Telephone Terminology Q-T

R

RBOC - Regional Bell Operating Company. Most often called Local Exchange Carriers (LEC’s) at the time of this writing. See CLEC and LEC.

RCF – Remote Call Forwarding, a telephone company service that provides local “virtual numbers” from distant locations. Customers are responsible for the cost of calls forwarded through the RCF number. VoIP service providers can offer similar services at greatly reduced costs since the numbers are delivered via the Internet (“backhauled”) at no cost.

RD - Receive Data. Data coming from the network, or DCE towards the DTE. Also, a light on a modem or CSU/DSU that lights to indicate the presence of this signal.

Red Alarm - An alarm state on a T-carrier circuit that indicates that the incoming signal at the network interface has lost frame for more than a few seconds. Normally a Yellow alarm is then returned (i.e. sent back) if a Red alarm is present. A Red Alarm indicates a loss of inbound signal; a Yellow alarm indicates (indirectly) a loss of outbound signal. See also Yellow Alarm, Blue Alarm, and LOS.

Regional Bell Operating Company - See RBOC or LEC.

Repeater - A device intended to extend ISDN telephone service to sites further from the central office than could normally be served. i.e.: beyond 18,000 feet. ISDN repeater technologies include “BRITE”, “Virtual ISDN”, “Lightspan”, and “Total Reach”. Some Telcos do not use repeaters. Compatibility between a given NT1 (CPE) and a repeater is less certain than if that CPE were directly connected to the switch.

Robbed Bit Signaling - A signaling scheme that “borrows” bits on each T1 channel for use as signaling channels. On SF T1s, there are two bits in each direction: The A bit and the B bit. On ESF T1s, there is also a C and D bit in each direction although they are rarely used. Using these bits, various older analog trunk interfaces can be emulated over a T1. For instance, dial pulse address signaling using 10 pulses per second (rotary style) digit groups over these bits. Since robbed bit signaling interferes with the least significant bit, only 7 bits can be used for sensitive data applications, leaving only a 56kbps channel for data applications. See also CAS and CCIS.

Rollover – See Hunt Group.

S

SDSL - SDSL is a rate-adaptive Digital Subscriber Line (DSL) variant with T1/E1-like data rates (T1: 1.544 Mbps, E1: 2.048 Mbps). It runs over one pair of copper wires with a maximum range of 10,000 feet. It cannot co-exist with a conventional voice service on the same pair as it utilizes the entire bandwidth of the subscriber loop.

Sealing Current - Unlike telegraphy, teletypewriter, and POTS lines, most digital lines such as ISDN use a voltage mode rather than a current mode of operation. Sealing Current allows a controlled amount of current to be passed through a telecom circuit for purposes of “healing” resistive faults caused by corrosion. Bellcore specifies sealing current on the ISDN U interface in the U.S. The Siemens EWSD switch does not provide sealing current. Most other ISDN-capable switches used in North America do.

SF - Superframe. A type of line format supported on T1 circuits. The Telco determines the line format and line encoding of your line. ESF is the preferred Line Format on T1 circuits. See Line Format.

Silence Suppression - See Statistical Multiplexing.

SIP – Session Initiation Protocol, the most common IP protocol at the time of this writing for providing telephone service over IP facilities. It is used by most Voice Over Internet Protocol (VOIP) service providers.

SLC-96 – A Subscriber Loop Carrier Circuit system manufactured by AT&T (now Lucent). SLC-96 has its own version of T1 framing between it and the CO. SLC-96 and similar “SLIC” systems may or may not perform a concentration function. The interface is the Bellcore TR-008 or the newer GR-303 interfaces that are specialized versions of T1 intended to allow transparent transport of analog CLASS features such as Caller ID, Call Waiting, etc. The GR-303 interface is specifically intended to be used as a common point of interconnection between alternative equipment, technologies, and/or networks (i.e. voice-over-DSL, voice-over-IP, etc.) and the public switched network. See the following link for additional information from Telcordia: http://www.telcordia.com/resources/genericreq/gr303/index.html.

SLIC - Subscriber Line Interface Circuit. See “Line Card”.

SLIC - The equipment used with the AT&T (Lucent) SLCC Subscriber Loop Carrier Circuit, a system used to multiplex a number of subscriber loops onto a single circuit (usually a T1 circuit) to reduce fixed costs.

SLIC - Sometimes used generically for other brands of similar equipment. See also SLC-96.

Smart Jack – See NIU.

SS7 - Signaling System 7. The internationally adopted Common Channel Interoffice Signaling (CCIS) system. Previous to SS7, the Bell System used SS6 which did not support the International Standards. SS7 does. It allows for substantial flexibility and power in dynamically routings calls. An SS7 database lookup is how a call to a mobile telephone user can be handled transparently despite the fact that the user’s location may change. Also used to determine what carrier should handle a given toll free call. See also CCIS.

Station Line – A telephone circuit from a PBX to a telephone on that PBX. Since this is a telephone-to-switch connection, it is considered to be a “line”. See Line and Trunk.

Station Side - The user side of a PBX, that is, the side of the switch to which the telephones are attached. Also, occasionally called the "Line Side." The main reason for distinguishing between this and the trunk side is that certain customer related features (Such as Hold and Transfer) are inapplicable to most trunks. See also Trunk Side.

Statistical Multiplexing - Sometimes abbreviated as "Statmux," a method of improving the effective bandwidth of a Telco channel. Statistical Multiplexing improves efficiency by identifying the many pauses present in a typical conversation, and not sending those pauses. Also referred to as silence suppression. See Circuit Switched.

Subscriber - The customer of a Telecommunications company. This term dates back to when a local Telephone Company was formed at the specific request of a group of customers who agreed in advance to “subscribe” to the service.

Superframe - See SF.

