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PCN Working Group                                               D. Satoh
Internet-Draft                                                   H. Ueno
Intended status: Informational                                    NTT-AT
Expires: January 4, 2010                                        M. Menth
                                                     Univ. of  Wuerzburg
                                                            July 3, 2009


         Performance evaluation of termination in CL-algorithm
               draft-satoh-pcn-performance-termination-00

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Abstract

   Pre-congestion notification (PCN) gives information to support



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   admission control and flow termination in order to protect the
   quality of service (QoS) of inelastic flows.  [I-D.taylor-cl-edge-
   behaviour] describes one boundary node behaviours for three-state
   measurement-based load control, known informally as CL [I-D.briscoe-
   tsvwg-cl-phb].  In [I-D.taylor-cl-edge-behaviour], flow termination
   is required if excess-traffic-marked packets were observed and the
   end of one measurement period MUST be the beginning of the next one,
   independently of current flow conditions.  According to this
   termination, PCN-flows in some ingress-egress (IE) pairs may be
   terminated during measurement period of other IE pairs unless round-
   trip times (RTT) of all the IE pairs are the same.  We illustrate
   that this can lead to over-termination.  Our simulation confirms that
   accuracy of termination is improved when no PCN-flows in some IE
   pairs are terminated during measurement period of other IE pairs.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Unintended termination . . . . . . . . . . . . . . . . . . . .  3
     3.1.  Example 1  . . . . . . . . . . . . . . . . . . . . . . . .  4
     3.2.  Example 2  . . . . . . . . . . . . . . . . . . . . . . . .  7
     3.3.  Example 3  . . . . . . . . . . . . . . . . . . . . . . . .  7
   4.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  7
   5.  Appendix: Simulation evaluation  . . . . . . . . . . . . . . .  7
     5.1.  Network topology and rerouting . . . . . . . . . . . . . .  8
     5.2.  Traffic  . . . . . . . . . . . . . . . . . . . . . . . . .  8
     5.3.  Parameter setting for CL . . . . . . . . . . . . . . . . .  9
     5.4.  Simulation results . . . . . . . . . . . . . . . . . . . .  9
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 10
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 11
   8.  Informative References . . . . . . . . . . . . . . . . . . . . 11
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11

















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1.  Introduction

   Pre-congestion notification (PCN) gives information to support
   admission control and flow termination in order to protect the
   quality of service (QoS) of inelastic flows.  Flow termination is a
   new control whose function is terminating already admitted PCN-flows.
   Termination is necessary even if admission control is provided
   because rerouting by failures makes PCN traffic rate higher than PCN-
   supportable-rate.

   Menth and Lehrieder evaluate the performance of measured rate
   termination [I-D.menth-pcn-performance].  In [I-D.menth-pcn-
   performance], they pointed out that indirect measured rate
   termination can lead to substantial over-termination when packets are
   metered and marked before dropping.  Furthermore, they also pointed
   out that over-termination can occur without dropping of packets when
   the measurement periods of the ingress and the egress are not in
   synchronization, that is, both measurement intervals do not cover the
   same data.

   In this memo, we illustrate that over-termination also occurs when
   during a measurement period of an IE the load of another IE using the
   same bottleneck link is reduced due to termination.  This situation
   occurs when IEs sharing a common bottleneck have significantly
   different round trip times (RTT) within the PCN domain.


2.  Terminology

   The terminology used in this document conforms to the terminology of
   [RFC5559], [I-D.ietf-pcn-marking-behaviour], [ID.taylor-cl-edge-
   behaviour], [I-D.briscoe-tsvwg-cl-phb], and [I-D.menth-pcn-
   performance].


3.  Unintended termination

   [ID.taylor-cl-edge-behaviour] describes flow termination is required
   if excess-traffic-marked packets were observed.  It also describes
   the end of one measurement period MUST be the beginning of the next
   one, independently of current flow conditions.

