Video Conferencing Terminology [E - H]

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• » Echo Canceller [top]
  Used by the phone company, an echo canceller is an electronic circuit that eliminates echo (or positive feedback) on a phone network and on video conference telephony links.
   
• » Echo Effect [top]
  Eliminated by echo cancellers, an echo effect is an electronic ‘reflection’ of a speaker’s voice that is time-delayed.
   
• » Ethernet [top]
  Xerox Corporation first developed this local-area-network (LAN) architecture in 1976, and today it’s one of the most popular LAN standards. Ethernet can send information either wirelessly (known as WiFi) or, more commonly, over wires. It runs at 10mbps, and all terminals connect to a single common bus (sometimes called a highway). It serves as the IEEE (Institute of Electrical and Electronics Engineers) 802.3 standard, which ensures that networks adhere to a particular set of technical standards. A new type, known as Fast Ethernet, or 100Base-T, runs at 100Mbps, and the newest type, Gigabit Ethernet, runs at 1gigabit per second. Ethernet is so popular that many PC manufacturers build its functionality directly into their motherboards.
   
• » Ethernet Switch [top]
  This is a computer-networking device that connects several LANs. It contains a number of Ethernet bridges, which means that unlike a single Ethernet bridge, data cannot become as easily congested. An Ethernet switch accomplishes three things: it divides the network into several segments, functions as a high-speed bridge between these segments, and allows for numerous computers to be connected without them all competing for network bandwidth. The Ethernet switch memorizes the address for each computer’s specific port, then directly routes information addressed to that port, and then closes the connection.
   
• » Firewall [top]
  A firewall is a software or hardware application installed on a home or office computer that is intended to prevent unauthorized users from accessing that computer. With hacking and network intrusions on the rise, they are becoming essential in protecting private information. Four popular types of firewall are packet filtering, application gateways, circuit-level gateways, and proxy servers. Firewalls however can often block necessary video conferencing information. An H.323 Proxy solves this by establishing two connections – one to the caller and one to the person called. The information is then transferred from one side to the other, with necessary changes so that the information can go around the firewall. For firewalls that aren’t H.323 aware, it is necessary to manually open select ports. 
   
• » Flash-based Video Conferencing [top]
  Video conferencing that utilizes the Macromedia Flash graphics animation program is Flash-based. Flash Player 6 and beyond supports two-way streaming sound and video. It uses vector graphics that aren’t too demanding for lower end computers, and results in smaller files sizes. Flash is sometimes also referred to as Shockwave Flash, and is installed the majority of desktop PCs. 
   
• » fps (frames per second) [top]
  Fps is the unit that measures computer display performance, much like that in film. One frame consists of one scan of the screen. Fps is especially relevant to video conferencing, where a drop too far below 25-30, considered ‘full motion’ video, results in stuttering and pauses/dropouts in video and audio.
   
• » Frame Rate [top]
  This is basically a synonym for fps, since it means the frequency or speed in which video frames appear on a monitor. In order to appear to be in real time to our eye, frame rates must be around 30fps. 
   
• » Full-duplex [top]
  Full-duplex refers to the two-way, simultaneous transmission of data. A full-duplex device can send and receive data simultaneously. Most PC soundcards are now full-duplex.
   
• » Full-motion Video [top]
  In video conferencing, full motion video means that a video frame rate of 30fps (or Europe’s standard of 25fps) exists. In order to attain this frame rate, an Internet connection speed of 384kbps is required.
   
• » Gatekeeper [top]
  Gatekeepers can be hardware devices or software applications, and they act as management tools for the H.323 multimedia network standard. They monitor and control each zone of the network, translating addresses, controlling network access, and managing bandwidth. Their other tasks include overseeing authentication, call control and routing, detecting and preventing intrusions, and network load balancing.
   
• » Gateway [top]
  Gateways are protocol converters, connecting otherwise incompatible networks, much like translators facilitate communication between different languages. Most H.323 gateways link H.323 and H.320 systems over a LAN/WAN connection.
   
• » Groupware [top]
  Groupware is a type of collaborative software used on a LAN that allows co-workers to work together simultaneously on the same project. Many recent groupware apps now come with video capabilities. Groupware is often divided into three categories: communication, conferencing, and management. 
   
• » H.261 [top]
  This is a video coding standard enacted by the ITU in 1990. H.261 refers to differing video codecs being able to interpret both the encoding and compression of a signal, and to carry out decoding and decompression of that signal. H.261 was designed around ISDN lines, and it supports two resolutions: QCIF and CIF. 
   
• » H.263 [top]
  H.263 is a backwards-compatible update to H.261, and uses a pixel motion-estimation process, predicted frames, and a Huffman coding table to improve picture quality. It is designed for low bit rate communication, and is being used to replace H.261 in many applications. It supports five standard picture formats: QCIF, CIF, SQCIF, 4CIF, and 16IF.
   
• » H.264 [top]
  Another new video standard, H.264 advances coding efficiency beyond existing MPEG-based technology. Bit rate reduction of up to 70% enables smoother delivery of broadcast quality video. Other features, such motion estimation, inter-prediction, intra spatial prediction, and improved encoding algorithms, result in improved image quality. H.264 is often called H.264/AVC (Advanced Video Coding), since it is identical to ISO MPEG-4 (also known as AVC). H.264 accomplishes two goals: provide good video quality at low bit rates and do it flexibly enough so that a variety of applications work well on different networks. The H.264 standard will likely apply to many upcoming applications.  Some of these may include HD-DVD format, the Blu-Ray Disc, US Broadcast TV, MPEGs, Apple Computer’s new OS, and Playstation Portable consoles. 
   
• » H.320 [top]
  This ITU-T standard applies to point-to-point and multipoint video conferencing systems, and is known as an umbrella recommendation. It is actually several recommendations: H.221, H.230, H.321, H.242, and H.261 for video; and G.721, G.722, and G.728 for audio. It is used by nearly all group and room video conferencing systems because it guarantees participants the ability to communicate with each other using different types of equipment. 
   
• » H.323 [top]
  An extension of H.320, H.323 is a standard for transmission of real-time audio, video, and data across packet-based networks (usually IP, IPX, LAN, EN, MAN, or WAN). H.323 standardizes the multimedia components, protocols, and procedures across these networks. Version 2 of H.323 was introduced in 1998 to allow for compatibility with VoIP (voice-over-IP) applications. 
   
• » H.324 [top]
  H.324 provides point-to-point video and audio compression across analogue telephone lines, using H.263 video encoding. This allows for a frame rate increase. H.223, H.245, T.120, and V.34 protocols are all part of the H.324 family.