Patent Publication Number: US-6904056-B2

Title: Method and apparatus for improved scheduling technique

Description:
FIELD OF INVENTION 
     The field of invention relates to networking, generally; and, more specifically, to an improved scheduling technique and an improved port queuing technique. 
     BACKGROUND 
     User Granularity 
       FIG. 1   a  shows a network  100  having an access node  101   a.  An access node  101   a  acts as an reception point for traffic being sent into the network  100  and a transmission point for traffic being sent from the network  100 . Typically those that are sending/receiving traffic into/from the network may be referred to as “users” of the network. 
     A wide range of different users may exist. That is, some users may send/receive large amounts of traffic to/from the network  100  while other users may send/receive small amounts of traffic to/from the network  100 . For example, the access node  101   a  may be asked to provide access for the traffic from/to a large industrial campus while simultaneously providing access for the traffic from/to a single person within his or her own home. 
       FIG. 1   a  attempts to show a wide range of different users being serviced by access node  101   a.  Note that, as an example, access node  101   a  has four OC- 12  network lines  102   a,    104   a,    115   a,    117   a.  Each OC- 12  network line corresponds to a 622 Mb/s line. The traffic carried by these network lines  102   a,    104   a,    115   a ,  117   a  may be reduced to varying degrees of granularity depending on the users the access node  101   a  is configured to provide access for. 
     For example, in the exemplary deployment of  FIG. 1   a,  network line  117   a  corresponds to traffic being delivered to a single user. As such, the user coupled to network line  117   a  consumes 622 Mb/s worth of traffic. By contrast, note that network line  102   a  provides service for three hundred and thirty six different users. That is, multiplexer  103  reduces the 622 Mb/s network line  102   a  into three hundred and thirty six individual DS 1  lines  106   1  through  106   336  that each provide 1.544 Mb/s worth of service to a different user. 
     Network lines  115   a,    104   a  are reduced into degrees of granularity that fall between the degrees that network lines  117   a  and  102   a  are resolved. That is, multiplexer  116  reduces network line  115   a  into four individual OC- 3  lines that each provide 155.52 Mb/s worth of service to a different user. Multiplexers  105 ,  108 ,  110 ,  112 , 113 ,  114  together reduce network line  104   a  into: 1) two OC- 3  lines  107   1 ,  107   2  that provide 155.52 Mb/s worth of service to two different users; 2) three DS 3  lines  109   1 ,  109   2 ,  109   3  that provide 44.736 Mb/s worth of service to three different users; and 3) eighty four DS 1  lines  111   1  through  111   84  that provide 1.544 Mb/s worth of service to eighty four different users. 
     Thus, noting the wide range of granularity that may exist per network line: network line  117   a  has one user, network line  115   a  has four users, network line  104   a  has eighty nine users, and network line  102   a  has three hundred and thirty six users. Access node  101   a  is responsible for controlling information flow to/from each user on an independent basis (e.g., for proper billing, etc.). Thus, access node  101   a  is responsible for “keeping track of” individual users over a wide spectrum of granularities. 
     Network System Models 
     Various approaches may be used to model the functional layers that exist within a system that implements a node within a network such as access node  101   a.    FIG. 1   b  shows one such model for a networking system  101   b.  Packets are sent over network lines  102   b,    104   b,    115   b,    117   b  and  120   b  (which, as an example, may be viewed as corresponding to network lines  102   a,    104   a,    115   a,    117   a  and  120   a  of  FIG. 1   a ). 
     As discussed, network lines  102   b,    104   b,    115   b,    117   b  and  120   b  correspond to the physical wiring (such as copper cables or fiber optic cables) that emanate from the system  101   b.  Network lines  102   b,    104   b,    115   b,    117   b  and  120   b  are used to physically carry input traffic (i.e., traffic entering system  101   b ) and output traffic (i.e., traffic leaving system  101   b ) from/to other networking systems. 
     Line aggregation layer  190  is used to aggregate the input traffic from network lines  102   b,    104   b,    115   b,    117   b,  and  120   b  and segregate the output traffic to network lines  102   b ,  104   b ,  115   b ,  117   b , and  120   b . An input channel (e.g., input channel  191   a ) is used to carry aggregated input traffic from one or more network lines. For example, input channel  191   a  may be used to carry the input traffic only from network line  120   b . Thus each input channel  191   a,b,c  is a logical structure that carries the traffic arriving to system  101   b  from the channel&#39;s corresponding network lines. 
     The number of network lines that correspond to a particular input channel may vary depending upon the design and/or configuration of a particular system  101   b . Also, one or more input channels (e.g., input channels  191   a,b,c ) may exist, depending on the design point of a particular system. In an analogous fashion, line aggregation layer  190  is also used to segregate all the output traffic to network lines  102   b ,  104   b ,  115   b ,  117   b , and  120   b . As such each output channel  192   a,b,c  is a logical structure that carries the traffic leaving system  101   b  along the logical channels corresponding network lines. 
     Packet aggregation layer  180  is used to form input packets from the input traffic on input channels  191   a,b,c  and effectively send output packets over the output traffic existing on output channels  192   a,b,c.  Various packet forms may be implemented at packet aggregation layer  180 . For example, for ATM related network lines  102   b ,  104   b ,  115   b ,  117   b , and  120   b , AAL 0  and AAL 5  packet types may be recognized at packet aggregation layer  180 . Similarly, packets associated with the Point to Point Protocol, HDLC, Frame Relay and Ethernet may be used, as is known in the art, among others not listed above as well. 
     As an example of the operation of the packet aggregation layer  180 , assume that network lines  102   b ,  104   b ,  115   b ,  117   b , and  120   b  are ATM network lines carrying AAL 5  packets with ATM cells. ATM cells correspond to the traffic on network lines  102   b ,  104   b ,  115   b ,  117   b , and  120   b  and input/output channels  191   a-c ,  192   a-c . Packet aggregation layer  180  forms AAL 5  input packets in the input direction (i.e., cell reassembly) and breaks down AAL 5  output packets in the output direction (i.e., cell segmentation). 
     Within networking/transport layer  160   b , as shown in  FIG. 1 , an input packet is converted into an output packet. Input packets are presented to the networking/transport layer  160   b  by the packet aggregation layer  180  and output packets are presented to the packet aggregation layer  180  by the networking/transport Layer  160   b . Networking/transport layer  160   b  may be responsible for: 1) effectively identifying the networking node that an input packet should be transmitted over when it leaves the system  101   b  as an output packet; and 2) treating the input packet consistently with a service level agreement (SLA), or other service outline, applicable to that packet. For example, if a particular user agrees to a particular rate and quality of service (QoS) for his packets, networking/transport layer  160   b  checks to see if the user&#39;s packet is within the user&#39;s allotted rate and, if so, also prioritizes the packet within system  101   b  consistent with the user agreement. 
     EXAMPLE OF A NETWORKING/TRANSPORT LAYER 
       FIG. 1   c  shows an embodiment of a networking transport layer  160   c  that may be used for the networking/transport layer  160   b  of  FIG. 1   b . Referring to  FIG. 1   c , networking transport layer  160   c  has a packet processing pipeline  130 , output packet organizer  140  and a packet buffer  150  (which may also be referred to as packet buffer memory  150 , buffer memory  150  and the like). 
     In the case of packets that are sent from the service provider to a user (e.g., from network line  120   a  of  FIG. 1   a  to any of the users that access node  101   a  serves), networking transport layer  160   c  regulates the output rate associated with packets being sent from the service provider&#39;s network to a particular user. This may also be referred to as output rate regulation. 
     That is, packets arriving from the service provider&#39;s network (e.g., from network line  120   a  of  FIG. 1   a ) are stored into packet buffer  150  (via input  170   c ) from the packet aggregation layer. The packet aggregation layer also forwards to the pipeline  130   a  packet identifier that acts as reference (e.g., a memory pointer) to the packet being stored in the packet buffer memory  150 . Associated with the packet identifier is information that describes various characteristics of the packet (e.g., its destination address, its size, an indicator of its priority, etc.). 
     The operation of pipeline  130  and output packet organizer  140  affects when the packet will be removed from packet buffer memory  150  to the packet aggregation layer (along output  171   c ). In various packet processing pipeline  130  embodiments applied to the scenario of  FIG. 1   c , packet processing pipeline  130 : 1) identifies which user the packet is to be sent to; and 2) understands the output rate and priority applicable to the packet in order to release it from the networking/transport layer  160   c  at a time that is appropriate for the particular user; and 3) enters the packet identifier into the output packet organizer  140 . 
     Toward the output of pipeline  130 , the placement of a packet identifier into a specific location within the output packet organizer  140  affects when the packet will be released from packet buffer  150 . That is, output packet organizer  140  has locations that correspond or otherwise correlate to the time at which a packet is released from packet buffer  150 . When a packet identifier within output packet organizer  140  is processed, the release of the associated packet from the packet buffer  150  is triggered. This triggering is represented by trigger line  172 . Trigger line  172  may be any address line, control line or other logic used to release a packet from packet buffer  150 . 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is illustrated by way of example, and not limitation, in the Figures of the accompanying drawings in which: 
         FIG. 1   a  shows an example of an access node servicing different users; 
         FIG. 1   b  shows a model of a networking system; 
         FIG. 1   c  shows an example of a networking/transport layer; 
         FIG. 2  shows that the resources of an access node may be viewed as partitioned with respect to the users that are serviced by the access node. 
