A Rate Adaptive Shaper for Differentiated Services
draft-bonaventure-diffserv-rashaper-04

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Document Type RFC Internet-Draft (individual)
Authors Stefaan De Cnodder  , Olivier Bonaventure 
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Internet Engineering Task Force                      Olivier Bonaventure
INTERNET DRAFT                                                     FUNDP
draft-bonaventure-diffserv-rashaper-04.txt            Stefaan De Cnodder
                                                                 Alcatel
                                                              July, 2000
                                                   Expires January, 2001

           A rate adaptive shaper for differentiated services

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
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Copyright Notice

   Copyright (C) The Internet Society (2000).  All Rights Reserved.

Abstract

   This memo describes several Rate Adaptive Shapers (RAS) that can be
   used in combination with the single rate Three Color Markers (srTCM)
   and the two rate Three Color Marker (trTCM) described in [RFC2697]
   and [RFC2698], respectively. These RAS improve the performance of TCP
   when a TCM is used at the ingress of a diffserv network by reducing
   the burstiness of the traffic. With TCP traffic, this reduction of
   the burstiness is accompanied by a reduction of the number of marked
   packets and by an improved TCP goodput.  The proposed RAS can be used
   at the ingress of Diffserv networks providing the Assured Forwarding
   Per Hop Behavior (AF PHB). They are especially useful when a TCM is
   used to mark traffic composed of a small number of TCP connections.

1. Introduction

   In DiffServ networks [RFC2475], the incoming data traffic, with the
   AF PHB in particular, could be subject to marking where the purpose
   of this marking is to provide a low drop probability to a minimum

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   part of the traffic whereas the excess will have a larger drop
   probability.  Such markers are mainly token bucket based such as the
   single rate Three Color Marker (srTCM) and two rate Three Color
   Marker (trTCM) described in [RFC2697] and [RFC2698], respectively.

   Similar markers were proposed for ATM networks and simulations have
   shown that their performance with TCP traffic was not always
   satisfactory and several researchers have shown that these
   performance problems could be solved in two ways:

   1. increasing the burst size, i.e. increasing the Committed Burst
   Size (CBS) and the Peak Burst Size (PBS) in case of the trTCM, or

   2. shaping the traffic such that a part of the burstiness is removed.

   The first solution has as major disadvantage that the traffic sent to
   the network can be very bursty and thus engineering the network to
   provide a low packet loss ratio can become difficult.  To efficiently
   support bursty traffic, additional resources such as buffer space are
   needed.  Conversely, the major disadvantage of shaping is that the
   traffic encounters additional delay in the shaper's buffer.

   In this document, we propose two shapers that can reduce the
   burstiness of the traffic upstream of a TCM. By reducing the
   burstiness of the traffic, the adaptive shapers increase the
   percentage of packets marked as green by the TCM and thus the overall
   goodput of the users attached to such a shaper.

   Such rate adaptive shapers will probably be useful at the edge of the
   network (i.e. inside access routers or even network adapters).  The
   simulation results in [Cnodder] show that these shapers are
   particularly useful when a small number of TCP connections are
   processed by a TCM.

   The structure of this document follows the structure proposed in
   [Nichols]. We first describe two types of rate adaptive shapers in
   section two. These shapers correspond to respectively the srTCM and
   the trTCM. In section 3, we describe an extension to the simple
   shapers that can provide a better performance. We briefly discuss
   simulation results in the appendix.

2. Description of the rate adaptive shapers

 2.1. Rate adaptive shaper

   The rate adaptive shaper is based on a similar shaper proposed in
   [Bonaventure] to improve the performance of TCP with the Guaranteed

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   Frame Rate [TM41] service category in ATM networks. Another type of
   rate adaptive shaper suitable for differentiated services was briefly
   discussed in [Azeem].  A RAS will typically be used as shown in
   figure 1 where the meter and the marker are the TCMs proposed in
   [RFC2697] and [RFC2698].

