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Versions: (draft-baker-aqm-sfq-implementation) 00 01 02 03 04 05 RFC 7806

Active Queue Management                                         F. Baker
Internet-Draft                                                    R. Pan
Intended status: Informational                             Cisco Systems
Expires: May 4, 2016                                    November 1, 2015


                   On Queuing, Marking, and Dropping
                  draft-ietf-aqm-fq-implementation-05

Abstract

   This note discusses queuing and marking/dropping algorithms.  While
   these algorithms may be implemented in a coupled manner, this note
   argues that specifications, measurements, and comparisons should
   decouple the different algorithms and their contributions to system
   behavior.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on May 4, 2016.

Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.



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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Fair Queuing: Algorithms and History  . . . . . . . . . . . .   3
     2.1.  Generalized Processor Sharing . . . . . . . . . . . . . .   3
       2.1.1.  GPS Comparisons: transmission quanta  . . . . . . . .   4
       2.1.2.  GPS Comparisons: flow definition  . . . . . . . . . .   4
       2.1.3.  GPS Comparisons: unit of measurement  . . . . . . . .   5
     2.2.  GPS Approximations  . . . . . . . . . . . . . . . . . . .   5
       2.2.1.  Definition of a queuing algorithm . . . . . . . . . .   5
       2.2.2.  Round Robin Models  . . . . . . . . . . . . . . . . .   6
       2.2.3.  Calendar Queue Models . . . . . . . . . . . . . . . .   7
       2.2.4.  Work Conserving Models and Stochastic Fairness
               Queuing . . . . . . . . . . . . . . . . . . . . . . .   9
       2.2.5.  Non Work Conserving Models and Virtual Clock  . . . .   9
   3.  Queuing, Marking, and Dropping  . . . . . . . . . . . . . . .  10
     3.1.  Queuing with Tail Mark/Drop . . . . . . . . . . . . . . .  10
     3.2.  Queuing with CoDel Mark/Drop  . . . . . . . . . . . . . .  11
     3.3.  Queuing with RED or PIE Mark/Drop . . . . . . . . . . . .  11
   4.  Conclusion  . . . . . . . . . . . . . . . . . . . . . . . . .  12
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  13
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  13
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  13
   Appendix A.  Change Log . . . . . . . . . . . . . . . . . . . . .  15
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  15

1.  Introduction

   In the discussion of Active Queue Management, there has been
   discussion of the coupling of queue management algorithms such as
   Stochastic Fairness Queuing [SFQ], Virtual Clock [VirtualClock], or
   Deficit Round Robin [DRR] with mark/drop algorithms such as CoDel
   [I-D.ietf-aqm-codel] or PIE [I-D.ietf-aqm-pie].  In the interest of
   clarifying the discussion, we document possible implementation
   approaches to that, and analyze the possible effects and side-
   effects.  The language and model derive from the Architecture for
   Differentiated Services [RFC2475].

   This note is informational, intended to describe reasonable
   possibilities without constraining outcomes.  This is not so much
   about "right" or "wrong" as it is "what might be reasonable", and
   discusses several possible implementation strategies.  Also, while
   queuing might be implemented in almost any layer, specifically the
   note addresses queues that might be used in the Differentiated
   Services Architecture, and are therefore at or below the IP layer.



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2.  Fair Queuing: Algorithms and History

   There is extensive history in the set of algorithms collectively
   referred to as "Fair Queuing".  The model was initially discussed in
   [RFC0970], which proposed it hypothetically as a solution to the TCP
   Silly Window Syndrome issue in BSD 4.1.  The problem was that, due to
   a TCP implementation bug, some senders would settle into sending a
   long stream of very short segments, which unnecessarily consumed
   bandwidth on TCP and IP headers and occupied short packet buffers,
   thereby disrupting competing sessions.  Nagle suggested that if
   packet streams were sorted by their source address and the sources
   treated in a round robin fashion, a sender's effect on end-to-end
   latency and increased loss rate would primarily affect only itself.
   This touched off perhaps a decade of work by various researchers on
   what was and is termed "Fair Queuing," philosophical discussions of
   the meaning of the word "fair," operational reasons that one might
   want a "weighted" or "predictably unfair" queuing algorithm, and so
   on.

