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An aggregate marker for bandwidth fairness in DiffServ
Journal of Network and Computer Applications 35 (2012) 1973–1978
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Journal of Network and Computer Applications journal homepage: www.elsevier.com/locate/jnca
An aggregate marker for bandwidth fairness in DiffServ S. Sudha n, N. Ammasaigounden Department of Electrical and Electronics Engineering, National Institute of Technology, Tiruchirappalli, Tamil Nadu, India
a r t i c l e i n f o
abstract
Article history: Received 26 April 2012 Received in revised form 25 July 2012 Accepted 30 July 2012 Available online 24 August 2012
Surveys and studies on DiffServ exhibit existence of unfairness between aggregates in the excess bandwidth region. Many researchers have proved that providing a proportional fair share of the bandwidth between aggregates solve this. Based on this, aggregate markers such as ItswTCM and I2tswTCM are found to improve bandwidth fairness in DiffServ network among aggregates, when the aggregates are responsive in nature. However, co-existence of non-responsive aggregates with responsive aggregates leads to unfairness. Hence, in this paper an attempt has been made to evade the above unfairness by a new TSW based marker; where the drop precedence of the packet is arrived at an adaptive manner based on its estimated rate and the availability of the network resource. The unique feature of this proposed algorithm is that it provides enhanced fairness not only among responsive aggregates but also between responsive and non-responsive aggregates. Further, simulations have been carried out in NS-2 with changes in RTT, target rate of the aggregates and the number of flows in the aggregate. The results show that the proposed marker reduces the influence of these factors on the fairness performance exhibiting the suitability of the marker for different network topologies. & 2012 Elsevier Ltd. All rights reserved.
Keywords: Differentiated Services Bandwidth fairness Aggregate marker Packet marking algorithms Responsive flows Target rate
1. Introduction The Differentiated Services (DiffServ) Networks can provide Quality of Service (QoS) guarantee to its applications over and above the current best-effort service (Carpenter and Nichols, 2002). The Assured Forwarding per-hop behavior (AF PHB); a flavor of DiffServ is intended to assure a minimum level of throughput called the target rate or the Committed Information Rate (CIR) (Jacobson et al., 1999). AF introduces traffic conditioners at edge routers and a queue management mechanism at core routers. The traffic conditioner marks the packet depending upon the service level agreement while the queue management at the core is commonly the RED-based algorithm RIO (Floyd and Jacobson, 1993). Packet marking algorithms based on TB and TSW have been proposed to work with AF (Malouch and Liu, 2002; Clark and Fang, 1998; Chait et al., 2002). However, in these markers the excess bandwidth is not fairly shared and hence the individual flows of the aggregate suffer from unfairness issues. Many mechanisms have been proposed to assure the target rate (Chait et al., 2002; Feroz et al., 2000; Renjish Kumar et al., 2002). Moreover, considerable research has been done on
n Corresponding author. Tel.: þ91 9443329313 (mob); fax: þ 91 431 2500133. E-mail address: [email protected] (S. Sudha).
1084-8045/$ - see front matter & 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jnca.2012.07.020
modeling TCP behavior in DiffServ networks (Padhye et al., 1998; Baines et al., 2000) and on the conditions required for achieving the target rate (Sahu et al., 2000). Also, the results of both simulation (Su and Atiquzzaman, 2001; Zhu and Ansari, 2005; Alves et al., 2000) and mathematical model based research (Baines et al., 2000) show that the current DiffServ proposal has unfairness in bandwidth sharing between (i) TCP-friendly traffic and UDP like traffic, (ii) flows in an aggregate, and (iii) aggregates in the excess bandwidth region. It can be seen from the previous researches that the excess core bandwidth in a DiffServ network is shared among flows instead of aggregates and that the DiffServ tends to favor small service subscribers (Su and Atiquzzaman, 2001; Zhu and Ansari, 2005; Alves et al., 2000; Su and Atiquzzaman, 2003). Methods have been proposed to solve this problem by using an adaptive factor to adjust the target rates to their fair shares, based on TB mechanisms (Park and Chio, 2003; Park and Choi, 2004). However these techniques require two-bit feedback information to be conveyed in the packet headers. Several remedies have also been proposed to overcome the unfairness problems among aggregates in case of excess network bandwidth. Improved time sliding window based three color marker (ItswTCM) is proposed and compared with existing markers such as srTCM, trTCM and tswTCM (Su and Atiquzzaman, 2003). Although the results demonstrate better fairness, it is found to be sensitive to the number of flows in an aggregate. The unfairness that arises with ItswTCM when
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aggregates of best effort service class exist along with assured service class is solved by incorporating a modification in the buffer (Sudha and Ammasaigounden, 2008). The enhanced time sliding window based three color marker (I2tswTCM) shows better performance in terms of fairness compared to ItswTCM in addition to being insensitive to the number of flows in an aggregate (Elshaikh et al., 2005). However, deterioration in fairness occurs as the number of aggregates increase, which is alleviated by M-I2tswTCM (Sudha et al., 2008). The provision-aware Improved TSW based ThreeColour Marker (paItswTCM) and the Double Modified Double Improved time sliding window Three Colour Marker (M2I2tswTCM) proposed subsequently show better fairness compared to the previous markers. They perform well particularly for TCP aggregates only (Sani and Othman, 2011; Alkharasani and Othman, 2012). Though these algorithms provide fairness among TCP aggregates in the excess bandwidth region, they fail to provide fairness between TCP and UDP like traffic. The use of separate queues, one for each type has been proposed as a solution to this (El-Glendy and Shin, 2003). However, all recent proposed algorithms provide fairness either among TCP aggregates only or between TCP and UDP aggregates, but not both. The new Label Forwarding model devised to enhance the fast switching is only for IPv6 packets that require service differentiation (Chen, 2011). Further, the new Secure Bandwidth Broker Discovery Protocol (BBDP), allows Bandwidth Brokers to automatically discover other Bandwidth Brokers (Okumus and Cekerekli, 2012). BBDP uses certificate authorities and digital certificates for future secure transactions by signaling protocol that works between Bandwidth Brokers. However, this proposal concentrates on protocol design and its implementation details rather than on fairness issues. Yingfei Dong et al., suggested a Dynamic Allocation Adjustment (DAA) approach to improve bandwidth efficiency by spreading loads over a flow path and other related links not on the path. Although it outperforms the existing solutions by 30%, it is found to be better only under non-uniform and dynamic loads (Dong and Liu, 2010). Thomas Demoor et al., introduce a two-class priority queue in order to model a DiffServ router with Expedited Forwarding Per-Hop Behavior for high-priority traffic (Demoor et al., 2011). Whereas, the present proposal pertains to Assured Forwarding Per-Hop Behavior. In order to evade the above unfairness a new TSW based aggregate marker is proposed in this paper. The proposal is intended to study the influence of several factors such as number of flows in the aggregate, different target rates, RTT and UDP traffic on bandwidth assurance. Simulations are carried out using NS-2 and the results show that the proposed scheme can protect the throughput of TCP from unresponsive UDP flows and perform better both in terms of throughput assurance and fair distribution of excess bandwidth.
