US 20090213856 A1
A system and method for facilitating packet transformation of multi-protocol, multi-flow, streaming data. Packet portions subject to change are temporarily stored, and acted upon through processing of protocol-dependent instructions, resulting in a protocol-dependent modification of the temporarily stored packet information. Validity tags are associated with different segments of the temporarily-stored packet, where the state of each tag determines whether its corresponding packet segment will form part of the resulting modified packet. Only those packet segments identified as being part of the resulting modified packet are reassembled prior to dispatch of the packet.
1. A system comprising:
a programmable lookup word generator to receive a set of information and to produce a lookup word, the programmable lookup word generator including:
a profile memory configured to store a set of instructions for generating the lookup word; and
a selection mechanism for selecting portions of the set of information in response to the set of instructions retrieved from the profile memory, the selection mechanism including a matrix of storage elements and shift logic for use in generating the lookup word; and
a content-addressable memory, coupled to the programmable lookup word generator, configured to receive said generated lookup word and to perform a lookup operation based on said generated lookup word in order to generate one or more lookup result indications.
2. The system of
3. The system of
4. The system of
5. A method for generating a lookup word, the method comprising:
receiving a set of information including a profile identification;
retrieving a set of instructions from a profile memory based on the profile identification;
manipulating the set of information in response to the set of instructions to generate the lookup word, said manipulation including controlling a selection mechanism, the selection mechanism including a matrix of storage elements and shift logic for use in generating the lookup word; and
exporting the lookup word to a content-addressable memory for use by said content-addressable memory in performing a lookup operation to identify one or more content-addressable memory lookup results.
6. The method of
7. The method of
8. A system for generating a lookup word, the system comprising:
means for receiving a set of information including a profile identification;
means for retrieving a set of instructions from a profile memory based on the profile identification;
means for manipulating the set of information in response to the set of instructions to generate the lookup word, said means for manipulating the set of information includes a matrix of storage elements and shift logic for use in generating the lookup word; and
means for exporting the generated lookup word to a content-addressable memory for use by said content-addressable memory in performing a lookup operation to identify one or more content-addressable memory lookup results.
9. A packet editor module comprising:
an input memory configured to store incoming packet header information of a packet;
a packet processing unit configured to generate packet header information for the packet by operating on the packet header information stored in the input memory, the packet processing unit including a first processing component configured to generate layer 2 (L2) packet header information for the packet and a second processing component implemented in parallel with the first processing component and configured to generate layer 3 (L3) packet header information for the packet; and
a build component configured to receive the generated packet header information while the input memory stores incoming packet header information for a next packet.
This application is a divisional of U.S. patent application Ser. No. 11/224,692, filed Sep. 12, 2005, which is a continuation of U.S. patent application Ser. No. 09/849,804, filed on May 4, 2001, now U.S. Pat. No. 6,944,168.
The following co-pending patent applications of common assignee contains some common disclosure: “A Method And Apparatus For Providing Multi-Protocol, Multi-Stage, Real-Time Frame Classification”, U.S. patent application Ser. No. 09/849,913, filed concurrently herewith, which is incorporated herein by reference in its entirety;
“System And Method For Policing Multiple Data Flows And Multi-Protocol Data Flows”, U.S. patent application Ser. No. 09/849,914, filed concurrently herewith, which is incorporated herein by reference in its entirety;
“System And Method For Hierarchical Policing Of Flows And Subflows Of A Data Stream”, U.S. patent application Ser. No. 09/849,810, filed concurrently herewith, which is incorporated herein by reference in its entirety.
This invention relates in general to communication networks, and more particularly to a method and apparatus for transforming packets in a multi-protocol, multi-flow data stream.
Enhancing today's networking technology is a perpetual goal in the communications industry. As the raw speeds of large-scale and personal computing devices soar, the tremendous increase in data transmission demands continue to push the networking bandwidth envelope to capacity. As bandwidth-intensive multimedia content continues to gain popularity and course the veins of the Internet, the unrelenting bandwidth dilemma is no less urgent today than yesterday. This demand has fueled the need for high-bandwidth broadband systems.
The term “broadband” has often been used to describe high-bandwidth transmission of data signals, such as data, video, voice, video conferencing, etc. Broadband philosophies often address networking principles applicable to the backbone of the networking system, since the networking backbone generally faces the highest bandwidth demands. There are many competing technologies for delivering broadband access. For example, there are a number of standards used in digital telecommunications, including TCP/IP, Ethernet, HDLC, ISDN, ATM, X.25, Frame Relay, Digital Data Service, FDDI (Fiber Distributed Data Interface), Ti, xDSL, Wireless, Cable Modems, and Satellite among others. Many of these standards employ different packet and/or frame formats. The term “frame” is often used in reference to encapsulated data at OSI layer 2, including a destination address, control bits for flow control, the data or payload, and CRC (cyclic redundancy check) data for error checking. The term “packet” is often used in reference to encapsulated data at OSI layer 3. Further, the term “cell” is often used in reference to a group of bytes/octets conditioned for transmission across a network. However, it should be understood that for purposes of the present application, the terms packet, frame, and cell may be used interchangeably to refer to groups or collections of data. Further, a packet format or frame format generally refers to how data is encapsulated with various fields and headers for transmission across the network. For example, a data packet typically includes a destination address field, a length field, an error correcting code (ECC) field or cyclic redundancy check (CRC) field, as well as headers and trailers to identify the beginning and end of the packet. The terms “packet format” and “frame format”, also referred to as “cell format”, are generally synonymous for purposes of this application.
Packets transmitted across a network are associated with a transmission protocol. A protocol is a set of rules that governs how devices on a network exchange information. Packets traversing the network may be of differing formats or “protocols.” This is often due to the development of incompatible proprietary protocols by computer manufacturers. While protocol compatibility and standardization are becoming increasingly important, even standard protocols provide multiple options and are not always interchangeable between applications. Further, new protocols will continue to be developed to address certain network limitations, or to otherwise improve network data transmission. All of these factors contribute to the reality that multiple transmission protocols exist, and will likely continue to exist.
