Telephone Systems—PBXs, Centrex and Key Systems
When the telephone was first invented in 1876, each person's telephone line was wired directly to another individual user. By 1877, a switchboard was installed in Boston so that each telephone could be wired to the central switchboard instead of to every telephone. When an individual wished to call someone, he or she picked up the telephone handset and asked the operator to connect the call to a particular individual. The operator knew all of the town's business. In 1891, Almon Strowger patented a central office switch where operators were not required to complete each call. Strowger's motivation was privacy: He felt that operators were listening in on his telephone conversations.
What Is a PBX?
A PBX is an on-site telephone system that connects organizations to the public switched telephone network. The central office switch is the precursor to on-site private branch exchange (PBX) telephone systems. A central office switch is centrally located and routes calls between users in the public network. PBXs are private and located within an enterprise.
Just as a central office switch eliminates the need to wire each telephone to every other telephone, with a PBX, each telephone is wired to the PBX—not to each telephone in the company. Because the PBX is wired to the central office, each telephone does not need its own line wire to the central office. In essence, with a PBX, each employee does not have to pay for his or her own telephone line to the local telephone company. Nor are there charges for calls between people in the same office.
According to the Telecommunications Industry Association (TIA), PBX shipments in the United States were down 16% in 2000 and are expected to decline 14% in 2001. Various reasons are attributed to these declines. Some customers might be delaying purchases in anticipation of new IP-enabled PBXs (see Convergence and Telephone Systems later in this chapter). In other cases, customers upgrade existing PBXs rather than purchase completely new ones. Many PBXs can be upgraded to add capacity and new features rather than completely replaced.
The two market leaders in PBXs are Avaya Communications (formerly part of Lucent Technologies) and Nortel Networks. Companies with smaller market shares are Siemens, NEC and Mitel Networks. Mitel Networks was sold off from Mitel Corporation in early 2001 to Terry Matthews, one of its founders. Mitel Corporation will be renamed and is keeping the semiconductor operations. Other suppliers include Fujitsu, Ericsson, Intecom and Hitachi. Cisco Systems is investing in IP-based phone systems, voice messaging and speech recognition to position itself for both voice and data sales to enterprises. Alcatel, the largest provider of PBXs in Europe, has established operations to sell systems in the United States.
PBX Trunks
PBXs are connected to telephone company central offices by trunks that carry calls between the PBX and the telephone company. Depending on the volume of calls generated by the staff, eight to ten users can share each trunk. A PBX with 100 users might share 12 trunks. Most companies use T-1 for their trunking. Instead of having 24 separate pairs of wires, the T-1 can carry 24 incoming and/or outgoing calls on two pairs of wire or on fiber optic cable. Fiber optic cables have the ability to carry multiple T-1s.
Demarcation—The Location Where Telcos Wire Trunks
The local telephone company brings telephone lines into buildings and wires them to interfaces. The interface is called a jack or a punch-down block. Each outside line is punched down (wired) to the connecting block. Jacks that hold one line are called RJ11c jacks. The RJ stands for registered jack. These are the jacks found in most homes. The most common interface to which local telephone companies wire multiple outside lines in businesses is the RJ21x, which holds 25 lines. The RJ21x jack is a common point from which telephone lines and trunks can be tested. For instance, if there is a question on a repair problem as to where the problem lies, the telephone company can test its trunk to the RJ21x jack and the PBX vendor can test service between the PBX and the interface. The RJ21x jack is the demarcation point between the telephone company line and the inside wiring (see Figure 2.1).
Figure 2.1. A PBX connection to the central office.
PBX Telephones
Rotary telephones, called 500 sets, were introduced in 1896. When touch-tone became available in 1963, single-line touch-tone telephones, called 2500 sets, started being used. (Touch-tone originally was an AT&T brand name for dual tone multi-frequency, or DTMF.) In the 1950s, AT&T started selling electromechanical telephones with up to nine lines on each telephone. A hold button enabled users to put callers on hold to answer multiple calls on the same telephone.