2. Unfairness with previous markers In this section, the markers used for comparison in this simulation and the cause for their unfairness are described. 2.1. Improved TSW three color marker (ItswTCM) The problem of unfair sharing of the excess bandwidth among TCP aggregates with the existing tswTCM has been resolved by the improved TSW based three color marker (ItswTCM) (Su and Atiquzzaman, 2003). According to this scheme, the yellow packet marking probability of an aggregate
is proportional to its target rate. The basic idea of this marker is to allow an aggregate to inject yellow packets in proportion to its CIR which implies that a large service subscriber will be able to inject more yellow packets than a small service subscriber. This alleviates the unfairness that exists between the large service subscriber and the small service subscriber to some extent and also helps them to achieve a better proportional fair share of the excess bandwidth. The results of this marker show improved bandwidth distribution in comparison with the existing algorithms such as srTCM, trTCM and tswTCM. However, it is sensitive to the number of flows in the aggregate and the fairness provision among responsive aggregates is for 20% to 70% of the provision level and for a very narrow range of 40% to 50% between TCP and UDP aggregates. Algorithm ItswTCM is listed below:
Avg_rate = Estimated Avg Traffic Rate C= a constant ( c>l) If (Avg_rate<=CIR) the packet is marked as green else if (Avg_rate<= c*CIR) the packet is marked as yellow else P=((c*CIR)/Avg_rate) 2 with P the Packet is marked as yellow with (1- P) the Packet is marked as red
2.2. Enhanced TSW three color marker (I2tswTCM) In l2tswTCM, the constant c in ItswTCM is replaced with an adaptive factor (Elshaikh et al., 2005). The yellow packet marking probability of an aggregate is proportional to the availability of the network resource. This favors the large subscriber to inject more yellow packets in the excess bandwidth compared to that of ItswTCM. The results of this marker show enhanced fairness than ItswTCM, in addition to being insensitive to the number of flows in the aggregate. However, the fairness provision among responsive aggregates is for 20% to 70% of the provision level and for a very small range of only 20% to 30% between TCP and UDP aggregates. The algorithm for l2tswTCM is as follows:
Avg_Rate = Estimated Avg Traffic Rate (0
The quadratic term in the yellow packet marking probability in these markers punishes aggressive senders and the small service subscribers once their estimated sending rate
S. Sudha, N. Ammasaigounden / Journal of Network and Computer Applications 35 (2012) 1973–1978
exceeds a limit that is proportional to the target rate. This probability in fact allows a large subscriber to inject more yellow packets than a small service subscriber, thus enabling the large subscriber to achieve a better share of the excess bandwidth. The above two markers work well with responsive aggregates. But, unfairness arises when both TCP and UDP aggregates exist because of the following reason: as per the TCP congestion control algorithm, TCP flows respond to congestion by reducing their rates and thereby achieve their target rates by having all their packets marked as green. The UDP flows do not slow down and hence have all their packets marked as yellow once they exceed their target rate. These yellow packets suffer high drop percentage in the case of congestion. As the green packets have high priority than the yellow packets, they are forwarded easily even during times of congestion. It is these yellow packets that protect the TCP traffic from the unbehaved UDP ones, thereby enabling the responsive aggregate to achieve bandwidth greater than its fair share, leading to unfairness. The injection of right amount of yellow packets alone will not improve the unfair distribution of bandwidth between TCP and UDP. It is also essential to see that both TCP and UDP inject the right amount of green packets to be assured with their proportional fair share. This implies that a marker which allocates a fair share of bandwidth to the aggregates immaterial of the type of the protocol at the transport layer (TCP/UDP) is to be designed. In this paper, this is achieved by introducing an adaptive factor which changes with the estimated rate of the packet and the resource available in the network. The principle of the proposed marker is explained in the next section.
3. Proposed algorithm
been designed. The marking rule of the newly proposed algorithm is as follows:
The Etswm algorithm is summarized as follows: avg-rate = Estimated Average Sending Rate of Traffic Stream X = bottleneck bandwidth k = constant R= X/ Adaptive factor (F) = R *CIR For each packet arrival { If incoming traffic is TCP } if (avg-rate <= F) The packet is marked green else if (avg-rate <= k *F) and (avg-rate > F ) Calculate PO = (1 – F / avg-rate ) With probability PO the packet is marked yellow With probability (l-PO) the packet is marked green else Calculate P1 = (1– k*F /avg-rate) Calculate P2 = (k* F– F) / avg-rate With probability P1 the packet is marked red With probability P2 the packet is marked yellow With probability (l-(PI + P2)) the packet is marked green { If incoming traffic is UDP }
For simplicity a network with two aggregates, denoted by Agg0 and Agg1, with different target rates Rt,0 [packets/s] and Rt,1 [packets/s] competing with each other for the bandwidth of a common bottleneck link whose capacity is C [packets/s], the Fair Share of the ith aggregate, Rf,i is defined in (Park and Choi, 2004) as X R R Rf ,i ¼ Rt,i þ ðC Rt,i Þ P t,i ¼ P t,i C R Rt,i t,i i i
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ð1Þ
i
The network is considered to be under-subscribed or overP provisioned if i Rt,i oC and is over-subscribed or under-provisioned P if i Rt,i 4C. To achieve bandwidth fairness among aggregates, it is essential that each aggregate gets bandwidth in proportion to its target rate as in Eq. (1). To meet the above requirement, packet marking is done based on its estimated rate with that of its fair share. The enhanced time sliding window based marker aimed to improve the fairness among aggregates referred to as Etswm has
if (avg-rate <= F) the packet is marked green else the packet is marked red
(i). If the estimated average rate is less than or equal to the adaptive factor, packets of the stream are marked green. This corresponds to the fair share of an aggregate be it either TCP or UDP. (ii). If the estimated average rate is greater than the adaptive factor but less than or equal to the k times the adaptive factor (where k is a constant), packets are designated as yellow with probability P0 and green with probability (1 P0). P0 is the fraction of packets contributing to the measured rate beyond the adaptive factor, in case of TCP. Whereas, in case of UDP, if the estimated average rate is greater than the adaptive factor, packets are marked red (i.e. high drop precedence). By this, none of the UDP packets will be marked as yellow, thus controlling the injection of yellow packets. (iii). If the estimated average rate is greater than k* adaptive factor, packets are marked as red, yellow or green with probability P1, P2 and (1 (P1þP2)) respectively. P1 is the fraction of packets contributing to the measured rate beyond k* adaptive factor, P2 is the fraction of packets contributing to that part of the measured rate between adaptive factor and k times the adaptive factor. To compare the fairness between aggregates in the excess bandwidth region, the well known definition of Fairness Index (FI)
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among responsive TCP aggregates with variation in micro-flows. Hence, to study the effectiveness of the proposed marker in fairness provision among aggregates in the excess bandwidth region, simulation is carried out with (i) responsive aggregates and (ii) responsive and non-responsive aggregates. The fairness between aggregates in the excess bandwidth region is computed using Eq. (2). The fairness has been studied for ItswTCM, I2tswTCM and Etswm in the excess bandwidth region.
Fig. 1. Network topology.
