Telecom Definitions       


1/0 DCS (1/0 Digital Cross-connect System) - used as an “electronic switchboard” and mux to manage traffic, only for private lines.  The old system used 1/0 Muxes and patch panels.

3/1 DCS (3/1 Digital Cross-connect System) - used as an “electronic switchboard” and mux to manage traffic, only for private lines. The old system used 3/1 Muxes and patch panels - actually, the M 3/1’s are being phased out and replaced by 3/1 DCS units.

3/3 DCS (3/3 Digital Cross-connect System) - used as an “electronic switchboard” to manage traffic, only for private lines.

AAV (Alternate Access Vendor) - same as CAP - offers POP access to customers, competing with the LEC.  AAV’s typically have cheaper access rates that the LEC

AIN (Advanced Intelligent Network) - a term coined by Bellcore - a generic term describing advanced architectures - basically, the method in which a telephone company handles calls.  Before calls are connected, the network queries a database on what to do with the call.  Most telephone companies use SS7 to set up their ANI.

AMI (Alternate Mark Inversion) - A line code used for T-1 and E-1 lines that has a 12.5% ones density minimum (an average of at least one 1-bit for every eight bits), and the one conditions of the signal alternate between positive and negative polarity.

AS (Autonomous System)  a set of routers under a single technical administration, using an interior gateway protocol and common metrics to route packets within the AS and using an exterior gateway protocol to route packets to other AS's. Much of the traffic carried within an AS either originates or  terminates at that AS (i.e., either the source IP address or the  destination IP address of the IP packet identifies a host internal to  that AS).  Traffic that fits this description is called "local  traffic". Traffic that does not fit this description is called "transit traffic". A major goal of BGP4 usage is to control the flow of transit traffic.  Based on how a particular AS deals with transit traffic, the AS may now be placed into one of the following categories:

·     Stub AS: an AS that has only a single connection to one other AS.  Naturally, a stub AS only carries local traffic.

·     Multihomed AS: an AS that has connections to more than one other AS, but refuses to carry transit traffic.

·     Transit AS: an AS that has connections to more than one other AS, and is designed (under certain policy restrictions) to carry both transit and local traffic.

 B8ZS (Bipolar Eight Zero Substitution) - an improvement over AMI coding used with ESF framing in T1 carrier systems.  Both B8ZS and AMI alternate the polarity of consecutive 1’s.  But with AMI coding, the signalling is in-band, and “robs” a 1 bit from each byte for signaling - which limits each channel to 56 kbps. Out-of-band signaling frees up all 8 bits of each byte to carry data, allowing each channel 64 kbps. However, you need 1’s to synchronize off of (see “ones density requirement”) - and if the data has a continuous series of 0’s, the synch can be lost.  B8ZS replaces any byte containing all 0’s, with a specific eight bit pattern containing two deliberate bipolar violations (BPV’s) - the receiving end recognizes this pattern and replaces it with the original eight 0’s.. B8ZS satisfies T1 Carrier regenerator ones density requirement: that fifteen consecutive zeros cannot be sent and that an average of at least one out of eight bits contains a one. Although converting to B8ZS does not require modification of T1 repeaters, virtually every other piece of carrier equipment must be upgraded; PBX T1 boards, M13 multiplexers, CSU’s, and even test equipment. Fortunately, most equipment manufactured within the last few years can be optioned for B8ZS. B8ZS and ESF are deployed (together) as two of the three steps toward clear channel capability (64 kbps data rate). The third step is out-of-band signaling (via ISDN or SS7). T1 bandwidth is increased with B8ZS from 1.344 Mbps (AMI) to 1.536 Mbps, a 14% increase in throughput.

BGP (Border Gateway Protocol) - an Internet protocol that enables groups of routers (called autonomous systems) to share routing information so that efficient, loop-free routes can be established.  BGP is commonly used within and between Internet Service Providers (ISPs). The protocol is defined in RFC 1771.

bis - a designation meaning “2nd version” (from the French word bis - meaning “encore”) - used with the V.  standards from ITU-TSS (formerly CCITT)

BOC (Bell Operating Company) - any of the 22 local Bell Operating companies (LEC’s) owned by AT&T before divestiture.

