Systems : Key Telephone System (KTS)

Systems
The different types of systems used in private telephone networks include key telephone systems (KTS), private branch exchange (PBX), Centrex, and computer telephony integration (CTI). Key telephone and PBX systems often use proprietary specifications. There are several industry standards that are used for computer telephony and LAN telephony system.

Key Telephone System (KTS)
A key telephone systems (KTS or key systems) is a multi-line private telephone network that allows each key telephone station to select one of several telephone lines. Key systems contain a key service unit (KSU) that coordinates status lights and lines to key telephones (Key Sets). Key systems have some advanced call processing features such as call hold, busy status, and station-to-station intercom.

KTS are relatively simple non-switching telephone systems. The KSU only interfaces (connects) key sets to the public telephone lines allow calls to directly pass through. The KSU does sensing and provide display status lines to each key service unit. The first generation key systems allowed multi-button telephones to have an appearance (e.g., a button) for multiple end office lines. When the incoming telephone line received a ringing signal, the key system flashed the appropriate button. To answer the call, the user picked up the handset and pressed the flashing button. This off-hook indication is sensed by the KSU which results in the the key set’s line status light to become solid. This indicated to other telephone users that the line was being used.

To place a call, the user would first view the lights on telephone line buttons. If a button was not lit, the user pressed the button. Again, the KSU sensed the off-hook condition and a solid light came on on all key sets.

To allow key sets to talk with each other without connecting through the public telephone network, most KTS systems included an intercom feature. The intercom feature allowed a key set to call one or all the key sets that are connected to the KSU.

Figure 1 shows a typical key telephone system. This diagram shows telephones wired to a key service unit (KSU) that is connected to the PSTN. The KSU allows the telephones to have access to the outside lines to the PSTN. The KSU controls lights on the telephone sets, intercom access, and call hold.


Figure 1: Key Telephone System

Technologies : Automatic Call Distribution (ACD), Interactive Voice Response (IVR)

Technologies
Some of the key technologies used in private telephone systems include digital packet voice telephony, automatic call distribution (ACD), and interactive voice response (IVR).

Digital Packet Voice Telephony
Digital packet voice telephony is a communication system that uses digital data to represent and transfer analog signals. These analog signals can be audio signals (acoustic sounds) or complex modem signals that represent other forms of information.

Modern private telephone systems use digital telephony to connect the handset to the local switching system. The analog signal is converted to digital form in the telephone set. By using digital information to represent analog signals, the digital communication system can integrate digital voice information along with advanced signal processing control messages.

Figure 1 shows the digital communications process that uses packet data to connect telephone sets (packetized voice). This diagram shows that the sending telephone set samples and converts the audio signal into digital form. The telephone set may compress the digital information to increase the system efficiency. As data is created, it is divided into packets and the destination address is added to each packet along with a sequence number. Each packet is then transmitted through a packet switching network where they are reassembled at their destination. The received data is then decompressed in turned back into its original analog form.


Figure 1: Packetized Voice over Data Networks

Automatic Call Distribution (ACD)
ACD is a system that automatically distributes incoming telephone to specific telephone sets or stations calls based on the characteristics of the call. These characteristics can include an incoming phone number or options selected by a caller using an interactive voice response (IVR) system. ACD is the process of management and control of incoming calls so that the calls are distributed evenly to attendant positions. Calls are served in the approximate order of their arrival and are routed to service positions as positions become available for handling calls.

ACD systems allow for incoming calls to be distributed specific customer service representative (CSR) or among a group of people. The call distribution is based on previously stored programs, or algorithms that determine the routing of the incoming call. Application of ACD is found primarily in customer service, catalogue sales, and other customer relation areas. ACD systems can forward calls to CSR representatives that are located in other areas or even who are operating on other systems. This allows companies to locate CSRs anywhere in the country or possibly in other countries.

Figure 2 shows a sample ACD system that uses IVR system to determine call routing. When an incoming is initially received, the ACD system coordinates with the IVR system to determine the customer’s selection. The ACD system then looks into the databases to retrieve the customers’ account or other relevant information and transfer the call through the PBX to a qualified CSR. This diagram also shows that the ACD system may also transfer customer or related product information to the


Figure 2: Automatic Call Distribution (ACD)

Interactive Voice Response (IVR)
IVR is a process of automatically interacting with a caller through providing audio prompts to request information and store responses from the caller. The responses can be in the form of touch-tone(tm) key presses or voice responses. Voice responses are converted to digital information by voice recognition signal processing. IVR systems are commonly used for automatic call distribution or service activation or changes. IVR systems use pre-stored voice prompts and a structured menu system that is layered under each option. Layering allows callers to navigate to specific information areas.

