The Phone System The Phone System RoadmapRoadmap

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Public Switched Telephone NetworkPublic Switched Telephone Network

• The PSTN is the network of the world’s public circuit-switched telephone networks.

• It consists of telephone lines, fiberoptic cables, microwave transmission links, cellular networks, communications satellites, and undersea telephone cables.

• These are all inter-connected by switching centers which allows any telephone in the world to communicate with any other.

The Central Office The Central Office

• The Central Office (CO) refers to your telephone service provider’s physical building that houses the telephone switches used to connect calls in your area.

The Local LoopThe Local Loop• The local loop refers to the wired

connection from your demarcation point to the telephone service provider’s network.

• This connection usually runs from your building to the service provider’s Central Office.

Demarcation PointDemarcation Point• The demarcation point (“demarc”) is the point

at which the telephone company’s wiring ends and the customer’s wiring begins.

Residential demarcBusiness demarc

Analog LineAnalog Line

• A voice circuit historically made from copper wire that runs from your local telephone company’s Central Office building to your business location.

• Good points to remember:– One phone number is associated with one line– One line can handle one conversation at a time; when the line is

in use, a busy signal is heard

Digital LineDigital Line

• A digital telephone line is a type of telephone line that carries voice and/or data by using digital sampling.

• By converting analog signals to digital, it allows for more information to be transferred over a single connection.

• The most common digital line is a T1/PRI line. This type of line can carry up to 24 voice calls over a single line.

IP LineIP Line

• An IP line, or Voice over Internet Protocol (VoIP) line, sends voice calls by converting analog signals into digital packets that travel over the internet.

• The packets are then re-combined at their destination back into voice so that you can converse with your called party.

Common VoIP Services in use Common VoIP Services in use TodayToday

• Analog Telephone Adapter (ATA) – this allows you to connect a standard telephone to the internet. Vonage is a well known provider that employs these devices.

• It converts analog signals from your traditional phone into digital data packets to transmit over the internet.

• They are inexpensive, easy to set up, and simple to use.

Common VoIP Services in use Common VoIP Services in use TodayToday

• Computer-to-Computer – This was the earliest form of internet telephony.

• All that is needed is:– The software– Sound card– Good internet connection– A headset with a microphone

-or-– Speakers with a microphone

• Common services include Skype and Yahoo! Messenger.

Common VoIP Services in use Common VoIP Services in use TodayToday

• Hosted IP Phone Service – This uses a central IP softswitch that IP telephones connect to over the internet.

• Instead of having the traditional phone jack, they have an Ethernet connector.

• These phones connect directly to your internet router and contain all of the necessary technology to directly handle the IP phone call.

Private Branch ExchangePrivate Branch Exchange• Private Branch Exchange (PBX) is another way to say

“business phone system.”

• Basic features of almost all PBX’s include:– Transfer– Hold– Conference– Redial– Caller ID– Call forwarding– Speed dial– Calling groups– Various forms of call coverage

Private Branch ExchangePrivate Branch Exchange• Advanced features include:

– Call answer and voicemail service– Automated attendant– Call queues– Unified messaging– Call accounting– Call center applications– Networking

• PBX’s are connected to the outside world through your demarc to the local telephone company’s central office.

VoicemailVoicemail• Voicemail services on today’s PBX’s are

typically external computers or proprietary modules with the following components:– A processor to run the software that controls the

entire voicemail system– A hard disk drive to save recorded messages,

greetings, and system files– A telephone interface that communicates with the

phone system to answer calls, forward calls, accept touch-tone selections, and playback messages and greetings

Voicemail FeaturesVoicemail Features• Call answer• Greeting recording and playback• Message playback• Message forward• Message save and delete

iPhone with visual voicemail

Power over EthernetPower over Ethernet• Power over Ethernet (PoE) is a technology for

local area networks (LANs) that allows electrical current to be carried over data cables.

• This technology allows devices like IP Phones and IP cameras to be powered directly through the data cabling. This removes the need for external power supplies and AC outlets at each installation point.

http://searchnetworking.techtarget.com/definition/Power-over-Ethernet

Digital PhoneDigital Phone• Digital phones use digital signaling to transmit

voice calls.

• Digital signaling provides more bandwidth for advance features and multiple calls over a single wire run.

• These phones typically run proprietary signaling for use with a particular manufacturer’s PBX.

Analog PhoneAnalog Phone• Analog phones use standard analog

signaling for voice calls.

• Analog phones can have entry-level features like speed dialing, redial, and message waiting light.

• Analog phones can be used in homes and on business PBX.

IP PhoneIP Phone• IP Phones use Internet Protocol to

transmit voice calls.

• Connect directly to your data network cabling.

• Reduces wiring and infrastructure costs by sharing data cabling with data equipment like PCs.

Put everything together

Put everything together

and it looks like…

and it looks like…

……this!this!