2.1.  Generalized Processor Sharing

   Conceptually, any Fair Queuing algorithm attempts to implement some
   approximation to the Generalized Processor Sharing [GPS] model.

   The GPS model, in its essence, presumes that a set of identified data
   streams, called "flows", pass through an interface.  Each flow has a
   rate when measured over a period of time; A voice session might, for
   example, require 64 kbps plus whatever overhead is necessary to
   deliver it, and a TCP session might have variable throughput
   depending on where it is in its evolution.  The premise of
   Generalized Processor Sharing is that on all time scales, the flow
   occupies a predictable bit rate, so that if there is enough bandwidth
   for the flow in the long term, it also lacks nothing in the short
   term.  "All time scales" is obviously untenable in a packet network -
   and even in a traditional TDM circuit switch network - because a
   timescale shorter than the duration of a packet will only see one
   packet at a time.  But it provides an ideal for other models to be
   compared against.

   There are a number of attributes of approximations to the GPS model
   that bear operational consideration, including at least the
   transmission quanta, the definition of a "flow", and the unit of
   measurement.  Implementation approaches have different practical
   impacts as well.







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2.1.1.  GPS Comparisons: transmission quanta

   The most obvious comparison between the GPS model and common
   approximations to it is that real world data is not delivered
   uniformly, but in some quantum.  The smallest quantum, in a packet
   network, is a packet.  But quanta can be larger; for example, in
   video applications it is common to describe data flow in frames per
   second, where a frame describes a picture on a screen or the changes
   made from a previous one.  A single video frame is commonly on the
   order of tens of packets.  If a codec is delivering thirty frames per
   second, it is conceivable that the packets comprising a frame might
   be sent as thirty bursts per second, with each burst sent at the
   interface rate of the camera or other sender.  Similarly, TCP
   exchanges have an initial window, common values of which include 1,
   2, 3, 4 [RFC3390], and 10 [RFC6928], and there are also reports of
   bursts of 64 kB at the relevant MSS, which is to say about 45 packets
   in one burst, presumably coming from TCP Segment Offload (TSO, also
   called TOE) engines (at least one implementation is known to be able
   to send a burst of 256 kB).  After that initial burst, TCP senders
   commonly send pairs of packets, but may send either smaller or larger
   bursts [RFC5690].

2.1.2.  GPS Comparisons: flow definition

   An important engineering trade-off relevant to GPS is the definition
   of a "flow".  A flow is, by definition, a defined data stream.
   Common definitions include:

   o  Packets in a single transport layer session ("microflow"),
      identified by a five-tuple [RFC2990],

   o  Packets between a single pair of addresses, identified by a source
      and destination address or prefix,

   o  Packets from a single source address or prefix [RFC0970],

   o  Packets to a single destination address or prefix,

   o  Packets to or from a single subscriber, customer, or peer
      [RFC6057].  In Service Provider operations, this might be a
      neighboring Autonomous System; in broadband, a residential
      customer.

   The difference should be apparent.  Consider a comparison between
   sorting by source address or destination address, to pick two
   examples, in the case that a given router interface has N application
   sessions going through it between N/2 local destinations and N remote
   sources.  Sorting by source, or in this case by source/destination



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   pair, would give each remote peer an upper bound guarantee of 1/N of
   the available capacity, which might be distributed very unevenly
   among the local destinations.  Sorting by destination would give each
   local destination an upper bound guarantee of 2/N of the available
   capacity, which might be distributed very unevenly among the remote
   systems and correlated sessions.  Who is one fair to?  In both cases,
   they deliver equal service by their definition, but that might not be
   someone else's definition.

   Flow fairness, and the implications of TCP's congestion avoidance
   algorithms, is discussed extensively in [NoFair].

2.1.3.  GPS Comparisons: unit of measurement

   And finally, there is the question of what is measured for rate.  If
   the only objective is to force packet streams to not dominate each
   other, it is sufficient to count packets.  However, if the issue is
   the bit rate of an SLA, one must consider the sizes of the packets
   (the aggregate throughput of a flow, measured in bits or bytes).  And
   if predictable unfairness is a consideration, the value must be
   weighted accordingly.

   [RFC7141] discusses measurement.

