1. Telephone Systems and Cabling
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 customer’s 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 Provider 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 80’s 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 who’s 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