μ-law (Mu-Law)
μ-law(Mu-Law) is the standard codec (compression/decompression) algorithm for pulse code modulation (PCM) from the CCITT (Consultative Committee for International Telephone and Telegraph). A companding (compression/expanding) method, mud-Law makes it possible to improve the signal-to-noise ratio without requiring the addition of more data. Mu-Law, as a term, was derived from μ-Law, because the Greek letter µ is pronounced myoo. The term is sometimes seen as u-Law, although the pronunciation remains the same. Mu-Law is used in the United States and Japan. The other type of codec algorithm, A-Law, is the standard used in Europe and elsewhere.

114 Service
114 is the directory assistance service number in China. It is similar to the 411 service in the United States.

119 Service
119 is the official national emergency number in China. It is similar to the 911 service in the US.

110 Block
110 Block is a punch-down block used to connect wiring for telephone systems, data network wiring, and other low-voltage wiring applications. The 110 Block improves on the 66 Block by supporting higher frequencies and using space more efficiently.

1A
1A is the first generation of standardized key telephony system developed and used by former AT&T.

1A-ESS
1A-ESS refers to the Electronic Switching System of former AT&T that uses 1A processor. The 1A processor uses stored programs, and operates in a real time environment.

1PSS
1PSS refers to the Packet Switching System of former AT&T using X.25 protocol.

2500 Set
2500 Set refers to the single line desk telephone set using touchtone pad.

2B+D
2B+D is a simple way to say ISDN's Basic Rate Interface. 2B means two bearer channels and D refers to  one data channel.

2B1Q: 2 Binary 1 Quaternary
2 Binary 1 Quaternary (2B1Q)  is a full duplex physical layer encoding method used in ISDN and other digital communication technologies.  In 2B1Q, two binary bits are encoded into one quaternary signal, doubling the effectiveness of transmission.

2VSB: 2-level Vestigial SideBand modulation
2-level Vestigial SideBand  modulation (2VSB) is a type of  modulation that is capable of transmitting one bit at a time.

2-wire Facility
2-wire Facility refers to a telecommunication facility or equipment which supports transmission in two directions simultaneously. An ordinary telephone set is an example of 2-wire Facility.

411 Service
411 service is for local directory assistance in the United States and Canada. In recent years, 4-1-1 has been used for long distance directory assistance in most areas of the United States. 

4B/3T
4B/3T, also known as MMS43 code, is a type of line encoding method for ternary block encoding of binary signals, where four binary elements (binary block 4B) are represented as three ternary elements (ternary block 3T). 4B/3T encoding uses a matrix that maps each of the 16 bit patterns to 4 bits of the ternary signals. Four different ternary sequences are mapped to each 4 bit word. This encoding method is used by the ISDN Basic Rate Interface as a transmission method. 4B/3T encoding is also used in the exchange area between the ISDN exchange and the network terminator. The ternary representation of the data stream supports data rates of 160 kbit/s at a clock speed of 120 kbit/s. This allows for a maximum distance of 8 km between the network terminator and the ISDN exchange.

4ESS Switch
4ESS Switch is the world€™s first digital electronic switch developed by Lucent Technologies (formerly AT&T). The first 4ESS Switch was installed in 1976 in Chicago. 4ESS was mainly used in toll offices in the former AT&T PSTN.

4-wire Facility
4-wire Facility refers to a telecommunication facility or equipment which uses separate wiring for transmitting and receiving data. This means the transmission can only be carried in one direction. A lightwave carrier system is a four-wire Facility. 

4WL-WDM:  Four-Wavelength Wave Division Multiplexing 
Four-Wavelength Wave Division Multiplexing  (4WL-WDM) is  type of multiplexing introduced in 1996 by MCI Communications Corp, also known as Quad-WDM. It allows a single fiber to accommodate four light signals instead of one, by routing them at different wavelengths through the use of narrow-band wave division multiplexing equipment.

500 Service
500 Service refers to the telephone service as 1-500-xxx-xxxx. The 500 in the dialing code 1-500-xxx-xxxx is a non-geographic area code. It is designed specifically for Personal Communication services (PCS). 500 Service provides for Follow-Me service by allowing you to specify which telephone facility you want the incoming call to be routed to depending where you are and some other criteria of your choice.

500 Set
500 Set is the old rotary telephone set. 500 Set was the standard desk-top style telephone set used by former AT&T in North America from the late 1940s through the divestiture of AT&T in 1984.  There are many of such phones still in use today and supported by telephone systems.