Call Redirect (an alternative to the more expensive, call transfer) - an 800 feature that allows the original call to be redirected to a new location, as a new call, and the old call is torn down to prevent “double-charging”, as with call transfer (AT&T’s method).  The bill will include 2 calls and a 10 cent charge for the redirect - even if there is no redirect on a call, there will be a redirect charge.  the provider's DMS250’s contain the software to support this feature.

CAP (Commercial Access Vendor) - same as AAV - offers POP access to customers, competing with the LEC.  CAP’s typically have cheaper access rates that the LEC

CDR (Call Detail Record) – a database record of a call, which typically contains information such as time of the call, the caller ID, and the duration of the call, etc.

CHAP (Challenge Handshake Authentication Protocol) - a type of authentication in which the authentication agent (typically a network server) sends the client program a key to be used to encrypt the username and password. This enables the username and password to be transmitted in an encrypted form to protect them against eavesdroppers.

CIDR (Classless Inter-Domain Routing) – Short for Classless Inter-Domain Routing, an IP addressing scheme that replaces the older system based on classes A, B, and C. With CIDR, a single IP address can be used to designate many unique IP addresses. A CIDR IP address looks like a normal IP address except that it ends with a slash followed by a number, called the IP prefix. For example:          The IP prefix specifies how many addresses are covered by the CIDR address, with lower numbers covering more addresses. An IP prefix of /12, for example, can be used to address 4,096 former Class C addresses.   CIDR addresses reduce the size of routing tables and make more IP addresses available within organizations.

CO (Central Office) - houses telephone and data switching equipment - all customer lines lead to this office.  CO’s are owned by the LEC (some are also owned by an IXC).

companding - a technique used in some analog-to-digital conversion and digital-to-analog conversion processes to achieve consistent signal-to-quantization noise ratios, even though input signal varies in amplitude. Accomplished by assigning small quantization step sizes for signals of low amplitude, and gradually increasing the quantization step size as input signal amplitude increases. Termed companding, because the technique effectively results in COMpression of the input signal at the transmitting end, and exPANDING of the signal at the receiving end. Examples of coding techniques which use companding are A-law and mu-law PCM. the provider uses companding for voice encoding.

CPE (Customer Premise Equipment) - equipment located at the customer site

CTI (Computer Telephony Integration) - running a telephone network with computers

D4  (Digital 4) - a T1 transmission super frame format comprised of twelve frames of 192 bits each plus an additional 193rd bit used for link control and error checking. As an industry standard, D4,  also known as Super Frame (SF), has been superseded by the Extended Super Frame (ESF) format. However, because ESF is not backward compatible, and there continues to be a large installed base of channel banks and DS1 Multiplexers that are based upon D4, it is still the default private line formatting technique.  There is also D3 which is no longer used, and D5 (which is ESF).  D4 typically uses AMI coding for the frames, checks for BPV’s, and removes them.  Since D4 uses in-band signalling, it “robs” one bit from each byte for signalling - so that each of the 24 channels of a T1 can only carry 56 kbps.

DACS (Digital Access and Cross-connect System) - same as DCS or DXC

DAF (Dedicated Access Facility) – equipment at a site which interfaces a customer’s equipment with a dedicated circuit.  Typically a DAF will contain equipment such as a CSU/DSU, router, and possibly a mutiplexer, channel bank.

DCE (Data Communications Equipment) - a hardware interface (such as DSU/CSU) that allows a DTE to communicate with the rest of a network

DCS (Digital Cross-connect System) -  digital cross connects are electronic  patch panels, that can also perform multiplexing.  They have revolutionalized the IXC pops in that there is no longer a need for large, cumbersome, difficult to maintain patch panels.  DCS units are typically either 1/0 (DS1-to-DS0) and 1/3 (DS1-to-DS3).  The DCS 1/0 takes in DS1’s, demultiplexes them down into DS0’s, cross connects them, and multiplexes them back to DS1’s.