2.2.  GPS Approximations

   Carrying the matter further, a queuing algorithm may also be termed
   "Work Conserving" or "Non Work Conserving".  A queue in a "work
   conserving" algorithm, by definition, is either empty, in which case
   no attempt is being made to dequeue data from it, or contains
   something, in which case the algorithm continuously tries to empty
   the queue.  A work conserving queue that contains queued data, at an
   interface with a given rate, will deliver data at that rate until it
   empties.  A non-work-conserving queue might stop delivering even
   though it still contains data.  A common reason for doing this is to
   impose an artificial upper bound on a class of traffic that is lower
   than the rate of the underlying physical interface.

2.2.1.  Definition of a queuing algorithm

   In the discussion following, we assume a basic definition of a
   queuing algorithm.  A queuing algorithm has, at minimum:

   o  Some form of internal storage for the elements kept in the queue,

   o  If it has multiple internal classifications,

      *  a method for classifying elements,



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      *  additional storage for the classifier and implied classes,

   o  potentially, a method for creating the queue,

   o  potentially, a method for destroying the queue,

   o  an enqueuing method, for placing packets into the queue or queuing
      system

   o  a dequeuing method, for removing packets from the queue or queuing
      system

   There may also be other information or methods, such as the ability
   to inspect the queue.  It also often has inspectable external
   attributes, such as the total volume of packets or bytes in queue,
   and may have limit thresholds, such as a maximum number of packets or
   bytes the queue might hold.

   For example, a simple FIFO queue has a linear data structure,
   enqueues packets at the tail, and dequeues packets from the head.  It
   might have a maximum queue depth and a current queue depth,
   maintained in packets or bytes.

2.2.2.  Round Robin Models

   One class of implementation approaches, generically referred to as
   "Weighted Round Robin" (WRR), implements the structure of the queue
   as an array or ring of sub-queues associated with flows, for whatever
   definition of a flow is important.

   The arriving packet must, of course, first be classified.  If a hash
   is used as a classifier, the modulus of the hash might be used as an
   array index, selecting the sub-queue that the packet will go into.
   One can imagine other classifiers, such as using a Differentiated
   Services Code Point (DSCP) value as an index into an array containing
   the queue number for a flow, or more complex access list
   implementations.

   In any event, a sub-queue contains the traffic for a flow, and data
   is sent from each sub-queue in succession.

   On enqueue, the enqueue method places a classified packet into a
   simple FIFO sub-queue.

   On dequeue, the sub-queues are searched in round-robin order, and
   when a sub-queue is identified that contains data, the dequeue method
   removes a specified quantum of data from it.  That quantum is at
   minimum a packet, but it may be more.  If the system is intended to



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   maintain a byte rate, there will be memory between searches of the
   excess previously dequeued.

                            +-+
                          +>|1|
                          | +-+
                          |  |
                          | +-+               +-+
                          | |1|             +>|3|
                          | +-+             | +-+
                          |  |              |  |
                          | +-+      +-+    | +-+
                          | |1|    +>|2|    | |3|
                          | +-+    | +-+    | +-+
                          |  A     |  A     |  A
                          |  |     |  |     |  |
                         ++--++   ++--++   ++--++
                      +->| Q  |-->| Q  |-->| Q  |--+
                      |  +----+   +----+   +----+  |
                      +----------------------------+

                       Figure 1: Round Robin Queues

2.2.3.  Calendar Queue Models

   Another class of implementation approaches, generically referred
   Calendar Queue Implementations [CalendarQueue], implements the
   structure of the queue as an array or ring of sub-queues (often
   called "buckets") associated with time or sequence; Each bucket
   contains the set of packets, which may be null, intended to be sent
   at a certain time or following the emptying of the previous bucket.
   The queue structure includes a look-aside table that indicates the
   current depth (which is to say, the next bucket) of any given class
   of traffic, which might similarly be identified using a hash, a DSCP,
   an access list, or any other classifier.  Conceptually, the queues
   each contain zero or more packets from each class of traffic.  One is
   the queue being emptied "now"; the rest are associated with some time
   or sequence in the future.  The characteristics under load have been
   investigated in [Deadline].

