rfc3289.txt

RFC 的详细文档！

   Assured Forwarding PHB suggests that all traffic marked AF11, AF12 or
   AF13 be placed in the same queue, after metering, without reordering.
   To accomplish that, the upstream diffServAlgDropNext pointers each
   point to the same diffServQEntry.

   A common requirement of a queue is that its traffic enjoy a certain
   minimum or maximum rate, or that it be given a certain priority.
   Functionally, the selection of such is a function of a scheduler.
   The parameter is associated with the queue, however, using the
   Minimum or Maximum Rate Parameters Table.

   When the MIB is used for configuration, diffServQNextFree always
   contains a legal value for diffServQId that is not currently used in
   the system's configuration.

3.5.2.  diffServSchedulerTable - The Scheduler Table

   The scheduler, and therefore the Scheduler Table, accepts inputs from
   either queues or a preceding scheduler.  The Scheduler Table allows
   flexibility in constructing both simple and somewhat more complex
   queuing hierarchies from those queues.

   When the MIB is used for configuration, diffServSchedulerNextFree
   always contains a legal value for diffServSchedulerId that is not
   currently used in the system's configuration.

3.5.3.  diffServMinRateTable - The Minimum Rate Table

   When the output rate of a queue or scheduler must be given a minimum
   rate or a priority, this is done using the diffServMinRateTable.



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   Rates may be expressed as absolute rates, or as a fraction of
   ifSpeed, and imply the use of a rate-based scheduler such as WFQ or
   WRR.  The use of a priority implies the use of a Priority Scheduler.
   Only one of the Absolute or Relative rates needs to be set; the other
   takes the relevant value as a result.  Excess capacity is distributed
   proportionally among the inputs to a scheduler using the assured
   rate.  More complex functionality may be described by augmenting this
   MIB.

   When a priority scheduler is used, its effect is to give the queue
   the entire capacity of the subject interface less the capacity used
   by higher priorities, if there is traffic present to use it.  This is
   true regardless of the rate specifications applied to that queue or
   other queues on the interface.  Policing excess traffic will mitigate
   this behavior.

   When the MIB is used for configuration, diffServMinRateNextFree
   always contains a legal value for diffServMinRateId that is not
   currently used in the system's configuration.

3.5.4.  diffServMaxRateTable - The Maximum Rate Table

   When the output rate of a queue or scheduler must be limited to at
   most a specified maximum rate, this is done using the
   diffServMaxRateTable.  Rates may be expressed as absolute rates, or
   as a fraction of ifSpeed.  Only one of the Absolute or Relative rate
   needs to be set; the other takes the relevant value as a result.

   The definition of a multirate shaper requires multiple
   diffServMaxRateEntries.  In this case, an algorithm such as [SHAPER]
   is used.  In that algorithm, more than one rate is specified, and at
   any given time traffic is shaped to the lowest specified rate which
   exceeds the arrival rate of traffic.

   When the MIB is used for configuration, diffServMaxRateNextFree
   always contains a legal value for diffServMaxRateId that is not
   currently used in the system's configuration.

3.5.5.  Using queues and schedulers together

   For representing a Strict Priority scheduler, each scheduler input is
   assigned a priority with respect to all the other inputs feeding the
   same scheduler, with default values for the other parameters.
   Higher-priority traffic that is not being delayed for shaping will be
   serviced before a lower-priority input.  An example is found in
   Figure 2.





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   For weighted scheduling methods, such as WFQ or WRR, the "weight" of
   a given scheduler input is represented with a Minimum Service Rate
   leaky-bucket profile which provides a guaranteed minimum bandwidth to
   that input, if required.  This is represented by a rate
   diffServMinRateAbsolute; the classical weight is the ratio between
   that rate and the interface speed, or perhaps the ratio between that
   rate and the sum of the configured rates for classes.  The rate may
   be represented by a relative value, as a fraction of the interface's
   current line rate, diffServMinRateRelative, to assist in cases where
   line rates are variable or where a higher-level policy might be
   expressed in terms of fractions of network resources.  The two rate
   parameters are inter-related and changes in one may be reflected in
   the other.  An example is found in figure 3.

                                  +-----+
            +-------+             | P S |
            | Queue +------------>+ r c |
            +-------+-+--------+  | i h |
                      |Priority|  | o e |
                      +--------+  | r d +----------->
            +-------+             | i u |
            | Queue +------------>+ t l |
            +-------+-+--------+  | y e |
                      |Priority|  |   r |
                      +--------+  +-----+

            Figure 2: Priority Scheduler with two queues

   For weighted scheduling methods, one can say loosely, that WRR
   focuses on meeting bandwidth sharing, without concern for relative
   delay amongst the queues; where WFQ controls both queue the service
   order and the amount of traffic serviced, providing bandwidth sharing
   and relative delay ordering amongst the queues.