   If a bottleneck link that contains IE pairs whose RTTs are different,
   unintended termination can occur under the condition described above.
   We illustrate it by using a simple network model.

   We assume a network of Figure 1 after rerouting due to failure.
   Three ingress nodes: A, B, and C are connected to interior node D



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   with links of different propagation delay and interior node D is
   connected to egress node F. We assume propagation delay between nodes
   B and D is the same as that between nodes C and D, and they are
   different from that between nodes A and D to simplify the model.  We
   consider the case of bottleneck link between nodes D and F. We call
   IE pair A-F as IE#1, IE pair B-F as IE#2, and IE pair C-F as IE#3.
   We illustrate that unintended termination can occur by using the
   three examples in Table 1.  RTT of IE#1 is smaller than those of IE#2
   and IE#3 in Example 1.  RTT of IE#1 is larger than those of IE#2 and
   IE#3 in Example 2.  In Example 3, rates of IE pairs in Example 3 are
   twice higher than those in Examples 2 and 3 and RTTs in Example 3 are
   the same as those in Example 1.  The PCN-supportable rate(SR) is
   160Mbps in all the examples.  Thus, termination is necessary.  The
   link speed of the bottleneck is much more than 480 Mbps.  Thus no
   dropping occurs.  Furthermore, we assume the ratio of unmarked rate
   to total rate of an IE pair is that of SR to the total rate of the
   link.  The duration of the measurement period is 100 ms, but it does
   not influence the unintended termination directly.


                                A
                                  \
                               B - D - F
                                  /
                                C


        Figure 1: A network in which IE pairs have different RTTs.

   ----------------+----------------+----------------+-----------------
   IE pair|Ingress |   Example 1    |   Example 2    |    Example 3
          |        |----------------+----------------+-----------------
          |        | Rate  |  RTT   | Rate  |  RTT   | Rate  |  RTT
          |        | [Mbps]|   [ms] | [Mbps]|   [ms] | [Mbps]|   [ms]
   ----------------+----------------+----------------+-----------------
     IE#1 |    A   |  360  |   100  |  360  |   150  |  720  |   100
     IE#2 |    B   |   60  |   150  |   60  |   100  |  120  |   150
     IE#3 |    C   |   60  |   150  |   60  |   100  |  120  |   150
   ----------------+----------------+----------------+------------------


                   Table 1: Rates and RTTs of IE pairs.

3.1.  Example 1

   As seen in Figure 2, marked and unmarked rates of IE#1 just after
   failure are 240Mbps and 120Mbps, those of IE#2 are 40Mbps and 20Mbps,
   and those of IE#3 are 40Mbps and 20Mbps.  Sustainable aggregate rate



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   (SAR) of IE#1 is 120Mbps, that of IE#2 is 20Mbps, and that of IE#3 is
   20Mbps.  The sum of the three SAR is 160Mbps, which is equal to SR.

   PCN traffic rate
              +-----------------------------------------------+
              |                                               |
              |             IE#3(mark):   40Mbps              |
              |-----------------------------------------------|
              |             IE#3(unmark): 20Mbps              |
              +-----------------------------------------------|
              |                                               |
              |             IE#2(mark):   40Mbps              |
              |-----------------------------------------------|
              |             IE#2(unmark): 20Mbps              |
              +-----------------------------------------------|
              |                                               |
              |                                               |
              |                                               |
              |                                               |
              |                                               |
              |                                               |
              |             IE#1(mark):   240Mbps             |
              |                                               |
              |                                               |
              |                                               |
              |                                               |
              |                                               |
              |-----------------------------------------------|
              |                                               |
              |                                               |
              |                                               |
              |             IE#1(unmark): 120Mbps             |
              |                                               |
              |                                               |
           0  +-----------------------------------------------+---->
                                                             100
                                  time[ms]



    Figure 2: Marked and unmarked rate of IE pairs just after failure.

