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List of netowrking, wireless, broadband, satellite, telephony, general computing and other technical terms used throughout the site.
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Term Description
header header refers to the first part of a data cell or packet, containing such information as source and destination addresses, and instructions on how the telecommunications network is to handle the data. The header is part of the overhead in a data transmission protocol.

For typical TCP/IP transmissions (most Internet traffic), the header is usually 40 bytes of each packet (20-byte TCP and 20-byte IP headers). Note TCP and IP headers can be larger than 20 bytes if "options" are enabled. ICMP headers (as in pings) are 28 bytes. UDP headers are 8 bytes.
HFC HFC (Hybrid Fiber Coax) is a distribution network commonly used for Cable Television. The cable segments closer to the headend are optical fiber, while those closer to the customer are coaxial cable. The transition point from fiber to coax varies, and in many places, fiber is extended further into the network in successive upgrades. The signal is normally modulated onto an RF carrier throughout the system. Thus, HFC networks allow the physical medium to be upgraded without changing the signal format or capabilities.
HomePlug HomePlug is a set of standards developed by the HomePlug Powerline Alliance trade association for powerline home networking over existing AC home electrical wires.

HomePlug 1.0 - the first HomePlug specification, widh PHY data rate of 14Mbps

HomePlug AV - offers peak data rate of 200 Mbps at the physical layer, and about 80Mbps at the MAC layer. Some proprietary extensions allow for peak PHY-rate of 500 Mbps.

HomePlug AV2 - 20% faster than HomePlug AV 500, often sold as HomePlug 600.

HomePlug Green PHY - uses up to 75% less energy than AV and has peak rates of 10 Mbps. GreenPHY is a subset of HomePlug AV intended for use in the smart grid for smaller appliances, such as smart meters and HVAC thermostats.

HomePlug Access BPL - BPL (Broadband over Power Lines) internet access technology, subsequently merged into the IEEE 1901 standard.
HomeRF HomeRF is a 1.2Mbps wireless LAN (WLAN) standard, lagging behind 802.11 mainly because of its data rate.

A newer, HomeRF version 2.0 spec with 10Mbps throughput and the ability to support multiple channels of voice communication without interfering with or using data transmission bandwidth is being introduced.
hop A hop is the trip a data packet takes from one router to another in a packet-switching network. On a routed TCP/IP network, such as the Internet, the hop count is kept in the packet header and used to detect routing loops (packets with excessive hop count are discarded). The hop count is an important metric in finding the shortest path between nodes, and can be more significant than their geographical separation.
hotspot hotspot - an area covered by an access point providing a wireless internet connection.
HPNA Home Phone Networking Alliance
HSDPA HSDPA (High-Speed Downlink Packet Access) is a 3G mobile telephony communication protocol in the HSPA family, which allows higher data transfer speeds and capacity.

Current HSDPA deployments support down-link speeds of 1.8, 3.6, 7.2 and 14.4 Mbit/s. Further speed increases are available with HSPA+, which provides speeds of up to 42 Mbit/s downlink.
HSPA HSPA (High Speed Packet Access) is a collection of high-speed 3G digital data services provided by cellular carriers worldwide that use the GSM technology. HSPA protocols extend and improve the performance of existing UMTS (Universal Mobile Telecommunications System) protocols.

HSPA service works with HSPA cellphones as well as laptops and portable devices with HSPA modems. The two established standards of HSPA are HSDPA and HSUPA
HTPC HTPC ia an acronym for: Home Theater Personal Computer
IANA IANA (Internet Assigned Numbers Authority) assigns and coordinates the use of Internet Protocol (IP) parameters such as IP addresses, domain names, protocol numbers, and more.

The IANA website is at:
A list of IANA assigned ports can be found here:
ICMP ICMP (Internet Control Message Protocol) is a protocol designed to allow hosts to send error and control messages to other network devices. Basically ICMP provides communication between the Internet Protocol (IP) software on network devices. The short ICMP messages use IP packets and are usually processed by the IP software, rather than presented to the user at the application level.
ICS ICS (Internet Connection Sharing) enables a Windows computer to share its Internet connection with other client computers on a local area network.

To setup ICS, the host/server computer generally has two network adapters: one for the Internet, and one for the local area network. The Internet connection may be dial-up, ISDN or broadband. The LAN connection can be a wired, wireless, or even an USB ethernet connection.
ICSA ICSA (International Computer Security Association) formerly called NCSA (National Computer Security Association), is an organization founded in 1989, devoted to computer security issues in corporations, associations, and government agencies worldwide.

