Abstract:
A rapid method and apparatus for remapping the type of service (TOS) and source address information from an incoming communications packet according to the desired Quality of Service (QoS) required for the communications flow into a switch or router are described. The input source address field of the packet header is used to access a lookup table of corresponding source autonomous system (AS) labels. The appropriate AS label is combined with the input TOS yielding an intra-switch TOS optimized for the QoS appropriate to the received flow. Alternatively, the netID, a subset of the source address, may be used directly without resort to a lookup table. As a further alternative, the destination address may be used in conjunction with the above. The resulting intra-switch TOS expedites packet management and throughput in the switch/router, facilitating the efficient delivery of the required Quality of Service for that flow.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to internetworking systems and in particular to methods and apparatus for managing traffic flow and quality of service in routers and switches. 
     2. Description of the Related Art 
     Internetworking encompasses all facets of communications between and among computer networks. Such communications data flow streams may include voice, video, still images, and data traffic. All have widely varying needs in terms of propagation delay (or latency) during transit through the network. Various systems and devices, both in hardware and in software, have attempted to deal with the plethora of data flow requirements present in modern internetworking systems. 
     A particular problem in internetworking traffic regulation arises from the variety of traffic sources or flows presented to the router/switching device. Referring to FIG. 1, illustrating a high-level schematic view of the operation of a prior art router/switch  100 , a number of input flows  110  are presented to the unit. These flows each consist of multiple packets of data in a variety of sizes and presented at a variety of rates. Flows may also be presented in different protocols, such as the Transmission Control Protocol/Internet Protocol (TCP/IP) and the related User Datagram Protocol (UDP), File Transfer Protocol (FTP), Terminal Emulation Protocol (Telnet), and Hypertext Transfer Protocol (HTTP). Other protocols are found in the literature, such as Merilee Ford, et. al.,  Internetworking Technologies Handbook  (Cisco Press 1997) (hereinafter Ford), incorporated herein by reference in its entirety. The packets are buffered in a buffer pool  120 , which is typically random access memory (RAM). Buffering is accomplished according to the directives of a controller  130  and a buffer manager  140 . The flows are sent to the proper output port  150  by way of a set of output queues  160  and a port scheduler  170 . Controller  130 , buffer manager  140 , and port scheduler  170  are conventionally implemented as one or more high speed microprocessors with associated interface circuitry. 
     Quality of Service (QoS) is an attribute of the flow in a given data interchange, i.e., a specification placed on the internetworking devices participating in a communications session controlling the timeliness or latency of the communications. Several methods are known in the prior art for configuring QoS in a network, such as the Resource Reservation Protocol (RSVP) described in Chapter 41 of Ford. 
     One such scheme for ensuring QoS, known as Committed Access Rate (CAR) service, consists of attempting to regulate the traffic within the router or switch connecting multiple networks in the typical internetworking system. Such schemes attempt to provide fair allocation of data throughput capacity (bandwidth) by allocating router buffer and/or queue space according to the type of packets in each flow stream received. A user is, in essence, sold a certain bandwidth, “B.” Flows from that user are not allowed to exceed bandwidth B except when the flows have been consistently less than B for some period of time. Then, and only then, will the switch allow burst traffic (i.e., traffic with bandwidth greater than B) to pass. 
     Of course, QoS is only useful if there are multiple queues (input and/or output) wherein packets in one queue are given preferential treatment over packets in another queue. In such systems, a method of optimizing queue assignments that allows this differentiated service to be guaranteed (and thus sold to users) is needed. 
     FIG. 2 illustrates the standard bit configuration for an Internet Protocol packet, including the fields within its header. Flow type, also known as flow classification, information can be found in, for instance, the type of service (TOS) field  210  in the internet protocol (IP) header  200  or in the source address  220  of the received packet. It can also be deduced from the type of packet received, voice being of a higher priority and thus demanding of a larger buffer count than other flows. While dynamic buffer limiting (DBL) is known, current schemes are unable to update their limit values fast enough to keep up with the latest generation of ultra-fast (e.g., Gigabit speed) flows. 
     As an additional drawback, the use of TOS field  210  is not standardized among internetworking users. Many competing standards, in fact, exist to define how the TOS octet is interpreted. 
     Examples of competing definitions are found in P. Almquist,  Type of Service in the Internet Protocol Suite , Internet Request for Comments (RFC) 1349 (July 1992); D. Eastlake III,  Physical Link Security Type of Service , RFC 1455 (May 1993); and K. Nichols, et al.,  Definition of the Differentiated Services Field  ( DS Field )  in the IPv 4  and IPv 6  Headers , RFC 2474 (December 1998), all incorporated herein by reference in their entireties. Thus, neither TOS nor source address is a reliable means of identifying flow type at this time. 
