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 Multicasting The focus of this chapter is bidirectional real-time video and audio between two or few desktop systems, otherwise known as desktop videoconferencing or, in Internet terms, strictly a unicast transaction. For most who participate in unicast or simple point-to-point sessions, there comes a time when applications, especially meetings, require more than two participants. To execute on a network limited to unicast sessions, applications must generate a unique copy of each packet and send those packets to each participant’s desktop (by specifying the end-points’ IP address). This is inherently inefficient if there is an alternative. With Internet multicast protocols, an application generates a single copy of each packet and sends it to a group address. End-points (e.g., clients on the client/server network) can selectively choose to listen to the multicast address. Multicasting minimizes network traffic and gives all users on a network greater flexibility. For an application to take advantage of multicasting, the IP stack in the network software on the host must support multicast and broadcast addressing. Multicast is implemented at both the data link layer (layer 2) and the network layer (layer 3). For multicast confined to a single LAN, the data link layer implementation is sufficient. When a multicast application extends into different network media, such as frame relay, FDDI, or Ethernet, network layer implementations are recommended. Therefore, multipoint applications with both LAN and WAN participants must implement in both layers. For all vendors of end-point applications and network components to interoperate in multicast IP networks, several parameters must be defined. The IETF has standards specifying the addressing (i.e., network-layer address mapping onto data link layer multicast addresses), dynamic registration (i.e., a mechanism for clients to inform the network that they wish to be a member of a specific multicast group), and multicast routing (e.g., DVMRP and PIM). Monitoring and Managing a Videoconference Session In general, reflectors, as the servers are sometimes called, provide network bandwidth control, video “pruning,” audio prioritization, and a range of conference control software. Using network management utilities, the reflector/server can adjust transmission rates of specific individual users on-the-fly, if packet loss is running too high because of heavy network traffic. If contention is too heavy for a reliable conference, the transmission remains at the lowest setting and only moves up when the network is less congested. This is an important tool for network managers and ISPs who have to be concerned with balancing the needs of their other non-videoconferencing network users during peak load. Network monitoring utilities allow network managers to control the maximum bandwidth allocated per videoconference and the maximum of simultaneous videoconferences. In this way, sufficient bandwidth is reserved for other users who have conventional network applications. One of the freeware network monitoring tools for videoconferencing is Rtpmon. Rtpmon is a tool for viewing RTCP feedback packets from a session using the real-time transport protocol. It presents loss rate and jitter information from RTCP receiver report (RR) packets in a tabular format. The table can be sorted by various parameters and the recent history of reports from a particular receiver can be viewed in a stripchart. SUMMARY There are advantages and disadvantages in any network selection for any set of applications. The popularity of the Internet protocol for enabling a vast number of applications for users, as well as the advantages inherent in this network protocol, are fostering the development a new tools and technologies for real-time data types. Simultaneously, videoconferencing is coming to the desktop in force, largely because computers in business leverage LANs extensively and their users’ are interested in adding videoconferencing applications. As a result, network managers must become more familiar with the underlying real-time technologies for their Internet protocol networks. This chapter has introduced the basic terminology and concepts of videoconferencing, as well as the components that enable the desktop for real-time video and audio. The network must be prepared for maximum quality of service in videoconferencing without compromising other application users, as is a requirement in any high-bandwidth application. In the future, enterprise network managers can anticipate the very rapid deployment of new technologies as a result of: •  Ratification of protocols by the IETF and ITU, and the subsequent implementation of standard protocols. •  Reduction in cost of all video network system components, including those for end-points, LANs, gateway (internetworking) and WANs. Those who manage enterprise resources, from the CFO to the IS director, will experience a profound shift in the way “best of class” companies do business in the near future. The reduced cycle times and increased creativity and productivity made possible with real-time conferencing locally, nationally, and globally will justify—to different degrees—the investments necessary to deploy technologies such as described throughout this chapter. 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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