Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1998-03-31
2001-01-30
Hsu, Alpus H. (Department: 2662)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S392000, C370S432000, C370S401000, C709S203000, C709S238000
Reexamination Certificate
active
06181697
ABSTRACT:
TECHNICAL FIELD
This invention relates to data communications, and more particularly, to providing a endpoint client on a Unicast network with the ability to access a Multicast session on an Multicast network and re-Multicast that session to other endpoint clients.
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 or group address. 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 an endpoint client connected to a Unicast network to participate in sessions in which they have interest and in which they could be an active participant.
In co-pending patent application, Ser. No. 08/927,426, filed on Sep. 11, 1997, and assigned to the present assignee hereof, which application is incorporated herein by reference, a method and a system for a endpoint client on a Unicast network to access a Multicast Intenet Protocol (IP) session is described. As described therein, inter-connectivity between a endpoint client connected to a Unicast network and one or more clients connected to a Multicast network is effected through a Multicast-Unicast Server (MUS). Such a server obtains information about sessions on the Multicast network and makes such information available to the 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 on the Unicast network 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 client on the Unicast network 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 client on the Unicast network. The client on the Unicast network is then able to participate in the Multicast session as both a sender and a receiver of packets to and from other clients which are active during the session.
SUMMARY OF THE INVENTION
In accordance with the present invention, a endpoint client on a Unicast network, once enabled to access a Multicast session through a MUS, can then automatically redistribute that session by locally re-Multicasting that session to other endpoint clients on the same sub-network on the Unicast network to which it is connected or to other endpoint clients on any local Multicast-capable sub-networks to which it is directly connected. Thus, by means of the technique of re-Multicasting, these other endpoints can receive the session without independently retrieving the same session from the MUS, which could put an undue burden on the transmission facilities if a large plurality of endpoints simultaneously attempted to receive separate copies of the same data stream associated with a particular session from a MUS. In order to act as a re-Multicaster, the endpoint client on the Unicast network receiving the Unicast-addressed data packets associated with session from the MUS, re-translates these Unicast-addressed data packets to Multicast-addressed data packets by translating the Unicast address in the destination field of each packet's header into a Multicast address and overwriting the Unicast address in each header with the Multicast address. This overwriting Multicast address in the destination field of each header can be the Multicast address used by the original Multicast session, as delivered to the MUS, or it can be a new Multicast address assigned to the session on the local network.
A endpoint on the Unicast network receiving a Unicast session from the MUS can elect to be a re-Multicaster of the session as long as that session is not being re-Multicast by another endpoint on any sub-network on which the electing endpoint is connected. Further, if a Multicast router starts to forward packets from the session onto that sub-network when a re-Multicaster is already doing so, the re-Multicasting operation is halted.
REFERENCES:
patent: 5581552 (1996-12-01), Civanlar et al.
patent: 5905872 (1999-05-01), De Simone et al.
patent: 6011782 (2000-01-01), De Simone et al.
George C. Sackett & Christopher Y. Metz, “ATM and Multiprotocol Networking” CH13 ‘LAN Emulation & MPGA’ pp. 267-288, 1996.
Nurenberg Steven Howard
Shur David Hilton
Zelezniak Aleksandr
AT&T Corp.
Hsu Alpus H.
Qureshi Afsar M.
LandOfFree
Method for a unicast endpoint client to access a multicast... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for a unicast endpoint client to access a multicast..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for a unicast endpoint client to access a multicast... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2467113