Lecture 4

Telephone Systems and Cabling

This lecture will cover:

• On-site telephone systems

• Peripheral devices for telephone systems– voicemail– call center services

• Copper and fiber that connect telephones

• Computers and networks

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)

Switches

• PBX

• Centrex

• Key Systems

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

PBX and Centrex Systems

• Only difference between two systems:– location of equipment– ownership of equipment

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

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• 5-1855 Campus Operator

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

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

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

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

Features of Centrex

• No-requirement for on-site switching equipment

• Direct-inward dialing

• Direct-outward dialing

• Automatic identification of dialed calls

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

Key Systems

• Loop start system versus ground start (PBX)

• Analog home phones are loop start

• Provides all the functionality of a PBX

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

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

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

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

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

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

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

IP Telephone Vendors

• Lucent Technologies

• Cisco Systems

• 3Com

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

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

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

Voice Mail

• Based on a voice store and forward system

• Octel Communications first installed voicemail in 1980

• PC based systems now available

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

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

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

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

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

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

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

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

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

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

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

Components Fiber System

• Transmitters: convert electrical signals to light signals – LED– Laser: very powerful

• Transducers: convert light signals to electrical signals

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

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

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