                                     Result
                                  +----------+
                                  |          |
                                  |          V
                 +--------+   +-------+   +--------+
      Incoming   |        |   |       |   |        |   Outgoing
      Packet  ==>|  RAS   |==>| Meter |==>| Marker |==>Packet
      Stream     |        |   |       |   |        |   Stream
                 +--------+   +-------+   +--------+

                        Figure 1. Rate adaptive shaper

   The presentation of the rate adaptive shapers in Figure 1 is somewhat
   different as described in [RFC2475] where the shaper is placed after
   the meter.  The main objective of the shaper is to produce at its
   output a traffic that is less bursty than the input traffic, but the
   shaper avoids to discard packets in contrast with classical token
   bucket based shapers. The shaper itself consists of a tail-drop FIFO
   queue which is emptied at a variable rate.  The shaping rate, i.e.
   the rate at which the queue is emptied, is a function of the
   occupancy of the FIFO queue. If the queue occupancy increases, the
   shaping rate will also increase in order to prevent loss and too
   large delays through the shaper.  The shaping rate is also a function
   of the average rate of the incoming traffic.  The shaper was designed
   to be used in conjunction with meters such as the TCMs proposed in
   [RFC2697] and [RFC2698].

   There are two types of rate adaptive shapers. The single rate rate
   adaptive shaper (srRAS) will typically be used upstream of a srTCM
   while the two rates rate adaptive shaper (trRAS) will usually be used
   upstream of a trTCM.

 2.2. Configuration of the srRAS

   The srRAS is configured by specifying four parameters : the Committed
   Information Rate (CIR), the Maximum Information Rate (MIR) and two
   buffer thresholds : CIR_th (Committed Information Rate threshold) and
   MIR_th (Maximum Information Rate threshold). The CIR shall be
   specified in bytes per second and MUST be configurable. The MIR shall

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   be specified in the same unit as the CIR and SHOULD be configurable.
   To achieve a good performance, the CIR of a srRAS will usually be set
   to the same value as the CIR of the downstream srTCM.  A typical
   value for the MIR would be the line rate of the output link of the
   shaper. When the CIR and optionally the MIR are configured, the srRAS
   MUST ensure that the following relation is verified:

           CIR <= MIR <= line rate

   The two buffer thresholds, CIR_th and MIR_th shall be specified in
   bytes and SHOULD be configurable. If these thresholds are configured,
   then the srRAS MUST ensure that the following relation holds:

               CIR_th <= MIR_th <= buffer size of the shaper

   The chosen values for CIR_th and MIR_th will usually depend on the
   values chosen for CBS and PBS in the downstream srTCM. However, this
   dependency does not need to be standardized.

 2.3. Behavior of the srRAS

   The output rate of the shaper is based on two factors. The first one
   is the (long term) average rate of the incoming traffic. This average
   rate can be computed by several means. For example, the function
   proposed in [Stoica] can be used (i.e. EARnew = [(1-exp(-T/K))*L/T] +
   exp(-T/K)*EARold where EARold is the previous value of the Estimated
   Average Rate, EARnew is the updated value, K a constant, L the size
   of the arriving packet and T the amount of time since the arrival of
   the previous packet). Other averaging functions can be used as well.

   The second factor is the instantaneous occupancy of the FIFO buffer
   of the shaper. When the buffer occupancy is below CIR_th, the output
   rate of the shaper is set to the maximum of the estimated average
   rate (EAR(t)) and the CIR. This ensures that the shaper buffer will
   be emptied at least at a rate equal to CIR. When the buffer occupancy
   increases above CIR_th, the output rate of the shaper is computed as
   the maximum of the EAR(t) and a linear function F of the buffer
   occupancy for which F(CIR_th)=CIR and F(MIR_th)=MIR. When the buffer
   occupancy reaches the MIR_th threshold, the output rate of the shaper
   is set to the maximum information rate.  The computation of the
   shaping rate is illustrated in figure 2. We expect that real
   implementations will only use an approximate function to compute the
   shaping rate.

