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. Lines. End Point End in terminals (telephones, modems, faxes) New term: FX0 – Foreign Exchange Office Connection to analog POTS 2 wire, typically analog - PowerPoint PPT PresentationTRANSCRIPT
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Lines and Trunks (Ch. 7)PBX (Ch. 9)
Key Telephone Systems (Ch. 10)
ENGR 475 – TelecommunicationsHarding 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 don’t have enough incoming/outgoing lines to support all users at once.
• Handled by the PBX (routing)• You don’t have to go through an
operator.
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DOD• Direct Outward Dialing• Again, you don’t 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-PHONE-
EXCHANGE-4-x-16_W0QQitemZ230023614851QQihZ013QQcategoryZ11908QQrdZ1QQcmdZViewItem
• 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 PBX’s
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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.htm#features
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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.– There’s 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