Coordinated TCP Westwood Congestion Control for Multiple Paths over Wireless Networks

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1 Coordinated TCP Wetwood Congetion Control for Multiple Path over Wirele Network Tuan Anh Le, Choong eon Hong, and Eui-Nam Huh Department of Computer Engineering, Kyung Hee Univerity 1 eocheon, Giheung, Yongin, Gyeonggi, , Korea {letuanh, chong, johnhu}@khu.ac.kr, Abtract Multipath TCP (MPTCP) ha jut been approved by the IETF. It wa deigned to be fairly hared with regular TCP, o it performance i equivalent that of a regular TCP flow that on the bet path for it. However, regular TCP ha been proven it performance very poor in wirele network, where packet lo often i caued by random error rather than by network congetion a in wired network. TCP Wetwood (TCPW) ue the available bandwidth etimation technique to improve TCP performance in uch environment. In thi work, we propoe an extended verion of TCP Wetwood for multiple path, called MPTCPW. To tart with the analyi model of TCPW, MPTCPW i deigned a a coordinated congetion controller between path which allow load-balancing, fair haring to regular TCPW at bottleneck. Our imulation reult how that MPTCPW can achieve higher throughput than MPTCP in wirele environment, fairne to regular TCPW, and greater load-balancing than uncoordinated MPTCPW. I. INTODUCTION Nowaday portable device with multiple wirele interface are becoming more popular. If multiple link are ued imultaneouly for a tranport protocol eion, multipath tranport protocol would be able to avoid ending traffic on hotpot and failure link, and to upport mobility [1]. o far, the performance and reilience are improved. egular TCP [2] performance i degraded ignificantly a packet loe are occurred by random error (caued by ignal fading, or multiple-acce interference) in wirele link rather than by network congetion a in wired network. Thi i becaue regular TCP reduce blindly it congetion window by haft when a packet drop i detected. To overcome thi problem, TCP Wetwood (TCPW) [3] [4] ha been propoed. In TCPW cheme 1, the ender monitor ACK inter-arrival time in order to etimate the bottleneck bandwidth available. Intead of reducing congetion window by haft, TCPW update both congetion window and low-tart threhold to the etimated bandwidth (in term of the number of packet) whenever detecting packet drop. TCPW performance ha been proven ignificant improvement in wirele network. A multipath TCP protocol eion conit of imultaneou multiple ub-flow amongt path between two end-hot [5], where each ub-flow perform flow control function on a path. o there are ome requirement for congetion control 1 The original verion of TCP Wetwood [3] overetimate the available bandwidth in the preence of ACK compreion. TCP Wetwood+ [4] olve thi problem. deign for multiple path [6] a follow: (i) A multipath TCP protocol hould fairly hare bandwidth with ingle-path TCP protocol without any common bottleck detection mechanim; (ii) To improve multipath TCP performance in multipath environment. (iii) To exploit load-balancing between path. Multipath TCP (MPTCP) [6] ha jut been approved by the IETF. It deign aim to atify the above requirement. MPTCP end more traffic on lightly loaded path by grouping a et of reource on all path a a ingle reource, a uggeted by the reource pooling principle [7]. ince MPTCP performance i equivalent that of a regular TCP flow that on the bet path for it, MPTCP face with performance degradation over wirele network. In thi paper, we are intereted on an extended verion of TCP Wetwood for multiple path, called MPTCPW. To tart with the analyi model of TCPW, MPTCPW i deigned a a coordinated congetion controller between path which allow balancing the load between the path, while enuring fair bandwidth allocation to regular TCPW at the hared bottleneck. The ret of thi paper i organized a follow: ection II ummarized the previou work relevant to multipath congetion control. We decribe the detail of the TCPW analyi model, and then it extenion for multiple path in ection IV. We evaluate our propoal in term of fluctuation, fairne, throughput over wirele link and load-balancing capability. Finally, we conclude our work in ection VI. II. ELATED