DES (Data Encryption Standard)  -  a cryptographic algorithm as required by FIPS 140-1.  A mathematical algorithm for encrypting (enciphering) and decrypting (deciphering) binary coded information. Encrypting data converts it to an unintelligible form called cipher. Decrypting cipher converts the data back to its original form called plaintext. The algorithm described in this standard specifies both enciphering and deciphering operations which are based on a binary number called a key.  A key consists of 64 binary digits ("O"s or "1"s) of which 56 bits are randomly generated and used directly by the algorithm.  The other 8 bits, which are not used by the algorithm, are used for error detection. The 8 error detecting bits are set to make the parity of each 8-bit byte of the key odd, i.e., there is an odd number of "1"s in each 8-bit byte1. Data can be recovered from cipher only by using exactly the same key used to encipher it. Unauthorized recipients of the cipher who know the algorithm but do not have the correct key cannot derive the original data algorithmically. However, anyone who does have the key and the algorithm can easily decipher the cipher and obtain the original data. A standard algorithm based on a secure key thus provides a basis for exchanging encrypted computer data by issuing the key used to encipher it to those authorized to have the data.

DINA (Distributed Intelligent Network Achitecture)

DSU/CSU (Digital Service Unit/Channel Service Unit) - the DSU converts digital synchronous signals at the customer site to T-carrier bipolar signals.  The CSU is a termination for the LEC’s line which also includes error detection, “keep alive”, and remote loopbacks.

DTE (Data Terminal Equipment) - a piece of hardware where a comminication path begins or ends - a DTE is usually a terminal, or a PC running a terminal emulation program

EDMS (EDucation Maintenance  Systems) - on Herndon Server, allows you to view and enroll in courses offered by the University of Excellence

ESF (Extended Super Frame) - D5 (Digital 5) - a T1 transmission super frame format comprised of twelve frames of 192 bits each plus an additional 193rd bit used for link control and error checking. As an industry standard, D4,  also known as Super Frame (SF), has been superseded by the Extended Super Frame (ESF) format. However, because ESF is not backward compatible, and there continues to be a large installed base of channel banks and DS1 Multiplexers that are based upon D4, it is still quite common as a private line formatting technique.  There is also D3 which is no longer used, and D5 (which is ESF).  D4 typically uses AMI coding for the frames, checks for BPV’s, and removes them.  Since D4 uses in-band signaling, it “robs” one bit from each byte for signaling - so that each of the 24 channels of a T1 can only carry 56 kbps.

FANTM (Facilities Access Network Termination Management) - FANTM truck groups offer an access enhancement for switched T1 that provides T1 grooming and two-way calling.  Grooming is the act of moving DS0’s off of one T1 and placing them on another T1.  Two-way calling allows customers to have inbound and outbound services on the same trunk group.  

FCC (Federal Communications Commission) - regulates both intrastate and international transmissions in the U.S., as well as equipment, facilities, and frequency bands

GFE (Government Furnished Equipment) -  customer owned equipment

grooming - the act of moving DS0’s off of one T1 and placing them on another T1 to utilize lines efficiently

HFC (Hybrid Fiber Coax) - HFC uses fiber links from the central site to a neighborhood hub, and coax cable from there to approx. 500 to 2000 homes.  The developers hope that HFC will be the next generation transport for the information superhighway' -  it has the attraction of using existing infrastructure (cable television wiring) or newly installed networks. HFC enables cable operators to offer two-way communications, which will provide subscribers with telephone service over the cable as well as full interactive access to broadband signals, including hundreds of channels of interactive TV, digital services, and more. The theoretical size of the cable link is very large-a total of some 735 MHz usable bandwidth. HFC divides the total bandwidth into a downstream (to the home) band and an upstream (to the hub) band. The downstream band typically occupies 50-750 MHz, while the upstream band typically occupies from 5-40 MHz.  According to Bell Atlantic, a full HFC system could deliver Plain old telephone service (POTS), 23 to 37 broadcast analog TV channels, 188 broadcast digital TV channels, 272 to 464 digital point cast channels (that deliver customer requested programming at a time selected by the customer), and a high speed two-way digital link (could use it for Internet access, with HFC modems that are 1000 times faster than analog modems).  So far, the problems with HFC are that the coax portion is noisy (a storm wreaks havoc with coax lines), and the cable company infrastrusture was not built for incoming data - so they have a long way to go before widespread deployment.