         FIG. 3  shows a scheduling technique that may be used to properly schedule packets over a wide spectrum of user granularity. 
         FIG. 4  shows an embodiment of an output packet organizer that may be used in implementing the scheduling technique of FIG.  3 . 
         FIG. 5   a  shows a circular, per speed grade link list memory structure that may be used to implement the scheduling technique of FIG.  3 . 
         FIG. 5   b  shows an embodiment of a scheduler that may be used to implement the scheduling technique of FIG.  3 . 
         FIG. 6  shows a methodology that implements the scheduling technique of FIG.  3 . 
         FIG. 7  shows an output port divided into a plurality of queues. 
         FIG. 8  shows a methodology that services an output port having a plurality of queues, such as the output port observed in FIG.  7 . 
         FIG. 9  shows a detailed embodiment of a methodology that corresponds to the methodology shown in FIG.  8 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 2  shows an exemplary access node  200   a  having: 1) three OC- 3  users (that respectively use network lines  201   a  through  203   a ); 2) two DS 3  users (that respectively use DS 3  lines  204   a  and  205   a ); and  3 ) twenty-eight DS 1  users (that respectively use DS 1  lines  206   a  through  234   a ). Note that for simplicity, the access node  200   a  of  FIG. 2  supports a less complex mixture of users as compared to the access node  101   a  of  FIG. 1   a.    
     Note that because the access node has four OC- 3  network lines  201   a  through  203   a  and  235   a , the access node  200   a  may be viewed as having switching or routing resources (which may also be referred to as “resources” or “capacity” or “bandwidth”)  200   b  sufficient to handle approximately 622.08 Mb/s worth of traffic (i.e., 4×155.52 Mb/s per OC- 3  network line 622.08 Mb/s).  FIG. 2  shows these resources  200   b  partitioned according to a ranking of “speed grades” associated with the users that its serves. 
     A speed grade is an amount of bandwidth provided to a user. For example, with respect to the particular example of  FIG. 2 , note that the highest speed grade associated with the user of network line  201   a  is 155.52 Mb/s. According to the perspective of  FIG. 2 , the resources  200   b  of the access node  200   a  are partitioned according to the highest speed grade supported by the node. Because the highest speed grade supported by the node is 155.52 Mb/s and because the node has 622.08 Mb/s worth of resources, there are four partitions  201   b,    202   b ,  203   b , and  235   b  (i.e., 622.08/155.52=4.0). 
     The speed grades supported by the access node are also ranked from highest to lowest (e.g., from left to right as seen in FIG.  2 ). Thus, the first three resource partitions  201   b,    202   b ,  203   b  correspond to the three OC- 3  rate users. Users receiving service at less than the highest speed grade service (e.g., the DS 3  and DS 1  users of  FIG. 2 ) may be viewed as being “handled” within the highest speed grade partition  235   b  that is not associated with a highest speed grade user. Thus, resources devoted to the DS 3  users  204   b ,  205   b  and the DS 1  users  206   b  through  234   b  are shown within the fourth highest speed grade partition  235   b.    
     Scheduling Technique 
       FIG. 3  shows a scheduling technique that partitions each scheduling cycle according to the highest speed grade managed by the node. Scheduling is a process that organizes the forwarding of one or more packets within a node toward a particular user. For example, referring to  FIG. 1   c , scheduling corresponds to the timing in which trigger line  172  authorizes the release of one or more packets destined for a particular user from the packet buffer memory  150  onto output  171   c.    
     For simplicity, the scheduling example provided in  FIG. 3  corresponds to the scheduling performed by access node  200   a  of  FIG. 2  under maximum load conditions. According to the scheduling technique discussed herein, a node&#39;s switching or routing capacity (e.g., its bandwidth “B” as defined, for example, in terms of Mb/s or Gb/s) is viewed as being partitioned according to the highest speed grade managed by the node. 
     The switching or routing performed by a node may be viewed as a cyclical operation.  FIG. 3  shows a number of such cycles (e.g., “cycle  1 ”, “cycle  2 ”, “cycle  3 ”, “cycle  4 ”, “cycle  5 ”, etc.). A highest speed grade counting modulo, x 1 , may be given by:
 
 x   1 =min integer [ B/X]   Eqn. 1
 
where B is the switching or routing capacity of the node and X is the highest speed grade managed by the node. The “min integer” operation effectively equates x 1  to the maximum number of highest speed grade users that could be fully serviced by the node. As such, as described in more detail below, each scheduling cycle is partitioned into regions that are coextensive with the highest speed grade managed by the node; and, each scheduling cycle is coextensive with x 1  such partitions.
 
     For example, with respect to the example of  FIGS. 2 and 3 , the highest speed grade counter corresponds to the “OC 3  Count” seen in FIG.  3 . Here, the highest speed grade “X” managed by the node  200   a  of  FIG. 2  corresponds to an OC- 3  rate (155.52 Mb/s) and the routing or switching capacity “B” of the node  200   a  corresponds to 622.08 Mb/s. As a result, the highest speed grade counting modulo is 4.0 (from equation 1). Thus, as seen in  FIG. 3 , each scheduling cycle has four partitions (e.g., cycle  1  has partitions  301   1 ,  302   1 ,  303   1 ,  304   1 ; cycle  2  has partitions  301   2 ,  302   2 ,  303   2 ,  304   2 ; etc.,). A partition that is coextensive with the highest speed grade is a partition whose amount of data is such that one partition per scheduling cycle corresponds to a data rate that is equal to the highest speed grade managed by the node. For simplicity, except where noted, the phrase “a partition” or “a partition worth of data” is meant to refer to a “a partition worth of data that is coextensive with the highest speed grade.” 
     Partitioning each scheduling cycle according to the highest speed grade managed by the node allows for (as described in more detail below) straightforward bandwidth allocation not only to those users that receive information at the highest speed grade rate, but also those users that receive information at less than the highest speed grade rate (i.e., lower speed grade users). Furthermore, scheduling may be easily conformed to any network configuration and may also be implemented in a programmable fashion. The combination of these features allows for a low cost node that can be easily adapted in the field to schedule traffic for a wide variety of different users and their corresponding speed grades. 
     A user, regardless of speed grade, is serviced by forwarding a partition worth of data for the user. Each partition, as discussed above, is coextensive with the highest speed grade managed by the node. For the highest speed grade users, as developed in more detail below, this corresponds to each highest speed grade user being serviced during each scheduling cycle. However, because a lower speed grade user consumes less bandwidth than the highest speed grade user, a lower speed grade user does not require servicing across each scheduling cycle. 
     As a result, one or more scheduling cycles will occur between consecutive partitions dedicated to the same lower speed grade user. The slower of the lower speed grades have more scheduling cycles between their dedicated partitions than the faster of the lower speed grades. That is, because a partition worth of data is able to “last longer” in serving a slower lower speed grade user (e.g., a DS 1  user in FIG.  2 ), partitions may be spaced farther apart from one another over the course of time. Similarly, because a partition worth of data does not last as long in serving a faster lower speed grade user (e.g., a DS 3  user in FIG.  2 ), partitions are spaced closer together in time. 
     The partition modulo for servicing a particular lower speed grade user, x n , may be calculated according to:
 
x n   =kx   n-1   Eqn. 2
 
where: 1) k corresponds to the number of lower speed grade users that can be serviced by the next highest speed grade (from which the lower speed grade service is derived); and 2) x n-1  corresponds to the partition modulo of the next highest speed grade (from which the lower speed grade service is derived).
 
     For example, referring to the example of  FIG. 2 , note that a pair of DS 3  users (as coupled to DS 3  lines  204   a ,  205   a ) are serviced from an OC- 3  line  235   a . Referring to Equation 2, note that the DS 3  users correspond to the lower speed grade users for whom the partition modulo is to be determined. That is, x n  corresponds to the partition modulo of the DS 3  users, x n-1  corresponds to the partition modulo for the OC- 3  speed on line  235   a  that services the DS 3  users, and k is the number of DS 3  users that can be serviced from an OC- 3  line. 
     In this case, x n-1  corresponds to the partition modulo of the highest speed grade (OC- 3 ) as discussed above. That is, x n-1 =4.0. Furthermore, as a DS 3  service corresponds to a 44.736 Mbps service, three DS 3  users (3×44.736 Mbps=134.205 Mbps) can be serviced by an OC 3  service (which has a capacity of 155.52 Mbps). That is, k=3.0. From Equation 2 then, the partition modulo x n  of the DS 3  users is 12.0=3.0×4.0. 
     Thus, the pair of DS 3  users will be serviced properly if they are each provided a partition worth of data for every 12.0 partitions (i.e., once every three scheduling cycles as there are 4.0 partitions per scheduling cycle). Note that a partition modulo of 12.0 for the pair of DS 3  users has been mapped into the exemplary scheduling pattern of FIG.  3 . That is, as seen in  FIG. 3 , a first of the pair of DS 3  users (“DS 3 _ 1 ”) is serviced in the 1 st , 4 th , 7 th , . . . , etc. scheduling cycles while the second of the pair of DS 3  users (“DS 3 _ 2 ”) is serviced in the 2 nd , 5 th , 8 th , . . . , etc. scheduling cycles. 
