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rfc:rfc2963

Network Working Group O. Bonaventure Request for Comments: 2963 FUNDP Category: Informational S. De Cnodder

                                                                Alcatel
                                                           October 2000
         A Rate Adaptive Shaper for Differentiated Services

Status of this Memo

 This memo provides information for the Internet community.  It does
 not specify an Internet standard of any kind.  Distribution of this
 memo is unlimited.

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
 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:

Bonaventure & De Cnodder Informational [Page 1] RFC 2963 A Rate Adaptive Shaper October 2000

 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
 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].

Bonaventure & De Cnodder Informational [Page 2] RFC 2963 A Rate Adaptive Shaper October 2000

                                   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 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:

Bonaventure & De Cnodder Informational [Page 3] RFC 2963 A Rate Adaptive Shaper October 2000

             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.

Bonaventure & De Cnodder Informational [Page 4] RFC 2963 A Rate Adaptive Shaper October 2000

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

Bonaventure & De Cnodder Informational [Page 5] RFC 2963 A Rate Adaptive Shaper October 2000

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

Bonaventure & De Cnodder Informational [Page 6] RFC 2963 A Rate Adaptive Shaper October 2000

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

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

Bonaventure & De Cnodder Informational [Page 7] RFC 2963 A Rate Adaptive Shaper October 2000

3.3. Behavior of the G-srRAS

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

Bonaventure & De Cnodder Informational [Page 8] RFC 2963 A Rate Adaptive Shaper October 2000

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.
 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 particularly 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 developed 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 Considerations

 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.

Bonaventure & De Cnodder Informational [Page 9] RFC 2963 A Rate Adaptive Shaper October 2000

10. References

 [Azeem]       Azeem, F., Rao, A., Lu, X. and S. Kalyanaraman, "TCP-
               Friendly Traffic Conditioners for Differentiated
               Services", Work in Progress.
 [RFC2475]     Blake S., Black, D., Carlson, M., Davies, E., Wang, Z.
               and W. Weiss, "An Architecture for Differentiated
               Services", RFC 2475, December 1998.
 [Bonaventure] Bonaventure O., "Integration of ATM under TCP/IP to
               provide services with a minimum guaranteed bandwidth",
               Ph. D. thesis, University of Liege, Belgium, September
               1998.
 [Clark]       Clark D. and Fang, W., "Explicit Allocation of Best-
               Effort Packet Delivery Service", IEEE/ACM Trans. on
               Networking, Vol. 6, No. 4, August 1998.
 [Cnodder]     De Cnodder S., "Rate Adaptive Shapers for Data Traffic
               in DiffServ Networks", NetWorld+Interop 2000 Engineers
               Conference, Las Vegas, Nevada, USA, May 10-11, 2000.
 [Fang]        Fang W., Seddigh N. and B. Nandy, "A Time Sliding
               Window Three Colour Marker (TSWTCM)", RFC 2859, June
               2000.
 [Floyd]       Floyd S. and V. Jacobson, "Random Early Detection
               Gateways for Congestion Avoidance", IEEE/ACM
               Transactions on Networking, August 1993.
 [RFC2697]     Heinanen J. and R. Guerin, "A Single Rate Three Color
               Marker", RFC 2697, September 1999.
 [RFC2698]     Heinanen J. and R. Guerin, "A Two Rate Three Color
               Marker", RFC 2698, September 1999.
 [RFC2597]     Heinanen J., Baker F., Weiss W. and J. Wroclawski,
               "Assured Forwarding PHB Group", RFC 2597, June 1999.
 [Nichols]     Nichols K. and B. Carpenter, "Format for Diffserv
               Working Group Traffic Conditioner Drafts", Work in
               Progress.

Bonaventure & De Cnodder Informational [Page 10] RFC 2963 A Rate Adaptive Shaper October 2000

 [Stoica]      Stoica I., Shenker S. and H. Zhang, "Core-stateless
               fair queueuing: achieving approximately fair bandwidth
               allocations in high speed networks", ACM SIGCOMM98, pp.
               118-130, Sept. 1998
 [TM41]        ATM Forum, Traffic Management Specification, verion
               4.1, 1999

Bonaventure & De Cnodder Informational [Page 11] RFC 2963 A Rate Adaptive Shaper October 2000

Appendix

A. Simulation results

 We briefly discuss simulations showing the benefits of the 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 network, 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
 workstations on each LAN and each workstation implements SACK-TCP
 with a maximum window size of 64 KBytes.

Bonaventure & De Cnodder Informational [Page 12] RFC 2963 A Rate Adaptive Shaper October 2000

         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.

Bonaventure & De Cnodder Informational [Page 13] RFC 2963 A Rate Adaptive Shaper October 2000

      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 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

Bonaventure & De Cnodder Informational [Page 14] RFC 2963 A Rate Adaptive Shaper October 2000

 packets is equal to the difference between the total traffic and the
 green and the yellow 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 proportion 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 provide 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.

Bonaventure & De Cnodder Informational [Page 15] RFC 2963 A Rate Adaptive Shaper October 2000

    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 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

Bonaventure & De Cnodder Informational [Page 16] RFC 2963 A Rate Adaptive Shaper October 2000

 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.  Additional simulation results may be
 found in [Cnodder]

Bonaventure & De Cnodder Informational [Page 17] RFC 2963 A Rate Adaptive Shaper October 2000

Authors' Addresses

 Olivier Bonaventure
 Infonet research group
 Institut d'Informatique (CS Dept)
 Facultes Universitaires Notre-Dame de la Paix
 Rue Grandgagnage 21, B-5000 Namur, Belgium.
 EMail: Olivier.Bonaventure@info.fundp.ac.be
 URL:   http://www.infonet.fundp.ac.be
 Stefaan De Cnodder
 Alcatel Network Strategy Group
 Fr. Wellesplein 1, B-2018 Antwerpen, Belgium.
 Phone:  32-3-240-8515
 Fax:    32-3-240-9932
 EMail:  stefaan.de_cnodder@alcatel.be

Bonaventure & De Cnodder Informational [Page 18] RFC 2963 A Rate Adaptive Shaper October 2000

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Bonaventure & De Cnodder Informational [Page 19]

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