IETF (Internet Engineering Task Force) – the main standards organization for the Internet. The IETF is a large open international community of network designers, operators, vendors, and researchers concerned with the evolution of the Internet architecture and the smooth operation of the Internet. It is open to any interested individual.

IPL (International Private Line) - a private line (point-to-point) that runs from the U.S. to an International location

IXC (IntereXchange Carrier) - long distance carrier companies (such as Sprint, AT&T, MCI, etc.) that provide inter-LATA telephone and data services.  They connect to LEC ‘s at a POP.  In order to give all IXC’s equal opportunity to service all of the millions of customers - the IXC’s needed a POP reserved for them at the LEC’s.  So the FCC dictates that at each LEC, there must be a POP for each IXC.

LATA (Local Access and Transport Area) - the FCC divided the US into a number geographic areas called LATA’s.  Each LATA contains one or more LEC’s.  LATA’s are connected with “Intra-LATA” connections.  There were 196 LATA’s in the U.S. as of 8/96.

LEC (Local Exchange Company) - local service provider.  This can an RBOC, or a number of other companies that have recently began offering local services, such as Southern Bell, GTE, etc.  (most IXC’s have gotten into the LEC market).  The lines from the LEC to the IXC carry only DS3 data rates.

Line - (also called “circuit”) - connects a customer device (phone, modem, etc.) to a switch.  Typically a line infers that it is a local circuit, but there are exceptions, such as T1, T3, etc.

MIB (Management Information Base) - a file containing network management data such as ARP tables, statistics, etc. on a specific network component - such as a router, switch, or multiplexer. An SNMP "agent" (a software process) saves it’s info in the MIB, which is accessed by the SNMP Manager program via SNMP queries.  RFC1066 describes the objects (entries) that can be in a MIB - although vendors often stray from this standard. Objects in the MIB are defined using the subset of Abstract Syntax Notation One (ASN.1). There are two versions of MIB’s - MIB-I (RFC 1156), and MIB-II  (RFC 1213).  MIB-I is the core set of managed objects  for the Internet suite of protocols.  MIB II is a more powerful version of MIB-I, with objects.

MIME (Multipurpose Internet Mail Extensions) - the most poular standard for transmission of Email attachments over the internet. The internet cannot deliver files in 8-bit format.  RFC 821 restricts mail messages to 7-bit US-ASCII data with lines no longer than 1000 characters.  MIME allows 8-bit files to be encoded into ASCII characters represented by 7 bits or less - transmitted, and then decoded at the receiving end.  By far the most common MIME encoding structure is called “Base64” - which uses 64 characters. This encoding is virtually identical to the one used in Privacy Enhanced Mail (PEM) applications - both are derived from RFC1421. A 65-character subset of US-ASCII is used, enabling 6 bits to be represented per printable character. (The extra 65th character, "=", is used to signify a special processing function). The resulting encoded text file contains lines of no more than 76 characters each.  Unortunately, many Email applications do not auto-detect and decode the MIME attachment - and the receiver must save the file, strip off any extraneous header info, and decode the file with a base64 encode/decode program (a short C program).

MRC (Monthly Recurring Charges) - a monthly fee, not including usage - typically for leased lines, or switched 56 Kbps service.

MUX (MUltipleXer) - a device that interleaves a number of input signal into one output signal

NCC (Network Control Center) - monitors the network by listening for DCS alarms

NNX (Network Numbering eXchange) - the old local exchange, which limited the 2nd digit to only allow digits from 2 to 9.  This has been replaced by NXX, which allows the 2nd digit to be anything.  NNX has only 640 possible combinations, whereas NXX has 792.

