Multiplex communications – Communication over free space – Repeater
Reexamination Certificate
1999-01-15
2003-06-24
Nguyen, Duc (Department: 2682)
Multiplex communications
Communication over free space
Repeater
C370S326000, C370S487000, C455S003020, C455S422100, C455S426100
Reexamination Certificate
active
06584082
ABSTRACT:
COPYRIGHT NOTIFICATION
Portions of this patent application contain materials that are subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document, or the patent disclosure as it appears in the Patent and Trademark Office.
FIELD OF THE INVENTION
This invention generally relates to improvements in computer systems, and, more specifically, to utilizing satellite broadcast technology as a bridge between telephony operations and the Internet.
BACKGROUND OF THE INVENTION
Traditionally, data has been delivered to network-connected desktop personal computers either by broadcasting or unicasting, while the need for multicasting data has been unsatisfied. Broadcasting is a form of addressing wherein the destination address specifies all destinations; all destinations indiscriminately receive the data whether or not the data is needed by the destination computer. Where data is not needed at a particular network-connected personal computer, the transmission of the data is an inefficient use of resources. This can be particularly disabling to a network that does not have sufficient bandwidth capacity for all of the data traffic. Broadcasting is less efficient in direct relation to the proportion of users in the community of the broadcast that do not need the broadcast data.
In contrast, unicasting is a form of addressing where the destination address specifies a single destination. Unicasting eliminates the unnecessary transmission of data to destinations that have no need for the data, but is still inefficient because the data will be replicated on the network for each individual destination. For example, when data is transmitted to 20 personal computers connected to a server, 20 transmissions of the data will be made each with a different individual destination address.
Where data needs to be transmitted to a limited set of all network-connected personal computers, transmission-using broadcasting or unicasting falls short of efficient resource use. Multicasting offers more efficient resource use. Multicasting is a form of addressing wherein a source sends data to a server and the server sends one copy of the data to each of the destination computers. This form of addressing is particularly beneficial where the link between the source and the server has limited capacity or high cost because only one copy of the data that is intended for multiple recipients is transmitted to the server. Multicasting makes the most efficient use of an expensive link or a link that has insufficient capacity for transmission to multiple destinations by reducing the number of transmissions across the critical link to one, rather than requiring that multiple transmissions be made for each destination address.
One arena where multicasting is implemented is the Internet. Multimedia applications involve text, graphics, voice, video and hypertext operations. Multimedia applications typically require large amounts of data in comparison to traditional computer applications. The Internet has increasingly become the communication network of choice for the consumer marketplace. Multimedia applications exist on the Internet, but the throughput of the Internet limits the usefulness of multimedia applications because multimedia applications are highly interactive and require higher throughput than the Internet can provide. The limitations on bandwidth make the Internet more suitable and efficient for low bandwidth applications such as E-mail and smaller multimedia applications.
The Multicast backbone (MBONE) is a virtual network on top of the Internet which supports routing of Internet Protocol (IP) multicast packets, intended for multimedia transmission. MBONE enables public access to desktop video communications. However, the quality is poor, with only 3-5 frames per second instead of the 30 frames per second of commercial television. Therefore, transmission of multimedia data via the Internet is too slow, even using multicasting.
Two independent technologies have emerged that provide greater speed and throughput (Internet Protocol (IP) Multicast and Digital Video Broadcast) that together have the potential to provide for transmission of multimedia information over a network. IP Multicast is an important advance in IP networking that has been under development since the early 1990's but is only now receiving broad (and growing) practical industry backing through the commercial availability of network infrastructure elements.
An extension of standard IP, IP Multicast allows applications to send one copy of information to a group address, and have the information transmitted to each recipient of the group requiring receipt of the information. IP Multicast is more efficient than point-to-point unicast because the source need send only once, and more efficient than broadcast since only interested nodes are impacted by transmission of the information. IP Multicast thus scales well as the number of participant and collaborations expand, and it integrates well with other new IP protocols and services, such as Quality of Service requests to support real-time multimedia.
However, despite the advantages of IP Multicast, its terrestrial implementation may be slow because all routers between the sender and the receivers must be IP Multicast enabled. Even then, network bandwidth may be limited for some considerable time. The demand of consumers for digital satellite TV systems has driven the development of Direct Broadcast Satellite (DBS) systems that can broadcast directly to small, low cost receiver equipment. The standard likely to become dominant on a global basis is Digital Video Broadcast (DVB) which was developed by the European Broadcasting Union.
DVB specifies standards for the digital broadcast of video, sound and data across satellite (DVB-S), cable (DVB-C) and SMATV (DVB-CS) data link layers. DVB specifies common conformance standards at several levels including channel coding (Reed-Soloman forward error correction), transport layer (MPEG-2 Systems Transport bitstream) and elementary stream layers (MPEG-2 for video encoding and MPEG-1 for audio encoding). An elemental stream is a single, digitally coded component of a multimedia channel (e.g. a single coded video or audio stream). MPEG-2 elemental stream encoding thus provides good VHS quality video at 1.5-2 Megabits and studio production quality video at approximately 6-8 Megabits.
MPEG-2 transport enables video, audio and data to be multiplexed onto the physical channel of choice, with DVB specifying the remaining system elements for each transport media being used. For example, with satellite communications, DVB specifies the physical channel (single 38 Megabits satellite transponder), signal
oise ratio and channel coding (e.g. 2 bit/symbol QPSK modulation).
Satellite communications offer sufficient bandwidth for remote multimedia applications. However, satellite connections for the typical computer user are practically non-existent and expensive and do not allow for use of economical open client/server technologies. A client/server architecture is an economical, proven and common form of distributed system wherein software is split between server tasks and client tasks. A client sends requests to a server, according to some protocol, asking for information or action, and the server responds. There may be either one centralized server or several distributed ones. This model allows clients and servers to be placed independently on nodes in a network, possibly on different hardware and operating systems appropriate to their function, e.g. fast server with an inexpensive client.
There is a rapidly increasing market demand for network based application services that enable the efficient operation of computer applications which are one-to-many in their information flow and which require high network bandwidth. Major advances in digital transmission, encoding and internetworking technology and the advent of direct broadcast satellite have matched this. This market need, combined with the emerging
Garrity Martin M.
Heneghan John C.
Howser James L.
Willis Edward D.
Nguyen Duc
WorldCom, Inc.
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