KSU vs. non-KSU Systems
There are two types of high-end residential telephone systems available: KSU (key system unit) systems and KSU-less systems. Both KSU and KSU-less systems come in a variety of different sizes, measured by the number of outside lines (CO lines) and telephone extensions they can handle. While one system might support three incoming lines and eight extensions, another might be able to manage as many as 12 incoming lines and 24 extensions.

KSU systems, similar to security systems, use a central control unit that maintains the programming, connects available outside lines to extension phones, and handles all phone functions such as transferring calls between extensions, call hold, and so on. Control units can be programmed to assign system features selectively to each extension,

KSU systems also use special, proprietary, phones designed to work with the specific control unit. These phones have numerous special functions buttons to handle tasks such as selecting a specific outside line, transferring the call to another extension, hold, flash, and so on.

KSU phones require two or three pairs in the 4-pair TP cable to the extension outlet. One of the pairs is used for voice signals and the other one or two pairs are used for control functions between the phone and the system control unit. KSU phones typically have dedicated buttons for each phone function as well as the standard numeric keys and an LCD display to show everything from caller-ID information to the time and date.

KSU systems require that the system control unit be installed at a central location (usually mounted next to the structured wiring center) and that every telephone cable be wired to that box. These systems rely on either a structured wiring system with home-run wiring to each outlet or home run outlet cables to the control unit. This usually limits installation to new construction.

A "hybrid" KSU system is designed to work with proprietary phones but can also use "standard" telephone handsets and even cordless phones although all the control unit functions may not be accessible from the nonproprietary phone. For example, most of the functions that are accessible by a special button on the system phone may be accessed by pressing the * or # key and then a numeric key on a regular phone. Also, accessing an outside line may require dialing 9 first.

The second type of phone system, referred to as a "KSU-less" telephone system, does away with the special controller and cabling, usually making it a better option for existing homes. KSU-less systems rely on special proprietary phones that have the functions of a KSU system built -in to each phone. These phones have buttons specifically for functions such as call hold and transfer, intercom, conferencing and speakerphone and are designed to operate between themselves. Functions like intercom and call transfer will only work between like phones attached to the same telephone wiring.

KSU-less system phones can also operate on existing parallel or "daisy-chain" telephone wiring and use only one pair (the line-1 pair) of wires for all functions although many support 2 or 3 CO lines.

Note that there are NO standards in the phone system industry and that handsets or components from one manufacturer will not work with components from another manufacturer. There is also limited interoperability between components by the same manufacturer so be sure and check the interoperability with the company or representative before selecting handsets or other components.

Typical KSU telephone system components

All wiring originates at the KSU control unit. It contains all the switching and interface electronics, programming and intelligence for the system. Depending on the size of the system a residential sized control unit will handle between 4 and 6 incoming (CO) lines, and 12 to 24 extension lines. If needed, commercial versions will handle much larger configurations.

The extension lines may be wired directly to the control unit or routed through a structured wiring panel for added flexibility in connecting outlets to extension lines. Either proprietary phone handsets designed to work with the system or, if it is a hybrid system, standard handsets are attached at extension outlets.

Most systems provide a computer interface (EIA-232) for system setting up, programming or monitoring system operation. The interface can be connected to a computer, a CRT terminal, or possibly a home automation system.

Message Processing
Most systems can provide full voice message processing including voice-mail for each family member by an add-on voice processing system. Voice processing systems (VPS) can provide several voice mailboxes for different family members capable of storing hundreds of incoming messages digitally. The VPS will also auto-answer incoming calls with 20 or more custom greetings (some programmed to only play on specific days) and routes them to the appropriate extension mailbox. Using caller-ID the VPS can also announce incoming callers by prerecorded identification using the speakerphone feature of the system phones.

Messages can be retrieved by pressing a message-waiting key on in-home phones or remotely by entering a numeric password. Live call-screening from any extension is also provided so an incoming call can be monitored while it is being recorded.

A line-level music input is also provided to supply music on-hold for incoming calls or at an extension line when it is put on hold.

Remote Entry Options
Some systems have door intercoms and door locks that attach to the control unit. Pressing a button on the door intercom will announce someone is at the door on the intercom function of the system and allow hands-free conversion with the door intercom from a speakerphone extension. Any extension can also "buzz" the door open from the phone keypad.

KSU Handset Wiring
KSU handsets need two or three pairs (typically two) from the outlet to the system controller. Line one (the blue pair on pins 4-5) is used for normal analog voice and one or two other lines are used for digital communications from the phone to the system controller and to supply DC operating power to the handset. One of the advantages of KSU systems is that the handsets do not require separate power modules at each phone location.

In hybrid-KSU systems, line-1 from the system controller also provides normal phone line operating voltages, ring signals, busy signals, etc. to allow a standard phone to operate normally.

KSU-less Systems
Figure 4.5.2 illustrates how a KSU-less system is installed using proprietary "smart phones".

Typical KSU-less phone system.

Programming
All phone systems allow various features, options, and special functions to be programmed for each installation. Programming is usually done in one of two ways: by using one of the proprietary phones (with an LCD display and full key set), or by attaching a computer using an EIA-232 interface. Using a handset, features can be turned of/off or set to a value by using the keypad and LCD display. When using a PC, the PC must either run set-up software provided by the manufacturer or a "dumb terminal" software that allows the PC to emulate a CRT terminal function.

Once programmed, the system will retain the programming during power outages.

Equipment placement planning
KSU system controllers must always be located in a conditioned space. Operating limits are typically 40 - 90 degrees F. The most convenient mounting location is next to the structured cabling system panel to allow easy wiring between the units. The KSU controller will also require access to 110 V AC power and a good ground conductor to the building grounding electrode (typically installed for the structured cabling system).

Wiring
diagram of a telephone line wiring of a KSU system when used with a structured cabling system.

KSU integrated with a structured cabling system. CO lines go from cross-connect to CO line input on KSU. This example shows line 4 dedicated to a DSL modem. Extension lines from the KSU terminate on a line distribution block in the structured cabling panel. Voice outlet cables connect to the desired extension lines.

Incoming CO lines are wired from the NID to the auxiliary disconnect on the structured cabling system. Depending on the particular installation, the CO lines will connect from the structured cabling system cross-connect to the CO line inputs on the KSU system controller.

Lines can be shared with dedicated telecom applications such as fax machines or analog modems, but many KSU systems will attempt to connect to the line, even if it is in use (off-hook) by another device, causing possible data loss and disruption.

If a DSL modem is used, one CO line may be dedicated to the DSL modem or the line may be shared with a KSU system line. In which case, the DSL modem must be wired to the CO line side of the KSU, never to one of the extension lines.

The extension lines from the system controller to the outlet jack should be wired according to TIA-570A specifications using an 8-pin modular jack and plugs wired per T568A (see Section 3). A KSU system will use the blue, orange, and optionally the green pair for KSU handsets.

Typically, the extension lines are connected from the KSU controller to a structured cabling voice line panel or module. Extension cables to outlets are then plugged-in (or punched down) to the appropriate extension jack. This allows changes to be made in the structured cabling system instead of the KSU controller-usually a more convenient arrangement.

Wiring for optional system features such as music-on-hold, door intercoms, and so on will require home run wiring from the KSU controller to the optional device.

Use of KSU-less system phones with other phone-line applications
Some KSU-less system handsets may not be compatible with other services that use the active phone-lines in the house such as DSL modem signals or HomePNA home networking signals. Check carefully with the manufacturer to determine if these services can coexist. Special filters used to isolate phone devices from the phone lines that DSL signals or HomePNA signals use may defeat the KSU functions of KSU-less smart handsets.