Switch - Telephone switching device that “makes the connection” when you place a call. Modern switches are specialized computers. ISDN service is provided from a “Digital” switch, most commonly an AT&T model “5ESS”, Northern Telecom model “DMS-100”, or Siemens model “EWSD” in the U.S. & Canada. See also PBX.

Switched Circuit - A channel which is not permanent in nature, but rather is connected through a switching device of some kind. The switching device allows a switched circuit to access many other switched circuits (the usual “dial up” type of telephone channels). Once the connection is made however, the complete capacity of the channel is available for use. As opposed to a dedicated circuit or a packet based connection.

Switched-56 - Archaic term referring to a type of digital telephone service developed in the mid 1980’s which allows dialing on a single 56Kbps line. Each Switched-56 circuit has 1 or 2 copper wire pairs associated with it. Switched-56 was replaced with ISDN, which was cheaper and more flexible, and finally by DSL and IP variants. See also CSU/DSU.

Synchronous Data - A form of serial data which uses a clock signal to synchronize the bit stream. Since, unlike with asynchronous data, no start and stop bits are used, data throughput is higher than with asynchronous data. ISDN and T-1 use Synchronous data. See also Asynchro- nous Data.

T

T1 - A common type of digital telephone carrier widely deployed within the U.S., Canada, and Japan. Has 24 64Kbps channels (called DSØ’s). The most common use for a T1 at the time of this writing is for Telephone company “access service” via an ISDN Primary Rate Interface which 23 “bearer” channels and a single “Data” channel for call set up. A T1 can carry data service only or mixed data and voice when provisioned appropriately, but lower cost services such as DSL are largely supplanting T1 circuits for Internet access.

T-1 - An alternative expression for T1. See T1.

Tandem Switch - A switch which is between two others. It connects two trunks together. Long distance calls on a LEC line go through a long distance tandem that passes them through to the long distance provider’s switch.

Tandem Tie Trunk Switching - The condition when a PBX switch allows a tie line call to dial out of the switch. For example, if switch “A” in Arkansas has a tie line to switch “B” in Boise, Boise could use the tie line to make calls from switch “A”.

TD - Transmit Data. Data coming from the DTE towards the DCE or network. Also, a light on a modem or CSU/DSU that lights to indicate presence of this signal.

Telco - Telephone Company. Your local telephone service provider. In the 21st century, you generally have a choice of Telcos if you are a business in a major metropolitan area in the U.S. Competition is coming to the Telecom industry around the world.

Telcordia Technologies - Formerly Bellcore. The research and development organization owned by the telephone companies. Telcordia represents the phone companies in developing standards for Telco equipment and in testing equipment compliance to those standards. It promotes competition and compatibility through standards, promoting interoperability such as GR-303. Telcordia also offers educational and training programs open to all interested parties. Bellcore was sold to SAIC in 1997. Telcordia is responsive to both RBOCs and independent Telcos. Their web site is: http://www.telcordia.com. See GR-303.

Telephone Number - See DN and MSN.

Telos Customer Support - +1.216.622.0247. Available 24 hours a day, every day. You may also ask for assistance by visiting our website at https://success.telosalliance.com/support.

Tie Line - See Tie Trunk.

Tie Trunk - A Trunk between two PBXs. Note that a Tie Line is a dedicated circuit, not a switched circuit. See Trunk.

TR-008 - See SLC-96.

Trouble Ticket -A Telco “work order” used to track customer repairs within the Telco. If you call someone within the Telco’s repair department, they will need this number to proceed. It will also be needed whenever you call to check on the status of a repair. Always ask for this number when initiating a repair request.

Trunk - A communications path between two switching systems. Note that many trunks may exist on a single circuit (if that circuit has multiple channels). The trunks most users will deal with are between the Telco switch and a PBX. However, a Tie Trunk can connect two PBXs. See also Tie Trunk and Trunk Group.

Trunk Group - A number of telephone channels that are functionally related. Most common is the Hunt Group. Other common types include Incoming Trunk Groups and Outgoing Trunk Groups. See also Combination Trunks and Two-way DID Trunks.

Trunk Side- Central Office - The side of a central office between switches that faces the network. Historically, many CO switches could not make trunk-to-trunk connections, as opposed to tandem and long-distance switches that are always used to connect trunks together. Hence, the need to distinguish between the “line side” and the “trunk side” of the switch. See also Line Side.

Trunk Side- PBX - The side of a PBX that connects to the Telco. Historically, many PBXs could not make trunk to trunk connections, hence the need to distinguish between the “line side” and the “trunk side” of the switch. Since a trunk is a switch-to-switch circuit, these circuits can be called trunks. Beware that even though you have a PBX which may consider these to be "trunks", the Telco may still call these “lines” See also Trunk and Line Side.

Two-way DID trunk - An ISDN PRI equipped for direct inward dialing. Most PBX trunks are related to a given phone number, either alone or as part of a Hunt Group. In the case of a “normal” (i.e. analog) DID Trunk, a group of phone numbers is associated with that DID trunk (or group of trunks) and incoming calls include the DID number so that the PBX can route that call to the correct DID extension. These are one-way (i.e. inward only) trunks. This is exactly how ISDN PRI functions, with the DID information coming in over the D channel. There is a big difference between a normal DID Trunk and a Two-way DID trunk over ISDN PRI. For one thing, ISDN PRI is digital. Another distinction is that you cannot dial out over a true DID trunk, while you can dial out over a PRI (hence the conflicting designation “Two Way Direct Inward Dialing Trunk”).

Two-Wire – A circuit path where only a single pair of wires is used. A hybrid is used to convert from two-wire to four-wire circuits. No hybrid is perfect, and those used by the phone company can be poor. However, the hybrids in Telos Hx units are approaching perfection!