2B+D
The way a Basic Rate ISDN line is configured, using 2 B-channels and one D-channel.

Additional Primary Directory Number
If more than two terminals are connected to a digital subscriber loop, additional primary directory numbers are required. Included with each primary directory number is the standard set of voice and data features. Rates and charges are specified in the individual state offering and apply for each additional primary directory number.

Analog Call Appearance
This feature enables analog station users to share their call appearance on a Single Line ISDN Services user's terminal. The user's analog service must be provisioned from the same serving central office as the Single Line Service. One appearance, per number, per terminal is allowed. Some analog services are not compatible with Single Line ISDN Service.

B-Channel
A 64 kilobit-per-second bearer channel.

Bandwidth Allocation Control Protocol (BACP)
The set of rules that manage bandwidth over PPP dynamic multilink connections.

Basic Rate Interface (BRI)
The standard ISDN line, consisting of 2 B-channels and 1 D-channel.

Bridge
A device that connects two or more networks and forwards information between them. A bridge is sometimes called a data link relay or a level 2 relay. A bridge is typically simpler and less expensive than a router, but can only carry limited information from one network to another.

CALC
Customer Access Line Charge (CALC). In the FCC tariff it is referred to as End User Common Line (EUCL) Charge. Also referred to sometimes as Subscriber Line Charge (SLC)

FCC Rules (69.104) EUCL defines as follows:

A charge that is expressed in dollars and cents per line per month shall be assessed upon end users that subscribe to local exchange telephone service, Centrex or semi-public coin telephone service to the extent they do not pay carrier common line charges. Such charge EUCL shall be assessed for each line between the premises of an end user and a Class 5 office that is or may be used for local exchange service transmissions.

Each Single Line Service is charged one CALC or EUCL. The amount varies by state.

Call Exclusion
This feature has two options:

Automatic Exclusion
This option allows a user to restrict other users that share a Directory Number from bridging onto an active or retrieving a held call. This option is automatically invoked whenever the user goes off-hook to receive or place a call.

Manual Exclusion
This option allows a user to restrict other users that share a Directory Number from bridging onto an active call or retrieving a held call. This option is activated by pressing a feature button before dialing or during the call.

Call Forwarding Busy Line-All Calls
This feature allows all calls to a busy Primary Directory Number to be forwarded to another number either within the same central office, for the same customer at the same location, outside the customer system within the same central office, or in a different central office.

Call Forwarding-Don't Answer
This feature allows all calls terminating to an idle Primary Directory Number to be forwarded to another number when the called Primary Directory Number does not answer after a predetermined number of seconds.

Call Forwarding Variable-All Calls
The user can forward all Primary Directory Number calls to another number by pressing the Call Forwarding-Variable feature button. The user must activate or deactivate the forwarding function by using either an access code or a feature button. The standard configuration provides for this feature button.

Call Forwarding Busy Line For Circuit-Switched Data
This feature permits all circuit-switched data calls, attempting to terminate to a busy primary directory number, to be redirected to another customer-specific directory number. A busy line condition exists when a circuit-switched data B-channel is available. This feature can either be assigned to the user on an active basis or it can be assigned to a feature button that can be activated or deactivated by the user. If the feature is assigned to a feature button, the forward-to directory number can be changed by dialing an access code and programming the new forward-to directory number.

Call Forwarding Don't Answer For Circuit-Switched Data
This feature permits all circuit-switched data calls attempting to terminate to an idle primary directory number to ring a specified number of seconds prior to being forwarded to a previously specified directory number. This feature can either be assigned to the user on an active basis or it can be assigned to a feature button that can be activated or deactivated by the user. If the feature is assigned to a feature button, the forward-to directory number can be changed by dialing an access code and programming the new forward-to number directory number.

Call Forwarding Variable-All Calls For Circuit-Switched Data
This feature allows circuit-switched data calls, attempting to terminate to a line, to be redirected to another specified line. The user must activate or deactivate the forwarding function by either using an access code or a feature button. If the feature is assigned to a feature button, the forward-to directory number can be changed by dialing an access code and programming the new forward-to directory number.

Call Hold
This feature allows the user to place a call on hold by depressing a button.

Call Pickup
This feature allows a user to answer a call at another station, even when the user's station does not have a call appearance for the called directory number. While the other station is ringing, the user goes off-hook and enters a call pickup code or presses a call pickup feature button to answer the call.

