One document matched: draft-bonaventure-diffserv-rashaper-01.txt
Differences from draft-bonaventure-diffserv-rashaper-00.txt
October, 1999
Expires April, 2000
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.
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Task Force (IETF), its areas, and its working groups. Note that
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Abstract
This memo describes two rate adaptive shapers (RAS) that can be used
in combination with the Three Color Markers (srTCM and trTCM)
proposed in [Heinanen1]. 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 and thus increasing the proportion of
packets marked as green by the TCM. In addition, two colored rate
adaptive shapers (CRAS), which take into account the color of the
packet at the head of the shaper and the status of the meters, are
described. Simulation results showing the improved performance are
briefly discussed in the appendix.
1. Introduction
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In DiffServ networks, 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) described in [Heinanen1] and the two rates three
color marker (trTCM) in [Heinanen2].
Similar markers were proposed for ATM networks and simulations have
shown that their performance with TCP traffic was not always perfect
and several researchers have shown that these performance problems
could be solved in two ways :
1. increasing the burst size, i.e. increasing CBS and PBS, or
2. shaping the incoming 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 providing a low packet loss
ratio can become difficult. To efficiently support bursty traffic,
additional resources such as buffer space are needed. The major
disadvantage of shaping is that the traffic encounters some delay in
the shaper's buffers.
In this document, we propose two shapers that can reduce the
burstiness of the traffic upstream of a srTCM or trTCM. By reducing
the burstiness of the traffic, the shapers increase the percentage of
packets marked as greens by the TCMs and thus the overall goodput of
the users using such a shaper.
In addition, we also propose two colored shapers, which reduces the
delay in the shaper by taking into account the color of the packets
and the status of the meter.
A few simulation results showing the usefulness of the proposed
shapers may be found in the appendix.
The structure of this document follows the structure proposed in
[Nichols].
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 [Guerin] [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
[Heinanen1] and [Heinanen2].
Result
+----------+
| |
| V
+--------+ +-------+ +--------+
Incoming | | | | | | Outgoing
Packet ==>| RAS |==>| Meter |==>| Marker |==>Packet
Stream | | | | | | Stream
+--------+ +-------+ +--------+
Figure 1. Rate adaptive shaper
The rate adaptive shapers are thus different from the shapers
described in [RFC2475] since they shape the traffic before the
traffic is metered. 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 should avoid to discard packets in contrast with
classical leaky-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 at 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 [Heinanen1] and [Heinanen2].
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
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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
at 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 or packets 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 CIR_th and MIR_th may depend on the values chosen for the CBS and
the 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.
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 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.
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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 or packets 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 may depend on the values chosen for the
CBS and the PBS in the downstream trTCM. However, this dependency
does not need to be standardized.
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2.5. Behavior of the trRAS
The output rate of the trRAS is also based on two factors. The first
one 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 is increased 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.
^
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 colored RAS.
3.1. The colored rate adaptive shapers
The srRAS and the trRAS described in the previous section do not look
to the status of the meter nor to the color of the first packet at
the head of the shaper. This means that a RAS could delay a packet
even if this packet is in-profile. This could be a problem in some
environments. To solve this problem, we propose a colored RAS which
behaves as shown in figure 4.
Status Result
+----------+ +----------+
| | | |
V | | V
+--------+ +-------+ +--------+
Incoming |colored | | | | | Outgoing
Packet ==>| RAS |==>| Meter |==>| Marker |==>Packet
Stream | | | | | | Stream
+--------+ +-------+ +--------+
Figure 4. colored RAS
The two rate adaptive shapers (srRAS and trRAS), 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 calculates the time schedule at which the
next packet of the shaper must be released. The main idea of the
colored RAS is quite simple : if the packet at the head of the queue
of the colored RAS would be conforming at an earlier instant than the
time schedule computed by the RAS, then this packet can be
transmitted as soon as it becomes conforming. This means that when
the colored RAS has to schedule the release time of the next packet,
the colored RAS asks the meter for its status.
If the packet at the head of the queue of the colored RAS does not
become conforming at an earlier instant than the time schedule
computed by the RAS, then we have three possibilities:
1) transmit the packet at the time schedule computed by the RAS (we
call this the SHAPED mode further on),
2) transmit the packet immediately to prevent large delays (we call
this the FAST mode further on), or
3) we can transmit the packet at the time schedule when it becomes
conforming to the best color before the time schedule computed by the
RAS (we call this the PROMOTED mode further on).
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We make the assumption that these shapers are used for AF where green
packets will receive a better treatment than yellow and red packets,
and yellow packets will receive a better treatment than red packets
[Heinanen3].
3.2. Configuration of the C-srRAS
The C-srRAS must be configured in the same way as the srRAS (see
section 2.2) and in addition the mode of operation must be specified.