Examples of typical protocols used to communicate information include the Internet Protocol (IP), which is a “best-effort,” connectionless protocol responsible for delivering data from host to host across a network such as the Internet. IP is a predominant protocol used to transmit data across the Internet. Other protocols are used to transmit packets across the Internet as well, such as Framed ATM over SONET/SDH Transport (FAST) and IP on multiprotocol label switching (MPLS). FAST is a new protocol intended to improve the performance of asynchronous transfer mode (ATM). FAST introduces a variable length user data field, while preserving the proven advantages of ATM, such as real quality of service guarantees, the security and traffic isolation provided by virtual connections, network management, traffic management, control mechanisms for bandwidth on demand, etc. MPLS integrates layer-2 information about network links into layer-3 (IP) within a particular autonomous system in order to simplify and improve IP-packet exchange. MPLS essentially provides connection-oriented labeling in an otherwise connectionless environment, which has resulted in MPLS being considered associated with layer-2.5. With MPLS, different flows can be classified, and different service levels can be associated with the different flow classifications.
As described above, packets transmitted on a network such as the Internet may be associated with one of a number of different protocols, and thus packets associated with different protocols may be received at a given node, switch, router, etc. As described more fully below, the introduction of multiple packet protocols at a node requires special consideration when the entire data flow is subject to editing as the packets traverse the network.
Packets, frames, cells, and/or other data units traversing a network such as the Internet often face the possibility of being modified at a given network node. A variety of situations may result in a need to modify or “transform” the packet. For example, a packet reaching a node may need to be redirected from its original course to an alternate course. This can occur where an originally-intended node along the path becomes unavailable due to server problems, transmission cables being cut or otherwise damaged, and the like. In such a case, a “destination address” identified in a packet may require modification to alter the path of the packet in its quest to reach the ultimate destination. Another example of packet editing include the potential need to change header fields of the packet, such as packet length and checksum fields. If, for example, a packet is modified for any reason, the checksum and/or packet length fields are very likely to change, resulting in the need to further modify the packet to update such fields. Other fields include the time-to-live (TTL), packet conformance indicators such as colorations and drop priorities, etc. As can be seen, packets may require editing as they navigate the network towards their respective destination nodes.
At a particular network node or other ingress point, individual packets that make up a communications traffic stream can be classified into several flows or connections. Further, the traffic stream flows may include packets being transmitted in connection with different protocols. This can pose a challenge to editing systems, and typically requires that each of the flows be discretely handled. Due to very high data transmission speeds in today's networks, editing methods have conventionally required custom solutions, generally in the form of specialized, proprietary hardware engines in application-specific integrated circuits (ASICs). Because information may be transmitted across networks (e.g., the Internet) using a variety of different networking protocols, multiple specialized circuits are generally required to accommodate packets of each packet protocol that might traverse the network switch, router, bridge, or other intermediate system between the source and destination. For example, a separate packet transformation methodology, and therefore separate ASIC, may be required for each packet protocol used in the network. This results in higher costs, part counts, and general complexities, while adversely impacting system efficiencies.
Accordingly, there is a need in the communications industry for a method and apparatus for commonly transforming one or more packet flows of multiple transmission protocols. The present invention fulfills these and other needs, and offers other advantages over the prior art policing approaches.
To overcome limitations in the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention discloses a system, apparatus and method for facilitating packet transformation of multi-protocol, multi-flow, streaming data.
In accordance with one embodiment of the invention, a packet transformation module is provided for editing multi-protocol streaming data packets. An instruction memory receives search words identifying a packet type for the packet, and outputs appropriate instructions based on the packet type as indexed by the search words. A packet memory is coupled to receive one or more portions of the packet subject to editing, where each of the packet portions is stored in a respective memory segment of the packet memory. The packet transformation module further includes a valid bit array that has memory validity fields associated with respective memory segments. The state of each of the memory validity fields establishes whether the packet portion in the respective memory segment is to be incorporated into the resulting packet portion. A processing module receives the instructions from the instruction memory, and carries out the packet transformations on the packet portions in accordance with the instructions.
An ingress processing module is also provided. The ingress processing module includes such a packet transformation module, as well as a packet parser to parse each packet, and generate resulting search words based on the packet protocol. A network system is also provided which includes such an ingress processing module at an intermediary network node between the source and destination nodes, where the source node dispatches the information onto the network, and the destination node is the node to which the information is targeted.
In accordance with another embodiment of the invention, a method is provided for editing packets of a packet stream received at a network node. The method includes storing packet segments in partitionable memory segments of a modification memory. One or more editing instructions are elicited from an instruction memory, where the particular editing instructions elicited is based on characteristics of the packet. At least one packet segment stored in the modification memory is modified as directed by the editing instructions. Validity tags are associated with each of the memory segments to indicate whether or not their corresponding packet segments will be incorporated into a resulting modified packet. The resulting modified packet is created by assembling the packet segments associated with those validity tags that indicate incorporation into the resulting modified packet.
These and various other advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and form a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to accompanying descriptive matter, in which there are illustrated and described specific examples of an apparatus in accordance with the invention.
The invention is described in connection with the embodiments illustrated in the following diagrams.
In the following description of the exemplary embodiment, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration the specific embodiment in which the invention may be practiced. It is to be understood that other embodiments may be utilized, as structural and operational changes may be made without departing from the scope of the present invention.
Generally, the present invention provides a system and method for facilitating packet transformation of multi-protocol, multi-flow, streaming data. Packets of the data stream being communicated across the network using different transmission protocols can be appropriately edited regardless of the transmission protocol associated with the packets. Portions of each packet that are subject to change (but may not necessarily be changed) are temporarily stored. Certain instructions for effecting appropriate modifications to the particular packet are processed, with due consideration to the packet's protocol, which results in a protocol-dependent modification of the temporarily stored packet information. Validity tags are associated with different segments of the temporarily-stored packet, where the state of each tag determines whether its corresponding packet segment will form part of the resulting modified packet. Those packet segments identified as being part of the resulting modified packet are reassembled prior to dispatch of the packet.
Data transmitted over networks such as the Internet 10 may be in the form of e-mail messages, file transfers and downloads, web page loading, and the like. The data is generally broken up into a number of data packets, each of which is assigned a hierarchy of headers to direct the data packet to the desired destination, among other things. Each packet is separately dispatched to the destination, although more than one different route may be taken by the different packets associated with the data.
For example, the source computer 100 of
Because of the colossal bandwidth demands required of routers, a continual emphasis is placed on alleviating data throughput bottlenecks at routers, gateways, bridges, and other intermediate nodes along the network. Because routers take on the task of intercepting, analyzing, and moving on millions of packets per second along the best possible route, the processing occurring at these routers must be extremely efficient to avoid bogging down the system. The present invention may be used in connection with such routing systems, increasing speed and efficiencies of network data throughput.