Call Rejection
This feature enables a customer to reject call attempts from up to 15 numbers of calling parties by dialing a code and the telephone numbers of calls to be rejected. Any call attempts to the customer from these numbers will be prevented from terminating to the customer and will instead be connected to an announcement informing the caller that the call is not presently being accepted by the called party.

Call Transfer
This feature enables the user to transfer a call to a third party by depressing a button.

Caller Identification Blocking - All Calls
This feature provides a permanent private indicator on a per station basis. Once the blocking is established on the station, the private status cannot be deactivated by the customer. Federal, State and Local law enforcement agencies and non-profit domestic violence agencies may be provided additional arrangements for private status and/or all call blocking, on a per station basis, at no charge. Stations that share appearances of a restricted station must also be restricted to avoid passing caller identification information.

Caller Identification Blocking - Per Call
This feature enables a customer to control the disclosure of their name and/or Directory Number to a subscriber of Caller Identification (where technically feasible) by temporarily changing the public/private status indicator of the Directory Number. A customer must dial a code before each call to change the indicator from public to private. "Public status" allows delivery of the name and/or Directory Number. "Private status" prevents delivery of the name and/or Directory Number. Per Call Blocking is provided at no charge.

Calling Line Identification
Calling Line Identification is provided on both an incoming and outgoing basis.

Incoming
Calling Line Identification is provided on both an incoming and outgoing basis. This feature displays the call identification information and the calling party's Directory Number (including nonpublished and nonlisted directory numbers) prior to the call being answered. Calling party's name is not available. Callers have the ability to inhibit the display of calling party information to the terminating number. Incoming calling identification is provided to the Primary Directory Number and to any associated Secondary Directory Number. Incoming calling line identification cannot just display to the Primary Directory Number when the number is shared.

Outgoing
This feature provides a user who is originating a call with information about the called party and the facility or destination.

Central Office (CO)
The telephone company's local facility that provides telephone service in your area.

CENTREX
A service provided by a central office that provides a virtual PBX to a set of extensions. It offers features such as transfer, conference, and forward within that set of extensions. Conference
This feature allows a user to establish a three-way conference call by depressing a button.

Continuous Redial
This feature allows a customer to dial a code that will cause the feature to automatically redial the last number the customer dialed. If the called number is busy, the feature will redial the called number for a limited period of time. A tone alerts the customer when the called number becomes available.

Customer Access Line Charge (CALC)
A federal tariff for hooking up your ISDN line. Also referred to as an End User Common Line Charge (EUCL), or Subscriber Line Charge (SLC). Every ISDN line is charged one CALC or EUCL. The amount varies by state or province.

Demarc
The "demarcation point", or the point where the telephone company's wiring stops and your wiring begins. In other words, the phone company will charge you extra for any wiring work performed on your side of the demarc.

D-Channel
One of the three standard channels on a Basic Rate ISDN line. At 16 kilobits per second, a D-channel can carry signaling information and low-speed packet data.

Digital Subscriber Loop
The ISDN basic rate interface loop from the central office to the customer's premises.

DID/DOD
Direct Inward Dial/Direct Outward Dial. These are special trunks in trunking network. As their name implies, direct inward provides for direct inward dialing and direct outward provides for direct outward dialing.

This allows station users to place or receive calls by-passing the attendant.

Display
This feature provides the ISDN terminal a display of the time and date, calling number, call appearance identification, called number, incoming call identifier and feature activation operation.

DMS
The name of central office equipment manufactured by Northern Telecom.

Drop
The Drop button allows the user to drop the last party added to a conference call or disconnect a two-party call.

Hunting
Hunting is available for circuit-switched data on primary directory numbers.

Hunting Service will affect the operation or availability of some other optional features on the hunting B channel. The features most often affected include forms of Call Forwarding, Speed Calling, and others, depending on the Service Configuration. Call Forwarding features will override the Hunting Services.

Hunting is done sequentially by terminal within the group. One or two B channels are associated with each terminal in the group. One begin-hunt telephone number must be assigned to the first terminal within a Regular or Circular group of sequentially ordered terminals that form a multiline hunt group. Telephone numbers may be assigned, in any sequence, to terminals within a multiline hunt group

Multiline Hunt Service provides a hunting sequence that attempts to complete a call to the first available B channel associated with the lead telephone number of the group. Busy tone is not sent to the caller unless all remaining B channels in the hunt group list have been busy. The call will be completed to the first available B channel.

