Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1997-05-06
2001-10-30
Rao, Laura S. (Department: 2661)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S412000, C370S432000
Reexamination Certificate
active
06310879
ABSTRACT:
FIELD OF THE INVENTION
The present invention is related to the multicast of ATM cells. More specifically, the present invention relates to the multicast of ATMs through the use of multiple ports or a single port to multiple addresses where connections can be dynamically added or dropped.
BACKGROUND OF THE INVENTION
ATM (asynchronous transfer mode) is used for communication purposes in integrated digital networks. Through these networks, ATM cells travel to desired destinations. Due to the complexity and demands on a network, there exists concerns involving traffic control in regard to cells in the network. Moreover, in multicast (i.e. the transmission of a single ATM cell to multiple destinations), considerations must be given to memory utilization in regard to the storage of a cell going to a multitude of locations. Ideally, as little memory as possible should be utilized to maintain the cell for all the different locations to which it will be sent. The present invention provides an efficient approach to providing a cell to a multiplicity of connections for multicast.
The multicast function can be limited to the act of causing an individual ATM cell to be transmitted by multiple output ports of an ATM switching system, or it may include causing an individual output port to transmit an individual ATM cell multiple times. In the former case, it is possible to restrict the use of connection addresses so that the instances of a multicast ATM cell transmitted at different output ports will all have the same address information (known as the VPI and VCI). In the latter case, it is necessary for each copy of a multicast ATM cell to have a different VPI and/or VCI to indicate that each copy of the cell should be sent to a different final destination. The prior art for performing multicast in an ATM switch using multiple VPI/VCIs is to create and store multiple copies of the cell at some point within the ATM switching system.
Furthermore, a multicast VC (virtual connection) broadcasts the same packet to M destinations where M>1. It might travel through a number of intermediate nodes/switches before reaching the destinations. At each node, the intermediate VC might broadcast to more destinations generating a dynamic multicast graph as shown below. Each node might add or drop destinations/ports at any time. For example, a party can drop or add to a video conference call at any node any time. For instance, the port addition/drop mechanism implemented in the Series-C/Altantis netmods has severe flaws such as: Cells cannot be freed when a connection has been dropped (Series-C); The last cell of a multicast connection is reserved and is never freed (Series-C and Atlantis); not robust, i.e, misbehaves when adding a port to an existing port; and costly (per-port drop 16-bit pointer).
A mechanism which supports dynamic automatic destination (port) addition and drop would reduce the software interference and improve the system performance.
However, multicast VC frees cell at the speed of the slowest port since it frees a cell until all ports are served for that cell. This dramatically increases the size of the multicast buffer. A mechanism which supports cell discard based on selective ports would reduce multicast queue size and recover from the potential congestion and cell loss quickly, which further improves the performance of multicast VC.
The present invention relates to an efficient method and apparatus for multicasting a cell while preferably using different VPI/VCIs for each instance of the transmission of that cell and being able to add or drop connections from a conference or a broadcast at any time. The multiple transmissions of the cell can occur on the same output port or different output ports of an ATM switching system.
SUMMARY OF THE INVENTION
The present invention pertains to a multicast system. The system comprises an ATM network. The system comprises a source connected to the ATM network. The system also comprises a first destination connected to the ATM network. The system comprises at least a second destination connected to the ATM network. Additionally, the system comprises a mechanism for adding or dropping connections dynamically between the first source and any destinations at any time.
The present invention pertains to a method for multicasting ATM cells. The method comprises the steps of forming a first connection between a first source and a first destination for transmitting a first ATM cell therebetween. Next, there is be step of forming a second connection between the first source and a second destination while the first connection exists. Then there is the step of terminating the first connection while the second connection exists.
The present invention pertains to a method for multicasting ATM cells. The method comprises the steps of forming a first connection between a first source and a first destination. Next there is the step of obtaining a first ATM cell to the transmitted out the first source. Next there is the step of forming a second connection between a first source and a second destination while the first connection exists and after the first ATM cell has been obtained.
The present invention pertains to a linked list for multicast in an ATM network. The linked list comprises a first cell. The linked list also comprises a plurality of read pointers. Each read pointer is associated with a port. Each read pointer points to the first cell.
The present invention also pertains to a multicast system for an ATM network. The system comprises a first port through which a cell passes. The system also comprises a first read pointer associated with the first port. The multicast system additionally comprises at least a second port through which the cell passes. There is at least a second read pointer associated with the second port. The multicast system is comprised of a cell to which each read pointer points. Furthermore, the multicast system is comprised of a controller for controlling when a read pointer reads a cell. The system preferably includes a plurality of cells. Each cell has a cell pointer pointing to a next cell. The plurality of cells forms a linked list. The controller points a read pointer to the next cell after the cell the read pointer was pointing to is read.
The present invention additionally pertains to a method for multicasting. The method comprises the steps of forming a first read pointer and at least a second read pointer. Each read pointer corresponds to a first port and a second port, respectively. Each read pointer points to a cell. Then there is the step of choosing a port. Next there is the step of locating the read pointer for the port. Then there is the step of reading the cell to which the read pointer is pointing. Preferably, the cell includes data and the cell includes a cell pointer pointing to a second cell, if there is a second cell. The first cell and at least the second cell forms a linked list.
The present invention pertains to a multicast system for an ATM network. The multicast system comprises at least a first ATM cell pointer mechanism. The multicast system is also comprised of at least a first cell having data. The first ATM cell pointer mechanism points to the first ATM cell. The multicast system is additionally comprised of a first node having a first address for the first ATM cell and a node address pointer. The first ATM cell pointer mechanism points to the first node. The multicast system is comprised of a second node having a second address for the first ATM cell. The node address pointer of the first node points to the second node. The first and second nodes form a linked list of addresses. The multicast system preferably is also comprised of a controller in communication with the first ATM cell pointer mechanism, the first node and the second node. The controller causes the first ATM cell to be transmitted out a port to the first address and then to the second address.
The present invention pertains to a method for multicasting an ATM cell. The method comprises the steps of reading a first node having a first
Bennett Jon C. R.
Zhou Fan
Rao Laura S.
Schwartz Ansel M.
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