WOK In thi ection, we ummarize everal olution ha been propoed for multipath congetion control. Multiple path TCP (mtcp) [8] aggregate the available bandwidth of all path in parallel, and detect and remove path at hared bottleneck to alleviate unfair allocation. The congetion controller of each ub-flow in Parallel TCP (ptcp) [9], Concurrent Tranfer Multipath (CMT) over CTP [1] operate independently each other a ued in regular TCP. Therefore, they can not compete fairly with regular TCP flow at hared bottleneck becaue of no extra mechanim to handle or detect the bottleneck. eliable Multiplexing Tranport Protocol (-MTP) [11] wa deigned for wirele network. Baed on inter-arrival time, - MTP ub-flow adapt to rate control according to change in bandwidth on each channel and congetion /12/$ IEEE 92 ICOIN 212

2 To improve fairne to regular TCP at the hared bottleneck, the weighted TCP [12] ue a fixed weight in allocating bandwidth to each ub-flow. The weight i choen by 1/N 2, where N i the number of path in a multipath TCP eion. Obviouly the weighted TCP could fairly hare if TT of flow are equal. Thi mechanim take advantage of the implicity of deployment and fair allocation without any hared bottleneck detection mechanim. III. TCP WETWOOD BACKGOUND In thi ection, we briefly decribe TCPW algorithm [4] and then it performance analyi model. TCPW etimate bandwidth available baed on inter-arrival time of ACK packet at the ender. Whenever the ender receive an ACK, it compute a bandwidth ample a b k = d k /(t k t k 1 ), where d k denote the amount of data acknowledged by the k th ACK. t k and t k 1 denote the inter-arrival time of the k th ACK and the (k 1) th ACK, repectively. To mooth out hort-time variant in the bandwidth ample b k, a dicrete time-varying low-pa filter i ued a ˆbk = 2τ Δ k 2τ +Δ k ˆbk 1 + b k + b k 1 2τ +Δ k Δ k, where ˆb k i the moothed bandwidth at time t k, 1/τ i the cutoff frequency of the filter. Δ k denote the inter-arrival time between (k 1) th ACK and the k th ACK. The ender ue the etimated bandwidth to update the congetion window ize (w TCPW ) and the low-tart threhold (threh) after receiving duplicated ACK or detecting a timeout event, a threh = ˆb T T min /M, where T T min denote the minimum TT during TCPW connection. Now, we determine the fluid model of TCPW. In the congetion avoidance phae, TCPW remain the window growth baed on the additive increae function a ued in regular TCP (TCP eno) a follow: Whenever the ender receive a poitive ACK, it increae w TCPW by 1/w TCPW. Wherea, after detecting a lot packet, it et w TCPW and threh to ˆB T T min, where ˆB ( ˆB = ˆb/M ) i the etimated available bandwidth in term of the number of packet. The TCPW algorithm i expreed a Increae: w TCPW (t) w TCPW (t 1)+1/w TCPW (t 1), Decreae: w TCPW (t) ˆB(t) T T min, where ˆB(t) = ŵ TCPW (t)/t T [13]. The fluid model of TCPW correponding to uch increae-decreae function i expreed in repect with continuou time t a ( d dt wtcpw (t) = wtcpw (t) 1 p T T w TCPW (t) ) q T T wtcpw (t)p, (1) where q = T T T T min denote the total queueing delay meaured at two-end hot. p denote the packet drop probability. uppoe that the packet lo rate p i mall (i.e., 1 p 1), the fixed point equation of (1) give or 1 ŵ TCPW = q T T ŵtcpw p, p = T T q(ŵ TCPW ) 2, (2) where ŵ TCPW i the equilibrium value of w TCPW (t). IV. EXTENDING TCPW TOWAD MPTCPW In thi ection, baed on the fluid model of TCPW above, we carry out extending TCPW for multiple path with contrain about performance improvement, load-balancing between path and fair haring [6] [14] to regular TCPW, which are the goal to deign MPTCP [6]. Now, we propoe MPTCPW congetion window growth in additive increae function over path a follow: Whenever the ub-flow receive a poitive ACK on that path, it increae it congetion window (w ) by min(δ/w (t), 1/w (t)); when receiving duplicate ACK, it update w to ˆB T T min,. Therefore, the ub-flow congetion control algorithm on path i Increae: w (t) w (t 1) + min(δ/w (t 1), 1/w (t 1)), Decreae: w (t) ˆB (t) T T min,. o the fluid model correponding to uch increae-decreae function i d dt w (t) = w [ ( ) (t) δ min T T w (t), 1 w (t) q ] w (t)p, (3) T T where q = T T T T min,, δ denote the linking between path within an MPTCPW flow. min(.) function enure that ub-flow window increae (the left argument) doe not exceed that of ingle-path TCPW (the right argument) over that path. imilarly, we have the fixed point equation of (3) a ) ( δ min, ŵ ŵ TCPW 1 ŵ = q T T ŵ p. (4) If TCPW wa on path, from (2) it packet lo rate would be p = T T /q (ŵ TCPW ) 2. We ubtitute p into (4) to obtain ( ) ŵ = max, ŵ. (5) δ To improve throughput and to preerve fairne, the total throughput of a MPTCPW flow hould be equivalent that of a TCPW flow on the bet path for it [15]. Thi implie that {ŵtcpw ŵ = max T T T T }. (6) 93