Multiline hunt groups can be assigned two types of telephone numbers; begin hunt and non-hunting telephone numbers. The begin hunt telephone number has the multiline hunt feature and, when called, starts the hunting sequence associated with the hunt group. A multiline hunt group must have at least one begin hunt telephone number but can have essentially one per terminal in the group. Non-hunting telephone numbers can be assigned to terminals within a multiline hunt group; these terminals do not have multiline hunt feature. Incoming calls are terminated directly to the individual terminals.

Regular hunting starts when a begin hunt telephone number is called in a multiline hunt group. Hunting proceeds in ascending order through each subsequent terminal in the group until an idle terminal is reached or the last (highest numbered) terminal in the group is reached.

Circular hunting is provided optionally with regular hunting groups. Circular hunting occurs in these groups when the hunt for an idle terminal commences beyond the first terminal in the hunt group and finds all higher numbered terminals busy, the hunt returns to the first terminal in the group. The hunt ends with the terminal number preceding the terminal where the hunt in the group initially began.

This feature allows all terminals within a multiline hunt group to be tested for busy regardless of the point of entry into the group before returning busy tone.

Uniform call distribution is a hunting arrangement that provides uniform termination call assignment (distribution) to members of a multiline hunt group. Uniform call distribution does not include queuing or announcements.

Intra Wire Center
A wire center is the physical wires or facilities that extend from a central point and fan out in a tree-like manner into the serving areas - homes, businesses, etc. Intra wire center is within this network.

Intercom
Intercom service allows the user to establish a dedicated priority call to any other station that is a member of the same intercom group within the same central office. Special alerting, depending on customer premises equipment is provided for an incoming intercom call. As part of the standard package the user can select either Auto Intercom or Dial Intercom.

Auto Intercom
This feature allows two members to be part of an intercom group, which enables intercom calls to be completed by pressing the feature button. Dialed digits are not required.

Dial Intercom
This feature allows the user to establish a call to any other station that is a member of the same intercom group. This is done by pressing the Intercom button and dialing one or more digits. Special alerting, depending on customer premises equipment, is provided for an incoming Intercom call.

Integrated Services Digital Network (ISDN)
DN stands for "Integrated Services Digital Network." It is a digital architecture that provides an integrated voice/data capability to the customer premises facility, utilizing the public switched network. ISDN distributes voice, data, video, image and facsimile by two standard methods of access: a Basic Rate Service (BRS) or a Primary Rate Service (PRS). These are serving arrangements which conform to internationally developed, published and recognized standards generated by the International Telecommunications Union.

Basic Rate Service consists of up to three distinct channels on one pair of wires: one or two B (Bearer) Channels and one D (Delta) Channel. BRS is offered in a package offering referred to as Single Line Service.

The B channel carries circuit-switched voice and/or data communications at speeds up to 64 Kbps, from the customer's premises, over the loop facility to the central office.

Circuit switched data provides the capability of making data calls over the public switched network. Information is transmitted the very same way as digitized voice. Like a voice call, a circuit switched data call ties up the network/system resources for the duration of the call. Similar to voice, Calling Line Identification is provided.

The D channel carries signaling and/or packet data information, at speeds up to 16 Kbps on BRS and signaling only information up to 64 Kbps for PRS, from the customer's premises to the central office. The D channel has both data and signaling functionality; it does not have voice capability.

PRS has a capacity of 1.544 megabits per second and has multiple channels: 23 B channels and one D channel and is also known as 23B + D access. The B channels carry voice calls, circuit switched data, and video, while the D channel handles signaling information.

Inter Wire Center
A wire center is the physical wires or facilities that extend from a central point and fan out in a tree-like manner into the serving areas - homes, businesses, etc. Inter wire center is within this network.

Kbps
Transmission speeds are most accurately measured in bits per second, or bps. Commonly used abbreviations are:

The term bit is a contraction of binary digit, the smallest unit of digital information - either an on or off signal. The term byte is similar, but actually represents one full character - a letter, number or symbol - of seven or eight bits, depending on the computer code used. The term is an older analog designation, and refers to the number of times per second the sine wave of an analog voice line can be successfully modified.

Although the terms bit, byte and baud are frequently interchanged, they are not in fact the same. Speeds on these pages are consistently referenced in bits - kilobits, megabits and gigabits per second.

