H
H Channel
A transmission channel, defined in the CCITT ISDN standards, made up of multiple B channels. Currently defined H channels include H0 (384 kbit/s), H10 (1.472 Mbit/s), H11 (1.536 Mbit/s), and H12 (1.920 Mbit/s).
H.221
A CCITT standard describing a method of inverse multiplexing for videoconferencing terminals, to be used with Px64 videoconferencing.
H.261
A CCITT standard describing a protocol for digitally encoding and decoding video images to allow videoconferencing terminals from different manufacturers to interoperate.
H.320
A set of CCITT standards describing methods to allow videoconferencing terminals from different manufacturers to interoperate.
H.323
A set of International Telecommunication Union (ITU) standards that define a framework for the transmission of real-time voice communications by means of IP-based packet-switched networks. Created in response to customers who needed to use their existing IP networks to support voice communications, the H.323 standards define a gateway and a gatekeeper.
H.324
A standard that governs the transmission of video, audio, and computer data over low speed networks such as the public switched telephone network.
H.330
A set of International Telecommunication Union (ITU) standards that define a method of enabling videoconferencing systems from different manufacturers to interoperate.
H0 Channel
In switched-384 data service, a circuit consisting of 6 B channels, or 384 Kbps.
H0 channel
In Switched-384 data service, a circuit consisting of 6 B channels, or 384 kbps.
H0, ISDN H0
An H channel made up of 6 B channels to create a 384 kbit/s ISDN channel.
H11 Channel
In Switched-1536 data service, a circuit consisting of 24 B channels, or 1536 kbps.
H11, ISDN H11
An H channel made up of 24 B channels to create a 1536 kbit/s ISDN channel.
H12, ISDN H12
An H channel made up of 30 B channels to create a 1920 kbit/s ISDN channel.
HDLC
High-level Data Link Control A synchronous, bit-oriented Link Layer protocol for data transmission. Frame Relay is an example of an HDLC-based packet protocol.
HELLO
The protocol used by a group of cooperative trusting packets switches to allow them to discover minimal delay routes.
HMP
Host Monitoring Protocol
HSSI
High-Speed Serial Interface. A serial interface that operates at speeds up to 52 Mbps at distances up to 50 feet. It is similar to, but faster than, RS-232 and V.35 serial interfaces.
HTML
HyperText Markup Language. The authoring language used to create hypertext documents for the World Wide Web. Like the Standard Generalized Markup Language (SGML), on which it is based, HTML identifies the types of information in a document rather than the exact way it is to be presented. The presentation is left to the software that converts the contents to a suitable format for viewing.
HTTP
HyperText Transfer Protocol. The application protocol for moving hypertext files across the Internet. This protocol requires an HTTP client program on one end of a connection and an HTTP server program on the other.
Hacker
A term that connotes monotonous "hacking away" at bits and bytes. Hence, a programmer of assembly language or a system-level language such as C. Lately, the term has come to designate cyber-intruders who break into computer systems or networks illegally.
Half Duplex
A type of communications configuration in which data can be transmitted in only one direction at a time.
Handover (Handoff)
In cellular communications, a call in progress is automatically passed from one cell or zone to another by the cell sites computer as the user moves.
Handshaking
The process of exchanging signaling information between two communications devices in order to establish the manner and speed of data transmissions. You can use either hardware handshaking or software handshaking.
Hard hand-off (CDMA-to-analog)
in cellular communications, the switch over from digital CDMA to analog during a call.
Hardware Address
An address assigned by the hardware manufacturer and unique to a device.
Hardware Flow Control
A method of flow control that uses separate wires in the modem cable to signal stop and start requests between two directly connected systems.
Hardware Handshaking
A method of synchronizing data transmissions by suing the Request To Send (RTS) and Clear To Send (CTS) pins on a wire.
Hardware Interface
A hardware link between two devices. A hardware interface has electrical, physical, and functional specifications that determine how two devices communicate. An electrical specification defines the characteristics of the electrical signals. A physical specification might define the number of pins and wires required, and the order in which the pins and wires are laid out. The functional specification instructs the hardware on how to interpret the electrical signals. Examples of commonly used hardware interfaces are RS-232 and V.24
Hardwired
In data networking, a continuous connection between two nodes, or sites.
Headend
The originating point of a signal in a cable TV system.
Header
1. Protocol control information at the beginning of a protocol data unit. 2. Portion of a message containing information that guides the message to the correct destination. The information includes senders and receiver's address, precedence level, routing instructions, and synchronization pulses.
Hertz (Hz)
Measures a signal’s frequency as the number of cycles (waves) per second.
Hierarchical Routing
Routing is based on a hierarchical addressing scheme. Most Internet routing is base on a two-level hierarchy in which an Internet address is divided into a network portion and a host portion.
