78 results

H.264 Video codec. (AKA: MPEG-4 AVC)   Wikipedia         

H.323 ITU-T standard for A/V transmission through packets.   Wikipedia         

half duplex Only one device can talk at a time, similar to Nextel push-to-talk. Hubs should only be half duplex.            

Halftone    Wikipedia         

Hard Disk Drive (HDD) Usually shortened to hard drive, it uses a spinning platter to store information. Divided into tracks, sectors, clusters, and cylinders.            

hardware-assisted virtualization Intel VT-x or AMD-V   Wikipedia         

Harvard Mark II    Wikipedia         

hash (aka: message digest) Function that can be used to map data of arbitrary size to data of fixed size. Essentially, a number generated from a string of text. A given input will always generate the same output (deterministic algorithm). In networking, it ensures messages did not change in transit. Similar to a Cycle Redundancy Check (CRC), only stronger. Hard to reverse (one-way hash) but is not encryption. Typically 128 bit or longer output. Examples include MD5 and SHA.   Wikipedia  Netacad       

Hash-Based Message Authentication Code (HMAC) (aka: Keyed-Hash Message Authentication Code [KHMAC]) Data integrity algorithm guaranteeing the integrity of a message. Adds a secret key to the hash function.   Wikipedia         

Haskell programming language   Wikipedia         

Haswell Microarchitecture codename from Intel. Announced June 4, 2013.  Wikipedia         

HAVING clause The HAVING clause is used to restrict the output of a GROUP BY query by applying a conditional criteria to the grouped rows.            

Headend Where signals are first received in a cable network. Data is then distributed downstream to the cable network. Similar to a CO in a telephone network.            

Header Checksum             

heartbeats Packets sent between NLB cluster nodes.   Website  Wikipedia       

Heartbleed OpenSSL bug.   Wikipedia         

hello packet One of the OSPF protocol messages.            

help Command that provides Help information. Examples include;


henry (H) 1 volt-second per ampere. Symbolized by 'L'   WikiHow         

here string Multi-line string.   Wikipedia         

hertz (Hz) SI unit of frequency. One cycle per second.   Wikipedia         

Heterogeneous System Architecture (HSA) Not-for-profit group whose goal is to make it easy to program for parallel computing.   Website         

Heuristically Programmed Algorithmic (HAL) 9000 computer    Wikipedia  Wikipedia       

Hewlett Packard (HP) Tech company based in Palo Alto, California. Founded January 1, 1939.  Website  Wikipedia       

hexadecimal (hex) Base-16 number system. Used in IPv6 and MAC addresses. 4 hexadecimal units = 16 binary units. Usually represented in text by the value preceded by 0x.   Wikipedia         

hextet Unofficial term for every 16 bit segment in an IPv6 address   Wikipedia         

HFS Plus (HFS+)             

Hierarchical Network Design Access layer, Distribution layer, and Core layer.   Wikipedia         

High Availability (HA)             

High Efficiency Video Coding (HEVC) (aka: H.265 or MPEG-H Part 2) Video compression standard. Formally published by the ITU-T on June 7, 2013.  Wikipedia         

High Performance File System (HPFS)    Wikipedia         

High-Speed Serial Interface (HSSI) developed by Cisco   Wikipedia         

HMAC Header { Authentication Header | TCP header | data | IP address }   Wikipedia         

horizontal cross-connect Where horizontal cabling connects to a patch panel or punch block.   Wikipedia         

Huawei  Founded in 1987.  Wikipedia         

hub Basic network connectivity device that repeats any signal it receives on one port to all other ports. Operates at OSI layer 1. Succeeded by switches. As of 2011, connecting network segments by repeaters or hubs is deprecated by IEEE 802.3.  Wikipedia         

hub-and-spoke topology Has a WAN link from each remote site when interconnecting multiple sites (for example, multiple corporate locations). Similar to the star topology.            

HyperText Markup Language 5 (HTML 5)  First released as a standard October 28, 2014.  Wikipedia         

HAF X Computer case made by Cooler Master. Released May 2010.  Website  YouTube (Cooler Master)       

Hierarchical File System (HFS)    Wikipedia         

High Air Flow (HAF)             

High-speed WAN Interface Card (HWIC)    Cisco         

HMAC-Message Digest 5 (HMAC-MD5) (Legacy) 128-bit shared-secret key and hash.            

