Multiplex communications – Communication over free space – Repeater
Reexamination Certificate
2003-05-14
2004-08-03
Marcelo, Melvin (Department: 2663)
Multiplex communications
Communication over free space
Repeater
C370S349000
Reexamination Certificate
active
06771617
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates in general to satellite communication systems, and is particularly directed to a frame relay protocol-based earth station interface for providing full mesh, bidirectional signalling capability between a plurality of (diverse bandwidth) end terminal devices, including multiple audio (voice) circuits, for any of the stations of the network.
BACKGROUND OF THE INVENTION
The increasing availability of reasonably priced satellite communication services, and a variety of narrow bandwidth (voice/data) and wide bandwidth (video) devices to meet the needs of a broad spectrum of communication system users, has led to communication system architectures that can be tailored in terms of connectivity structure and customer utilization. This diversity of equipment types and signal processing capability has led to the desire to have ‘local’ area networks (LANs), customarily limited to a terrestrial-based systems, typically limited to geographical area, be expanded to encompass a much larger scale of communication services, preferably those employing satellite link transmission equipment to connect terminal devices among well dispersed office sites.
To facilitate inter-office communications, it is preferred to have such satellite-based systems configured as full mesh networks, diagrammatically illustrated in
FIG. 1
, where any terminal device
10
in the network (comprised of a non-limitative example of four earth stations
11
,
12
,
13
,
14
in the illustrated example) has a direct satellite link
20
(via one hop through a relay satellite
30
) to any other terminal device
10
in the network. Connectivity between a respective terminal device
10
that is ported to an associated station interface and a respective terminal device ported to another station interface may be effected by providing each earth station with a multiplexing, demultiplexing subsystem, that is operative to controllably uplink messages from any terminal device (e.g. audio (voice), data, video equipment) over an outbound link and to distribute downlink messages to their intended destination terminal devices.
One type of multiplexing scheme that might be used could involve a time division multiplexing (TDM) and demultiplexing arrangement through which a fixed number of bytes for each user port would be allocated within a fixed information frame. The frame size (total number of bytes) may be determined by the number of ports and their data rates, and the number of frames transmitted per second. The number of TDM frames per second determines the aggregate data rate. The aggregate data rate includes the total user port data rate plus framing overhead.
Interfacing respective terminal devices with the TDM subsystem may be effected by means of a dedicated multiport switch associated with the respective multiplexer and demultiplexer units of the earth station, with each multiport switch being configured for an equal number of data communications equipment (DCE) and data terminal equipment (DTE) ports, so as to provide full matrix capability between DCE and DTE ports. The port speed and format (DCE to DTE) must match; however, matrix switches can usually translate between different physical and electrical characteristics.
A problem associated with such a TDM-matrix switch earth station architecture proposal is the fact that its terminal-to-terminal connectivity involves dedicated port connections, which remain fixed unless the system is physically reconfigured. As a result, in such as system, only a very limited selectivity for voice calls is afforded, since only point-to-point connections can be effected between voice multiplexers and not among the voice circuits themselves that connect to the voice multiplexers. In addition, TDM schemes are very sensitive to timing and network synchronization, since no queuing is performed. A master network timing source is required for all network subsystems. Also, because suppliers of multiplexer and matrix switch components are not the same, different monitor and control mechanisms are required for each respective piece of equipment. This requirement is further burdened by the fact that, due to the unique character of a simplex data stream, the required multiplexer/demultiplexer is not an off-the-shelf product. Finally, the cost of such a system is not insubstantial, since each of the multiport switch and the multiplexer and demultiplexer components must be purchased separately.
SUMMARY OF THE INVENTION
In accordance with the present invention, the desire to provide full mesh connectivity for a relatively small number of network stations (e.g. on the order of sixteen or less, as a non-limitative example) is successfully addressed by a frame relay protocol-based earth station interface architecture. The fundamental component of this architecture is a frame relay protocol-based switch, or simply frame relay switch, which comprises a multiplex communication component recently introduced for use in voice/facsimile communication multiplex applications, and which employs a network interface ‘frame relay’ standard to define the multiplexing of multiple virtual ports across single physical communications port. The interface standard ‘frame relay’ is based upon the transmission and reception of individual frames or packets of information serially through a port, with respective frame of digital data containing additional address and control bytes for routing and elementary error detection and flow control.
In the novel earth station environment of the present invention, the frame relay switch is ported, via a first set of terminal ports, to a plurality of ‘local’ terminal devices, which may include respective voice, data and video signalling equipments. A voice signal link transports low bit rate digitized voice signals, such as those having an encoding rate of less than 10 kb/s, to and from a voice signal multiplexer, in order to interface voice traffic with a plurality of voice signalling circuits that are selectively accessible through the multiplexer. The voice signalling link also conveys call supervision signals, including dial tone detection, dialing, circuit busy, call connect and call termination control and status signals. The voice signal multiplexer is operative to append and decode terminal device selectivity information to the address field portion of a frame processed by the frame relay switch.
Also ported to the frame relay switch are one or more data links that may be coupled to two-way synchronous data terminal devices, providing data rate signalling on the order of 256 Kb/s, for example. An additional port of the frame relay switch may be coupled to a link for wide bandwidth signals, such as a video teleconferencing terminal. The teleconferencing video and its associated voice signals may be digitized and compressed into a single data stream at aggregate data rates on the order of from 112 to 384 kb/s, for example. Because of the wider bandwidth required for video teleconferencing capability, the video communication port of the frame relay switch is intended to be used on only an occasional basis, and may require one or more other signalling channels to be turned off during the teleconferencing period.
Through address and control fields employed by frame relay connectivity control software, the frame relay switch can be dynamically configured to provide multilayer addressing and device selectivity (filtering), thereby enabling point-to-point connectivity of multiple terminal devices, such as a plurality of voice circuits served by the voice circuit multiplexer unit to which a voice signal port of the frame relay switch is coupled. Dial codes on the trunk or station side of the voice signal link are translated into frame relay addresses (data link connection identifiers) that are added to each frame of data for routing through the network. With this additional layer of routing information, voice connectivity is now available between any two voice terminal devices (e.g. trunks) in the network.
On its satellite link side, the fra
Feilding Dennis E.
Gross Todd W.
Banner & Witcoff , Ltd.
Gilat Satellite Networks Ltd.
Marcelo Melvin
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