Reframing circuitry with virtual container drop and insert functionality to support circuit emulation protocols

Reframing circuitry controls communications between a physical layer device and a link layer device. In a first direction of communication, the reframing circuitry receives a container frame with the container frame having a first arrangement of columns, and outputs a virtual container frame that includes a modified version of the container frame received by the reframing circuitry, with the modified version of the container frame having a second arrangement of columns different than the first arrangement of columns. For example, the reframing circuitry in generating the modified version of the container frame may remove a path overhead column of the container frame and replace that path overhead column with a stuff column in the modified version of the container frame. The virtual container frame may be configured to include the path overhead column that was removed from the container frame in generating the modified version of the container frame.

FIELD

The field relates generally to network-based communication systems, and more particularly to communication devices which process overhead information or other framing information in such systems.

BACKGROUND

Conventional network-based communication systems include systems configured to operate in accordance with well-known synchronous transport standards, such as the synchronous optical network (SONET) and synchronous digital hierarchy (SDH) standards.

The SONET standard was developed by the Exchange Carriers Standards Association (ECSA) for the American National Standards Institute (ANSI), and is described in the document ANSI T1.105-1988, entitled “American National Standard for Telecommunications—Digital Hierarchy Optical Interface Rates and Formats Specification” (September 1988), which is incorporated by reference herein. SDH is a corresponding standard developed by the International Telecommunication Union (ITU), set forth in ITU standards documents G.707 and G.708, which are incorporated by reference herein.

The basic unit of transmission in the SONET standard is referred to as synchronous transport signal level-1(STS1). It has a serial transmission rate of 51.84 Megabits per second (Mbps). The corresponding unit in the SDH standard is referred to as synchronous transport module level-0(STM0). Synchronous transport signals at higher levels comprise multiple STS1or STM0signals. For example, an intermediate unit of transmission in the SONET standard is referred to as synchronous transport signal level-3(STS3). It has a serial transmission rate of 155.52 Mbps. The corresponding unit in the SDH standard is referred to as STM1.

A given STS3or STM1signal is organized in frames having a duration of 125 microseconds, each of which may be viewed as comprising nine rows by 270 columns of bytes, for a total frame capacity of 2,430 bytes per frame. The first nine bytes of each row comprise transport overhead (TOH), while the remaining 261 bytes of each row are referred to as a synchronous payload envelope (SPE). Synchronous transport via SONET or SDH generally involves a hierarchical arrangement in which an end-to-end path may comprise multiple lines with each line comprising multiple sections. The TOH includes section overhead (SOH), pointer information, and line overhead (LOH). The SPE includes path overhead (POH). Additional details regarding signal and frame formats can be found in the above-cited standards documents.

In conventional SONET or SDH network-based communication systems, synchronous transport signals like STS3or STM1are mapped to or from corresponding higher-rate optical signals such as a SONET OC-12signal or an SDH STM4signal. An OC-12optical signal carries four STS3signals, and thus has a rate of 622.08 Mbps. The SDH counterpart to the OC-12signal is the STM4signal, which carries four STM1signals, and thus also has a rate of 622.08 Mbps. The mapping of these and other synchronous transport signals to or from higher-rate optical signals generally occurs in a physical layer device commonly referred to as a mapper, which may be used to implement an add-drop multiplexer (ADM) or other node of a SONET or SDH communication system.

Such a mapper typically interacts with a link layer processor. A link layer processor is one example of what is more generally referred to herein as a link layer device, where the term “link layer” generally denotes a switching function layer. Another example of a link layer device is a field programmable gate array (FPGA). These and other link layer devices can be used to implement processing associated with various packet-based protocols, such as Internet Protocol (IP) and Asynchronous Transfer Mode (ATM), as well as other protocols, such as Fiber Distributed Data Interface (FDDI). A given mapper or link layer device is often implemented in the form of an integrated circuit.