By the 1970s, other manufacturers such as Rolm, initially acquired by IBM, now part of Siemens AG, sold competing PBXs. This was the start of the interconnect industry for customer premise equipment (CPE). On-site telephone systems have become more complex over the years. More features often have been synonymous with more complexity for the end user. Many people in the 1990s were nostalgic for the days when using a phone was as easy as dialing a call and everyone had the same type of “plain vanilla” telephone, and they all worked the same way.
User-Friendly TechnologyThe telecommunications industry has made strides in developing affordable, easier-to-use telephones. Features such as conference calling, speed dialing and transfer are available at the touch of a button on the telephone or softkey associated with a liquid crystal display (LCD). LCDs are getting larger and are no longer limited to two-line displays. New ones have eight lines and more displays. Liquid crystal displays have made phones easier to use by:
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Prices of user-friendly phones with feature buttons such as hold, transfer and conference and LCDs have dropped to the point where they are affordable for more employees. This has made it easier for people to use more of the telephone system's features.
Centrex—Telephone Company Supplied Service
The term Centrex is derived from the two words “central exchange.” In contrast to PBXs, where the switching equipment is located on organizations' sites, Centrex switching equipment is part of the telephone company's central office. Centrex serves only 15% of the total lines in the United States. This statistic was reported in an article titled, “IP Centrex—Are We Ready for It?” published in Voice 2000, supplement to Business Communications, page 42, May 2000, by Robert A. Gable. Many local telephone companies are not investing heavily in new Centrex functionality such as IP service. They are concentrating more of their efforts on high-speed data networking and cellular where they see more revenue potential.
The first fully automated Centrex system was installed in l965 at Prudential Life Insurance Company in Newark, New Jersey. The original motivation for Centrex is much the same as the motivation behind such automated services as voice mail today. Organizations wished to save money on operators, administration and space. Centrex provided four ways of realizing these savings:
No requirement for on-site switching equipment. The main Centrex switching equipment is in the telephone company's central office.
Direct-inward dialing to telephone users, saving money on operators to answer calls.
Direct-outward dialing without having an operator place calls.
Automatic identification of dialed calls. The telephone company bill identifies the telephone extension from which each outgoing toll call was made.
Where Centrex Is Used
Centrex is used by organizations with buildings spread out across a campus. Centrex provides connections between sites so that enterprises do not need to obtain rights of way for cable connections or purchase wireless infrastructure to connect buildings separated by public streets. Campus-type environments include those for:
Hospitals
Cities and towns
Universities
Large businesses with many buildings in an area
After divestiture when the local Bell telephone companies were split off from AT&T, local phone companies could no longer sell PBXs and key systems. Therefore, they turned to Centrex as a source of revenue. Regional Bell Operating Companies (RBOCs) such as Ameritech (now part of SBC) and BellSouth broadened their marketing of Centrex to the under-100-line market. Marketing campaigns stressed the reliability, ease of growth and phone company maintenance of Centrex for customers.
Centrex Sales Channels
The Regional Bell Operating Companies did not have the marketing expertise to effectively follow through on the preceding strategy. They therefore turned to sales agents as a channel to sell both Centrex and local toll-calling services. Sales agents generally also sell customer premise equipment such as PBXs, key systems, voice mail, cabling installation and equipment maintenance services. Sales agents receive a monthly fee from the local phone company plus extra commissions for installation of services such as T-1 and data communications lines. In return, the sales agent places all of the end users' repair, installation and change orders with the telephone company. They also sell voice mail and feature-rich telephones as a substitute for Centrex's usually plain vanilla phones.
Competitive local exchange carriers (CLECs) also sell Centrex in areas where they have their own central office switches and fiber optic facilities—generally large cities.
Centrex Telephone Sets
Three choices for Centrex telephone sets are:
Analog sets, the same type available for homes with or without features built into the telephone
ISDN and proprietary phones with features provided by the central office
Proprietary telephones with features provided by on-site key service units
The limitation with off-the-shelf analog telephones is that although they might have feature buttons for speed dial, transfer and conference, each holds only one or two lines. If a user with heavy telephone calling requirements needs two lines, he must pay the monthly fee for two Centrex lines.
