Multicasting method and system using an ATM switch

A computer readable storage medium carrying one or more sequences of instructions for causing a switch to minimize resources required to support a point-to-multi-point application from a server system to a plurality of subscribers, wherein said resources comprise a plurality of entries in a forwarding table, wherein execution of said one or more sequences of instructions by one or more processors contained in said switch causes said one or more processors to perform the actions of:

• providing a point-to-multi-point virtual connection containing a plurality of branches, wherein each of said branches is provisioned as a permanent virtual circuit (PVC) and allows data received from said server system to be forwarded to at least one subscriber contained in said plurality of subscribers;
• determining whether each branch contained in said plurality of branches is active, wherein a branch is determined to be not active if a segment loopback cell for the branch is not received for a pre-specified amount of time, and to be active otherwise, wherein said segment loopback cell is designed to confirm whether the corresponding branch is operational end-to-end, wherein a set of active branches comprise the specific ones of said plurality of branches determined to be active by said determining;
• storing a set of VPI/VCIs in said forwarding table, with each of said set of VPI/VCIs identifying a corresponding one of said set of active branches and being stored in a corresponding one of said plurality of entries;
• deleting a VPI/VCI in an entry of said forwarding table if a branch corresponding to the VPI/VCI is determined to be not active, thereby allocating more resources to each of said branches if the corresponding branch is active than if the corresponding branch is not active, wherein each of said branches need not be established by a signaling process if the corresponding branch changes from said inactive state to said active state, and wherein each of the cells received from said server on said point-to-multi-point virtual connection is transmitted on all of said branches which are active,
• receiving a plurality of cells from said server system for transmission on said point-to-multi-point virtual connection;
• and
• forwarding said plurality of cells on all the branches corresponding to the VPI/VCIs of said point-to-multi-point connection in said forwarding table.

A switch for minimizing resources used in supporting a point-to-multi-point application from a server system to a plurality of subscribers, wherein said resources comprise a plurality of entries in a forwarding table, said switch comprising:

• means for providing in said switch a point-to-multi-point virtual connection containing a plurality of branches, wherein each of said branches is provisioned as a permanent virtual circuit (PVC) and allows data received from said server system to be forwarded to at least one subscriber contained in said plurality of subscribers;
• means for determining whether each branch contained in said plurality of branches is active, wherein a branch is determined to be not active if a segment loopback cell for the branch is not received for a pre-specified amount of time, and to be active otherwise, wherein said segment loopback cell is designed to confirm whether the corresponding branch is operational end-to-end, wherein a set of active branches comprise the specific ones of said plurality of branches determined to be active by said determining;
• and
• a memory to storing a set of VPI/VCIs in said forwarding table, with each of said set of VPI/VCIs identifying a corresponding one of said set of active branches and being stored in a corresponding one of said plurality of entries;
• means for deleting a VPI/VCI in an entry of said forwarding table if a branch corresponding to the VPI/VCI is determined to be not active, thereby allocating more resources to each of said branches if the corresponding branch is active than if the corresponding branch is not active,
• wherein each of said branches need not be established by a signaling process if the corresponding branch changes from said inactive state to said active state,
• wherein each of the cells received from said server on said point-to-multi-point virtual connection is transmitted on all of said branches which are active,
• means for receiving a plurality of cells from said server system for transmission on said point-to-multi-point virtual connection;
• and
• means for forwarding said plurality of cells on all the branches corresponding to the VPI/VCIs of said point-to-multi-point connection in said forwarding table.

A switch minimizing resources used for supporting a point-to-multi-point application from a server system to a plurality of subscribers, wherein said resources comprise a plurality of entries in a forwarding table, said switch comprising:

• an inbound interface receiving a cell from said server system;
• a first memory storing forwarding information representing a point-to-multi-point virtual connection containing a plurality of branches, wherein each of said plurality of branches is provisioned as a permanent virtual circuit (PVC) and connected to at least one subscriber system permitted to access said point-to-multi-point application;
• a resource allocation block determining whether each branch contained in said plurality of branches is active, and allocating more resources to each of said branches if the corresponding branch is active than if the corresponding branch is not active,
• wherein a branch is determined to be not active if a segment loopback cell for the branch is not received for a pre-specified amount of time, and to be active otherwise, wherein said segment loopback cell is designed to confirm whether the corresponding branch is operational end-to-end, wherein a set of active branches comprise the specific ones of said plurality of branches determined to be active by said determining,
• wherein said resource allocation block stores a set of VPI/VCIs in said forwarding table, with each of said set of VPI/VCIs identifying a corresponding one of said set of active branches and being stored in a corresponding one of said plurality of entries, and deletes a VPI/VCI in an entry of said forwarding table if a branch corresponding to the VPI/VCI is determined to be not active;
• and
• a forwarding engine forwarding said cell according to the resources allocated by said resource allocation block, wherein said forwarding block forwards said plurality of cells on all the branches corresponding to the VPI/VCIs of said point-to-multi-point connection in said forwarding table,
• wherein each of said plurality of branches need not be established by a signaling process if the corresponding branch changes from said inactive state to said active state, and
• wherein each of the cells received from said server on said point-to-multi-point virtual connection is transmitted on all of said branches which are active.