     As another example, referring back to  FIG. 2 , consider the 28 DS 1  users that are each respectively associated with lines  206   a  through  234   a . Note that these DS 1  lines are sourced by a third DS 3  line  237  that, in turn, is fed by OC- 3  line  235   a . As such, referring to Equation 2, the DS 1  users correspond to the lower speed grade users for whom the partition modulo is to be determined; and, the DS 3  service associated with line  237  is the next highest speed grade from which the DS 1  users&#39; service is derived. 
     The partition modulo for the DS 3  service, x n-1 , corresponds to 12.0 as discussed just above. The number of DS 1  users that can be serviced by a DS 3  service, k, corresponds to 28.0 (as 28 DS 1  channels are typically carried by a DS 3  service). As such, from Equation 2, the partition modulo for the DS 1  users (x n ) is 336.0=28.0×12.0. Note that a partition modulo of 336.0 has been mapped into the exemplary scheduling pattern of FIG.  3 . This corresponds to a partition worth of data being provided to a particular DS 1  user every 84 scheduling cycles. Thus, as seen in  FIG. 3 , a first of the DS 1  users (“DS 1 _ 1 ”) is serviced in the 3 rd , 87 th , etc. scheduling cycles. 
     Implementation of Scheduling Technique 
     a. Overview 
     Recall the networking/transport layer architecture originally shown in  FIG. 1   c . Referring to  FIG. 1   c , the operation of the pipeline  130  and the output packet organizer  140  affects when a packet will be removed from the packet buffer memory  150  (so as to be forwarded to the packet aggregation layer along output  171   c ). In an embodiment where the scheduling technique discussed above is implemented upon a node architecture that corresponds to  FIG. 1   c , the servicing of a partition corresponds to a partition worth of data being removed from the packet buffer  150  along output  171   c.    
     The release of a partition of data is triggered by the signaling along trigger line  172 . The substantive content of the signaling indicates which data is to be removed from the packet buffer memory  150 . For example, a plurality of memory read addresses may be used to read a series of packets from the packet buffer memory  150  (e.g., where the series of packets correspond to a partition worth of data for a particular user) to effectively service a user as described above with respect to the scheduling technique of FIG.  3 . 
     The placement of a packet identifier (that is issued from the pipeline  130 ) into a specific location within the output packet organizer  140  affects when the packet identifier&#39;s corresponding packet will be released from the packet buffer memory  150 . That is, output packet organizer  140  has locations that correspond or otherwise correlate to the time at which a packet is released from the packet buffer  150 . When a packet identifier within the output packet organizer  140  is processed, the release of the associated packet from the packet buffer memory  150  is triggered. 
     For ease of conception, the discussion of the scheduling technique of  FIG. 3  described each scheduling cycle partition as servicing a particular “user” that communicates with a node. It is important to point out that dedicating each scheduling partition on a “per user” basis is just one embodiment for implementing the scheduling technique discussed above. For example, more generally, each scheduling partition may service a “port” within a node. The various “locations” within the output packet organizer  140  (referred to above) correspond to different ports implemented within the node. 
     In an embodiment, a port may be viewed as a location that: 1) collects packet identifiers for packets having one or more common characteristics (such as a common header parameter and/or other label that characterizes the packet); and 2) has an allocated amount of bandwidth. The ports having the most amount of bandwidth are referred to as the highest speed grade ports, while ports receiving less than this maximum amount are referred to as lower speed grade ports. 
     Consistent with this, as a broader alternative embodiment, the word “port” may replace the word “user” in the description provided above in FIG.  3 . For example, the amount of bandwidth assigned to a port corresponds to the variable X provided in equation 1 (for a highest speed grade port). As such, the node may be viewed as servicing various speed grade ports that have been configured within the node; and, the scheduling cycle may be viewed as being divided into partitions that are coextensive with the highest speed grade port. 
     Recall that a port may not only be assigned a bandwidth but may also collect packet identifiers for packets that have at least one common characteristic (such as a common header parameter or other label that characterizes the packet). As a result, a variety of ports may be implemented within a node so that packets having one or more common characteristics are treated in like fashion (as caused by the manner in which their particular port is constructed and/or serviced). 
     For example, one way of implementing the particular approach described above in  FIG. 3  (where partitions worth of data are provided to each “user”) is to configure each port to collect packet indentifiers for a particular user. As such, packet identifiers may be placed into ports based upon packet header information that is indicative of the packet&#39;s destination (e.g., the IP destination address of the user, the TCP Port ID of the user, a combination of both, etc.). By also configuring the bandwidth allocated to each port to be commensurate with the bandwidth consumed by each user (e.g., a 155.52 Mb/s port bandwidth for an OC 3  user), the servicing of each port corresponds to the servicing of each user as described above in FIG.  3 . 
     In other nodal configurations, ports may be configured to collect packet identifiers based upon header information that is indicative of a packet&#39;s traffic class or priority (e.g., such as the TOS value within an IP header). In other cases, packet identifiers may be placed into ports based upon a label assigned to the packet by the node (e.g., such as a connection identifier used to keep track of the various connections supported by a service provider&#39;s network). In summary, by segregating the flow of packet identifiers into different ports based upon one or more common characteristics shared by their respective packets, the node may be configured in a number of different ways to orchestrate its treatment of different types of packets. 
       FIG. 4  shows an embodiment of an output packet organizer  440  having a plurality of ports  401  through  433 . The particular embodiment of  FIG. 4  corresponds to the example mentioned just above where each port  401  through  433  corresponds to a different user. Thus each port receives packet identifiers for packets that are destined for a particular user. For further simplicity, the particular embodiment of  FIG. 4  corresponds to the exemplary node  200   a  of FIG.  2  and the scheduling example discussed in FIG.  3 . 
     The highest speed grade ports correspond to three ports  401 ,  402 ,  403  that are each provided 155.52 Mb/s of bandwidth. Packet identifiers for packets destined for the first OC 3  user (OC 3 _ 1 ) are entered into port  401 ; packet identifiers for packets destined for the second OC 3  user (OC 3 _ 2 ) are entered into port  402 ; and packet identifiers for packets destined for the third OC 3  user (OC 3 _ 3 ) are entered into port  403 . 
     The lower speed grade ports correspond to: 1) two ports  404 ,  405  that are each provided 44.736 Mb/s of bandwidth to properly control the flow of information to the pair of DS 3  users (DS 3 _ 1 , DS 3 _ 2 ); and 2) twenty eight ports  406  through  433  that are each provided 1.544 Mb/s worth of bandwidth so as to properly control the flow of information to the twenty eight DS 1  users (DS 1 _ 1  through DS 1 _ 28 ). Packet identifiers for packets destined for a particular lower speed grade user are entered into the user&#39;s corresponding port. 
     Packet identifiers identify where their corresponding packet may be found in buffer memory (e.g., a memory read address that points to the memory location where the packet is found). Thus, by releasing a stream of packet identifiers from a port (e.g., along its corresponding trigger line), a corresponding stream of packets are removed from the packet buffer memory. The stream of packet identifiers are used, after their release from their port, to remove their corresponding packets from the packet buffer memory (e.g., a series of read addresses are collected and a memory read is performed for each read address). 
     Scheduler  450  authorizes ports to release a stream of packet identifiers and; as such, controls the timing associated with servicing of the ports. Each authorization from the scheduler  450  (which is presented to a port upon its release line as seen in  FIG. 4 ) authorizes a partition worth of data that is coextensive with a highest speed grade partition to be removed from a port. Each port may be told how much a partition worth of data is (e.g., in terms of how bytes, kilobytes, megabytes, etc.). For example, the scheduler  450  may inform a port upon each authorization or the partition size may be stored as a configuration parameter within the port itself. Upon authorization by the scheduler  450 , a port releases a sequence of packet identifiers whose corresponding collection of packets consume an amount of data within the packet buffer memory that is coextensive with a partition worth of data. 
     In an embodiment, each packet identifier has a “size” parameter that indicates how much data a packet consumes. As such, a port may effectively release a partition worth of data by adding together the packet sizes over all packet identifiers to be released (per authorization), and limiting the released stream of packet identifiers to an amount that corresponds to the partition size. Recalling that each port has an associated bandwidth, note that the frequency at which the scheduler  450  authorizes a particular port to release a partition worth of data corresponds to the bandwidth allocated to the port. In an embodiment, each port has a trigger output that corresponds to trigger  171  of  FIG. 1   c.    
     Before moving on to  FIGS. 5   a  and  5   b , it is important to note that networking architectures other than the particular networking architecture of  FIG. 1   c  may be used to implement the scheduling technique discussed herein. For example, rather than a pipeline, a routing machine (e.g., a processor that executes networking/transport layer software) may be used to forward packet identifiers into their appropriate port. In alternate embodiments, application specific logic designed to perform the routing or switching function may be used in place of the pipeline  130  of FIG.  3 . 
     b. Circular, Per Speed Grade Servicing 
     Together,  FIGS. 5   a  and  5   b  relate to an embodiment  550  of a scheduler that may be used for the scheduler  450  of FIG.  4 .  FIG. 5   a  shows a memory structure  500   a  that may be used for the memory structure  500   b  of  FIG. 5   b . The particular exemplary embodiment of  FIG. 5   a  applies to the nodal configuration discussed so far with respect to  FIGS. 2 ,  3 , and  4 . That is, the memory structure  500   a  of  FIG. 5   a  applies to an 622 Mb/s capacity node having three OC 3  users/ports (i.e., users OC 3 _ 1 , OC 3 _ 2 , and OC 3   — 3 which are respectively handled through ports  1 ,  2  and  3 ); two DS 3  users/ports (i.e., users DS 3 _ 1 , DS 3 _ 2  which are respectively handled through ports  4  and  5 ); and twenty eight DS 1  users/ports (i.e., users DS 1 _ 1 , DS 1 _ 2 , DS 1 _ 28  which are respectively handled through ports  6  through  33 ). 