   On enqueue, the enqueue method, considering a classified packet,
   determines the current depth of that class with a view to scheduling
   it for transmission at some time or sequence in the future.  If the
   unit of scheduling is a packet and the queuing quantum is one packet
   per sub-queue, a burst of packets arrives in a given flow, and at the
   start the flow has no queued data, the first packet goes into the
   "next" queue, the second into its successor, and so on; if there was
   some data in the class, the first packet in the burst would go into



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   the bucket pointed to by the look-aside table.  If the unit of
   scheduling is time, the explanation in Section 2.2.5 might be
   simplest to follow, but the bucket selected will be the bucket
   corresponding to a given transmission time in the future.  A
   necessary side-effect, memory being finite, is that there exist a
   finite number of "future" buckets.  If enough traffic arrives to
   cause a class to wrap, one is forced to drop something (tail-drop).

   On dequeue, the buckets are searched at their stated times or in
   their stated sequence, and when a bucket is identified that contains
   data, the dequeue method removes a specified quantum of data from it
   and, by extension, from the associated traffic classes.  A single
   bucket might contain data from a number of classes simultaneously.

                             +-+
                           +>|1|
                           | +-+
                           |  |
                           | +-+      +-+
                           | |2|    +>|2|
                           | +-+    | +-+
                           |  |     |  |
                           | +-+    | +-+      +-+
                           | |3|    | |1|    +>|1|
                           | +-+    | +-+    | +-+
                           |  A     |  A     |  A
                           |  |     |  |     |  |
                          ++--++   ++--++   ++--++
                  "now"+->| Q  |-->| Q  |-->| Q  |-->...
                          +----+   +----+   +----+
                             A       A         A
                             |3      |2        |1
                          +++++++++++++++++++++++
                          ||||     Flow      ||||
                          +++++++++++++++++++++++

                         Figure 2: Calendar Queue

   In any event, a sub-queue contains the traffic for a point in time or
   a point in sequence, and data is sent from each sub-queue in
   succession.  If sub-queues are associated with time, an interesting
   end case develops: If the system is draining a given sub-queue, and
   the time of the next sub-queue arrives, what should the system do?
   One potentially valid line of reasoning would have it continue
   delivering the data in the present queue, on the assumption that it
   will likely trade off for time in the next.  Another potentially
   valid line of reasoning would have it discard any waiting data in the
   present queue and move to the next.



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2.2.4.  Work Conserving Models and Stochastic Fairness Queuing

   Stochastic Fairness Queuing [SFQ] is an example of a work conserving
   algorithm.  This algorithm measures packets, and considers a "flow"
   to be an equivalence class of traffic defined by a hashing algorithm
   over the source and destination IPv4 addresses.  As packets arrive,
   the enqueue method performs the indicated hash and places the packet
   into the indicated sub-queue.  The dequeue method operates as
   described in Section 2.2.2; sub-queues are inspected in round-robin
   sequence, and if they contain one or more packets, a packet is
   removed.

   Deficit Round Robin [DRR] model modifies the quanta to bytes, and
   deals with variable length packets.  A sub-queue descriptor contains
   a waiting quantum (the amount intended to be dequeued on the previous
   dequeue attempt that was not satisfied), a per-round quantum (the
   sub-queue is intended to dequeue a certain number of bytes each
   round), and a maximum to permit (some multiple of the MTU).  In each
   dequeue attempt, the dequeue method sets the waiting quantum to the
   smaller of the maximum quantum and the sum of the waiting and
   incremental quantum.  It then dequeues up to the waiting quantum, in
   bytes, of packets in the queue, and reduces the waiting quantum by
   the number of bytes dequeued.  Since packets will not normally be
   exactly the size of the quantum, some dequeue attempts will dequeue
   more than others, but they will over time average the incremental
   quantum per round if there is data present.

   [SFQ] and [DRR] could be implemented as described in Section 2.2.3.
   The weakness of a WRR approach is the search time expended when the
   queuing system is relatively empty or the overhead of obviating that
   issue, which the calendar queue model also obviates.

2.2.5.  Non Work Conserving Models and Virtual Clock

   Virtual Clock [VirtualClock] is an example of a non-work-conserving
   algorithm.  It is trivially implemented as described in
   Section 2.2.3.  It associates buckets with intervals in time, with
   durations on the order of microseconds to tens of milliseconds.  Each
   flow is assigned a rate in bytes per interval.  The flow entry
   maintains a point in time the "next" packet in the flow should be
   scheduled.

