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 –Called DS-0 –64 Kbps –Nothing special

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

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.

DOD Direct Outward Dialing Again, you don’t have to go through an operator. Handled by the PBX

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

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?

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

PBX Functions DID / DOD Auto Attendant Call transfer Speed Dialing Voice mail Follow-me Call forwarding on absenceCall forwarding Call forwarding on busyCall forwarding Music on hold Automatic ring back

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

PBX Cost EXCHANGE-4-x- 16_W0QQitemZ QQihZ013QQcategoryZ11908QQrdZ1QQcmd ZViewItemhttp://cgi.ebay.com/NEW-SOHO-PBX-PABX-AUTOMATED-PHONE- EXCHANGE-4-x- 16_W0QQitemZ QQihZ013QQcategoryZ11908QQrdZ1QQcmd ZViewItem Can be found cheaply Others can be very expensive Installation and maintenance can be expensive

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).

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

Asterisk PCI card

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

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

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

Channel Banks

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.

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.

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

PBX/Centrex Boxes

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.

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.

Key Telephone Systems