As will be described more fully below, the present invention may be used in connection with multiprotocol route/flow classifying and policing engines. In one embodiment of the invention, the packet transformation in accordance with the present invention is housed in a package or chip common to the classifier and policing functionalities. The device enables advanced services to be applied at speeds of 10 Gbps or more. Tightly coupled parsing, policing, and packet transformation allows the collective device to perform dynamic packet transformation for quality of service (QoS) based on the current flow state and also effectively handles dynamic header processing such as required by multiprotocol label switching (MPLS) routers.
Referring now to
The line card-0 204 of the illustrated embodiment receives as input packet-over-SONET/SDH (POS) frames via the network. As is known in the art, SONET/SDH is a high-speed time division multiplexing (TDM) physical-layer transport technology. POS provides a means for using the speed and management capabilities of SONET/SDH to optimize data transport, although originally optimized for voice. A SONET/SDH frame is 810 bytes and is normally represented as a two-dimensional byte-per-cell grid of 9 rows and 90 columns. The SONET/SDH frame is divided into transport overhead and payload bytes. The transport overhead bytes include section and line overhead bytes, while the payload bytes are made up of the payload capacity and some more overhead bytes referred to as path overhead. The overhead bytes are responsible for the management capabilities of SONET/SDH. The basic transmission rate of SONET (51.840 Mbps), referred to as Synchronous Transport Signal level 1 (STS-1), is achieved by sampling the 810-byte frames at 8000 frames per second. SONET features an octet-synchronous multiplexing scheme with transmission rates in multiples of 51.840 Mbps, whereby STS-192 thereby provides transmission at approximately 10 Gbps. Packet Over SONET/SDH (POS) allows core routers to send native IP packets directly over SONET/SDH frames. POS provides a relatively low packet overhead and cost per Mbit than other data transport methods, which allows POS to efficiently support increases in IP traffic over existing and new fiber networks.
As shown in the exemplary embodiment of
Ingress processing circuit 214, which in one embodiment of the invention is housed in a single chip, performs the necessary lookups, policing, and editing of the packet. If necessary, the frame can be redirected to the host processor. The frames are fed out of the ingress processing circuit 214 via an OIF SPI-4 interface 218 to a Fabric Interface Chip (FIC) circuit 220. The FIC 220 converts the stream from one format to another, such as from POS frames to Common Switch Interface (CSIX) cells, and distributes the cells over the switch fabric 202.
Similarly, cells switched at the switch fabric 202 may be received at the FIC 222 and provided to the egress processing circuit 224. Frames are transferred to the egress framer 226, and output as POS OC-192 frames 228. A processor 230 may be coupled to the ingress processing circuit 214 and the egress processing circuit 224 to perform a variety of functions, including providing coprocessor support. Memories 232, 234 represent one or more memories associated with the ingress processing module 214 and the egress processing module 224 respectively.
Referring now to
The interface 306, such as an OIF interface, provides the interface between the ingress processing circuit 304 and the framer 302. In one embodiment, the interface 306 is a 200 MHz OIF SPI-4 interface including a 64-bit data input. An elasticity buffer 308, which in one embodiment is a first-in-first-out (FIFO), provides temporary packet storage which allows table maintenance updates to be performed without dropping frames.
The pre-processor 310 performs a variety of functions, including packet verification and discarding, packet protocol identification, statistics compilation, and others. The packet protocol identification includes classifying the type of frame that has been received. The pre-processor identifies each layer protocol using a multistage algorithm coupled with a content-addressable memory (CAM) and memory (such as an SRAM) for resolving protocols. The frame is then stored in a memory along with the result of the preprocessor, i.e., the protocol layer code.
The parsing engine 312 performs layer classification and tagging via a search engine. One of the various functions of the parsing engine 312 is to parse the frames processed by the pre-processor, and generate search keys from data anywhere within the frame. The protocol layer code is used as a start vector into an instruction memory, which contains instructions for the parsing engine 312 and pointers to access selected words in a frame buffer. The parsing engine 312 receives the instruction and performs the functions selected by the corresponding instruction operational code. The results are used with an extractor that builds search keys which can be applied against a CAM (or indexed directly to a memory) to generate “search results” that contain the frame classification. Such parsing/classifying may be performed in a manner described herein and in copending U.S. patent application Ser. No. 09/849,913, entitled “A Method And Apparatus For Providing Multi-Protocol, Multi-Stage, Real-Time Frame Classification,” filed concurrently herewith and assigned to the assignee of the instant application, the contents of which are incorporated herein by reference in its entirety.
The policing engine 313 performs a variety of functions, including ensuring flow conformance to a maximum allowed peak rate and a contractually obliged committed rate flow, utilizing, for example, DiffServ IP and MPLS. The policing engine 313 works with memory, such as policing RAM 315 which stores a drop policy for each connection.
The editor 314, also referred to as a packet transformation engine, utilizes the search results to index the appropriate editing instructions to be executed by an editing module. The editor 314 facilitates execution of multiple edits or “transformations” per packet as streaming data of various networking protocols associated with different networking layers is input into the editing module. The editor 314 supports comprehensive packet manipulation capability, including full MPLS labels, DAC operations such as multiple push and pop operations, as well as traditional routing operations such as TTL edits, checksum edits, policing edits, and other routing operations. The editor 314 therefore performs required frame/packet transformations to support routing of multi-protocol packets, such as IP, FAST, VPN, MPLS, etc. The editor is described more fully below.
The labeled traffic is ultimately directed to the switch fabric interface 316 through one or more traffic directors 318, 320 and output buffer 322. The traffic director 318 accepts frames from the editor 314, which are then passed to an output buffer 322 and/or the processor buffer 340 via the interface 341. Traffic director 320 accepts frames from the output buffer 322 and the processor transmit buffer 342, and passes the frames to the OIF interface 344 to the switch fabric interface 316.
Referring briefly to the block diagram of
In one embodiment of
It should be recognized that the buffers and memory identified in
Inputs to the editing system 700 include packet/frame input ultimately originating from the pre-processor or the classifier and labeled as the “packet input” 706. Also input to the editing system 700 are the search results 708. These search results provide indices into the editor's 702 instruction memory 704, which is part of a memory 703 such as an SRAM. Policing results 710 from the policer 711 are also input to the editing module 702 to provide, for example, packet color modifications. The editing system 700 outputs modified packets 712, and in one embodiment, outputs the modified (and unmodified) packets to an elastic queue that is accessible by the traffic director.
