For those of us old enough to remember rotary dial telephones and dialing without an area code (to really date ourselves), the telephone and telephone service has drastically changed over the past couple of decades. In this chapter, we discuss telecommunications systems for the home, including telephone and intercom systems, their functions, operations, and characteristics. We also discuss the possibilities of integrating a home telecommunications system into control and data networks.
In most cases, a home telephone and telecommunications system is limited to RJ-11 outlet jacks (Figure 26-1) in one or two rooms of a home that is more than seven to ten years in age or in just about every room of a newer home. The telephone outlet jack can be used for local and long distance calling, to support a fax machine, as a part of a cable or direct satellite TV system, or to support a dial-up modem connection for either a single computer or a computer network. Actually, when you think about it, that little telephone jack really has quite a bit of capability, which is generally underutilized in most homes.
Figure 26-1: An RJ-11 jack faceplate
Photo courtesy of Belkin Corporation.
Most people take the telephone system for granted and get very used to the idea that, for the most part, it always works. Before you can begin designing a home telecommunications system, you should have some understanding of how this system works and its various components.
The telephone network consists of two network layers: the Plain Old Telephone System (POTS) and the Public Switched Telephone Network (PSTN). POTS service consists of the wiring and cabling that connects a house to the local telephone company switching system at the telephone company’s network interface device (NID) on the side of the house. PSTN includes the switching system and all of the equipment and transmission lines used to carry the voice signals to the house by the phone company.
The Connection to the Central Office
The line that runs back to the telephone company or the telephone service provider (aka the Telco) terminates at a house in what is called the demarc. The demarc (short for demarcation point) is a terminating device that connects the wires in the Telco bundle to the home. In many respects, the demarc is very much like a network’s patch panel (see Chapters 11 and 13) in that it interconnects the telephone wiring in the home to the Telco’s cabling and switching systems.
Demarcation PointThe demarc device is typically located on an outside wall of a home or in an easily accessed location, such as inside a garage or basement. The official name for the telephone demarc is a Network Interface Device (NID), and it is commonly a gray plastic or metal box with a snap-tight cover (see Figure 26-2).
Figure 26-2: A Network Interface Device (NID) showing both the Telco-only side (left panel) and the owner-access side (right panel) connections
As shown in Figure 26-2, an NID has two sections, the panel of connections on the right side of the box are accessible by the homeowner or their contractors for testing and connection purposes, and the panel of connections on the left has an inside cover and is accessible only by Telco personnel. The owner-accessible panel, Figure 26-3 gives a zoomed-in view, has four to six screw connectors that connect the Telco’s incoming lines (the connections made in the Telco-accessible panel) to the short piece of telephone cables that are plugged into the RJ-11 jacks. When the RJ-11 plug is removed from the jack, the line (and service) from the Telco is disconnected. However, if a phone is plugged into this jack and works during a service test, any problem with the phone system in the house is being caused by the inside wiring, not by the Telco service.
Figure 26-3: A close-up of the owner-accessible panel in an NID
The demarc is where the Telco’s lines and system meet the telephone lines of the homeowner. The Telco owns the lines up to the demarc (and most times the demarc itself), but no further. Beyond the demarc, everything belongs and is the responsibility of the homeowner. However, especially on new homes, some homeowners are choosing to install their own NIDs, which aren’t expensive. Installing and owning the demarc allows for more flexibility for expanding the telephone system inside the home, better quality connections at the demarc, the ability to complete the inside wiring (to the demarc) even before the telephone service is installed, and perhaps the best reason, the homeowner can put the demarc wherever they wish. However, the Telco’s responsibility ends at the terminator on their cable, which may be a good reason to let them install their NID.
The Central OfficeThe wiring that connects a house to the telephone network actually connects the NID to the wiring and intermediate devices that lead back to the nearest switching center for the Telco, called a central office (CO). Figure 26-4 illustrates the basics of the connections that link a house to the CO.
Figure 26-4: Telco lines connect a house to the Central Office for telephone service.