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                   ^
     Shaping rate  |
                   |
                   |
              MIR  |                      =========
                   |                    //
                   |                  //
           EAR(t)  |----------------//
                   |              //
                   |            //
             CIR   |============
                   |
                   |
                   |
                   |------------+---------+----------------------->
                             CIR_th      MIR_th Buffer occupancy

              Figure 2. Computation of shaping rate for srRAS

 2.4. Configuration of the trRAS

   The trRAS is configured by specifying six parameters : the Committed
   Information Rate (CIR), the Peak Information Rate (PIR), the Maximum
   Information Rate (MIR) and three buffer thresholds : CIR_th, PIR_th
   and MIR_th. The CIR shall be specified in bytes per second and MUST
   be configurable. To achieve a good performance, the CIR of a trRAS
   will usually be set at the same value as the CIR of the downstream
   trTCM.  The PIR shall be specified in the same unit as the CIR and
   MUST be configurable. To achieve a good performance, the PIR of a
   trRAS will usually be set at the same value as the PIR of the
   downstream trRAS.  The MIR SHOULD be configurable and shall be
   specified in the same unit as the CIR. A typical value for the MIR
   will be the line rate of the output link of the shaper. When the
   values for CIR, PIR and optionally MIR are configured, the trRAS MUST
   ensure that the following relation is verified :

               CIR <= PIR <= MIR <= line rate

   The three buffer thresholds, CIR_th, PIR_th and MIR_th shall be
   specified in bytes and SHOULD be configurable. If these thresholds
   are configured, then the trRAS MUST ensure that the following
   relation is verified:

               CIR_th <= PIR_th <= MIR_th <= buffer size of the shaper

   The CIR_th, PIR_th and MIR_th will usually depend on the values

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   chosen for the CBS and the PBS in the downstream trTCM. However, this
   dependency does not need to be standardized.

 2.5. Behavior of the trRAS

   The output rate of the trRAS is based on two factors. The first is
   the (long term) average rate of the incoming traffic. This average
   rate can be computed as for the srRAS.

   The second factor is the instantaneous occupancy of the FIFO buffer
   of the shaper. When the buffer occupancy is below CIR_th, the output
   rate of the shaper is set to the maximum of the estimated average
   rate (EAR(t)) and the CIR. This ensures that the shaper will always
   send traffic at least at the CIR. When the buffer occupancy increases
   above CIR_th, the output rate of the shaper is computed as the
   maximum of the EAR(t) and a piecewise linear function F of the buffer
   occupancy. This piecewise function can be defined as follows.  The
   first piece is between zero and CIR_th where F is equal to CIR.  This
   means that when the buffer occupancy is below a certain threshold
   CIR_th, the shaping rate is at least CIR.  The second piece is
   between CIR_th and PIR_th where F increases linearly from CIR to PIR.
   The third part is from PIR_th to MIR_th where F increases linearly
   from PIR to the MIR and finally when the buffer occupancy is above
   MIR_th, the shaping rate remains constant at the MIR.  The
   computation of the shaping rate is illustrated in figure 3. We expect
   that real implementations will use an approximation of the function
   shown in this figure to compute the shaping rate.

                   ^
     Shaping rate  |
                   |
             MIR   |                               ======
                   |                            ///
                   |                         ///
             PIR   |                      ///
                   |                    //
                   |                  //
           EAR(t)  |----------------//
                   |              //
                   |            //
             CIR   |============
                   |
                   |
                   |
                   |------------+---------+--------+------------------------>
                           CIR_th      PIR_th    MIR_th        Buffer occupancy

              Figure 3. Computation of shaping rate for trRAS

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3. Description of the green RAS.

 3.1. The green rate adaptive shapers

   The srRAS and the trRAS described in the previous section are not
   aware of the status of the meter.  This entails that a RAS could
   unnecessarily delay a packet although there are sufficient tokens
   available to color the packet green. This delay could mean that TCP
   takes more time to increase its congestion window and this may lower
   the performance with TCP traffic. The green RAS shown in figure 4
   solves this problem by coupling the shaper with the meter.