Based on the search results 708, the editing system 700 retrieves instructions and data from memory 703 to perform corresponding actions. In one embodiment of the invention, the memory 703 and the instruction memory 704 are comprised of SRAM, and together comprise an external, non-embedded circuit to the editing module 702. The memory 703 is accessed independent of the editor itself, and configuration is performed with a register access interface (not shown).
During normal operation, the instruction memory 704 is read via an index provided in the search result 708. The search result 708 includes a “valid flag” indicating the search result is usable, and an “editor use” identifier within the search result 708 data indicating that the editing system 700 is to use the corresponding search result. As editor instructions and associated editor data are read from the external memory 703, they are provided to the editing processor 714. In one embodiment of the invention, the editing processor 714 includes a processing module such as a microprocessor, RISC processor, central processing unit, arithmetic processing unit (ALU), or other processor known in the art.
The editing processor 714 is provided with editor instructions from the instruction memory 704 and associated editor data from the memory 703. The editor instructions are executed to perform packet modifications and provide packet steering information. These instructions include general purpose data manipulation instructions such as write instructions, register swap instructions, etc., and also may include special purpose instructions specifically crafted to perform one or more predetermined operations. Such special purpose instructions may be particularly useful to perform certain networking-specific tasks that depend on the particular networking protocol. For example, specific instructions can be created to “pop” the top label in an MPLS label stack and swap the next MPLS label with a new label. This can be performed through a specifically-created instruction, or alternatively may be performed through a series of more generic instructions. For purposes of example, and not of limitations, example operations corresponding to editor instructions in accordance with one embodiment of the invention are provided in
The editing instructions illustrated in
As can be seen in the example of
With certain editor instructions, associated editor data is provided. This editor data is, in one embodiment, stored with the instruction in the external memory 703. Depending on the editor instruction executed, the width of the editor data may vary. For example, in one embodiment, a 32-bit data segment is used in connection with the Swap, Push, Pop1/Swap, Write 1, and Read-Modify-Write with Default Mask editor instructions. Further, a 64-bit data segment is used in connection with the Swap/Push1, Push2, Read-Modify-Write with Mask, and Write2 editor instructions. Finally, in accordance with this particular embodiment, a 96-bit data segment is used in connection with the Swap/Push2 editor instruction, as three data words are used for the Swap and either Push operations.
Editor instructions, such as those set forth in
The index field 906 indicates various header type encodings. For example, a 0.times.18 may indicate a FAST Modify, a 0.times.1C may indicate an LLC/SNAP push, a 0.times.24 may indicate an MPLS swap, etc. In one embodiment, this field is seven bits to allow for a sufficient number of different currently-known or future types. In another embodiment, the seven bits provide an index into a 128-location memory, such as that shown in
Field 908 is the decrement time-to-live (TTL) field, which identifies whether to decrement an incoming TTL/Hop count. Update (Ud) field 910 identifies an update of IP DiffServ (Differentiated Service) DSCP field to match information carried in the top MPLS label. Analogously, the update (Ut) field 912 identifies an update of IP TTL to match TTL carried in the top MPLS label.
Field 914 is the opcode field in which the instruction operational code is presented. An opcode for each different instruction operation is used, to identify the particular function (such as shown in
Packet direction field 916 provides an indication of the downstream packet direction, such as to drop the packet, direct the packet to the control plane, direct the packet to the data plane, or direct the packet to the control plane and the data plane. The packet direction is applied from multiple search results according to the direction function presented in the direction function field 918. Various direction functions may be applicable, such as an OR function where the packet direction bits in the current instruction are logically “OR'ed” with the other search results, and such as an AND function where the packet direction bits in the current instruction are logically “AND'ed” with the other search results. Another bit code available in the direction function field 918 can cause the packet direction in the current instruction to override the previous search results.
Fields 920 and 922 correspond to per-hop-behavior (PHB) groups. PHB refers to the forwarding treatment given to a specific class of traffic, based on DiffServ criteria. Routers and switches use PHBs to determine priorities for servicing various traffic flows. A PHB group is a set of one or more PHBs that can only be meaningfully specified and implemented simultaneously. This often occurs where a constraint commonly applies to all PHBs in the set, such as a queue servicing or queue management policy. A PHB group provides a service building block that allows a set of related forwarding behaviors to be specified together (e.g., four dropping priorities). Field 920 is the “apply PHB group” which indicates whether to apply a PHB group identified in field 922 to the packet. This forces a new (or initial) DiffServ PHB group onto the packet, and overrides any previous PHB group assignments from preceding search results. The DiffServ PHB group field 922 identifies the PHB group to be applied to the packet. The multi-bit field 922 allows multiple PHB groups to be defined, such as various Assured Forwarding (AF) classes, expedited forwarding (EF), etc.
It should be recognized that the instruction format provided in
The memory 716 is organized into a finite number of segments that may include one or more of the memory locations 718-734. The memory 716 is partitioned such that at least some of these segments are allocated to store data corresponding to certain portions of the packet(s) 706. In one embodiment of the invention, these packet portions correspond to headers of the various protocol layers associated with the incoming packet. For example, header information corresponding to OSI networking layers two through four may each correspond to a segment of the memory 716, such that a segment of memory 716 is allocated to store a layer-2 header (e.g., a PPP header), a segment corresponding to a layer-2.5 header (e.g., an MPLS label stack), a segment corresponding to a layer-3 header (e.g., an IP header), and a segment corresponding to a layer-4 header (e.g., a TCP header). The input controller properly directs this information to the memory 716 based on upstream information developed by a packet classification engine that determines where one networking layer header ends and the next networking layer header begins.
The memory 716 in one embodiment of the invention is a dual-port memory. A dual-port memory can be simultaneously read and/or written by two different data sources, or more generally, a shared memory accessible by two processes. In one embodiment, the data stream is a 64-bit data stream, and the memory 716 is a 32-bit wide, 128-word deep, dual-port memory. In this manner, two 32-bit words may be simultaneously written to the memory 716 to write the 64-bit data. Alternatively, data can be concurrently written to and read from the memory 716. A dual-port memory could also be utilized to streamline the data flow through the editor, for instance, by “overlapping” the input write stage of the processing with the output read stage of the processing. In other embodiments of the invention, a single-port memory may be used, or two physically distinct yet logically coupled memories may also be used. Using a quad-port memory or other multi-port memory will produce analogous results and provide similar advantages.