It is dedicated to continuously improving commercial computer security through certification, sharing of knowledge, and dissemination of information.

Check the ISCA website for additional information, publications, conferences, seminars:
IDS IDS (Intrusion Detection System) refers to a system that aims at detecting network attacks by analyzing traffic flow and looking for known malicious signatures, then matching them with a comprehensive database of exploits. This is refered to as rule-based IDS. More advanced and complex IDS systems might also use anomaly-based solutions for detecting not just known paterns but unknown attacks as well.

IDS are generally concerned with external attacks, and are only as effective as their databases/pattern recognition. They can prove a valuable tool in troubleshooting network problems and detecting/alerting about potential attacks.
IDSL IDSL (ISDN Digital Subscriber Line) is a cross between ISDN and xDSL. It uses ISDN-based technology to provide a data communication channel across existing copper telephone lines at a rate of 144 kbit/s, slightly higher than a bonded dual channel ISDN connection at 128kbit/s. The digital transmission bypasses the telephone company's central office equipment that handles analogue signals. IDSL uses a single-wire pair to transmit full-duplex data at at distances of up to RRD range.
IEEE Institute of Electrical and Electronics Engineers
IETF Internet Engineering Task Force - an open international community that standardizes most Internet communication protocols.
IGMP IGMP (Internet Group Membership Protocol) is protocol used by IP hosts to report their host group memberships to any immediately neighboring multicast routers.

The use of IP multicasting in TCP/IP networks is defined as a TCP/IP standard in RFC 1112. In addition to defining address and host extensions for how IP hosts support multicasting, this RFC also defines the IGMP version 1. Version 2 of IGMP is defined in RFC 2236. Both versions of IGMP provide a protocol to exchange and update information about host membership in specific multicast groups.
ILEC ILEC (Incumbent Local Exchange Carrier) refers to the dominant phone carrier within a geographic area according to the FCC. The Telecommunications Act of 1996 defined an ILEC as the carrier that provided local exchange in a specified area when the act was passed.
IMAP IMAP (Internet Message Access Protocol) is email protocol similar to POP3, used for receiving of email from a local mail server.

IMAP differs from POP3 however, in that email resides on the server while working with it, requiring continual access to the server during the time that you are working with your mail. In POP3 on the other hand, email is downloaded into your client system.

Both IMAP and POP3 are protocols that deal with receiving mail from a local IMAP/POP3 mail server with a system that's not continuously conencted to the Internet. Sending/transfering email between nodes on the Internet is assumed to be done via some other protocol, such as SMTP.
ingress ingress refers to the passage of outside signals into a nominally closed/shielded coaxial cable distribution system. Ingress can originate from broadcast signals, electrical noise, or equipment that the end-user has connected to the network. Ingress noise often originates within an end-user's premises and is, therefore, difficult to locate or correct.
Interleaving Interleaving is DSL forward error correction by spreading your packet bits in time and interleaving them with bits from other packets. This is a feature designed for more robust video streaming (ADSL was originally developed for "cable TV on copper loops"), in theory a noise spike would have lower impact on data loss...

Since TCP/IP has it's own error correcting interleaving is not as important. Fast Path (fastcells, fast switched) disables or greatly reduces the interleaving "spread" of the bits, decreasing latency. Lower ping time/latency improves overall performance, makes browsing more snappy, and is critical for online gaming.
IoT IoT(Internet of Things) is a term for all connected "smart" devices, and other computing objects. It relates to any gadget, appliance, or device that is connected to the internet and can communicate with other devices without human intervention.

Some examples of smart devices:
smart TVs - stream video/audio/photos from local computers or online services.
smart thermostats - learn and adapt to your lifestyle for both comfort and energy efficiency
IP security cameras - send feeds to online servers and can be viewed from smartphone apps
smart lighting - can be controlled remotely, set on schedule, etc.
smart door locks - send alerts to your smartphone, can be controlled remotely, log entries, etc.
IP Address IP Address (Internet Protocol Address) is used to identify a computer to a network. It is, in essence your address on the Internet. Each packet of data on the Internet contains the source and destination IP address, so information can be routed accordingly.

The Internet Protocol (version 4) identifies each host with a 32-bit IP address. IP addresses are written as four dot-separated decimal numbers between 0 and 255, e.g., The leading 3 bytes of the IP identify the network and the remaining bytes identify the hosts on that network. The network portion of the IP is assigned by InterNIC Registration Services, under the contract to the National Science Foundation, and the host portion of the IP is assigned by the local network admins.

