.320 H.321 H.322 H.323 V1/V2 H.324
Year 1990 1995 1995 1996/1998 1996
Audio G.711, G.711, G.711, G.711, G.723.1,
Codec G.722, G.722, G.722, G.722, G.729
G.728 G.728 G.728 G.723.1,
G.728, G.729
Audio Rates 64, 48-64 64, 48-64, 64, 48-64, 64, 48-64, 16, 8, 5.3/6.3
kbps 16 16 8, 5.3/6.3
Video H.261 H.261, H.261, H.261 H.261
Codec H.263 H.263 H.263 H.263
Data Sharing T.120 T.120 T.120 T.120 T.120
Control H.230, H.242 H.242, H.245 H.245
H.242 H.230
Multiplexing H.221 H.221 H.221 H.225.0 H.223
Signaling Q.931 Q.931 Q.931 Q.931 -
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H.323 Protocols
Multimedia over LANs
Provides component descriptions, signaling
procedures, call control, system control, audio/video
codecs, data protocols
Video Audio Control and Management Data
G.711, G.722, H.225.0 H.225.0 H.245 T.124
RTCP
H.261
G.723.1, G.728, RAS Signaling Control
H.263
G.729
RTP X.224 Class 0 T.125
UDP TCP T.123
Network (IP)
Datalink (IEEE 802.3)
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H.323 Components
Terminals Gatekeeper Multipoint Control
Unit
SDN Firewall H.32
Router Proxy
STN
Router To Internet
TM
Gateway Raj Jain
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H.323 Gatekeepers
Provide call control services to registered end points.
One gatekeeper can serve multiple LANs
Address translation (LAN-IP)
Admission Control: Authorization
Bandwidth management
(Limit number of calls on the LAN)
Zone Management: Serve all registered users within
its zone of control
Forward unanswered calls
May optionally handle Q.931 call control
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