The Telco’s CO is a switching station that routes calls (including signals on DSL and ISDN services) to the location of the number being called. A CO handles all of the telephone traffic in a particular area. In smaller towns, the CO handles all calls and in larger areas, the CO handles a certain area of a city, county, or a specific area code.
Cabling and Entrance BridgesIf we look at the cabling used to provide a telephone service connection to a residence and start at the CO, in older situations, copper cabling with tens or even hundreds of wire pairs and, in newer lines, fiber optic cabling is used to distribute “dial-tone” (analog telephone services) to every home. In areas where the telephone cabling is installed underground, a device called an entrance bridge is located in the yards of each or every two, three, or more houses. This device is about 2 to 3 feet tall and about 8 inches square (see Figure 26-5) and is where 50 pairs of wiring comes up from underground to be interconnected into houses. On occasion, larger boxes that are about 4 or 5 feet tall and 2 feet wide are also located in neighborhoods that serve as intermediary bridges that distribute wiring to the entrance bridges.
Figure 26-5: An entrance bridge is used to distribute telephone system wiring to individual houses.
Analog LinesAnalog telephone systems operate using voice and sound signals. Analog phone equipment is designed to interpret audible signals (of the number dialed) and route each call to its destination to build a temporary virtual circuit where the caller and the called can speak over their own private circuit. This circuit is torn down after the call is disconnected. Analog telephone lines support modem connections made by computers, as well as most of the voice transmissions over the Telco system.
Digital LinesDigital telephone circuits convert sound waves into digital (binary) signals for transmission to the other end of the connection where another telephone, modem, or even a television, converts the digital signals back to audible tones. The primary difference to the telephone user is clarity, because the digital system is able to remove any distortion in the signal. In addition, more features can be carried over the digital line than over an analog line.
By installing the proper switching and bridging equipment, existing telephone wiring can also be used to transmit digital data, such as with Digital Subscriber Lines (DSL), Integrated Systems Digital Network (ISDN), and frame relay services. Digital services use the existing copper and fiber optic cabling to transmit digital (binary) data rather than analog (audible) signals.
DSL is able to transmit data only over copper wiring and so it is available only to those houses that have only copper lines connecting them to the CO. Even if only copper wiring connects the home to the CO, DSL is a distance-limited service and may not be available to every home. The wire distance used to determine DSL service availability is the length of the wire itself. Table 26-1 lists the various flavors of DSL and the standard wire distance limitations for each.
144 Kbps ISDN over DSL (IDSL)
256 Kbps Symmetrical DSL (SDSL)
384 Kbps SDSL
768 Kbps SDSL
1.1 Mbps SDSL
1.5 Mbps / 384 Kbps Symmetrical DSL (SDSL)
ISDN and other digital transmission services can operate over both copper and fiber optic, so they are generally available to most homes, without wire distance limitations. However, ISDN requires that the residential terminating equipment match the type of ISDN switching used at the CO. The most common types of ISDN switching are AT&T 5ESS, Northern Telecom (NT) DMS-100, and National (ANSI) ISDN-1.
To place either a local call or a long-distance call requires a number of elements to be available:
Telephone Key SetsA telephone, or what is also commonly called a key set, has four primary parts:
Dial ToneThe dial tone, as well as the tones representing the numbers dialed and several other common dialing sounds, such as busy, off-hook, and others, are recorded sounds embedded on a chip on the telephone’s circuitry.
All of the tones produced by a telephone are a combination of two frequencies. For example, combining a 350-hertz tone with a 440-hertz tone creates the dial tone and the busy signal is a combination of a 480-hertz tone and a 620-hertz tone that is cycled on and off.
System BandwidthThe public telephone system limits transmitted sounds to not less than 400 hertz and not more than around 3,000 hertz. Any sounds with frequencies below 400 hertz or above 3,000 hertz are discarded and this is why a person may sound completely different over the phone than in person, where you can receive the full range of their voice’s frequencies.