This mode can be FAST, PROMOTED, or SHAPED.
3.3. Behavior of the C-srRAS
First of all, an output shaping rate is calculated in the same way as
the srRAS did. With the srRAS, this shaping rate determines a time
schedule at when the next packet has to be released from the shaper.
For the C-srRAS, this shaping rate is used to deterime a latest
possible release time, called TRAS. TRAS is calculated as the
previous TRAS + L/SR(t), where L is the packet length of the
previously transmitted packet and SR(t) the shaping rate as
determined by the srRAS.
Then all time instants at when the packet at the head of the shaper
will become conforming to the current color or a better color are
calculated. From these time instants, the time instant belonging to
the best color which falls before the latest possible release time,
TRAS, will be selected as the release time of the next packet. The
value for TRAS is then set equal to the maximum of this release time
and the previous TRAS, and this new value for TRAS will act as the
previous TRAS value for the next packet (see first paragraph).
If no such time instants exist we have to demote the packet (i.e. we
have to give the packet a worse color than its current color) and the
behavior of the C-srRAS will be determined by the selected mode. In
the SHAPED mode, the packet will be release at the latest possible
release time as calculated with the C-srRAS. In the FAST mode, the
packet is sent immediately without any additional delay. The
PROMOTED mode will try to give the packet a color as close as
possible to the current color. This means that now all time instants
at when the packet at the head of the shaper will become conforming
to a worse color than the current color are calculated. From these
time instants, the time instant belonging to the best color which
falls before the latest possible release time TRAS will be selected
as the release time of the packet.
Let us define Tcon(x) as the time instant at when the packet at the
head of the shaper becomes conforming with respect to color x. Then
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the behavior when the next packet has to be scheduled can be
described more formally as follows:
1) TRASprime <- TRAS
2) calculate TRAS <- TRASprime + L/SR(t)
3) if it is possible to keep the color of the packet or to promote
the packet earlier than TRAS, i.e.
if Tcon(color of packet at the head of the shaper) <= TRAS,
then promote the packet as much as possible, i.e.
if Tcon(green) <= TRAS, then send the packet at Tcon(green), else
if the packet is yellow or red and Tcon(yellow) <= TRAS then send the
packet at Tcon(yellow), else
the packet must be sent immediately (here, the packet is red and
Tcon(yellow) > TRAS.
Finally, set TRAS <- max(release time packet, TRASprime).
4) else sent the packet according to the selected mode
3.4 Configuration of the C-trRAS
The C-trRAS must be configured in the same way as the trRAS (see
section 2.4) and in addition the mode of operation must be specified.
This mode can be FAST, PROMOTED, or SHAPED.
3.5. Behavior of the C-trRAS
The behavior of the C-trRAS is the same as with the C-srRAS except
that now the shaping rate, SR(t), is determined by the trRAS.
3.6. Examples of the different modes SHAPED, FAST, and PROMOTED.
Table 3.1, Table 3.2, and Table 3.3 show the time instants (marked
with a X) at when the next packet will be released. Note that in
these examples, we put the marker in the color-blind mode such that
it is possible to promote packets. Tcon(x) in the tables represent
the time instant at which the packet at the head of the shaper
becomes conforming with respect to color x. In case the marker are
put in the color-aware mode, it is impossible to promote packets due
to the definition of the color-aware mode (see [Heinanen1] and
[Heinanen2]) and Tcon(green) for example will not exist in case there
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is a yellow or a red packet at the head of the shaper.
As you can see, the only difference between FAST and PROMOTED is when
there is a green packet at the head of the shaper and only
Tcon(green) is beyond TRAS. The mode has no impact when the packet
is red as can be seen from Table 3.3.
When we put the marker in the color-aware mode, and the packet at the
head of the shaper is red, then this packet will always sent
immediately when the shaper is put into the color-aware mode. In
this case, green packets can never be delayed behind red packets.
Table 3.1: green packet at the head of shaper.
selection Tcon(red) Tcon(yellow) Tcon(green) TRAS time
rules |-------------+-----------------+------------+--------->
RAS X
SHAPED X
FAST X
PROMOTED X
Tcon(red) Tcon(yellow) TRAS Tcon(green) time
|-------------+-----------------+------------+--------->
RAS X
SHAPED X
FAST X
PROMOTED X
Tcon(red) TRAS Tcon(yellow) Tcon(green) time
|-------------+-----------------+------------+--------->
RAS X
SHAPED X
FAST X
PROMOTED X
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Table 3.2: yellow packet at the head of shaper.