In accordance with the invention, the allocated segments of memory are interleaved with segments of the memory 716 that are unused during the input stage, each unused segment including one or more of the memory locations 718-734. This allows selected ones of the allocated memory segments to be edited for subsequent serial output. For example, if memory location 718 stores an Ethernet header and memory location 722 stores an IPv4 header, the Ethernet header can be modified by writing a new Ethernet header into an otherwise unused, interleaved memory location 720, and disregarding the original Ethernet header in memory location 718. When the memory locations are read out in the proper order, the new Ethernet header in memory location 720 effectively replaces the original (now-disregarded) Ethernet header at memory location 718. In this manner, editing of packet layer headers can be effectively and efficiently performed.
The present invention also facilitates editing through the use of a valid bit array 750, which includes a field for each of the various memory segments, or memory locations, of the memory 716. Information in each field of the valid bit array 750 identifies whether or not its corresponding memory segment/location is currently housing valid data—that is, whether its corresponding memory segment/location will ultimately be part of the resulting output packet. For example, if the indicators in fields 752, 756 and 758 are set to signify valid data in corresponding memory locations 718, 722 and 724, then the resulting output packet will include the data in memory locations 718, 722 and 724. If the indicator in field 754 is not set, it signifies that the data in corresponding memory location 720 is not to be included with the resulting output packet. Each of the fields in the valid bit array 750 is therefore associated with a portion of the memory 716, in order to indicate whether or not the corresponding memory portion is storing valid data.
Using the valid bit array 750 and due to the interleaving of available memory space with the designated data storage areas, data in the memory 716 may be overwritten, deleted, or added. For example, the data in a memory segment may be overwritten by actually overwriting the data at that memory segment, and keeping the associated indicator in the valid bit array 750 in a state indicating the corresponding data is valid. Alternatively, the data in the memory segment may be effectively overwritten by inserting replacement data in the available memory space proximate the original data, and manipulating the bits in the corresponding fields of the valid bit array 750 such that the original data is no longer “valid” and the newly inserted data is now deemed valid. This is accomplished by setting the indicator in the field of the valid bit array 750 corresponding to the newly inserted data to an asserted state, and setting the indicator in the field of the valid bit array 750 corresponding to the original data to an unasserted state. Further, the data in the memory segment may effectively be “deleted” from consideration in the resulting output packet by setting the indicator in the field of the valid bit array 750 corresponding to the data to be deleted to an unasserted state. As a further example of a modification to data in the memory 716, a new data segment (e.g., a new header corresponding to a new network layer) may be inserted into the reserved, available memory space that was interleaved with the designated data storage areas. For example, assume that memory location 718 stores a PPP header and memory location 722 stores an IPv6 header, an MPLS header can be injected between the PPP header and the IPv6 header by writing the MPLS header into otherwise unused memory location 720.
In one embodiment of the invention, the valid bit array is implemented in one or more registers, where each bit of the register provides the field in which an indicator or flag relating to the validity of the corresponding data may be set or cleared. As will be readily apparent to those skilled in the art from the description provided herein, the number of bits used in each field may be one or more bits, as long as it adequately identifies the status of the data in its corresponding field in the memory 716.
Further, from the description provided herein, it will be readily appreciated by those skilled in the art that data in the memory 716 may be added, deleted, amended, moved, expanded in size, reduced in size, or otherwise manipulated within the memory 716, as long as the appropriate indicators in the valid bit array 750 are appropriately manipulated. For example, the interleaving of unused memory space with the various designated data storage areas (e.g., partitioned to store header data) allows the data in memory location 726 to be expanded to memory locations 726 and 728. This might be the case where a header needs to be modified such that it increases in length. While headers generally have a fixed length, it is conceivable that network layer headers are of variable length, requiring header length expansion, or reduction. The present invention allows for such modifications.
As another example, it may be desirable in some instances to move the data in the memory 716 to a different location, and the interleaved unused memory space facilitates such movement. In some instances, it is conceivable that multiple new headers will need to be inserted between two existing headers, and the existing headers stored in the memory 716 may be moved farther apart to make room for the new headers. As can be seen, a wide range of flexibility and efficiency is provided by the editing configuration of the present invention.
The memory 716 may, in one embodiment, be configured and partitioned such that all header information and data is stored within the memory 716. However, the “data” that is being transmitted generally should not be modified along the way between the source and the destination. This would in effect be corrupting the data, and it is thus generally the case that the data being transmitted will remain unchanged from source to destination. Therefore, a preferred embodiment of the invention includes an additional memory module, illustrated in
Other packet information other than the associated data may also be stored in the overflow memory module 770. For example, the memory 716 may be configured to allow editing of certain, predetermined network layer headers, such as the headers including and between network layer-2 and network layer-4. In this example, headers corresponding to higher network layers (e.g., network layer-5) may remain embedded with the data portion of the packet, thereby being sent to the overflow buffer 770. In this particular example, this also means that headers outside of the layer-2 through layer-4 range are not available for modification at the editor module 702. The particular information allowed to be edited may therefore be configured into the system, such that as much or as little of the packet as desired may be configured or partitioned into the editing memory 716 as dictated by the particular implementation.
After the packet information in memory 716 has been edited, the editor module will reassemble and output the packet. This is accomplished by outputting the information in the memory 716 in the proper order, followed by the data stored in the overflow buffer 770. In one embodiment of the invention, the information in the memory 716 (e.g., network layer header information) is output in an order from lower memory addresses to high memory addresses (or alternatively from high to low memory addresses). The header information in these memory locations 718-734 will therefore be output in the order that it is stored, and only if its corresponding indicator in the valid bit array 750 is asserted. In an alternative embodiment of the invention, additional indicator bits, either associated with the valid bit array 750 or in an independent memory, identify the order in which the memory locations 718-734 will be read out.