The telephone key set also limits the bandwidth requirement of voice communications by transmitting sound samples rather than the entire sound it receives. A concentrator circuit works with the telephone’s microphone to create 8,000 samples per second of the sound it hears and transmits the sound samples across the public telephone system for playback by the speaker at the other end’s handset.
Telephone Number DigitsLike the physical address of a networked computer (see Chapter 12) or the address of a home, a telephone number is a unique address for a destination circuit. Each part of a telephone number has meaning, from a country code used to dial an international call, the area code, the prefix, and the line number. For example, in the number 509-555-1212, the 509 is the area code, the 555 is the prefix, and the 1212 is the line number.
Caller IdentityMost newer telephone key sets are able to display the identity (the phone number and the name the phone number is registered to) of the calling party either on the phone itself or on a satellite caller ID box.
The technology used to provide caller ID isn’t new, in fact it is the same used by modems to set up a connection—frequency shift keying (FSK). This technology uses certain tone frequencies to represent binary digits, such as 1,200 hertz for a one and 2,200 hertz for a zero, and the telephone or caller ID box converts these to ASCII characters for display.
To this point, we have been discussing telephones in general, so most of this information applies to the standard wire-connected telephone and key sets. However, it is common for today’s homes to include one or many cordless or wireless telephones, either in addition to or in replacement of standard telephones.
A cordless telephone, like the one shown in Figure 26-6, allows a user to talk through the telephone’s handset without being tethered to the telephone’s base unit. As far as functionality goes, cordless phones have essentially the same features offered by a standard or corded telephone.
Figure 26-6: A cordless phone has two parts: a base and a handset, which is portable and not attached to the base with a cord.
Photo courtesy of Siemens Information and Communication Mobile, LLC.
RF FunctionsCordless telephones combine the functions of a standard telephone with those of radio frequency (RF) transmitter/receiver. The base of a common cordless phone is wired into the telephone system just like a standard telephone. However, the base communicates to the handset using RF communications and a frequency modulation (FM) signal. The handset receives the FM radio signal and converts it back to an audio signal and is sent to the handset’s speaker. The microphone on the handset performs an opposite action, translating the audio signals into FM radio signals for transmission to the base unit that converts the RF signals to voice signals for transmission through the telephone wiring.
The handset and base of a cordless telephone use a pair of different frequencies, one for incoming signals and one for outgoing signals. A frequency pair that is used this way is referred to as a duplex frequency. For example, the base unit may use 44 MHz to transmit and 49 MHz to receive, which is reversed on the handset where 49 MHZ is used to transmit and 44 MHz is used for the receiver.
Operational IssuesA cordless telephone does have a few operational issues that a standard telephone doesn’t have:
Operating Range (Upper Limit)
250 feet (75 meters)
1,500 feet (450 meters)
2,000 feet (600 meters)
2,000 feet (600 meters)
The performance issues of a cordless phone are the result of the phone’s design and features, primarily the phone’s RF band, whether the phone is analog or digital, and the number of channels it has available.
Inexpensive cordless phones are commonly analog devices that are generally electrically noisier, susceptible to interference, and more easily intercepted by other RF devices. Digital cordless phones provide a better sound quality and, because they also use digital spread spectrum (DSS) signaling, they are generally more secure than an analog phone. DSS uses several frequencies to transmit signals between the base and the handset and this makes it very hard for another device to intercept an entire conversation.
RF frequency bands can be divided into several channels and the more channels available, the better chance the base unit is able to find a channel pair that is relatively free from interference. Typically, a 49MHz cordless telephone has from 10 to 25 channels available; a low-end 900 MHz phone has from 20 to 60 channels; and higher-end 900 MHz, 2.4 GHz, and 5.8 GHz phones have as many as 100 channels.
If the homeowner desires only a single telephone line with multiple extensions without any added features, beyond those provided by the Telco, once the wiring and the phone jack outlets are installed during pre-wire, chances are that the house has everything it needs to fulfill this requirement.