High Bandwidth Networking
The ability to connect nodes and devices over a network that can handle digital services at the rate of 150 Mbps or more.
High Definition Television (HDTV)
A television standard with double the resolution of the current National Television Standards Committee TVs.
High Level Data Link Control
A link level protocol standard ISO. CCITT later adapted HDLC for its link access protocol (LAP) used with X.25 networks. HDLC is increasingly important to the Internet because PSN interface now use it to transfer frames between the host and the PSN. Frame relay is an example of an HDLC-based packet protocol.
High-Watermark
The number of bytes of queued network traffic required to open an additional dial-out line to a remote location.
High-level Entity Management System (HEMS)
A generalization of early host monitoring protocols that uses the Internet to send statistics to central monitoring site.
High-speed Serial Interface
A serial interface that operates at speeds up to 52 Mbps at distances up to 50 feet. It is similar to, but faster than, RS-232 and V.35 serial interfaces.
Home Location Register (HLR)
The database in charge of managing mobile phone subscribers that stores subscription information, and some location information, enabling calls to be routed to a roaming subscriber's location.
Hop
The transmission of a data packet between two network nodes - for example, between two routers.
Hop Count
A measure of distance between two points on the Internet.
Hop count
In data networking, measurement of the distance between a source and destination. It is used to compare route length. If a packet passes through six routers between source and destination nodes, the hop count for the packet will be six when it arrives at its destination.
Host
A computer on a network.
Host Monitoring Protocol
A protocol still used by the Internet Network Operations Center to monitor computers. Its is especially pertinent because the operations center uses HMP to monitor Internet gateways.
Hot Swappable
The ability of a component to be added or removed from a device without requiring that the device be powered down.
Hundred Call Seconds (CCS)
A measure of telephone traffic equal to a single call of 100 seconds duration.
Hunt Group
A group of channels that share the same phone number is called a hunt group. When a call comes in using the phone number assigned to the hunt group, the switch hunts for an available channel in the group.
Hybrid LAN
A hybrid network is one in which some links are capable of sending and receiving only analog signals while others handle digital signals only. Another definition is the division of a network into public and private sections.
Hybrid private/public networking
The creation of a network using both private leased lines and public switched facilities (digital dial-up bandwidth). The goals of combining both networking technologies are increased performance and flexibility at reduced cost. I-NLSP
A transmission channel, defined in the CCITT ISDN standards, made up of multiple B channels. Currently defined H channels include H0 (384 kbit/s), H10 (1.472 Mbit/s), H11 (1.536 Mbit/s), and H12 (1.920 Mbit/s).
H.221
A CCITT standard describing a method of inverse multiplexing for videoconferencing terminals, to be used with Px64 videoconferencing.
H.261
A CCITT standard describing a protocol for digitally encoding and decoding video images to allow videoconferencing terminals from different manufacturers to interoperate.
H.320
A set of CCITT standards describing methods to allow videoconferencing terminals from different manufacturers to interoperate.
H.323
A set of International Telecommunication Union (ITU) standards that define a framework for the transmission of real-time voice communications by means of IP-based packet-switched networks. Created in response to customers who needed to use their existing IP networks to support voice communications, the H.323 standards define a gateway and a gatekeeper.
H.324
A standard that governs the transmission of video, audio, and computer data over low speed networks such as the public switched telephone network.
H.330
A set of International Telecommunication Union (ITU) standards that define a method of enabling videoconferencing systems from different manufacturers to interoperate.
H0 Channel
In switched-384 data service, a circuit consisting of 6 B channels, or 384 Kbps.
H0 channel
In Switched-384 data service, a circuit consisting of 6 B channels, or 384 kbps.
H0, ISDN H0
An H channel made up of 6 B channels to create a 384 kbit/s ISDN channel.
H11 Channel
In Switched-1536 data service, a circuit consisting of 24 B channels, or 1536 kbps.
H11, ISDN H11
An H channel made up of 24 B channels to create a 1536 kbit/s ISDN channel.
H12, ISDN H12
An H channel made up of 30 B channels to create a 1920 kbit/s ISDN channel.
HDLC
High-level Data Link Control A synchronous, bit-oriented Link Layer protocol for data transmission. Frame Relay is an example of an HDLC-based packet protocol.
HELLO
The protocol used by a group of cooperative trusting packets switches to allow them to discover minimal delay routes.
HMP
Host Monitoring Protocol
HSSI
High-Speed Serial Interface. A serial interface that operates at speeds up to 52 Mbps at distances up to 50 feet. It is similar to, but faster than, RS-232 and V.35 serial interfaces.
