Port and link identification

[0002] This application is related to U.S. Provisional Patent Application Ser. No. 60/001,498, filed Jul. 19, 1995.

[0003] This invention relates generally to the field of communication systems, and more particularly to port and link identification.

[0004] A communication system includes a collection of components that communicate, manipulate, and process information in a variety of ways. This system may support different access technologies, such as frame relay, circuit services, and new and evolving connection-based or connectionless services, that communicate information, such as data, voice, and video. Switches in the communication system employ hardware and software to route information generated by access technologies to an intended destination.

[0005] In such switches, different types of data cells are utilized to control switching connections. For example, a control cell can be used to establish communication on a connection or link. When a control cell of a particular type, such as a cell relating to an interim local management interface (ILMI), is processed at a switch control module, the switch control module (SCM) must be able to identify the port and link of origin for the control cell in order to establish communication. However, regardless of which link and processing port in a switch receives the cell of a particular type, the virtual path identification (VPI) field and the virtual channel identification (VCI) field of the control cell typically will be the same as the VPI field and VCI field, respectively, of other control cells of the same type. Thus, in some instances, the VPI/VCI identifier of a control cell cannot be used to identify a link and a port of origin for the control cell in a communication switch.

[0006] In accordance with the present invention, the disadvantages and problems associated with identifying a port and link of origin for a cell in a communication switch have been substantially reduced or eliminated.

[0007] In accordance with one embodiment of the present invention, a system is provided for identifying a processing port and a link at which a cell is received. The system includes a logical link table having a plurality of logical link entries. Each logical link entry, which corresponds to a particular link of a processing port associated with the logical link table, specifies a numerical value. The processing port may receive a cell at one of a plurality of links. The processing port can convert the cell by replacing a numerical value of an identification field, such as a virtual channel identification field, of the cell with the numerical value specified by the logical link entry corresponding to the link at which the cell is received. A switch control module, which is connected to the processing port, may receive the converted cell. The switch control module can identify the link and the processing port at which the cell corresponding to the converted cell was received by referencing a reverse mapping table using the numerical value of the logical link entry in the converted cell.

[0008] In accordance with another embodiment of the present invention, a method is provided for identifying a processing port and a link at which a cell is received. The method includes receiving a cell at one of a plurality of links of a processing port. A logical link table associated with the processing port is then referenced. The logical link table includes a plurality of logical link entries, each logical link entry corresponding to a particular link of the processing port and specifying a numerical value. The received cell is converted by replacing a numerical value of an identification field, such as a virtual channel identification field, of the cell with the numerical value specified by the logical link entry corresponding to the link at which the cell is received. The link and the processing port at which the cell was received can be identified by referencing a reverse mapping table using the numerical value specified by the logical link entry in the converted cell.

[0009] An important technical advantage of the present invention includes replacing a VCI value of a control cell with a specific logical link number corresponding to the link and port at which the control cell is received. A reverse mapping table contains information specifying which link and port are associated with each logical link number. The reverse mapping table may be accessed by the switch control module. Thus, when the switch control module processes the control cell, the switch control module is able to identify the link and port of origin for the cell using the reverse mapping table. This alleviates the need to set up a separate connection to receive control cells uniquely at each input link. A connection requires resources (queues, topology information) and is a resource to be conserved. This method allows there to be a single multipoint to point connection. Other important technical advantages are readily apparent to one skilled in the art from the following FIGURES, descriptions, and claims.

[0010] For a more complete understanding of the present invention, and for further features and advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which:

[0011] FIG. 1 illustrates a system for identifying a port and link of origin for a control cell in a communication switch; and

[0012] FIG. 2 is a flow chart of a method for identifying a link and port of origin for a control cell in a communication switch.

[0013] The preferred embodiment of the present invention and its advantages are best understood by referring to FIGS. 1 and 2 of the drawings, like numerals being used for like and corresponding parts of the various drawings.

[0014] FIG. 1 illustrates a system 10 for identifying a link and a processing port of origin for a control cell in a communication switch. System 10 includes at least one to-switch processing port (TSPP) 12, at least one logical link table 14, switching fabric 16, a switch control module (SCM) 18, and a reverse mapping table 20.

