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Glossary : C

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collapse/expand C Band
  • Microwave frequency band in the range of 4 - 8 GHz that corresponds to wavelength of 7.5 - 3.8 cm.

collapse/expand Cable modem
  • A modem that is used for connecting a computer or home network to the Internet via cable TV (CATV) network. Cable modem provides broadband connection with maximum downstream data rate of 40 Mbps and upstream of 30 Mbps that is shared among neighbors who are connected to the same CATV service distribution point.
    Also see CATV.

collapse/expand CAP
  • Carrier-less Amplitude and Phase Modulation. A modulation technique used in some ADSL modems in which the transmit and receive signals are modulated into two frequency bands.
    Also see ADSL. Compare with DMT.

collapse/expand Carrier
  • A signal or wave that is modulated by information (baseband signal) to carry the information efficiently from transmitter to receiver. A carrier is usually a higher frequency signal.
    The term carrier also refers to a telecom or backbone network operator.
    Also see modulation.

collapse/expand Cat 5
  • Category 5 cable. Cat 5 cable is a type of twisted pair cable that is commonly used in Ethernet and Fast Ethernet networks. Cat 5 cable has 8 wires inside. However, only 4 wires are used for transmit and receive, i.e. wires 1, 2, 3, and 6. The wire colors inside a Cat 5 cable based on EIA/TIA-568B standard are as follows:
    Wire 1 : Orange/White
    Wire 2 : Orange
    Wire 3 : Green/White
    Wire 4 : Blue
    Wire 5 : Blue/White
    Wire 6 : Green
    Wire 7 : Brown/White
    Wire 8 : Brown
    Cat 5 cable is terminated with RJ-45 connectors.
    Also see twisted pair and RJ-45.

collapse/expand CATV
  • Community Antenna Television or Cable Television. A network that carries television broadcast over fiber optic infrastructure from a cable operator site (headend) to distribution points and coaxial cable from a distribution point to each subscriber home. Because CATV is a closed network, only registered and paying subscribers can view its broadcast.
    Older CATV networks only provide downstream Internet connection as additional service with upstream carried by telephone line using dial-up connection, now it has become the norm for a CATV provider to serve both downstream and upstream Internet connection over the same coaxial cable.
    Also see cable modem.

collapse/expand CBR
  • Constant Bit Rate. A service class in ATM that guarantees bandwidth for real time services, such as voice call and video conferencing.
    Also see ATM.

collapse/expand CCITT
  • Consultative Committee on International Telegraphy and Telephony. Now it is under ITU, called ITU-T (ITU-Telecommunications Standardization Sector).
    Also see ITU.

collapse/expand CDMA
  • Code Division Multiple Access. A multiple access technique in which signal from each station is provided with an individual and distinctive pseudo-random code. The codes for all stations are uncorrelated with one another.
    Also see multiple access.

collapse/expand Cell Switching
  • Cell switching refers to the switching that is done by ATM switches in which information is divided into fixed-length 53-byte cells.
    Also see ATM. Compare with circuit switching and packet switching.

collapse/expand Centrino
  • Intel integrated support for mobility that includes built-in Wi-Fi adapter, smaller form factor (size), and lower power consumption. Therefore, a Centrino notebook user doesn't need to buy a Wi-Fi adapter separately to connect to a Wi-Fi hotspot and she will enjoy a lighter notebook with longer battery life.
    Also see Wi-Fi.

collapse/expand CF
  • Compact Flash. CF card is a small size removable memory card that is used to store files or provide additional services (GSM, GPRS, GPS, etc.) to mobile devices such as PDAs, mobile phones, and digital cameras.
    With a CF card, you can do any file operation (e.g. copy, paste, erase, rename, format) like when you work with floppy disk.

collapse/expand Certificate
  • A digitally signed document that is issued by a certification authority to authenticate a user, a computer, a device, or service when exchanging information over public network like the Internet.

