Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1998-07-06
2002-04-16
Vu, Huy D. (Department: 2663)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
Reexamination Certificate
active
06373850
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to the field of data communications, or teleprocessing and specifically relates to a videoconferencing system using switches of the stand alone routing type.
DESCRIPTION OF RELATED ART
There are known videoconferencing systems which link a limited number of specialized rooms in which conference participants gather. Each room is equipped with a television system constituted by at least one camera, one or more screens and sending and receiving means for allowing the participants in each room to communicate with the participants in other rooms while watching and listening to what takes place in the its other rooms. The communications take place by means of specialized high-speed links for conveying images synchronized with sound. These systems require a costly investment in specialized rooms. Organizing a videoconference requires physically gathering the participants into specialized rooms.
Promising developments in microprocessing, on the other hand, make it possible for two speakers to communicate through the exchange of voice-frequency sounds, synchronized with their corresponding images. Each speaker in this case uses a microcomputer equipped with a camera and means for perceiving and producing sound. By establishing a connection between the two microcomputers, each speaker can display on his screen an animated image of his partner and carry on a discussion with him via the means for perceiving and producing sound. Each microcomputer constitutes data processing terminal equipment, hereinafter simply called DTE (for data terminal equipment). The connection can be established through a modem with which each DTE is equipped. If the two speakers are not too far apart, it is possible to consider establishing the connection through a local area network, for example using the method known as Carrier Sense Multiple Access with Collision Detection, or CSMA/CD.
Without enlarging on the CSMA/CD method defined by the well-known IEEE standard 802.3, let it be noted that a method of this type makes it possible to establish connections between more than two DTEs. A DTE must detect the absence of a signal, or silence, on the hardware line that links it to the other DTEs in order to send a data frame to the other DTEs. The physical properties of the hardware line between DTEs result in a time lag between the sending of a frame by a DTE and the reception of this frame by another DTE. This time lag increases with the distance that separates the DTEs. In order to eradicate the collisions resulting from this delay, a link protocol makes it possible to interrupt the sending of a frame after the detection of a collision, then to resend this frame after a random delay. Moreover, the length of a frame is proportional to the quantity of data transmitted, with a minimal length for detecting a collision. The result of the characteristics of the CSMA/CD method is that average is transmission delays remain short on physical lines that are short in length and have a low utilization rate. For example, a transmission that is isolated in time is executed without any preliminary wait. If a plurality of DTEs are constantly sending frames, the effective order of transmission of the frames through the hardware line does not necessarily comply with the order desired by the DTEs. This can cause problems in conveying a large quantity of data through the physical line to a plurality of DTEs, which requires perfect synchronization of their reception, a problem exacerbated by a large distance between DTEs.
The need to convey a large quantity of data that must be received in perfect synchronization exists in various technical fields in which there is high interactivity between a sizeable number of DTEs.
In the field of videoconferencing, in order for several participants to be able to attend the same conference without having to change locations, each participant must be able to send at least one animated image synchronized with sound to the other participants and receive at least one animated image synchronized with sound from the other participants, either in real time or delayed in order to produce, for example, a synthesis of the conference. The image received is for example the image of another participant, a composite image combining the images of other participants, an image from an image bank or any combination of the animated images synchronized with sound cited above. These images are sent and received by means of various DTEs which include, for example, a video server and one or more routers which communicate images with one or more participants connected to the same local area network. Thus, the sending and receiving of animated images synchronized with sound involves a high level of interactivity between a sizeable number of DTEs.
In the field of high-speed industrial processes, a plurality of remote machines may each need to execute, in real time, part of a process having a high level of hardware interaction with other parts of the same process, for example, a process involving the control of material or energy flows. The occurrence of a failure in the industrial process is capable of causing a series of failures, for which it is important to detect an absolute order of occurrence of the failures. The servomechanisms between the parts of a process may require exchanges of large quantities of perfectly synchronized parameters. Thus, each machine constitutes a DTE which communicates digital data with other DTEs.
The CSMA/CD method makes it possible to connect a plurality of DTEs, but it is not satisfactory when the DTEs are remote from one another, since retransmissions over long distances after the detection of collisions result in asynchronous receptions of the frames transmitted.
To avoid the problems cited above, it is preferable to establish point-to-point type links between DTEs by means of one or more group switching centers, or stand alone routing switches in such a way that one and only one two-way physical connection exists between a given DTE and a group switching center. This avoids the problem of collisions between the DTE in question and this switch. This switch is provided in order to establish links with the DTEs that are connected to it and possibly with one or more other similar switches to which other DTEs are connected. By establishing links between switches, it is possible to establish links between DTEs connected to different switches.
The group switching center or stand alone routing switch must be designed to establish links from a sending DTE to one or more receiving DTEs and from a plurality of sending DTEs to a receiving DTE or a plurality of receiving DTEs. For example, in a videoconference, links from a sending DTE to one or more receiving DTEs are necessary in order to send a global image of the videoconference from an image server, in this case the sending DTE, to each receiving DTE used by a participant in the videoconference. Links from a plurality of sending DTEs to a receiving DTE are necessary in order to send an image of each participant using a sending DTE to the image server, in this case the receiving DTE, in order to compose the global image of the video conference. Links from a plurality of sending DTEs to a receiving DTE can be used to send an image of each participant using a sending DTE to the image server and an image bank, in this case the receiving DTEs.
Likewise, the group switching center or stand alone routing switch must be designed to establish additional links at any time with new DTEs that are connected. This is the case, for example, when a new participant arrives while the conference is in progress.
SUMMARY OF THE INVENTION
In order to meet the needs indicated above and to respond to the problems cited, the invention proposes a group switching center comprising a plurality of sending ports and a plurality of receiving ports, each sending port is adapted to be connected to a receiving data terminal equipment unit or to a receiving port of another group switching center, or stand alone routing switch each rec
Kaszynski Anne
Lecourtier Georges
Bull S.A.
Kondracki Edward J.
Miles & Stockbridge P.C.
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