In a preferred embodiment, the information stored in memory locations 718-734 will be output in a predetermined order, such as from the lowest memory 716 address to the highest memory 716 address. This corresponds to first outputting the information in memory location 718, then in memory location 720, and so forth, as dictated by the state of the corresponding bits in the valid bit array 750. The valid bit array 750 is read by a priority encoder 772. A priority encoder assigns a code representation to the outputs, represented by line 774 to the output controller 776. Therefore, depending on which of the fields of the valid bit array 750 are set, the priority encoder 772 instructs the output controller 776 to pass information in corresponding memory locations 718-734 to the multiplexer 778. In one embodiment of the invention, the priority encoder 772 is configured as part of the output controller 776.
The output controller outputs the header information stored in the memory 716 in the order dictated by the valid bit array 750 and designated in response thereto by the priority encoder 772. The priority encoder 772 takes a snapshot of the valid bit array 750 when editing is complete to identify the populated memory locations that will form the resulting packet header. The multiplexer 778 passes this resulting header information, and upon reaching the end of the header information, the multiplexer controllably switches to pass the information at its other input, which is fed from the overflow buffer 770. Therefore, the multiplexer 778 first passes the edited header information from the populated, valid memory locations in memory 716. The multiplexer then appends the associated data stored in the overflow buffer 770 to reassemble the packet as a modified packet 712.
Returning again to
One task of the macro sequencer is to perform functions on the data in the memory 716 that it is inefficient or otherwise undesirable to dedicate editor instructions to. The macro sequencer 780 also gathers certain information to make its final adjustments to the data. For example, a particular header, such as an IP header, may include a field for a checksum value. If one or more of the headers in the memory 716 are edited, the checksum value must be updated. Because the editing module 702 operates on streaming data, the macro sequencer operates as a state machine and monitors the activity occurring on the data in the memory 716. When the editor 714 has completed its modifications to the data in the memory 716, the macro sequencer 780 will have monitored the activity, ascertained the new checksum value, and input it into the precise location within the appropriate memory location. Thus, the macro sequencer 780 monitors activity as the editing process continues, and when the editing process is complete, then the macro sequencer performs some “after-the-fact” modifications that it learned throughout the editing process.
There are numerous examples in which the macro sequencer will perform these post-editing-processor modifications. The checksum described above is one example. Another example is the update of the time-to-live (TTL) field of an IP packet header. The TTL field represents an amount of time that the packet has been in the network, and suggests, upon expiration or reaching a predetermined value, that the packet has been in the network too long and should be discarded. The TTL is therefore decremented at each router, thereby requiring special modification of the TTL field in the IP header of the memory 716 after editor 714 manipulation of the data. The TTL generally corresponds to the number of hops that have been encountered by a packet, but can also reflect a particular passing of time. Still other examples in which post-editing-processor modifications will be performed include policing colorations, and packet length. For example, a proprietary packet length may result from the addition of a local header as the packet travels through the router. The addition of a local header changes any packet length fields stored in the header information of the memory 716.
The macro sequencer 780 also works in connection with the policer 711. Generally, network policing allows subscriber bandwidth to be controlled in terms of the contracted service levels that were provisioned and is typically used at the ingress of the network. One manner for policing, for example in an MPLS network, is Single Rate Tri-Color Marker (srTCM) or (trTCM) Two Rate Tri-Color Marker. Tri-Color marking provides a mechanism for marking packets when they exceed the contracted bandwidth.
The srTCM meters a traffic stream and marks its packets according to three traffic parameters, Committed Information Rate (CIR), Committed Burst Size (CBS), and Excess Burst Size (EBS), to be either green, yellow, or red. A packet is marked green if it doesn't exceed the CBS, yellow if it does exceed the CBS, but not the EBS, and red otherwise. The trTCM meters an IP packet stream and marks its packets based on two rates, Peak Information Rate (PIR) and Committed Information Rate (CIR), and their associated burst sizes to be either green, yellow, or red. A packet is marked red if it exceeds the PIR. Otherwise it is marked either yellow or green depending on whether it exceeds or doesn't exceed the CIR. These techniques help manage network congestion at the output link, allowing the right packets to be discarded while facilitating fairness of resource usage.
The policer 711 performs packet conformance functions, and deals with such coloration issues. The macro sequencer 780 is coupled to receive information such as the coloration, and an indication of whether or not to drop the packet, from the policer 711. The macro sequencer can manipulate the appropriate bits in the appropriate header field in the memory 716 in response to coloration issues. For example, if the policer 711 determines that the current packet has exceeded its bandwidth, the policer 711 will provide a particular color to the macro sequencer 780. In response, the macro sequencer 780 modifies the bits in the appropriate network layer header to reflect the particular color, such as by modifying the type of service (TOS) field in an IPv4 header.
Policing may be determined in a manner described herein and in copending U.S. patent application Ser. No. 09/849,914, entitled “System and method For Policing Multiple Data Flows And Multi-Protocol Data Flows,” and copending U.S. patent application Ser. No. 09/849,810, entitled “System And Method For Hierarchical Policing Of Flows And Subflows Of A Data Stream,” both filed concurrently herewith and assigned to the assignee of the instant application, the contents of both being incorporated herein by reference in their respective entireties.
The macro sequencer 780 may therefore be represented by a state machine that is snooping what stage of the editing process is occurring, snooping the incoming data, snooping the actual editing process, collecting input from the policer, and performing final modifications to the stored packet header information before it is output. The macro sequencer 780 allows various specific modifications on the data in the memory 716.
The editor module 702, using at least the policer 711 and the macro sequencer 780, therefore also handles packet dropping for nonconforming packets. The policer 711 informs the macro sequencer 780 when a packet is to be dropped and the macro sequencer 780 in turn directs the editor module 702 to deny passage of the header information in the memory 716 and the data in the overflow buffer 770 to the output stage. Therefore, to drop a packet currently in the memories 716, 770, the corresponding information is not allowed to be output and attention simply turns back to the input stage to receive the next packet and store the packet in the memories 716, 770.
The editor module 702 of
The processing functions described herein in connection with the packet transformation function of the editor module may be performed by one or more different processors. For example, one or more physical chips may correspond to various processing modules of the invention, such as the editing module, input processor, output processor, etc. Alternatively, these functions may be carried out by a single processor configured to perform each of the various functions. In accordance with a preferred embodiment of the invention, these functional elements are embodied on a single physical chip, however various processing modules are embedded therein to perform the described functions.
