International Telecommunication Union
VoIP Signaling Protocols
Framework
N. Rajagopal,
MindTree Consulting Pvt Ltd
ITU-T and ITU-D Workshop
Bangalore (India), 30-31 August 2001
Agenda
o
o
o
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H.323
MGCP/MeGaCo
SIP
Deployment scenarios in India
Summary
ITU-T and ITU-D Workshop - Bangalore (India), 30-31 August 2001
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H.323 Family of protocols
o ITU Recommendation
• V1 approved in 1996, V2 in 1998
o Defines multimedia applications over
packet based networks
o Originally developed for voice over
LANs
o Widely deployed
31.05.2016
ITU-T and ITU-D Workshop - Bangalore (India), 30-31 August 2001
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H.323 Protocol Stack
o Peer to Peer nature
o Family of protocols
o H.225.0: Call signaling
o H.225.0 RAS
o H.245 Conference control
o RTP/RTCP for transport
31.05.2016
ITU-T and ITU-D Workshop - Bangalore (India), 30-31 August 2001
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H.323 Components
H.323 MCU
H.323
Gatekeeper
H.323
Terminal
LAN
H.323
Gateway
PSTN
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ISDN
ITU-T and ITU-D Workshop - Bangalore (India), 30-31 August 2001
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MGCP
o
o
o
o
o
Media Gateway Control Protocol
Based on master –slave architecture
“Call agent” – master
“Media gateways” – slave
Call agent
• Setups the calls between end points
o Media gateways
• Does IP <-> voice media conversion
31.05.2016
ITU-T and ITU-D Workshop - Bangalore (India), 30-31 August 2001
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MGCP Protocol stack
o RFC 2705
o Supports “packages” for different
applications
• DTMF, Trunking
• IVR, Media Server
o Uses RTP/RTCP for transport
o Designed for TCP/IP network
o Text based messages
31.05.2016
ITU-T and ITU-D Workshop - Bangalore (India), 30-31 August 2001
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MGCP Network architecture
Call Agent
Trunking
Gateway
IP Network
Network
IP
Trunking
Gateway
Media Gateway
Analog Phones
31.05.2016
ITU-T and ITU-D Workshop - Bangalore (India), 30-31 August 2001
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MeGaCo
o Media Gateway Control Protocol
o Similar to MGCP
o More complete
• Flexibility
• Extensibility
o Video support
o Other transport support
• ATM
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ITU-T and ITU-D Workshop - Bangalore (India), 30-31 August 2001
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SIP
o Session Initiation Protocol (RFC 2543)
o Management of multimedia sessions
o Simple, easy protocol
• 6 messages to get started
o Uses RTP for media transport
o Lots of extensions being proposed
o Standards evolving
o Possibility of different services
o Good potential
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ITU-T and ITU-D Workshop - Bangalore (India), 30-31 August 2001
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Comparison between
Protocols
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Protocol->
H.323
MGCP/MeGa
Co
SIP
Purpose
Multimedia
conferencing;
Media
gateway
control
Multimedia
conferencing
Defined by
ITU-T
IETF
IETF
Complexity
High (multiple
protocols:
H.225.0 for
signaling, H.225
RAS for GK
communication,
H.245 for call
signaling
Moderate
Simple (6
messages)
Endpoint
requirements
Intelligent
Dumb (POTS
will do)
Intelligent
PSTN
connectivity
thru
Gateway
Media
Gateway +
Signaling
Gateway
Outbound
proxy
ITU-T and ITU-D Workshop - Bangalore (India), 30-31 August 2001
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Comparison between
protocols (cont’d)
Number of
messages
H.323/100+
MGCP/~10
SIP/6
Type of messages
Binary
Text, readable
Text, readable
SDP
SDP
Media description
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Voice Transport
RTP
RTP
RTP
Signaling transport
TCP
UDP
UDP/TCP
Capabilities
H.245 for
capabilities
exchange to support
different transfers
Limited
SDP; limited
abilities
Extensibility
Difficult
Easy
Easy
Remarks
Legacy; Need to
support for today’s
networks
May get relegated
to trunking after
widespread
deployment of SIP
Likely Signaling
protocol of future!
ITU-T and ITU-D Workshop - Bangalore (India), 30-31 August 2001
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Deployment Scenarios in
India
o H.323
• LAN Telephony
• Inter office PSTN toll bypass
• Remote office connectivity
• IP Phones
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ITU-T and ITU-D Workshop - Bangalore (India), 30-31 August 2001
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Deployment scenarios in
India
Office 1
Office 2
IP
Network
Leased
lines
IP
Phone
PC
Office 3
PC
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IP Phone
PC
ITU-T and ITU-D Workshop - Bangalore (India), 30-31 August 2001
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Deployment scenarios in
India
o SIP
• Experimental
• Promises are high
• Windows XP support – ubiquitous
o Likely areas of usage
• Desktops
• LAN telephony
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ITU-T and ITU-D Workshop - Bangalore (India), 30-31 August 2001
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Deployment scenarios in
India
o SIP
• Services
• Presence, messaging
• Integrated services
• Productivity improvement
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ITU-T and ITU-D Workshop - Bangalore (India), 30-31 August 2001
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Deployment scenarios in
India
o SIP
• Call Centers
PC
Phone
Call Desk
Network
Cabling
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PC
Phone
Cabling
PC with SIP
Call Desk
Network
Cabling
ITU-T and ITU-D Workshop - Bangalore (India), 30-31 August 2001
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Deployment scenarios in
India
o MGCP
• Cable telephony
• MTU telephony
Headend
(CallAgent)
TV
Set Top
Box (Media
Gateway)
Ethernet
POTS
Home
Cable
PSTN
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ITU-T and ITU-D Workshop - Bangalore (India), 30-31 August 2001
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Summary
o H.323, SIP, MGCP all have their space in
o
o
o
o
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VoIP space
Likely coexistence
“Softswitch architecture” to control the
elements in VoIP network
“Services” will be key differentiator for
customer
CLECs/new generation service providers
likely to go for softswitch based solution
ITU-T and ITU-D Workshop - Bangalore (India), 30-31 August 2001
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References
o http://www.softswitch.org
o http://www.ietf.org
o http://www.sipcenter.org
o http://www.cs.columbia.edu/sip
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ITU-T and ITU-D Workshop - Bangalore (India), 30-31 August 2001
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