rfc2963.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

                      |          | |          |
                      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).








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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.






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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.





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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.








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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












































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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.




























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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.