In accordance with embodiments where various processing modules are employed, whether embedded within a chip or not, a primary control processor may be implemented to help manage and control each of the implemented processing modules. Referring to
The embodiment of
The editor 1104 and primary processor 1102 may be part of a common processing module, or alternatively may be distinct processing modules. For example, in the example of
More particularly, the editor 1104, macro sequencer 1110, input processor 1106, output processor 1108, and the memory 1130 are all coupled to the primary processor 1102. The memory 1130 is analogous to the memory 716 that stores the information that is to be edited, and in the embodiment of
A demultiplexer 1150 receives packet input, and in the present example, separates the header information from the non-header information. The separation need not be between the header and non-header information, but in the present example, all editing is to be performed on header information. Therefore, the header information is recognized by the input processor 1106, which marks the appropriate fields in the valid bit array 1160, and provides write instructions to indicate where in the memory 1130 the primary processor should store the header information. The non-header information (or alternatively, the information that is not to be available for editing) is sent to the buffer 1170.
Upon completion of editing of the header information in the memory 1130, due at least to the editing instructions identified by the editor 1104 and the macro sequencer 1110, the header and non-header information is reassembled into a resulting modified packet. This is accomplished using the output processor 1108 which reads the valid bit array 1160, and initiates forwarding of information in the memory 1130 to the multiplexer 1180 if the state of the valid bit array 1160 dictates the forwarding of that information. The header information, shown in
As described above, the embodiment of
Also supplying information to the primary processor 1202 is the macro sequencer 1210. As earlier described, the macro sequencer 1210 may operate on the data being edited to perform certain predefined specific modifications thereto. Such modifications include updating a checksum value, or a time-to-live (TTL) parameter. Policing colorations and changes to packet length due to the addition of local headers are still other examples in which post-editing-processor modifications will be performed. These, or other, commands 1244, 1246 are written from the macro sequencer 1210 to the primary processor 1202, so that the primary processor can carry out the operations to actually modify the packet, particularly the information stored in the editor memory (not shown).
The primary processor 1202 operates as a state machine, as represented in
Referring first to
As previously discussed, the parsing engine associated with the classifier module (not shown) acts on the incoming packet to produce search results that index editor instructions. For purposes of example, the resulting editor instructions to the editor module in the present example instruct the editor to replace the Ethernet source address field. The Ethernet source address field may need to be modified or replaced since a router at a node declares itself the new source address as the packet is transmitted through the network to the destination.
Since Ethernet addresses are generally forty-eight bits in length, the forty-eight bit Ethernet address is modified to change the Ethernet source address. For purposes of the present example, the editor memory in the present example is a 32-bit wide memory. Therefore, to modify the 48-bit Ethernet source address, one 32-bit operation is performed on the lower thirty-two bits of the address, and a read-modify-write operation is performed on the upper sixteen bits of the address. This is depicted by the memory state block 1320, showing state-A and the modified state-B of the memory 1310. The original state, state-A, has a lower 32-bit field of the Ethernet source address, labeled Ethernet Address-B1, stored at memory location 1322. The modified state, state-B, occurs due to a write command on the lower 32-bit field of the Ethernet source address, resulting in the modified address portion Ethernet Address-B2 stored at memory location 1322. For the upper sixteen bits, the original state-A has an upper 16-bit field of the Ethernet source address labeled Ethernet Address-A1 stored at memory location 1324. To modify only the desired sixteen bits of the thirty-two bit address field, a read-write-modify (RWM) instruction is executed by the editing processor. This results in the modified state-B, shown as the Ethernet Address-A2 stored at memory location 1324.
In this example, the IPv4 header stored at memory location 1314 may also be operated on by the macro sequencer to perform specific modifications after the editor instructions have been executed. For example, a TTL value may be decremented in the TTL field (not shown) of the IPv4 header at location 1314. The checksum value in the IPv4 header may also be updated to reflect the change to the TTL field.
Following macro sequencer modifications, the header information has been fully modified, and is ready to be output from the editor memory 1310. The fields to be output from the memory 1310 are identified by a corresponding indicator in the valid bit array 1330. For example, the valid bit array 1330 of
According to tunneling methodologies, an additional layer will be required in the outgoing packet than that which was present in the incoming packet. Therefore, the instant example is one which the state of the valid bit array changes to identify another one or more memory locations that must be considered in the outgoing modified information. More particularly, the tunneling header is wedged in between two existing header information blocks, using the unused memory space interleaved throughout the editor memory. These changes are more clearly described in connection with the example of
The modifications to the editor memory are illustrated by the memory state block 1420, showing state-A and the modified state-B of the memory 1410. The original state of the particular memory locations, shown as state-A, has no valid information associated therewith. The editing processor executes instructions from the instruction memory, which in the present example includes a series of write instructions. More particularly, the tunneling IPv4 header is written to the editor memory 1410, as depicted by the new state-B in memory state block 1420. As can be seen, memory locations 1422, 1424 and 1426 change from being unused at state-A to storing tunneling IPv4 header information at state-B. More particularly, a write command to write the first two words (IPv4-T-A) of the tunneling IPv4 header is first written to memory location 1422, then another write command writes the next two words (IPv4-T-b) of the tunneling IPv4 header to memory location 1424, and a final write command writes a final word (IPv4-T-c) of the tunneling IPv4 header to memory location 1426. These stored words collectively comprise the tunneling IPv4 header, which resides at memory location 1419. Adding the new tunneling IPv4 header causes an indicator in field 1433 of the valid bit array to be set, thereby confirming its ultimate inclusion in the modified output packet.
In this example, the original IPv4 header stored at memory location 1414 may also be operated on by the macro sequencer to perform specific modifications after the editor instructions have been executed. For example, a TTL value may be decremented in the TTL field (not shown) of the original IPv4 header at location 1414. The checksum value in the original IPv4 header may also be updated.
Following macro sequencer modifications, the header information has been fully modified, and is ready to be output from the editor memory 1410. The fields to be output from the memory 1410 are identified by a corresponding indicator in the valid bit array 1430. For example, the valid bit array 1430 of
Referring now to
The incoming packet 1500 includes various embedded headers including a layer-4 transmission control protocol (TCP) header 1502, a layer-3 internet protocol version-4 (IPv4) header 1504A, a layer-2.5 MPLS header 1506A, and a layer-2 point-to-point protocol (PPP) header 1508. A packet classifier module (not shown) determines where in the packet these different headers start and stop, and the input controller receives this information and writes the packet layers into the editor memory 1510. The packet layers are written to the editor memory 1510, where the PPP header is stored at one or more memory locations 1512, the MPLS header is stored at one or more memory locations 1514, the IPv4 header is stored at one or more memory locations 1516, and the TCP header is stored at one or more memory locations 1518. In accordance with the present invention, available memory locations 1519 may be interleaved with the stored header information.