However, if the homeowner wishes to have multiple phone lines accessible throughout the house, careful consideration must be given to exactly what features the homeowner is looking for and if a telephone system will meet their needs.
There are several advantages to a telephone system over the standard telephone service found in most homes. These advantages include:
A KSU is a central device that provides the switching and control services for the entire network of key sets on a telephone system. In some cases, the KSU may also be referred to as a Public Branch Exchange (PBX) or a computerized PBX (C-PBX). Regardless, a KSU provides additional or advanced features to standard telephone sets, including such features as call forwarding, extension dialing, voice mail, music on hold, and more. The fact that a KSU must be configured in a star topology is considered a drawback to many, but structured wiring provides “star” topology, and a phone system can easily be installed on structured wiring. Most KSU-based systems may require proprietary or specially configured key sets that add to the overall cost of the system.
KSU systems provide many “business” functions as well, including auto-attendant that answers the phone with a recording and allows the caller to select an extension from a recorded menu, such as “For Ron, press 1; for Connie, press 2,” and so on.
KSU-based systems also offer a wide range of optional features as well, including:
Another type of KSU system, at least in terms of functionality, is the KSU-less system. KSU-less systems are relatively low-cost options for residential phone systems with two to seven telephone lines. The primary attractiveness to a KSU-less telephone system, beyond its features that is, is that it can work with nearly any ordinary phone, including both rotary dial and touch-tone. However, to realize all of the features of the system, a central unit or specialized telephone stations may be required. KSU-less systems typically provide all, or at least the majority, of the features of a KSU-based system, but commonly at a much lower cost.
Digital telephone systems are key systems like KSU-based systems and rely on a central processor for many of their functions. Digital key systems, also like a KSU system, allow the telephone system to share multiple CO lines across a number of key stations. Figure 26-7 shows the central unit and samples of the digital key stations for one residential and small business system.
Figure 26-7: A digital telephone system with a digital PBX, key station, and cordless phone
Photo courtesy of Panasonic USA.
Because they have what amounts to a computer at their core, digital telephone systems are programmable, typically through a graphical user interface that can be accessed either by attaching a monitor to the central unit or connecting the central unit to a data network.
One of the downsides to a digital telephone system is that they require the use of special digital telephone key sets and any existing fax machines and modems must continue to use separate analog phone lines. On the other hand, however, the digital phones are feature-rich, including such features as:
IP Telephone Systems
Internet Protocol (IP) telephone systems operate over the cabling and computers of a data network. Residential IP telephone systems replace the existing residential gateway with one (see Figure 26-8) that provides both the RJ-45 network connections required by the data network and RJ-11 connections used to provide phone service to IP telephone key stations.
Figure 26-8: An IP telephone system residential gateway
Photo courtesy of Mediatrix Telecom, Inc.
The benefits of an IP telephone system are several, including cost-effective access through phones anywhere in the world that are connected to the Internet, and the fact that the system is relatively easy to install. The drawbacks of an IP telephone system primarily have to do with the performance. Sometimes there is a delay in the speaking, and clarity is not as consistently good as on a standard phone line. Also, signals can be lost more easily than on standard phone lines.
IP telephones use a technology called Voice over IP (VoIP) to transmit telephone calls over a data network in the same way that data messages are sent over the network. VoIP converts voice samples into network packets that are transmitted over both the local in-home network and the Internet.
VoIP uses coder/decoder (codec) circuitry to convert audio signals into compressed digital format for transmission and back to voice signals at the receiving station for playback. Two primary protocols are used by VoIP to transmit voice signals:
The primary ways VoIP can be used across the PSTN is in computer to telephone, telephone to computer, and telephone to telephone calling.
There are two general categories of intercom systems that can be installed in a home: wired and wireless. There are two ways to implement an intercom system in a home: through the telephone system or through the installation of an independent, stand-alone wall-mounted intercom system.