selection Tcon(red) Tcon(yellow) Tcon(green) TRAS time
rules |-------------+-----------------+------------+--------->
RAS X
SHAPED X
FAST X
PROMOTED X
Tcon(red) Tcon(yellow) TRAS Tcon(green) time
|-------------+-----------------+------------+--------->
RAS X
SHAPED X
FAST X
PROMOTED X
Tcon(red) TRAS Tcon(yellow) Tcon(green) time
|-------------+-----------------+------------+--------->
RAS X
SHAPED X
FAST X
PROMOTED X
Table 3.3: yellow packet at the head of shaper.
selection Tcon(red) Tcon(yellow) Tcon(green) TRAS time
rules |-------------+-----------------+------------+--------->
RAS X
SHAPED X
FAST X
PROMOTED X
Tcon(red) Tcon(yellow) TRAS Tcon(green) time
|-------------+-----------------+------------+--------->
RAS X
SHAPED X
FAST X
PROMOTED X
Tcon(red) TRAS Tcon(yellow) Tcon(green) time
|-------------+-----------------+------------+--------->
RAS X
SHAPED X
FAST X
PROMOTED X
3.7. Behavior of colored RAS when there are only green packets
The colored RAS results in a lower delay in the shaper and tries to
keep the current color of the packet. It could also be possible that
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the packets are not yet colored or that we are not interested in the
current color of the packets while still optimizing the delay and the
amount of green packets. For this, we can use the green colored RAS,
which is the same as the colored RAS where all packets are pre-
colored as green, so it is not really a new shaper. This means that
the algorithm in section 3.2 becomes much simpler and is as follows:
1) TRASprime <- TRAS
2) calculate TRAS <- TRASprime + L/SR(t)
3) if Tcon(green) <= TRAS then
release packet at Tcon(green), and
set TRAS <- max(release time packet, TRASprime)
4) else (if Tcon(green) > TRAS) sent the packet according to the
selected mode
It is the same as the colored RAS but now we take in step 3 of the
algorithm in section 3.2 the green color instead of the color of the
packet at the head of the shaper.
This green colored RAS tries to optimize the delay in the shaper and
the number of green packets. In fact, this green colored RAS is the
same as the colored RAS where all packets are pre-colored as green.
This means that the configuration and the behavior is exactly the
same as the colored RAS. Here, we have described how the colored RAS
can be used when the packets where not yet colored or when their
color was of no importance. This also means that the marker (srTCM
or trTCM) also has to ignore the color of the packet and thus the
marker has to be put in the color-blind mode.
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.
5. Example services
The shapers discussed in this document can be used in most situations
where the TCMs proposed in [Heinanen1] and [Heinanen2] are used. In
fact, simulations briefly discussed in Appendix A show that the
performance of TCP can be improved when the trTCM is used in
conjunction with one of the shapers described in this document than
when the trTCM is used alone. We expect that similar simulations
results would be found with the srTCM.
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The RAS makes the traffic stream smooth such that as much as possible
packets are colored as green. The colored RAS (in particular the
green colored RAS) tries in addition to decrease the delay in the
shaper.
6. Security Issues
The shapers described in this document have no known security
concerns.
7. Acknowledgement
We would like to thank Emmanuel Desmet for his comments.
8. References
[Azeem] Feroz Azeem, Amit Rao,Xiuping Lu and Shiv Kalyanaraman, TCP-
Friendly Traffic Conditioners for Differentiated Services,
draft-azeem-tcpfriendly-diffserv-00.txt, March 1999, Work in
progress.
[Bonaventure]
Olivier Bonaventure, "Integration of ATM under TCP/IP to provide
services with a guaranteed minimum bandwidth", Ph. D. thesis,
University of Liege, September 1998.
[Clark] David D. Clark, and Wenjia Fang, "Explicit Allocation of Best-
Effort Packet Delivery Service", IEEE/ACM Trans. on Networking,
Vol. 6, No. 4, August 1998.
[Guerin]R. Guerin and J. Heinanen, UBR+ service category definition, ATM
Forum contribution ATM96-1598, December 1996.
[Heinanen1]
J. Heinanen, and R. Guerin, "A Single Rate Three Color Marker",
RFC 2697, September 1999.
[Heinanen2]
J. Heinanen, and R. Guerin, "A Two Rate Three Color Marker", RFC
2698, September 1999.
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[Heinanen3]
J. Heinanen, F. Baker, W. Weiss, and J. Wroclawski, "Assured
Forwarding PHB Group", RFC 2597, June 1999.
[Floyd1]Sally Floyd, and Van Jacobson, "Random Early Detection Gateways
for Congestion Avoidance", IEEE/ACM Transactions on Networking,
August 1993.
[Floyd2]Sally Floyd, "RED : Optimum functions for computing the drop
probability", email available at http://www-
nrg.ee.lbl.gov/floyd/REDfunc.txt, October 1997.