   We assume that the next measurement period at the PCN egress node
   begins after the termination of IE#1 but before the termination of
   IE#2 and IE#3.  This is likely since these IEs have significantly
   larger RTTs.  Figure 2 shows the measured rates of marked and
   unmarked traffic in this measurement period.  The total rate is
   240Mbps, marked and unmarked rates of IE#1 are 40Mbps and 80Mbps,



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   those of IE#2 are 20Mbps and 40Mbps, and those of IE#3 are 20Mbps and
   40Mbps in the first half of the measurement period.  The total rate
   is 160Mbps, unmarked rate of IE#1 is 120Mbps, that of IE#2 is 20Mbps,
   and that of IE#3 is 20Mbps in the second half of the measurement
   period.  The total rate of the three IE pairs is 160Mbps, which
   equals SR.  If the measurement period begin with the half of the
   period, no termination is necessary.  However, egresses of IE#1,
   IE#2, and IE#3 measure SAR as 100Mpbs(=(80+120)/2), 30Mbps(=(40+
   20)/2), 30Mbps(=(40+20)/2).  The sum of the SAR equals SR.


    PCN traffic rate
              +-----------------------+
              | IE#3(mark):   20Mbps  |
              |-----------------------|
              |                       |
              | IE#3(unmark): 40Mbps  |
              +-----------------------+
              | IE#2(mark):   20Mbps  |
              |-----------------------|-----------------------+
              |                       |IE#3(unmark):   20Mbps |
              | IE#2(unmark): 40Mbps  |IE#2(unmark):   20Mbps |
              +-----------------------+-----------------------+
              |                       |                       |
              | IE#1(mark):   40Mbps  |                       |
              |-----------------------|                       |
              |                       | IE#1(unmark): 120Mbps |
              |                       |                       |
              | IE#1(unmark): 80Mbps  |                       |
              |                       |                       |
           0  +-----------------------+-----------------------+--->
                                        50                   100
                                                      time[ms]

    Figure 3: Marked and unmarked rate of IE pairs after termination of
     IE#1 and before termination IE#2 and IE#3 at the beginning of the
                            measurement period.

   Figure 3 illustrates that the second half of the measurement period
   shows that sufficiently many flows are already terminated.  However,
   SAR is calculated over the entire measurement period and, therefore,
   it is underestimated.  Thus, the PCN ingress node of IE#1 again
   terminates flows because the reported SAR is 100Mbps which is smaller
   than the existing 120 Mbps PCN traffic rate in IE#1.  The ingresses
   of IE#2 and IE#3 receive SAR=30 Mbps which is 10 Mbps more than their
   existing PCN traffic rates of 20 Mbps.  Figure 4 shows the situation
   in the next measurement interval.  Then, over-termination of 20Mbps
   is visible because IE#1 has terminated another 20 Mbps by then.



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   PCN traffic rate
           SR +----------------------------------------------------
              |            Over-termination: 20Mbps
              +----------------------------------------------------
              |                IE#3(unmark): 20Mbps
              +----------------------------------------------------
              |                IE#2(unmark): 20Mbps
              +----------------------------------------------------
              |
              |
              |                IE#1(unmark): 100Mbps
              |
              |
           0  +-------------------------------------------------------->
                                                            time[ms]

              Figure 4: Rates of IE pairs after termination.

3.2.  Example 2

   Flows of IE#1, which has the highest rate, are terminated at first
   and flows of IE#2 and IE#3 are terminated in Example 1. by using
   example 2, we show that over-termination also occurs and the amount
   of unintended termination is changed when the flows of an IE pair
   whose rate is not highest rate are terminated first.  According to
   the similar discussion in Example 1, the amount of unintended
   termination is 12Mbps although that in Example is 20Mbps.

3.3.  Example 3

   Example 3 has the twice higher load than Example 1.  According to the
   similar discussion in Example 1, the amount of unintended termination
   is 33.35Mbps although that in Example 1 is 20Mbps.


