Burst Cloning: A Proactive Scheme to Reduce Data Loss in Optical Burst-Switched Networks

Transcription

1 Burst Clonng: A Proactve Scheme to Reduce Data Loss n Optcal Burst-Swtched Networks Xaodong Huang, Vnod M. Vokkarane, and Jason P. Jue Department of Computer Scence, The Unversty of Texas at Dallas, TX Computer and Informaton Scence Department, The Unversty of Massachusetts Dartmouth, MA Emal: {xxh02000@utdallas.edu, vvokkarane@umas.edu, jjue@utdallas.edu} Abstract In ths paper, we propose a novel proactve scheme, burst clonng, to reduce data loss due to burst contenton n optcal burst-swtched (OBS) networks. The dea s to replcate a burst and send duplcated copes of the burst through the network smultaneously. If the orgnal burst s lost, the cloned burst may stll be able to reach the destnaton. Prmary desgn ssues n burst clonng are to select the optmal nodes at whch to do clonng and to prevent cloned bursts from contendng for resources wth orgnal bursts. An analytcal model s developed to evaluate the proposed scheme. The model s verfed through extensve smulatons. We observe that burst clonng could sgnfcantly reduce data loss n OBS networks. I. INTRODUCTION Optcal burst swtchng (OBS) s beleved to be an effectve paradgm to effcently utlze the huge bandwdth of wavelength dvson multplexng networks for bursty IP traffc []. At each ngress node, packets to the same egress node are packed together as a data burst, whch wll then be routed through the network all-optcally. The control nformaton for a data burst, contaned n a burst head packet (BHP), s separated from the data and s transmtted on a dedcated control channel. BHPs are processed electroncally at each ntermedate node to reserve network resources before the data burst arrves. A man concern n burst schedulng s the data loss due to burst contenton. A contenton occurs f and only f multple bursts contend for the same outgong channel on the same wavelength at the same tme nterval. Three well known contenton resoluton schemes are wavelength converson [2], fber delay lne bufferng [3], and deflecton routng [4]. When a contenton cannot be resolved, we can ether drop an entre burst or just drop the contendng part of a burst. The latter scheme, burst segmentaton [5], can further reduce packet loss. A common feature of the above solutons s that, f a burst (or a packet n a burst) s dropped, the burst (or the packet) can only be recovered by retransmsson at a hgher layer. In ths paper, we propose a new proactve scheme, burst clonng, to reduce data loss n OBS networks. The dea s to replcate a burst and send duplcated copes of the burst through the network smultaneously. If the orgnal burst s lost, the cloned burst may stll be able to reach the destnaton. The destnaton egress nodes, wth addtonal ntellgence, wll select one of the bursts, dsassemble the burst, and forward the packets on to the correspondng destnaton hosts. Prmary desgn ssues n burst clonng are to select the optmal nodes at whch to do clonng and to prevent cloned bursts from contendng for resources wth orgnal bursts. We nvestgate and provde solutons to both problems. An analytcal model s developed to evaluate the proposed scheme. The model s verfed through extensve smulatons. We observe that burst clonng could sgnfcantly reduce data loss n OBS networks. It s worth notng that burst clonng s not a replacement of, but a complement to, exstng contenton resoluton schemes. Burst clonng may be used along wth any exstng contenton resoluton scheme, whch makes the proposed scheme qute unversal and practcal. The rest of ths paper s organzed as follows. Secton II explans the aspects of the proposed scheme. In Secton III, we nvestgate node archtectures to support burst clonng. An analytcal model s developed n Secton IV and numercal results are shown n Secton V. We conclude the paper n Secton VI. II. BURST CLONING In ths secton, we descrbe the detals of burst clonng. We refer the orgnal copy of a burst as the orgnal burst, and the duplcated copy of a burst as the cloned burst. The traffc consstng of orgnal bursts and cloned bursts s referred to as orgnal traffc and cloned traffc, respectvely. The node at whch the clonng s done s referred to as the clonng node. In burst clonng, there are several aspects to be conered: the number