50-Pin Telco
50-Pin Telco, also known as RJ21, is a connector very common in 10BASE-T wiring. As opposed to the RJ45 connector, the 50-pin Telco connector concentrates up to 12 UTP connections onto one connection. This concentration of UTP ports is then broken out for connection to a punch-down block inside a building's wiring closet. 50-pin Telco connections provide a very clean, uncluttered interface to the building's wiring. 50-Pin Telco is used to attach 25 pairs of telephone wires. It is also used for SCSI-1 connections and is the 50-pin version of the widely-used centronics connector found on the back of PC printers. 

56 kbps
56 kbps is short for 56 kilobits per second. It is the data capacity of a normal single channel digital telephone channel in North America.

56 Kbps Modem
56 Kbps Modem is also known as V.pcm Modem. It uses v.90, an ITU standard (1998) for a modem that communicates at 56 Kbps downstream and 33.6 Kbps upstream. It is intended for use only with ISPs and online services that are digitally attached to the telephone system. Most service providers are typically connected with high-speed digital T1 or T3 circuits.
In practice, the downstream link isn't generally faster than 45 Kbps in these PCM modems, so called because they use pulse code modulation downstream and standard V.34 upstream. Initially, two incompatible technologies competed in this arena: x2 from U.S. Robotics and K56Flex from Rockwell and Lucent. Such modems can be upgraded to V.90 if they contain software-upgradable memory chips

5ESS Switch
5ESS Switch is a telephone switching system first introduced in 1982 by Lucent Technologies ( formerly AT&T). It has evolved into a truly universal digital switch that meets all the telecommunications needs of the modern information age. Its versatility, flexibility, reliability, quality of service, and economic benefits are a direct result of using state-of-art designs and technologies for the system's hardware and software implementation. 5ESS has a wide variety of applications. It can serve as a local, toll or international gateway exchange, or a combination of these functions. It provides the following major applications: Local exchange, tandem exchange, Toll or transit exchange, Operator Services Position System (OSPS), Signal Transfer Point (STP) for a common channel signaling system, International gateway exchange, Wireless (cellular) switch (Mobile Switching Center/Mobile Telephone Switching Office; MSC/MTSO), Remote (switching) operations. 

5ESS-2000
5ESS-2000 is an improved version of the original 5ESS switching developed by Lucent Technologies (former AT&T). It is one of the most common switches used in the North American digital networks. It can be used for wireline and wireless network applications. 5ESS-2000 switching platform utilizes a common software and distributed hardware architecture simultaneously supporting both wireless and wireline applications. There are three sizes of 5ESS-2000 available: 1. Large switches called 5ESS-2000 Digital Cellular Switch (DCS).  2. Compact switch called 5ESS-2000 Compact Digital eXchange (CDX). 3. Very Compact Switch called 5ESS-2000 Very Compact Digital eXchange (VCDX).

64 Kbps
64 Kbps is short for 64K bits per second. This is the standard speed for a phone line.

66 Block
66 Block is a widely-used common type of connecting terminal board for terminating twisted-pair cables. The 66  Block is designed for telephone systems, PBX systems and other low-speed or low-voltage terminal equipment. 

66-type Connecting Block
66-type Connecting Block is the connecting block used to terminating twisted-pair cables. All the wires have to be cut manually with a special tool to connect to the terminating telephone equipment or to make connections between them.

66-type Cross Connect
66-type Cross Connect is a cross connect system using 66-type connecting blocks and jumper wires. This is the most common cross connect systems in telephone system in North America.

700 Service
700 Service refers to a telephone service that uses dialing plan pattern 1-700-xxx-xxxx. The 700 is a non-geographic area code which reserved just for the provisioning of special Inter-Exchange Carrier services. The 700 service was once deployed by former AT&T in the form of easy reach that allows your incoming calls to follow you in the same way as would 500 Service. 700 Service were also used for many different purposes and it is still evolving as the result of change of telecommunication regulations. Currently, it is commonly used in both voice and data VPNs (Virtual Private Networks).

711 Service
711 refers to the Services Code on a nationwide basis (US) for accessing Telecommunications Relay Access (TRS).

800 Portability
800 Portability refers to a requirement in the 800 service that allows customers to keep their 800 number with them when move to any other long distance carriers (service providers). As part of its efforts to promote competition, in 1991, the FCC endorsed the idea of phone number portability.