In many communication system applications, it is necessary to carry circuit-switched traffic such as T1/E1 traffic over a packet network such as an IP network or an ATM network. For example, T1/E1 traffic from a SONET/SDH network or other circuit-switched network may be carried using virtual containers (VCs) that are mapped to packets of an IP network or other packet network. Such VCs contain both POH and payload information. The first column of a given VC is used for the POH, and the remaining 260 columns are the payload, which may comprise one or more containers.

The mapping of VCs or other time-division multiplexed (TDM) data to IP packets or other types of packets may be performed in accordance with a circuit emulation protocol, such as the CEP protocol described in IETF RFC 4842, “Synchronous Optical Network/Synchronous Digital Hierarchy (SONET/SDH) Circuit Emulation over Packet (CEP),” April 2007, which is incorporated by reference herein.

SUMMARY

One or more illustrative embodiments of the invention provide synchronous transport signal mappers or other communication devices that are configured to perform drop and insert of overhead information, such as POH information associated with a VC within a given frame of a synchronous transport signal, in a manner that facilitates the mapping of VCs or other TDM data to packets for transmission over a packet network. For example, a given such embodiment allows a synchronous transport signal mapper that does not otherwise support drop and insert of POH information associated with VCs to nonetheless provide that functionality, thereby permitting the mapping of the VCs to packets in accordance with a circuit emulation protocol such as the above-noted CEP protocol.

In one embodiment, reframing circuitry controls one or more communications between a physical layer device and a link layer device. In a first direction of communication, which may be a drop path direction of communication between the physical layer device and the link layer device, the reframing circuitry receives a container frame with the container frame having a first arrangement of columns, and outputs a VC frame that includes a modified version of the container frame received by the reframing circuitry, with the modified version of the container frame having a second arrangement of columns different than the first arrangement of columns.

For example, the reframing circuitry in generating the modified version of the container frame may remove a POH column of the container frame and replace that POH column with a stuff column in the modified version of the container frame. The VC frame in this example is configured to include the POH column that was removed from the container frame in generating the modified version of the container frame. The reframing circuitry in generating the modified version of the container frame may also reorder multiple synchronous transport signal data columns of the container frame.

In a second direction of communication, which may be an insert path direction of communication from the link layer device to the physical layer device, the reframing circuitry receives from the link layer device a VC frame comprising a container frame with the container frame having the second arrangement of columns. The reframing circuitry outputs to the physical layer device a modified version of the container frame, with the modified version of the container frame provided by the reframing circuitry to the physical layer device having the first arrangement of columns.

For example, the reframing circuitry in generating the modified version of the container frame may remove a POH column of the VC frame and replace a stuff column of the container frame with the removed POH column in the modified version of the container frame. The reframing circuitry in generating the modified version of the container frame may also reorder multiple synchronous transport signal data columns of the container frame.

Multiplexing circuitry of the physical layer device may be used in conjunction with the reframing circuitry in order to allow an otherwise conventional container frame to be modified to carry a POH column needed to support drop and insert functionality for the VC frame.

Other embodiments may make other types of container frame modifications in order to support virtual container drop and insert functionality.

DETAILED DESCRIPTION

Embodiments of the invention will be illustrated herein in conjunction with an exemplary network-based communication system which includes a physical layer device, a link layer device and other elements configured in a particular manner. It should be understood, however, that the disclosed techniques are more generally applicable to any communication system application in which it is desirable to provide virtual container drop and insert functionality to support circuit emulation protocols.

FIG. 1shows a network-based communication system100in an illustrative embodiment. The system100includes a node102arranged to support communication between a SONET/SDH network104and a packet network106. The packet network106may comprise, for example, an IP network, an ATM network or other type of network utilizing packet switching functionality. The networks104and106may comprise routers, switches or other network elements of respective SONET/SDH and packet networks operating in accordance with known standards. It should be noted that the term “SONET/SDH” as used herein refers to SONET and/or SDH. Embodiments to be described herein with reference to SDH synchronous transport signal terminology such as STM0and STM1should be understood to encompass analogous SONET embodiments using corresponding synchronous transport signal terminology such as STS1and STS3.