of cloned bursts for each orgnal burst, the selecton of the clonng node, and the routng for the orgnal burst and the cloned burst. In burst clonng, one or more cloned bursts can be made for each orgnal burst. On one hand, f more copes are made for a burst, the possblty of data loss for the burst s lower. On the other hand, f more copes are made, then more cloned traffc s added to the network. Cloned bursts may contend for network resources wth orgnal bursts, whch may result n ncreasng loss for orgnal bursts, whch n turn may ncrease data loss nstead of reducng t. To prevent cloned traffc from nterferng wth orgnal traffc, we ntroduce a traffc solaton mechansm by usng prorty-based preemptve burst schedulng. Orgnal bursts are assgned hgh prorty whle cloned bursts are assgned low prorty. When schedulng bursts, the hgh prorty burst wll always be scheduled f there s a contenton between /05/$20.00 (C) 2005 IEEE 673

2 source node A 000 H common path 00 Orgnal Burst Fg.. clonng node C 00 H shortest path clonng path H3 H2 prmary path Cloned Burst General path structure for burst clonng destnaton node a hgh prorty burst and a low prorty burst, even f the low prorty burst has already been scheduled. From the hgh prorty traffc s pont of vew, there s no low prorty traffc present n the network. The traffc solaton guarantees that the performance s at least as good wth burst clonng as wthout clonng. Another vtal problem n burst clonng s the selecton of the clonng node for a burst. In prncple, the clonng node for each source destnaton par could be dfferent. A tghtly related problem s the routng of the orgnal burst and the cloned burst. The general path structure for burst clonng s shown n Fg.. An orgnal burst s frst sent along the common path. After the cloned copy s made at the clonng node, the orgnal burst wll then contnue along the prmary path whle the cloned burst wll be routed through the clonng path. The common path would be null f the clonng node s the source node. The prmary path and clonng path would be null f there s no clonng for the burst. (We can also vew ths stuaton as the case n whch the clonng node s the destnaton). Snce a cloned burst s a backup n case the orgnal burst s lost, t s reasonable to keep the loss of orgnal bursts as low as possble. Hence, we choose the common path and the prmary path to be on the shortest path from the source to the destnaton. Accordngly, the clonng node s on the shortest path between the node par. So we have: H + H 2 = H () where H, H 2, and H are the number of physcal hops of the common path, the prmary path, and the shortest path from the source to the destnaton, respectvely. After choosng the prmary path, we must make a decson on whether the clonng path should be lnk-dsjont or even node-dsjont from the prmary path. In ths paper we are amng to mnmze data loss, and are not conerng the protecton ssues. Therefore, the clonng path s allowed to be partally overlapped wth the prmary path, except on the frst hop of both paths. The clonng path, as the second shortest path, wll not be shorter than the prmary path. Then we have: H 3 H 2 0. (2) Even wth Equatons () and (2), t s stll not clear whch node along the shortest path should be the clonng node. B The schedulng of orgnal bursts, due to the traffc solaton mechansm, s ndependent of the selecton of the clonng nodes. Hence, we focus on the cloned bursts. On one hand, f the orgnal burst s lost on the common path, the burst cannot be cloned. Thus, the common path should be shorter. On the other hand, the shorter the common path, the longer the prmary path by equaton (), and the longer the clonng path by equaton (2). Ths may n turn result n hgher loss for cloned bursts. Thus a trade-off must exst between these two factors to acheve the best performance. Through our analytcal model and smulatons, we fnd that the former factor has a much greater effect on performance. One brute force approach to fnd the optmal clonng node s to enumerate all possble clonng node confguratons. For an OBS network wth N nodes, there N(N ) sourcedestnaton pars. It may be mpractcal to try all possble clonng confguratons. As a compromse, n ths paper we frst classfy source-destnaton pars nto D categores, where D s the dameter of a network. We set one clonng confguraton for each