Customers can get multiline capability that operate off central office intelligence by purchasing ISDN telephones or Nortel's P phones (the “P” stands for proprietary). Integrated Service Digital Network (ISDN) carries voice and data signals on one pair of wires so phones can handle multiple lines and features. (See Chapter 6 for ISDN.) However, ISDN is not available from all central offices and distance limitations prohibit customers far from the central office from having ISDN. The end result is that Centrex customers also often purchase customer premise equipment (key systems) to power user-friendly telephones. These systems generally include voice mail.
Centrex Connections to Central Offices via T-1
T-1, which can carry 24 lines, often is used to transport Centrex service from the telephone company's office to the customer. (See Chapter 6 for T-1.) The telephone company saves money on outside copper cabling when it supplies Centrex service on T-1 lines rather than on individual copper pairs for each Centrex line. For example, it might use one strand of fiber to carry four T-1s capable of carrying 96 (4 × 24) Centrex lines rather than laying 96 pairs of copper wire to a customer's premise.
Key Systems
Key systems are telephone systems for smaller organizations. While there are some technical differences in the way they handle calls, new key systems have all of the features and most of the functionality of private branch exchanges. Key systems generally serve the under-70-user-per site market.
The major difference between key systems and PBXs is the connection between the central office and the key system. Key systems are loop start and PBXs are ground start. With a ground-start PBX, a trunk is seized or grounded by the PBX or central office before a call is sent between the two locations. With a loop-start key system, if a path is available, the call is sent either to the key system from the central office or to the public network from the key system. The line between the customer location and the central office is not seized by the central office before the call is sent. Analog home phones also are loop start, which is why a person can pick up the handset to make a call and find that someone calling them is already on the phone even though the telephone has not rung.
On a key system, dial tone is derived from the central office. A person making an outside call on a key system does not have to dial an access code such as “9.” Pressing an outside line button on a key system telephone signals the central office that the end user wishes to make or receive a telephone call. This is the reason key systems have an outside line button to make or receive outside calls and an intercom button for internal calls.
In PBXs, the PBX provides the dial tone to the user. Users dial an access code, usually “9,” to make an outside call. The PBX responds to a lifted handset by sending a dial tone to the end user and then requesting that a trunk to the central office be “grounded” or seized to make a telephone call.
New key systems provide most of the functionality of a PBX. In fact, many larger key systems are “hybrid” systems. They can be installed as either key systems with outside lines, or PBXs with grounded trunk connections to the central office and the requirement to dial an access code such as “9” to make outside calls.
Wireless PBX and Key System Telephones—On-Site Mobility
Anyone who has waited for an important telephone call knows that as soon as you step away from the telephone for a coffee break or to take part in a meeting, the call you have been waiting for arrives. Staff such as nurses, warehouse employees and technicians spend more time away from their desks than at their desks. Wireless telephones enable workers to be reached (and interrupted!) at all times if they take their phones with them and turn them on.
PBX and key system wireless telephones are high profit-margin peripherals. The high costs, about $2000 per telephone, have limited the number of wireless telephones sold. The telephones have the features associated with the PBXs and key telephone systems with which they work. These features include:
Hold buttons
Speed dial buttons that enable abbreviated dialing of frequently called numbers
The same extension number for both the wireless and desk telephone
LCD screens to show the name of the person calling
Voice mail message waiting lights
The structure of in-building wireless systems resembles cellular service described in Chapter 9. In-building systems consist of base stations, cards in the telephone system and antennas. However, instead of being connected to a mobile switching office (cellular central office), the base station is connected to the PBX. Base stations and antennas are located on every floor (see Figure 2.2). The base stations are wired to radio controller circuit cards in the telephone system cabinet. Each circuit pack supports two to four base stations. Base stations generally support four antennas. Like cellular systems, base stations hand off calls to nearby antennas and base stations as workers move around the building. Because in-building base stations cover smaller areas, their coverage areas are referred to as picocells. Picocell refers to very small cell sizes.
Figure 2.2. In-building wireless telephones.
Outdoor antennas are available for coverage between buildings on a campus. All buildings need to be connected to the same telephone system for this arrangement to work. An engineering study needs to be conducted to determine placement of antennas.