Figure 3 shows a sample IVR system that is used to route an incoming call. When this call is received by the PBX, an initial voice prompt informs the user of the system along with initial menu options. The user selects and option. This results in the playing of another prompt indicating new menu options. The user enters the data for the option and the IVR system retrieves data and creates a new verbal response.


Figure 3: Interactive Voice Response (IVR)

To avoid some of the customer dissatisfaction and to handle miscellaneous customer needs, there are often options available in each layer that allows the caller to switch other main menus or to switch to a live “operator.” IVR systems may also regularly provide feedback to the caller of the timing of queuing delays.

Market Growth : Private Branch Exchange Market

Market Growth
The market for key systems has primarily been replaced by PBX systems and the market for PBX systems is decreasing as they are being replaced by computer telephony systems.

Private Branch Exchange Market
The PBX market has been experiencing a decrease in annual sales since the mid 1990s. In 2000, sales of PBX systems declined by 10%. With computer telephony becoming a cost-effective solution for most companies, traditional PBX systems are slowly being phased out. However, there continues to be a growing market for small PBX that are used in small office/home office (SOHO).

Figure 1 shows the trend that has sent PBX manufacturers scurrying to shore up other technological areas. Emphasis has been recently shifted to networks and distributed intelligence via those networks. PBX’s have not become the networking “mother ship” predicted in the 1980’s and early 90’s. The Internet, VPN’s, and ATM functionality are replacing larger PBX systems.


Figure 1: PBX Market Growth

Computer Telephony Market
The computer telephony market is the key growth area in the private networking industry. In the year 2000, 17% of all U.S. businesses with existing PBX systems began a transition to computer telephony systems.

By 2005, CTI systems are expected to penetrate into 80% of all United States businesses. Computer telephony systems are becoming popular because CTI systems only cost $300-$500 per seat compared to PBX systems that cost $800 or more per seat.

Sales of computer telephony equipment in 2000 was $138 million dollars, up from less than $10 million in 1998. CTI equipment sales are expected to exceed to $3.2 billion dollars by 2005. Figure 2 shows a growth of CTI market worldwide.


Figure 2: Computer Telephony Market Growth

Private Telephone Networks : Switching Systems, Numbering Plan

Switching Systems
Private telephone switching systems are network devices that are small versions of telephone switching systems. Early key telephone switches used mechanical levers (crossbars) to interconnect lines. These were called key service units (KSUs). PBX systems use a time slot interchange (TSI) memory matrix to dynamically connect different communications paths through software control. Computer telephony and LAN telephony systems use packet switching systems to interconnect one of more telephone station with each other.

For large private telephone systems, some of the switching functions may be distributed to remote points. An example of distributed switching is the Nortel RPE that allows the Meridian PBX to remote a portion of its station interface to a remote site via a pair T1’s or E1’s.

Numbering Plan
Each extension in a private telephone system has a unique extension number. The station numbering plan for private telephone systems is controlled by the owner of the private telephone system. Many private systems have a limited range for extension numbers (e.g., 1000 -1999. This extension range is restricted due to hardware configurations.

When private telephone systems are interconnected to the public telephone network, the CCITT world numbering plan (E.164) and national numbering plans are used. PBX call processing systems are able to filter numbers to enable least cost routing (LCR). LCR is a telephone system feature that routes the connection of a call over the least expensive route available at the time the call is originated.

To allow automatic routing of incoming calls, direct inward dialing (DID), or higher-level trunk lines (e.g., T1 or E1) with advanced signaling may be used. DID connections are 2-wire trunk-side (network side) EO connections that provide additional information to the PBX to allow the automatic routing of calls within the PBX system. Although network signaling on incoming 2-wire circuits is primarily limited to one-way, incoming service, DID connections employ different supervision and address pulsing signals than dial lines. Typically, DID connections use a form of loop supervision called reverse battery, which is common for one-way trunk-side connections. Until recently, most DID trunks were equipped with either Dial Pulse (DP) or dual tone multifrequency (DTMF) address pulsing. While many carriers would have preferred to use multifrequency (MF) address pulsing, a number of LEC’s prohibited the use of MF on DID trunks.