category wth d hops, where d {, 2,..., D}. III. NETWORK ARCHITECTURE In OBS networks, there are two types of nodes: electronc edge nodes and optcal core nodes. Edge nodes are the gateways between OBS networks and tradtonal networks, such as IP networks and ATM networks. Core nodes route bursts hop-by-hop all-optcally through the OBS network. A general archtecture of edge nodes and core nodes n OBS networks was proposed n [6]. Edge nodes are responsble for burst assembly and deassembly. In burst clonng, f the clonng node s the source node (referred to as source clonng), ngress nodes are also responsble for duplcatng bursts. In source clonng, clonng can be done n the electronc doman. Wth burst clonng, egress nodes also have more work to do than just deassemblng bursts. The desgnated egress node may receve both the orgnal burst and the cloned burst. To avod sendng duplcated packets to hgher layers, the dentty number of packets may be buffered at the egress node untl a tme out occurs or the other copy s receved. Core nodes provde all-optcal routng, enablng data bursts to bypass the node. If the clonng node s an ntermedate node (referred to as ntermedate clonng), the clonng core node should have optcal splttng capablty, whch duplcates an ncomng data burst nto two or more copes. Multcast capable optcal crossconnect [7], MC-OXC, can be conered for ntermedate clonng. In general, MC-OXCs are much more expensve than regular OXCs. However, as we wll show wth our analytcal model and smulatons n the followng sectons, source clonng has the best loss performance. Hence, n our proposed scheme, we need only regular OXCs nstead of expensve MC-OXCs. Another archtectural ssue comes from the combnaton of burst segmentaton and burst clonng. One of the e-effects of burst segmentaton s that the length of the burst can decrease due to possble contentons as t travels towards the destnaton. 674

3 Hence, some packets n the data burst can be lost before they reach the destnaton. Specfcally, when a strct tal-droppng technque s adopted, the probablty of packets toward the tal beng dropped s much hgher than the packets toward the head of the burst. When combned wth burst clonng, t s very lkely that both bursts reach the destnaton but that each burst has lost a part of ts tal. In order to counter ths effect, we can reverse the order of packets n the cloned burst at the clonng node whle sendng out the orgnal burst as t s. Ths reversal of packets ensures that packets n the tal of the orgnal burst wll be n the head of the cloned burst. At the destnaton, f both burst copes are receved, even though the tal of each burst may be lost due to segmentaton, the entre burst may be recovered from these two burst copes. If the clonng node s not a source node, t may be too complex to mplement the burst reversal operaton n the optcal doman. For source clonng, we nvestgate the performance of a complete reversal polcy, under whch the packet order n the cloned burst s a complete reversal of that n the orgnal burst. At destnaton nodes, after both copes are receved or tme out, a post-process procedure wll begn. Let L 0, L and L 2 be the number of packets n the orgnal burst, n the receved prmary burst, and n the receved cloned burst, respectvely. It s easy to obtan the number of packets receved for complete reversal and wthout burst reversal as mn{l 0,L + L 2 } and mn{l,l 2 }, respectvely. If any copy of the burst s lost, we can thnk the correspondng L or L 2 to be 0. It can be seen that complete reversal can further reduce data loss compared to no reversal. IV. ANALYTICAL MODEL In ths secton, we extend the analytcal model n [5] to calculate the average packet loss probablty n burst clonng wth burst segmentaton. Interested readers are referred to [5] for the detals. Frst, let us defne the followng notaton: /µ: average burst length; K : total number of hops from the source s to the destnaton d; kl : total number of hops from the source s untl to the lnk l, along the path ; λ : burst arrval rate from source s to destnaton d; λ l : arrval rate of orgnal bursts to the lnk l on the path from source s to destnaton d; γl : arrval rate of cloned bursts to the lnk l on the path from source s to destnaton d; λ l = λ l : arrval rate of orgnal bursts to lnk l, due to all source-destnaton