Limited-Range Cordless Phones
Many PBX and key system suppliers provide lower priced “home type” or proprietary 900-megahertz (MHz) wireless phones. Limited-range cordless phones do not work on an in-building cellular structure previously described. The phones only work within range of the antenna in the phone and the phone's base unit. The 900-MHz phones have a range of about 125 to 150 feet, depending on building conditions. There also is an upper limit of about 20 cordless phones supported in the same building.
Proprietary cordless phones have features powered by the phone system to which they are connected. These features, voice mail message lights, multiple call appearances and hold buttons, make the phones easier to use and more functional. In-building wireless phones are used for the following personnel who often use headsets with their phones:
Console operators, to be able to take calls when they step away from their desk for functions such as making copies
Warehouse employees
Retail store personnel who can take calls from anywhere in the store
Call center agents
People who work at home
In-Building Wireless Connections to Public Cellular Networks
There are systems on the market in which users can receive cellular calls on their PBX phones. This enables them to use one telephone number for all business calls and check one voice mail system for messages. Unanswered calls to both cellular and PBX phones are answered by the same PBX voice mailbox. The PBX senses when it is out of range for internal PBX calls, which are then sent to the cellular network.
AT&T Wireless and Nextel have offerings that let employees receive four-digit PBX and key system calls on their digital cellular phone. The service works on their cellular phones in their building (but away from their desk) and, when they are out of their building, in an area with digital AT&T Wireless and Nextel service. The AT&T system uses signaling bits in the TDMA digital control channel to notify the cellular network that the subscriber is part of a particular organization. Calls made within the customer building are routed through the PBX and do not incur cellular air-time fees.
The in-building system is made up of the following devices as depicted in Figure 2.3:
Picocells located throughout a building contain antennas (transmitter and receiver) and a base station. They are connected to the system controller.
A controller located adjacent to the PBX. A serial port connects the controller to the PBX by a Primary Rate Interface (PRI) ISDN link. PRI ISDN are digital trunks with 23 voice/data channels and one signaling channel. (See Chapter 6 for PRI ISDN.) The signaling channel carries information about the cellular user's telephone status and dialing. The controller manages network configuration, controls operation of the picocells and is used for maintenance, billing and provisioning.
A system administration computer connected to the controller.
Cellular calls and billing information are routed to the PBX from the on-site controller connected to the network by a Frame Relay data communications link. Frame relay service provides access to carriers' data networks. (See Chapter 6 for Frame Relay service.)
Figure 2.3. In-building Wireless Service
Ericsson, Hughes Network System, Inc., Ascendent Telecommunications and AG Communications manufacture in-building wireless systems that let employees use one number for in-building and cellular digital calls. AT&T Wireless and Nextel sell these products to end users. Siemens is close to offering a product in the United States and Alcatel sells a Global System for Mobile Communications (GSM)-based system in Europe. (See Chapter 9 for a description of GSM cellular service.)
Direct-Inward Dialing—Bypassing the Operator for Incoming Calls
Direct-inward dialing (DID) was a major innovation for handling incoming calls. DID routes incoming calls directly to a PBX or key system telephone without operator intervention. Before the late 1980s, local telephone companies priced DID so high that only large organizations purchased it. Pricing has been lowered considerably, and now small organizations use direct-inward dialing.
Organizations purchase groups of “software” telephone numbers. As Figure 2.4 illustrates, these numbers share trunks. Each number is not assigned a specific trunk. Depending on the traffic requirements at the site, there generally is one trunk per eight to ten DID numbers. The central office looks at the number dialed on the incoming call and identifies it as belonging to a particular organization. The central office then passes the last three or four digits of the dialed number to the organization's key system or PBX. The on-site telephone system reads the digits and passes the call directly to the correct telephone.
Figure 2.4. Direct-inward dialing from the central office to each telephone in a building. There are 10 trunks and 100 software numbers.
Most medium and large companies receive their DID calls over the same T-1 used for their other incoming and outgoing calls. (See Chapter 6 for T-1.) Instead of separate media for each type of service, all services share the same wires, fiber optic cable or fixed wireless service. (See Chapter 4 for fixed wireless service.) For backup purposes, customers may leave a few telephone numbers on individual analog lines or order T-1 from multiple carriers. In the case of a T-1 failure, calls can be routed on the individual analog or the backup T-1 lines.