     The memory structure  500   a  of  FIG. 5   a  includes a data entry for each address where a port and its corresponding user are associated with each data entry. For example the first OC 3  user, OC 3 _ 1 , is represented within the memory  500   a,b  at address  501 . In the embodiment of  FIG. 5   a , associated with each data entry is: 1) a link pointer to the next user/port associated with a circular, per speed grade link list; 2) a port identification (PID) data structure that is used to authorize the release of a partition worth of data from the port that is represented by the data entry (e.g., port  1 /user OC 3   — 1 for address  501 ); and 3) a “done bit” which signifies that the end of a circular speed grade link list has been reached. A discussion of each of these parameters as well as an example of scheduling operation immediately follows. 
     Note that the memory structure  500   a  of  FIG. 5   a  is organized according to circular, per speed grade link lists. That is, the highest speed grade (OC 3 ) has its own associated circular link list; the next highest speed grade (DS 3 ) has its own associated circular link list; and the next highest speed grade (DS 1 ) has its own associated circular link list. A link list is a chain of data entries that are logically strung together by including, within a first data entry, a link pointer that effectively points to a second, next data entry in the chain. 
     For example, as seen in  FIG. 5   a , the data entry for port  1  (which is found at address  501 ) includes a link pointer having the address  502  for the data entry of the second OC 3  user (OC 3 _ 2 ) at port  2 . Thus, the data entries at addresses  501  and  502  correspond to neighboring links in a link list. Furthermore, note that the data entry for port  2  (at address  502 ) has a pointer to the data entry for port  3  (at address  503 ) and that the data entry for port  3  (at address  503 ) has pointer that points back to the data address for port  1  (at address  501 ). The link list is therefore circular as the link points back upon itself. That is, by following the links in the link list, a circular pattern results. 
     Note also that the circular link list described above effectively links all the ports associated with the same, highest (OC- 3 ) speed grade. Furthermore, note that a second circular link list is also formed within memory structure  500   a  that effectively includes all the ports associated with the next highest speed grade DS 3  (i.e., the second circular link list includes the DS 3 _ 1  and DS 3 _ 2  ports that are represented at addresses  504  and  505 , respectively). A third circular link list is also formed within memory structure  500   a  that effectively includes all the ports associated with next highest speed grade (i.e., the third circular link list includes users DS 1 _ 1  through DS 1 _ 28  at ports  6  though  33 , respectively). 
     As such, a circular link list exists for each speed grade managed by the system. Such an arrangement may also be referred to as a collection of circular, per speed grade link lists. The circular per speed grade link list arrangement within the memory structure  500   a  of  FIG. 5   a  effectively controls the circular servicing of each of the users within a particular speed grade. As described in more detail below, the reading of a data entry from the memory  500   a,b  triggers the release of a partition worth of data from the port that the data entry corresponds to. 
     A servicing circle for a particular speed grade corresponds to one complete “run through” of the circular link list within the memory  500   a ,  500   b . For example, in the exemplary configuration and scheduling of FIGS.  2  and  3 : 1) the circular link list for the OC 3  users is run through once for every scheduling cycle (i.e., the data entries at addresses  501 ,  502 ,  503  are each read from once per scheduling cycle); 2) the circular link list for the DS 3  users is run through once for every three scheduling cycles (i.e., the data entries at address  504  and  505  are each read from once per three scheduling cycles); and  3 ) the circular link list for the DS 1  users is run through once for every  84  scheduling cycles (i.e., the data entries at addresses  506  through  533  are each read from once per eighty four scheduling cycles). 
       FIG. 6  shows an embodiment of a scheduling strategy  600  that may be executed by the scheduling logic  510  of FIG.  5 . The scheduling strategy  600  of  FIG. 6  emphasizes the identification of an “active” speed grade. If a particular speed grade is deemed “active”, the next port within the active speed grade&#39;s servicing “circle” is authorized to release a partition worth of data  601 . That is, in the embodiment of  FIG. 5   b , the address corresponding to the next port in the active speed grade&#39;s link list is read from by the scheduler logic  510 . 
     Referring back to  FIG. 3 , observe that separate speed grade counts are provided for each speed grade. The speed grade counts have a modulo provided by Equation 1 (for the highest speed grade) or Equation 2 (for speed grades beneath the highest speed grade). Each speed grade may be viewed as possessing its own count and modulo, where a count “tick” corresponds to the servicing of a partition worth of data. 
     The separate count and modulo for each speed grade may be used by the methodology of  FIG. 6  to control the appropriate circular servicing for each speed grade. As seen in  FIG. 6 , after the next port in the active speed grade&#39;s “circle” has been serviced  601 , an inquiry  602  is made as to whether or not a higher speed grade (relative to the active speed grade) count has timed out. If so, the highest of the speed grades to have timed out is set  604  as the active speed grade. 
     Thus, if a lower speed grade is set as the active speed grade, the methodology  600  of  FIG. 6  allows for a higher speed grade to usurp “active” status once its corresponding count times out. An example of such a case is seen in  FIG. 3  at the transition from the first to second scheduling cycle. That is, partition  304   1  of the first scheduling cycle is devoted to the DS 3 _ 1  user. As such, the DS 3  rate is the active speed grade for this partition  3041 . 
     However, after the servicing of this partition  304   1  the OC 3  count times out (i.e., reaches zero). As a result of the contention resolution strategy  610  of  FIG. 6 , the active speed grade is set to the OC 3  speed grade and the next partition  301   2  is devoted to servicing an OC 3  user. As the last OC 3  user to be serviced was the OC 3   — 3 user (during the servicing of partition  303   1 ), the next user in the OC 3  servicing circle is the OC 3   — 1 user. As such, partition  301   2  is devoted to servicing the OC 3   — 1 user. 
     It is important to point out that the contention resolution strategy  610  of  FIG. 6  is just one of many embodiments that could be employed. Examples of when contention for the switching/routing resources of the node may arise include: 1) a first speed grade is deemed active when another speed grade times out; or 2) two different speed grades have timed out. Generally, the scheduler logic  510  has to “decide” which port to service in light of a speed grade count timeout. This decision may or may not involve a change in the active speed grade. Other contention resolution approaches are described in more detailed below. 
     Note that if the contention resolution strategy does not result in a change in the active speed grade (e.g., the condition of the inquiry  602  is not met because a higher speed grade count has not timed out), a second inquiry  603  is made as to whether or not the servicing circle for the active speed grade has just been completed. That is, has a complete “run-through” of the active speed grade&#39;s servicing circle just been made? If not, the next port in the active speed grade&#39;s servicing circle is serviced  601 . If so, the active speed grade is set  605  to the next lowest speed grade. 
     An example of the former and the later is seen in each of the scheduling cycles of FIG.  3 . As an example of the former (where the speed grade servicing circle has not been completely run through), note that the highest speed grade count (OC 3  count) times out at the end of each scheduling cycle. As such, consistent with the first inquiry  602  and the resetting  604  of the active speed grade to the highest speed grade (as just discussed just above), the first partition in every scheduling cycle (i.e., partitions  301   1 ,  301   2 , . . .  301   x ) is devoted to the servicing of an OC 3  port. 
     After the servicing of an OC 3  port in each scheduling cycle&#39;s first partition  301   x , the first inquiry  601  does not rise to a logical truth because the OC 3  count has just restarted (i.e., the OC 3  count has a value of 3.0 as seen in FIG.  3 ). As such, the active speed grade remains at the highest speed grade and the methodology  600  of  FIG. 6  flows to the second inquiry  603 . The second inquiry  603  also does not rise to a logical truth because only the first port in the highest speed grade circle has been serviced. 
     As described in more detail below, within the embodiment of  FIGS. 3 and 5   a , the “done” bit within each memory structure  500   a  data entry indicates whether or not the servicing of the corresponding port is to be regarded as a completion of the corresponding speed grade&#39;s servicing circle. Better said, after the servicing of a port having a “done” bit value of “1”, the state of the corresponding speed grade&#39;s servicing circle changes from “not completed” to “completed”. As such, the highest speed grade servicing circle is not deemed “completed” until the third port (which serves the third OC 3  user OC 3 _ 3 ) has been serviced. 
     Furthermore, upon the timeout of a speed grade&#39;s corresponding count, the state of that speed grade&#39;s servicing circle changes from “completed” to “not completed”. Thus, according to the operation of the methodology of  FIG. 6  (as observed in FIG.  3 ), the status a speed grade&#39;s servicing circle: 1) changes from “not completed” to “completed” upon the reception of an active “done” bit; and; 2) changes back to “not completed” from “completed” upon a timeout of that speed grade&#39;s corresponding count. Thus, for the OC 3  speed grade in the first scheduling cycle of  FIG. 3 , the OC 3  servicing cycle is deemed “not completed” between times T 0  and T 1  and “completed” between times T 1  and T 2 . As such, the servicing of the first port (which serves the first OC 3  user OC 3 _ 1 ) is deemed the start of each OC 3  servicing circle. 
