VoIP

1
VoIP

• Advanced Networks

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Content

• Introduction
• Standard/Protocol
• Applications
• QoS
• Future
• Q A Session

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Why VoIP?

• Circuit switching was designed for voice
• Circuit switching is an expensive solution
• Not a effective way to transfer data
• IP is an attractive choice for voice transport
  because
• Low Requirement Cost
• Integration of voice and data applications
• Lower Bandwidth

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VoIP Standard/Protocol

• There are two main standards for VoIP
• H.323
• SIP

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H.323

• Specify technical requirement for real-time audio
  and video over LANs
• Establish by ITU (International
  Telecommunication Union)

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H.323 Architecture (1)

• Involves with four main components
• Terminals
• Gateways
• Gatekeepers
• Multipoint Controller Units (MCUs)

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H.323 Architecture (2)
PSTN
ISDN
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H.323 Call Setup Tear Down
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H.323 Protocol Stack
Audio I/O
Video I/O
System Control Unit
Data I/O
H.225.0 Q.931 Call Signaling
H.245 Control Signaling
H.225.0RAS
Audio Codec
Video Codec
RTCP
T.120Data
RTP
UDP
TCP
Network Layer
Data Link Layer
Physical Layer
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SIP

• Session Initial Protocol
• Application Layer Control Protocol for Internet
  telephony service
• Architecture similar to Hypertext Transfer
  Protocol (HTTP)

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SIP Components

• Two Major Parts

• Client Side
• Terminal User Agent Client (UAC)

• Server Side
• 3 types of server User Agent Server (UAS) a)
  Registration Server b) Proxy Server c)
  Redirect Server

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SIP Messaging Syntax (1)

• SIP Request 6 Methods
• INVITE
• ACK
• OPTIONS
• BYE
• CANCEL
• REGISTER

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SIP Messaging Syntax (2)

• SIP Response
• First line of response is status line
• Contains 3 digit number status code
• 1XX - Informational (e.g., 100 Trying)
• 2XX - Success (e.g., 200 OK)
• 3XX - Redirection (e.g., 380 Alternative service)
• 4XX - Request Failure (e.g., 404 Not Found)
• 5XX - Server Failure (e.g., 504 Gateway timeout)
• 6XX - Global Failure (e.g., 606 Not acceptable)

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Sample SIP Operation
Caller
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Comparison H.323 Vs SIP
H.323
SIP
Original Approach

• Circuit-Switching Network

• Lightweight Internet

Complexity
Compatibility

• Need full backwards compatibility

Advantage

• Current large share market

• Backed by IETF

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Voice Codec (Coder/Decoder)

• Not only provide analog-to-digital conversion
• But also apply sophisticated predictive patterns
  to analyze voice input transmit using minimum
  bandwidth
• By encoding speech samples into smaller bits, it
  can make the speech in a robust way
• In the presence of Link Errors, Jittery Networks
  Bursty transmissions.

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Types of Speech Coders

• Waveform Coding
• Reproduce the analog waveform with background
  noise.
• Since operating on all input signals, produce
  high quality samples
• Vocoding (Source Codec)
• Do not reproduce original waveform
• Encoders builds a set of parameters, sent to
  receiver to drive a speech production model.
• Hybrid Coding
• Melds attractive features of waveform coding
  vocoding
• Operate at very low bit rate (4-16 bit/s)

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Pulse Code Modulation (PCM)

• Waveform codec
• 2 basic variations of 64kbps A-law,Mu-law
• Use logarithmic compression to achieve 12-13 bits
  of linear PCM quality in 8 bits.

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Code Excited Linear Prediction (CELP)

• Use pre-stored codebook of optimized parameters
  to encode a representative vector of the input
  speech signal.

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Summary Of Different Compression Method
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Codec Evaluation

• Frame Size
• Processing Delay
• Lookahead Delay
• Frame Length
• Voice Bit Rate
• DSP MPS
• Required RAM
• Time Required for encoding.(One-way latency)
• Sum of frame size processing delays lookahead
  delay

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What is ENUM?

• ENUM Telephone Number Mapping
• Function for mapping E.164 numbers into Uniform
  Resource Identifiers (URIs) corresponding to
  communication applications associated with those
  numbers
• Fully Qualified E.164 numbers County Code
  Area Code Telephone NumberExample 44 113 496
  0000
• E.164 numbers can be used to provide calling
  users with a variety of addresses, including
  those used for phone, fax and email, by which the
  called user can be contacted

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Possible Applications Associated with E.164
numbers
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Sample call flow from IP based network to
switched circuit network
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QoS for VoIP

• There are 2 approaches
• IntServ Approach
• DiffServ Approach

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The DiffServ Approach

• Discriminates and treats data flows according
  to their traffic classes
• Based upon traffic contracts agreed at each
  edge of network
• Within the domain the service provider is
  responsible
• Traffic Conditioning Agreements (TCA) between
  domains
• Service Level Agreements (SLAs) in the DiffServ
  network
• Packets get marked (DiffServ Codepoint) at the
  ingress to specify the traffic class
• The network selects the appropriate per-hop
  behavior(PHB) for each packet

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Scenario of DiffServ
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Per-hop Behaviors (PHBs)

• Describes the forwarding behavior of a DS node
  applied to a particular DS behavior
  aggregate(packets having same DSCP)
• Implemented at nodes through buffer management
  and packet scheduling
• Multiple PHBs grouped together to form a PHB
  group
• There are 2 PHB types
• Assured forwarding
• Expedited forwarding

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Marking packets for DiffServ

• IPv4
• IPv6
• same as TOS
  of IPv4

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Expedited Forwarding

• Also known as Premium Service
• Similar to Virtual leased line
• Guarranteed minimum service rate
• Policed Arrival rate lt Minimum Service Rate
• ?no queuing delay, jitter
• Not affected by other data PHBs
• ÞHighest data priority (if priority queueing)
• DS Code point 101 110

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Security of VoIP

• ITU-T for H.323 (using H.235)
• IETF for SIP (using general purpose security
  mechanisms)

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Issues and Solution
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VPN for data, voice and video (IPSec tunnels)
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Other Solution of Security

• Firewall
• Policy and filter the traffic
• SIP Proxy Server
• Provide authentication
• External RADIUS Server
• Proxy itself

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VOIP is a trend

• Networks trend
• Technical trend of VoIP

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Networks Trend

• Todays world, voice network, cellular networks,
  and data networks tend to be separate
• In the future, networks are going to converge.

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Technical trend of VoIP

• High-speed switching and transmission technology
• Paradigm shift of information communication
• Packetizing voice
• Computer Telephony Interface (CTI )

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Current Market Status

• ATT
• ATT Managed Internet Service
• ATT Managed Router Service
• BT
• VoIP VPN multimedia calling service
• Public VoIP multimedia calling

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Q A Session

• Any Questions?

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End of Presentation

• Thank you