     Source address  220  is a 32-bit value that describes the source of the IP packet. Since the Internet Protocol is connection-less, i.e., data is transmitted onto the network without first establishing an explicit “connection” between sender and receiver, each packet must contain both the full address of the sender and of the recipient. The content and use of the information contained within IP packet header  200  is described in further detail in K. S. Siyan,  Inside TCP/IP  (New Riders Publishing, 3d ed. 1997) (hereinafter Siyan), incorporated herein by reference in its entirety. 
     The source address consists of two fields, a network ID and a host ID. The network ID is n bits long (minimum of 8 bits, originally in 8 bit increments, e.g., 8, 16, or 24 bits) and identifies the sending network or “autonomous system” (AS). The autonomous system (AS) is an independently managed network of host computers within an interconnected network of networks. The host ID is (32−n) bits and identifies the particular host computer within the sending AS. 
     The source address clearly provides an indication of the sender, but, by itself, it does not reveal the priority or required timeliness (i.e., the QoS specified by the sender) for the flow. Indeed, in the modern network, certain flows are actually aggregations of many lower rate flows, each potentially having its own QoS requirement. For example, the Internet backbone carries flows consisting of consolidated traffic from one Internet Service Provider (ISP) to another ISP. Within this aggregated flow are individual packets from multiple discrete flows such as a Voice-over-Internet Protocol (VoIP) call between two users, an HTTP request, and an FTP download. Each packet has its own latency limitation requirement, yet all are within the same ISP-to-ISP aggregated flow. Simply classifying the aggregated flow based on its source address (or AS label) is not sufficient to efficiently allocate switch resources and provide the desired packet level QoS. 
     A further drawback in the prior art lies in the fact that while all packets within an autonomous system (by definition) use the same TOS field definition, those definitions frequently do not cross AS boundaries. In other words, at the AS-to-AS connection, TOS field meanings are lost. 
     Thus, in the era of high volume aggregated flows containing packets with numerous divergent QoS requirements, prior art per-flow classification systems are unable to provide the necessary packet-tailored QoS to satisfy users. Such systems are known as “policy” routing schemes for their method of directing resources to flows based on external system administrator decisions on the appropriate flow QoS. Policy routing can define a limited number of custom routing paths for selected packets based on certain criteria (such as source address or physical flow input port). For instance, particular traffic flows, such as VoIP, may be sent over special routes that minimize hop counts and other delay characteristics well-known in the art to ensure high QoS. An example of an element of policy routing is Committed Access Rate (CAR) service, discussed above, wherein three bits in the TOS field  210  are used to identify the packet based on a classification according to certain limited criteria. However, the rules for these policy routing decisions are set a priori (for the most part) by the system administrator and are not flexible and adaptable enough to accommodate the extremely high bandwidth of backbone-level, carrier class (ISP-to-ISP) traffic. Also, mechanisms such as CAR are perceived to be too slow to handle ultra-high bandwidth flows. 
     What is needed is a method to rapidly and adaptably remap packet header data so that the queuing and forwarding portion of the switch/router can efficiently deliver the packet-wise desired quality of service to ultra-high bandwidth, carrier-class flows. 
     SUMMARY 
     The present disclosure provides a method and apparatus for rapidly remapping the type of service (TOS) and source address information from an incoming packet according to the desired Quality of Service (QoS) required for that flow. Both the input TOS bits and the source address data are used to compute an intra-switch TOS value (the “internal identifier”) that helps expedite packet management and throughput. The input source address field of the packet header is used to access a lookup table of corresponding source autonomous system (AS) labels. The appropriate AS label is combined with the input TOS yielding an intra-switch TOS internal identifier optimized for the QoS appropriate to the received flow. 
     In an alternate embodiment, the AS label is refined into a peer group number that indexes one of a predetermined set of TOS/AS label transforms to map the incoming packet TOS directly onto the appropriate intra-switch TOS internal identifier. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present disclosure may be better understood, and its numerous objects, features, and advantages made apparent to those skilled in the art by referencing the accompanying drawings. 
     FIG. 1 is a high-level schematic representation of the data flow and control in a prior art switch/router. FIG. 1 is also used to illustrate the invention, where prior art circuitry within the blocks is replaced with circuitry in accordance with the invention. 
     FIG. 2 is a bitmap of a prior art Internet Protocol (IP) packet showing the fields within its header. 
     FIG. 3 is a high-level flow chart representation of TOS remapping, according to one embodiment of the present invention. 
     FIG. 4 is a high-level flow chart representation of a destination AS processing alternate embodiment of the present invention. 
     FIG. 5 is a high-level flow chart representation of a peer grouping alternate embodiment of the present invention. 
     FIG. 6 is a top-level schematic of one embodiment of the present invention. 
     FIG. 7 is a top-level schematic of an alternate embodiment of the present invention. 
    