HTML
HyperText Markup Language. The authoring language used to create hypertext documents for the World Wide Web. Like the Standard Generalized Markup Language (SGML), on which it is based, HTML identifies the types of information in a document rather than the exact way it is to be presented. The presentation is left to the software that converts the contents to a suitable format for viewing.
HTTP
HyperText Transfer Protocol. The application protocol for moving hypertext files across the Internet. This protocol requires an HTTP client program on one end of a connection and an HTTP server program on the other.
Hacker
A term that connotes monotonous "hacking away" at bits and bytes. Hence, a programmer of assembly language or a system-level language such as C. Lately, the term has come to designate cyber-intruders who break into computer systems or networks illegally.
Half Duplex
A type of communications configuration in which data can be transmitted in only one direction at a time.
Handover (Handoff)
In cellular communications, a call in progress is automatically passed from one cell or zone to another by the cell sites computer as the user moves.
Handshaking
The process of exchanging signaling information between two communications devices in order to establish the manner and speed of data transmissions. You can use either hardware handshaking or software handshaking.
Hard hand-off (CDMA-to-analog)
in cellular communications, the switch over from digital CDMA to analog during a call.
Hardware Address
An address assigned by the hardware manufacturer and unique to a device.
Hardware Flow Control
A method of flow control that uses separate wires in the modem cable to signal stop and start requests between two directly connected systems.
Hardware Handshaking
A method of synchronizing data transmissions by suing the Request To Send (RTS) and Clear To Send (CTS) pins on a wire.
Hardware Interface
A hardware link between two devices. A hardware interface has electrical, physical, and functional specifications that determine how two devices communicate. An electrical specification defines the characteristics of the electrical signals. A physical specification might define the number of pins and wires required, and the order in which the pins and wires are laid out. The functional specification instructs the hardware on how to interpret the electrical signals. Examples of commonly used hardware interfaces are RS-232 and V.24
Hardwired
In data networking, a continuous connection between two nodes, or sites.
Headend
The originating point of a signal in a cable TV system.
Header
1. Protocol control information at the beginning of a protocol data unit. 2. Portion of a message containing information that guides the message to the correct destination. The information includes senders and receiver's address, precedence level, routing instructions, and synchronization pulses.
Hertz (Hz)
Measures a signal’s frequency as the number of cycles (waves) per second.
Hierarchical Routing
Routing is based on a hierarchical addressing scheme. Most Internet routing is base on a two-level hierarchy in which an Internet address is divided into a network portion and a host portion.
High Bandwidth Networking
The ability to connect nodes and devices over a network that can handle digital services at the rate of 150 Mbps or more.
High Definition Television (HDTV)
A television standard with double the resolution of the current National Television Standards Committee TVs.
High Level Data Link Control
A link level protocol standard ISO. CCITT later adapted HDLC for its link access protocol (LAP) used with X.25 networks. HDLC is increasingly important to the Internet because PSN interface now use it to transfer frames between the host and the PSN. Frame relay is an example of an HDLC-based packet protocol.
High-Watermark
The number of bytes of queued network traffic required to open an additional dial-out line to a remote location.
High-level Entity Management System (HEMS)
A generalization of early host monitoring protocols that uses the Internet to send statistics to central monitoring site.
High-speed Serial Interface
A serial interface that operates at speeds up to 52 Mbps at distances up to 50 feet. It is similar to, but faster than, RS-232 and V.35 serial interfaces.
Home Location Register (HLR)
The database in charge of managing mobile phone subscribers that stores subscription information, and some location information, enabling calls to be routed to a roaming subscriber's location.
Hop
The transmission of a data packet between two network nodes - for example, between two routers.
Hop Count
A measure of distance between two points on the Internet.
Hop count
In data networking, measurement of the distance between a source and destination. It is used to compare route length. If a packet passes through six routers between source and destination nodes, the hop count for the packet will be six when it arrives at its destination.
Host
A computer on a network.
Host Monitoring Protocol
A protocol still used by the Internet Network Operations Center to monitor computers. Its is especially pertinent because the operations center uses HMP to monitor Internet gateways.
Hot Swappable
The ability of a component to be added or removed from a device without requiring that the device be powered down.
Hundred Call Seconds (CCS)
A measure of telephone traffic equal to a single call of 100 seconds duration.
Hunt Group
A group of channels that share the same phone number is called a hunt group. When a call comes in using the phone number assigned to the hunt group, the switch hunts for an available channel in the group.
Hybrid LAN
A hybrid network is one in which some links are capable of sending and receiving only analog signals while others handle digital signals only. Another definition is the division of a network into public and private sections.
Hybrid private/public networking
The creation of a network using both private leased lines and public switched facilities (digital dial-up bandwidth). The goals of combining both networking technologies are increased performance and flexibility at reduced cost. I-NLSP
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