Convergence and Telephone Systems
Traditional proprietary PBXs and key systems such as Avaya, Nortel and Toshiba systems, carry circuit-switched voice. Circuit-switched networks save a path in the network for the entire duration of a call. Converged phone systems use voice over IP (VOIP) packet technology. Packet-switched networks send traffic in envelopes of bits called packets. Individual packets to the same address can be sent over different routes depending on traffic on a particular route. Because capacity is not saved for the entire length of a transmission, packets of data and voice can share the same LAN infrastructure. Moreover, packets from multiple sources can be sent on the same “path” during very small pauses between messages. However, if traffic is heavy, the voice quality might be degraded if packets are dropped or delayed because of congestion. For telephone systems that share the LAN, two issues are critical: The LAN must have enough capacity and voice needs to be adequately compressed to travel efficiently over the LAN.
Most people with IP-based phone systems have them connected to the public switched network for the majority of their calls. They use their LAN to carry internal calls. They also can use Frame Relay or other connections to carry VOIP between their own sites. Frame Relay service is a way to access carrier networks for traffic between LANs. They also use these links to transfer customer calls between sites. (See Chapter 6 for Frame Relay service.)
IP-Based Telephone Systems
IP-based telephone systems are installed on standard servers such as Windows NT– or Windows 2000–based servers connected to local area networks (LANs). They share the LAN wiring for switching and routing calls. (See Figure 2.5.) Many companies have unveiled telephone systems that work on organizations' LANs using the IP (Internet Protocol). According to Alan Sulkin as cited in the article titled, “IP-PBXs—More Than Technical Hurdles to Overcome,” published in Business Communication Review, page 80, April 2001, by Richard A. Kuehn, shipments of IP-based PBXs represented 3.5% of total year 2000 sales. While market penetration is still low, potential of the technology and interest in its benefits are high.
Figure 2.5. IP PBX connection to the LAN.
Traditional PBX manufacturers such as Avaya, Alcatel, Siemens and Mitel have equipped their key systems and switches with IP capabilities. Data networking vendors Cisco, with its AVVID (Architecture for Voice, Video and Integrated Data) product, and 3Com, with its NBX system, also have premises-based IP solutions for voice. The 3Com system mainly is sold to small locations.
Other vendors of IP-based telephone systems are:
Shoreline Communications
Altigen
Sphere
Vertical
Nortel
Centrex-Based IP Systems
Telephone companies have announced their intention to offer IP service that customers can use for some employees while retaining their traditional circuit switched Centrex. IP Centrex is available with specialized IP telephones, or softphones. Its advantage is that it enables workers to telecommute and to use their phone service when they travel. As long as they can log in remotely to their LAN, their phone service will work if they have a computer or laptop with a microphone. Outside calls to and from Centrex IP would use the public switched network. Gateway devices to convert between circuit switched and IP formats are located at the telephone company offices and are connected to traditional central office switches. It is not currently widely available.
Impetus for IP-Based Phone Systems
The impetus behind IP-based telephone systems is cost savings on hardware, implementation, wiring and the addition of new applications, as well as total cost of ownership. Total cost of ownership refers to not only the purchase price but also the cost of a system over its life including maintenance, upgrades and changes. Because IP-based systems operate on standard servers, synergy in staffing may be possible by having the same staff support voice and data networks.
Current PBXs and key systems are based on proprietary protocols and signaling. Adding new applications such as call centers, voice mail and customer service systems to handle Web-originated requests often is costly because of their proprietary nature. An advantage to standards-based products is the development of peripheral products such as “click to talk” service for customer service at Web sites. These enhancements currently require costly links between proprietary PBXs and corporate databases to translate between the unlike platforms. When services work on standards-based platforms, they can interoperate without costly interfaces between them because they use like protocols.
Phones for IP-Based Telephone Systems
IP-based systems support analog phone, multifeatured telephones and softphones. Softphones are PC-based phone software that enable users to plug telephone handsets into personal computers. Softphones enable employees to use their PC instead of a phone for telephone calls. Features such as hold buttons, caller ID and message waiting alerts appear on their PC screen. The advantages of softphones are savings on telephone hardware and increased mobility for users. If the software is installed on a laptop, staff can use the softphone anywhere on the corporate network or remotely if remote access is enabled. Because IP systems are in their infancy, not all systems support each of these types of phones.
