Buffering of point-to-point and/or point-to-multipoint ATM cells

• US 6,128,295 A
• Filed: 07/11/1997
• Issued: 10/03/2000
• Est. Priority Date: 07/11/1997
• Status: Expired due to Term

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Fransson, Clarence, Larsson, Gunnar, Sissonen, Raimo, Bjenne, Anders
• Primary Examiner(s): RAO, SEEMA SRINIVAS
• Application Number:
  US08/893,677
• Time in Patent Office: 1,180 Days
• Field of Search: 370/412, 370/413, 370/414, 370/417-419, 370/427-429, 370/432, 370/395-399, 370/400, 370/409, 370/390, 370/389, 711/147-153
• US Class Current: 370/389
• CPC Class Codes: H04L 49/203 ATM switching fabrics with multicast or broadcast capabilities
• CPC Class Codes: H04L 49/3081 ATM peripheral units, e.g. policing, insertion or extraction
• CPC Class Codes: H04Q 11/0478 Provisions for broadband connections
• CPC Class Codes: Y10S 370/905 Asynchronous transfer mode, ASN

Abstract

An Asynchronous Transfer Mode (ATM) switching device (20) has ATM cells (both point-to-point and point-to-multipoint) routed therethrough to one or more physical output links (31-38). The switching device (20) includes a cell buffer memory (92) which is the sole storage area on an egress exchange terminal for all cells, including point-to-multipoint cells, regardless of to which physical output link the cell is destined. For point-to-multipoint cells, pointers to the location of the cell in the cell buffer memory (92) are stored in one or more pointer queues (114), the pointer queues (114) corresponding to physical output links over which the point-to-multipoint cells are expected to be propagated. As each physical output link is selected, the pointer in the corresponding pointer queue is used to obtain the cell from the cell buffer memory (92) for readout on the selected link.

Claims

1. An Asynchronous Transfer Mode (ATM) switching device through which ATM cells are routed to one or more of a plurality of physical output links, the switching device comprising:

a plurality of pointer queues respectively corresponding to the plurality of physical output links;

a cell memory wherein ATM cells destined are stored, the cell memory having stored therein ATM cells destined for output on differing ones of the physical output links;

wherein pointers are stored in a selected pointer queue corresponding to a selected physical output link, the pointer serving to locate in the cell memory an output-destined ATM cell for the selected physical output link;

a connection data record memory wherein is stored;

a first connection data record for each cell, the first connection data record having stored therein a next leaf pointer for each of the physical output links which are active for the cell as well as an indicator of which physical output links are active for the cell; and

a second connection data record which, for an active one of the physical output links, is pointed to by the next leaf pointer of the first connection data record for the respective physical output link, the second connection data record having stored therein a last leaf flag which indicates whether there is a further connection data record for the respective physical output link, the second connection data record having a further next leaf pointer stored therein in the case that the last leaf flag of the second connection data record indicates there is a further connection data record, the further next leaf pointer pointing to the further connection data record.

2. The apparatus of claim 1, wherein the second connection data record has at least one of a virtual path identifier (VPI) and a virtual circuit identifier (VCI) stored therein for inclusion in the output-destined ATM cell.

3. A method of handling Asynchronous Transfer Mode (ATM) in an ATM switching device through which ATM cells are routed to one or more of a plurality of physical output links, the method comprising:

storing ATM cells destined for output to one or more of the plurality of physical output links in a common cell buffer;

for each of the physical output links to which a specific cell is to be outputted, storing a pointer in a queue corresponding to the physical output links to which the specific cell is to be outputted, the pointer specifying a location of the specific cell in the common cell buffer;

selecting a first physical output link included in the plurality of links as a selected physical output link to which the specific cell is to be outputted;

for the first physical output link, obtaining the pointer from the queue corresponding to the first physical output link and using the pointer to obtain the ATM cell from the common cell buffer;

obtaining a first connection data record for the specific cell, the first connection data record having stored therein a next leaf pointer for each of the physical output links which are active for the specific cell as well as an indicator of which physical output links are active for the specific cell; and

obtaining a second connection data record which, for an active one of the physical output links, is pointed to by the next leaf pointer of the first connection data record for the respective physical output link, the second connection data record having stored therein a last leaf flag which indicates whether there is a further connection data record for the respective physical output link, the second connection data record further having a further next leaf pointer stored therein in the case that the last leaf flag of the second connection data record indicates there is a further connection data record, the further next leaf pointer pointing to the further connection data record.