                         Status       Result
                      +----------+ +----------+
                      |          | |          |
                      V          | |          V
                 +--------+   +-------+   +--------+
      Incoming   | green  |   |       |   |        |   Outgoing
      Packet  ==>|  RAS   |==>| Meter |==>| Marker |==>Packet
      Stream     |        |   |       |   |        |   Stream
                 +--------+   +-------+   +--------+

                            Figure 4. green RAS

   The two rate adaptive shapers described in section 2 calculate a
   shaping rate, which is defined as the maximum of the estimated
   average incoming data rate and some function of the buffer occupancy.
   Using this shaping rate, the RAS computes the time schedule at which
   the packet at the head of the queue of the shaper is to be released.
   The main idea of the green RAS is to couple the shaper with the
   downstream meter so that the green RAS knows at what time the packet
   at the head of its queue would be accepted as green by the meter. If
   this time instant is earlier than the release time computed from the
   current shaping rate, then the packet can be released at this time
   instant. Otherwise, the packet at the head of the queue of the green
   RAS will be released at the time instant calculated from the current
   shaping rate.

 3.2. Configuration of the Green single rate Rate Adaptive Shaper (G-
   srRAS)

   The G-srRAS must be configured in the same way as the srRAS (see
   section 2.2).

 3.3. Behavior of the G-srRAS

   First of all, the shaping rate of the G-srRAS is calculated in the

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   same way as for the srRAS.  With the srRAS, this shaping rate
   determines a time schedule, T1, at which the packet at the head of
   the queue is to be released from the shaper.

   A second time schedule, T2, is calculated as the earliest time
   instant at which the packet at the head of the shaper's queue would
   be colored as green by the downstream srTCM. Suppose that a packet of
   size B bytes is at the head of the shaper and that CIR is the
   Committed Information Rate of the srTCM in bytes per second. If we
   denote the current time by t and by Tc(t) the amount of green tokens
   in the token bucket of the srTCM at time t, then T2 is equal to
   max(t, t+(B-Tc(t))/CIR).  If B is larger than CBS, the Committed
   Burst Size of the srTCM, then T2 is set to infinity.

   When a packet arrives at the head of the queue of the shaper, it will
   leave this queue not sooner than min(T1, T2) from the shaper.

 3.4 Configuration of the Green two rates Rate Adaptive Shaper (G-trRAS)

   The G-trRAS must be configured in the same way as the trRAS (see
   section 2.4).

 3.5. Behavior of the G-trRAS

   First of all, the shaping rate of the G-trRAS is calculated in the
   same way as for the trRAS.  With the trRAS, this shaping rate
   determines a time schedule, T1, at which the packet at the head of
   the queue is to be released from the shaper.

   A second time schedule, T2, is calculated as the earliest time
   instant at which the packet at the head of the shaper's queue would
   be colored as green by the downstream trTCM. Suppose that a packet of
   size B bytes is at the head of the shaper and that CIR is the
   Committed Information Rate of the srTCM in bytes per second. If we
   denote the current time by t and by Tc(t) (resp. Tp(t)) the amount of
   green (resp. yellow) tokens in the token bucket of the trTCM at time
   t, then T2 is equal to max(t, t+(B-Tc(t))/CIR,t+(B-Tp(t))/PIR).  If B
   is larger than CBS, the committed burst size, or PBS, the peak burst
   size, of the srTCM, then T2 is set to infinity.

   When a packet arrives at the head of the queue of the shaper, it will
   leave this queue not sooner than min(T1, T2) from the shaper.

4. Assumption

   The shapers discussed in this document assume that the Internet
   traffic is dominated by protocols such as TCP that react
   appropriately to congestion by decreasing their transmission rate.

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   The proposed shapers do not provide a performance gain if the traffic
   is composed of protocols that do not react to congestion by
   decreasing their transmission rate.

