Handbook of Local Area Networks, 1998 Edition:Applications of LAN Technology Click Here! Search the site:   ITLibrary ITKnowledge EXPERT SEARCH Programming Languages Databases Security Web Services Network Services Middleware Components Operating Systems User Interfaces Groupware & Collaboration Content Management Productivity Applications Hardware Fun & Games EarthWeb sites Crossnodes Datamation Developer.com DICE EarthWeb.com EarthWeb Direct ERP Hub Gamelan GoCertify.com HTMLGoodies Intranet Journal IT Knowledge IT Library JavaGoodies JARS JavaScripts.com open source IT RoadCoders Y2K Info Previous Table of Contents Next Quantitative QOS Parameters End-to-end quality of service (QOS) in videoconferencing and visual collaboration is defined as the level of satisfaction a user has with a given session. It is a function of many independent and interdependent factors (e.g., window size, processor speed, network bandwidth), which together influence frame rate, bit depth, image clarity and resolution, audio clarity, lip synchronization, and latency. In contrast to conventional data applications in which data transmission is bursty, digital video and audio applications require continuous data transmission. In IP environments, precise bit rates during the transmission vary. In the following list, the factors influencing bit rates (bandwidth) during videoconferencing and collaborative computing are presented as a function of the media (i.e., video, audio, and data): •  Video factors include: —  Bit depth (number of colors). —  Resolution (size of the image being captured, compressed, transmitted, and decompressed). Resolution is contrasted with window size, which is the size of the image that is displayed for viewing. If the window size is different from resolution, then interpolation is used to generate a new image that fits the window. —  Q factor (sharpness of edges in any given frame). —  Smoothing (this is a result of—and dependent on—motion estimation algorithms and content changes from one frame to the next). —  Frame rate (frames per second). For example, NTSC video, the US standard, is 30 fps; PAL, the European standard, is 25 fps. •  Audio factors include: —  Sampling rate (the number of audio samples captured, compressed, and transmitted, expressed KHz cycles per second). For example, telephony is 6.3 KHz, FM radio is 36 KHz, music CDS 44.1 KHz. (See Exhibit 5-2-1.) —  Bit rate (the number of bits the system has in order to accurately represent different tones; for example, 8-bit or 16-bit). —  Mono and stereo sound. •  Data factors include: —  Quantity of data. —  Frequency of transmissions. —  Latency of transmission (how long it takes to send at a given bit rate). Exhibit 5-2-1.  Audio Sampling The central processor, any additional compression/decompression (codec) circuits, network infrastructure, and the user’s network connection directly affect these quantitative factors. Qualitative QOS Experience Depending on the quantitative parameters, the users experience with multimedia (which is a combination of audio, video, and data) may be qualitatively different. Exhibit 5-2-2 is intended to help readers understand the interdependence of various quality of service parameters in time-dependent streaming media. Exhibit 5-2-2.  Interdependence of QOS Parameters in Time-Dependent Streaming Media The users’ experience with bidirectional, live video and visual collaboration over any network can be expressed quantitatively and qualitatively; in general, though, the objective is to reproduce a live meeting or conversation. For the interaction to be as close to natural as possible, it is especially important that both (or all) users in a videoconference experience a uniformly low latency (minimum delay). Any variation in the frame rate between points is perceived as jitter. Poor synchronization between lips and audio is also distracting. Thus, the most important factors in the user’s qualitative experience of a videoconferencing system are: •  Synchronization of audio, video, and data. •  End-to-end latency. •  Window size. •  Jitter. •  Richness and clarity of audio. •  Image clarity (bit depth, sharpness, smoothing, and resolution). All these quality of service concepts are critical to the reader’s overall understanding of the pros and cons of selecting IP networks for videoconferencing. PROS/CONS OF VIDEOCONFERENCING OVER IP NETWORKS Founders of the Internet were academics driven by four guiding principles: •  Reliability (guaranteed delivery of packets), not efficiency. •  End systems’ interoperability, and information or packet loss recovery. •  Variable quality of service, not guaranteed bandwidth, so that any network bandwidth can be accommodated by a single protocol. •  No support for charging mechanisms, since commercial traffic was not envisioned. Internet protocols have withstood the test of multiple applications at the user interface, new operating systems in end-points, and ever-changing transport media in the physical layers (e.g., SONET, ATM). For videoconferencing and visual collaboration, there are fundamental principles that determine bandwidth use in any session. Previous Table of Contents Next Use of this site is subject certain Terms & Conditions. Copyright (c) 1996-1999 EarthWeb, Inc.. All rights reserved. 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