     After the first port has been serviced (which corresponds to the servicing of partition  301   x ), the second inquiry  603  is therefore a logical false. As a result, the next port in the active speed grade circle is serviced. That is, port  2  is serviced (via partition  302   x ) so as to service the second OC 3  user: OC 3 _ 2 . Again, after servicing port  2 , both the first and second inquiries  602 ,  603  are a logical false. As a result, the last port in the active speed grade circle is serviced. That is, port  3  is serviced (via partition  303   x ) so as to service the third OC 3  user: OC 3 _ 3 . 
     Thus according to the operation of the methodology  600  of FIG.  6  and the example of  FIG. 3 , within each scheduling cycle, the highest speed grade “circle” is completely run through after the servicing of the third partition  303   x . After the third partition  303   x  is serviced, the first inquiry  602  is a logical false (because the highest speed grade count is a 1.0 (i.e., has not timed out) as seen in FIG.  3 ). The second inquiry, however, is a logical truth because the highest speed grade circle (being the active speed gra circle) has just been completed. As such, the active speed grade is set  605  the next lowest speed grade. 
     The next lowest speed grade in this case corresponds to the DS 3  speed grade. Note that when the active speed grade is set  605  to the next lowest speed grade, the second inquiry  603  is reasked. This allows for the servicing of an even lower speed grade if the next lowest speed grade has already completed its servicing circle. Thus, in some cases the next lower speed grade remains as the active speed grade while in other cases an even lower speed grade may be set as the active speed grade. 
     An example of the former may be observed in the first and second scheduling cycles of FIG.  3 . During the first and second scheduling cycles, after the servicing of the third partition  303   1  and  303   2 , the second inquiry  603  results in a logical truth as discussed just above. That is, the highest speed grade has completed its servicing circle. As such, the active speed grade is set  605  to the DS 3  speed grade and the second inquiry  603  is re-asked. 
     As discussed above, the transition as to where the DS 3  servicing circle starts and ends is signified by the presence of the “done” bit in the memory architecture  500   a  of  FIG. 5   a . As the “done” bit resides in the data entry corresponding to the second DS 3  port (i.e., user DS 3 _ 2  in this example) at address  505 , the DS 3  servicing circle is not deemed “completed” until the second DS 3  port is serviced. Furthermore, the DS 3  service is deemed “not completed” because, as seen in  FIG. 3 , the DS 3  count had timed out at time T 0 . 
     As such, the DS 3  speed grade servicing circle is deemed “not completed” after the third partition  303   1  and  303   2  have been serviced in either of the first or second scheduling cycles. That is, in the case of the first scheduling cycle (after the servicing of partition  303   1 ), the first DS 3  port has not yet been serviced; and, in the case of the second scheduling cycle (after the servicing of partition  303   2 ), the second DS 3  port has not yet been serviced. As a result, in both of these instances, the re-asking of the second inquiry  603  results in a logical false. 
     In response, the first DS 3  port (which corresponds to the first DS 3  user: DS 3 _ 1 ) is serviced with the fourth partition of the first scheduling cycle  304   1  while the fifth port (which corresponds to the second DS 3  user: DS 3 _ 2 ) is serviced with the fourth partition of the second scheduling cycle  304   2 . An example of where the re-asking of the second inquiry  603  results in a logical truth (so as to set the active speed grade to even lower speed grade) may be seen in the third scheduling cycle of FIG.  3 . 
     After the servicing of the highest speed grade with the third partition  303   3  of the third scheduling cycle, the methodology of  FIG. 6  flows to the second inquiry  603 . In this case, as discussed above, the highest speed grade circle has been completed and the second inquiry  603  results in a logical truth. As such, the active speed grade is set  605  to the next lowest speed grade which corresponds to the DS 3  speed grade. 
     The second inquiry  603  is reasked. Here, however, a logical truth results because (as of the servicing of partition  303   3 ) the DS 3  scheduling circle has been completed. That is, as there are two DS 3  users, both were serviced through the previous two scheduling cycles. Because the re-asking of the second inquiry  603  results in a logical truth, the active speed grade is set to the next lower speed grade with respect to the DS 3  speed grade. That is, the active speed grade is set to the DS 1  speed grade. 
     The second inquiry  603  is again re-asked. Again, the transition as to where the DS 1  servicing circle starts and ends is signified by the presence of the “done” bit in the memory architecture  500   a  of  FIG. 5   a . As the “done” bit resides in the data entry corresponding to the twenty eighth DS 1  port (i.e., user DS 1 _ 28  in this example) at address  533 , the DS 1  servicing circle is not deemed “completed” until the twenty eighth DS 1  port is serviced. 
     Furthermore, the DS 1  service is deemed “not completed” because the DS 1  count had timed out as of time T 0 . Thus, in this case, the inquiry  603  with respect to the DS 1  servicing circle results in a logical false and; as such, causes the first DS 1  port to be serviced  601  with partition  304   3 . The pattern observed over the first three scheduling cycles is essentially repeated, with the exception that the last partition (e.g., the partition that is positioned analogous to partition  304   3 ), over the course of execution by the scheduler logic  510 . 
     The partition that is positioned analogous to partition  304   3  services the next DS 1  user in the DS 1  servicing cycle. Eventually, after the 84 th  scheduling cycle, the twenty eighth DS 1  user (DS 1 _ 28 ) will be serviced as seen in partition  304   84  of FIG.  3 . In this example, under full load conditions, the pattern of the  84  scheduling cycles observed in  FIG. 3  will then be repeated over the following scheduling cycles. 
     c. Implementation of Circular, Per Speed Grade Servicing 
     Referring to the memory structure  500   a  of  FIGS. 5   a , note that each data entry has an associated port identification (PID) value. When a data entry is read from the memory structure  500   a ,  500   b , the data entry&#39;s PID value is used to authorize the release of a partition worth of data from the port that corresponds to the PID value. Note that the actual packet data may be released from a packet buffer memory and that the actual flow of information from a port may correspond to a flow of packet identifiers that point to the packets to be released from buffer memory. The phrase “release of a partition worth of data from a port” and the like may be construed as to include such an approach. 
     For example, in the embodiment of  FIG. 5   a , PID 1  is used to release a partition worth of data from port  1  (for the first OC 3  user OC 3 _ 1 ); PID 2  is used to release a partition worth of data from port  2  (for the second OC 3  user OC 3 _ 2 ); PID 3  is used to release a partition worth of data from port  3  (for the third OC 3  user OC 3 _ 3 ), etc. In the embodiment shown in  FIG. 5   b , the PID value corresponds to a multiplexer  520  “channel select” value. The channel select value determines which port (of the ports configured in the node) is sent a release signal that effectively authorizes the release of a partition worth of data from the port. 
     That is, for example, the PID 1  value enables the “Port  1 ” output of multiplexer  520  (which would trigger the release of a partition worth of data from port  401  of FIG.  4 ); the PID 2  value enables the “Port  2 ” output of multiplexer  520  (which would trigger the release of a partition worth of data from port  402  of FIG.  4 ), etc. In an alternate embodiment, the PID data structure is routed to the appropriate port (in response to its value). Regardless, when an address for a particular port is offered to the memory  500   a ,  500   b , the PID value read from that address is used to release a partition worth of data from the port that corresponds to the PID value. Each port  401  through  433  may be realized with an organized memory or register structure (e.g., where each port corresponds to a region of a memory or register). The scheduler  450  may be implemented as a processor that runs software or as a logic circuit (or as a combination of both) that has an understanding of the memory organization for the ports and reads or otherwise authorizes the release of a proper number of packet identifiers from the proper memory or register location(s) to the release line according to the scheduling technique methodology described above. 
     Coupled to the PID value within each data entry, as shown in  FIG. 5   a , is the aforementioned: 1) link pointer to the next data entry in the circular link list for the speed grade to which the PID value belongs; and 2) the “done” bit value that indicates whether the port marks the end of the speed grade servicing circle. When a data entry is read from the memory  500   a ,  500   b , the PID value is forwarded to the multiplexer  520  (to release a partition worth of data from the port represented by the PID value) while the link list pointer and “done” bit are forwarded to the scheduler logic  510 . 
     In the embodiment of  FIG. 5 , the scheduler logic  510  keeps track of information that is sufficient to execute the methodology of FIG.  6 . For example in an embodiment the scheduler logic  510  keeps track of, for each speed grade: 1) the next port to be serviced according to the circular servicing approach discussed above; 2) the status of each circular service (i.e., “completed” or “not completed”); and  3 ) contention resolution information such as whether or not a higher speed grade count has timed out. 
     In order to keep track of the next port to be serviced according to the circular servicing approach, the scheduler logic  510  may be designed to maintain storage space (e.g., either internal or external register or memory space) for each speed grade. Recall that the next port to be serviced in the circular link list (for a particular speed grade) is stored as a link pointer in the data entry that corresponds to the prior port. Thus, as the PID value for a particular port is being read from memory, the address for the next port (at the same speed grade) is simultaneously being read. 