collapse/expand CHAP
  • Challenge Handshake Authentication Protocol. An authentication  protocol that is used to log on to an ISP. An ISP network access server (NAS) sends a random value (named "challenge") to a client (subscriber) computer which then encrypts it using a password and sends the encrypted value back to the NAS. The NAS forwards it along with the challenge and the client's user name to authentication server.
    CHAP is used with PPP. The presence of encryption makes it more secure than PAP.
    Also see PPP and PAP.

collapse/expand Circuit Switching
  • Circuit switching is the switching that is done by a PSTN switch where a dedicated circuit (path) is allocated for each telephone call. The circuit is occupied until the call ends thereby guarantees the connection.
    See picture. Also see PSTN. Compare with cell switching and packet switching.

collapse/expand Class 1 Bluetooth
  • Bluetooth transceiver power class with transmit power of 20dBm (100 mW) and coverage area of 100 meters.

collapse/expand Class 2 Bluetooth
  • Bluetooth transceiver power class with transmit power of 4 dBm (2.5 mW) and coverage area of about 20 meters.

collapse/expand Class 3 Bluetooth
  • Bluetooth transceiver power class with transmit power of 0 dBm (1 mW) and coverage area of up to 10 meters.

collapse/expand Class A GPRS device
  • A GPRS device (e.g. mobile phone) that has the ability to simultaneously connect to the Internet and make/send or receive phone call or message.

collapse/expand Class A IP Address
  • IP addresses in the range from to The leftmost byte refers to the network ID (i.e. identity). The rest refers to the host (i.e. node or device) ID. IP addresses in this range - are reserved for loopback test, while those in this range - are zero addresses. So, there are only 126 network IDs available but each network can have more than 16 million nodes.

collapse/expand Class B GPRS device
  • A GPRS device (e.g. mobile phone) that suspends an Internet connection when making/sending or receiving phone call or message and continue the Internet connection when the call ends.

collapse/expand Class B IP Address
  • IP addresses in the range from to The leftmost two bytes refer to the network ID. The rest refers to the host (node) ID. That means there are more than 16 thousands network IDs available and each network can have more than 65 thousands nodes.

collapse/expand Class C GPRS device
  • A GPRS device (e.g. mobile phone) that must be disconnected from the Internet when making/sending or receiving phone call or message. The device can only be used for one type of service at any given time.

collapse/expand Class C IP Address
  • IP addresses in the range from to The leftmost three bytes refer to the network ID. The rest refers to the host (node) ID. That means there are more than 2 million network IDs available.

collapse/expand Class D IP Address
  • IP addresses in the range from to These addresses are reserved for multicast and not used by any node for communication over the Internet.

collapse/expand Class E IP Address
  • IP addresses in the range from to Like Class D addresses, class E addresses are used for research only, not for node identification on the Internet.

collapse/expand CLEC
  • Competitive Local Exchange Carrier. Refers to new telecom operators that don't own existing telecom network infrastructure.
    Contrast with ILEC.

collapse/expand Client
  • A computer or a device or a program that uses network resources (data, program, or peripheral) stored in or provided by a server.
    For example, when you visit a website, your Internet browser as a web client reads web pages stored in the website's server.
    A.k.a. workstation. Also see server.

collapse/expand Cluster-tree Topology
collapse/expand CMTS
  • Cable Modem Termination System. An equipment at a CATV operator site (Head End) that contains modems which terminate and communicate with all its subscribers cable modems.
    Also see CATV and cable modem

collapse/expand C/N
  • Carrier-to-Noise Ratio or CNR. The ratio of carrier signal level to noise level in decibel (dB).

collapse/expand Coaxial cable
  • A type of cable that has a solid or stranded conductor in the center, surrounded by an insulating material, then surrounded again by a metal sheath, and finally protected by an outer insulator. Coaxial cable is terminated with BNC connectors.
    Coaxial cable is commonly used in cable TV, Ethernet (10Base2 and 10Base5), antenna connections, and video equipment.
    See picture. Also see BNC connector.

collapse/expand Collision
  • A condition in which two Ethernet nodes detect that the shared medium is idle and start sending packets at exactly the same time.
    Also see CSMA/CD.

collapse/expand COM Port
  • COMmunication Port. Another name for serial port in a computer, used for serial data communication.
    Also see serial port and parallel port.

