VoIP

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VoIPVoice over Internet Protocol

• EE290F Spring 2004
• Xiaoxue Zhao

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Content

• PSTN-Public Switch Telephone Network
• Packet-Switched Network
• Comparison between PSTN and IP Network
• VoIP Standards
• VoIP Services
• QoSQuality of Service

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PSTNComponents

• Access Lines (Local Loops)
• Connects customer premises to the local voice
  switch
• Switches
• Connect access line to each other
• Trunks
• Connects voice switches to each other
• PBXPrivate Branch Exchange
• SignalingConnectionless PSTN
• Used for basic call set up, management, tear
  down and enhanced call features etc.

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PSTNStructure
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PSTNFeatures

• Connection-Oriented, Circuit-Switched
• Guaranteed Bandwidth
• All the bandwidth all the time.
• Stable Delays

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Packet-Switched Network

• PacketUnit of data containing the network
  address information
• Network Layers
• Best effort

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Virtual Circuits
Virtual Circuit Data
Design philosophy Connection-oriented Connectionless
Addressing entity Circuit identifiers Node and network addresses
Unit of information Packet, frame, cell Packet, frame, cell
Network entities Switches Routers
Bandwidth use All allowed by network Depends on number and size of frames
Examples Frame relay, X.25, ATM, most other WANs Internet Protocol (IP), Ethernet, most other LANs
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Comparison
Network Features PSTN (Voice) Internet (Data)
Switch Circuit Switched Packet Switched
Connection Connection Oriented Connectionless
Bit Rate Fixed and low lt64kb/s Wide variation to Gb/s
Bursts Nonexistent High (100/10001)
Error tolerance User error control Error free
Info resending Can not (real time) Can be done very fast
Delay Must be low and stable Can be high and vary
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Packetizing Voice
VoIP Issues Solutions
Packetizing delay Small packets for VoIP
Serial delay Priorities and jitter buffers
High bit-rate voice (64kb/s) Voice compression
Constant-bit-rate voice (PMC) Silence suppression and comfort noise
Resend due to errors Real-time Transport Protocol (RTP)
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Why VoIP?

• Cost Reduction
• Simplicity
• Advanced Applications
• Web-enabled call centers
• Collaborative white boarding
• Remote telecommuting

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VoIP Standards

• H.323ITU-T
• Session Initialization Protocol (SIP)IETF

Voice Coding Methods (ITU-T G series, etc.) Voice Coding Methods (ITU-T G series, etc.)
Call Control/Session Initialization (H.225, H.245, SIP) Call Control/Session Initialization (H.225, H.245, SIP)
Timing (RTP) Gateway/Gatekeeper Control (GLP, MGCP)
Reliable/Unreliable Transport services (TCP/UDP) Reliable/Unreliable Transport services (TCP/UDP)
Internet Protocol (IP) Internet Protocol (IP)
Packet Network Infrastructure Packet Network Infrastructure
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H.323

• Packet-Based Multimedia Communications Systems
• H.323 Architecture
• H.323 for IP Telephony

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H.323 Architecture
LAN
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H.323 for IP Telephony
Video Video Audio Audio Control Control Control Data
H.261 H.263 (video coding) H.261 H.263 (video coding) G.711 G.722 G.723 G.728 G.729 G.711 G.722 G.723 G.728 G.729 H.225 Terminal to gatekeeper signaling H.225 Call signaling H.245 T.120 (Multipoint data transfer)
RTP (Real-time Protocol) RTCP (Real-time Control Protocol) RTP (Real-time Protocol) RTCP (Real-time Control Protocol) H.225 Terminal to gatekeeper signaling H.225 Call signaling H.245 T.120 (Multipoint data transfer)
Unreliable transport (UDP) Unreliable transport (UDP) Unreliable transport (UDP) Unreliable transport (UDP) Unreliable transport (UDP) Reliable transport (TCP) Reliable transport (TCP) Reliable transport (TCP)
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SIP

• Proposed by Internet Engineering Task Force
  (IETF)
• Application layer control protocol
• Borrow design and architecture from the Hypertext
  Transfer Protocol (HTTP)

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VoIP Services

• Self-provided Customer
• Independent of Internet access
• Provided by broadband access service provider
• Corporate Internal Use on Business LAN / WAN
• Carrier Internal Use

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Self-Provided Customer

• IP connection
• Voice-enabled device
• Examples Skype, MSN

Address Info
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Independent of Internet Access

• Customer in agreement with IP telephony company,
  independent of ISP
• Uses gateway to connect to PSTN
• Calls can be made to either VoIP users or PSTN
  users
• IP connection and Voice-enabled device
• Examples Vonage, Packet8, Net2Phone

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Provided by Broadband Access Service Provider

• Customer in agreement with IP telephony company
  with is also ISP
• Uses gateway to connect to PSTN
• Provider is in control of the network so offer
  quality guarantees
• Analogue terminal adapters are provided
• Example Yahoo!BB (Japan)

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Corporate Internal Use on Business LAN / WAN

• No service provider
• In-house telephony on LAN or WAN
• Services are those of a full-featured PBX

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Carrier Internal Use

• Softswitch instead of circuit switch, including
  H.323 gatekeeper or SIP server
• Most based on H.323
• Mostly in international calls

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QoSQuality of Service
QoS Parameters

• Bandwidth
• Delay
• Jitter (Delay Variation)
• Information Loss
• Reliability
• Security

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References

• IP Telephony Walter J. Goralski and Matthew C.
  Kolon McGraw-Hill
• Final Report for the European CommissionIP Voice
  and Associated Convergent Services