Vidyo VidyoGateway Administrator's Manual page 174

9. Appendix A. Definitions
external traffic. A NAT box located where the LAN meets the Internet makes all necessary IP
address translations.
 Prefix – A unique identifier for a call service.
 Point-to-Point Call (Direct Call) – A videoconference that takes place between just two users.
No additional participants can join a point-to-point call.
 Protocols
H.235 – The H.3xx encryption protocol over H.323 connections for secured

videoconferencing. Vidyo supports AES 128 bits.
H.239 – The standard used in H.323 and H.320 videoconferencing that enables two

simultaneous media channels in a single video conference. The second channel is used for
data presentation. For example, it's possible to see a speaking person within a main video
screen and see their computer screen with diagrams, documents, screenshots, and so on.
H.245 – A control signaling protocol for the exchange of end-to-end messages between

communicating H.323 and H.234 endpoints/terminals.
H.264/AVC – Also called Advanced Video Coding (AVC). A simple and straightforward

video codec that provides enhanced compression performance and a network-friendly
video representation.
H.264/SVC – Also called Scalable Video Coding. A new video compression standard that

enables a video stream to be broken into multiple resolutions, quality levels and bit rates.
Vidyo uses this technology in its video conferencing products.
H.323 – A standard that addresses call signaling and control, multimedia transport and

control, and bandwidth control for point-to-point and multi-point conferences. The H.323
protocol provides audio-visual communication sessions on any packet network.
SIP – Session Initiation Protocol. A signaling protocol used for controlling multimedia

communication sessions such as voice and video calls over Internet Protocol (IP).

QoS – Quality of Service. A networking term that specifies a guaranteed throughput level.
 SD (Standard Definition) – A video format with a 640 x 360 resolution and a 16 to 9 aspect
ratio. (Traditional broadcast television SD has a different format. The definition given here is the
one referred to in this document.) Starting with version 2.2, VidyoGateway provides a better SD
experience by supporting an adaptive aspect ratio for SD calls. With this feature, the aspect
ratio automatically changes as needed when you are in an SD call.
 Standby VidyoGateway – One of a cluster of VidyoGateways that are controlled by a single
Controller VidyoGateway.
 TCS4 – Terminal Control String. A special routing method for incoming H.320 video calls. TCS4
allows direct inward dialing (DID) to an endpoint on the IP network through the gateway when
DID is not available. H.323 endpoints on the IP network register with the gatekeeper using
extension numbers. When an ISDN terminal dials one of the gateway phone numbers followed
by a TCS4 extension, the call is routed directly to the corresponding IP endpoint registered with
that extension.
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