5. Example services

   The shapers discussed in this document can be used where the TCMs
   proposed in [RFC2697] and [RFC2698] are used. In fact, simulations
   briefly discussed in Appendix A show that the performance of TCP can
   be improved when a rate adaptive shaper is used upstream of a TCM. We
   expect such rate adaptive shapers to be particuarly useful at the
   edge of the network, for example inside (small) access routers or
   even network adapters.

6. The rate adaptive shaper combined with other markers

   This document explains how the idea of a rate adaptive shaper can be
   combined with the srTCM and the trTCM.  This resulted in the srRAS
   and the G-srRAS for the srTCM and in the trRAS and the G-trRAS for
   the trTCM.  Similar adaptive shapers could be developped to support
   other traffic markers such as the Time Sliding Window Three Color
   Marker (TSWTCM) [Fang].  However, the exact definition of such new
   adaptive shapers and their performance is outside the scope of this
   document.

7. Security Issues

   The shapers described in this document have no known security
   concerns.

8. Intellectual Property Rights

   The IETF has been notified of intellectual property rights claimed in
   regard to some or all of the specification contained in this
   document.  For more information consult the online list of claimed
   rights.

9. Acknowledgement

   We would like to thank Emmanuel Desmet for his comments.

10. References

[Azeem] F. Azeem, A. Rao,X. Lu and S. Kalyanaraman, "TCP-Friendly
        Traffic Conditioners for Differentiated Services", draft-azeem-
        tcpfriendly-diffserv-00.txt, March 1999, Work in progress.

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[RFC2475]S. Blake, et al., "An Architecture for Differentiated Ser-
        vices", RFC 2475, December 1998.

[Bonaventure]
        O. Bonaventure, "Integration of ATM under TCP/IP to provide ser-
        vices with a guaranteed minimum bandwidth", Ph. D. thesis,
        University of Liege, September 1998.

[Clark] D. D. Clark, and W. Fang, "Explicit Allocation of Best-Effort
        Packet Delivery Service", IEEE/ACM Trans. on Networking, Vol. 6,
        No. 4, August 1998.

[Cnodder]S. De Cnodder, "Rate Adaptive Shapers for Data Traffic in
        DiffServ Networks", NetWorld+Interop 2000 Engineers Conference,
        Las Vegas, Nevada, USA, May 10-11, 2000.

[Fang]  W. Fang, N. Seddigh, and B. Nandy, "A Time Sliding Window Three
        Colour Marker (TSWTCM)", Internet draft draft-fang-diffserv-tc-
        tswtcm-01.txt

[Floyd] S. Floyd, and V. Jacobson, "Random Early Detection Gateways for
        Congestion Avoidance", IEEE/ACM Transactions on Networking,
        August 1993.

[RFC2697]J. Heinanen, and R. Guerin, "A Single Rate Three Color Marker",
        RFC 2697, September 1999.

[RFC2698]J. Heinanen, and R. Guerin, "A Two Rate Three Color Marker",
        RFC 2698, September 1999.

[RFC2597]J. Heinanen, F. Baker, W. Weiss, and J. Wroclawski, "Assured
        Forwarding PHB Group", RFC 2597, June 1999.

[Nichols]K. Nichols and B. Carpenter, "Format for Diffserv Working Group
        Traffic Conditioner Drafts", Internet draft draft-ietf-
        diffserv-traffcon-format-00.txt, February 1999, work in progress

[Stoica]I. Stoica and S. Shenker and H. Zhang, "Core-stateless fair
        queueuing : achieving approxiamtely fair bandwidth allocations
        in high speed networks", ACM SIGCOMM98, pp. 118-130, Sept. 1998

[TM41]  ATM Forum, Traffic Management Specification, verion 4.1, 1999

Appendix

 A. Simulation results

        We briefly discuss simulations showing the benefits of the

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        proposed shapers in simple network environments. Additional
        simulation results may be found in [Cnodder].