Although shown in the figure as being separate from the networks104and106, the node102may be viewed as being part of one of the networks104or106. For example, the node102may comprise an edge node of network104or network106. Alternatively, the node may represent a standalone router, switch, network element or other communication device arranged between nodes of the networks104and106.

The node102of system100comprises reframing circuitry110coupled between a mapper112and a link layer processor114. The node102also includes a host processor116that is used to configure and control one or more of reframing circuitry110, mapper112and link layer processor114. Portions of the host processor functionality may be incorporated into one or more of elements110,112or114in other embodiments. Also, although the reframing circuitry110is shown inFIG. 1as being separate from the mapper112and link layer processor114, in other embodiments the reframing circuitry110may be implemented at least in part within at least one of the mapper112and the link layer processor114. Accordingly, it is to be appreciated that reframing circuitry incorporated into mapper112or link layer processor114may be used to control one or more communications between those devices.

The reframing circuitry110, mapper112, link layer processor114, and host processor116in this illustrative embodiment may be installed on a line card or other circuit structure of the node102. Each of the elements110,112,114and116may be implemented as a separate integrated circuit, or one or more of the elements may be combined into a single integrated circuit. Various elements of the system100may therefore be implemented, by way of example and without limitation, utilizing a microprocessor, an FPGA, an application-specific integrated circuit (ASIC), a system-on-chip (SOC) or other type of data processing device, as well as portions or combinations of these and other devices. One or more other nodes of the system100in one or both of networks104and106may each be implemented in a manner similar to that shown for node102inFIG. 1.

The reframing circuitry controls certain communications between the mapper112and the link layer processor114, in order to allow the mapper112to communicate with a virtual container (VC) interface of the link layer processor114. The mapper112and link layer processor114are examples of what are more generally referred to herein as physical layer devices and link layer devices, respectively. The term “physical layer device” as used herein is intended to be construed broadly so as to encompass any device which provides an interface between a link layer device and a physical transmission medium of a network-based system. The term “link layer device” is also intended to be construed broadly, and should be understood to encompass any type of processor which performs processing operations associated with a link layer of a network-based system.

The mapper112and link layer processor114may include functionality of a conventional type. Such functionality, being well known to those skilled in the art, will not be described in detail herein, but may include functionality associated with known mappers, such as the LSI Hypermapper™, Ultramapper™ and Supermapper™ devices, and known link layer devices, such as the LSI Link Layer Processor. These LSI devices are commercially available from LSI Corporation of Milpitas, Calif., U.S.A.

The node102may also include other processing devices not explicitly shown in the figure. For example, the node may comprise a conventional network processor such as an LSI Advanced PayloadPlus® network processor in the APP300, APP500 or APP650 product family, also commercially available from LSI Corporation.

In this embodiment, the mapper112is more particularly referred to as a “legacy” mapper. This is intended to denote a mapper that has a container frame interface but not a VC frame interface, such that the mapper would not otherwise be able to communicate with a VC frame interface of the link layer processor114, and therefore could not be used to support the mapping of VCs to packets using a circuit emulation protocol, such as the CEP protocol described in IETF RFC 4842. Additional details regarding conventional aspects of a legacy mapper can be found in, for example, TMXF84622 Ultramapper™ 622/155 Mbits/s SONET/SDH×DS3/E3/DS2/DS1/E1/DS0, Ultramapper™ Resource Document, Jun. 6, 2002, which is incorporated by reference herein.

Although only single instances of the reframing circuitry110, mapper112and link layer processor114are shown in theFIG. 1embodiment, other embodiments may comprise instances of these and other system elements. For example, a group of multiple mappers may be arranged in a master-slave configuration that includes at least one master mapper and a plurality of slave mappers. Other embodiments may include only a single slave mapper, rather than multiple slave mappers. Numerous other configurations of system elements are possible, as will be appreciated by those skilled in the art.