Last Call Return
This feature allows a customer to automatically redial the number of the last incoming call to that line, whether the call was answered or not. The customer does not have to know the number of the calling party. If the called number is busy, the feature will redial the called number for a limited period of time. A tone alerts the customer when the called line is available.

Line Extension
A means for providing ISDN at distances beyond the normal limit between the central office and your location.

Loop Qualifications Requirements
Single Line Service is offered where ISDN compatible facilities and equipment are available. Service is generally considered available for loops 18,000 feet or less in length. Loops greater than 18,000 feet must meet ISDN extension technology design requirements and will be considered available if ISDN compatible pair gain systems are in place or planned to serve the area based on scheduled placement of compatible pair gain systems. If no pair gain system is in place or planned, loops greater than 18,000 feet in length will also be considered available if single line loop extension equipment can be deployed and the loop is within the design limitation of this type of extension equipment. There will be cases where it will be impossible to provide Single Line ISDN Service to a location immediately due to the inherent restrictions that must be met as part of the ISDN design requirements. In other words because of the nature of the existing loop network some customers may not receive service.

One of the first steps in the ordering process is the determination of whether or not the local loop or the facility between the central office and the customer premises meets the design criteria for an ISDN loop. When special action is required the order interval may have to be lengthened in order to provide the service.

Mbps
Transmission speeds are most accurately measured in bits per second, or bps. Commonly used abbreviations are:

The term bit is a contraction of binary digit, the smallest unit of digital information - either an on or off signal. The term byte is similar, but actually represents one full character - a letter, number or symbol - of seven or eight bits, depending on the computer code used. The term is an older analog designation, and refers to the number of times per second the sine wave of an analog voice line can be successfully modified.

Although the terms bit, byte and baud are frequently interchanged, they are not in fact the same. Speeds on these pages are consistently referenced in bits - kilobits, megabits and gigabits per second.

Measured Service (Usage)
In addition to the regular monthly charge for access to the local and toll network, local usage charges apply for outgoing calls completed on a local basis. The rates for usage vary by state and may be based on one or more of the following: the number of local messages, the duration (holding time) of each message, the distance between calling and called numbers, and the time of day the call is made. Chargeable time begins when connection is established between the calling station and the called station. Chargeable time ends when the calling station hangs up, thereby releasing the network connections. If the called station hangs up, but the calling station does not, chargeable time ends when the network connection is released by automatic timing equipment in the telephone network.

Message Waiting Indication
This feature is available on Primary Directory Number's and notifies the user of a message waiting by providing either an audible stuttered dial tone or visually by illuminating a light on the customer's telephone set. Messages may be retrieved by calling the message service center or by accessing a voice mail system.

Multi-link PPP
Allows you to combine two or more B Channels into a single, faster PPP connection. With Multi-link PPP, you could have a 128 kilobit/second PPP connection over a Basic Rate ISDN line. The next releases of Windows 95 and Windows NT will include Multi-Link PPP support.

National ISDN - National Integrated Services Digital Network
Beginning in 1992, telephone companies and network switching system manufactures committed to provide standard ISDN services. This commitment is called National ISDN. National ISDN specifies the way that telephones and computers - Customer Premises Equipment (CPE) - communicate with the ISDN network. The National ISDN agreements ensure that each central office switch operates in a standard way, providing a uniform interface to CPE. With National ISDN conformance, a phone (for example) will work on any type of National ISDN switch and will interwork with the analog public switched network.

For some customers without National ISDN, such as those who began using ISDN before 1993, there can be some minor variations in the service they receive, depending on the brand of central office switch that provides their service. These variations can effect CPE configurations, but generally, these customers can place ISDN calls to other ISDN customers, as well as to analog phones.

Stated a little differently, it is a set of standards defined in technical documents written by Bellcore in agreement among telephone companies, switch manufactures, and Customer Premises Equipment (CPE) vendors. This agreement allows consumer provided equipment to work across different telephone company switches using the Basic and Primary Rate Interfaces. CPE is the equipment after the point at which the telephone company terminates the line to the premises. This includes the Network Termination -1 (NT-1) device.

Non-Standard Configuration Group
This is a terminal arrangement, associating buttons of a terminal with a feature, which differs from the standard arrangement.