  A.1 description of the model

        To evaluate the rate adaptive shaper through simulations, we use
        the simple network model depicted in Figure A.1.  In this net-
        work, we consider that a backbone network is used to provide a
        LAN Interconnection service to ten pairs of LANs. Each LAN
        corresponds to an uncongested switched 10 Mbps LAN with ten
        workstations attached to a customer router (C1-C10 in figure
        A.1).  The delay on the LAN links is set to 1 msec. The MSS size
        of the workstations is set to 1460 bytes.  The workstations on
        the left hand side of the figure send traffic to companion
        workstations located on the right hand side of the figure. All
        traffic from the LAN attached to customer router C1 is sent to
        the LAN attached to customer router C1'. There are ten worksta-
        tions on each LAN and each workstation implements SACK-TCP with
        a maximum window size of 64 KBytes.

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              2.5 msec, 34 Mbps                      2.5 msec, 34 Mbps
             <-------------->                      <-------------->
        \+---+                                                     +---+/
        -| C1|--------------+                       +--------------|C1'|-
        /+---+              |                       |              +---+\
        \+---+              |                       |              +---+/
        -| C2|------------+ |                       | +------------|C2'|-
        /+---+            | |                       | |            +---+\
        \+---+            | |                       | |            +---+/
        -| C3|----------+ | |                       | | +----------|C3'|-
        /+---+          | | |                       | | |          +---+\
        \+---+          | | |                       | | |          +---+/
        -| C4|--------+ +-+----------+     +----------+-+ +--------|C4'|-
        /+---+        |   |          |     |          |   |        +---+\
        \+---+        +---|          |     |          |---+        +---+/
        -| C5|------------|   ER1    |-----|   ER2    |------------|C5'|-
        /+---+        +---|          |     |          |---+        +---+\
        \+---+        |   |          |     |          |   |        +---+/
        -| C6|--------+   +----------+     +----------+   +--------|C6'|-
        /+---+            ||||                     ||||            +---+\
        \+---+            ||||      <------->      ||||            +---+/
        -| C7|------------+|||       70 Mbps       |||+------------|C7'|-
        /+---+             |||       10 msec       |||             +---+\
        \+---+             |||                     |||             +---+/
        -| C8|-------------+||                     ||+-------------|C8'|-
        /+---+              ||                     ||              +---+\
        \+---+              ||                     ||              +---+/
        -| C9|--------------+|                     |+--------------|C9'|-
        /+---+               |                     |               +---+\
        \+---+               |                     |               +----+/
        -|C10|---------------+                     +---------------|C10'|-
        /+---+                                                     +----+\
                       Figure A.1. the simulation model.

        The customer routers are connected with 34 Mbps links to the
        backbone network which is, in our case, composed of a single
        bottleneck 70 Mbps link between the edge routers ER1 and ER2.
        The delay on all the customer-edge 34 Mbps links has been set to
        2.5 msec to model a MAN or small WAN environment.  These links
        and the customer routers are not a bottleneck in our environment
        and no losses occurs inside the edge routers.  The customer
        routers are equipped with a trTCM [Heinanen2] and mark the
        incoming traffic. The parameters of the trTCM are shown in table
        A.1.

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           Table A.1: configurations of the trTCMs

           Router          CIR               PIR             Line Rate
           C1              2 Mbps            4 Mbps          34 Mbps
           C2              4 Mbps            8 Mbps          34 Mbps
           C3              6 Mbps           12 Mbps          34 Mbps
           C4              8 Mbps           16 Mbps          34 Mbps
           C5             10 Mbps           20 Mbps          34 Mbps
           C6              2 Mbps            4 Mbps          34 Mbps
           C7              4 Mbps            8 Mbps          34 Mbps
           C8              6 Mbps           12 Mbps          34 Mbps
           C9              8 Mbps           16 Mbps          34 Mbps
           C10            10 Mbps           20 Mbps          34 Mbps

        All customer routers are equipped with a trTCM where the CIR are
        2 Mbps for router C1 and C6, 4 Mbps for C2 and C7, 6 Mbps for C3
        and C8, 8 Mbps for C4 and C9 and 10 Mbps for C5 and C10. Routers
        C6-C10 also contain a trRAS in addition to the trTCM while
        routers C1-C5 only contain a trTCM.  In all simulations, the PIR
        is always twice as large as the CIR.  Also the PBS is the double
        of the CBS.  The CBS will be varied in the different simulation
        runs.

