Lines and Trunks Ch. 7 PBX Ch. 9 Key Telephone Systems Ch. 10

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Lines and Trunks (Ch. 7)PBX (Ch. 9)Key
Telephone Systems (Ch. 10)

• ENGR 475 Telecommunications
• Harding University
• Jonathan White

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Lines

• End Point
• End in terminals (telephones, modems, faxes)
• New term FX0 Foreign Exchange Office
• Connection to analog POTS
• 2 wire, typically analog
• Called DS-0
• 64 Kbps
• Nothing special

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Trunks

• Connection between points
• Carry many lines
• Connects 2 intelligent switching systems
• PBX/Centrex/CO
• Digital
• Multiplexed
• Expensive

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DID

• Direct Inward Dialing
• Everyone has their own unique telephone number at
  a business
• However, you dont have enough incoming/outgoing
  lines to support all users at once.
• Handled by the PBX (routing)
• You dont have to go through an operator.

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DOD

• Direct Outward Dialing
• Again, you dont have to go through an operator.
• Handled by the PBX

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WATS

• Wide Area telephone service
• Same thing as 800/888/877/866 service
• A way to reduce long distance costs

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PBX - Review

• Private Branch Exchange
• Owned by an individual company
• Performs call routing and switching
• Allows the business to save money because not as
  many connections to the PSTN are provided.
• Keeps calls between employees internal to the
  network.
• How many lines would a call between employees
  normally use?

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PBX - Review

• How does the individual telephone numbers within
  a PBX system work?
• Takes the cooperation of the Telco and the
  organization.
• Some trunks can be dedicated strictly to Direct
  Inward Dialing.
• Page 179 graphic

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PBX Functions

• DID / DOD
• Auto Attendant
• Call transfer
• Speed Dialing
• Voice mail
• Follow-me
• Call forwarding on absence
• Call forwarding on busy
• Music on hold
• Automatic ring back

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PBX Functions

• Night service
• Automatic call distributor
• Call waiting
• Call pick-up
• Call park
• Conference call
• Call accounting
• Voice paging (PA system)
• Custom greetings
• Shared message boxes

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PBX Cost

• http//cgi.ebay.com/NEW-SOHO-PBX-PABX-AUTOMATED-PH
  ONE-EXCHANGE-4-x-16_W0QQitemZ230023614851QQihZ013Q
  QcategoryZ11908QQrdZ1QQcmdZViewItem
• Can be found cheaply
• Others can be very expensive
• Installation and maintenance can be expensive

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Asterisk

• Open source implementation of a PBX
• Runs on Windows/Linux/UNIX and performs all the
  features of a proprietary PBX
• DID/DOD, voice mail, conference calling,
  interactive voice response (phone menus), and
  automatic call distribution.
• Runs on a standard desktop computer
• Needs a special PCI card to attach to the PSTN or
  other analog phones (a modem will not work).

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Asterisk

• Can also be used to run a VOIP network with
  connections to the PSTN
• With VOIP, this can be incredibly cheap.

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Asterisk PCI card
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Asterisk PCI Cards

• PCI cards exist in several flavors
• 1 inward/outward phone line (20)
• 2 inward/outward (225)
• 4 inward/outward (380)
• T1 connection (24 inward/outward) (890)
• Very comparable in price to the cheapest of
  proprietary PBXs

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Asterisk Analog PCI Hubs

• Act as the Main Distribution Frames
• Kind of like a router or hub
• Allow the users of analog telephones to connect
  to the PBX server
• Necessary if you want to run a non VOIP network
• Cost 12 port (1400)
• Not many people actually run analog Asterisk
• http//www.voicetronix.com/hda.htmfeatures

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Non PCI Switches

• Called Channel Banks
• Connects many phone lines to 1 main trunk
• Not incredibly expensive.
• Provide the multiplexing/demultiplexing

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Channel Banks
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VOIP Asterisk

• If the PBX is already running digitally, why not
  run digital phones using VOIP?
• Phones can be computers
• Or special VOIP phones
• Instead of buying a 1400 switch, you can buy an
  Ethernet switch for incredibly cheap.

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Skype

• Allows computer to computer conversations that
  only cross the Internet.
• Theres one main difference between Skype and
  Asterisk.
• Skype is free or almost free.
• Skype has very good security.

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Centrex

• Owned by the Telco
• Same features as a PBX
• Features are leased by businesses
• Each user has their own external phone line.

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PBX/Centrex Boxes
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Key Telephone Systems

• Multi-line telephone system used in SMALL office
  environments
• Very old technology
• Similar to a PBX.
• Many telephone lines come into certain phones. A
  light comes on if the line is busy. A user takes
  control of a line by pressing a button.

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Key Telephone Systems

• Provided intercom capabilities.
• Often 6, 12, or 25 lines would come into a phone.
• In North America, these type of phones were known
  as 1A2.
• They are still manufactured and supported today,
  though they are rapidly becoming outdated.

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Key Telephone Systems