(Jain, 1991) in Eq. (2) has been used. P 2 ð N i ¼ 1 xi Þ FI ¼ PN N n i ¼ 1 xi 2
ð2Þ
where 0 oFI o1, N is the total number of aggregates under consideration (in this case, N ¼2) xi ¼
Excess bandwidth obtained by aggregatei CIR of aggregatei
ð3Þ
According to this definition, closer the fairness index to unity, the fairer is the distribution of the excess bandwidth between the aggregates. The provision level has been defined as the ratio of total provisioned bandwidth to the bandwidth of the bottleneck link, which is 10 Mbps in the present case. The fairness has been studied for ItswTCM, I2tswTCM and Etswm in the excess bandwidth region.
4. Simulation topology Figure 1 shows the network topology used in this study. Two aggregates namely aggregate -0 and aggregate-1 are taken into consideration. Aggregate-0 sends traffic through the edge router E0 to the destination D0, while the aggregate-1 sends traffic through edge E1 to D1. Aggregate-0 and aggregate-1 have ‘n1’ and ‘n2’ number of flows respectively. E0 and E1 are the edge routers responsible for monitoring and marking the respective traffic aggregates 0 and 1. The core router, C implements the active queue management scheme and provides service differentiation among aggregates according to the drop precedences carried out in the packet headers. In all the simulations, the M-RED queue management scheme has been used. The notation {x, y, z} represents minimum threshold, maximum threshold and weight parameter of the RED queue respectively. The corresponding settings of the core router for Red, Yellow and Green packets are {20, 40, 0.2}, {40, 80, 0.1} and {80, 120, 0.02} and PIR set to 1.2* CIR. In ItswTCM and Etswm, the constant is set to 2, gamma to 0.6 in I2tswTCM. The information required is the number of aggregates (N) in the DiffServ domain and their target requirements. The proposed algorithm is evolved based on fact that these parameters are obtained as state information.
Case A: Fair distribution of excess network bandwidth among responsive aggregates. Both aggregate-0 and 1 of Fig. 1 correspond to long lived FTP/TCP flows with MSS¼536 bytes (the default value), packet size ¼1000 bytes and RTT¼40 ms with TCP NewReno. Simulations are carried out keeping CIR of aggregate-1 fixed at 1 Mbps and that of aggregate-0 varying from 1 Mbps to 8 Mbps with variation in the number of flows (i.e. ‘n1’ and ‘n2’) for which the results are presented below. The graphs of ItswTCM (Figs. 2 and 3) show variation in the fairness index due to the following reasons: at largely overprovisioned scenario (20% to 40%) and above 60%, the small service subscribers mark more of their packets as red on exceeding their target rate which allows them to gain more bandwidth. In the range 50% to 60% of the provision level, the green and yellow packets help both the subscribers to achieve their fair share. Apart from this, the number of flows in the aggregate also influences the fairness performance. The plots of I2tswTCM (Figs. 2 and 3) illustrate a gradual degradation in fairness as the subscription of the large service subscriber increases. Here as the target rate of the large service subscriber increases the marking of the green and yellow packets also increases. However, the small subscriber marks more of its packets as red which allows it to acquire more bandwidth. (i) Aggregate-0 and Aggregate-1 with equal number of flows Figure 2 depicts the fairness performance by the various markers, when both aggregates have equal number of (i.e. n1¼n2¼16) TCP flows. From this plot, the fairness indices of ItswTCM and I2tswTCM are observed to fall with increase in target rate. This is because the small service subscribers achieve higher bandwidth than their fair share compared to that of the large service subscriber. On the other-hand, with Etswm both aggregates are found to achieve a proportional fair share of the excess bandwidth. This is clear from Fig. 2, where the fairness index for the entire excess bandwidth region is almost 1 by the proposed marker, while with others
5. Results and analysis The fair share of the excess bandwidth for AF PHB in DiffServ can be classified into two classes: one is fairness between responsive and non-responsive aggregates, which is due to different reactions to congestion signals; the other is the fairness
Fig. 2. Aggregates with equal number of flows n1¼ n2¼ 16.
S. Sudha, N. Ammasaigounden / Journal of Network and Computer Applications 35 (2012) 1973–1978
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Fig. 4. Impact of the constant k.
Fig. 3. Aggregates with different number of flows (a) n1¼ 16 and n2 ¼32; (b) n1¼ 32 and n2¼ 16.
it is only for 70%. This shows that Etswm outperforms other markers by injecting green packets in the excess bandwidth region. (ii) Aggregate -0 and Aggregate-1 with different number of flows The performance results pertaining to aggregate-0 having 16 flows and aggregate-1 having 32 flows are presented in Fig. 3(a), while Fig. 3(b) shows the case of aggregate-0 having 32 flows and aggregate-1 with 16 flows. From Figs. 2 and 3, it is observed that Etswm in addition to being insensitive to the number of flows in the aggregates provides fairness over a large range of provision level of 20%–90%. This is indeed a significant improvement of the proposed marker, revealing a fair distribution of the excess bandwidth among TCP aggregates. Case B: Variation of the constant k. A constant k is introduced in the algorithm to have a better performance. Hence, simulation for different values of k for the same network scenario as the previous case is carried out to study the effect of k on marking decisions. The results corresponding to this are plotted in Fig. 4. From the plot, it is seen that k for any value greater than 1.5 (or even 1.2), the fairness exists and is also for a provision level of up to 80%. Thus, the impact of k on the fairness is almost negligible. Case C: Fairness between responsive (TCP traffic) and non-responsive (UDP like traffic). To show that the proposed marker can provide a fair distribution of bandwidth among TCP and UDP aggregates also, simulations have been carried out with aggregates-0 and 1 corresponding to FTP/TCP New Reno and CBR/UDP source respectively. The sending rate of CBR traffic is set to 1.5 Mbps. The CIR of aggregate-1 is fixed at 1 Mbps, while the CIR of aggregate-0 varies from 1 Mbps to 8 Mbps, the network
operating at excess bandwidth region. As in the previous case, n1 and n2 are varied and the corresponding fairness performances from the results are depicted in Fig. 5. Figure 5(a) depicts the performance when the aggregates have equal number of flows (i.e. 16 flows each) and Fig. 5(b) with different number of flows (i.e. 16–32). From the graphs (Fig. 5(a) and (b)) degradation in fairness with ItswTCM is observed which is due to the following reasons: in the range 20% to 40%, the aggressive senders (small service subscribers) mark more of their packets as red which allows them to acquire more bandwidth than the large subscribers (responsive flows). At 50% of the provision level, the fairness is better as both the subscribers achieve their fair share. Above 60% as the responsive flows mark more of their packets as green and yellow compared to the small subscribers, they gain more bandwidth. With I2tswTCM, in the range 30% to 70% the aggressive senders mark more of their packets as red allowing them to get more bandwidth than the responsive flows. And above 70% the responsive flows mark more of their packets as green and yellow enabling them to obtain more bandwidth. The results of the proposed marker show that both the large and small service subscribers get a proportional share of the excess bandwidth when the number of flows in the aggregate is same and different. This concludes the insensitivity of the marker to the number of flows in the aggregate (i.e. TCP or TCP and UDP). Further, simulation has been carried out with 32–16 flows, which yields the same result. For the sake of brevity, this graph is not shown. This concludes the insensitivity to the number of flows in an aggregate, be it TCP/UDP. Case D: Analysis on variation of RTT. For the same setup as the above and each aggregate with 16 flows, simulation has been done is to study the interaction of TCP and UDP with changes in Round Trip Time (RTT). Figure 6. presents the results related to RTT of aggregate-0 (TCP) being varied, while that of aggregate-1 set to 40 ms. Fairness is found to vary with change in RTT. In all cases, the fairness provision is found to be better except for RTT¼170 ms. This is because as RTT of TCP flows take a large value UDP will inject more packets and hence achieve more bandwidth than TCP. However, the fairness provision is for 20% to 70% of the provision level. 6. Conclusion With ItswTCM and I2tswTCM, unfairness among aggregates in the excess bandwidth region is observed in the DiffServ network.