   A queue or scheduled set of queues (which is an input to a scheduler)
   may also be capable of acting as a non-work-conserving [MODEL]
   traffic shaper: this is done by defining a Maximum Service Rate
   leaky-bucket profile in order to limit the scheduler bandwidth
   available to that input.  This is represented by a rate, in
   diffServMaxRateAbsolute; the classical weight is the ratio between
   that rate and the interface speed, or perhaps the ratio between that
   rate and the sum of the configured rates for classes.  The rate may
   be represented by a relative value, as a fraction of the interface's
   current line rate, diffServMaxRateRelative.  This MIB presumes that
   shaping is something a scheduler does to its inputs, which it models
   as a queue with a maximum rate or a scheduler whose output has a
   maximum rate.




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                                  +-----+
            +-------+             | W S |
            | Queue +------------>+ R c |
            +-------+-+--------+  | R h |
                      |  Rate  |  |   e |
                      +--------+  | o d +----------->
            +-------+             | r u |
            | Queue +------------>+   l |
            +-------+-+--------+  | W e |
                      |  Rate  |  | F r |
                      +--------+  | Q   |
                                  +-----+

            Figure 3: WRR or WFQ rate-based scheduler with two inputs

   The same may be done on a queue, if a given class is to be shaped to
   a maximum rate without shaping other classes, as in Figure 5.

   Other types of priority and weighted scheduling methods can be
   defined using existing parameters in diffServMinRateEntry.  NOTE:
   diffServSchedulerMethod uses OBJECT IDENTIFIER syntax, with the
   different types of scheduling methods defined as OBJECT-IDENTITY.

                                  +---+
            +-------+             | S |
            | Queue +------------>+ c |
            +-------+-+--------+  | h |
                      |        |  | e +----------->
                      +--------+  | d +-+-------+
                                  | u | |Shaping|
            +-------+             | l | | Rate  |
            | Queue +------------>+ e | +-------+
            +-------+-+--------+  | r |
                      |        |  +---+
                      +--------+

            Figure 4: Shaping scheduled traffic to a known rate














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                                  +---+
            +-------+             | S |
            | Queue +------------>+ c |
            +-------+-+--------+  | h |
                      |Min Rate|  | e +----------->
                      +--------+  | d |
                                  | u |
            +-------+             | l |
            | Queue +------------>+ e |
            +-------+-+--------+  | r |
                      |Min Rate|  |   |
                      +--------+  |   |
                      |Max Rate|  |   |
                      +--------+  +---+

            Figure 5: Shaping one input to a work-conserving scheduler

   Future scheduling methods may be defined in other MIBs.  This
   requires an OBJECT-IDENTITY definition, a description of how the
   existing objects are reused, if they are, and any new objects they
   require.

   To implement an EF and two AF classes, one must use a combination of
   priority and WRR/WFQ scheduling.  This requires us to cascade two
   schedulers.  If one were to additionally shape the output of the
   system to a rate lower than the interface rate, one must place an
   upper bound rate on the output of the priority scheduler.  See figure
   6.

3.6.  Example configuration for AF and EF

   For the sake of argument, let us build an example with one EF class
   and four AF classes using the constructs in this MIB.

3.6.1.  AF and EF Ingress Interface Configuration

   The ingress edge interface identifies traffic into classes, meters
   it, and ensures that any excess is appropriately dealt with according
   to the PHB.  For AF, this means marking excess; for EF, it means
   dropping excess or shaping it to a maximum rate.











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                                                  +-----+
      +-------+                                   | P S |
      | Queue +---------------------------------->+ r c |
      +-------+----------------------+--------+   | i h |
                                     |Priority|   | o e +----------->
                                     +--------+   | r d +-+-------+
                            +------+              | i u | |Shaping|
      +-------+             | W S  +------------->+ t l | | Rate  |
      | Queue +------------>+ R c  +-+--------+   | y e | +-------+
      +-------+-+--------+  | R h  | |Priority|   |   r |
                |Min Rate|  |   e  | +--------+   +-----+
                +--------+  | o d  |
      +-------+             | r u  |
      | Queue +------------>+   l  |
      +-------+-+--------+  | W e  |
                |Min Rate|  | F r  |
                +--------+  | Q    |
                            +------+

      Figure 6: Combined EF and AF services using cascaded schedulers.

        +-----------------------+
        | diffServDataPathStart |
        +-----------+-----------+
                    |
         +----------+