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Lecture 4 Telephone Systems and Cabling. This lecture will cover: On-site telephone systems Peripheral devices for telephone systems –voicemail –call.

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Presentation on theme: "Lecture 4 Telephone Systems and Cabling. This lecture will cover: On-site telephone systems Peripheral devices for telephone systems –voicemail –call."— Presentation transcript:

1 Lecture 4 Telephone Systems and Cabling

2 This lecture will cover: On-site telephone systems Peripheral devices for telephone systems –voic –call center services Copper and fiber that connect telephones Computers and networks

3 Telephone Connections The first telephones were wired from one user directly to another user (1876) Later switchboards were installed, operated by individuals (1877) Automatic switching or a central office switch patented by Almon Strowger (1891)

4 Switches PBX Centrex Key Systems

5 PBX and Centrex Systems All provide: –connections between staff in organizations –connections to the outside world –the ability for on-site personnel to make calls within the call territory without paying telephone usage fees

6 PBX and Centrex Systems Only difference between two systems: –location of equipment –ownership of equipment

7 PBX Private Branch Exchange Located on the customers premises Owned by the user Eliminates the need to wire each on-site individual telephone to a central office All lines wire to PBX switch, which connects to a central switch operated by provider

8 PBX Each employee does not have to pay for: –telephone line to central office –telephone calls made between people in the same office –dialing within the system can be done with fewer digits Campus Operator

9 Centrex Central Exchange Located on the local telephone providers premises Equipment owned by the telephone provider Offers same features as PBX in terms of costs per call, and reduced digit dialing

10 Key Systems Function like a PBX Often smaller, but nowadays differences hard to see Formerly had less features than PBX User base around 50 to 125 telephones

11 Connecting Phones to Switches Local provider will bring wire into a building to an interface called rj11cjack Most common interface used rj21x jack has larger capacity, 25 lines

12 rj11c Location of jack important Common point from which to test telephone lines and trunks This is where service begins/ends –up to jack telephone provider responsibility –from jack to PBX PBS vendor must test demarcation point between provider/user

13 Features of Centrex No-requirement for on-site switching equipment Direct-inward dialing Direct-outward dialing Automatic identification of dialed calls

14 Appeal of Centrex User –Save on operator costs, none required –Detailed billing reports –Zero on-site space requirements Provider –stimulation of long distance calling –less use of long distance circuits for call setup –reduction in staff requirements to place calls

15 Key Systems Loop start system versus ground start (PBX) Analog home phones are loop start Provides all the functionality of a PBX

16 Starting a Line You start a phone line by seizing the handset A supervisory signal is sent to central office Two ways to send this signal –loop start –ground start

17 Loop Start Most common type of trunk found in residential installations To initiate a call you form a loop ring between your set and the central office –AC sent to your ringer –when handset lifted AC interrupted –DC loop then formed to support the call

18 Ground Start A handshaking routine between CO and PBX Initiated by the PBX to get dial tone To see if a trunk is dedicated to the call the PBX checks to see if the tip lead is grounded Once a trunk is dedicated, the CO will close the relay and ground the tip lead

19 Direct Inward Dialing Routes calls directly from a local telephone company to telephone connected to a PBX or Centrex switch without operator intervention Prior to 80s expensive feature Now commonly sold Companies buy entire blocks of phone #s

20 Networks Send traffic in two main ways: –circuit-based switching Dedicates a path through the network for the entire duration of the call –packet-based switching Breaks up the message in packets and send packets over network when available routes become available, message assembled at final destination

21 IP Networks for Calls Voice calling over IP networks is uneven Packets share the network Congestion causes delays Primarily used within sites and not to customer Low incentive to pursue, long-distance telephone costs are low

22 IP Based Phone Systems Special phone and routers used Equipment digitizes voice traffic and assembles it into packets Compresses the signal so that it takes up less capacity on the network

23 IP Telephone Vendors Lucent Technologies Cisco Systems 3Com

24 Why slow to take off? Cost: still too high Reliability: local area networks tend to crash, choppy when network congested Existing phone base: works great, not expensive, lasts about 10 after initial investment

25 Add-On Features Maintenance contracts Moves and changes to telephone equipment Upgrades to the hardware and software Feature telephones Wireless phone systems Peripheral devices: voice mail, automatic call distribution, call accounting systems

26 Call Accounting Track all phone calls made by users (SMDR: station message detail recording) Allows for charging department for usage Indicates amount of traffic on each phone line

27 Voice Mail Based on a voice store and forward system Octel Communications first installed voic in 1980 PC based systems now available

28 Automated Attendants Programmed statements to answer calls Or programs that direct calls at busy times Formerly not a part of voice mail Voice mail vendors bought out automated vendors and made it a part of voice mail

29 Voice Mail Components CPU: executes the application programs Codecs: convert analog signals to digital signals and visa versa, compress voice to decrease storage space Software: determines the feature I/O cards: to connect phone system with VM

30 Voice Mail Components Speech recognition cards: specialized cards and software to recognize spoken commands such as the numbers 1-10 Other system components: ports, scanners, high-speed buses, power supplies, tape and disk drives

31 Automatic Call Distribution Enable companies to manage incoming calls and maximize use of employee time –route calls to agent whos been idle the longest –route calls to appropriate agent groups –if all agents busy, will hold caller in a queue, route call to another agent, or take voice mail –provide reports that measure productivity of agents, trunk usage, number of abandoned calls

32 Media Carry voice and data traffic Characteristics of media determine its speed, accuracy and distance at which traffic can be carried –copper –high-quality copper –fiber

33 Copper Cabling Electrical properties to copper cabling create resistance and interference problems Signals weaken as they travel Resistance of copper slows down signal Signals are direct current, very susceptible to outside electrical sources Two copper wires twisted together to limit interference problems

34 Twisted Copper Used in: –from set to PBX –from set to key systems –from PCs to wiring closet of a LAN –from homes to nearest local telephone wiring center

35 Cat 5 Unshielded Twisted Pair Typically installed for voice and data Carries traffic at 100 Mbps within buildings Cat 5 or 3 most commonly used Name indicates that cabling tested and meats standards set for this type of copper cabling

36 Fiber Optics Immune to electrical interference Signals transmitted in the form of light No electricity present in signal Highly resistant to taps Small in size, requires less conduit Lightweight, no sparking hazard Enormous bandwidth

37 Disadvantages Fiber Termination and connection costs high Needs more care in handling, not flexible like copper Extra electrical power needed Specialized technicians needed to install and test fiber

38 Fiber Usage In all long distance networks Between central offices From central offices to neighborhood wire centers Internet services provider networks Undersea cable runs Electric utility networks

39 Components Fiber System Transmitters: convert electrical signals to light signals –LED –Laser: very powerful Transducers: convert light signals to electrical signals

40 DWDM Dense Wavelength Division Multiplexing important part of infrastructure for carrying high-speed voice, data, streaming video and audio Key reason for convergence Convergence: applied to high-speed networks that carry traffic using IP

41 Advantages DWDM Higher capacity over fewer strands of fiber Lower costs to upgrade networks, same fiber used by multiplexing Space saving, less amplifying equipment needed Lower ongoing maintenance expenses, less equipment necessary

42 Amplifiers and Multiplexers Key components of DWDM networks amplifiers boost the signal –every60 miles multiplexers combine light from multiple sources onto a single strand of fiber –every 360 miles

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