        The edge routers, ER1 and ER2, are connected with a 70 Mbps link
        which is the bottleneck link in our environment. These two
        routers implement the RIO algorithm [Clark] that we have
        extended to support three drop priorities instead of two. The
        thresholds of the parameters are 100 and 200 packets (minimum
        and maximum threshold, respectively) for the red packets, 200
        and 400 packets for the yellow packets and 400 and 800 for the
        green packets. These thresholds are reasonable since there are
        100 TCP connections crossing each edge router. The parameter
        maxp of RIO for green, yellow and red are respectively set to
        0.02, 0.05, and 0.1.  The weight to calculate the average queue
        length which is used by RED or RIO is set to 0.002 [Floyd].

        The simulated time is set to 102 seconds where the first two
        seconds are not used to gather TCP statistics (the so-called
        warm-up time) such as goodput.

  A.2 Simulation results for the trRAS

        For our first simulations, we consider that routers C1-C5 only
        utilize a trTCM while routers C6-C10 utilize a rate adaptive
        shaper in conjunction with a trTCM. All routers use a CBS of 3
        KBytes. In table A.2, we show the total throughput achieved by
        the workstations attached to each LAN as well as the total

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        throughput for the green and the yellow packets as a function of
        the CIR of the trTCM used on the customer router attached to
        this LAN. The throughput of the red packets is equal to the
        difference between the total traffic and the green and the yel-
        low traffic. In table A.3, we show the total throughput achieved
        by the workstations attached to customer routers with a rate
        adaptive shaper.

           Table A.2: throughput in Mbps for the unshaped traffic.
                         green           yellow          total
           2Mbps [C1]    1.10            0.93            2.25
           4Mbps [C2]    2.57            1.80            4.55
           6Mbps [C3]    4.10            2.12            6.39
           8Mbps [C4]    5.88            2.32            8.33
           10Mbps [C5]   7.57            2.37            10.0

           Table A.3: throughput in Mbps for the adaptively shaped
        traffic.
                         green           yellow          total
           2Mbps [C6]    2.00            1.69            3.71
           4Mbps [C7]    3.97            2.34            6.33
           6Mbps [C8]    5.93            2.23            8.17
           8Mbps [C9]    7.84            2.28            10.1
           10Mbps [C10]  9.77            2.14            11.9

        This first simulation shows clearly that the workstations
        attached to an edge router with a rate adaptive shaper have a
        clear advantage, from a performance point of view, with respect
        to workstations attached to an edge router with only a trTCM.
        The performance improvement is the result of the higher propor-
        tion of packets marked as green by the edge routers when the
        rate adaptive shaper is used.

        To evaluate the impact of the CBS on the TCP goodput, we did
        additional simulations were we varied the CBS of all customer
        routers.

        Table A.4 shows the total goodput for workstations attached to ,
        respectively, routers C1 (trTCM with 2 Mbps CIR, no adaptive
        shaping), C6 (trRAS with 2 Mbps CIR and adaptive shaping), C3
        (trTCM with 6 Mbps CIR, no adaptive shaping), and C8 (trRAS with
        6 Mbps CIR and adaptive shaping) for various values of the CBS.
        From this table, it is clear that the rate adaptive shapers pro-
        vide a performance benefit when the CBS is small. With a very
        large CBS, the performance decreases when the shaper is in use.
        However, a CBS of a few hundred KBytes is probably too large in
        many environments.