The modifications to the editor memory are illustrated by the memory state block 1520, showing state-A and the modified state-B of the memory 1510. The original state of the particular memory locations, shown as state-A, includes an MPLS label stack including label MPLS-A at location 1522, label MPLS-B1 at location 1524, label MPLS-C at location 1526, through a finite number of labels represented by MPLS-n at location 1528. The editing processor executes instructions from the instruction memory, which in the present example includes instructions to pop the top MPLS label and swap the next MPLS label with a new MPLS label. This is depicted in the memory state block, where label MPLS-A at memory location 1522 is “popped” off the top of the state-A stack through editor processing of a pop instruction, resulting in no label stored at location 1522 as shown at state-B. A second editor instruction, a “swap” instruction, causes the MPLS-B1 label at location 1524 to be swapped with a new label, shown in modified state-B as label MPLS-B2 at location 1524.
In this example, the IPv4 header stored at memory location 1516 may also be operated on by the macro sequencer to perform specific modifications after the editor instructions have been executed. For example, a TTL value may be decremented in the TTL field (not shown) of the IPv4 header at location 1516.
Following macro sequencer modifications, the header information has been fully modified, and is ready to be output from the editor memory 1510. The fields to be output from the memory 1510 are identified by a corresponding indicator in the valid bit array 1530. For example, the valid bit array 1530 of
A final example is provided in
In this embodiment, the incoming packet 1600 includes various embedded headers including a layer-4 transmission control protocol (TCP) header 1602, a layer-3 internet protocol version-6 (IPv6) header 1604A, a layer-2.5 MPLS header 1606A, and a layer-2 point-to-point protocol (PPP) header 1608. A packet classifier module (not shown) determines where in the packet these different headers start and stop, and the input controller receives this information and writes the packet layers into the editor memory 1610. The packet layers are written to the editor memory 1610, where the PPP header is stored at one or more memory locations 1612, the MPLS header is stored at one or more memory locations 1614, the IPv6 header is stored at one or more memory locations 1616, and the TCP header is stored at one or more memory locations 1618. In accordance with the present invention, available memory locations 1619 may be interleaved with the stored header information.
Some modifications to the editor memory are illustrated by the memory state block 1620, showing state-A and the modified state-B of the memory 1610. The original state of the particular memory locations, shown as state-A, includes an MPLS label stack including label MPLS-A at location 1625, MPLS-B at location 1626, MPLS-C at location 1627, through MPLS-n at location 1628. The editing processor executes a “PopAll” instruction to remove all MPLS labels. This is depicted in the memory state block, where all labels MPLS-A, MPLS-B, MPLS-C, MPLS-D at memory locations 1625, 1626, 1627, 1628 respectively are “popped” from the state-A stack through editor processing of a PopAll instruction, resulting in no label stored at locations 1625, 1626, 1627, 1628 as shown at state-B. At this point, the resulting packet would be PPP/IPv6/TCP. However, the present example also contemplates another editor instruction, which is a write instruction to write one or more words of a local header which is inserted on the editor memory 1610 at location 1624 preceding the layer-2 PPP header. This local header will allow the router to direct the packet through the switch fabric to a specific output port.
In this example, the IPv6 header stored at memory location 1616 may also be operated on by the macro sequencer to perform specific modifications after the editor instructions have been executed. For example, a TTL value may be decremented in the TTL field (not shown) of the IPv6 header at location 1616. Further, the local header of the present example includes a packet length field which can be updated by the macro sequencer after all editor instructions have been executed. A new coloration to the packet based on input from the policer may also be included by the macro sequencer.
Following macro sequencer modifications, the header information has been fully modified, and is ready to be output from the editor memory 1610. The fields to be output from the memory 1610 are identified by a corresponding indicator in the valid bit array 1630. For example, the valid bit array 1630 of
Referring now to
In addition to storing the various packet segments in the modification memory, an instruction memory (which may include a data storage portion) may be called upon to output instructions for modifying the data temporarily stored in the modification memory. Thus, the appropriate editing instructions are indexed or otherwise elicited from the instruction memory, where the particular editing instructions being elicited depends on the characteristics of the packet, as shown at block 1704. For example, if the packet includes an embedded MPLS header, this MPLS header information is a “characteristic” of the packet that may be used to designate the appropriate one or more instructions from the instruction memory. In one embodiment, these characteristics are determined via the classification/parsing engine (e.g., classifier 502 shown in
The indexed editing instructions are processed to execute modification operations on the packet segments in the modification memory. Thus, modifications are effected 1706 as dictated by the indexed editing instructions. A “modification” may include altering existing packet segment data, inserting new packet segment data, deleting or otherwise canceling existing packet segment data, or any other manner of changing the packet data.
In order to identify packet segments to be included in the resulting output packet (whether altered, added, canceled, etc.), validity tags are associated with each of the memory segments of the modification memory, as shown at block 1708. A “validity tag” represents any stored indicator, such as one or more bits in a memory or register field. As previously described, one such embodiment is a valid bit array which includes a plurality of fields, each of which stores a validity tag. In a more particular embodiment provided for purposes of example, each of the individual bits of a register can represent the fields of a valid bit array, such that each bit in the register therefore represents a validity tag.
Upon consideration of a first packet segment as illustrated at block 1710, it is determined 1712 whether or not that packet segment's associated validity tag is set. It should be noted that the particular logical state of a “set” validity tag is not of particular relevance to the invention, and a “set” validity tag may therefore be represented by a high logic state, a low logic state, a bit pattern, or any other such determinable electronic representation. If the validity tag associated with a particular packet segment is set, then that packet segment is included 1714 in the resulting modified packet. If the validity bit is not set, that memory segment is disregarded 1716, i.e., the data at that memory segment is not included in the resulting modified packet. Where more packet segments are stored as determined at decision block 1718, these additional packet segments are considered 1710 to determine whether they too will, or will not, be included in the resulting modified packet. As can be seen, a modified packet is thus created by assembling the packet segments associated with asserted or “set” validity tags.
The foregoing description of the exemplary embodiment of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be limited not with this detailed description, but rather by the claims appended hereto.