   On enqueue, the method determines whether the "next schedule" time is
   "in the past"; if so, the packet is scheduled "now", and if not, the
   packet is scheduled at that time.  It then calculates the new "next
   schedule" time, as the current "next schedule" time plus the length
   of the packet divided by the rate; if the resulting time is also in
   the past, the "next schedule" time is set to "now", and otherwise to



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   the calculated time.  As noted in Section 2.2.3, there is an
   interesting point regarding "too much time in the future"; if a
   packet is scheduled too far into the future, it may be marked or
   dropped in the AQM procedure, and if it runs beyond the end of the
   queuing system, may be defensively tail dropped.

   On dequeue, the bucket associated with the time "now" is inspected.
   If it contains a packet, the packet is dequeued and transmitted.  If
   the bucket is empty and the time for the next bucket has not arrived,
   the system waits, even if there is a packet in the next bucket.  As
   noted in Section 2.2.3, there is an interesting point regarding the
   queue associated with "now".  If a subsequent bucket, even if it is
   actually empty, would be delayed by the transmission of a packet, one
   could imagine marking the packet ECN CE [RFC3168] [RFC6679] or
   dropping the packet.

3.  Queuing, Marking, and Dropping

   Queuing, marking, and dropping are integrated in any system that has
   a queue.  If nothing else, as memory is finite, a system has to drop
   as discussed in Section 2.2.3 and Section 2.2.5 in order to protect
   itself.  However, host transports interpret drops as signals, so AQM
   algorithms use that as a mechanism to signal.

   It is useful to think of the effects of queuing as a signal as well.
   The receiver sends acknowledgements as data is received, so the
   arrival of acknowledgements at the sender paces the sender at
   approximately the average rate it is able to achieve through the
   network.  This is true even if the sender keeps an arbitrarily large
   amount of data stored in network queues, and is the basis for delay-
   based congestion control algorithms.  So, delaying a packet
   momentarily in order to permit another session to improve its
   operation has the effect of signaling a slightly lower capacity to
   the sender.

3.1.  Queuing with Tail Mark/Drop

   In the default case, in which a FIFO queue is used with defensive
   tail-drop only, the effect is therefore to signal to the sender in
   two ways:

   o  Ack Clocking, pacing the sender to send at approximately the rate
      it can deliver data to the receiver, and

   o  Defensive loss, when a sender sends faster than available capacity
      (such as by probing network capacity when fully utilizing that
      capacity) and overburdens a queue.




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3.2.  Queuing with CoDel Mark/Drop

   In any case wherein a queuing algorithm is used along with CoDel
   [I-D.ietf-aqm-codel], the sequence of events is that a packet is
   time-stamped, enqueued, dequeued, compared to a subsequent reading of
   the clock, and then acted on, whether by dropping it, marking and
   forwarding it, or simply forwarding it.  This is to say that the only
   drop algorithm inherent in queuing is the defensive drop when the
   queue's resources are overrun.  However, the intention of marking or
   dropping is to signal to the sender much earlier, when a certain
   amount of delay has been observed.  In a FIFO+CoDel, Virtual
   Clock+CoDel, or FlowQueue-Codel [I-D.ietf-aqm-fq-codel]
   implementation, the queuing algorithm is completely separate from the
   AQM algorithm.  Using them in series results in four signals to the
   sender:

   o  Ack Clocking, pacing the sender to send at approximately the rate
      it can deliver data to the receiver through a queue,

   o  Lossless signaling that a certain delay threshold has been
      reached, if ECN [RFC3168][RFC6679] is in use,

   o  Intentional signaling via loss that a certain delay threshold has
      been reached, if ECN is not in use, and

   o  Defensive loss, when a sender sends faster than available capacity
      (such as by probing network capacity when fully utilizing that
      capacity) and overburdens a queue.