4. The method of claim 3, further comprising obtaining from the second connection data record at least one of a virtual path identifier (VPI) and a virtual circuit identifier (VCI) stored therein for inclusion in the output-destined ATM cell.

5. An Asynchronous Transfer Mode (ATM) switching device through which ATM cells are routed to plural physical output links including a selected pysical output link, the switching device comprising:

a cell buffer in which the multicast cell is stored in a cell location;

a connection data record memory which has stored therein connection data information for the multicast cell for indicating to which of the plural physical output links the multicast cell is to be readout;

a readout queue for the selected output link;

wherein, when plural leafs for the cell location in the buffer are to be readout on the selected output link, the readout queue is kept pointing to the cell location in the buffer for the multicast cell until the multicast cell is readout on the selected output link for each of the plural leafs.

6. The apparatus of claim 5, wherein the connection data record memory has stored therein a first connection data record for the multicast cell and a second connection data record for the multicast cell, the first connection data record including a next leaf pointer field (NLF) for the selected output link, the second connection data including VPI/VCI information.

7. The apparatus of claim 6, further comprising a buffer circuit which:

(1) obtains the first connection data record for the multicast cell and uses contents of the next leaf pointer field to fetch the second connection data record for the multicast cell;

(2) enters a pointer in the readout queue, the pointer pointing to the cell location in the buffer; and

(3) when the selected output link is selected for readout;

(a) accesses the readout queue to obtain the cell location, and then reads out the cell to the selected output link, including in the cell as read out the VPI/VCI information obtained from the second connection data record;

(b) if there is not a next leaf pointer in the second connection data record for the selected output link;

removing the pointer to the cell location from the readout queue; and

(c) if there is a next leaf pointer in the second connection data record for the at least one output link;

uses contents of the next leaf pointer field of the second connection data record to readout the cell for another leaf.

8. A method of handling Asynchronous Transfer Mode (ATM) in an ATM switching device through which ATM cells are routed to plural physical output links including a selected output link, the method comprising:

(1) storing a multicast cell in a cell location in a buffer;

(2) obtaining connection data information for the multicast cell for indicating to which of the plural physical output links the multicast cell is to be readout;

(3) entering a pointer in a readout queue for the at least one output link, the pointer pointing to the cell location in the buffer; and

(4) when plural leafs for the cell location in the buffer are to be readout on the selected output link, maintaining the pointer in the readout queue pointing to the cell location in the buffer for the multicast cell until the multicast cell is readout on the selected output link for each of plural leafs.

9. The method of claim 8, wherein the step of obtaining connection data information further comprises obtaining from the a first connection data record a next leaf pointer field for the selected output link.

10. The method of claim 9, further comprising, when the selected output link is selected for readout, the steps of:

(a) fetching a second connection data record using the contents of the next leaf pointer field, the second connection data record including VPI/VCI information;

(b) accessing the readout queue to obtain the cell location, and then reading out the cell to the selected output link to include in the cell as read out the VPI/VCI information obtained from the second connection data record;

(c) checking the second connection data record to determine whether there is a next leaf pointer for the at least one output link;

(d) if the check of step (c) is negative, removing the pointer of step (3) from the readout queue; and

(e) if the check of step (c) is positive, using contents of the next leaf pointer field of the second connection data record as the contents of the next leaf pointer field when the selected output link is selected for readout for a repetition of steps (a)-(e).

11. The method of claim 9, wherein the first connection data record includes a next leaf pointer field for each of plural output links;

and wherein steps (3)-(4) are performed for each of plural output links in addition to the selected output link.

12. The method of claim 9, further comprising copying contents of the next leaf pointer field into the cell location in the buffer.

13. The method of claim 8, wherein step (2) comprises using an internal channel identifier included in the multicast cell to obtain the first connection data record.