Private Telephone Networks : Telephone Stations, Local Wiring

Telephone Stations
Telephone stations are telephone instruments that are connected to a telephone network for the purpose of telephony. When these telephone stations are used as part of the private network, they are often identified by the type of system they are connected with. For example, telephone stations that are connected to key systems are called key telephones.

Telephone stations can vary from simple POTS telephones (sometimes called 2500 telephones) to complex Internet telephones (IP Telephones). Telephone stations usually receive their power from the telephone line (loop current) but may receive it from an external source (such as the PBX switching system).

Figure 1 shows a typical telephone station that is used in a PBX system. This diagram shows the difference between standard analog telephone stations and more advanced PBX stations. This diagram shows that analog telephones receive their power directly from the telephone line and digital PBX telephones require a control section that gets its power from the PBX system. Analog telephones also use in-band signaling to sense commands (e.g., ring signals) and to send commands (e.g., send dialed digits). Digital telephones use out-of-band signaling on separate communication lines to transfer their control information (e.g., calling number identification).


Figure 1: Analog and Digital Telephone Stations

Local Wiring
The local wiring for private telephone systems includes the lines between the telephone stations and switching assemblies or interconnection equipment. Local wiring systems may include interconnection points or wiring rooms. Incoming trunks enter the building in a main distribution frame (MDF). Trunks between multiple floors or other buildings are called intermediate distribution frames (IDFs). These IDF areas are often referred to as “wiring closets” because in the past telecommunications wiring was seldom considered when designing a building and the space available for terminating cables was usually in utility closets.

Private telephone system wiring is usually connected through unshielded twisted pair (UTP) wire. There are exceptions where shielded cable, coaxial cable, or fiber is used. Shielded cable is used in areas the may cause or be sensitive to electromagnetic interference (EMI) such as hospital radiology areas or near high voltage equipment in manufacturing plants. Coaxial cable and fiber is used for high-speed data inter-connection trunks or for LAN backbone systems that are part of the private telephone system.

Figure 2 shows the typical wiring systems that are used for private telephone systems. Key systems required many pairs (12 or 25 pairs typical) of lines for each telephone. These telephones were wired to a punch block (splice point) near the telephones. The punch block was connected to the key service unit (KSU). Analog PBX systems usually required 4 wire connections from extension telephones to the PBX switching unit. Two wires were used for audio and two (or more) wires for status or special feature lines. Digital PBX systems connect to each extension using 4 wires. Two wires are used for audio (analog or digital) and two are used for external power. This diagram shows that some digital PBX systems may use multiplexed digital lines to allow multiple phones to share a single line (e.g., a line between building). When this occurs, it is called a remote peripheral equipment (RPE). The RPE separates (demultiplexes) the digital line from the PBX to multiple digital stations.


Figure 2: PBX Local Wiring

Private Telephone Networks : Overview

Private Telephone Networks
Private telephone networks are communication systems that are owned, leased or operated by the companies that use these systems. These telephone systems include key systems, private branch exchange (PBX) systems, computer telephony, and local area network (LAN) telephones. Private telephone systems that are owned or operated by a company or private individual are called customer premises equipment (CPE).

Private telephone systems primarily allow the interconnection of multiple telephones within the private network with each other and provide for the sharing of telephone lines from a public telephone network. Private telephone systems can vary from simple multi-line telephones (key systems) to integrated voice and data service LAN telephone networks.

The first private telephone systems were key telephone systems. These systems used multi-line telephones to provide access to outside lines and used intercom features to allow inter-station connections.

As switching technology improved, small switching systems were installed to provide private branch exchange (PBX) systems. PBX systems provide switching between incoming trunk lines (multiple channel lines) and provide for advanced inter-system calling features.

To offer similar services as PBX systems, central exchange (Centrex) services were developed for end office (EO) switches. Centrex software allows local telephone companies to provide similar features as private telephone systems. These features include 3 or 4 digit abbreviated dialing, automated attendant (call transfer), least cost routing (LCR), and other local switching functions.