The reframing circuitry110is coupled between the legacy mapper112and the link layer processor114and includes a drop path reframer120and an insert path reframer122. The drop path refers to a direction of communication through node102from the SONET/SDH network104to the packet network106, and the insert path refers to a direction of communication through node102from the packet network106to the SONET/SDH network104. The reframing circuitry110operates in conjunction with multiplexing circuitry124of the legacy mapper112to allow the mapper to communicate with the VC frame interface of the link layer processor114, and therefore to support the mapping of VCs to packets using the CEP protocol or other circuit emulation protocols.

The multiplexing circuitry124is used to control the ordering of columns of a container frame generated by the mapper112in the drop path so as to provide an output container frame having an arrangement of columns other than that which would normally be provided by the mapper at its container frame interface. By changing the column arrangement, the legacy mapper112can utilize the container frame interface to provide path overhead information to the reframing circuitry110. The drop path reframer120uses the received container frame with the path overhead information to generate a standard VC frame for delivery to the link layer processor114.

The VC frame provided by the drop path reframer120includes not only the path overhead information needed by the VC frame, but also a modified version of the received container frame, with this modified version of the container frame having the arrangement of columns that would normally be provided by the mapper at its container frame interface. Thus, the column arrangement that is normally provided at the output of the legacy mapper112in the drop path is altered using the multiplexing circuitry124in a manner that allows the path overhead information needed by the VC frame to be included in the container frame that is output from the mapper. The drop path reframer120takes this path overhead information from the received container frame, and generates an appropriate VC frame that includes the path overhead information as well as a standard container frame that does not include the path overhead information.

In the insert path, the process is reversed. The link layer processor114provides a standard VC frame to the insert path reframer122. This standard VC frame includes path overhead information, but as a separate column and not as part of its associated container frame. The insert path reframer122takes the path overhead information from its position in the standard VC frame and provides an input container frame to the legacy mapper112. The input container frame provided by the insert path reframer122to the legacy mapper112has an arrangement of columns other than that which would normally be received by the mapper at its container frame interface, in that one of those columns of the input container frame incorporates the path overhead information taken by the insert path reframer122from the standard VC frame. Thus, the container frame column arrangement that is normally expected at the input of the legacy mapper112in the insert path is altered by insert path reframer122in order to allow the path overhead information to be incorporated. The multiplexing circuitry124is then utilized to generate a standard container frame for further processing in the legacy mapper112.

The operation of the reframing circuitry110and multiplexing circuitry124will now be described in greater detail with reference toFIGS. 2 through 8.

FIG. 2illustrates a synchronous transport signal frame200, in this case an STM1frame, that includes a virtual container frame denoted VC4. The STM1frame comprises the data payloads of three STM0signals, and is organized in the form of array of bytes, having nine rows and 270 columns, such that the entire STM1frame comprises a total of 2,430 bytes. The first nine bytes of each row of the frame comprise transport overhead (TOH), while the remaining 261 bytes of each row comprise the virtual container frame VC4. The virtual container frame VC4comprises one column of path overhead (POH), followed by a container frame C4having 260 columns.

For circuit emulation protocols such as the CEP protocol, the TOH information is not needed, and so SONET/SDH data from the STMT frame is packed into packets using virtual container frames such as VC4.

Virtual container frames such as VC4may be configured to carry multiple tributary units (TUs) that are arranged in TU groups (TUGs). More specifically, the VC4frame may comprise three TUG3s (TUG3×3), with each TUG3 possibly having a different arrangement of TUs. In this embodiment, it is assumed that the C4frame is mapped from a TUG3×3, as indicated in the figure.

The C4frame has two columns of stuff bits202-1and202-2, also referred to herein as stuff columns and implemented as all logic ‘1’ values. This is followed by a repeating sequence of three STM0signal byte columns that repeat in the order STM0#1, STM0#2and STM0#3. This C4frame format is an example of a standard container frame that would normally be output by the legacy mapper112in the drop path and received by the legacy mapper112in the insert path. It can be seen that, because the mapper is a legacy mapper as previously described, the mapper does not support direct communication with a virtual container interface of the link layer processor114, at least in part because the standard C4frame that it generates or receives does not include the POH information required by the VC4frame.