4.  Acknowledgements

   This research was partially supported by the National Institute of
   Information and Communications Technology (NICT), Tokyo, Japan.


5.  Appendix: Simulation evaluation

   The unintended termination illustrated in the previous section can be
   avoided if SAR is measured only after all IEs have finished their
   termination and the effect of their termination steps have become
   visible at the PCN egress node.  We evaluated how much unintended
   termination can be avoidable by simulation.



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5.1.  Network topology and rerouting

   We simulated flow termination with CL for the simple topology given
   in Figure 1 when the number of ingresses were 3, 11, 36, 71, and 101.
   One IE pair had the highest rate and others had the same rate.  The
   total rate without the IE pair whose rate was the highest was the
   same as PCN-admissible-rate.  The IE pair was rerouted by failure.
   Hence, the load was higher than SR at the bottleneck link.  We
   simulated the load of 1.25SR and 2.0SR with CBR and VBR traffic.

   All links had different propagation delays which were chosen randomly
   in the range of 1ms - 100 ms.  The bottleneck link D-F was modeled
   with a 10ms propagation delay in all simulations.  Therefore, the
   range of round-trip delays in the experiments ranged from 22ms to
   220ms.

5.2.  Traffic

   We used the same types of traffic as those of [I-D. briscoe-tsvwg-cl-
   phb], [I-D. charny-pcn-single-marking], [I-D.zhang-pcn-performance-
   evaluation].  These were CBR and on/off process (VBR) that was
   described with two state Markov chain and whose on and off periods
   were exponentially distributed with the specified mean.  The
   distribution of flow duration of all the flows was infinity in order
   to eliminate other causes to decrease the number of flows than
   termination.

   Traffic parameters for each type are summarized below:

   CBR voice

   o  Packet length: 160 bytes

   o  Packet inter-arrival time: 20ms ((160*8)/(64*1000)sec)

   o  Average rate: 64Kbps

   On-off traffic approximating voice with silence compression

   o  Packet length: 160 bytes

   o  Packet inter-arrival time during On period: 20ms

   o  Long-term average rate: 21.76 Kbps

   o  On period mean duration: 340ms; during the on period traffic is
      sent with CBR voice parameters described above




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   o  Off period mean duration 660ms; no traffic is sent for the
      duration of the off period

5.3.  Parameter setting for CL

   All the simulations were run with 5ms at PCN-supportable-rate as
   token bucket size for Termination.  The value of 5ms at PCN-
   supportable-rate as the token bucket size corresponds to 500 packets
   in the case of CBR and VBR.

5.4.  Simulation results

   We evaluated over-termination percentages to terminate the necessary
   amount of traffic when the load of the bottleneck was 1.25 and 2.0
   times SR.  Over-termination percentages is defined as (SR - the rate
   after termination)/SR) expressed in percentage.  SR was 40% of the
   link speed in the link D-F.  The load was lower than PCN-admissible-
   rate at the beginning of the simulation.  The simulation time was
   100s.  One IE-pair was generated at half the simulation time (50s).
   Each flow of the IE-pair arrived according to uniform distribution
   within the average of the packet interval in a flow.  This simulated
   the change of a route when there was a failure.  Over-termination
   percentages were calculated using the average rate during the time
   interval between 80 and 100s.  During this period, no termination
   occurred.

   When the traffic type was CBR, the link speed was 320 Mbps and the
   load was the rate of 2500 and 4000 flows.  When the traffic type was
   VBR, the link speed was 109 Mbps and the load was the rate of 2500
   and 4000 flows.  We used randomized CBR and VBR in termination
   simulations.  Each packet of the randomized CBR and VBR traffic was
   added a delay distributed uniformly from 0 to 50ms.  We show the
   average of the results of five simulations with different random
   seeds for each traffic type.  In Tables 2 and 3, we show over-
   termination percentages in the case of no inter-measurement period
   time(IMPT) and the case of 350ms as IMPT.  In this simulation, no
   termination of some IE pairs occurred during measurement period of
   other IE pairs because the maximum of RTT was 220ms and measuring
   time at an ingress was 100ms and the sum of them was less than IMPT
   350ms.