3 By ubtituting (5) into (6), we obtain { ( )} ŵ ŵ ŵ = max max,. T T δt T T T Obervably, in the above equality, the total throughput cannot equal that on a path ince ŵ never equal zero, therefore { } ŵ ŵ = max. T T δt T n m link 1 5Mbp, 6m 75 packet link 2 link 1 1Mbp, 58m 5Mbp, 2m 5Mbp, 6m 75 packet Multipath TCPW egular TCPW By olving for δ, we obtain { ( ) } 2 /( ŵ δ = max T T ŵ T T ) 2. (7) Fig. 1. link 2 (c) 5Mbp, 2m imulation cenario. δ in the equation above i hared between path and depend on only the maximum throughput among path. However, the congetion window on the congeted path i alway maller than that on the lightly loaded path. To perform load-balancing between the path, the congetion window on the congeted path mut be grown more gradually than that on the lightly loaded path [14]. Thi implie that δ for the wore path would be the maller value. Therefore, we lightly modify δ, and then replace δ with δ a { }/( ) 2 δ =ŵ γ max ŵ2 γ ŵ T T 2, (8) T T where γ i a trade-off parameter between load-balancing and protocol fluctuation, γ 2. In our experiment (not reported in thi paper due to pace limit), γ = 1 give a reaonable trade-off between fluctuation and load-balancing. V. PEFOMANCE EVALUATION In thi ection, we evaluate fluctuation, fairne and loadbalancing of MPTCPW, and compare it performance with MPTCP [6] in wirele network. Load-balancing capability of MPTCPW i compared with uncoordinated MPTCPW (named unmptcpw), in which each ub-flow perform the flow control function independently. To enure fairne to regular TCPW at the hared bottleneck, we chooe the traffic plitting factor value of (1/2) 2 for two-path unmptcpw uch that each ub-flow get half throughput of what a regular TCPW get. We ue N-2 [16] in our experiment, and the elective acknowledgment (ACK) option [17]. The cenario hown in Fig. 1 with a 1-byte data packet, and random early drop (ED) queue management [18] to prevent router from globally ynchronized packet drop. A. Fluctuation Invetigation Aume that the traffic load on two path i the ame. I a multipath protocol table when ome packet are ent on one path for moment, and then on the other, and o on?. Thi implie that the path are not ued imultaneouly at almot time [15] [14]. o any multipath tranport protocol performance and reource pooling would be poor in uch tate. cwnd cwnd 1 cwnd cwnd 1 Fig. 2. The congetion window evolution of two-path MPTCPW flow; that of two-path MPTCP flow. Now, we invetigate protocol fluctuation in a typical network configuration, where two-eparate path multipath protocol competing with background load generated by ten regular TCPW/TCP flow 2 on each path (n = m = 1) a hown in Fig. 1. Becaue of the ame load on both path, each ub-flow experience the ame congetion condition. Fig. 2 how that the congetion window on and 2 (cwnd 1, cwnd 2 ) in MPTCPW are increaed regularly rather than biaing on any ide (i.e., the protocol i fluctuation in it data rate on each path). Thi reult i imilar to that of MPTCP a hown in Fig. 2. Another imulation reult in the ame bottleneck i hown in Fig. 3, the evolution of congetion window on two path i almot ame. B. Fair haring In thi ection, we how how a multipath tranport protocol fairly hare with a ingle-path protocol at a common bottleneck without any common link detection mechanim. We ue a dumbbell cenario a hown in Fig. 1, where a two-path MPTCPW flow compete againt a regular TCPW flow at the hared link. Fig. 3 how that the ingle-path TCPW get it congetion window twice. It i reaonable when total of data ent by the two-path MPTCPW flow i cloe the amount of data ent by the ingle-path TCPW flow a hown in Fig If multipath tranport protocol i MPTCPW, we will ue ten regular TCPW flow a background load. Otherwie, ue regular TCP flow. 94

