Glossary-C - Industrial Ethernet switches|Ethernet|USB|RS485|RS232|media converter|optic fiber modem|protocol converters|video converters
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A Certification Authority (CA) issues certificates and guarantees the identity of each certificate owner.


Cable Modem Channels

To connect to the cable providers network, a cable modem must first find and lock onto the downstream and upstream communication frequencies (or channels). The downstream channel is for receiving data from the cable provider's network and the upstream.



Calibration resets the SELT parameters on a switch to achieve high SELT accuracy.


Caller ID

Caller ID allows you to see the originating number of an incoming call (on a device with a suitable display).


Call Filtering

Call filtering is used to determine if a packet should be allowed to trigger a call. Outgoing packets must undergo data filtering before they encounter call filtering.


Call Mute

When you mute a call you can hear the sound from the other end of the line, but you do not transmit a signal and the person on the other end of the line cannot hear you.


Call Overload Protection

Some VoIP line cards allow you to configure how many calls the H.248 interface is to handle. This protects against overloading the VoIP line cards or the MGC.


Call Parking

Parking a call places that call on hold at a specific extension. The call can then be picked up again from another telephone in your organization.


Call Routing

This defines how an IPPBX routes internal calls and handles calls to and from the outside world.


Call Scheduling

Configure call time periods to restrict and allow access for users on remote nodes.


Call Transfer

Call Transfer allows you to transfer an incoming call that you have answered to another phone.


Call Waiting

Call waiting allows you to place a call on hold while you answer another incoming call on the same telephone (directory) number.


Call Scheduling

Configure call time periods to restrict and allow access for users on remote nodes.


CAM (Constantly Awake Mode)

CAM (Constantly Awake Mode) keeps a wireless AP from going to "sleep" when no wireless activity is running in the wireless network. This is useful for establishments, such as coffee shops, that offer wireless Internet to their customers.



Control And Provisioning of Wireless Access Points (CAPWAP) is an Internet Engineering Task Force (IETF) protocol allowing multiple wireless access points to be managed by a single controller access point. The CAPWAP dataflow is protected by Datagram Transport Layer Security (DTLS).



In telephone networks that use CAS (Channel Associated Signaling), each channel carries both the control signal and voice signal. CAS is commonly used in America.


Category 5 

Twisted-pair cable with electrical characteristics suitable for all twisted-pair Ethernet media systems, including 10BASE-T and 100BASE-TX. Category 5 and Category 5e cable are preferred cable types for structural cabling systems.

Category 5e 

An enhanced version of Category 5 cable, developed to improve certain cable characteristics important to Gigabit Ethernet operation. It is recommended that all new structured cabling systems be based on Category 5e cable; however, this cable may not be the best for use in industrial installations because of noise susceptibility.



Constant Bit Rate is an ATM service category that provides a fixed amount of bandwidth for streaming data (like voice or video). The bandwidth is always reserved, even when streaming data is not being sent.


CCD (-Sensor)

A charge-coupled device (CCD) is a device for the movement of electrical charge, usually from within the device to an area where the charge can be manipulated, for example conversion into a digital value. This is achieved by "shifting" the signals between stages within the device one at a time. Technically, CCDs are implemented as shift registers that move charge between capacitive bins in the device, with the shift allowing for the transfer of charge between bins.

Often the device is integrated with a sensor, such as a photoelectric device to produce the charge that is being read, thus making the CCD a major technology for digital imaging. Although CCDs are not the only technology to allow for light detection, CCDs are widely used in professional, medical, and scientific applications where high-quality image data is required.


CC Packets

These are the connectivity check (CC) packets used in CFM.



Complementary Code Keying (CCK) is a type of modulation utilized for 5.5 and 11Mbps transmission in IEEE 802.11b and IEEE 802.11g wireless LANs.



Cryptographic technique which ensures message integrity by encrypting each block of plain text in such a way that its encryption is dependent on the block before it. This series of "chained" blocks creates a message authentication code (MAC or CMAC) that ensures the encrypted data has not been tampered with. Also known as CBC-MAC.



The Central Coordinator of the powerline network is the powerline adapter which keeps track of which devices are part of the network and synchronizes communication within the powerline network. If the Central Coordinator is removed from the powerline network, another powerline adapter takes its place. The powerline adapters in a powerline network automatically select the Central Coordinator.