NT-1 (Network Termination-1)
The device that connects to your ISDN hardware and works as a converter between an ISDN U-interface and an ISDN S/T-Interface. Some ISDN adapters have a NT-1 already built into them. This is easier and less expensive than an external NT-1, but may prevent you from connecting other equipment to your ISDN line.

Packet Switch Network
Packet switching is a data transmission technique whereby user information is segmented and routed in discrete data envelopes called packets, each with its own appended control information for routing, sequencing, and error checking; allows a communication channel to be shared by many users, each using the circuit only for the time required to transmit a single packet. Packets are sent using a store-and-forward method across nodes in a network. Packet switching network then is a network that operates in this manner. A common use for this technology in the ISDN environment is for point of sale or credit card validation.

Packet Switching Usage Charges
Packet transport provides for the routing of data through the public packet switched network in both the originating and terminating directions. Usage charges are billed monthly based on the number of kilosegments transmitted through the public packet switched network for all types of access, and is rated on a per kilosegment basis. A segment consists of 64 octets of customer data. For example, a packet of 128 octets will be billed as 2 segments.

The Packet Usage rate provides a rate for day usage (6:00 a.m. - 6:00 p.m.) and a lower rate for night usage (after 6:00 p.m. and before 6:00 a.m.), as measured at the Signaling Network Control Center, Denver, CO. The rate period in effect at the time the packet segment originated will apply.

Packet Usage will be rounded up to the next whole kilosegment within the billing period. Day and night usage will not be combined. A call overlapping from Day Usage to Night Usage or vice versa will be billed at the appropriate rate for the time period.

PBX
Private Branch eXchange. Telephone switching equipment dedicated to one customer and connected to the public switched telephone network.

Point-to-Point Protocol (PPP)
A protocol that allows a computer to use TCP/IP to connect to other computers over a standard phone line using a high-speed modem.

POP
(Point Of Presence): A long distance carrier's office in your local community. A POP is the place where your long distance carrier, or IXC, terminates your long distance lines just before those lines are connected to your local phone company's lines or to your own direct hookup. Each IXC can have multiple POPs within one LATA. All long distance phone connections go through the POPs.

POTS
Plain Old Telephone Service: an analog (non-digital) telephone line.

Primary Rate Interface (PRI)
A type of ISDN service that offers 23 B channels at 64 kbs and one D channel at 64 kbs (23B+D). In Europe, PRI provides for 30 B channels and two D channels (30B+2D). See also: Basic Rate Interface.

Primary Directory Number
Each ISDN terminal is assigned one Primary Directory Number. If more than two terminals are attached to a digital subscriber loop, an additional Primary Directory Number charge will apply.

Priority Call
This feature allows a customer to assign a maximum of 15 callers' telephone numbers to a special list. The customer will hear a distinctive ring at their location, when calls are received from callers' telephone numbers on that list. The distinctive ring may be customer premises equipment.

Provisioning
The combination of device and service options that make up your ISDN line. You order your ISDN line, but the telephone company provisions the line, i.e.-- it configures your ISDN service according the physical capabilities of the switch, as well as the options you choose.

Public Switched Telephone Network
The telephone network, called the Public Switched Telephone Network, is based on the principle of providing 2-wire analog circuits for voice transmission. The most common phone line, such as the one in your home, is the dial-up line, or switched circuit, which uses two wires to connect your phone jack to the phone network. Inside of the PSTN, you will find lots of digital gear. But at your home prior to Integrated Services Digital Network, it was all analog. Integrated Services Digital Network provides the capability for end-to-end digital connectivity.

Rate Stabilized Contract
This plan is for customers who are willing to commit to a specific number of ISDN Single Line Service lines over an extended period. Because of this commitment the customer enjoys a discount and stable price.

Ringing Options
Ringing options allow ISDN station users to establish flexible call handling arrangements for answering incoming calls that terminate on the shared call appearances of a directory number. The ringing options available on a per station basis for a shared directory number are:

Abbreviated Ringing
Ringing begins immediately for an incoming call and stops ringing after a number of seconds.

Delayed Ringing
Ringing for an incoming call is delayed for a number of seconds, however, the call appearance indicator or "status" lamp begins flashing immediately.

No Ringing
There is no ringing for an incoming call that terminates on a call appearance of that directory number.

Normal Ringing
Ringing begins immediately for an incoming call and continues until the call is forwarded, answered, or abandoned.

Second Directory Number
A second directory number is any directory number other than the primary directory number assigned to an ISDN terminal. If more than one secondary directory number is assigned to a terminal, additional charges will apply.