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based on which the drop precedence of the packets is arrived at. This factor depends on the availability of the network resource and the target rate of an aggregate. Added to this, Etswm provides fairness among TCP and UDP flows sharing the same AF class. References
Fig. 5. Interaction of UDP and TCP (a) aggregates with equal number of flows(16–16); (b) aggregates with diffrent number of flows(16–32).
Fig. 6. Variation of RTT.
Hence to lessen this, a new marking algorithm called Etswm has been proposed in this chapter. The unique feature of this proposed algorithm is that it provides enhanced fairness not only among TCP aggregates but also between TCP and UDP aggregates. Further, the simulation studies show that the effect of constant k on fairness performance is negligible. The performance of the proposed marker is evaluated using extensive simulation studies in NS-2. The results emphasize the superiority of the marker by an enhanced improvement in fairness over an extended range of network provision level (20%–90%) compared to ItswTCM and I2tswTCM. Moreover, the performance of Etswm is neither affected either by the number of flows in an aggregate nor the variation in the target rate. The improved fairness is achieved by introducing an adaptive factor
Alves J, De Rezende L, De Moraes. Evaluating fairness in aggregated traffic marking. Proceedings of IEEE Globecom 2000;1:445–9. Alkharasani Ameen M, Othman Mohamed. M2I2tswTCM: A new efficient optimization marker algorithm to improve fairness bandwidth in DiffServ networks. Journal of Network and Computer Applications 2012;35:1361–6. Baines M, Nandy B, Pieda P, Seddigh N, Devetsikiotis M. Using TCP models to understand bandwidth assurance in a differentiated services network. Nortel Technical Report; July-2000. Carpenter BE, Nichols K. Differentiated services in the Internet. Proceedings of the IEEE 2002;90(9):1479–94. Chait Y, Hollot C, Misra V, Towsley D, Zhang H. Providing throughput differentiation for TCP flows using adaptive two color marking and multi-level AQM. Proceedings of IEEE—INFOCOM 2002:837–44. Chen Chin-Ling. A study of IPv6 labeling forwarding model supporting DiffServ. Procedia Engineering 2011;15:5590–4. Clark DD, Fang W. Explicit allocation of best effort packet delivery service. IEEE/ACM Transactions on Networking 1998;6(4):362–73. Demoor Thomas, Walraevens Joris, Fiems Dieter, Bruneel Herwig. Performance analysis of a priority queue: expedited forwarding PHB in DiffServ. Interna¨ 2011;65:190–7. tional Journal of Electronics and Communication (AEU) El-Glendy AMohamed, Shin Kang G. Assured forwarding fairness using equation based packet marking and packet separation. Computer Networks 2003;41: 435–50 [Elsevier]. Elshaikh MA, Othman M, Shamala S, Johari R. Enhanced tswTCM to improve fairness in DiffiServ networks. In: Proceedings of the IEEE international conference on networks; 2005. vol. 1, p. 302–6. Feroz A, Rao A, Kalyanaraman S. A tcp-friendly traffic marker for IP differentiated services. In: Proceedings of the IEEE/IFIP 8th international workshop on quality of services (IWQoS); 2000. p. 138–47. Floyd S, Jacobson V. Random early detection gateways for congestion avoidance. IEEE/ACM Transactions on Networking 1993;1(4):397–413. Jacobson V, Nichols K, Poduri K. An expedited forwarding PHB. RFC; 1999. vol. 2598. Jain R. The art of computer systems performance analysis: techniques for experimental design, measurement, simulation and modeling.New York, NY: John Wiley and Sons Inc.; 1991 [p. 366 & 387]. Malouch N, Liu Z. Performance analysis of TCP with RIO routers. Proceedings of IEEE Globecom 2002;2:1623–7. Okumus Ibrahim Taner, Cekerekli Sezgin. Design and implementation of a Secure Bandwidth Broker Discovery Protocol. Computer Standards & Interfaces 2012;34:231–7. Padhye J, Firoiu V, Towsley D, Kurose J. Modeling TCP throughput: a simple model and its empirical validation. Proceedings of ACM SIGCOMM 1998;98. Park E, Chio C. Adaptive token bucket algorithm for fair bandwidth allocation in DiffServ networks. Proceeding of IEEE Globecom 2003;6:3176–80. Park Eun-Chan, Choi Chong-Ho. Proportional bandwidth allocation in DiffServ networks. IEEE INFOCOM 2004;3:2038–49. Renjish Kumar KR, Ananda AL, Jacob LillyKutty. TCP-friendly traffic conditioning in DiffServ networks: a memory-based approach. Computer Networks 2002;38(6): 731–43 [Elsevier]. Sahu S, Nain P, Diot C, Firoiu V, Towsley D. On achievable service differentiation with token bucket marking for TCP. In: Proceedings of the ACM SIGMETRICS international conference on measurement and modeling of computer systems; 2000. p. 23–33. Sani Yusuf, Othman Mohamed. A provision-aware fair bandwidth distribution marker algorithm for DiffServ networks. Journal of Network and Computer Applications 2011;34:715–21. Su H, Atiquzzaman M. Performance analysis of differentiated services network with token bucket marker. 11th IEEE workshop on local and metropolitan area networks; 2001. p. 81–2. Su H, Atiquzzaman M. Comprehensive performance model of differentiated service with token bucket marker. IEE Proceedings on Communications 2003;150(5):347–53. Su H, Atiquzzaman M. ItswTCM: a new aggregate marker to improve fairness in DiffServ. Computer Communications 2003;26:1018–27. Sudha S, Ammasaigounden N. A modified approach for fair bandwidth allocation between TCP and UDP traffic in DiffServ network. In: Proceedings of the IEEE international conference on computer and communication engineering; 2008. p. 788–91. Sudha S, Rao Srinivasa, Ammasaigounden N. A modified I2TSWTCM to improve bandwidth fairness in DiffServ. In: Proceedings of the IEEE region 10 colloquium and third international conference on industrial and information systems; 2008. Dong Yingfei, Liu Xiaojiang. Novel dynamic delay allocation adjustment for improving bandwidth efficiency. Computer Communications 2010;33:463–76. Zhu Li, Ansari Nirwan. Fair bandwidth allocation for assured forwarding (AF) services. In: Proceedings of the IEEE international conference on networks; 2005. p. 374–8.