    
     The use of the same reference symbols in different drawings indicates similar or identical items. 
     DETAILED DESCRIPTION 
     Overview 
     FIG. 3 is a flow chart of one embodiment of the present invention. Incoming packet header  200  (FIG. 2) is parsed  300  to extract type of service field  210  and source address  220 . Source address  220  consists of 32 bits, representing the network ID (netID) and host ID of the sender. As discussed above, the netID (also referred to as the autonomous system [AS] number) can be readily extracted from the source address by means well known in the art. See, e.g., Sivan; John Postel,  Internet Protocol , Request for Comments (RFC) 791 (September 1981) (defining internet addressing protocols and conventions) and W. Richard Stevens,  TCP/IP Illustrated , Vol. 1 (Addison Wesley 1994), both incorporated herein by reference in their entireties. 
     The extracted netID (AS number) then indexes  310  a table  315  containing predetermined autonomous system labels corresponding to each unique netID. This list is defined by the system administrator and stored in the switch memory. It can be updated by the system administrator at any time. As there are a smaller number of AS labels than unique netIDs, fewer bits are required to hold the AS label. Typically, the AS label set defines the “nearest neighbor” autonomous systems connected to a particular switch/router. 
     In one embodiment, the high order 16 bits of the source address are used as the AS number and mapped (by lookup table  315 ) to a label of less than 16 bits. In one embodiment, the 16 bit AS number is mapped to an 8 bit AS label. One of ordinary skill in the art will recognize that a variety of mappings of the source address  220  or portions thereof to a smaller number of bits representing a unique autonomous system are possible. Accordingly, the present invention is not limited to any one mapping or to AS labels of any particular length. 
     In an alternate embodiment, the netID is used directly in subsequent processing, i.e., the AS label equals the entire AS (netID) number. While this embodiment requires more bits to hold the longer netID, it uses fewer switch memory resources since it eliminates the need for AS label lookup table  315 . Additionally, this alternate embodiment requires less processing time. 
     In yet a further alternate embodiment, the AS label mapping table  315  is updated automatically as the local routing tables are updated by methods well-known in the art. As the routing tables are updated, AS label table  315  is updated to reflect “new” nearby autonomous systems (i.e., those newly identified in the routing table). In this way, the correspondence between source AS and the AS label used to create an intra-switch TOS is dynamically updated. 
     Next (in any of the foregoing alternate embodiments), the AS label or, in the alternate, the netID, is combined  320  with TOS  210  to form an index to intra-switch TOS (IS-TOS) lookup table  325 . Intra-switch TOS lookup table  325  contains a limited set of internal TOS (also referred to as “internal identifiers”) values, represented by substantially fewer bits than the strict concatenation of input TOS  210  and the AS label (or netID). In other words, intra-switch TOS lookup table  325  maps multiple input TOS/AS label combinations to a single intra-switch TOS value. 
     Combination  320  is a function of parameters input TOS  210  and the derived AS label (or, alternatively, the netID). The combination is, in one embodiment, a simple concatenation of the fields, such as: 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Source AS Label 
                 TOS 
               