[0015] As shown in FIG. 1, system 10 includes two TSPPs 12, labeled as TSPP0 and TSPP1. Each TSPP 12 can be implemented as an application specific integrated circuit (ASIC). Each TSPP 12 may include a number of connections or links 22. Links 22 may support asynchronous transfer mode (ATM) cell relay (OC-12, OC-3c,155 Mbps UTP), frame relay (T1, E1, T3, E3, V.35), circuit emulation (T1, E1, T3, E3), internetworking using Ethernet, Fast Ethernet, Internet Protocol (IP), or IP over ATM, or any other communications protocol or access technology. In the embodiment shown in FIG. 1, each TSPP 12 may support or include eight links 22, which are labeled as LINK0-LINK7. Each link 22 is operable to receive a data cell, including control cells 24 which are labeled as CELL1, CELL2, and CELL3. The term “control cells” refers to cells that contain signaling or administration information. Each control cell 24 includes a virtual path identification (VPI) field 26 and a virtual channel identification (VCI) field 28. VPI field 26 and VCI field 28 may be numerical values. For a particular type of control cell 24, the numerical values for VPI field 26 and the VCI field 28 are specific. For example, as shown in FIG. 1, CELL1, CELL2 and CELL3 may each be an interim local management interface (ILMI) control cell where VPI field 26 has a value of “0” and VCI field 28 has a value of “16.” These values for VPI field 26 and VCI field 28 are the same for every ILMI control cell, regardless of the link 22 or TSPP 12 at which the control cell 24 is received. As described below in more detail, each TSPP 12 is operable to convert the control cells 24 that it receives into converted cells 38, which are labeled as CCELL1, CCELL2, and CCELL3 in FIG. 1. Each of these converted cells 38 may have a VPI 40 and a VCI 42. The values of the VCI 42 in converted cells 38 differ even if the converted cells 38 all correspond to the same type of control cell 24.

[0016] A separate logical link table 14 is associated with each TSPP 12. The logical link tables 14 shown in FIG. 1 are labeled as LLT0 and LLT1. LLT0 and LLT1 are associated with TSPP0 and TSPP1, respectively. Each logical link table 14 may be implemented on a memory internal or external to its associated TSPP 12, such as an external random access memory (RAM). Logical link tables 14 each comprise a plurality of logical link entries 30, which are labeled as LL#0-LL#7 in FIG. 1. Each logical link entry 30 corresponds to a particular link 22 in the TSPP 12 associated with the logical link table 14. For example, LL#0-LL#7 in LLT0 correspond to LINK0-LINK7 in TSPP0, respectively. Likewise, LL#0-LL#7 in LLT1 correspond to LINK0-LINK7 in TSPP1, respectively. Each logical link entry 30 may specify a numerical value, which is unique to a particular link 22 of a particular TSPP 12. In one embodiment, each numerical value may be implemented as a nine-bit binary number. Consequently, five hundred and twelve numerical values may be supported for the various logical link entries 30. The logical link entries 30 are used in converting control cells 24 to converted cells 38, as described below. The information in logical link tables 14 can be configured or initialized by software.

[0017] Switch fabric 16 is connected to each TSPP 12. Switch fabric 16 is operable to transfer a data cell, such as control cells 24, from a TSPP 12 to a from-switch processing port (FSPP). Switch fabric 16 can be implemented as an ECL cross-point device for transferring signals. In one embodiment, switch fabric 16 supports sixteen TSPPs 12.

[0018] SCM 18 is connected to switch fabric 16. SCM 18 may be implemented as one or more ASICs. SCM 18 includes an FSPP 32 having a special queue 34. FSPP 32 may also be implemented as an ASIC. Special queue 34 may be dedicated to receiving converted cells 38 corresponding to control cells of a particular type, such as ILMI control cells. As shown in FIG. 1, special queue 34 receives or contains CCELL1, CCELL2, and CCELL3.

[0019] Reverse mapping table 20 may be associated with special queue 34 in FSPP 32 of SCM 18. Reverse mapping table 20 may be implemented on memory (e.g., RAM) internal or external to FSPP 32. Reverse mapping table 20 comprises a plurality of reverse mapping entries 36. Each of reverse mapping entries 36 comprises information identifying a specific link 22 and TSPP 12 at which a control cell 24 can be received. Reverse mapping table 20 can be indexed by the numerical values specified in logical link entries 30. Like logical link tables 14, the information in reverse mapping table 20 can be configured or initialized by software.