Contents lists available at SciVerse ScienceDirect
Journal of Network and Computer Applications journal homepage: www.elsevier.com/locate/jnca
An aggregate marker for bandwidth fairness in DiffServ S. Sudha n, N. Ammasaigounden Department of Electrical and Electronics Engineering, National Institute of Technology, Tiruchirappalli, Tamil Nadu, India
a r t i c l e i n f o
abstract
Article history: Received 26 April 2012 Received in revised form 25 July 2012 Accepted 30 July 2012 Available online 24 August 2012
Surveys and studies on DiffServ exhibit existence of unfairness between aggregates in the excess bandwidth region. Many researchers have proved that providing a proportional fair share of the bandwidth between aggregates solve this. Based on this, aggregate markers such as ItswTCM and I2tswTCM are found to improve bandwidth fairness in DiffServ network among aggregates, when the aggregates are responsive in nature. However, co-existence of non-responsive aggregates with responsive aggregates leads to unfairness. Hence, in this paper an attempt has been made to evade the above unfairness by a new TSW based marker; where the drop precedence of the packet is arrived at an adaptive manner based on its estimated rate and the availability of the network resource. The unique feature of this proposed algorithm is that it provides enhanced fairness not only among responsive aggregates but also between responsive and non-responsive aggregates. Further, simulations have been carried out in NS-2 with changes in RTT, target rate of the aggregates and the number of flows in the aggregate. The results show that the proposed marker reduces the influence of these factors on the fairness performance exhibiting the suitability of the marker for different network topologies. & 2012 Elsevier Ltd. All rights reserved.
Keywords: Differentiated Services Bandwidth fairness Aggregate marker Packet marking algorithms Responsive flows Target rate
1. Introduction The Differentiated Services (DiffServ) Networks can provide Quality of Service (QoS) guarantee to its applications over and above the current best-effort service (Carpenter and Nichols, 2002). The Assured Forwarding per-hop behavior (AF PHB); a flavor of DiffServ is intended to assure a minimum level of throughput called the target rate or the Committed Information Rate (CIR) (Jacobson et al., 1999). AF introduces traffic conditioners at edge routers and a queue management mechanism at core routers. The traffic conditioner marks the packet depending upon the service level agreement while the queue management at the core is commonly the RED-based algorithm RIO (Floyd and Jacobson, 1993). Packet marking algorithms based on TB and TSW have been proposed to work with AF (Malouch and Liu, 2002; Clark and Fang, 1998; Chait et al., 2002). However, in these markers the excess bandwidth is not fairly shared and hence the individual flows of the aggregate suffer from unfairness issues. Many mechanisms have been proposed to assure the target rate (Chait et al., 2002; Feroz et al., 2000; Renjish Kumar et al., 2002). Moreover, considerable research has been done on
n Corresponding author. Tel.: þ91 9443329313 (mob); fax: þ 91 431 2500133. E-mail address: [email protected] (S. Sudha).
1084-8045/$ - see front matter & 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jnca.2012.07.020
modeling TCP behavior in DiffServ networks (Padhye et al., 1998; Baines et al., 2000) and on the conditions required for achieving the target rate (Sahu et al., 2000). Also, the results of both simulation (Su and Atiquzzaman, 2001; Zhu and Ansari, 2005; Alves et al., 2000) and mathematical model based research (Baines et al., 2000) show that the current DiffServ proposal has unfairness in bandwidth sharing between (i) TCP-friendly traffic and UDP like traffic, (ii) flows in an aggregate, and (iii) aggregates in the excess bandwidth region. It can be seen from the previous researches that the excess core bandwidth in a DiffServ network is shared among flows instead of aggregates and that the DiffServ tends to favor small service subscribers (Su and Atiquzzaman, 2001; Zhu and Ansari, 2005; Alves et al., 2000; Su and Atiquzzaman, 2003). Methods have been proposed to solve this problem by using an adaptive factor to adjust the target rates to their fair shares, based on TB mechanisms (Park and Chio, 2003; Park and Choi, 2004). However these techniques require two-bit feedback information to be conveyed in the packet headers. Several remedies have also been proposed to overcome the unfairness problems among aggregates in case of excess network bandwidth. Improved time sliding window based three color marker (ItswTCM) is proposed and compared with existing markers such as srTCM, trTCM and tswTCM (Su and Atiquzzaman, 2003). Although the results demonstrate better fairness, it is found to be sensitive to the number of flows in an aggregate. The unfairness that arises with ItswTCM when
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aggregates of best effort service class exist along with assured service class is solved by incorporating a modification in the buffer (Sudha and Ammasaigounden, 2008). The enhanced time sliding window based three color marker (I2tswTCM) shows better performance in terms of fairness compared to ItswTCM in addition to being insensitive to the number of flows in an aggregate (Elshaikh et al., 2005). However, deterioration in fairness occurs as the number of aggregates increase, which is alleviated by M-I2tswTCM (Sudha et al., 2008). The provision-aware Improved TSW based ThreeColour Marker (paItswTCM) and the Double Modified Double Improved time sliding window Three Colour Marker (M2I2tswTCM) proposed subsequently show better fairness compared to the previous markers. They perform well particularly for TCP aggregates only (Sani and Othman, 2011; Alkharasani and Othman, 2012). Though these algorithms provide fairness among TCP aggregates in the excess bandwidth region, they fail to provide fairness between TCP and UDP like traffic. The use of separate queues, one for each type has been proposed as a solution to this (El-Glendy and Shin, 2003). However, all recent proposed algorithms provide fairness either among TCP aggregates only or between TCP and UDP aggregates, but not both. The new Label Forwarding model devised to enhance the fast switching is only for IPv6 packets that require service differentiation (Chen, 2011). Further, the new Secure Bandwidth Broker Discovery Protocol (BBDP), allows Bandwidth Brokers to automatically discover other Bandwidth Brokers (Okumus and Cekerekli, 2012). BBDP uses certificate authorities and digital certificates for future secure transactions by signaling protocol that works between Bandwidth Brokers. However, this proposal concentrates on protocol design and its implementation details rather than on fairness issues. Yingfei Dong et al., suggested a Dynamic Allocation Adjustment (DAA) approach to improve bandwidth efficiency by spreading loads over a flow path and other related links not on the path. Although it outperforms the existing solutions by 30%, it is found to be better only under non-uniform and dynamic loads (Dong and Liu, 2010). Thomas Demoor et al., introduce a two-class priority queue in order to model a DiffServ router with Expedited Forwarding Per-Hop Behavior for high-priority traffic (Demoor et al., 2011). Whereas, the present proposal pertains to Assured Forwarding Per-Hop Behavior. In order to evade the above unfairness a new TSW based aggregate marker is proposed in this paper. The proposal is intended to study the influence of several factors such as number of flows in the aggregate, different target rates, RTT and UDP traffic on bandwidth assurance. Simulations are carried out using NS-2 and the results show that the proposed scheme can protect the throughput of TCP from unresponsive UDP flows and perform better both in terms of throughput assurance and fair distribution of excess bandwidth.