HMAC-Secure Hash Algorithm 1 (HMAC-SHA-1) 160-bit secret key and hash.            

hold time The amount of time a neighbor should wait before considering the advertising router to be down. Used in EIGRP.            

holddown timer    Wikipedia         

HoloLens Holographic headset made by Microsoft.   Website         

HOME ~ Environment variable for the home directory in Bash. Use echo $HOME or echo ~ to display.            

Homebrew Computer Club Early computer hobbyist group in Menlo Park, California. Met from March 1975 to December 1986. First meeting held on March 5, 1975.  Wikipedia         

HomeGroup Allows Windwos users to share files across computers on a home network. Introduced with Windows 7  Website  Wikipedia  Netacad     

Honeypot-based detection Decoy setup on the network to make a hacker think they get away with infecting a system or stealing information.   Wikipedia         

hop The jump from one outgoing interface on a router to another outgoing interface.            

Hop Limit The amount of hops a packet can take before it is dropped.            

Horizontal cabling Inside Wiring (IW) or plenum that connects the telecommunication room to individual outlets in the wall or floor.   Wikipedia         

horsepower (HP) (1 hp = 550 ft-lb/s, 1 hp = 746w) Average horse can do 550 foot-pounds of work per second.             

host An end device with a configured IP address.            

Host Bus Adapter (HBA) Connects a computer to network and storage devices.   Wikipedia         

hostname The network name of a host. Can be show in the CLI of Windows and UNIX-Like operating systems by entering hostname.   Wikipedia         

Hosts file A text file used by an OS to map IP addresses. Windows filepath: "%WinDir%\System32\Drivers\Etc\Hosts"   Wikipedia  Microsoft Support       

Hot Standby Router Protocol (HSRP) Cisco proprietary protocol.   Wikipedia  RFC 2281  Cisco     

hot swap Allows a piece of hardware to be removed without powering down the device.   Wikipedia         

HP Compaq dc5800 Small Form Factor PC Desktop computer from HP. Released Q4 2008.  Website  Wikipedia       

HP Integrated Lights-Out (iLO) Out-of-band management used with HP servers.   Website  Wikipedia       

hping Command-line TCP/IP packet assembler/analyzer. Tool used by security testers to bypass filtering devices by injecting modified IP packets. Developed by Salvatore Sanfilippo.  Website  Wikipedia  sectools.org     

href HTML tag attribute. Specifies a URL.   W3Schools         

HTC Taiwanese consumer electronics company headquartered in Xindian District, New Taipei City, Taiwan. Founded May 15, 1997.  Website  Wikipedia       

HTML attachment File often sent by email that can contain malicious code and can be downloaded and executed on a client’s computer. When a user clicks the attachment, it opens a browser session and could open a malicious web site.   Netcraft          

HTTP Strict Transport Security (HSTS) Protects HTTPS traffic.   Wikipedia         

HTTP version 2 (HTTP/2)  Published as RFC 7540 May 14, 2015.  Wikipedia  RFC 7540  IETF     

Hybrid Fiber-Coaxial (HFC) Part of the link to the service provider uses fiber while the other part (usually the last mile) uses coaxial cable.   Wikipedia         

Hyper-V Native hypervisor that runs in Windows.   Wikipedia         

Hypertext Markup Language (HTML) Common language that most web pages are coded with in conjunction with CSS. Other programs may use HTML to display information including emails.   Wikipedia  Khan Academy       

Hypertext Transfer Protocol (HTTP) (port 80) Transfers webpages that make up the World Wide Web (WWW). When a request for a webpage is made to a web server, HTTP specifies the message types used for communication. The three common message types are GET, POST, and PUT. Introduced under RFC 2068 in January 1997.  Wikipedia  RFC 2068  RFC 2616  RFC 7540   

Hypertext Transfer Protocol Secure (HTTPS) (port 443) A more secure form of HTTP that encrypts data with either Transport Layer Security (TLS) or Secure Sockets Layer (SSL) protocols.   Wikipedia  EFF       

Hypervisor Two types;

type 1 hypervisor Runs directly (bare-metal) on hardware in place of an OS to run guest hosts.
type 2 hypervisor Runs on top of the host OS.

hypotenuse Longest side of a right-angled triangle.   Wikipedia  Khan Academy