     By accepting and storing this address for the next port, the scheduler logic  510  is able to keep track of the next port to be serviced for a particular speed grade. Thus, whenever the speed grade becomes active, the scheduler logic  510  can refer to this stored address and use it to perform a memory read. Once an address is used it may be flushed and replaced with the new, next address for that speed grade as it is received from the read operation. By storing an address for each speed grade, the scheduler logic  510  can easily change to any new active speed grade and continue its proper circular service. 
     The status of the circular service for each speed grade (i.e., “completed” or “not completed”) may be determined, as described above, in light of the reception of the “done” bit and the count for each speed grade. Thus, the scheduler logic  510  may be designed to store the modulo value for each speed grade as well as perform the corresponding count for each speed grade. When the count for a particular speed grade times out, the status of the circular service for that speed grade may be deemed “not completed”. Furthermore, as discussed above, when a “done” bit value of “1” is observed during a memory read, the scheduler  510  may be designed to recognize that the servicing circle for the speed grade has just been “completed”. 
     It is important to note the ease at which new ports (and their corresponding users) may be configured into a networking system that employs the scheduling approach discussed above. That is, a new port may be entertained for a new user by simply upgrading the memory structure  500   a . For example, the number of DS 3  users may be expanded simply by inserting another data entry into the memory and configuring the link pointers of the DS 3  speed grade to effectively include the new entry into the servicing circle (e.g., by modifying a present link pointer entry to point to the new data entry; and, having the new data entry link pointer maintain the value originally held by the data entry being modified). 
     Similarly, a port or user may be easily removed from service by simply cutting a data entry out of its speed grade link list circle. For example, by modifying the link pointer entry that points to the data entry to be removed so as to, instead, point to the data entry that is pointed to by the data entry to be removed, the data entry to be removed is removed from the speed grade servicing circle. As the ports themselves may be implemented as organized memory or register structures (as discussed above), ports may also be easily added or removed as well. 
     Note that the particular resource contention resolution approach  610  of  FIG. 6  effectively serves higher speed grades at the expense of slower speed grades. For example, if a node is configured to be oversubscribed (i.e., the aggregate bandwidth of all the ports/users it handles is greater than the routing or switching bandwidth of the node), higher speed grade users may not suffer any detriment in service while lower speed grade users may be completely starved. This follows from the fact that the contention resolution methodology  610  of  FIG. 6  automatically changes the active speed grade to the highest, timed out speed grade. 
     Alternate contention resolution embodiments may exist. For example, in an approach that more evenly distributes the service degradation associated with over subscription, the contention resolution methodology may instead decide to change the active speed grade to the speed grade having the port or user that has waited the longest time after its count has timed out and was not serviced within the speed grade count (i.e., a speed grade count expired before all of its users or ports could be serviced). 
     d. Port Queuing 
       FIG. 7  shows an embodiment of a port  700  that may be used for any of the ports  401  through  433  shown in FIG.  4 . That is, for example, if port  701  of  FIG. 7  corresponds to the first port  401  of  FIG. 4 , release line  409  of FIG.  4  and release line  709  of  FIG. 7  may be viewed as the same release line. Similarly, trigger line  408  of FIG.  4  and trigger line  708  of  FIG. 7  may be viewed as the same trigger line. Note also that, referring to  FIG. 5   b , release line  509  may correspond to release lines  409  and  709  of  FIGS. 4 and 7 , respectively. 
     As mentioned above, release line  709  effectively provides port  700  with authorization to release a partition worth of data. As such, after this notification, a series of packet identifiers (e.g., that each point to a memory location where a packet may be found) flow from one or more of queues  701  through  705  to the output  708  of the port. As discussed above, the emission of a packet identifier along the port output  708  triggers the release of a packet (e.g., from a packet buffer memory). The combined total size of all the packets that are released from the packet buffer memory corresponds to a partition worth of data. 
     Each packet identifier that is placed into the port (via the port input  707 ) is stored into a particular queue. For example, in an embodiment, each packet identifier not only points to a packet but also signifies which of the port queues  701  through  705  the packet identifier should be stored within. Referring to  FIG. 1   c , in an embodiment, integrating a “queue id” as part of a packet identifier is part of the processing that is performed by the packet processing pipeline  130 . 
     In an embodiment, each port queue  701  through  705  corresponds to a different priority. That is, for example, port queue priority increases from right to left (thus port queue  701  corresponds to the highest priority queue and port queue  705  corresponds to the lowest priority queue). Packet identifiers stored in higher priority queues generally experience less delay than packet identifiers stored in lower priority queues. That is, packet identifiers that are stored in higher priority queues tend to be released from their respective queue (and forwarded to port output  708 ) after having “waited” for less time than other packet identifiers that are stored in lower priority queues. 
     As such, if a port is provided for each user, the networking system is able to differentiate the traffic being sent to the same user. For example, a user may be interested in receiving both traditional data traffic (e.g., emails, files, etc.) and real time traffic (e.g., a live telephone call conversation). As real time traffic generally requires low latency while traditional data traffic is usually indifferent to the amount of latency, packet identifiers that point to packets associated with real time traffic may be placed in a high priority queue while packet identifiers that point to packets associated with traditional data traffic may be placed in a lower priority queue. 
     In one embodiment, there are five port queues  701  through  705  as seen in FIG.  7 . As such there are five different priority levels. One queue, such as the highest priority queue  701 , may be used to hold packet identifiers that point to networking control packets. Networking control packets are used for networking maintenance purposes (e.g., upgrading network topology information, failure reporting, etc). 
     In an embodiment a queue, such as the second highest priority queue  702 , is used to store packet identifiers that point to packets associated with a user&#39;s “real time” traffic. As discussed, “real time” traffic is traditionally viewed as a “live” transaction where the failure to quickly receive information results in poor communication. Examples include a “live” telephone conversation or video conference. 
     Verbal communication between people can become disruptive if there exists too long a latency between the speaking of a first person and the listening of a second person. As such, a network attempts to send this type of information through a network “faster” than other types of information (e.g., within 1.0 second or less or within 0.1 second or less). In an embodiment, queue  702  may be used to store packet identifiers that point to this type of traffic. 
     In an embodiment a queue, such as the third highest priority queue  703 , is used to store packet identifiers that point to a user&#39;s “fast data” traffic. Fast data traffic may be characterized as being somewhere between “real time” traffic and “traditional” data traffic. As such, fast data traffic corresponds to traffic that should have lower latency than traditional data traffic but does not necessarily require the low latencies of real time traffic (e.g., less than a few seconds or less than a minute). Examples include Automatic Teller Machine transactions or credit card transactions. In these applications, for example, a customer typically does not mind waiting a few seconds or minutes for his/her transaction. As such, a corresponding latency is appropriate. 
     In an embodiment a queue, such as the fourth highest priority queue  704 , is used to store packet identifiers that point to a user&#39;s traditional data traffic. Traditional data traffic is traffic that is relatively indifferent to the latency through the network. As such, latencies beyond a few minutes or higher may be acceptable. Examples include various files and e-mail traffic. 
     In an embodiment a queue, such as the lowest priority queue  705 , is used to store packet identifiers that point to “best effort” traffic. Best effort traffic is, typically, traffic that has exceeded a user&#39;s allocated bandwidth or otherwise goes beyond the resources of the network or networking system. Note that in various embodiments, however, a best effort queue (e.g., queue  705 ) may be configured to store packet identifiers that point to a user&#39;s traditional data traffic as well. 
     This may allow for multiple grades of “fast traffic”. For example, packet identifiers for a first, higher priority fast traffic may be stored in the third highest priority queue  703 ; packet identifiers for a second, lower priority fast traffic may be stored in the fourth highest priority queue  704 ; and packet identifiers for traditional data traffic and best effort traffic may be queued together in the lowest priority queue  705 . Note that the above examples provided for the temporal characteristics of each type of traffic (e.g., less than a second for “real time” traffic) are exemplary and may vary from embodiment to embodiment. As such, other embodiments are possible that exist outside the ranges provided above. 
     In an embodiment the packet processing pipeline  130  of  FIG. 1   c  is able to identify the type of traffic that each packet identifier corresponds to and, in response, integrate the proper queue id into each packet identifier. It is important to point out that other embodiments are also possible (as to both the number of queues and the types of traffic that are effectively queued by them). 
     As discussed above, the port bandwidth is controlled by controlling how often a partition worth of data is released from the port. In an embodiment, a partition worth of data, P, may be expressed as:
 
P=XT  Eqn.3
 
where X is the rate of the highest speed grade serviced by the node and T is the amount of time consumed per scheduling cycle. For example, referring to  FIG. 3 , T corresponds to the temporal width of each scheduling cycle (i.e., the temporal distance between T 2  and T 0  for the first scheduling cycle) and X corresponds to a rate of 155.52 Mb/s.
 
     Thus, for a scheduling cycle width of 1 second (i.e., T=1 sec), a partition worth of data P corresponds to 155.52 Mb of data. In this case, the release of a partition worth of data corresponds to a number of packet identifiers flowing from the port output  708  where the combined size of all the packets pointed to by the flow of packet identifiers is 155.52 Mb. As another example, for a scheduling cycle width T=0.001 sec, a partition worth of data P is 155.52 Kb. In this case, the combined size of all the packets pointed to by the flow of packet identifiers from the port output  708  will be 155.52 Kb. 