2. Unfairness with previous markers In this section, the markers used for comparison in this simulation and the cause for their unfairness are described. 2.1. Improved TSW three color marker (ItswTCM) The problem of unfair sharing of the excess bandwidth among TCP aggregates with the existing tswTCM has been resolved by the improved TSW based three color marker (ItswTCM) (Su and Atiquzzaman, 2003). According to this scheme, the yellow packet marking probability of an aggregate
is proportional to its target rate. The basic idea of this marker is to allow an aggregate to inject yellow packets in proportion to its CIR which implies that a large service subscriber will be able to inject more yellow packets than a small service subscriber. This alleviates the unfairness that exists between the large service subscriber and the small service subscriber to some extent and also helps them to achieve a better proportional fair share of the excess bandwidth. The results of this marker show improved bandwidth distribution in comparison with the existing algorithms such as srTCM, trTCM and tswTCM. However, it is sensitive to the number of flows in the aggregate and the fairness provision among responsive aggregates is for 20% to 70% of the provision level and for a very narrow range of 40% to 50% between TCP and UDP aggregates. Algorithm ItswTCM is listed below:
Avg_rate = Estimated Avg Traffic Rate C= a constant ( c>l) If (Avg_rate<=CIR) the packet is marked as green else if (Avg_rate<= c*CIR) the packet is marked as yellow else P=((c*CIR)/Avg_rate) 2 with P the Packet is marked as yellow with (1- P) the Packet is marked as red
2.2. Enhanced TSW three color marker (I2tswTCM) In l2tswTCM, the constant c in ItswTCM is replaced with an adaptive factor (Elshaikh et al., 2005). The yellow packet marking probability of an aggregate is proportional to the availability of the network resource. This favors the large subscriber to inject more yellow packets in the excess bandwidth compared to that of ItswTCM. The results of this marker show enhanced fairness than ItswTCM, in addition to being insensitive to the number of flows in the aggregate. However, the fairness provision among responsive aggregates is for 20% to 70% of the provision level and for a very small range of only 20% to 30% between TCP and UDP aggregates. The algorithm for l2tswTCM is as follows:
Avg_Rate = Estimated Avg Traffic Rate (0
The quadratic term in the yellow packet marking probability in these markers punishes aggressive senders and the small service subscribers once their estimated sending rate
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exceeds a limit that is proportional to the target rate. This probability in fact allows a large subscriber to inject more yellow packets than a small service subscriber, thus enabling the large subscriber to achieve a better share of the excess bandwidth. The above two markers work well with responsive aggregates. But, unfairness arises when both TCP and UDP aggregates exist because of the following reason: as per the TCP congestion control algorithm, TCP flows respond to congestion by reducing their rates and thereby achieve their target rates by having all their packets marked as green. The UDP flows do not slow down and hence have all their packets marked as yellow once they exceed their target rate. These yellow packets suffer high drop percentage in the case of congestion. As the green packets have high priority than the yellow packets, they are forwarded easily even during times of congestion. It is these yellow packets that protect the TCP traffic from the unbehaved UDP ones, thereby enabling the responsive aggregate to achieve bandwidth greater than its fair share, leading to unfairness. The injection of right amount of yellow packets alone will not improve the unfair distribution of bandwidth between TCP and UDP. It is also essential to see that both TCP and UDP inject the right amount of green packets to be assured with their proportional fair share. This implies that a marker which allocates a fair share of bandwidth to the aggregates immaterial of the type of the protocol at the transport layer (TCP/UDP) is to be designed. In this paper, this is achieved by introducing an adaptive factor which changes with the estimated rate of the packet and the resource available in the network. The principle of the proposed marker is explained in the next section.
3. Proposed algorithm
been designed. The marking rule of the newly proposed algorithm is as follows:
The Etswm algorithm is summarized as follows: avg-rate = Estimated Average Sending Rate of Traffic Stream X = bottleneck bandwidth k = constant R= X/ Adaptive factor (F) = R *CIR For each packet arrival { If incoming traffic is TCP } if (avg-rate <= F) The packet is marked green else if (avg-rate <= k *F) and (avg-rate > F ) Calculate PO = (1 – F / avg-rate ) With probability PO the packet is marked yellow With probability (l-PO) the packet is marked green else Calculate P1 = (1– k*F /avg-rate) Calculate P2 = (k* F– F) / avg-rate With probability P1 the packet is marked red With probability P2 the packet is marked yellow With probability (l-(PI + P2)) the packet is marked green { If incoming traffic is UDP }
For simplicity a network with two aggregates, denoted by Agg0 and Agg1, with different target rates Rt,0 [packets/s] and Rt,1 [packets/s] competing with each other for the bandwidth of a common bottleneck link whose capacity is C [packets/s], the Fair Share of the ith aggregate, Rf,i is defined in (Park and Choi, 2004) as X R R Rf ,i ¼ Rt,i þ ðC Rt,i Þ P t,i ¼ P t,i C R Rt,i t,i i i
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ð1Þ
i
The network is considered to be under-subscribed or overP provisioned if i Rt,i oC and is over-subscribed or under-provisioned P if i Rt,i 4C. To achieve bandwidth fairness among aggregates, it is essential that each aggregate gets bandwidth in proportion to its target rate as in Eq. (1). To meet the above requirement, packet marking is done based on its estimated rate with that of its fair share. The enhanced time sliding window based marker aimed to improve the fairness among aggregates referred to as Etswm has
if (avg-rate <= F) the packet is marked green else the packet is marked red
(i). If the estimated average rate is less than or equal to the adaptive factor, packets of the stream are marked green. This corresponds to the fair share of an aggregate be it either TCP or UDP. (ii). If the estimated average rate is greater than the adaptive factor but less than or equal to the k times the adaptive factor (where k is a constant), packets are designated as yellow with probability P0 and green with probability (1 P0). P0 is the fraction of packets contributing to the measured rate beyond the adaptive factor, in case of TCP. Whereas, in case of UDP, if the estimated average rate is greater than the adaptive factor, packets are marked red (i.e. high drop precedence). By this, none of the UDP packets will be marked as yellow, thus controlling the injection of yellow packets. (iii). If the estimated average rate is greater than k* adaptive factor, packets are marked as red, yellow or green with probability P1, P2 and (1 (P1þP2)) respectively. P1 is the fraction of packets contributing to the measured rate beyond k* adaptive factor, P2 is the fraction of packets contributing to that part of the measured rate between adaptive factor and k times the adaptive factor. To compare the fairness between aggregates in the excess bandwidth region, the well known definition of Fairness Index (FI)
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among responsive TCP aggregates with variation in micro-flows. Hence, to study the effectiveness of the proposed marker in fairness provision among aggregates in the excess bandwidth region, simulation is carried out with (i) responsive aggregates and (ii) responsive and non-responsive aggregates. The fairness between aggregates in the excess bandwidth region is computed using Eq. (2). The fairness has been studied for ItswTCM, I2tswTCM and Etswm in the excess bandwidth region.
Fig. 1. Network topology.