In telephone networks that use CCS (Common Channel Signaling), one channel carries the control signal and a separate channel carries the voice signal. CCS is commonly used in Europe.



In code division multiplexing (CDM), the communications stream is divided in time and frequency. An individual data channel may transmit on one frequency at one time, and another frequency at another time. CDM is used in GSM cellular communications.



CDMA (Code Division Multiple Access) is a form of multiplexing and a method of multiple access that uses different codes for each user to divide up a radio channel. The same channel is occupied by many codes, but only the users given a shared code can understand each other. CDMA also refers to a digital mobile telephony system with this multiple access scheme. The GSM standard specifies an entire network infrastructure, while CDMA relates only to the radio part of the technology. See also GSM.



CDP (Cisco Discovery Protocol) allows Cisco devices to be discovered through the service provider's network.


Compact Disc - Read Only Memory. An optimal disc that is used to store text, graphics and audio data for computer applications. The contents may not be changed or rewritten.



In ATM, the Cell Delay Variation Tolerance is the accepted tolerance of the difference between a cell's transfer delay and the expected transfer delay. CDVT controls the time scale over which the PCR is enforced. CDVT is used to determine if a cell arrived too early in relation to the PCR (see PCR).



In a wireless metropolitan area network (MAN), a cell is the geographical area of wireless coverage provided by a base station. A MAN is made up of many overlapping cells. Also: This is the data packet unit that ATM transmits. One cell consists of 53 bytes.



Certificates (also called digital IDs) can be used to authenticate users. Certificates are based on public-private key pairs. They provide a way to exchange public keys for use in authentication.


Certificate Authority

A Certification Authority (CA) issues certificates and guarantees the identity of each certificate owner. There are commercial certification authorities like CyberTrust or VeriSign and government certification authorities.


Certification Path

A certification path is the hierarchy of certification authority certificates that validate a certificate.


Certification Request

A certification request contains identifying information and public keys. You can send a certification request to a certification authority. The certification authority signs the certification request and issues a certificate.



IEEE 802.1ag is a Connectivity Fault Management (CFM) specification which allows network administrators to identify and manage connection faults. Through discovery and verification of the path, CFM can detect, analyze, and isolate connectivity faults in bridged LANs.


CFM Domain

A CFM domain is a group identified by an MD level and an MA VLAN ID. For example, ports in MD level 1 and MA VLAN 2 are in the same CFM domain while ports in MD level 7 and MA VLAN 2 are in another CFM domain. See also MD and MA.



Common Gateway Interface (CGI) allows a web server to obtain information from a database, documents or other programs and present the retrieved information to the subscribers.



Like radio stations or television channels, each wireless network uses a specific channel, or frequency, to send and receive information. The number and type of available channels are depending on your geographical area.



Challenge Handshake Authentication Protocol is an alternative protocol that avoids sending passwords over the wire by using a challenge/response technique.



CIFS is a file-sharing protocol supported by any operating system that supports Server Message Block (SMB).



An indication of overall radio signal quality, usually measured in decibels (dB). A higher CINR value indicates a higher signal quality, and a lower CINR value indicates a lower signal quality.


CINR Deviation

The amount of change in the Carrier to Interference plus Noise Ratio level. An indication of radio signal stability, usually measured in decibels (dB). A lower CINR deviation value indicates higher signal stability, and a higher CINR deviation value indicates lower signal stability.



A cipher is a code that uses substitution at a basic level (individual letters or bits). See also Encryption, Decryption, Plaintext, Ciphertext.



Ciphertext is another term for encrypted data. A text that has been scrambled or encrypted so that it cannot be read without deciphering it.See also Encryption, Decryption, Cipher, Plaintext.



The carrier programs virtual circuits into the network between your sites and charges customers for a specific level of service called the committed information rate (CIR). The CIR is a negotiated rate and is basically a guarantee that the carrier will always have that bandwidth available.


Circuit Switching

This is the use of switches to set up a dedicated physical connection between two endpoints until it receives a disconnect signal.


Circuit Switched Network

This is a network that sets up a temporary physical circuit when a telephone receiver is picked up (goes off hook) and holds the circuit open until it receives a disconnect signal.