800 Service
800 Service generally refers to the toll free services including 800, 888, 877, 866 number services that former AT&T, MCI, Sprint and the Bell operating companies used for so called IN-WATS service. Those 800, 888, 877, 866 numbers in the dialing plan are served as "area code" by analogy with normal telephone dialing plan. Dialing of 800 service is free to the person making the call.  However the call is billed to the person or company being called. 800 calls can terminate on any telephone or cell phone with their own normal telephone numbers. This is a way to charge the called parties who have their own "normal" phone number and subscribe to the 800 service so that the calling party can be free of charge. This 800 service is basically a database lookup and translation service for  incoming phone calls. The 800 service works like this: If a 800 number dialed, which means a 1-800 plus seven digits, the LEC (Local Exchange Carrier, i.e. the local phone company) central office sees the "1" and recognizes the call as long distance. It ships that call to a next level or a bigger central office depending on where the routing information is stored. The processing central office recognizes the 800 "area code" and examines the next seven digits. At this point, the LEC switch holds the call, while it queries a centralized database, usually over a SS7 (Signaling System 7) link. That centralized database identified the LEX or IXC (Inter Exchange Carrier) providing the 800 number, as well as translating the 800 number into a "real telephone number". Based on that "real telephone number", the LEC switch will then route the call to the proper IXC (long distance company). Once the long distance company has the 800 call, there are many way it can send the call to the the phone it's intended for. 

800 Valuflex Service
800 Valuflex Service is a service provided by former Nynex (NYNEX Corporation was acquired by Bell Atlantic Corporation (BNTR) on 8/14/1997). This service allows customer to make and receive regular phone calls and 800 number calls from local areas on their normal business phone lines. This allows customers to combine the regular business phone line (usually have regular non-800 phone number) with 800 number service to the same business phone without adding additional phone line. In the meantime, the 800 number calls can also share all the call features that the normal business phone line would have without subscribing them separately. 

877 Service
877 Service is a toll-free service, the same as 888 and 800 services. 877 was introduced by NANP (North American Numbering Plan) in April 1998 as the result of running out of 888 numbers. 

888 Service
888 Service is the toll-free service, the same as the 800 services. It was introduced by NANP (North American Numbering Plan) in April 1996 to include 888 numbers as part of the toll-free service. 

8B10BLF
8B10BLF is short for 8-Byte/10-Byte Local Fiber. It refers to a multimode fiber optic channel that can support data rates up to 150mpbs.

900 Service
900 service, also called a pay-per-call service, permits callers to place calls to 1-900 prefixed telephone numbers and connect to a program delivered by a third party called a 900 content provider. This is a tariffed network service provided by certain telephone companies to 900 content providers. Those program include live and pre-recorded services such as adult chat lines, vote casting, psychic consultations, horoscopes, games, donations processing, weather forecasts, translation, and medical, legal or government services, etc. 

905-928 MHz
905-928 MHz is a frequency spectrum band segment that is mostly and commonly used by cordless phones (so called 900 MHz phone).

911 Service
911 is the official national emergency number in the United States and Canada. Dialing 911 quickly connects caller to a Public Safety Answering Point (PSAP) dispatcher trained to route your call to local emergency medical, fire, and law enforcement agencies. The 911 network is a vital part of emergency response and disaster preparedness system.

958 Number
958 number is testing prefix number in the dialing plan structure NPA-NXX-XXXX where NPA stands for the area code and NXX stands for the Prefix. This means that the prefix number 958 is reserved only for testing purpose and will not be available for customers. 958 numbers (NPA-958-XXXX) are reserved for general testing, while 959 numbers (NPA-959-XXXX) are reserved for inter-exchange carrier testing.

959 Number
959 number, similar to 958, is the prefix number (NPA-959-XXXX) reserved for inter-exchange carrier testing. The only way to reach a 959 numbers is being pre-subscribed to that inter-exchange carrier or using an access code 101xxxx as in dialing plan 101xxxx-1-NPA-959-XXXX. 

976 Service
976 service, similar to 900 service, allows customers to place calls to 1-976 prefixed telephone numbers and connect to a pay-per-call program delivered by a third party. Rules of 976 is not exactly the same as for 900.

999 Service
999 service is the phone number for emerfency services in Great Britain, which is equivalent to the 911 service in the US.