Selective Call Forwarding
This feature allows a customer to specify a special list of a maximum of 15 telephone numbers. Incoming calls placed to the customer from telephone numbers on that list will automatically be forwarded to a predefined telephone number. All other calls will be handled normally.

Service Profile Identifier (SPID)
A number or set of numbers assigned to your ISDN line by your phone company. In the U.S., one SPID is assigned to each channel. The switch uses SPIDs as unique identification numbers for each ISDN line, so it can determine where to send calls and signals.

Shared Call Appearance
This allows several users to share one or more call appearances for a particular directory number. Origination of and termination of calls on one terminal will affect all terminals sharing the call appearance. All secondary call appearances must be provisioned from the same serving central office. If more than two secondary call appearances are assigned to a terminal, additional charges will apply.

Single Line ISDN Service
Single Line ISDN Service (SLS) is a platform based switched digital service offering fast, flexible, highly reliable, and digitally clear connections with the simplicity of dialing a telephone. Based upon international communications standards, ISDN provides users access to the powerful capabilities of today's Public Telephone Network for communicating across town, or around the world. With Single Line ISDN Service, the same pair of wires that now delivers one communication at-a-time basic phone service to business or residence customers provides two primary, high speed (64 Kbps) communications channels that can be used simultaneously and independently to carry any combination of data, image, video, or voice calls. By combining these channels, data transfer at up to 128 Kbps may be achieved. Single Line ISDN Service also provides a third, auxiliary channel for low to moderate speed data communications which is ideal for point of sale, remote monitoring or telemetry applications.

No special handling is required when voice calls are made between ISDN phones and conventional telephones -- the network manages the necessary conversions. When conducting data calls, in order to utilize the B Channels for digital communications, ISDN based equipment is required at both ends of the communications path; as is the case with conventional modem connections or fax machine transmissions. Certain ISDN equipment also allows for modem-to-modem communications, providing the ISDN subscriber the best of both worlds!

Single Line ISDN Service is the name for Basic Rate Service. Single Line ISDN Service includes a comprehensive 2B + D package. Contained in the standard package are numerous voice and data features. The standard features and functions support two terminals per basic rate service. Within the standard package there is limited flexibility for customization and various optional features can be added. Single Line ISDN Service does not offer B channel packet service capability.

Six Call Appearances
Call Appearances are the positions on a terminal to which directory numbers are assigned. A Primary Directory Number (PDN) can be shared by more than one ISDN terminal. The quantity and/or position of PDNs, Secondary Directory Numbers (ISDN) Analog Call Appearance (ACA) and Shared Call Appearances are limited by the standard configuration developed for the Customer Premises Equipment. The standard package has six call appearances.

The six call appearances will include one Primary Directory Number and five call appearances, on consecutive buttons, made up of the following:

Maximum of five call appearances of the Primary Directory Number
Maximum of one Secondary Director Number
Maximum of four call appearances of the Secondary Directory Number
Maximum of one Analog Call Appearance
Maximum of two shared Directory Numbers

Intercom call appearances do not count against the standard.

Six-Way Conference
This feature allows the user to sequentially add additional parties (up to five), and add them together to make a six-way call.

64CCC
Offers 64 Kbps Unrestricted (transport of voice and data - rated adapted up to 64 Kbps) Clear Channel Capability (64CCC) data connectivity. Customers will be connected to an ISDN interoffice communication using the Common Channel Signaling - Signaling System 7 Network in accordance with Bellcore Technical Reference TR-NWT-000444.

64k Clear Channel Capability
Offers 64 Kbps Unrestricted (transport of voice and data - rated adapted up to 64 Kbps) Clear Channel Capability (64CCC) data connectivity. Customers will be connected to an ISDN interoffice communication using the Common Channel Signaling - Signaling System 7 Network in accordance with Bellcore Technical Reference TR-NWT-000444.

Speed Calling
Speed calling permits the user to dial pre-programmed numbers using fewer digits than normally required. A speed call list allows for up to 30 preprogrammed numbers per terminal.

Speed Calling 8
This feature permits the user to dial pre-programmed numbers using fewer digits than normally required. It allows the customer to change speed calling lists directly from their terminal.

Standard Configuration Group
The standard arrangement which associates a button of an ISDN station to a feature.

