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Bc. Martin Zikmund
Telephony of the new century
URL www.zikmund.cz e-mail martin_at_zikmund.cz Tel
. 420 608 82 82 82
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Content

• How do we talk
• History of telephony
• Integrated networks
• VoIP - drawbacks and benefits

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How do we talk
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How do we talk

• What do we transmit
• Human voice is mainly concentrated within 300 Hz
  3400 Hz range
• The base frequency, which predefines the tone of
  the voice, lies under 1000 Hz and differs for
  children, men and women. The value of the base
  frequency depends on the individual structure of
  the vocal chords.
• Voice is generated by filtering the base
  frequency created in vocal chords through larynx
  and its resonation and reflection in mouth and
  nose. Some vocals are generated just by letting
  the air through the mouth regulating it by tongue
  and teeth (e.g. she, the, etc.)

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How do we talk

• How do we transmit
• The analogue telephony also known as POTS (Plain
  Old Telephone Service), which has basically not
  changed since the times of Alexander Graham Bell,
  works on a very simple principle by direct
  conversion of acoustic signals to the electrical
  ones in the microphone and back again in the
  headphone.
• The ISDN (Integrated Services Digital Network)
  uses similar principals like e.g. CD and
  digitalizes the analogue voice signal to a
  digital PCM (Pulse Code Modulation) signal and
  then applies the compression known as A law (used
  e.g. in the Czech Republic) or ? law (used e.g.
  in the UK). The bandwidth needed for the voice
  transmission is then 64 kbps

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How do we talk

• How do we transmit
• During the WWII, Bell Labs introduced so called
  vocoder a system, which did not transmit the
  analogue signal representing the voice, but just
  a set of parameters used by the human vocal tract
  to create it. The last frequently used vocoder
  LPC-10 needed just 2.4 kbps of bandwidth.
  However, significant problem rested in the
  impossibility to recognize the specific speaker
  based on the reproduced voice.
• In the 1970s NSA introduced an advanced system,
  which used a combination of the vocal tract
  parameters and brief analogue signal description.
  This Federal Standard 1016 used in NSA secure
  telephone units STU-III is also known as CELP
  (Code Excited Linear Prediction) and is the
  origin of extremely popular LD-CELP known as the
  ITU-T G.728 (16 kbps) codec highly used in VoIP
  networks together with more advanced G.729 (8
  kbps) working on similar principles.

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History of telephony
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History of telephony

• Circuit switching
• In the past, human operators were needed to
  directly connect one user line with the other to
  establish the voice call and disconnect it after
  its termination
• After the WWII, human operators were replaced by
  analogue automatic switching system
• Today, the core networks and switches are fully
  digital using advanced signalling etc., but the
  principle is exactly the same
• Once you dial a number, you just specify to the
  switch (digital operator) which plug should be
  connected with which line.
• During the whole voice call, two lines and
  several switches are occupied
• The logical consequence is that you have to pay
  per minute, because you exclusively occupy a part
  of the operators infrastructure during the call

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History of telephony

• What is a packet
• Data networks are completely different from
  voice ones
• Generally, computers need to talk for a very
  short amount of time, but they like to talk
  incredibly often
• The length of the talk varies extremely in
  time depending on the specific action done on the
  computer (e.g. a length of e-mail)
• It is also usual that 20 computers want to
  talk to one computer (server) all at once
• Based on these facts it was found out that it
  would be most useful to allocate for each
  computer a limited amount of time in the network
  shared by all computers, when he can transmit its
  data.
• This amount of time was determined as a specific
  number of bits (1s or 0s) called the packet

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History of telephony

• Packet switching
• A packet consists of user data, source address,
  destination address, payload description, etc.
• A data switch or a router receives packets from
  a variety of computers (sources)
• Every single packet is examined and sent to its
  destination address through the shortest free
  route gt subsequent packets can travel to their
  destination through different routes because the
  load of each part of the network on the route
  changes in time, while every part of network is
  used by a number of users (computers)
• A packet point to point connection (e.g. VoIP
  call) therefore does not occupy exclusively any
  part of the network except the so called last
  mile, which is the connection to the nearest
  switch.
• Therefore, you pay for the amount of data
  transmitted and not for the time spent by that
  transmission

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Integrated networks
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Integrated networks

• Packet switching is suitable for all
• Packet switching is excellent for data and
  suitable for voice, when realized properly
• Circuit switching is suitable for voice but
  unacceptable for data because of its high costs
  and poor utilization
• ISDN contained also a new phase, which has never
  been implemented the B-ISDN (Broadband ISDN)
  xDSL was used instead
• BT is going to launch first all IP
  telecommunications network in the next year (21st
  Century Network project) based on xDSL and VoIP
• All new telecommunications networks will be like
  21CN based on All IP architecture called also NGN
  (Next Generation Network)

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Integrated networks

• What is Voice over Internet Protocol (VoIP)
• IP is a packet based protocol using packets of
  variable sizes (e.g. 1440 bits) to transmit any
  kind of user data
• Voice is transmitted within IP packets just like
  data
• VoIP employs a new payload description to
  differentiate voice packets from the data ones
• There is a combination of voice tract and signal
  descriptors (codec) used instead of transmitting
  the digitalized signal itself
• Nevertheless the bandwidth necessary for VoIP is
  almost the same or higher as with ISDN this is
  caused by the additional data transmitted within
  a packet and the use of the whole packet, which
  is not optimal (part of the packet is usually
  empty, because the packet size suitable for data
  is not suitable for voice)

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VoIP drawbacks and benefits
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VoIP drawbacks and benefits

• Drawbacks
• Every packet can be transmitted by a different
  route within a different amount of time, but it
  is necessary to have complete information with
  the right order of received packets to understand
  the transmitted voice
• The time required to transmit the packets varies
  according to the utilization of the active parts
  of the network (jitter)
• The voice packets cannot be thrown away in case
  of overloading of a network component
• The voice packets have to have priority within
  the queues in switches, because the latency is
  critical in telephony applications

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VoIP drawbacks and benefits

• Consequences
• We need to reconfigurate the network for optimal
  routing of VoIP packets (optimal structure copies
  the structure of a telephony network)
• We need to have intelligent switches and routers
  to prevent throwing away the VoIP packets
• We need to prioritize the voice packets (need to
  buy new switches and routers)
• It is highly recommended to separate VoIP phones
  in the network from the rest of it (e.g. by
  VLANs) that needs advanced switches

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VoIP drawbacks and benefits

• Benefits
• VoIP brings ultimate security functions
  (sufficient even for army and intelligence
  agencies for top secret classification)
• We can use much more secured networks than those
  for voice
• We can use a single network for data, voice (and
  TV, video on demand, etc.)
• We can save money by purchasing much cheaper
  data infrastructure compared to voice (TDM)
  infrastructure
• We can use internet to communicate for free
  (more precisely with no additional costs)
• We can be anywhere in the world, but still
  reachable on our work phone number and still
  reachable for free from within our company

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VoIP drawbacks and benefits

• VoIP and eBusiness
• VoIP enables close cooperation with companys
  ISs
• Integration with CRM brings you the benefit of
  knowing the customers needs even before you
  answer the call
• VoIP in call-centres passes on you huge
  benefits such as unified messaging, enhanced
  statistical tools, etc.
• Integration with IS provides you with the click
  to call functionality
• VoIP gives you the freedom of place just like
  the ISs do

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Questions?
URL www.zikmund.cz e-mail martin_at_zikmund.cz Tel
. 420 608 82 82 82