This deficiency of the legacy mapper112is overcome by using the reframing circuitry110in combination with the multiplexing circuitry124to provide virtual container drop and insert functionality for the legacy mapper, thereby allowing the mapper to support circuit emulation protocols such as the CEP protocol.

Referring now toFIG. 3, the multiplexing circuitry124of mapper112is operated to produce in place of the standard container frame C4a modified container frame C4′ in which one of the stuff columns is replaced with the POH column of the virtual container and the STM0signal byte columns are reordered so as to repeat in a different sequence given by the order STM0#2, STM0#1, STM0#3. It should be noted that this particular reordering is only an example, and other reorderings of the STM0byte columns could be used in other embodiments, such as the order STM0#2, STM0#3, STM0#1.

The modification of the C4frame to form the C4′ frame may be viewed as producing a switched VC4frame in each STM0#2column is switched with the corresponding STM0#1column and in which the POH column is switched with one of the stuff columns of the C4frame so as to allow the POH column to be dropped or inserted.

The drop path functionality is illustrated in greater detail inFIGS. 4A-4Cand5. Referring initially toFIG. 4A, the drop path reframer120is shown as comprising a FIFO control and data rate adapter400coupled to a FIFO buffer402. The modification of the C4frame to form the C4′ frame is performed by the multiplexing circuitry124of mapper112, and the C4′ frame is supplied by the mapper112to the drop path reframer120. The drop path reframer processes the received C4′ frame to generate a standard VC4frame for delivery to the LLP114. This processing involves removing the POH column from the C4′ frame and placing that column in its appropriate position in the VC4frame, padding out an additional stuff column for the C4frame portion of the VC4frame, and reordering the synchronous transport signal data back to the normal ordering of STM0#1, STM0#2, STM0#3.

FIG. 4Bshows a more detailed view of the circuitry used to perform the above processing in the drop path reframer120. In this embodiment, the FIFO control and data rate adapter402is more particularly shown as comprising a counter410, a write enable element412coupled to an input of the FIFO buffer402, and a multiplexer414. The counter410counts from 0 to 260 and generates a buffer write enable signal for application to the write enable element412and an output select signal for application to a select line of the multiplexer414. One of the inputs of the multiplexer414is coupled to the C4′ input of the drop path reframer120, and the other input of the multiplexer is coupled to the output of the FIFO buffer402. The output of the multiplexer414provides the VC4output of the drop path reframer120.

At the C4′ input, the drop path reframer120receives the C4′ frame in the form of a 9 row by 260 column array as shown inFIG. 3. At the VC4output, the drop path reframer provides a standard VC4frame in the form of a 9 row by 261 column array as shown inFIG. 2. The C4′ frame is received sequentially on a row-by-row basis, where each row corresponds to a line of the frame. Thus, the counter reaches 260 on the last byte of each line of the C4′ frame. In this embodiment, the FIFO buffer402need only buffer a single byte at a time. The timing diagram ofFIG. 4Cshows the counter values, C4′ input bytes, FIFO buffer contents and VC4output bytes for the processing of one line of the C4′ frame. The other lines of the C4′ frame are processed in a similar manner.

With reference now to the flow diagram ofFIG. 5, the processing of the C4′ frame by the drop path reframer120to produce the standard VC4frame is shown. The process includes steps500through518. The process begins in step500.

The first byte of the received C4′ frame is the first POH byte, and this byte is directly output as indicated in step502.

The second byte of the received C4′ frame is the first byte of stuff column2, and so this byte is stored in the FIFO buffer402and an all ‘1’ byte is output to form the first byte of stuff column1, as indicated in step504.

The third byte of the received C4′ frame is the first byte of STM0#2, and so in step506this byte is stored in the FIFO buffer while the previously-stored first byte of stuff column2is output from the FIFO buffer.

The fourth byte of the received C4′ frame is the first byte of STM0#1, and in step508this byte is directly output.