4 Congetion window (pkt) , MPTCPW On, MPTCPW ingle-path TCPW ent data (MByte) On ingle-path TCPW ent total data on 2 path Time () Time () Fig. 3. The congetion window evolution of a two-path MPTCPW flow competing againt a regular TCPW flow in the hared bottleneck; their amount of data tranferred. Another experiment reult i hown in Fig. 5 with the network configuration detailed in ection V-B. In Fig. 5, MPTCPW move more traffic from the congeted path (path 1) to the lightly loaded path (), o the ub-flow rate on urge, but not exceed the average throughput of ingle-path TCPW flow on that path. Therefore, MPTCPW can preerve fairne to ingle-path TCPW in the general configuration. C. Throughput over Wirele Link In thi ection, we evaluate throughput performance of MPTCPW compared with that of regular MPTCP. The imulation cenario i hown in Fig. 1(c). The experiment were run for 6 econd under wirele link random error varying from.1% to 5% in packet lo rate. Fig. 4 how the average throughput of MPTCPW and MPTCP when the packet lo rate on two path are equal. In Fig. 4, MPTCPW throughput i higher than that of MPTCP in any packet lo rate. Outperforming of MPTCPW i come from adaptive updating threh and cwnd to the etimated available bandwidth on path a detecting a packet lo or timeout event. In the next experiment, we fix the packet lo rate at.1% on and vary the lo rate from.1% to 5% on. Fig. 4 how that MPTCP throughput i degraded ignificantly when packet lo rate on increae to 1%. ince MPTCPW can recover from random lo, it outperform at any condition. In Fig. 4, when random lo on i very high (greater than 1%), the total throughput of two-path tranport protocol i dominated by only the bet path,. D. Load-Balancing In thi ection, we invetigate the capability of hifting traffic from the congeted path in an advere configuration, where T T on the lightly loaded path i longer than that on the congeted one 3. We ue uch advere configuration in order to demontrate the prominent feature of MPTCPW compared with uncoordinated MPTCPW. 3 For packet lo-baed tranport protocol uch a regular TCP, TCPW, MPTCP, and MPTCPW, their congetion window ize on the longer TT path are increaed more lowly than that on the horter TT path. The coordinated congetion control in multipath i able not only to gather bandwidth on all path into a bigger bandwidth but alo to move traffic among path according traffic load on each path. For uch configuration, if we did not ue δ a (8), the congetion window of ub-flow on the lightly loaded and longer TT path wa increaed more lowly than expected. Baed on computing δ a (8), the ub-flow can compenate congetion window increae for the longer TT path. Experiment were run in the imulation cenario a hown in Fig. 1, where link capacity and propagation delay of link 1 and 2 are et (1Mbp, 4m) and (6Mbp, 16m), repectively. To generate heavy load in link 1 and light load in link 2, we ue TCPW flow a the background traffic with eight flow on link 1, and three flow on link 2. The oberved packet lo rate at link 1 and 2 after experiment are 2.% and.56%, repectively. Fig. 5 how that the data rate of ub-flow on the congeted and hort TT path () i very low. While the longer T T path () ha light load, the ub-flow on that path urge it rate up. Therefore, the total throughput of two ub-flow reache the expected value, which i equivalent to the average rate of three TCPW flow that over the bet path,. In contrat to load-balancing capability of MPTCPW, un- MPTCP jut plit the traffic acro path with factor of (1/2) 2. We alternated MPTCPW protocol in the above experiment with unmptcp. Fig. 5 how that each ub-flow get half TCPW flow average rate that they are haring. The packet lo rate at link 1 and 2 are meaured to be 2.8% and.35%, repectively. Although i congeted, the ub-flow on that path till end blindly packet at haft rate. Therefore, two-path unmptcp can get the total throughput lower than TCPW flow in uch advere configuration. VI. CONCLUION In thi paper, we propoe an extended verion of regular TCP Wetwood for multiple path over wirele network, called MPTCPW. To tart with the analyi model of TCPW, MPTCPW congetion control i deigned a a coordinated control between path which allow load-balancing feature beween path, fair haring to regular TCPW at bottleneck. Our imulation how that MPTCPW can achieve tability, higher throughput compared with MPTCP, fairne to regular TCPW, 95