NOC (Network Operations Center) - a central location used to monitor and troubleshoot the network.  The NOC has full visibility of the entire network. 

NOCC (National Operations Control Center) - the main NOC, which has the added responsibility of coordinating all the smaller NOC's

NPA (Numbering Plan Area) - 3 digit area code, as in NPA-NXX-5555 - for a given NPA, no 2 phones can have the same 7-digit number that follows the NPA

NXX (the N and X just refer  to digits, not words as NNX does) - the replacement for NNX - a 3 digit local exchange, as in NPA-NXX-5555, where N=any digit except 1 (2 to 9), and X=any digit (0 to 9). N cannot be “1”, because the LEC will mistake a local call for a long distance call.  The plan is to eventually go to 10 digit dialing for all national and local calls, which will allow N to be a “1”, and then the local exchange will be denoted as “XXX”.

ones density requirement  - on digital transmission facilities for sufficient signal transitions to allow the clock in receiving equipment (e.g. regenerators) to maintain synchronization. Typically associated with T1 carrier which has a requirement that no more than 15 consecutive zeros may be transmitted at the line level.

PABX (Private Automatic Branch eXchange) - a PBX that is completely electronically operated.  Virtually all modern PBX’s are now PABX’s, so the terms are used interchangeably.

PAD (Packet Assembler/Disassembler) - software subsystem (or system) that enables a non-packet-switching device (e.g., asynchronous data terminal equipment [DTE]) to communicate over a packet switching network.  In the provider-based data networks, a PAD resides in a TP8000 concentrator or a TP4900 packet switch.  (Some refer to TP8000 as a PAD; although it is generally accepted, it is not correct to do so.)

PAP (Password Authentication Protocol) – the most basic form of authentication, in which a user's name and password are transmitted over a network and compared to a table of name-password pairs.  Typically, the passwords stored in the table are encrypted. The Basic Authentication feature built into the HTTP protocol uses PAP. The main weakness of PAP is that both the username and password are transmitted "in the clear" -- that is, in an unencrypted form.  Therefore,  by default, most provider’s intranets use “CHAP”.

PAX (Private Automatic eXchange) - a small, local automatic telephone office that has no connection to the public network

PBX (Private Branch eXchange) - a piece of hardware that resides at a customer business,  handles telephone extensions, and connects the phones at those extensions to the public domain (to the CO)

PDN (Public Data Network) - also called “the cloud” - usually refers to X.25 and Frame Relay networks - but is sometimes used to describe other non-dedicated data services, such as dial-up analog and DDS services.

POP (Point of Presence) - the physical connection at an LEC, where a IXC (long distance carrier company) connects.

POTS (Plain Old Telephone System) - the old standard - twisted pair wiring - the typical wiring used to connect the customer phones to the demarcation point

PSN (Public Switched Network) - any public switching system

PSTN (Public Switched Telephone Network) - a public network that supplies end-to-end transport of voice and switched data (such as switched 56 and ISDN).  The PSTN is the main telephone system for residential and commercial use.

PUC (Public Utilities Commision) - the public watchdog - regulates intrastate transmission services

PVC (Permanent Virtual Circuit) - an end to end permanent connection - has the same function as a dedicated circuit, but travels through a series of switches, hence the term “virtual circuit”.  Unlike dedicated circuits, a PVC route can change almost instantly if the is congestion or failure.

RDPS (Reverse Direction Protection Switch) - used in bi-directional SONET rings to detect outages or fiber cuts and reroute traffic in about 50 ms.  Most provider’s SONET rings have a bi-directional “working ring”, and a bi-directional “protected ring”.  When an outage occurs, the disabled segment (all 4 lines) is taken out of commission, and the traffic that was moving across that segment is sent by the RDPS back around the other way.  Now, on the still active segments, all 4 lines are used as a “working ring”.

Regenerators - located along fiber routes (usually every 22 miles) to amplify and reshape the signals.