Telephone-Based IntercomNewer key stations and analog telephones feature intercom and speaker-phone capabilities that allow the telephone to be used to call room-to-room, typically with the press of a single button, and talk with someone in another location in the house with a totally hands-free conversation.
Stand-alone Intercom SystemsWe refer to these systems as independent only to differentiate them from telephone-based intercom systems. This type of intercom system consists of master units, remote controls, speakers, and now even displays that are typically wall-mounted devices placed at the mouth-level of the average person.
There are a variety of stand-alone intercom systems available:
The telephone network consists of two network layers: the Plain Old Telephone System (POTS) and the Public Switched Telephone Network (PSTN). POTS refers to the wiring and cabling connecting a house or building to the local CO. The PSTN includes CO and the equipment and transmission lines that carry voice signals to a destination.
The Telco’s POTS line, which terminates at a house at the demarcation point (demarc) or Network Interface Device (NID), is a terminating device that interconnects Telco wiring to a home’s telephone wiring. The demarc is commonly located on an outside wall of the house. The Telco owns the lines up to the demarc (and most times the demarc itself), but all internal telephone wiring is the responsibility of the homeowner. The POTS lines connect a house to the Telco’s central office (CO) or switching facility. The CO routes calls to the CO and switching associated with the number being called.
Analog telephone systems transmit voice and audio signals. Analog telephone lines also provide support for modem connections made by computers. Digital services use the existing copper and fiber optic cabling to transmit digital (binary) data rather than analog (voice) signals. Digital services include DSL and ISDN.
A telephone set has four primary parts: hook switch, keypad or rotary dial, microphone, and speaker. Combining two audible frequencies creates the tones produced by a telephone. For example, combining a 350-hertz tone with a 440-hertz tone creates the dial tone.
The telephone system transmits sounds between 400 hertz and 3,000 hertz. Sounds below or above this range are discarded and this is why people sound different on the phone than in person. Telephone key sets transmit sound by creating 8,000 sound samples per second.
Each part of a telephone number has meaning. A telephone number typically consists of an area code, a prefix, and a line number. Caller ID uses frequency shift keying (FSK) to transmit ASCII caller identification information.
A cordless telephone includes a stationary base unit and a portable (unwired) handset. Cordless telephones combine a standard telephone with a radio frequency (RF) transmitter/receiver. The cordless phone base communicates to the handset using RF communications and a frequency modulation (FM) signal.
There are three primary types of residential home telephone systems: KSU-based systems, KSU-less systems, and digital key systems. A KSU is a central device that provides the switching and control services for the entire telephone system. KSU-less systems are relatively low-cost options for residential phone systems with two to seven telephone lines and work with standard telephones. Digital key systems rely on a central processor for their functions and provide advanced features.
Common features for residential telephone systems are: Automatic Call Distribution (ACD), Computer Telephony Integration (CTI), intercom capability, programmable key set buttons, speaker-phone compatibility, and speech recognition.
Internet Protocol (IP) telephone systems operate over the cabling and computers of a data network. Residential IP telephone systems replace the existing residential gateway with one that provides both RJ-45 network connections and RJ-11 connections to IP telephone key stations.
IP telephones use a technology called Voice over IP (VoIP) to transmit telephone calls over a data network in the same way that data messages are sent over the network. VoIP converts voice samples into network packets that are transmitted over the local in-home network and the Internet. VoIP uses coder/decoder (codec) circuitry to convert audio signals into compressed digital format for transmission and back to voice signals at the receiving station for playback. VoIP provides support for computer to telephone, telephone to computer, and telephone to telephone calling.
Three general types of intercom system can be used in a home setting: doorbell intercoms, stand-alone voice intercom systems, and intercoms integrated into phone systems.
Part I - Home Technology Installation Basics
Part II - Structured Wiring
Part III - Home Computer Networks
Part IV - Audio/Video Systems
Part V. Home Lighting Management Systems
Part VI - Telecommunications
Part VII - HVAC and Water Management
Part VIII - Security System Basics
Part IX - Home Technology Integration
Part X - Appendices