The fifth byte of the received C4′ frame is the first byte of STM0#3, and so in step510this byte is stored in the FIFO buffer while the previously-stored first byte of STM0#2is output.

The sixth byte of the received C4′ frame is the second byte of STM0#2, so steps506,508and510are repeated. These steps will continue to be repeated until it is finally determined in step512that the last byte of the first line has been processed. At this point, the previously-stored STM0#3byte corresponding to the last byte of the VC4frame is output as indicated in step514.

After all of the bytes of the first line have been processed, a determination is made in step516as to whether or not the current line is the last line of the frame. If not, steps502through516are repeated for the next line, until the last line has been processed, at which point the process ends in step518.

Again, since the amount of data to be stored in the FIFO buffer402at any given time is only a single byte, the buffer depth need only be one byte. It is therefore apparent that the drop path reframer120comprising FIFO buffer402, counter410, write enable element412and multiplexer414exhibits minimal complexity, and can be implemented within limited circuit area and at low cost.

The insert path functionality is illustrated in greater detail inFIGS. 6A-6Cand7. Referring initially toFIG. 6A, the insert path reframer122is shown as comprising a FIFO control and data rate adapter600coupled to a FIFO buffer602. The insert path reframer processes the standard VC4frame received from the LLP114to generate a C4′ frame for delivery to the legacy mapper112. This processing involves removing the POH column from the input VC4frame and placing that column into the output C4′ frame in place of one of the stuff columns of a standard C4frame, and reordering the synchronous transport signal data from the standard C4ordering of STM0#1, STM0#2, STM0#3into the modified ordering of STM0#2, STM0#1, STM0#3. The multiplexing circuitry124of mapper112can then further process the C4′ frame received from the insert path reframer122in order to form a standard C4frame of the type shown inFIG. 2.

FIG. 6Bshows a more detailed view of the circuitry used to perform the above processing in the insert path reframer122. In this embodiment, the FIFO control and data rate adapter602is more particularly shown as comprising a counter610, a write enable element612coupled to an input of the FIFO buffer602, and a multiplexer614. The counter610counts from 0 to 261 and generates a buffer write enable signal for application to the write enable element612and an output select signal for application to a select line of the multiplexer614. One of the inputs of the multiplexer614is coupled to the VC4input of the insert path reframer122, and the other input of the multiplexer is coupled to the output of the FIFO buffer602. The output of the multiplexer614provides the C4′ output of the insert path reframer122.

At the VC4input, the insert path reframer122receives the VC4frame in the form of a 9 row by 261 column array as shown inFIG. 2. At the C4′ output, the insert path reframer provides the C4′ frame in the form of a 9 row by 260 column array as shown inFIG. 3. The VC4frame is received sequentially on a row-by-row basis, where each row corresponds to a line of the frame. Thus, the counter reaches 261 on the last byte of each line of the VC4frame. In this embodiment, the FIFO buffer602need only buffer a single byte at a time. The timing diagram ofFIG. 6Cshows the counter values, VC4input bytes, FIFO buffer contents and C4′ output bytes for the processing of one line of the VC4frame. The other lines of the VC4frame are processed in a similar manner.

With reference now to the flow diagram ofFIG. 7, the processing of the standard VC4frame by the insert path reframer122to produce the C4′ frame is shown. The process includes steps700through720. The process begins in step700.

The first byte of the received VC4frame is the first POH byte, and this byte is stored in the FIFO buffer as indicated in step702.

The second byte of the received VC4frame is the first byte of stuff column1. This byte is discarded in step704as it is not needed in the C4′ frame.

The third byte of the received VC4frame is the first byte of stuff column2, and so in step706this byte is stored in the FIFO buffer while the previously-stored first byte of POH is output from the FIFO buffer.

The fourth byte of the received VC4frame is the first byte of STM0#1, and in step708this byte is stored in the FIFO buffer, while the previously-stored first byte of stuff column2is output.

The fifth byte of the received VC4frame is the first byte of STM0#2, and so in step710this byte is directly output.