collapse/expand Contention
  • A LAN access method that allows any node to initiate data transmission at any time. Examples:  CSMA/CD that is used in Ethernet and CSMA/CA in wireless LAN.
    Compare with demand priority and token passing.

collapse/expand Cookie
  • Cookie is not an executable program. Cookie is a small text file stored on someone's hard drive after he/she visited a website. Cookie is employed by the visited website to allow a personalized session during his/her visit or to record his/her personal preferences, such as the kinds of goods or services he/she has bought or websites he/she has visited.
    Cookie may be created by the visited website (i.e. first party cookie) or its advertising partner (i.e. third party cookie). A session cookie is temporary, it's only active during an Internet session. A persistent cookie can follow his/her movement on the Internet.
    Due to privacy concern, many Internet users want to reject cookies although cookies aren't always harmful. Because of that, today's generation of Internet browsers can be configured to prompt a user whether he/she will accept or reject cookies before such cookies enter his/her computer hard-drive.
    If you want to know what a cookie really looks like, check your Temporary Internet Files folder (In IE, go to Tools>Internet Options, on General tab find "Browsing history" then click "Setting". On Temporary Internet Files and History Settings, click "View Files"). Chances are you have collected hundreds cookies there, except if you have always rejected cookies before or emptied the folder regularly. You can use any text editor, such as Notepad, to open a cookie file.

collapse/expand Copper cable
  • A type of cable that is made from copper wires. In telecom and networking, copper wires are structured as twisted pair. Because it is cheaper than other types of cables and reliable enough in normal condition, copper cable is still the most widely used, even though wireless comes to an edge and fiber optic cable has finer quality and larger bandwidth.

collapse/expand CPE
  • Customer Premises Equipment. Refers to a telecom device that is installed at a customer site to terminate an access network and provides interfaces to end user (customer) terminals such as telephone, computer, TV, game console, etc.
    Also known as NT.

collapse/expand Cracker
  • A person who tries to gain illegal access to a computer or a server and if succeeds will do harmful activities on it that may stop its operation or change its data structure.

collapse/expand CRC
  • Cyclic Redundancy Check. A method of detecting errors in a message.

collapse/expand Crossover cable
  • An Ethernet cable (i.e. Cat 5, Cat 5e, or Cat 6) that has one end pinned according to EIA/TIA-568A and the other 568B. The order of the 4 wires (out of the cable's 8 wires) is reversed at both ends of the cable, that's wire/pin 1 becomes 3, and 2 becomes 6.
    Crossover cable is used to connect two computers directly or to connect two hubs or switches in a daisy-chain configuration. But if a hub has an uplink port, it doesn't need a crossover cable to connect to another hub.
    Also see Cat 5 cable. Compare with straight-through cable.

collapse/expand Crosstalk
  • The induction of signals into neighboring pairs of adjacent wire pairs in a cable by either capacitive or inductive coupling.
    Also see NEXT and FEXT.

collapse/expand CSMA/CD
  • Carrier Sense Multiple Access with Collision Detection. An access method used in Ethernet in which each node always listens to detect if another node is already transmitting. Once it finds that the shared medium is idle, it starts sending its packets while listening to detect if another node also starts sending at the same time. If a collision happens, it retransmits the packets after sensing that the line is clear again.
    Also see contention, multiple access, collision and Ethernet.

collapse/expand CSMA/CA
  • Carrier Sense Multiple Access with Collision Avoidance. CSMA/CA is only different with CSMA/CD in that CSMA/CA employs collision avoidance scheme instead of collision detection. In CSMA/CA, a node sends intention to transmit message before it really transmits any packet.
    Also see contention, multiple access, collision and Ethernet.

collapse/expand CTS
  • Clear To Send. A message from a DCE to inform its corresponding DTE that the DCE is ready to receive data from the DTE.
    Also see DCE and DTE. Contrast with RTS.

collapse/expand CWDM
  • Coarse Wavelength Division Multiplexing. A WDM technology that multiplexes less wavelengths in a fiber optic strand thus the wavelengths are widely spaced.
    Also see WDM and fiber optic. Contrast with DWDM.