Chapter 17 Voice over IP

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Chapter 17Voice over IP

• Information Technology in Theory
• By Pelin Aksoy and Laura DeNardis

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Objectives

• Understand the concept of VoIP and how it enables
  the transmission of voice over the Internet
• Gain familiarity with VoIP protocols such as SIP,
  H.323, and RTP
• Understand options for implementing voice over
  the Internet

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Objectives (continued)

• Recognize the business drivers and advantages of
  using VoIP rather than traditional telephone
  system architectures
• Understand the security and performance
  challenges of VoIP and consider various solutions
• Identify the policy questions arising from the
  proliferation of VoIP services

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VoIP

• VoIP Voice over Internet Protocol
• Also called Internet telephony or IP telephony
• Refers to voice communications transmitted over
  the Internet or other IP network, as opposed to
  the public switched telephone network

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Voice over the Internet

• Many businesses, institutions, and individual
  users place telephone calls over the Internet
• Rather than through a traditional telephone
  network, completely bypassing the
  circuit-switching approach of the telephone
  system
• A VoIP call does not necessarily remain solely on
  the Internet or other TCP/IP network
• Uses packet switching, not circuit switching

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VoIP Protocols

• A set of standards designed for transmitting
  voice calls over the Internet or other IP network
  
• VoIP calls have several functional components
• The signaling information that establishes the
  telephone call
• The process that digitizes the audio signal and
  places the information into packets
• The process of actually transmitting the
  packetized speech

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VoIP Protocols (continued)
Voice communication over the Internet
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Signaling Protocols

• Signaling protocols assess user availability,
  ring the destination device, establish a call,
  and terminate a call session
• Two of the most well-known VoIP signaling
  protocols
• The Session Initiation Protocol (SIP), developed
  by the IETF
• H.323, a family of standards developed by the ITU

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Session Initiation Protocol

• SIP is a signaling protocol that creates,
  manages, and terminates multimedia sessions
  between end-user devices, such as two telephones
• A session is a voice conversation or other
  exchange of information between users
• SIP operates at the Application layer of the OSI
  model using an information exchange that is
  similar to HTTP

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Session Initiation Protocol (continued)
Establishment of a VoIP session using SIP
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SIP Functions

• End-user locationFind the end-user location with
  which to communicate
• End-user availabilityDetermine whether the end
  user is available and willing to engage in
  conversation
• End-user capabilityDetermine what type of media
  content will be used and what constraints might
  be in effect
• Session setupEstablish the session between
  parties (also called ringing)
• Session managementHandle changes to the
  communication session while the call is in
  process and terminate the session upon completion

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H.323

• An ITU-developed signaling standard for
  multimedia communications over the Internet and
  other IP networks
• The first widely implemented signaling protocol
  that supported real-time voice and video over IP
  networks
• Strictly speaking, H.323 is actually a series of
  many protocols

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VoIP Transport Protocols

• Handle the transmission of the voice call between
  endpoints
• Real-time Transport Protocol (RTP) is a popular
  VoIP transport protocol

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Real-Time Transport Protocol

• Known by its acronym, RTP
• Establishes the standard for end-to-end
  transmissions that carry actual digitized speech
  in packets
• Designed to transport voice, video, and other
  information that have real-time properties

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Implementation Options

• Soft phones
• Analog telephony adapters
• IP phones
• Wi-Fi phones
• Residential VoIP offerings
• Business VoIP alternatives

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Soft Phones

• Install VoIP software on a computer and use it
  with a headset to make a voice call
• Requires
• Headset (or microphone and speakers)
• Sound card
• Freely available VoIP software
• Broadband Internet connection

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Soft Phones (continued)
Computer-to-computer Internet telephony with soft
phones
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Soft Phones (continued)
Computer-to-computer Internet telephony via
cordless telephone
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Analog Telephony Adapters

• This device serves as an analog-to-digital
  converter (ADC) between an analog phone and an
  Ethernet network connection to an IP network
• Other analog devices, like fax machines, can also
  be plugged into the ATA
• This option does not require the installation of
  VoIP software on a computer

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Analog Telephony Adapters (continued)
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IP Phones and Wi-Fi Phones

• An IP phone connects directly to an IP network
  without an adapter because it internally converts
  the telephone audio signal into digital format
  for transmission over the IP network
• Has the same features traditional phones provide
  including, speed dial, voice mail, call
  forwarding, and conferencing
• Also supports non-voice information

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IP Phones and Wi-Fi Phones (continued)

• Some IP phones, called Wi-Fi phones, are
  wirelessthey can connect to the Internet via a
  Wi-Fi connection

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IP Phone
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Wi-Fi Phones
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Analog Telephony Adapters
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Residential Broadband VoIP Services

• Services provided by local cable provider or
  phone company
• Work with existing phone jacks and phones
• Offer unlimited voice for fixed monthly fee
• Requires a high-speed Internet connection
• Allow users to retain their existing phone number

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Residential Broadband VoIP Services

• Offer the advanced features of any phone service
  
• Voice mail
• Call waiting
• VIP ringing
• Caller ID and caller ID blocking
• Call forwarding
• 69 call return
• Multiple party calling
• Anonymous call blocking