The sixth byte of the received VC4frame is the first byte of STM0#3. This byte is stored in the FIFO buffer, while the previously-stored first byte of STM0#1is output, as indicated in step712.

Step714determines if the current byte is the last byte of the first line of the VC4frame. If it is not the last byte, steps708,710and712are repeated. These steps will continue to be repeated until it is finally determined in step714that the last byte of the first line has been processed. At this point, the previously-stored STM0#3byte corresponding to the last byte of the C4′ frame is output as indicated in step716.

After all of the bytes of the first line have been processed, a determination is made in step718as to whether or not the current line is the last line of the frame. If not, steps702through718are repeated for the next line, until the last line has been processed, at which point the process ends in step720.

As in drop path reframer120, the amount of data to be stored in the FIFO buffer602at any given time is only a single byte, and therefore the buffer depth need only be one byte. The insert path reframer122can therefore also be implemented within limited circuit area and at low cost.

One embodiment of the multiplexing circuitry124of the mapper112is illustrated inFIG. 8. In this embodiment, the multiplexing circuitry comprises FIFO data buffers802-1and802-1, and drives downstream processors804-1,804-2and804-3of the mapper112, each associated with one of the synchronous transport signals STM0#1, STM0#2and STM0#3. The multiplexing circuitry124further comprises a counter810, write enable elements812-1and812-2coupled to respective inputs of the buffers802-1and802-2, and a multiplexer814. The counter810counts from 0 to 2 and generates a buffer write enable signal for application to the write enable elements812and an output select signal for application to a select line of the multiplexer814. One of the inputs of the multiplexer814is coupled to an STM1data stream input of the multiplexing circuitry124, and the other two inputs of the multiplexer are coupled to respective outputs of the buffers802-1and802-2. The output of the multiplexer814provides the multiplexed STM1data output comprising the three STM0signals for delivery to the respective downstream processors804-1,804-2and804-3.

It is to be appreciated that the particular circuitry arrangements shown inFIGS. 4B,6B and8, the signaling arrangements illustrated in the timing diagrams ofFIGS. 4C and 6C, and the process steps ofFIGS. 5 and 7, may be varied in other embodiments. Numerous alternative arrangements of circuitry, signal timing and process flow may be used to implement the described drop and insert functionality.

Also, although described primarily in the context of POH information of a VC4frame, the disclosed techniques can be adapted for use with a wide variety of other types of synchronous transport signal information.

It should be noted that the portions of the reframing circuitry110, and possibly other components of the node102, may be implemented at least in part in the form of one or more software programs running on a processor. A memory associated with the mapper112, link layer processor114or host processor116may be used to store executable program code of this type. Such a memory is an example of what is more generally referred to herein as a “computer program product” having executable computer program code embodied therein. The computer program code when executed in a mapper, link layer processor or other communication device processor causes the device to perform one or more operations associated with reframing circuitry110. Other examples of computer program products in embodiments of the invention may include, for example, optical or magnetic disks.

Also, reframing circuitry in accordance with embodiments of the invention may be implemented as part of an integrated circuit device suitable for installation on a line card or port card of a router, switch, network element or other communication device. Numerous other configurations are possible.

In a given integrated circuit implementation, identical die are typically formed in a repeated pattern on a surface of a semiconductor wafer. Each die includes reframing circuitry as described herein, and may include other structures or circuits. The individual die are cut or diced from the wafer, then packaged as an integrated circuit. One skilled in the art would know how to dice wafers and package die to produce integrated circuits. Integrated circuits so manufactured are considered embodiments of the invention.

Again, it should be emphasized that the embodiments described herein are intended to be illustrative only. For example, the particular arrangement of physical layer device, link layer device, host processor and other elements as shown inFIG. 1may be varied in alternative embodiments. Also, the particular signals shown in the drawings and described above are presented by way of example, and those skilled in the art will recognize that alternative signal configurations and associated timing arrangements may be used. Furthermore, other types of circuitry may be used to implement reframing functionality as disclosed herein. These and numerous other alternative embodiments within the scope of the following claims will be readily apparent to those skilled in the art.