3.3.  Queuing with RED or PIE Mark/Drop

   In any case wherein a queuing algorithm is used along with PIE
   [I-D.ietf-aqm-pie], RED [RFC2309], or other such algorithms, the
   sequence of events is that a queue is inspected, a packet is dropped,
   marked, or left unchanged, enqueued, dequeued, compared to a
   subsequent reading of the clock, and then forwarded on.  This is to
   say that the AQM Mark/Drop Algorithm precedes enqueue; if it has not
   been effective and as a result the queue is out of resources anyway,
   the defensive drop algorithm steps in, and failing that, the queue
   operates in whatever way it does.  Hence, in a FIFO+PIE, SFQ+PIE, or
   Virtual Clock+PIE implementation, the queuing algorithm is again
   completely separate from the AQM algorithm.  Using them in series
   results in four signals to the sender:

   o  Ack Clocking, pacing the sender to send at approximately the rate
      it can deliver data to the receiver through a queue,





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   o  Lossless signaling that a queue depth that corresponds to a
      certain delay threshold has been reached, if ECN is in use,

   o  Intentional signaling via loss that a queue depth that corresponds
      to a certain delay threshold has been reached, if ECN is not in
      use, and

   o  Defensive loss, when a sender sends faster than available capacity
      (such as by probing network capacity when fully utilizing that
      capacity) and overburdens a queue.

4.  Conclusion

   To summarize, in Section 2, implementation approaches for several
   classes of queuing algorithms were explored.  Queuing algorithms such
   as SFQ, Virtual Clock, and FlowQueue-Codel [I-D.ietf-aqm-fq-codel]
   have value in the network, in that they delay packets to enforce a
   rate upper bound or to permit competing flows to compete more
   effectively.  ECN Marking and loss are also useful signals if used in
   a manner that enhances TCP/SCTP operation or restrains unmanaged UDP
   data flows.

   Conceptually, queuing algorithms and mark/drop algorithms operate in
   series, as discussed in Section 3, not as a single algorithm.  The
   observed effects differ: defensive loss protects the intermediate
   system and provides a signal, AQM mark/drop works to reduce mean
   latency, and the scheduling of flows works to modify flow interleave
   and acknowledgement pacing.  Certain features like flow isolation are
   provided by fair queuing related designs, but are not the effect of
   the mark/drop algorithm.

   There is value in implementing and coupling the operation of both
   queuing algorithms and queue management algorithms, and there is
   definitely interesting research in this area, but specifications,
   measurements, and comparisons should decouple the different
   algorithms and their contributions to system behavior.

5.  IANA Considerations

   This memo asks the IANA for no new parameters.

6.  Security Considerations

   This memo adds no new security issues; it observes on implementation
   strategies for Diffserv implementation.






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7.  Acknowledgements

   This note grew out of, and is in response to, mailing list
   discussions in AQM, in which some have pushed an algorithm the
   compare to AQM marking and dropping algorithms, but which includes
   Flow Queuing.

8.  References

8.1.  Normative References

   [RFC2475]  Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
              and W. Weiss, "An Architecture for Differentiated
              Services", RFC 2475, DOI 10.17487/RFC2475, December 1998,
              <http://www.rfc-editor.org/info/rfc2475>.

8.2.  Informative References

   [CalendarQueue]
              "Calendar queues: a fast 0(1) priority queue
              implementation for the simulation event set problem",
              Communications of the ACM 1988, October 1988,
              <http://dl.acm.org/citation.cfm?id=63045>.

   [Deadline]
              , , , and , "Heavy Traffic Analysis For Edf Queues With
              Reneging", Annals of Applied Probability 2011, 2011,
              <http://www.math.cmu.edu/users/shreve/Reneging.pdf>.

   [DRR]      Microsoft Corporation and Washington University in St.
              Louis, "Efficient fair queueing using deficit round
              robin", ACM SIGCOMM 1995, October 1995,
              <http://ieeexplore.ieee.org/stamp/
              stamp.jsp?tp=&arnumber=502236>.

   [GPS]      Xerox PARC, University of California, Berkeley, and Xerox
              PARC, "Analysis and simulation of a fair queueing
              algorithm", ACM SIGCOMM 1989, September 1989,
              <http://blizzard.cs.uwaterloo.ca/keshav/home/Papers/
              data/89/fq.pdf>.

   [I-D.ietf-aqm-codel]
              Nichols, K., Jacobson, V., McGregor, A., and J. Jana,
              "Controlled Delay Active Queue Management", draft-ietf-
              aqm-codel-01 (work in progress), April 2015.






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   [I-D.ietf-aqm-fq-codel]
              Hoeiland-Joergensen, T., McKenney, P.,
              dave.taht@gmail.com, d., Gettys, J., and E. Dumazet,
              "FlowQueue-Codel", draft-ietf-aqm-fq-codel-02 (work in
              progress), October 2015.