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           Table A.4: goodput in Mbps (link rate is 70 Mbps) versus CBS
        in KBytes.
           CBS  2_Mbps_unsh     2_Mbps_sh      6_Mbps_unsh    6_Mbps_sh
           3       1.88            3.49          5.91           7.77
           10      2.97            2.91          6.76           7.08
           25      3.14            2.78          7.07           6.73
           50      3.12            2.67          7.20           6.64
           75      3.18            2.56          7.08           6.58
           100     3.20            2.64          7.00           6.62
           150     3.21            2.54          7.11           6.52
           200     3.26            2.57          7.07           6.53
           300     3.19            2.53          7.13           6.49
           400     3.13            2.48          7.18           6.43

  A.3 Simulation results for the Green trRAS

        We use the same scenario as in A.2 but now we use the Green
        trRAS (G-trRAS).

        Table A.5 and Table A.6 show the results of the same scenario as
        for Table A.2 and Table A.3 but the shaper is now the G-trRAS.
        We see that the shaped traffic performs again much better, also
        compared to the previous case (i.e. where the trRAS was used).
        This is because the amount of yellow traffic increases with the
        expense of a slight decrease in the amount of green traffic.
        This can be explained by the fact that the G-trRAS introduces
        some burstiness.

           Table A.5: throughput in Mbps for the unshaped traffic.
                         green           yellow          total
           2Mbps [C1]    1.10            0.95            2.26
           4Mbps [C2]    2.41            1.66            4.24
           6Mbps [C3]    3.94            1.97            6.07
           8Mbps [C4]    5.72            2.13            7.96
           10Mbps [C5]   7.25            2.29            9.64

           Table A.6: throughput in Mbps for the adaptively shaped
        traffic.
                         green           yellow          total
           2Mbps [C6]    1.92            1.75            3.77
           4Mbps [C7]    3.79            3.24            7.05
           6Mbps [C8]    5.35            3.62            8.97
           8Mbps [C9]    6.96            3.48            10.4
           10Mbps [C10]  8.69            3.06            11.7

        The impact of the CBS is shown in Table A.7 which is the same
        scenario as Table A.4 with the only difference that the shaper

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        is now the G-trRAS.  We see that the shaped traffic performs
        much better than the unshaped traffic when the CBS is small.
        When the CBS is large, the shaped and unshaped traffic performs
        more or less the same.  This is in contrast with the trRAS,
        where the performance of the shaped traffic was slightly worse
        in case of a large CBS.

           Table A.7: goodput in Mbps (link rate is 70 Mbps) versus CBS
        in KBytes.
           CBS  2_Mbps_unsh     2_Mbps_sh      6_Mbps_unsh    6_Mbps_sh
           3       1.90            3.44          5.62           8.44
           10      2.95            3.30          6.70           7.20
           25      2.98            3.01          7.03           6.93
           50      3.06            2.85          6.81           6.84
           75      3.08            2.80          6.87           6.96
           100     2.99            2.78          6.85           6.88
           150     2.98            2.70          6.80           6.81
           200     2.96            2.70          6.82           6.97
           300     2.94            2.70          6.83           6.86
           400     2.86            2.62          6.83           6.84

  A.4 Conclusion simulations

        From these simulations, we see that the shaped traffic has much
        higher throughput compared to the unshaped traffic when the CBS
        was small.  When the CBS is large, the shaped traffic performs
        slightly less than the unshaped traffic due to the delay in the
        shaper.  The G-trRAS solves this problem.  Additionnal simula-
        tion results may be found in [Cnodder]

Authors Addresses

   Olivier Bonaventure
   Institut d'Informatique (CS Dept)
   Facultes Universitaires Notre-Dame de la Paix
   Rue Grandgagnage 21, B-5000 Namur, Belgium.
   E-mail: Olivier.Bonaventure@info.fundp.ac.be
   URL   : http://www.info.fundp.ac.be/~obo

   Stefaan De Cnodder
   Alcatel Network Strategy Group
   Fr. Wellesplein 1, B-2018 Antwerpen, Belgium.
   Phone : 32-3-240-8515
   Fax   : 32-3-240-9932
   E-mail: stefaan.de_cnodder@alcatel.be

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