     It is important to point out, however, that the phrase “a partition” or a “partition worth of data”, with respect to port queuing, may not only correspond to “a partition worth of data that is coextensive with a highest speed grade” (as explicitly defined in Equation 3) but also may correspond to “an amount of data”. That is, in one embodiment, the discussion of port queuing discussed herein with respect to  FIGS. 7 ,  8  and  9  may be used to support the scheduling technique discussed with respect to  FIGS. 3 ,  5  and  6  (as evident from Equation 3). 
     However, the discussion of port queuing discussed herein with respect to  FIGS. 7 ,  8  and  9  may also be used to support other scheduling techniques that simply provide an amount of data for a port to release (i.e., that does not necessarily correspond to an amount that is coextensive with a highest speed grade). As such, with respect to port queuing, use of the term “partition” and the like should not be construed as being automatically limited to include the scheduling technique outlined with respect to  FIGS. 3 ,  5 , and  6 . 
     In an embodiment that may be implemented with the approach of  FIG. 7 , each queue  701  through  705  is given a “weight” that corresponds to a service rate that it will receive. That is, the amount of bandwidth given to a particular port may be viewed as being subdivided. Each subdivision of the port&#39;s bandwidth may be used to service a particular port queue. Thus, assigning a unique weight to a queue may be achieved by assigning to a queue a fixed amount of data that it may release for each authorization received on the release line  709 . 
     The fixed amount of data, which may also be referred to as a sub-partition P x , may be expressed as:
 
P x =wt x P; for x=1 to N  Eqn. 4
 
where: 1) P x  is the sub partition for queue “x”; 2) wt x  is the port bandwidth sub division that is given to queue “x” (e.g., as expressed in decimal percentage terms); and 3) N is the number of queues that are given a guaranteed percentage of the port&#39;s bandwidth. For example, if each of the queues  701  through  705  of  FIG. 7  are given 20% of the port&#39;s bandwidth, then (from Equation 4) the sub partition allocated to each queue is 0.2P.
 
     As such (from the examples just above), for a scheduling cycle of T=1 sec employed by the exemplary node that was discussed with respect to  FIGS. 2 through 5 , each queue is allocated a sub partition of 31.104 Mb (i.e., 155.52 Mb×0.2=31.104 Mb); and, for a scheduling cycle of T=0.001 sec, each queue is given a sub partition of 31.104 Kb. Thus, in the former case, each queue  701  through  705  can release a flow of packet identifiers (for each authorization received upon release line  709 ) that point to a series of packets whose combined size corresponds to 31.104 Mb. This corresponds to a permitted flow of 155.53 Mb worth of data from all of the queues combined. 
     Thus, to review, each queue can be configured with a priority and a bandwidth. Higher priority queues generally have lower latency than higher priority queues. Latency is a function of the offered load and service rate for each queue. Generally, latency increases as the offered load to a queue increases and/or the service rate from a queue decreases. Thus, a queue&#39;s latency increases as the number of packet identifiers it receives over time (i.e., its offered load) increases and/or the sub division of the port bandwidth that it receives (i.e., its service rate) decreases. 
     In an embodiment, the node or networking system is configured to limit traffic flows assigned to a higher priority queue such that the combined rate of these flows does not exceed the port bandwidth sub division allocated to the higher priority queue. Here, as the maximum offered load to the queue is less than its service rate, the latency through the higher priority queue is minimal. In a further embodiment, the node is configured such that the combined rate of traffic flows assigned to a lower priority queue may exceed the sub division of port bandwidth allocated to the lower priority queue. As the maximum offered load to the queue may be greater than its service rate, the latency through the lower priority queue will increase as the ratio of offered load to service rate rises. 
     The queue scheduler  706  is responsible for controlling, from each queue  701  through  705 , the appropriate flow of packet identifiers per authorization received on release line  709 .  FIG. 8  shows a methodology that may be employed by the queue scheduler  706  of FIG.  7 . As seen in  FIG. 8 , upon the reception of an authorization to release a partition worth of packets, the scheduler  706  effectively distributes  801   a  partition worth of bandwidth to the queues according to their weight. A partition worth of bandwidth corresponds to the service rate provided to the port as a whole. 
     In one approach, the queue scheduler  706  maintains the sub partition P X  that is allocated to each queue (as expressed in Equation 4) as well as maintains the total partition worth of data, P. For example, in an embodiment, the queue scheduler has associated storage space  711  (e.g., an internal or external register or memory location) that keeps track of the sub partition P X  for each queue as well as the total partition P. Upon the reception (from release line  709 ) of an authorization to release a partition worth of data, the queue scheduler  706  reads the information from the storage space. 
     In an alternate embodiment, the storage space  711  maintains the weight for each queue wt x  and the total partition size (P) is stored in the queue scheduler&#39;s storage space  711 . In this case, upon the reception of an authorization to release a partition worth of data, the queue scheduler  706  calculates (rather than simply reads) the sub partition Px for each queue. In another alternate embodiment, the authorization received on release line  709  takes the form of a binary word having a value that corresponds to the total partition size (P). In this case, the storage space  711  only needs to store the sub partition (or weights) for each queue. 
     Referring to  FIGS. 7 and 8 , once the queue scheduler  706  has possession of the sub partitions allocated to each queue (which may be viewed as a form of distribution of the entire partition), it initiates the consumption  802  of the distributed partition worth of bandwidth, at the populated queues, according to their priority. That is, those queues having at least one packet identifier (i.e., a populated queue) are serviced in accordance with their priority. 
     In an embodiment, the priority of a queue is reflected not only in its latency but also in its servicing position with respect to other queues. That is, a higher priority queue is serviced by the scheduler  706  before a lower priority queue is serviced. For example, if the priority ranks from highest to lowest from left to right in  FIG. 7  (i.e., queue  701  is the highest priority queue and queue  705  is the lowest priority queue), a queue is serviced by the scheduler  707  only after those populated queues on its left have been serviced to the extent of their sub partition. 
     As such, with respect to the embodiment of  FIG. 7 , the consumption  802  of the distributed partition worth of bandwidth is implemented by servicing the populated queues, from left to right, to the extent of the sub partition for each. For example, if queue  701  and  703  through  705  are populated (i.e., only queue  702  is empty), queue  701  is serviced to the extent of its sub partition P 1 , then queue  703  is serviced to the extent of its sub partition P 3 , then queue  704  is serviced to the extent of its sub partition P 4  and then queue  705  is serviced to the extent of its sub partition P 5 . 
     Again, servicing a queue to the extent of its sub partition corresponds to controlling the flow of packet identifiers from the queue such that the combined size of all the packets pointed to by the flow is approximately the same as the sub partition allocated to the queue. As this activity effectively consumes the port bandwidth that was distributed to the queue, servicing a queue to the extent of its sub partition corresponds to the consumption of a piece of the distributed partition worth of bandwidth that is allocated to the port as a whole. 
     As described in more detail, initially consuming  802  the distributed partition worth of bandwidth, at the populated queues, in accordance with their priority effectively breaks the queue servicing into two components: 1) a first component devoted to the providing of a “guaranteed” amount of bandwidth to one or more queues (as configured through their weights); and 2) a second component devoted to providing any excess bandwidth (should it exist) to the queues (e.g., according to a fairness routine). Referring to  FIG. 8 , the first component corresponds to methodology  802  while the second component corresponds to methodology  803 . 
     For configurations where the combined total of the queue weights add to a value of 1.00 or less, the sub-partitions may be viewed as a guaranteed amount of service that is provided to its corresponding queue—regardless of its priority. Here, as the combined total of the queue weights add to a value of 1.00 or less, the combined data total of all the sub partitions adds to no more than the total partition of data, P, that is serviced from the port as whole. Thus, focusing initially on the servicing of each queue&#39;s sub-partition ensures that lower priority queues receive their guaranteed amount of service even under heavy traffic loading conditions. 
     In alternate configurations, the combined total of all the queue weights may add to a value that is greater than 1.00. Here, as the combined total of the queue weights add to a value greater than 1.00, the combined data total of all the sub partitions is greater than the total partition of data, P, that is serviced from the port as whole. In a sense, the port is “oversubscribed”. Under modest traffic loading conditions, the over subscription may not be noticeable because various queues may be empty (i.e., unpopulated) or only slightly populated (i.e., the offered load to the port is less than the partition P provided to the port). 
     As such, the queues still enjoy their guaranteed service rate. Under heavy traffic loading conditions, however, the over subscription may cause some queues to receive less than their guaranteed service rate. Nevertheless, the priority aspect of the servicing (i.e., where higher priority queues are served to the extent of their sub partition before lower priority queues) guarantees the service rate of the higher priority queues “up to” a combined queue weight of 1.00. 
     That is, starting from the highest priority queue and working downward (e.g., to the right as seen in FIG.  7 ), each queue is fully serviced to the extent of its sub partition before the next lower priority queue is serviced. Eventually the total amount of data that has been released corresponds to a full partition and the servicing of the port as a whole stops. In this case, those queues that fall within the first 1.00 of combined total queue weight still enjoy their guaranteed service rate. 
     Thus, by initially servicing the queues to the extent of their sub partition in light of their priority, the highest priority queues are guaranteed their “configured for” service rate in all cases. Furthermore, in cases where the combined queue weight is less than 1.00, all of the queues are guaranteed their “configured for” service. Whether the combined weights are greater than or less than 1.00 (as well as how the weights are distributed), is a decision made available to those who configure the node. 