A method of supporting a point to multi-point application from a server system to a plurality of subscriber systems according to asynchronous transfer mode (ATM) protocol, said method being performed in an ATM switch, said method comprising:

• providing each of a plurality of branches to a corresponding one of said subscriber systems;
• storing in a state table information representing a VPI/VCI information corresponding to each of said plurality of branches;
• receiving a plurality of cells related to said point to multi-point application from said server system;
• forwarding all of said plurality of cells on all of a set of branches, with each of said set of branches having a corresponding one of a set of entries in a forwarding table, wherein said set of branches are comprised in said plurality of branches;
• determining whether each of said plurality of branches is active or not active, wherein a first set of branches are determined to be not active and a second set of branches has changed status from not active to active, said first set of branches and said second set of branches being contained in said plurality of branches;
• deleting the entry corresponding to each of said first set of branches from said forwarding table if a branch is determined to be not active;
• adding an entry corresponding to each of said second set of branches to said forwarding table using the VPI/VCI information in said state table if a branch is determined to be active,
• wherein more resources are allocated to active branches than to branches that are not active;
• wherein said forwarding forwards cells from said server system to all active branches and entries in said forwarding table are used only for active branches.

A computer readable storage medium carrying one or more sequences of instructions for causing a switch to support a point to multi-point application from a server system to a plurality of subscriber systems according to asynchronous transfer mode (ATM) protocol, wherein execution of said one or more sequences of instructions by one or more processors contained in said switch causes said one or more processors to perform the actions of:

• providing each of a plurality of branches to a corresponding one of said subscriber systems;
• storing in a state table information representing a VPI/VCI information corresponding to each of said plurality of branches;
• receiving a plurality of cells related to said point to multi-point application from said server system;
• forwarding all of said plurality of cells on all of a set of branches, with each of said set of branches having a corresponding one of a set of entries in a forwarding table, wherein said set of branches are comprised in said plurality of branches;
• determining whether each of said plurality of branches is active or not active, wherein a first set of branches are determined to be not active and a second set of branches has changed status from not active to active, said first set of branches and said second set of branches being contained in said plurality of branches;
• deleting the entry corresponding to each of said first set of branches from said forwarding table, wherein each of said first set of branches is determined to be not active;
• adding an entry corresponding to each of said second set of branches to said forwarding table using the VPI/VCI information in said state table, wherein each of said second set of branches is determined to be active,
• wherein more resources are allocated to active branches than to branches that are not active;
• wherein said forwarding forwards cells from said server system to all active branches and entries in said forwarding table are used only for active branches.

A switch supporting a point to multi-point application from a server system to a plurality of subscriber systems according to asynchronous transfer mode (ATM) protocol, said switch comprising:

• means for providing each of a plurality of branches to a corresponding one of said subscriber systems;
• a memory to store a state table information representing a VPI/VCI information corresponding to each of said plurality of branches;
• means for receiving a plurality of cells related to said point to multi-point application from said server system;
• means for forwarding all of said plurality of cells on all of a set of branches, with each of said set of branches having a corresponding one of a set of entries in a forwarding table, wherein said set of branches are comprised in said plurality of branches;
• means for determining whether each of said plurality of branches is active or not active, wherein a first set of branches are determined to be not active and a second set of branches has changed status from not active to active, said first set of branches and said second set of branches being contained in said plurality of branches;
• means for deleting the entry corresponding to each of said first set of branches from said forwarding table, wherein each of said first set of branches is determined to be not active;
• means for adding an entry corresponding to each of said second set of branches to said forwarding table using the VPI/VCI information in said state table, wherein each of said second set of branches is determined to be active,
• wherein more resources are allocated to active branches than to branches that are not active;
• wherein said forwarding forwards cells from said server system to all active branches and entries in said forwarding table are used only for active branches.

A switch supporting a point to multi-point application from a server system to a plurality of subscriber systems according to asynchronous transfer mode (ATM) protocol, said switch comprising:

• a memory to store a state table containing store information representing a VPI/VCI information corresponding to each of a plurality of branches connecting said switch to a corresponding one of said subscriber systems;
• a forwarding table to contain a set of entries for corresponding set of branches, wherein said set of branches are comprised in said plurality of branches;
• a resource allocation block determining to determine whether each of said plurality of branches is active or not active, wherein a first set of branches are determined to be not active and a second set of branches has changed status from not active to active, said first set of branches and said second set of branches being contained in said plurality of branches,
• said resource allocation block to delete the entry corresponding to each of said first set of branches from said forwarding table, wherein each of said first set of branches is determined to be not active,
• said resource allocation block to add an entry corresponding to each of said second set of branches to said forwarding table using the VPI/VCI information in said state table, wherein each of said second set of branches is determined to be active,
• wherein more resources are allocated to active branches than to branches that are not active;
• an input interface to receive a plurality of cells related to said point to multi-point application from said server system;
• and
• a forwarding block forwarding to forward all of said plurality of cells on each of said set of branches,
• wherein said forwarding block forwards cells from said server system to all active branches and entries in said forwarding table are used only for active branches.