               
                   
                   
               
             
          
         
       
     
     Alternatively, the TOS may come first, occupying the high order bits. The ordering of the AS label and TOS fields is not important. The fact that both the TOS information and the derived AS label (or netID) are combined in the IS-TOS lookup index is what is significant in this embodiment. Accordingly, the invention is not limited to any one string of fields in the intra-switch TOS lookup index. 
     The resulting intra-switch TOS value  330  (also referred to as the “internal identifier”) is then used to determine packet queuing  340 . Queuing may be accomplished according to any of several schemes known in the art, such as Committed Access Rate (CAR) or weighted fair queuing (WFQ). The intra-switch TOS serves as a standardized priority (or precedence) identifier for the queuing decisions. It is not passed out of the switch when the packet is transmitted; rather, it is used internally by the switch to make queuing decisions and does not supersede or overwrite input TOS  210  in packet header  200 . 
     Although a switch and/or router is described, those skilled in the will art realize that communications systems other than routers and switches can be used. Accordingly, the invention is not limited to any particular type of communications or internetworking device. Likewise, while numerous examples are given in the context of Internet Protocol devices and methods, persons of ordinary skill in the art will also recognize that the present disclosure is equally applicable to communications protocols other than the Internet Protocol. Accordingly, the present invention is not limited to any particular protocol. 
     FIG. 6 shows a simplified schematic block diagram of one embodiment of the present invention. Remapper  600  comprises parser  610 , address-to-label mapper  620 , combiner  630 , TOS remapper  640 , and IS-TOS table  650  connected as shown in FIG.  6 . In one embodiment, remapper  600  forms part of controller  130 , shown in FIG.  1 . Remapper  600  (and controller  130  ) may be implemented in either conventional hardware circuitry or in computer instructions (e.g., software or firmware) executed by a computer system. 
     Computer instructions implementing the method of the present invention may be embodied in any computer readable media including but not limited to magnetic disks, magnetic tape, optical storage such as CD-ROM, and a carrier wave containing digital signals representing the computer instructions. 
     Incoming packets are parsed by parser  610  to extract the packet source address and TOS fields. The source address is mapped to an autonomous system (AS) label in address-to-label mapper  620 . As discussed above, many mappings are possible, including a direct mapping, i.e., AS label =source address. 
     The AS label and the TOS field are combined in combiner  630  to form an index. TOS remapper  540  uses this index to read the intra-switch TOS (IS-TOS) value from IS-TOS table  650 . The IS-TOS value is then used to control packet queuing in output queues  160  by means well-known in the art. 
     Destination AS Processing Alternate Embodiment 
     The intra-switch TOS may also be determined by using a combination of three input parameters: input TOS  210 , source AS label (or source netID), and destination AS label (or, alternatively, destination netID). FIG. 4 is the flowchart corresponding to this alternative embodiment. Destination address  230  (referring to FIG. 2) is extracted by parse step  400 , in addition to input TOS  210  and source address  220 . Processing proceeds analogously to FIG. 3, though here both the source and destination AS labels (or netIDs) are used to independently index  410  AS label lookup table  415 . Since the number of autonomous systems typically encountered in backbone-level high bandwidth internetworking is relatively small, and because such autonomous systems both send and receive, a single lookup table  415  will suffice. 
     As a further alternative, the process may also be accomplished using the destination netID itself, avoiding the use of AS label lookup table  415  at the cost of additional bits in the computations. As in the discussion of source AS to AS label mapping above, various other mappings are also possible and accordingly the present invention is not limited to any particular mapping. 
     Next (in any of the foregoing alternate embodiments), both the source and destination AS labels or, in the alternate, the netIDs, are combined  420  along with TOS  210  to form an index to intra-switch TOS lookup table  425 . Intra-switch TOS lookup table  425  contains a limited set of internal TOS values, represented by substantially fewer bits than the strict concatenation of input TOS  210  and the source and destination AS labels (or netIDs). In other words, intra-switch TOS lookup table  425  maps multiple input TOS/AS label combinations to a single intra-switch TOS value. 
     The resulting intra-switch TOS value (internal identifier) is then used to determine packet queuing. As above, queuing may be accomplished according to any of several schemes known in the art. 
     Combination  420  proceeds as combination  320  above, though with a third parameter, the destination AS label (or netID). Combination  420  is, in one embodiment, a simple concatenation: 
     