A CIST (Common and Internal Spanning Tree) represents the connectivity of the entire network and is equivalent to a spanning tree in an STP/RSTP. See also MSTP.

Class of Service (CoS)

As related to network technology, “Class of Service” (CoS) is a 3 bit field within an Ethernet frame header when using 802.1Q tagging. The field specifies a priority value of between 0 and 7 inclusive that can be used by Quality of Service (QoS) disciplines to differentiate traffic.

While CoS operates only on Ethernet at the data link layer, other QoS mechanisms (such as DiffServ) operate at the network layer and higher. Others operate at the physical layer.

Although 802.1Q tagging must be enabled to communicate priority information from end station to switch, or switch to switch, some switches use CoS to internally classify traffic for QoS purposes.

The term can be used generically to refer to the classification of network traffic within network equipment based on packet inspection.


Class 5 Switch

This is a PSTN (Public Switched Telephone Network) switch in a CO.



In computer networking, a classifier groups traffic based on specific criteria such as the IP address, port or protocol, etc.


Cleared Alarms

An administrator clears an alarm after solving its cause. When an alarm is cleared, it is removed from the current alarm screen and becomes an historical alarm.


A Competitive Local Exchange Carrier is a Local Exchange Carrier (LEC) that competes with the market leading or Incumbent LEC (ILEC). This type of carrier may offer Internet Access, video on demand/cable TV, long distance or local exchange service. It also includes wireless (cellular/PCS) providers.



In this interface, you can use line commands to configure the device or perform advanced device diagnostics and troubleshooting.


Click-To-Talk (CTT)

CTT allows a person browsing the Internet to click an embedded VoIP object in a web page or email and place a call from directly from his or her web browser to a specific recipient on the other end.



When two or more devices are connected digitally to form a network, the one that contacts and obtains data from a server is known as the “client”. Each client is designed to work with one or more specific kinds of servers, and each server requires a specific kind of client.


Client program

A software program that is used to contact and obtain data from a server software program to another computer. Each client program is designed to work with one or more specific kinds of server programs and each server requires a specific kind of client. A web browser, for example, is a specific kind of client.



Caller Line Identifier Presentation (CLIP) lets the user transmit caller ID over SIP.



Caller Line Identifier Restriction (CLIR) lets the user restrict the transmission of caller ID over SIP.


Cluster Management

Cluster management allows you to manage switches through one switch, called the cluster manager. The switches must be directly connected and be in the same VLAN group so as to be able to communicate with one another.


Cluster Manager

The cluster manager is the switch through which you manage the cluster member switches.


Cluster Members

The cluster members are the switches being managed by the cluster manager switch.


Clustering Candidates

Clustering candidates are switches that are potential cluster members.



Certificate Management Protocol (CMP) is a TCP-based certificate enrollment protocol that was developed by the Public Key Infrastructure X.509 working group of the Internet Engineering Task Force (IETF) and is specified in RFC 2510.


CMOS (-Sensor)

An active-pixel sensor (APS), also commonly written active pixel sensor, is an image sensor consisting of an integrated circuit containing an array of pixel sensors, each pixel containing a photodetector and an active amplifier. There are many types of active pixel sensors including the CMOS APS used most commonly in cell phone cameras, web cameras and in some DSLRs. Such an image sensor is produced by a CMOS process (and is hence also known as a CMOS sensor), and has emerged as an alternative to charge-coupled device (CCD) imager sensors.



Vantage Centralized Network Management is a software suite that allows you to manage many geographically dispersed devices from one location.



A CO is a facility that serves local telephone subscribers. In the CO, subscriber’s lines are joined to switching equipment that allows them to connect to each other for both local and long distance calls.


Coaxial Cable

This type of cable has a braided copper shield that surrounds a single insulated copper wire.



A codec (coder/decoder) codes analog voice signals into digital signals and decodes the digital signals back into voice signals.



COE is where home and office phone lines terminate and connect to a much larger switching system.



The result of having two or more simultaneous transmissions on a common signal channel such as half-duplex Ethernet or shared Ethernet.


Collision Domain

The set of all stations connected to a network where faithful detection of a collision can occur. A collision domain terminates at a switch port.


COM Port

The communications port is used for local management of the device. In some devices, it may also be used for uplinking.