pars ; γ l = γ l : arrval rate of cloned bursts to lnk l, due to all source-destnaton pars ; λ l : arrval rate of all orgnal bursts on the th hop lnk of the path between source s and destnaton d. Letl = l, then λ l = λ l ; r : prmary route from source s to destnaton d; : clonng route from source s to destnaton d. r The offered load on lnk l by traffc from source s to destnaton d depends on whether lnk l s on the path from s to d. Wth segmentaton, burst length may decrease along the path from s to d. However, there s no reducton of the arrval rate of bursts. Thus, λ l = { λ, f l r 0, otherwse Followng [5], we obtan the packet loss probablty of orgnal bursts (wth hgh prorty) as Ploss0 µ = (4) K λ l + µ = and the utlzaton due to orgnal bursts on lnk l as ρ l = s,d kl = λ l λ l + µ (3). (5) Clonng traffc s treated as the same as the low prorty traffc n [5]. Thus, λ, f l r γl,l = l 0 = γh ( ρ h), f l, h r,h= l, (6) 0, otherwse. Followng [5], we obtan the packet loss probablty of cloned bursts (wth low prorty) as P loss = K = K (λ l j= ( ρ ) µ j + γ l j )+µ. (7) After we obtan the packet loss probabltes for both orgnal bursts and cloned bursts, we can calculate the endto-end packet loss probablty Ploss by Ploss = Ploss0 sc +( Ploss0) sc Ploss0 cd Ploss cd (8) where c s the clonng node of source-destnaton par. Takng the traffc weghted average of end-to-end packet loss probabltes, we obtan the average packet loss probablty for the network as P loss = λ λ P loss. (9) s d V. NUMERICAL RESULTS In ths secton, we present the numercal results from our analytcal model and smulatons. We evaluate the performance of our proposed scheme n the 4-node NSFNET as shown n Fg. 2, n whch the number on a lnk s the dstance n klometers between two adjacent nodes. Bursts arrve to the network accordng to a Posson process. Incomng traffc s evenly dstrbuted among all source-destnaton pars. Packets n a burst have a fxed length of 250 bytes. The length of a burst s exponentally dstrbuted. The lnk transmsson rate s 0 Gb/s, and the speed of lght n optcal fbers s assumed to 675

4 be 250 km/ms. There are no wavelength converters or optcal buffers n the network. TAG sgnallng protocol s assumed, wth each node equpped wth fxed FDLs to buffer data bursts whle BHPs are beng processed. To avod the effect of wavelength assgnment algorthms, we run the smulaton on one wavelength. The dameter of the 4-node NSFNET s D =3. Accordng to the proposed scheme, we dvde source-destnaton pars nto 3 categores: -hop pars, 2-hop pars, and 3-hop pars. We number the nodes along the k-hop (k =, 2, 3) path as 0,, 2,...,k. Then, we use a vector C =[c,c 2,c 3 ] to denote clonng confguratons, where c k denotes the clonng node for all k-hop source-destnaton pars. c k =0means source clonng; c k = k means no clonng; c k {, 2,...,k } means ntermedate clonng. For example, f we do clonng for all pars at the source node, we set C =[0, 0, 0]; fwe do not do clonng for any node par, we set C = [, 2, 3]. All possble clonng confguratons wth clonng confguraton ndex (denoted by I C ) are lsted n Table I. We frst study the performance of dfferent clone confguratons wthout the burst reversal operaton. Fg. 3 and Fg. 4 show the packet loss probablty wth dfferent clonng confguratons by smulaton and analyss, respectvely. In both fgures, each curve denotes the loss performance under one specfc network load, whch vares from to 64. We observe that the results for dfferent clonng confguratons are qute consstent under dfferent network loads for smulaton and for the analytcal model. Source clonng (I C = 0 wth C =[0, 0, 0]) always has the best loss performance, followed by confguraton I C = 2 (.e., C = [, 0, 0], no clonng for -hop node pars and source clonng for all other node pars). From Fg. 3 and Fg. 4, we fnd that any clonng confguraton (wth I C between [0, 22]) has better loss performance than wthout clonng (.e., I C =23wth C =[, 2, 3]). Ths performance s due to the traffc solaton mechansm and preemptve schedulng n our proposed scheme. Thus, cloned bursts do not nterfere wth orgnal bursts. Cloned bursts just try to utlze network resources whch are not occuped by orgnal bursts. It s qute nterestng to notce n Fg. 3, Fg. 4, and Fg. 5 that there are consstently 6 ncreasng segments n each curve. We fnd that