NEC Visualink 128/384 General Description Manual
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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. This can be a cost effective solution where existing video/audio equipment is already in place. VisuaLink & ViewPoint VBX Gateway A VisuaLink 128/384 unit could be used with a NEC ViewPoint VBX system. The VBX connects all local users, and VisuaLink provides the videoconferencing and interface functions (through the local PBX) to the Telco digital network. VisuaLink is then shared between all users through the VBX. A cost affordable multi-user solution. VisuaLink & ViewPoint VBX Gateway to Telco Digital Network VBX DesktopVideoconferencingViewPoint VBXVisuaLink 128/384 NEAX 2400 IMX PBX VisuaLink can be mounted ina Video Equipment rack Te l c o ISDN AT MPRI BRI T1 VBX Equipment Rack NEAX 2000 PBX (Direct Connection to National ISDN1)or or POWER HEADSET POWERLI NEB1 B2-B6
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 VisuaLink unit, depending on user requirements. The VisuaLink units then provide a direct interface to the Telco digital network. This gateway application configuration could utilize existing: Desktops video/audio systems, Roll-Abouts, video/audio meeting rooms, and multimedia areas. With existing equipment, VisuaLink adds high quality videoconferencing and ISDN BRI interface. VisuaLink Direct Gateway to Telco Digital Network Desktops BRI BRI BRI 3-BRI 3-BRI Executive Offices Roll-Abouts Training Classrooms Cable Patch Panel VisuaLink 128 VisuaLink 384 VisuaLink 128 VisuaLink 128 VisuaLink 384 Tel c o Common Equipment Rack Existing Equipment Videoconference Room ... Video Monitor(s) Room Cameras Microphones
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 Echo Canceller H.320 Codec Video Sources & Monitors BRI Line Network Interface System Control Line Interface Audio Sources & Speaker Infrared Remote Control, Serial Port, Analog Telephone or VoicePoint+
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 multi-location and far-end camera control. •H.243 Multipoint Chairman for multi-location chairman control and browse functions. •T.120 Multipoint Data Sharing & Collaboration compliance for multi-location data conferencing. Line Interface This circuit provides the correct electrical and protocol connections for ISDN-1 BRI line interface. VisuaLink 128 supports one NT-1 (Network Terminal Devices) terminated ISDN-1 BRI line connection. The VisuaLink 384 has an on-board IMUX (Inverse Multiplexer) which supports ISDN BRI bonding calling. This allows users to connect up to three NT1-terminated ISDN BRI line connections to VisuaLink. This makes it possible to combine three signals from three separate BRI lines into one contiguous data channel.
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. In addition to the minimum requirements, certain optional requirements and standards are also part of, or are used in conjunction with H.320. The implementation of these options is left up to the individual manufacturers. Implementing or not implementing these options can significantly impact the video, audio and transmission quality. This is why not all manufacturer’s H.320 compliant systems operate the same. Five quality factors determine the overall performance of a videoconferencing system: Picture Resolution, Video Frame Rate, Video Processing, Audio Quality, and Data Transmission Rate. A fully compliant (including options) H.320 system addresses these factors: Picture Resolution Picture Resolution is defined by two options: H.261 for low resolution high bandwidth systems and the new H.263 for high resolution low bandwidth systems. Option H.263 supports five resolutions. In addition to Quarter Common Intermediate Format (QCIF) and Common Intermediate Format (CIF) that were supported by H.261 there is SQCIF, 4CIF, and 16CIF. SQCIF is approximately half the resolution of QCIF. 4CIF and 16CIF are 4 and 16 times the resolution of CIF respectively. (VisuaLink supports QCIF and CIF). The H.263 support of 4CIF and 16CIF means a videoconference system could use higher bitrate video processing standards such as MPEG. The H.263 option also corrects some processing flaws and improves performance over H.261 only systems. H.263 should be used in all new systems for optimum performance. Manufacturers who provide compatibility with older systems and peripherals will also incorporate H.261. Video Frame Rate The Video Frame Rate (also known as the number of frames per second (fps)) is the number of times a second the picture image is captured and refreshed. Frame rate is also defined by H.261 and H.263. The H.261 option allows frame rates of 7.5, 10, and 15 fps. (Standard broadcast television is 30 fps). A low frame rate can cause any motion in the picture to appear jerky. H.263 provides higher performance than H.261 by allowing frame rates to 30 fps. This higher frame rate will show much smoother motion and a higher quality image.
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 of picture information that must be transmitted to the far end (for each frame) and provides a higher quality picture. Audio Three options for H.320 define the audio requirements used for a videoconference: • G.711 - for narrowband transmission (at 48-56 Kbps) • G.722 - for wideband transmission (at 48-56 Kbps) • G.728 - for narrowband transmission (at 16 Kbps) G.711 is telephone quality audio (narrow band - 3 KHz), while G.722 is used for stereo quality audio (wideband - 7 KHz). G.728 offers the highest quality audio providing a narrow band 16 Kbps rate. This is necessary for low bit rate transmissions. A manufacturer’s videoconferencing system that supports all three audio requirements has the greatest capability and flexibility to provide the highest quality video at all data rates. for Example: In a 128 Kbps videoconference connection (typically BRI), the G.722 (48-56 Kbps rate) or G.728 (16 Kbps rate) options would be employed. If audio quality is more important than video quality (48 Kbps for the audio and 80 Kbps for video), the system could use G.722. If video quality is more important than audio quality, the system employs G.728. The audio uses 16 Kbps leaving 112 Kbps for the video. Data Transmission Rate Data Transmission Rates impact the perceived quality of the video picture. The higher the data rate the better the video quality. At T1 speeds (1,536 Kbps) the video quality will be best. However, many connections will not use this rate because of cost. In today’s systems, some users connect at the 768 Kbps rate as a trade-off between high quality video and cost. Most use the 384 Kbps rate. The 128 Kbps rate is becoming more widely used with the increased availability of ISDN service.
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 set, modem, or other device on top of the VisuaLink unit, ensure their weight will not cause damage to the VisuaLink unit. • VisuaLink requires adequate ventilation to properly operate. Do not block the openings on the top and sides of the unit. Maintain a 2-4 inch spacing on the sides to allow for proper unit cooling. • If VisuaLink is to be mounted in an equipment rack, ensure adequate conditions and temperature requirements are met. Refer to the VisuaLink Quick Installation Guide, Stock # 0293885 for complete installation procedures.
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 VisuaLink configuration are working properly, with no broken wires or connectors. • Ensure all settings and parameters for VisuaLink operation are correctly set via the on-screen menus. • Verify the VisuaLink unit has adequate ventilation. (see previous section-- Installation Requirements) Note: A user can unpgrade a VisuaLink 128 to a VisuaLink 384. Refer to the VisuaLink Quick Installation Guide, Stock # 0293885. If problems still exist after completing the maintenance guidelines, contact your NEC representative or the NEC Technical Assistance Center.