This is the SNMP equivalent of a password.



This is a method of reducing the size of a signal.


Compression/Decompression Algorithm

A compression/decompression algorithm (codec) encodes/compresses data into digital data and decodes/decompresses it back again. Data passed through a codec can either be analog or digital in origin. Some codecs work better with analog data (such as an audio codec that converts a telephone conversation from an analog phone and then sends it over the Internet), while others are dedicated exclusively to digital data (such as a video codec that re-compresses existing digital film footage).


CON/AUX Switch and Port

Set the CON/AUX switch to the "CON" side when using the CON/AUX port as a regular console port for local device configuration and management. Set this switch to the "AUX" side when using the CON/AUX port as an auxiliary dial-up WAN connection.


Configuration Genie

Configuration Genie is a program that helps you to configure your device for Internet access. It configures some settings automatically and may prompt you for others.


Connection Identifier (CID)

When a WiMAX base station receives a mobile station connection request, the base station classifies the service type and negotiates a 16-bit connection identifier (CID) with the mobile station. The connection can be established after both sides agree with the CID based on service type.



This is a device (usually a computer) that you use to manage a networking device via a serial port (RS232) connection.


Content Filtering

Content filtering restricts or blocks access to certain web features or content from web pages.



When adjusting video setup, contrast controls the white levels in the television picture.


Controller Access Point (controller AP)

When a network administrator assigns one AP as the controller AP and sets others as managed APs, the controller AP is capable of storing and editing the device configurations of the managed APs. The network administrator does not need to configure the managed APs manually one-by-one and can just use the web configurator of the controller AP to configure them.



A string of characters saved by a web browser on the user's hard disk. Is a piece of text that a web site can store on your computer to enable it to recognize you when you return to the site.


Core Network

This refers to switching offices and the transmission plants that link them together. Competing Interchange networks connect Core Networks in the US, while in other countries the Core Networks reach to the borders of the country they are in.



Class of Service is a form of priority queuing that promises a level of service to a client. CoS classifies packets by examining the packet parameters and placing the packets in queues of different priorities based on predefined criteria. QoS guarantees a level of network performance to meet these service agreements. See QoS.


Cost of Transmission

This is also called the "metric". It sets the priority for devices' routes to the Internet. A router determines the best route for transmission by choosing the path with the lowest "cost".



Techniques, programs or other tools that can protect your computer against threats.


Counter Mode

In cryptography, the encryption of each block of plain text with an arbitrary number, known as the counter. This number changes each time a block of plain text is encrypted. Counter mode avoids the security weakness of repeated identical blocks of encrypted text that makes encrypted data vulnerable to pattern-spotting.



Coverage, or range, is the distance over which wireless devices can communicate.



A Cyclic Redundancy Check (CRC) is a method of checking for errors in data that has been transmitted on a communications link.



A CRL (Certificate Revocation List) is a directory of certificates that have been revoked before their scheduled expirations.


Crossover Ethernet Cable

A cable that wires a pin to its opposite pin, for example, RX+ is wired to TX+. This cable connects two similar devices, for example, two data terminal equipment (DTE) or data communications equipment (DCE) devices.



The act of analyzing (or breaking into) secured documents or systems that are protected with encryption.



Carrier Sense Multiple Access (CSMA) Media Access Control (MAC) protocol is used in shared networks (for example Ethernet). Devices verify that other traffic is not present before transmitting. “Carrier Sense” means that the devices listen to make sure there is not already a carrier wave before transmitting. “Multiple Access” means multiple devices send and receive through the same medium. See also CSMA/CA.



Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) reduces the number of collisions in shared networks (such as Ethernet) by having each device notify other devices before transmitting. See also CSMA.



Carrier Sense Multiple Access/Collision Detect. The medium access control (MAC) Protocol used in Ethernet.



CSUs and DSUs are actually two separate devices, but they are used in conjunction and often combined into the same box. CSU/DSU are hardware devices that convert digital signals used on a LAN into a digital signal used on a WAN and vice-versa (over a T-1 line, for example).


CTS (Clear To Send)

A signal sent by a device to indicate that it is ready to receive data.




In VLAN translation, CVID (Customer VLAN ID) is the VLAN tag carried in the received packets and will be translated into a SVID. See also SVID.