Using multicast in the global communications infrastructure for group communication
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Using multicast in the global communications infrastructure for group communication


International Monitoring System (IMS) stations and the International Data Centre (IDC) of the Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization generate data and products that must be transmitted to one or more receivers. The application protocols used to transmit the IMS data and IDC products will be CD-x and IMS-x and the World Wide Web (WWW). These protocols use existing Internet applications and Internet protocols to send their data. The primary Internet applications in use are electronic mail (e-mail) and the file transfer protocol (ftp). The primary Internet communication protocol in use is the Transmission Control Protocol (TCP), which provides reliable delivery to the receiver. These Internet applications and protocol provide unicast (point-to-point) communication. A message sent using unicast has a single recipient; any message intended for more than one recipient must be sent to each recipient individually. In the current design, the IDC and the National Data Centres (NDC's) provide data forwarding to the appropriate receivers. The overhead associated with using unicast to transmit messages to multiple receivers either directly or through a forwarder increases linearly with the number of receivers. In addition, using a forwarding site introduces possible delays and possible points of failure in the path to the receivers. Reliable multicast provides communication services similar to TCP but for a group of receivers. The reliable multicast protocol provides group membership services and message delivery ordering. If an IMS station were to send its data using reliable multicast instead of unicast, only sites that are members of the multicast group would receive the data at approximately the same time. This might provide an efficient means of disseminating station data or IDC data products to all receivers and eliminate or greatly reduce the need for data forwarding. Several commercial and research reliable multicast protocols exist for the Internet. Each of these protocols is designed to serve a specific community of users and applications. The author has undertaken a study to determine if reliable multicasting is appropriate for use in the Global Communication Infrastructure (GCI).

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