Each telephone is connected to the organization's local area network. It can share the same telephone cable as the end-user's PC or have its own cable to the wall jack. On some systems, each telephone needs its own power. They can be powered locally or from a power supply in the wiring closet. Most traditional PBX and key system telephones get their power from the telephone system. In a power outage, a two-hour backup of the phone system keeps all of the phones working as well as the telephone system processor.
Voice Quality
Quality of voice on voice over IP (VOIP) systems is improving because of better digital signaling process (DSP) chips and higher capacity LANs with capacity for both voice and data. DSP chips digitize voice and compress it into smaller chunks so that it can be sent on the LAN without disrupting other traffic. Most systems support H.232 and/or Session Initiation Protocol (SIP) VOIP standards. When voice is sent on the LAN, the DSP puts it into packets, which are like envelopes of data. Many of the systems also have ways to give voice priority over data on the LAN to maintain the quality of voice calls.
Barriers to Acceptance
Factors in the slow acceptance of local-area-based phone systems are:
Cost— As is often the case with new technology, initial releases are more expensive than existing technology because of high startup expenses.
Reliability— PBXs and key systems rarely crash. Users are concerned about replicating this reliability on LAN-connected systems. Interestingly, Avaya's small office IP product is based on a proprietary processor board that, according to the article, “More IP-PBX Options,” published in Business Communication Review, November 2000, page 86, by Alan Sulkin, is more reliable than standards-based servers. Servers are high-capacity computers that store corporate files such as email on LANs.
Features— New systems are just starting to have the features of proprietary PBXs and key systems. To date, many of them don't have the full array of features.
Existing installed base of telephone systems— The average telephone system lasts 10 years. Firms with working telephone systems do not rush to replace them with new technology. Many telephone systems can be upgraded at a lower cost than buying a total replacement because the upgraded systems reuse certain cards, telephone sets or cabinetry.
IP-based telephone systems have had more initial acceptance by small or startup firms who wish to use their data wiring for both telephone and computer connections. Many of these firms are more open to innovation and don't have legacy proprietary systems. To overcome concerns about reliability of the LANs that support IP-based phone systems, companies sometimes install the system on LANs segregated from their main LAN. If their main LAN crashes, the LAN that supports the telephone system will still operate.
Connecting Telephone Systems to Intracompany IP Networks
Often, customers with private-line, Frame Relay or virtual private network (VPN) connections between their locations use these connections for voice and fax as well as data. (Frame relay and VPN-accessed networks connect locations together via carrier services; see Chapter 6.) If calls are answered in a central location, customer calls are transferred over the voice over Internet protocol (VOIP) links as well. As illustrated in Figure 2.6, the transfers are made by connecting telephone systems to on-site routers. The voice and facsimile traffic use spare capacity in the VPN or private lines. Often, the data connections are upgraded for more capacity to handle voice and fax traffic. The upgrade is less costly than separate T-1s for voice.
Figure 2.6. PBX connected to an IP network.
At the sending end, the voice is:
Digitized
Assembled into packets
Compressed, or made smaller
At the receiving end, the voice is:
Put into a format readable by the telephone system
Reordered into the order in which it was sent
Decompressed
Voice is converted to IP in gateway devices. Gateways translate protocols so that incompatible devices can communicate with each other. The gateway can be in the telephone system, a separate device or in a router. Gateway functionality in routers is located on cards with digital signal processors in them. For example, Cisco Systems has a voice card that uses Texas Instruments DSPs. The digital signal processor (DSP) compresses the voice from 64,000 bits per second to 8,000 bps. The header adds 4,000 bits per second for a total of 12,000 instead of 64,000 bps.
Certain PBX vendors such as Avaya and Nortel Networks manufacture cards that sit within their telephone systems to convert voice from analog to digitized IP-compatible voice. In this case, the voice can be transmitted from a router not equipped with a voice card. Some gateways have the capability to monitor traffic on IP data lines and route traffic over the public switched network in the event of congestion on the data line.