Repeaters - typically just amplify and pass along a signal - however, there is a grey area here, since some repeaters do reshape signals (in which case they are serving the same function as regenerators)

SCP (Service Control Point) - a remote database (located outside the DMS250 switches) within the SS7 network, used to supply translation, routing data, accounting codes, call controls, etc., to the DMS250 via the STP (Signal transfer point).  The SCP is contained in a the provider-owned supercomputer.  

SF (Super Frame) - see D4

SLC96 (Subscriber Loop Carrier 96) - pronounced “Slick 96” - a small local unmanned box in the ground (sometimes an underground room) that acts as an intermediate  multiplexing station between the customers and the CO.

SONET (Synchronous Optical Network) - standard for connecting fiber-optic transmission systems. SONET was proposed by Bellcore in the middle 1980s and is now an ANSI standard.   SONET defines interface standards at the physical layer of the OSI seven-layer model. The standard defines a hierarchy of interface rates that allow data streams at different rates to be multiplexed. SONET establishes Optical Carrier (OC) levels from 51.8 Mbps  (about the same as a T-3 line) to 2.48 Gbps.  Prior rate standards used by different countries specified rates that were not compatible for multiplexing. With the implementation of SONET, communication carriers throughout the world can interconnect their existing digital carrier and fiber optic systems.   The international equivalent of SONET, standardized by the ITU, is called SDH. 

SS7 (Signaling System #7) - the heart of an AIN (Advanced Intelligent Network) system.  It’s main function is to handle calls by first checking the SCP (System Control Point) database to see if the called party is reachable - which saves unnecessary connections, and leaves more ports available on the DMS250.  SS7 is actually a huge, complex, custom configurable system - which is tailored to the company’s needs by programmers.

Static IP – a permanent IP address which is manually entered into a system by the administrator.  Unlike dynamic IP addresses, a user with a static IP address, will be given the same IP address each time he or she connects.

STP (Signal Transfer Point) - a high speed switch that acts as an interface between the SCP and the DMS250’s.  

SVC (Switched Virtual Circuit) - packet switching (routing) that uses one specific route, connection oriented (usually X.25).  The route will only change if there is a failure. 

TACACS (Terminal Access Controller Access Control System) - a protocol for identifying and verifying user ID and password.

TACACS (Terminal Access Controller Access Control System) - a protocol for identifying and verifying user ID and password.  Cisco uses TACACS to control access to their routers.

ter - a designation meaning “3rd version”  - used with the V.  standards from CCITT.  For example, there are 3 V.26 standards:  V.26, V.26 bis, and V.26 ter

TIMS (Transmission Impairment Measurement Set) - hardware to run a 3-tone slope test at 404 Hz, 1004 Hz, and 2804 Hz to check db

TIOC (Technology Integration and Operations Center) - same as TOC

TRS (Trouble Reporting System) - system to receive, manage, and track Trouble Tickets.  Not to be confused with Telecommunications Relay Service (for the hearing impaired)

Trunks - high capacity circuits that connect switches together.  Two-way calling allows customers to have inbound and outbound services on the same trunk group.

vocoder - a device for converting analog speech to a digital bit stream using a compression mechanism which is specifically optimized for the human voice. Instead of requiring a 64 Kb/s channel (as does an A-Law or Mu-Law codec) the coder can operate with a smaller channel (16 Kb/s or less). Because the coding algorithm is optimized for speech it typically provides poor performance for voiceband modem or fax applications. Vocoders are used in situations where bandwidth is a premium such as cellular networks.

X.400 - an ITU-T standard which defines translations between disparate email platforms.  Unbelievably, one major flaw with X.400 is that the sender’s name is not sent with the email.  So if you send an email via X.400, be sure to include your name in the body of the email.

X.500 - the ITU-T  (ITU-TSS) standard which defines a method for central and distributed directory services.  Typically refers to email, where X.500 servers exchange email directory info with one another.  Also, so long as an email application is X.500 compliant or has an X.500 gateway - the users can be listed in the central email directories on the X.500 servers.