NEC Visualink 128/384 General Description Manual

Application Configurations   2-9
VisuaLink 128/384 General Description
Gateway
The VisuaLink Gateway application configuration allows shared 
VisuaLink 128/384 units between many users. Existing desktop video/
audio equipment users can now have high quality videoconferencing 
with VisuaLink. VisuaLink units can be configured in one of two typical 
gateway applications:
• ViewPoint VBX Gateway
• VisuaLink Direct Connect
Either application configuration allows shared VisuaLink 128/384 units 
between users....

2-10    Application Configurations
VisuaLink 128/384 General Description
VisuaLink Direct Connect Gateway
The VisuaLink Direct Connect Gateway application configuration uses 
VisuaLink 128/384 units as shared resources for different video/audio 
users and groups in a facility. 
The diagram shows VisuaLink units and a cable patch panel mounted 
in an equipment rack. Video/audio cabling from various areas would 
connect to the patch panel. The patch panel would connect select 
areas with a particular...

3-1
VisuaLink 128/384 General Description
Technical Description
VisuaLink 128 and VisuaLink 384 employ the latest Codec (coder/
decoder) technology for digital video/audio applications. VisuaLink 
employs echo cancelling and control system logic to enhance the 
signal clarity and ease of use.
The diagram illustrates the main functional elements of VisuaLink.
VisuaLink Functional Block Diagram
The following sections provide a technical overview for each of these 
elements.
Video
Interface
Audio
Interface...

3-2    Technical Description
Video & Audio Interfaces
Echo Canceller
H.320 Codec
Video:
Audio: 

Technical Description   3-3
VisuaLink 128/384 General Description
System Control
The System Control circuit manages the many separate functions of 
VisuaLink. This circuit provides control for the Codec and other 
devices. Various control devices can be used for VisuaLink: VisuaLink 
infrared remote control, any analog phone, an NEC VoicePoint+ 
speaker phone, and a Personal Computer (connected via the RS-232 
serial ports).
System Control provides three videoconference control modes:
•H.281 
for...

3-4    Technical Description
VisuaLink 128/384 General Description
...more on H.320 Videoconferencing
ITU-T H.320 specifies technical requirements for narrow-band visual 
telephone systems and terminal equipment-- typically for 
videoconferencing and videophone services.
The H.320 standard defines the minimum requirements that all 
videoconferencing manufacturers must support to comply with H.320. 
These minimum requirements ensure all manufacturer’s H.320 
compliant systems will communicate with other....

Technical Description   3-5
VisuaLink 128/384 General Description
Video Processing
Video Processing is a complex process to reduce the amount of image 
data that must be processed on any given picture frame. If processing 
is not used, videoconference performance is reduced by conditions 
such as complex picture backgrounds, poor camera lighting 
conditions, and object movement. This ensures a H.320 system 
processes image objects in the picture that actually move. This lowers 
significantly the amount...

3-6    Technical Description
VisuaLink 128/384 General Description 

4-1
VisuaLink 128/384 General Description
Installation & Maintenance
Installation Requirements
The compact VisuaLink units need no special installation. However, 
the following should be considered when using or mounting the 
VisuaLink units.
• Place the VisuaLink unit on a stable surface (such as: a desk, or 
mounted in a video or equipment rack).
• VisuaLink may cause possible video interference if placed directly 
on top of a TV set or monitor. This placement is not recommended.
• If placing a phone...

4-2    Installation & Maintenance
VisuaLink 128/384 General Description
Maintenance Requirements
There are no user serviceable (see Note) components, modules, or 
circuits inside the VisuaLink units. If experiencing problems, follow 
these guidelines:
• Ensure a power source is connected to the VisuaLink unit and the 
power control is set to on.
• Check all connections to the VisuaLink unit. Sometimes the wrong 
cable may be connected or perhaps loosely plugged-in.
• Make sure all cables used in a...