[0020] In operation, the TSPPs 12 may receive control cells 24 at various links 22. As shown in FIG. 1, CELL1 and CELL2 may be received at LINK2 and LINK7 of TSSP0, respectively, and CELL3 may be received at LINK6. If these control cells 24 are the same type, the numerical value for the VPI field 26 of all cells will be the same. Likewise, the numerical value for the VCI field 28 of all cells will be the same. VPI field 26 and VCI field 28 of the cells shown in FIG. 1 have numerical values of 0 and 16, respectively. If the control cells 24 received by a TSPP 12 are of a certain type as determined by the VPI and VCI, then the TSPP 12 replaces the numerical value for VCI field 28 of the received cells with a numerical value stored in the logical linking table 14 associated with that TSPP 12. In particular, the TSPP 12 uses the logical link entry 30 corresponding to the link 22 at which the control cell 24 is received to replace the numerical value of the VCI field 28. In this manner, TSPP 12 converts control cells 24 to converted cells 38.

[0021] For example, because CELL1 is received at LINK2 of TSSP0, the numerical value of “285” specified in LL#2 of LLT0 is used to replace the VCI value of “16”. Likewise, because CELL2 is received at LINK7 of TSSP0, the VCI value of “16” in CELL2 is replaced with a VCI value of “220” specified in LL#7 of LLT0. Similarly, because CELL3 is receive at LINK6 of TSPPI, the VCI value of “16” in CELL3 is replaced with the value of “96” specified in LL#6 of LLT1. In this manner, CELL1, CELL2, and CELL3 may be converted into CCELL1, CCELL2, and CCELL3. TSPPs 12 transmit the converted cells 38 to SCM 18, which receives the converted cells 38 at special queue 34 dedicated to this particular type of control cell. When SCM 18 receives a converted cell 38, it is able to identify the link and processing port at which the corresponding control cell 24 was received using reverse mapping table 20.

[0022] It should be understood that a separate set comprising one or more logical link tables 14, a special queue 34, and a reverse mapping table 20 can be maintained for each type of control cell in a switch.

[0023] FIG. 2 is a flow chart of a method 100 for identifying a link 22 and a TSPP 12 of origin for a control cell 24 in a communication switch. Method 100, which corresponds to the operation of system 10 shown in FIG. 1, is described with particular reference to the processing of exemplary CELL1. Method 100 begins at step 102, where a TSPP 12 receives an information cell 24 at one of its links 22. For example, TSSP0 receives CELL1 at LINK2. At step 104, TSPP 12 determines whether the cell is a control cell 24. For example, in one embodiment, a queue number associated with the cell is used to look-up a queue descriptor. The queue descriptor may contain a logical link (LL) bit that specifies whether the cell should be converted.

[0024] If the received cell is not a control cell 24, method 100 ends. Otherwise, if the received cell is a control cell 24, then at step 108 TSPP 12 references its associated logical link table 14 and converts the control cell 24 into a converted cell 38. In particular, TSPP 12 replaces the value of VCI field 28 in the control cell 24 with a numerical value specified by the logical link entry 30 corresponding to the link 22 at which control cell 24 was received. Thus, because CELL1 was received at LINK2 of TSSP0, TSSP0 replaces the VCI field 28 value of “16” with a value of “285” specified by LL#2 in LLT0. This results in CCELL1, a converted cell 38 having a VCI 42 value of “285.”

[0025] At step 110, TSPP 12 transmits the converted cell 38 to special queue 34 of FSPP 32 in SCM 18. Special queue 34 receives only information cells of a particular type, such as cells relating to ILMI control.

[0026] SCM 18 receives the converted cell 38 from special queue 34 at step 114. At step 116, SCM 18 extracts the VCI 42 value from the converted cell 38. The VCI 42 value is used to index a reverse mapping entry 36 in reverse mapping table 20 at step 118. The reverse mapping entry 36 specifies the link 22 and TSPP 12 at which the control cell 24 corresponding to the converted cell 38 was received. Accordingly, SCM 18 is able to identify the TSPP 12 and link 22 of origin for the control cell 24 at step 128. Thus, with regard to the example, the VCI 42 value of “285” is used to reference the reverse mapping entry 30 specifying “LINK2 TSPP0.” SCM 18 may then respond at the link 22 and TSPP 12 of origin if appropriate.

[0027] Although the present invention and its advantages have been described detail, it should be understood that various changes, substitutions, and alterations can be made therein without departing from the spirit and scope of the invention as defined by the appended claims.