[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
[RFC2475]S. Blake, et al., An Architecture for Differentiated Services.
RFC 2475, December 1998.
[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
A.1 description of the model
To evaluate the rate adaptive shaper through simulations, we use
the network model depicted in Figure A.1. In this network, we
consider that a backbone network is used to provide a LAN Inter-
connection 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 worksta-
tions 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
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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.
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|------------+||| 60 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 34 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
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A.1.
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 60 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 preferences 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. The parameter maxp of RIO was set to 0.02 and we
used as drop function the function proposed in [Floyd2] such
that when the average queue length exceeds the maximum thres-
hold, the drop probability does not suddenly jumps to 1. The
weight to calculate the average queue length which is used by
RED or RIO is set to 0.002 [Floyd1].
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
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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 goodput achieved by the
workstations attached to each LAN as a function of the CIR of
the trTCM used on the customer router attached to this LAN. In
table A.3, we show the total goodput achieved by the worksta-
tions attached to customer routers with a rate adaptive shaper.
Table A.2: throughput in Mbps for the unshaped traffic.
green yellow total
2Mbps [C1] 1.09 0.83 1.94
4Mbps [C2] 2.30 1.39 3.71
6Mbps [C3] 3.70 1.60 5.30
8Mbps [C4] 5.47 1.66 7.13
10Mbps [C5] 7.08 1.66 8.74
Table A.3: throughput in Mbps for the shaped traffic.
green yellow total
2Mbps [C6] 2.00 0.81 2.81
4Mbps [C7] 3.98 1.08 5.06
6Mbps [C8] 5.86 0.74 6.60
8Mbps [C9] 7.76 0.58 8.34
10Mbps [C10] 9.79 0.52 10.3
This first simulation shows clearly that the workstations
attached to an edge router with a rate adaptive shaper havea
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.
Table A.4 shows the total goodput for workstations attached to
routers C1 (trTCM - 2_Mbps_unsh), C5 (trTCM - 10_Mbps_unsh), C6
(trRAS and trTCM 2_Mbps_sh), and C10 (trRAS and trTCM
10_Mbps_sh) for various values for the maximum burst size when
the rate adaptive shaper is used. It is clear that routers with
the rate adaptive shaper perform better if the CBS is small.
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 (rate adaptive shaper, link rate
is 60 Mbps) versus CBS in KBytes.
CBS 2_Mbps_unsh 2_Mbps_sh 10_Mbps_unsh 10_Mbps_sh
3 1.84 2.71 8.37 9.98
10 2.62 2.40 8.09 9.68
25 2.49 2.26 8.33 9.49
50 2.37 2.15 8.69 9.40
75 2.32 2.10 8.77 9.22
100 2.35 2.11 8.88 9.17
150 2.36 2.12 8.95 9.12
200 2.33 2.10 9.10 9.06
300 2.33 2.10 9.24 8.69
400 2.33 2.04 9.32 8.77
A.3 Simulation results for the C-trRAS
We use the same shaper as in A.2 but now we use the C-trRAS.
The mode used in these simulations is SHAPED and we assume that
all packets are pre-colored as green.
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 colored
shaper. We see that the shaped traffic performs again much
bette, 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
colored shaper introduces some burstiness.
Table A.5: throughput in Mbps for the unshaped traffic.
green yellow total
2Mbps [C1] 1.04 0.77 1.83
4Mbps [C2] 2.25 1.24 3.51
6Mbps [C3] 3.62 1.38 5.01
8Mbps [C4] 5.15 1.51 6.67
10Mbps [C5] 6.70 1.54 8.24
Table A.6: throughput in Mbps for the shaped traffic.
green yellow total
2Mbps [C6] 1.89 1.46 3.34
4Mbps [C7] 3.46 2.08 5.54
6Mbps [C8] 5.04 2.13 7.18
8Mbps [C9] 6.80 1.82 8.62
10Mbps [C10] 8.58 1.43 10.0
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 C-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 (rate adaptive shaper, link rate
is 60 Mbps) versus CBS in KBytes.
CBS 2_Mbps_unsh 2_Mbps_sh 10_Mbps_unsh 10_Mbps_sh
3 1.73 3.23 7.91 9.66
10 2.54 2.67 8.21 9.26
25 2.47 2.42 8.35 9.21
50 2.32 2.33 8.68 8.98
75 2.32 2.26 8.84 8.90
100 2.26 2.22 8.81 8.99
150 2.24 2.17 8.72 9.04
200 2.21 2.17 8.89 9.14
300 2.19 2.13 9.06 9.10
400 2.18 2.12 9.06 9.10
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
RAS. The colored RAS solves this problem.
Other scenarios and simulations with the modes FAST and PROMOTED
are for further work.
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 Corporate Research Center
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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