       
         
               
               
               
             
           
               
                   
               
             
             
               
                 Source AS Label 
                 Destination AS Label 
                 TOS 
               
               
                   
               
             
          
         
       
     
     As discussed above, other orderings of the resulting intra-switch TOS  330  are possible as well. Accordingly, the invention is not limited to any one sequence of fields in intra-switch TOS  330 . 
     Referring to FIG. 6, in this alternate embodiment both the packet source address (SA) and the packet destination address (DA) fields are parsed out of the incoming packet in parser  610 . Address-to-label mapper maps both the SA and DA to a source AS label and a destination AS label, respectively. Both of these AS labels are then combined with the TOS field in combiner  630  and processing proceeds as described above. 
     Peer Grouping Alternate Embodiment 
     As a further alternative, the AS label (derived from any of the above-described mappings) may be used to define a peer group number, shown in FIG.  5 . The peer group number, consisting of the AS label only, is used to select from a predefined list of mappings that convert input TOS  210  directly into an intra-switch TOS. This alternative is possible when the source address is known to the switch as one that consistently uses input TOS field  210  in a predictable manner, i.e., a sender who applies a known, standard meaning to the packet TOS bits. Because the switch is programmed with the TOS bit definitions used by these peer groups, as identified by specific AS labels, a direct TOS mapping is possible. 
     This alternative is potentially the most efficient, as it requires the least overhead and resources to remap the TOS received in an incoming packet. 
     FIG. 7 shows a simplified schematic block diagram of this alternate embodiment. Parser  710  extracts the TOS and packet address fields as above. The AS label is determined in address-to-label mapper  720  by any of the above-defined mappings. Transform selector  720  selects the corresponding TOS transform function by using the resulting AS label to index a list of possible functions. Transformer  740  applies the selected function to the extracted TOS field to determine the IS-TOS value. As above, the IS-TOS value is then used to control packet queuing by means well-known in the art. 
     Software Alternate Embodiments 
     While the above-disclosed method may be embodied in a computer system apparatus (i.e., hardware), one of ordinary skill in the art will appreciate that other embodiments in the form of computer readable instructions for carrying out the disclosed method are equally possible. Such computer readable instruction forms are generally known in the art as such as software or firmware. Accordingly, the present invention is not limited to a particular hardware form of computer system or apparatus. Consequently, in one alternate embodiment the present invention is realized in computer instructions for carrying out the disclosed method on a general purpose digital computer. In a further alternate embodiment of the present invention, a computer readable storage medium comprising the above-mentioned computer instructions is provided. In a still further alternate embodiment, a computer readable carrier wave comprising computer instructions for carrying out the disclosed method is provided. 
     Conclusion 
     The techniques described herein rapidly and adaptably remap packet header data so that the queuing and forwarding portion of the switch/router can efficiently delivery the packet-wise desired quality of service to ultra-high bandwidth, carrier-class flows. 
     While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from this invention in its broader aspects and, therefore, the appended claims are to encompass within their scope all such changes and modifications as fall within the true spirit and scope of this invention.