CTI systems integrate computer networks and telephony systems. CTI allows PBX technology to provide for voice mail, interactive voice response (IVR), and automatic call distribution (ACD) functions.

The combining of LAN systems with telephone systems is called LAN telephony. LAN telephony allows the sharing of equipment data network cost with telephone system cost.

Figure 1 shows the different types of private telephone systems. This diagram shows the first telephone systems were multiple line key telephone systems. This changed to private branch exchange (PBX) systems. Computer telephony (CT) systems are communication networks that merge computer intelligence with telecommunications devices and technologies. Local access network (LAN) telephony (sometimes called TeLANophy) use LAN systems to transport voice communications.


Figure 1: Private Telephone Systems


Overview
Private telephone systems are composed primarily of telephones (called “stations”), local wiring, and switching systems. Telephone stations are the interface between the user and the telephone network. Wiring connects telephone stations to switching systems or distribution points. Local wiring in private systems varies from shared lines (key systems) to individual lines (digital stations). Switching systems interconnect stations to each other or to outside telephone lines or interoffice trunks.

Companies purchase or lease private telephone system and have one or more of their personnel trained to handle day-to-day administrative functions of the system. Practically all PBX’s and key systems today are computer-based and thus allow for soft changes to be made through an administration terminal or PC. Unless the business has a need for technical telecommunications personnel on staff for other reasons, the business will normally contract with their vendor for routine adds, moves, and changes of telephone equipment.

PBX systems are often equipped with key assemblies and systems including voice mail, call accounting, a local maintenance terminal, and a dial-in modem. The voice mail system is controlled by the PBX only receiving calls when the PBX software determines a message can be left or retrieved. The call accounting system receives system message details on all call activities that occur within the PBX. The local terminal provides onsite access to the PBX for maintenance activities. The dial-in capability also provides access to the PBX for maintenance activities.

Future Enhancements: Packetized Voice, High-Speed Multimedia Services, Fiber Distribution Networks, Soft Switches

The future enhancements to public switched telephone networks include the conversion from circuit switched systems to packet networks, expanded fiber networks, multimedia services, and soft switching systems.

Packetized Voice
Packetized voice is the process of converting audio signals into digital packet format, transferring these packets through a packet network, reassembling these packets into their original data form, and then recreating the audio signals.

By the end of 2001, over 5% of international calls from the United States were over the Internet and more than 9.5% of all inter-exchange telecommunications calls were on managed packet switching networks [7]. Packetized voice transmission allows for key features such as dynamic bandwidth allocation and advanced services. To convert to packetized voice, the EO exchange is either replaced or supplemented by a packet switch.

Various protocols such as resource reservation protocol (RSVP) and real time protocol (RTP) have been developed to ensure the quality of service of voice packets that are transmitted through a packet network.

High-Speed Multimedia Services
High-speed multimedia services is the term used to describe the delivery of different types of information such as voice, data or video. Communication systems may separately or simultaneously transfer multimedia information. High-speed multimedia usually refers to image based media such as pictures, animation, or video clips. High-speed multimedia usually requires peak data transfer rates of 1 Mbps or more.

The providing (provisioning) of multimedia services requires communication lines that can have multiple channels and each of these channels may have different quality of service (QoS) levels. As a result, many emerging multimedia services are likely to use ATM.

Fiber Distribution Networks
Fiber distribution networks use optical fiber to distribute communication channels from the PSTN to end customers. There are three key distribution networks: fiber to the neighborhood (FTTN), fiber to the curb (FTTC), and fiber to the home (FTTH).

Figure 1 shows that public telephone networks have growth options. Initially, they are likely to install (FTTN) and use existing copper lines to reach the home. As demand grows for high-speed data communication services, additional fiber may be installed from the node to the curb (FTTC) to replace copper lines. Eventually, to achieve extremely high data rates to the home or business, FTTH or fiber to the basement (FTTB) may be installed.


Figure 1: Fiber Optic Networks

Soft Switches
Soft switches are interconnection switching systems that can dynamically change its connection data rates and protocols types by software control to provide for voice, data, and video services. Soft switches were developed to replace existing EO switches that have limited interconnection capabilities. Soft switches are packet based and can simulate multiple protocols such as Internet protocol and ATM. This allows for multiple types and simultaneous services to each customer with varying levels of QoS.