     Note that, in one embodiment, a strict round robin approach can be emulated by the port as a whole if the queue weights are set identically to one another and add to a combined value of 1.00. In cases that deviate from this approach (i.e., where queue weights are individually tailored), the overall port behavior may correspond more to that of a weighted fair queue. 
     Regardless of how the queue weights are distributed, in various instances there may be “unused” bandwidth remaining after each of the populated queues have been serviced to the extent of their sub partition. For example, if a particular queue is experiencing light loading conditions, it may be unpopulated or (although populated) may have less stored traffic than its sub partition allows. 
     In the former case, no queue service transpires while in the latter case the servicing corresponds to less than a full sub partition. As such, after all the populated queues have been serviced to the extent of their sub partition (note that the phrase “to the extent of their sub partition” may be read as “to no more than a full sub partition”), the combined size of all the packets pointed to from the resulting flow of packet identifiers may be less than a full partition worth of data P. 
     As such, the difference between a full partition worth of data P and the combined size of all the packets that have been pointed to may be viewed as “unused” bandwidth. This unused bandwidth may then be applied to one or more populated queues that exist within the port. As such, as seen in  FIG. 8 , the second component of queue servicing involves the servicing  803  of remaining populated port queues (e.g., coextensively) with any unused bandwidth. 
     In various instances, the unused bandwidth helps “clear out” a queue who has just experienced an exceptionally high offered load. For example, if a queue suddenly receives a large number of packet identifiers, the guaranteed service rate (as fulfilled by the servicing of a full sub partition) may not be sufficient to empty out the queue. In this case, the application of any unused bandwidth to the queue will help reduce the population of the queue. 
     In an embodiment, the unused bandwidth is applied “fairly” to all the queues. For example, in one approach, a “round robin” pointer is kept by the queue scheduler  706 . Whenever unused bandwidth arises from an authorization to release a partition worth of data, the queue scheduler  706  applies the unused bandwidth to the queue that is pointed to by the round robin pointer. The round robin pointer is then incremented so as to point to the “next” queue (e.g., queue  704  is queue  703  is being serviced with the unused bandwidth). 
     Once the queue originally pointed to by the round robin pointer is empty, the queue scheduler  706  applies the unused bandwidth to the “next” queue (as its currently specified by the round robin pointer) and increments the pointer again. In many cases, eventually, the unused bandwidth is completely consumed such that a full partition worth of data is serviced from the port. At this point, the servicing of the port is completed. 
     The next amount of unused bandwidth (that arises from a following authorization to release a partition worth of data) will be applied to the queue specified in the round robin pointer. In alternate embodiments, the unused bandwidth may be applied in a less fair manner. For example, rather than a strict round robin approach, higher priority queues may be serviced with the unused bandwidth more frequently than the lower priority queues (e.g., in a weighted fashion as discussed above). 
       FIG. 9  shows a possible, more detailed, embodiment of portions of the methodology outlined in FIG.  8 . Specifically, flow  902  of  FIG. 9  may be viewed as an embodiment of flow  802  of FIG.  8 . Also, flow  903  of  FIG. 9  may be viewed as an embodiment of flow  803  of FIG.  8 . In the approach of  FIG. 9 , the queue scheduler  706  controls the proper release of packet identifiers from the various queues by maintaining: 1) a “queue count” for each queue that counts the size of the packets being released from the queue (recalling that packet identifiers may be configured to specify the size of the packet that it refers to); and 2) a “total count” that counts the size of the packets being released from the port as a whole. 
     The queue count is used to control the first (“guaranteed”) component of a queue&#39;s servicing as described above. Here, a queue&#39;s sub partition size P X  is used to limit the queue count. That is, initially the queue count is set equal to the queue&#39;s sub partition size. The queue count counts down by an amount that corresponds to the size of a packet effectively released from the queue (e.g., as measured in bytes). Once the queue count reaches zero, the queue scheduler  706  understands that a full sub partition for the queue has just been serviced. 
     The “total count” is used to terminate the servicing of a port after it services the queues in response to an authorization to release a partition worth of data. Here, the port&#39;s full partition size P is used as a limit on the total count. That is, initially the total count is set equal to the full partition size P. The total count counts down by an amount that corresponds to the size of each packet that is released from the port. Once the total count reaches zero, the queue scheduler  706  understands that a full partition worth of data has been serviced from the port. 
     As discussed above, after the queue scheduler  706  receives authorization to release a partition worth of data, the queue scheduler  706  obtains an understanding of the individual sub partitions to be applied to each queue. This activity effectively distributes a full partition worth of bandwidth to the individual queues and corresponds to the START methodology seen in FIG.  9 . That is, the methodology of  FIG. 9  assumes that the authorization to release a partition worth of data has already been received and that the queue scheduler  706  has already distributed the full partition of bandwidth to the individual queues. 
     The scheduling methodology can emphasize the identification of an “active” queue who is currently being focused upon for servicing. Thus, after receiving authorization to release a partition worth of data, the queue scheduler  706  sets the active queue  905  to the highest priority, populated queue whose queue count is greater than zero (if such a queue exists). The queue scheduler  706  may be configured to inquire as to the population and count status of each queue before declaring an active queue; or, may simply refer to the highest priority queue and declare it active if these conditions are met. 
     The active queue is then serviced  906 . That is, a packet identifier is released from the queue and emitted from the port output  708 . The queue count and total count are decremented in proportion to the size of the packet effectively released from the queue. If the total count reaches or falls below zero the servicing of the port is terminated  907 . If the total count is greater than zero, the active queue is serviced again  906  provided that the queue count is greater than zero  908 . The process iterates until the queue count reaches or falls below zero (or the queue becomes empty). At this point, a full sub partition has been serviced from the active queue 
     Note that some queue counts may fall below zero as a result of this methodology. In an embodiment, the negative queue counts are “deficit adjusted” on the following authorization. For example, if a particular queue has a sub partition size of P X  and the queue count falls below zero to a value of −Z (which stops the servicing of that queue); upon the next authorization to release a partition worth of data for that port, the queue count value is initially set to P X −Z (rather than P X ) so that the integrity of the bandwidth configured for that queue is maintained. 
     After a full sub partition has been serviced from the active queue, the queue scheduler  706  sets the active queue to the next highest priority populated queue whose queue count is greater than zero  905 . The process of continually servicing the next highest priority, populated queue (to the extent of a full sub partition of data) continues until the total count reaches or falls below zero or until each queue given a sub partition has either  904 : 1) had its queue count reach or fall below zero; or 2) become empty. 
     At this point, the first servicing component (i.e., the guaranteed service rate component) is complete. As such, if any unused bandwidth remains (i.e., the total count is greater than zero), the active queue falls to the next populated queue  909 . Note that the scheduler may be configured to have a round robin pointer that points to the next queue to be serviced with unused bandwidth. 
     If the queue that is pointed to is unpopulated, the round robin pointer is incremented until a populated queue is pointed to (which then becomes the active queue). The populated queues are then serviced in round robin fashion until the total count reaches or falls below zero. In an embodiment, if every queue is empty before the total count reaches of falls below zero, the servicing of the port terminates and the unused bandwidth is simply disposed of. 
     The queue scheduler  706  may be designed with logic that performs consistent with the methodology described above. The queues may be implemented as link lists within a memory device. For example, in one embodiment, each packet identifier data entry in the memory includes a pointer to the next packet identifier in the queue. Thus, the scheduler logic  706  can service the queues by reading a packet identifier from a memory device. The address for the next packet identifier in the queue is grasped by the queue scheduler  706  while the memory is being read. 
     Referring to  FIG. 7  note that the queues  701  through  705  may be implemented as organized memory or register structures. That is, for example, a first queue (e.g., queue  701 ) corresponds to a first memory or register region, a second queue (e.g., queue  702 ) corresponds to a second memory or register region, etc. The queue scheduler  706  may be implemented as a processor with software or as a logic circuit (or combination of both) that implements the queue servicing processes and methodologies just described above. 
     Note also that embodiments of the present description may be implemented not only within a semiconductor chip but also within machine readable media. For example, the designs discussed above may be stored upon and/or embedded within machine readable media associated with a design tool used for designing semiconductor devices. Examples include a netlist formatted in the VHSIC Hardware Description Language (VHDL) language, Verilog language or SPICE language. Some netlist examples include: a behaviorial level netlist, a register transfer level (RTL) netlist, a gate level netlist and a transistor level netlist. Machine readable media also include media having layout information such as a GDS-II file. Furthermore, netlist files or other machine readable media for semiconductor chip design may be used in a simulation environment to perform the methods of the teachings described above. 
     Thus, it is also to be understood that embodiments of this invention may be used as or to support a software program executed upon some form of processing core (such as the CPU of a computer) or otherwise implemented or realized upon or within a machine readable medium. Note also that, the methodologies described above may be implemented as a software program and executed by a processor (e.g., microprocessor, collection of microprocessors, embedded processor, etc.). A machine readable medium includes any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computer). For example, a machine readable medium includes read only memory (ROM); random access memory (RAM); magnetic disk storage media; optical storage media; flash memory devices; electrical, optical, acoustical or other form of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.); etc. 
     In the foregoing specification, the invention has been described with reference to specific exemplary embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention as set forth in the appended claims. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.