(Jain, 1991) in Eq. (2) has been used. P 2 ð N i ¼ 1 xi Þ FI ¼ PN N n i ¼ 1 xi 2
ð2Þ
where 0 oFI o1, N is the total number of aggregates under consideration (in this case, N ¼2) xi ¼
Excess bandwidth obtained by aggregatei CIR of aggregatei
ð3Þ
According to this definition, closer the fairness index to unity, the fairer is the distribution of the excess bandwidth between the aggregates. The provision level has been defined as the ratio of total provisioned bandwidth to the bandwidth of the bottleneck link, which is 10 Mbps in the present case. The fairness has been studied for ItswTCM, I2tswTCM and Etswm in the excess bandwidth region.
4. Simulation topology Figure 1 shows the network topology used in this study. Two aggregates namely aggregate -0 and aggregate-1 are taken into consideration. Aggregate-0 sends traffic through the edge router E0 to the destination D0, while the aggregate-1 sends traffic through edge E1 to D1. Aggregate-0 and aggregate-1 have ‘n1’ and ‘n2’ number of flows respectively. E0 and E1 are the edge routers responsible for monitoring and marking the respective traffic aggregates 0 and 1. The core router, C implements the active queue management scheme and provides service differentiation among aggregates according to the drop precedences carried out in the packet headers. In all the simulations, the M-RED queue management scheme has been used. The notation {x, y, z} represents minimum threshold, maximum threshold and weight parameter of the RED queue respectively. The corresponding settings of the core router for Red, Yellow and Green packets are {20, 40, 0.2}, {40, 80, 0.1} and {80, 120, 0.02} and PIR set to 1.2* CIR. In ItswTCM and Etswm, the constant is set to 2, gamma to 0.6 in I2tswTCM. The information required is the number of aggregates (N) in the DiffServ domain and their target requirements. The proposed algorithm is evolved based on fact that these parameters are obtained as state information.
Case A: Fair distribution of excess network bandwidth among responsive aggregates. Both aggregate-0 and 1 of Fig. 1 correspond to long lived FTP/TCP flows with MSS¼536 bytes (the default value), packet size ¼1000 bytes and RTT¼40 ms with TCP NewReno. Simulations are carried out keeping CIR of aggregate-1 fixed at 1 Mbps and that of aggregate-0 varying from 1 Mbps to 8 Mbps with variation in the number of flows (i.e. ‘n1’ and ‘n2’) for which the results are presented below. The graphs of ItswTCM (Figs. 2 and 3) show variation in the fairness index due to the following reasons: at largely overprovisioned scenario (20% to 40%) and above 60%, the small service subscribers mark more of their packets as red on exceeding their target rate which allows them to gain more bandwidth. In the range 50% to 60% of the provision level, the green and yellow packets help both the subscribers to achieve their fair share. Apart from this, the number of flows in the aggregate also influences the fairness performance. The plots of I2tswTCM (Figs. 2 and 3) illustrate a gradual degradation in fairness as the subscription of the large service subscriber increases. Here as the target rate of the large service subscriber increases the marking of the green and yellow packets also increases. However, the small subscriber marks more of its packets as red which allows it to acquire more bandwidth. (i) Aggregate-0 and Aggregate-1 with equal number of flows Figure 2 depicts the fairness performance by the various markers, when both aggregates have equal number of (i.e. n1¼n2¼16) TCP flows. From this plot, the fairness indices of ItswTCM and I2tswTCM are observed to fall with increase in target rate. This is because the small service subscribers achieve higher bandwidth than their fair share compared to that of the large service subscriber. On the other-hand, with Etswm both aggregates are found to achieve a proportional fair share of the excess bandwidth. This is clear from Fig. 2, where the fairness index for the entire excess bandwidth region is almost 1 by the proposed marker, while with others
5. Results and analysis The fair share of the excess bandwidth for AF PHB in DiffServ can be classified into two classes: one is fairness between responsive and non-responsive aggregates, which is due to different reactions to congestion signals; the other is the fairness
Fig. 2. Aggregates with equal number of flows n1¼ n2¼ 16.
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Fig. 4. Impact of the constant k.
Fig. 3. Aggregates with different number of flows (a) n1¼ 16 and n2 ¼32; (b) n1¼ 32 and n2¼ 16.
it is only for 70%. This shows that Etswm outperforms other markers by injecting green packets in the excess bandwidth region. (ii) Aggregate -0 and Aggregate-1 with different number of flows The performance results pertaining to aggregate-0 having 16 flows and aggregate-1 having 32 flows are presented in Fig. 3(a), while Fig. 3(b) shows the case of aggregate-0 having 32 flows and aggregate-1 with 16 flows. From Figs. 2 and 3, it is observed that Etswm in addition to being insensitive to the number of flows in the aggregates provides fairness over a large range of provision level of 20%–90%. This is indeed a significant improvement of the proposed marker, revealing a fair distribution of the excess bandwidth among TCP aggregates. Case B: Variation of the constant k. A constant k is introduced in the algorithm to have a better performance. Hence, simulation for different values of k for the same network scenario as the previous case is carried out to study the effect of k on marking decisions. The results corresponding to this are plotted in Fig. 4. From the plot, it is seen that k for any value greater than 1.5 (or even 1.2), the fairness exists and is also for a provision level of up to 80%. Thus, the impact of k on the fairness is almost negligible. Case C: Fairness between responsive (TCP traffic) and non-responsive (UDP like traffic). To show that the proposed marker can provide a fair distribution of bandwidth among TCP and UDP aggregates also, simulations have been carried out with aggregates-0 and 1 corresponding to FTP/TCP New Reno and CBR/UDP source respectively. The sending rate of CBR traffic is set to 1.5 Mbps. The CIR of aggregate-1 is fixed at 1 Mbps, while the CIR of aggregate-0 varies from 1 Mbps to 8 Mbps, the network
operating at excess bandwidth region. As in the previous case, n1 and n2 are varied and the corresponding fairness performances from the results are depicted in Fig. 5. Figure 5(a) depicts the performance when the aggregates have equal number of flows (i.e. 16 flows each) and Fig. 5(b) with different number of flows (i.e. 16–32). From the graphs (Fig. 5(a) and (b)) degradation in fairness with ItswTCM is observed which is due to the following reasons: in the range 20% to 40%, the aggressive senders (small service subscribers) mark more of their packets as red which allows them to acquire more bandwidth than the large subscribers (responsive flows). At 50% of the provision level, the fairness is better as both the subscribers achieve their fair share. Above 60% as the responsive flows mark more of their packets as green and yellow compared to the small subscribers, they gain more bandwidth. With I2tswTCM, in the range 30% to 70% the aggressive senders mark more of their packets as red allowing them to get more bandwidth than the responsive flows. And above 70% the responsive flows mark more of their packets as green and yellow enabling them to obtain more bandwidth. The results of the proposed marker show that both the large and small service subscribers get a proportional share of the excess bandwidth when the number of flows in the aggregate is same and different. This concludes the insensitivity of the marker to the number of flows in the aggregate (i.e. TCP or TCP and UDP). Further, simulation has been carried out with 32–16 flows, which yields the same result. For the sake of brevity, this graph is not shown. This concludes the insensitivity to the number of flows in an aggregate, be it TCP/UDP. Case D: Analysis on variation of RTT. For the same setup as the above and each aggregate with 16 flows, simulation has been done is to study the interaction of TCP and UDP with changes in Round Trip Time (RTT). Figure 6. presents the results related to RTT of aggregate-0 (TCP) being varied, while that of aggregate-1 set to 40 ms. Fairness is found to vary with change in RTT. In all cases, the fairness provision is found to be better except for RTT¼170 ms. This is because as RTT of TCP flows take a large value UDP will inject more packets and hence achieve more bandwidth than TCP. However, the fairness provision is for 20% to 70% of the provision level. 6. Conclusion With ItswTCM and I2tswTCM, unfairness among aggregates in the excess bandwidth region is observed in the DiffServ network.