   [I-D.ietf-aqm-pie]
              Pan, R., Natarajan, P., and F. Baker, "PIE: A Lightweight
              Control Scheme To Address the Bufferbloat Problem", draft-
              ietf-aqm-pie-02 (work in progress), August 2015.

   [NoFair]   British Telecom, "Flow rate fairness: dismantling a
              religion", ACM SIGCOMM 2007, April 2007,
              <http://dl.acm.org/citation.cfm?id=1232926>.

   [RFC0970]  Nagle, J., "On Packet Switches With Infinite Storage",
              RFC 970, DOI 10.17487/RFC0970, December 1985,
              <http://www.rfc-editor.org/info/rfc970>.

   [RFC2309]  Braden, B., Clark, D., Crowcroft, J., Davie, B., Deering,
              S., Estrin, D., Floyd, S., Jacobson, V., Minshall, G.,
              Partridge, C., Peterson, L., Ramakrishnan, K., Shenker,
              S., Wroclawski, J., and L. Zhang, "Recommendations on
              Queue Management and Congestion Avoidance in the
              Internet", RFC 2309, DOI 10.17487/RFC2309, April 1998,
              <http://www.rfc-editor.org/info/rfc2309>.

   [RFC2990]  Huston, G., "Next Steps for the IP QoS Architecture",
              RFC 2990, DOI 10.17487/RFC2990, November 2000,
              <http://www.rfc-editor.org/info/rfc2990>.

   [RFC3168]  Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
              of Explicit Congestion Notification (ECN) to IP",
              RFC 3168, DOI 10.17487/RFC3168, September 2001,
              <http://www.rfc-editor.org/info/rfc3168>.

   [RFC3390]  Allman, M., Floyd, S., and C. Partridge, "Increasing TCP's
              Initial Window", RFC 3390, DOI 10.17487/RFC3390, October
              2002, <http://www.rfc-editor.org/info/rfc3390>.

   [RFC5690]  Floyd, S., Arcia, A., Ros, D., and J. Iyengar, "Adding
              Acknowledgement Congestion Control to TCP", RFC 5690,
              DOI 10.17487/RFC5690, February 2010,
              <http://www.rfc-editor.org/info/rfc5690>.







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   [RFC6057]  Bastian, C., Klieber, T., Livingood, J., Mills, J., and R.
              Woundy, "Comcast's Protocol-Agnostic Congestion Management
              System", RFC 6057, DOI 10.17487/RFC6057, December 2010,
              <http://www.rfc-editor.org/info/rfc6057>.

   [RFC6679]  Westerlund, M., Johansson, I., Perkins, C., O'Hanlon, P.,
              and K. Carlberg, "Explicit Congestion Notification (ECN)
              for RTP over UDP", RFC 6679, DOI 10.17487/RFC6679, August
              2012, <http://www.rfc-editor.org/info/rfc6679>.

   [RFC6928]  Chu, J., Dukkipati, N., Cheng, Y., and M. Mathis,
              "Increasing TCP's Initial Window", RFC 6928,
              DOI 10.17487/RFC6928, April 2013,
              <http://www.rfc-editor.org/info/rfc6928>.

   [RFC7141]  Briscoe, B. and J. Manner, "Byte and Packet Congestion
              Notification", BCP 41, RFC 7141, DOI 10.17487/RFC7141,
              February 2014, <http://www.rfc-editor.org/info/rfc7141>.

   [SFQ]      SRI International, "Stochastic Fairness Queuing", IEEE
              Infocom 1990, June 1990,
              <http://www2.rdrop.com/~paulmck/scalability/paper/
              sfq.2002.06.04.pdf>.

   [VirtualClock]
              Xerox PARC, "Virtual Clock", ACM SIGCOMM 1990, September
              1990,
              <http://www.cs.ucla.edu/~lixia/papers/90sigcomm.pdf>.

Appendix A.  Change Log

   Initial Version:  June 2014

Authors' Addresses

   Fred Baker
   Cisco Systems
   Santa Barbara, California  93117
   USA

   Email: fred@cisco.com










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   Rong Pan
   Cisco Systems
   Milpitas, California  95035
   USA

   Email: ropan@cisco.com













































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