Internet Engineering Task Force Olivier Bonaventure INTERNET DRAFT FUNDP Stefaan De Cnodder Alcatel 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. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. 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 Bonaventure & De Cnodder A rate adaptive shaper [Page 1] Internet Draft draft-bonaventure-diffserv-rashaper-01.txt June 1999 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 Bonaventure & De Cnodder A rate adaptive shaper [Page 2] Internet Draft draft-bonaventure-diffserv-rashaper-01.txt June 1999 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 Bonaventure & De Cnodder A rate adaptive shaper [Page 3] Internet Draft draft-bonaventure-diffserv-rashaper-01.txt June 1999 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. Bonaventure & De Cnodder A rate adaptive shaper [Page 4] Internet Draft draft-bonaventure-diffserv-rashaper-01.txt June 1999 ^ 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. Bonaventure & De Cnodder A rate adaptive shaper [Page 5] Internet Draft draft-bonaventure-diffserv-rashaper-01.txt June 1999 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 Bonaventure & De Cnodder A rate adaptive shaper [Page 6] Internet Draft draft-bonaventure-diffserv-rashaper-01.txt June 1999 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). Bonaventure & De Cnodder A rate adaptive shaper [Page 7] Internet Draft draft-bonaventure-diffserv-rashaper-01.txt June 1999 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 Bonaventure & De Cnodder A rate adaptive shaper [Page 8] Internet Draft draft-bonaventure-diffserv-rashaper-01.txt June 1999 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 Bonaventure & De Cnodder A rate adaptive shaper [Page 9] Internet Draft draft-bonaventure-diffserv-rashaper-01.txt June 1999 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 Bonaventure & De Cnodder A rate adaptive shaper [Page 10] Internet Draft draft-bonaventure-diffserv-rashaper-01.txt June 1999 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 Bonaventure & De Cnodder A rate adaptive shaper [Page 11] Internet Draft draft-bonaventure-diffserv-rashaper-01.txt June 1999 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. Bonaventure & De Cnodder A rate adaptive shaper [Page 12] Internet Draft draft-bonaventure-diffserv-rashaper-01.txt June 1999 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. Bonaventure & De Cnodder A rate adaptive shaper [Page 13] Internet Draft draft-bonaventure-diffserv-rashaper-01.txt June 1999 [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 Bonaventure & De Cnodder A rate adaptive shaper [Page 14] Internet Draft draft-bonaventure-diffserv-rashaper-01.txt June 1999 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 Bonaventure & De Cnodder A rate adaptive shaper [Page 15] Internet Draft draft-bonaventure-diffserv-rashaper-01.txt June 1999 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 Bonaventure & De Cnodder A rate adaptive shaper [Page 16] Internet Draft draft-bonaventure-diffserv-rashaper-01.txt June 1999 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. Bonaventure & De Cnodder A rate adaptive shaper [Page 17] Internet Draft draft-bonaventure-diffserv-rashaper-01.txt June 1999 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 Bonaventure & De Cnodder A rate adaptive shaper [Page 18] Internet Draft draft-bonaventure-diffserv-rashaper-01.txt June 1999 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 Bonaventure & De Cnodder A rate adaptive shaper [Page 19] Internet Draft draft-bonaventure-diffserv-rashaper-01.txt June 1999 Bonaventure & De Cnodder A rate adaptive shaper [Page 20]