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based on which the drop precedence of the packets is arrived at. This factor depends on the availability of the network resource and the target rate of an aggregate. Added to this, Etswm provides fairness among TCP and UDP flows sharing the same AF class. References
Fig. 5. Interaction of UDP and TCP (a) aggregates with equal number of flows(16–16); (b) aggregates with diffrent number of flows(16–32).
Fig. 6. Variation of RTT.
Hence to lessen this, a new marking algorithm called Etswm has been proposed in this chapter. The unique feature of this proposed algorithm is that it provides enhanced fairness not only among TCP aggregates but also between TCP and UDP aggregates. Further, the simulation studies show that the effect of constant k on fairness performance is negligible. The performance of the proposed marker is evaluated using extensive simulation studies in NS-2. The results emphasize the superiority of the marker by an enhanced improvement in fairness over an extended range of network provision level (20%–90%) compared to ItswTCM and I2tswTCM. Moreover, the performance of Etswm is neither affected either by the number of flows in an aggregate nor the variation in the target rate. The improved fairness is achieved by introducing an adaptive factor
Alves J, De Rezende L, De Moraes. Evaluating fairness in aggregated traffic marking. Proceedings of IEEE Globecom 2000;1:445–9. Alkharasani Ameen M, Othman Mohamed. M2I2tswTCM: A new efficient optimization marker algorithm to improve fairness bandwidth in DiffServ networks. Journal of Network and Computer Applications 2012;35:1361–6. Baines M, Nandy B, Pieda P, Seddigh N, Devetsikiotis M. Using TCP models to understand bandwidth assurance in a differentiated services network. Nortel Technical Report; July-2000. Carpenter BE, Nichols K. Differentiated services in the Internet. Proceedings of the IEEE 2002;90(9):1479–94. Chait Y, Hollot C, Misra V, Towsley D, Zhang H. Providing throughput differentiation for TCP flows using adaptive two color marking and multi-level AQM. Proceedings of IEEE—INFOCOM 2002:837–44. Chen Chin-Ling. A study of IPv6 labeling forwarding model supporting DiffServ. Procedia Engineering 2011;15:5590–4. Clark DD, Fang W. Explicit allocation of best effort packet delivery service. IEEE/ACM Transactions on Networking 1998;6(4):362–73. Demoor Thomas, Walraevens Joris, Fiems Dieter, Bruneel Herwig. Performance analysis of a priority queue: expedited forwarding PHB in DiffServ. Interna¨ 2011;65:190–7. tional Journal of Electronics and Communication (AEU) El-Glendy AMohamed, Shin Kang G. Assured forwarding fairness using equation based packet marking and packet separation. Computer Networks 2003;41: 435–50 [Elsevier]. Elshaikh MA, Othman M, Shamala S, Johari R. Enhanced tswTCM to improve fairness in DiffiServ networks. In: Proceedings of the IEEE international conference on networks; 2005. vol. 1, p. 302–6. Feroz A, Rao A, Kalyanaraman S. A tcp-friendly traffic marker for IP differentiated services. In: Proceedings of the IEEE/IFIP 8th international workshop on quality of services (IWQoS); 2000. p. 138–47. Floyd S, Jacobson V. Random early detection gateways for congestion avoidance. IEEE/ACM Transactions on Networking 1993;1(4):397–413. Jacobson V, Nichols K, Poduri K. An expedited forwarding PHB. RFC; 1999. vol. 2598. Jain R. The art of computer systems performance analysis: techniques for experimental design, measurement, simulation and modeling.New York, NY: John Wiley and Sons Inc.; 1991 [p. 366 & 387]. Malouch N, Liu Z. Performance analysis of TCP with RIO routers. Proceedings of IEEE Globecom 2002;2:1623–7. Okumus Ibrahim Taner, Cekerekli Sezgin. Design and implementation of a Secure Bandwidth Broker Discovery Protocol. Computer Standards & Interfaces 2012;34:231–7. Padhye J, Firoiu V, Towsley D, Kurose J. Modeling TCP throughput: a simple model and its empirical validation. Proceedings of ACM SIGCOMM 1998;98. Park E, Chio C. Adaptive token bucket algorithm for fair bandwidth allocation in DiffServ networks. Proceeding of IEEE Globecom 2003;6:3176–80. Park Eun-Chan, Choi Chong-Ho. Proportional bandwidth allocation in DiffServ networks. IEEE INFOCOM 2004;3:2038–49. Renjish Kumar KR, Ananda AL, Jacob LillyKutty. TCP-friendly traffic conditioning in DiffServ networks: a memory-based approach. Computer Networks 2002;38(6): 731–43 [Elsevier]. Sahu S, Nain P, Diot C, Firoiu V, Towsley D. On achievable service differentiation with token bucket marking for TCP. In: Proceedings of the ACM SIGMETRICS international conference on measurement and modeling of computer systems; 2000. p. 23–33. Sani Yusuf, Othman Mohamed. A provision-aware fair bandwidth distribution marker algorithm for DiffServ networks. Journal of Network and Computer Applications 2011;34:715–21. Su H, Atiquzzaman M. Performance analysis of differentiated services network with token bucket marker. 11th IEEE workshop on local and metropolitan area networks; 2001. p. 81–2. Su H, Atiquzzaman M. Comprehensive performance model of differentiated service with token bucket marker. IEE Proceedings on Communications 2003;150(5):347–53. Su H, Atiquzzaman M. ItswTCM: a new aggregate marker to improve fairness in DiffServ. Computer Communications 2003;26:1018–27. Sudha S, Ammasaigounden N. A modified approach for fair bandwidth allocation between TCP and UDP traffic in DiffServ network. In: Proceedings of the IEEE international conference on computer and communication engineering; 2008. p. 788–91. Sudha S, Rao Srinivasa, Ammasaigounden N. A modified I2TSWTCM to improve bandwidth fairness in DiffServ. In: Proceedings of the IEEE region 10 colloquium and third international conference on industrial and information systems; 2008. Dong Yingfei, Liu Xiaojiang. Novel dynamic delay allocation adjustment for improving bandwidth efficiency. Computer Communications 2010;33:463–76. Zhu Li, Ansari Nirwan. Fair bandwidth allocation for assured forwarding (AF) services. In: Proceedings of the IEEE international conference on networks; 2005. p. 374–8.