Note: Some IP addresses are internal to your local network, and not routable to the Internet. The following 3 blocks of the IP address space have been reserved by the Internet Assigned Numbers Authority (IANA) for private Intranets: - (10/8 prefix) - (172.16/12 prefix) - (192.168/16 prefix)

If your PC is assigned an IP address in one of the above ranges, it is most probably behind a firewall, running NAT or SOCKS. In this case, the IP packets sent to the Internet are addressed from the firewall, and not from your PC.
IPC IPC (Inter-Process Communication) is in essense exchange of data between one process and another, either within the same computer or over a network.
IPSec IPSec (short for IP Security) is a group of related protocols for negotiating encryption and authentication at the IP (host-to-host) level. IPSec is a security extension of IPv4 and a requirement for IPv6 that encrypts all transmissions over a TCP/IP network.

The IPSec protocols are defined in the new RFC 2401-2411 and 2451 (the original IPSec RFCs 1825-1829 are now obsolete).

IPSsec tunnels use port 500/udp for Internet Key Exchange (IKE), as well as port 50 for Encapsulation Header (ESP), and/or port 51 for Authentication Header (AH).
IPTV IPTV (Internet Protocol television) is a system through which digital television service is delivered over a packet switched network, i.e. the Internet and broadband internet access networks, instead of being delivered through traditional radio frequency broadcast, satelite signal, or CATV (cable television) formats.
IPv4 IPv4 (Internet Protocol version 4) is still the most commonly used Internet Protocol (IP) version, initially deployed in 1983.

IPv4 addresses are 32-bit numbers often expressed as 4 octets in "dotted decimal" notation (for example,

IPv6 is the newer version of the Internet Protocol (deployment began in 1999) that offers many improvements over IPv4, such as 128-bit IP addresses, and will eventualy completely replace IPv4.
IPv6 Currently there are two types of IP addresses in active use: IP version 4 (IPv4) and IP version 6 (IPv6).

IPv6 (Internet Protocol Version 6) is the newest version of the Internet Protocol (IP), based on a set of IETF specifications.

IPv6 has been designed as an evolutionary set of improvements to the current IPv4, one of the main being a larger IP Address space. IPv6 addresses are 128-bit numbers (as opposed to the 32-bit IPv4 IP addresses) and are conventionally expressed using hexadecimal strings (for example, 1080:0:0:0:8:800:200C:417A).
IRDP ICMP Router Discovery Protocol (RFC 1256).

Using router discovery, clients dynamically discover routers and can switch to backup routers if a network failure or administrative change is needed.
ISDN ISDN (Integrated Services Digital Network) is an older form of broadband connectivity that transports voice, data, and other applications over digital telephone lines and normal telephone wires at 64 Kbps. ISDN lines can also be bonded to form a 128 Kbps pipe.
ISO International Organization for Standartization which is based in Geneva. Publishes national and international standards for data communications.
ISP Internet Service Provider
ITSP ITSP (Internet Telephony Service Provider) refers to a service provider that offers an Internet data service for making telephone calls using VoIP (Voice over IP) technology.
ITU International Telecommunication Union
IXC IXC (Inter-Exchange Carrier) refers to a carrier with national backbones - the term indicates that such carrier provides connectivity over a wide area between local LEC networks. Examples include AT&T, Qwest, Sprint and other national backbone carriers.
jabber jabber is a Ethernet frame greater than the maximum of 1518 bytes with a bad CRC. Often indicative of a hardware problem with a NIC or transceiver.

See also: runt
JBOD JBOD (Just a Bunch Of Disks, a.k.a spanning) refers to hard disks that can be combined to act as a single larger volume. It is not a RAID configuration.

For example, a 20 GB and a 60 GB drive can be combined to make a 80 GB JBOD volume.
jitter jitter (in the context of computer networks) is a measure of the variance of latency (pings) accross the network. Jitter in a network can be measured using the time variation in successive pings. The jitter (packet delay variation) is the amount by which pings vary.

Zero jitter in a network means that all pings to a host are exactly the same every time. While some jitter should be expected over the Internet, a lower jitter value is better, having it be a small fraction of the ping result is ideal.

In general, jitter is a significant, and usually undesired factor in the design of almost all communications links (e.g. USB, SATA, as well as all network/internet connections).

Jitter buffers or de-jitter buffers are used to counter jitter introduced by queuing in packet switched networks so that a continuous playout of audio or video transmitted over the network can be ensured. This works, however the buffer adds delay, and is finite in size (if it gets full packets will get discarded).
Term Description
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