these segments have clonng confguraton ndex I C as follows: {0,, 2, 3}, {4, 5, 6, 7}, {8, 9, 0, }, {2, 3, 4, 5}, {6, 7, 8, 9} and {20, 2, 22, 23}. In each segment, the four confguratons have the same settng for - hop and 2-hop node pars, whle the clonng node for 3-hop pars moves further and further from the source node. The further the clonng node s from the source, the less chance that the burst s cloned. Fg. 5 and Fg. 6 compare the loss performance of the analytcal model wth that of the smulatons. We can see that the analytcal model s qute accurate. Fg. 5 emphaszes the loss performance wth dfferent clonng confguratons under a fxed network load (). Under other network loads, there s smlar relatve performance. Fg. 6 gves a global vew of Fg. 3. Fg Fg node NSFNET wth dstance n klometers TABLE I NUMBERING THE CLONE CONFIGURATIONS I C C I C C I C C 0 [0,0,0] 8 [0,2,0] 6 [,,0] [0,0,] 9 [0,2,] 7 [,,] 2 [0,0,2] 0 [0,2,2] 8 [,,2] 3 [0,0,3] [0,2,3] 9 [,,3] 4 [0,,0] 2 [,0,0] 20 [,2,0] 5 [0,,] 3 [,0,] 2 [,2,] 6 [0,,2] 4 [,0,2] 22 [,2,2] 7 [0,,3] 5 [,0,3] 23 [,2,3] smu Clonng Confguraton Packet loss vs. clone confguratons under load (-64) (Smulaton) anal Clonng Confguraton Packet loss vs. clone confguratons under load (-64) (Analytcal)

5 anal smu 0 Clonng Confguraton No Clonng Source clonng - No Reversal Source clonng - Complete Reversal Fg. 5. Packet loss vs. clone load () Fg. 7. Packet loss comparson of burst reversal scheme No Clonng (anal) No Clonng (smu) Source Clonng (anal) Source Clonng (smu) Average Physcal Hops No Clonng Source clonng - No Reversal Source clonng - Complete Reversal Fg. 6. Packet loss vs. network load (-) Fg. 8. Average physcal hop comparson of burst reversal scheme source clonng under dfferent network loads (-). Fg. 6 clearly shows agan, from another pont of vew, that source clonng can sgnfcantly mprove the loss performance. We also study the performance of burst reversal. Snce we fnd that source clonng has the best loss performance among all possble clonng confguratons, we wll focus on source clonng wth burst reversal. From Fg. 7, we observe that complete reversal can sgnfcantly reduce data loss. Fg. 8 shows that burst clonng results n a small ncrease n the average number of packet hops than wthout clonng. Wth burst clonng, some otherwse lost packets wll arrve at the destnaton n the cloned burst. Between any node par, cloned bursts undergo a greater number of hops than orgnal bursts. Thus, bursts have a greater number of hops wth burst clonng than wthout burst clonng. For the same reason, complete reversal results n more packets n the cloned burst reachng the destnaton compared to clonng wthout burst reversal. Thus, complete reversal also results n more hops. However, the ncrease n hops s not sgnfcant. VI. CONCLUSIONS Ths paper addresses the ssue of data loss n OBS networks due to burst contenton. A new proactve scheme, called burst clonng, was proposed, and an analytcal model was developed to calculate the packet loss probablty. Extensve smulatons verfed the analytcal model and showed that burst clonng can sgnfcantly mprove the loss performance wthout sgnfcant ncrease n packet delay. REFERENCES [] C. Qao and M. Yoo, Optcal Burst Swtchng (OBS) - A New Paradgm for an Optcal Internet, Journal of Hgh Speed Networks, vol. 8, no., pp , Jan [2] B. Ramamurthy and B. Mukherjee, Wavelength Converson n WDM Networkng, IEEE Journal on Selected Areas n Communcatons, vol. 6, no. 7, pp , Sept [3] C. Gauger, Dmensonng of FDL Buffers for Optcal Burst Swtchng Nodes, Proceedngs, Optcal Network Desgn and Modelng (ONDM 2002), Torno, Feb [4] C. Hsu, T. Lu, and N. Huang, Performance Analyss of Deflecton Routng n Optcal Burst Swtched Networks, Proceedngs, IEEE INFOCOM 2002, vol., Jun [5] V. M. Vokkarane and J. P. Jue, Prortzed Burst Segmentaton and Composte Burst Assembly Technques for QoS Support n Optcal Burst- Swtched Networks, IEEE Journal of Selected Areas of Communcatons, vol. 2, no. 7, pp , Sept [6] Y. Xong, M. Vandenhoute, and H. Cankaya, Control Archtecture n Optcal Burst-Swtched WDM Networks, IEEE Journal of Selected Areas of Communcatons, Vol. 8, No. 0, pp , Oct [7] W.S. Hu and Q.J. Zeng, Multcastng optcal cross connects employng spltter-and-delvery swtch, IEEE Photoncs Technology Letters, vol. 0, no. 7, pp , Jul