   In the case of no IMPT in Table 2, over-termination percentages in
   the case of 2.0SR load is higher than those in the case of 1.25SR
   load.  The more bandwidth was terminated during measurement period,
   the more over-termination was observed as shown in the previous
   section.  On the other hand, in the case of 350ms as IMPT, over-
   termination percentages were the same in both loads.




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               ---------------------------------------------
                No. of   |Load    |   Over-termination %
                Ingress  |(x SR)  |-------------------------
                         |        | IMPT=None |IMPT=350ms
               ---------------------------------------------
                   3     |        |   3.611   |   0.121
                  11     |  1.25  |   4.070   |   0.400
                  36     |        |   5.740   |   1.250
                  71     |        |   7.570   |   2.380
               ---------------------------------------------
                   3     |        |   8.910   |   0.119
                  11     |  2.0   |   9.670   |   0.371
                  36     |        |  11.080   |   1.150
                  71     |        |  12.570   |   2.271
               ---------------------------------------------


         Table 2: Over-termination percentage statistics with CBR.

   The same phenomena as the case of CBR were observed in the case of
   VBR as seen in Table 3.  However, the phenomena in the case of CBR
   were more clearly observed than those in the case of VBR.

               ---------------------------------------------
                No. of   |Load    |   Over-termination %
                Ingress  |(x SR)  |-------------------------
                         |        | IMPT=None |IMPT=350ms
               ---------------------------------------------
                   3     |        |   8.873   |   5.398
                  11     |  1.25  |   8.891   |   5.582
                  36     |        |  12.952   |   5.457
                 101     |        |  18.733   |   6.704
               ---------------------------------------------
                   3     |        |  10.195   |   5.617
                  11     |  2.0   |  12.373   |   5.516
                  36     |        |  15.935   |   5.267
                 101     |        |  17.796   |   4.923
               ---------------------------------------------


         Table 3: Over-termination percentage statistics with VBR.


6.  IANA Considerations

   TBD





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7.  Security Considerations

   TBD


8.  Informative References

   [I-D.briscoe-tsvwg-cl-phb]
              Briscoe, B., "Pre-Congestion Notification Marking",
              October 2006.

   [I-D.charny-pcn-single-marking]
              Charny, A., "Pre-Congestion Notification Using Single
              Marking for Admission and Termination", November 2007.

   [I-D.ietf-pcn-marking-behaviour]
              Eardley, P., "Marking behaviour of PCN-nodes", June 2009.

   [I-D.menth-pcn-performance]
              Menth, M. and F. Lehrieder, "Performance Evaluation of
              PCN-Based Algorithms", July 2008.

   [I-D.zhang-pcn-performance-evaluation]
              Zhang, J., "Performance Evaluation of CL-PHB Admission and
              Termination Algorithms", July 2007.

   [RFC5559]  Eardley, P., "Pre-Congestion Notification Architecture",
              June 2009.


Authors' Addresses

   Daisuke Satoh
   NTT Advanced Technology Corporation
   1-19-18, Nakacho
   Musashino-shi, Tokyo  180-0006
   Japan

   Email: daisuke.satoh@ntt-at.co.jp












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   Harutaka Ueno
   NTT Advanced Technology Corporation
   1-19-18, Nakacho
   Musashino-shi, Tokyo  180-0006
   Japan

   Email: harutaka.ueno@ntt-at.co.jp


   Michael Menth
   University of Wuerzburg
   room B206, Institute of Computer Science
   Am Hubland, Wuerzburg  D-97074
   Germany

   Email: menth@informatik.uni-wuerzburg.de



































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