T1 Facility
This element is the digital facility transmitting at a rate of 1.544 Mbps. The T1 signal provided to the customer's premises will have a loss not greater than 16.5 dB. The T1 facility may be provided, at the customers request, via fiber optic facility between the central office and the customer's premises.

Transaction Initiation Charge
A transaction initiation charge is defined as any action taken that leads to a call of acceptance by the called party. A transaction initiation charge will apply for each originating or terminating call connected to a network address. This charge does not apply for unsuccessful call attempts.

Twisted Pair
Another term for regular telephone wiring. Each telephone "wire" is actually a pair of wires.

U-Interface
A 2-wire ISDN circuit that connects the ISDN line to the central office. The most common ISDN interface.

23B+D
PRS has a capacity of 1.544 megabits per second and has multiple channels: 23 B channels and one D channel and is also known as 23B + D access. The B channels carry voice calls, circuit switched data, and video, while the D channel handles signaling information.

Centrex Plus Service
Centrex Plus is a family name for business communications systems furnished from Stored Program Control central offices - both analog and digital. It is offered with the intention of grandparenting all previous Centron and Centrex services. Centrex Plus does require special central office equipment and consequently is offered subject to the availability of facilities and applicable generic feature programs as determined by U S WEST.

A Centrex Plus system is defined by dedicated central office software called a common block. The common block identifies dialing patterns, code access dialing plans, restrictions and system and station features - much of which can be changed through software programming changes administered by the telephone company or by the customer using their Centrex Management System.

The common block is connected to the customer's premises by station lines. Station lines may be terminated at one location or combined from different locations so long as they all originate in the same central office. They are used by the Centrex Plus customer to place and receive calls, to access special facilities and to access/activate special features. In general, outgoing calls are placed by first dialing "9". Centrex Plus offers customers a wide variety of standard and optional features, allowing their systems to be tailored to meet specific and unique requirements.

Usage Allowance
The tariffs for Single Line ISDN Service include an option with an outgoing call usage allowance. This allowance includes up to 200 hours per month of aggregate usage for B channel circuit-switched voice and circuit-switched data. Additional usage in excess of the 200 hours in a monthly billing period will incur usage charges as specified in the individual state Basic Local Exchange Tariff.

Usage Charge
In addition to the regular monthly charge for access to the local and toll network, local usage charges apply for outgoing calls completed on a local basis. The rates for usage vary by state and may be based on one or more of the following: the number of local messages, the duration (holding time) of each message, the distance between calling and called numbers, and the time of day the call is made. Chargeable time begins when connection is established between the calling station and the called station. Chargeable time ends when the calling station hangs up, thereby releasing the network connections. If the called station hangs up, but the calling station does not, chargeable time ends when the network connection is released by automatic timing equipment in the telephone network.

X.25 Fast Select
Fast Select is a function of the customer premises equipment and is used on a per call basis allowing the user to send up to 128 octets in the user data field of the call request packet to a terminal with Fast Select Acceptance.

X.25 Fast Select Acceptance
This packet feature authorizes incoming packets from a sending data terminal equipped with Fast Select.

X.25 Flow Control Parameter Negotiation
This packet feature permits negotiation on a per-call basis of the flow control parameters associated with a given virtual call, such as packet size and window size for each direction of data transfer. The data window size and the maximum packet size is negotiated automatically during an X.25 data call.

X.25 Logical Channels
Virtual circuits rather than physical circuits are used to establish packet switch calls. When a virtual circuit is established, a logical channel is assigned at the customer premises equipment and the switch for the duration of the call. A virtual circuit does not use any capacity of the facility unless data is actually being transferred. Two logical channels are provided per digital subscriber loop.

X.25 Reverse Charging Acceptance
This packet feature authorizes transmission of incoming calls identified as Reverse Charge calls.

X.25 Throughput Class Negotiation
This packet feature permits negotiation on a per call basis of the throughput class for each direction of data transfer associated with a virtual call. The data terminal can negotiate the throughput class for X.25 data call.

X.75 Gateway
Packet switching networks use protocols that are internationally sanctioned by the International Telecommunications Union. The two prime protocols are X.25 and X.75. In order for a packet switching ISDN user to transmit data outside their serving central office, an X.75' link must be available between the serving office and a packet switching network. A user wishing to send packet switching traffic InterLATA must do so via a packet switching interexchange carrier. This link is referred to as an X.75' gateway.