3-4 Technical 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.

VisuaLink 128/384 General Description

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NEC 128 manual More on H.320 Videoconferencing, Picture Resolution, Video Frame Rate

128 specifications

The NEC 128 is a remarkable microprocessor that represents a significant leap in technological innovation during its time. Introduced in the early 1980s, this processor was designed to meet the demands of increasingly sophisticated computing tasks, primarily aimed at the burgeoning field of personal computing and embedded systems.

One of the standout features of the NEC 128 is its 16-bit architecture, which was quite advanced for its era. This architecture allows for a greater data throughput, enabling the handling of larger data sets and providing improved performance over its predecessors. The NEC 128 operates on a clock speed that typically ranges from 4 to 8 MHz, making it capable of executing instructions efficiently and swiftly, which was crucial for running more complex applications.

The processor is built using CMOS technology, which offers significant advantages in terms of power consumption compared to earlier bipolar technology. This characteristic made the NEC 128 not only suitable for desktop computing but also an appealing choice for battery-operated devices, enhancing its versatility. The use of CMOS allowed for a reduced heat output, contributing to the reliability and longevity of devices powered by this microprocessor.

Another noteworthy aspect of the NEC 128 is its support for a variety of addressing modes. This flexibility enables programmers to write more efficient and compact code, optimizing the use of memory resources. By supporting both immediate and indirect addressing, the NEC 128 allows for more dynamic programming, which is essential for developing applications that require real-time processing.

The processor's architecture also includes a robust instruction set that facilitates arithmetic operations, logical operations, and control flow management. This comprehensive instruction set is instrumental for developers, as it provides the necessary tools for creating a wide range of applications, from simple utilities to more complex software systems.

In summary, the NEC 128 microprocessor is characterized by its 16-bit architecture, efficient CMOS technology, and a versatile instruction set, making it a compelling choice for its era. Its combination of performance, power efficiency, and flexibility positioned it as a formidable player in the personal computing market and laid the groundwork for future advancements in microprocessor technology. With its various applications and features, the NEC 128 remains a noteworthy chapter in the history of computing.