5 Two-path MPTCPW/MPTCP v. packet lo Two-path MPTCPW/MPTCP v. packet lo Average throughput (Mbp) MPTCPW MPTCP Average throughput (Mbp) MPTCPW MPTCP 1E Packet lo rate (%) 1E Packet lo rate on (%) Fig. 4. The average throughput of two-path MPTCPW and MPTCP v. varying packet lo on and 2; that of two-path MPTCPW and MPTCP v. varying packet lo on. Data rate (Mbp) MPTCPW v. TCPW On Total rate on 2 path Average rate of 8 TCPW flow hared link 1 Average rate of 3 TCPW flow hared link 2 Data rate (Mbp) Uncoordinated MPTCPW v. TCPW On Total rate on 2 path Average rate of 8 TCPW flow hared link 1 Average rate of 3 TCPW flow hared link Time () Time () Fig. 5. Load-balancing capability of MPTCPW; lack load-balancing capability of uncoordinated MPTCPW when two-path MPTCPW compete againt eight TCPW flow at link 1 and three TCPW flow at link 2. and greater load-balancing than uncoordinated MPTCPW under variou network condition. We believe that our extenion technique can be generalized for extending current tranport protocol, uch a TCP Vega, FAT TCP, and Compound TCP for multiple path. ACKNOWLEDGMENT Thi reearch wa upported by the IT &D program of KCA ( : tudy on Architecture of Future Internet to upport Mobile Environment and Network Diverity). Dr. C Hong i the correponding author. EFEENCE [1] C. aiciu, D. Niculecu, M. Bagnulo, and M. Handley, Opportunitic mobility with multipath TCP, in Proc. of the MobiArch Workhop, 211. [2] V. Jacobon and M. J. Karel, Congetion avoidance and control, in ACM IGCOMM, [3] M. Gerla, B. K. F. Ng, M. Y. anadidi, M. Valla, and. Wang, TCP Wetwood with adaptive bandwidth etimation to improve efficiency/friendline tradeoff, in Computer Communication, Jan. 24. [4]. Macolo, L. A. Grieco,. Ferorelli, P. Camarda, and G. Picitelli, Performance evaluation of Wetwood+ TCP congetion control, in Performance Evaluation, Jan. 24. [5] A. Ford, C. aiciu, and M. Handley, TCP extenion for multipath operation with multiple addree, IETF Internet Draft, July 211. [6] C. aiciu, M. Handley, and D. Wichik, Coupled congetion control for multipath tranport protocol, IETF FC 6356, Oct [7] D. Wichik, M. Handley, and M. B. Braun, The reource pooling principle, in ACM IGCOMM CC, Oct. 28. [8] M. Zhang, J. Lai, A. Krihnamurthy, L. Peteron, and. Wang, A tranport layer approach for improving end-to-end performance and robutne uing redundant path, in Proc. of the UENIX 4 Annual Technical Conf., June 24. [9] H. Heih and. ivakumar, A tranport layer approach for achieving aggregate bandwidth on multi-homed mobile hot, in Proc. of the MobiCom 2 Conf., 22. [1] J.. Iyengar, K. C. hah, P. D. Amer, and. tewart, Concurrent multipath tranfer uing CTP multihoming over independent end-toend path, IEEE/ACM Tranaction on Networking, pp , 26. [11] L. Magalhae and. Kravet, Tranport level mechanim for bandwidth aggregation on mobile hot, in Proceeding of the Ninth International Conference on Network Protocol. Wahington, DC, UA: IEEE Computer ociety, 21, pp [12] M. Honda, Y. Nihida, L. Eggert, P. arolahti, and H. Tokuda, Multipath congetion control for hared bottleneck, in Proc. PFLDNeT, May 29. [13] L. A. Grieco and. Macolo, Mathematical analyi of Wetwood+ TCP congetion control, in IEE POCEEDING-CONTOL THEOY AND APPLICATION, Jan. 25. [14] D. Wichik, C. aiciu, A. Greenhalgh, and M. Handley, Deign, implementation and evaluation of congetion control for multipath TCP, in Proc. of the UENIX NDI 11 Conf., Mar [15] D. Wichik, M. Handley, and C. aiciu, Control of multipath TCP and optimization of multipath routing in the Internet, in Network Control and Optimization, 29. [16] N-2 network imulator. [Online]. Available: [17] M. Mathi, J. Mahdavi,. Floyd, and A.omanow, TCP elective acknowledgment option (ACK), IETF FC 218, Oct [18]. Floyd,. Gummadi, and. henker, Adaptive ED: An algorithm for increaing the robutne of ED active queue management, Tech. report, Tech. ep.,