Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1997-09-11
2001-07-10
Chin, Wellington (Department: 2664)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S252000, C370S432000
Reexamination Certificate
active
06259701
ABSTRACT:
TECHNICAL FIELD
This invention relates to data communications, and more particularly, to providing a Unicast endpoint client on a Unicast network with the ability to access a Multicast session on an Multicast network.
BACKGROUND OF THE INVENTION
In conventional packet, frame or cell based systems there are typically two modes of communication: point-to-point (also known as Unicast) and point-to-multipoint (also known as Multicast). Multicast addresses typically differ from Unicast addresses in that they refer to an intermediate abstraction known as a group. All senders address their transmitted information to this group and all receivers are “tuned” to “listen” to that address to receive the information transmitted to that group by the senders. The senders of information are thus effectively de-coupled from the set of receivers. Senders do not need to know who the receivers are—they simply transmit packets addressed to the group. Similarly, receivers do not need to know who the senders are—they simply send a request to the network (routers) to join a specific group of interest.
Multimedia distribution and conferencing/collaboration systems are advantageously and efficiently supported by Multicast communication methods. As will be used herein, a specific Multicast communication is referred to as a session. In the prior art, it is not possible for Unicast endpoints to access Multicast sessions, due to the differences in addressing modes and receiving modes. This disadvantageously limits the ability of a user at a Unicast endpoint client to participate in sessions in which they have interest and in which they could be an active participant.
SUMMARY OF THE INVENTION
In accordance with the present invention, Unicast endpoint clients are enabled to access Multicast sessions. Furthermore, in accordance with the present inventions, Unicast endpoint clients are enabled to request network-based recording systems to perform recordings of the Multicast session on behalf of clients. Even furthermore, in addition to LAN attached endpoints, analog dial-up (e.g., 28.8 kbps) as well as ISDN Unicast endpoints are enabled to access appropriately bandwidth-reduced versions of nominally high bandwidth sessions.
Inter-connectivity between a Unicast client connected to a Unicast network and one or more Multicast clients connected to a Multicast network is effected through a Multicast-Unicast Server (MUS), in accordance with the present invention. Such a server obtains information about sessions on the Multicast network and makes such information available to the Unicast client on the Unicast network upon request by the client. Upon being presented with a list describing the subject matter of each session, the user at the Unicast client selects the session to which he or she wants to join, which causes the Multicast-Unicast server to join the appropriate session on behalf of the requesting client for each media type for which the joining client wants to be a participant. The server then sets a bi-directional Unicast User Datagram Protocol (UDP) stream between itself and the client. All packets then received by the server from the Unicast client are address-translated to the appropriate Multicast session address. In addition, all packets received by the server on the Multicast session address are address-translated and sent to the Unicast client. The Unicast client is then able to participate in the Multicast session as both a sender and a receiver of packets to and from other Unicast and Multicast clients which are active during the session. Further, such a Unicast client, if authenticated to do so, is capable of creating a new session, and of recording a session in the network for later retrieval and playback. Furthermore, transcoding and rate adapting gateways are deployed within the Multicast network that map existing sessions into low bandwidth versions. If the Unicast client is a dial-up user connected to the Unicast network over analog or ISDN facilities, these rate-controlled sessions can then be accessed by the dial-up users.
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Shur David Hilton
Zelezniak Aleksandr
AT&T Corp.
Chin Wellington
Nguyen Steven
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