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Residential Broadband VoIP Services (continued)
Commercial VoIP services seamlessly interoperate
with other voice services
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Business VoIP Options

• Organizations that implement VoIP can choose from
  one of several alternatives
• They can completely replace existing phone
  systems with VoIP systems
• They can adopt a hybrid approachadding some IP
  components in current systems or running some
  completely VoIP-based systems and some
  traditional phone systems, with a gateway between
  the two systems to interface them

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Business VoIP Options (continued)

• One option for business VoIP implementations is
  to use an IP PBX (IP-based private branch
  exchange)
• VoIP implementations can use an IP PBX as an
  option for processing VoIP calls
• Another option is to implement a router-based
  VoIP architecture
• A PBX-based approach is usually a more
  centralized design, while the router approach is
  more distributed

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Private IP Network
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Internet Telephony Benefits

• Two primary drivers
• Cost savings
• Network unification

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Cost Savings

• Rather than paying a per-minute or per-unit fee
  for calls, VoIP customers usually pay a fixed
  monthly fee (or nothing)
• Customers can make unlimited calls, participate
  in multiparty teleconferencing, and make
  facsimile transmissions anywhere in the world
• Customers also save money by consolidating data
  and voice networks into a single integrated IP
  network

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Cost Savings (continued)

• For businesses, the consolidated network results
  in fewer network devices, which reduces equipment
  costs
• For new wiring in buildings, a single cable can
  be run to each office or unit rather than running
  different sets of wires for network connections
  and telephone connections
• Reduces costs of operation, administration,
  personnel, security, accounting, and network
  management

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Unified Communications

• For businesses, running voice and data over the
  same network architecture can reduce the
  diversity of network equipment and standards,
  which in turn reduces the human expertise
  required and simplifies the administration,
  implementation, and maintenance of networks
• Using a single unified network is much simpler
  than using two or more networks

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Summary of Business VoIP Drivers

• Cost savings
• Network uniformity
• Operational efficiency
• Application integration
• Inevitability

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Internet Telephony Challenges

• Service quality
• Reliability
• Power outages
• Security

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Quality of Service (QoS)

• The Internets technical infrastructure was not
  designed for real-time voice communications
• Packet loss
• Latency
• Jitter

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Power Outages

• During power outages, many users of Internet
  telephony will lose service
• Battery backup necessary
• UPS
• Cell phone backup

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Uninterruptible Power Supply (UPS)
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Reliability

• The decades-old industry metric for phone service
  reliability is five nines, or 99.999
• This means that telephone service should be
  available 99.999 of the time
• All but 5 minutes and 15 seconds of a year
• Internet telephony doesnt provide anything close
  to this reliability

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Reliability (continued)
Network Availability Approximate Downtime
90 36 Days
92 29 Days
95 18 Days
96 15 Days
97 11 Days
98 7 Days
99 4 Days
99.9 9 Hours
99.99 53 Minutes
99.999 5 Minutes
Network availability and corresponding downtime
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VoIP Security

• Voice communications over the Internet face the
  same security threats as other types of
  information exchanged over the Internet
• Worms
• Distributed denial-of-service attacks
• Protocol vulnerabilities
• Operating system security flaws
• Information interception
• Network intrusion

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Public Policy Issues

• Public safety
• Regulatory jurisdiction
• Taxation

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Public Safety

• Some VoIP services initially did not connect to
  911 power outages impede service
• VoIP services have evolved to include 911 access
  as part of their standard Internet telephony
  services, and they now require customers to
  provide their residential addresses, but this is
  complicated by mobile VoIP telephony
• In VoIP there is no rigid relationship between a
  users telephone number and physical location
• Creates complications for traditional 911
  emergency services

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Public Safety (continued)
Emergency dispatch accessible via VoIP
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Regulatory Jurisdiction Taxation

• Internet telephony makes voice just another
  Internet application
• Who should regulate it?
• Should VoIP be taxed like traditional voice?

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Summary

• VoIP refers to voice communications transmitted
  over the Internet or other IP network
• VoIP products convert an analog waveform into a
  digital signal format, break the digital signal
  into packets, and transmit the packets over the
  Internet
• The VoIP approach of sending voice over a
  packet-switching network is different from the
  circuit-switching approach of traditional phone
  networks
• VoIP is not a single protocol, but many different
  standards that handle functions such as
  signaling, digitization, and transport

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Summary (continued)

• Two examples of VoIP signaling protocols are the
  H.323 protocol and Session Initiation Protocol
  (SIP)
• Real-time Transport Protocol is a popular
  protocol for VoIP transport
• VoIP has many implementation options, including
  soft phones, analog telephony adapters, Wi-Fi
  phones, and IP phones
• Businesses can use a private or virtual private
  network (VPN) to carry VoIP and other traffic

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Summary (continued)

• Compared with other types of traffic, voice
  transmissions have different performance
  characteristics that require prioritizing voice
  packets through class of service (CoS)
  designations
• The two most significant business drivers for
  using VoIP are cost savings and network
  integration and unification
• Some challenges presented by VoIP, such as
  quality of service and reliability, are related
  to security and performance
• VoIP also presents some public policy questions
  such as its ability to reach 911 emergency
  services reliably and whether it should be taxed
  like traditional phone service