📄 rfc2963.txt
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| | | |
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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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.
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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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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.
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