Optical burst switched networks part 2
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Optical burst switched networks part 2
Chapter 6CHANNEL SCHEDULINGWhen a burst arrives to a node, it must be assigned a wavelength on the appropriate outgoing link. In this problem, all-opt Optical burst switched networks part 2 tical wavelength conversion is assumed to be available at each node, and the scheduling occurs at intermediate core nodes as well as ingress nodes. The primary objective in this type of scheduling is to minimize the “gaps” in each channel’s schedule, where a gap is the idle space between two bursts Optical burst switched networks part 2 which are transmitted over the same output wavelength. Channel scheduling in OBS networks is different from traditional IP scheduling, since, in IP. eOptical burst switched networks part 2
ach core node stores the packets in electronic buffers and schedules them on the desired output port. In OBS, once a burst arrives at a core node, it Chapter 6CHANNEL SCHEDULINGWhen a burst arrives to a node, it must be assigned a wavelength on the appropriate outgoing link. In this problem, all-opt Optical burst switched networks part 2 ersion.When a BHP arrives at a core node, a channel scheduling algorithm is invoked to assign the unscheduled burst to a data channel on the outgoing link. The channel scheduler obtains the burst arrival time and duration of the unscheduled burst from the BHP. The algorithm may need to maintain the Optical burst switched networks part 2 latest available unscheduled time (LAƯT) or the horizon, gaps, and voids on every outgoing data channel. Traditionally, the LAUT of a data channel isOptical burst switched networks part 2
the earliest time at which the data channel is available for an unscheduled data burst to be scheduled. A gap is the time difference between the arrivChapter 6CHANNEL SCHEDULINGWhen a burst arrives to a node, it must be assigned a wavelength on the appropriate outgoing link. In this problem, all-opt Optical burst switched networks part 2 bursts on a data channel. For void filling algorithms, the starting and the ending time for each burst on every data channel must also be maintained.Channel Scheduling82The following information is used by the scheduler for most of the scheduling algorithms:-Lf,: Unscheduled burst length duration.-t Optical burst switched networks part 2 ub‘. Unscheduled burst arrival time.-IV; Maximum number of outgoing data channels.-Nị,: Maximum number of data bursts scheduled on a data channel.-Dị’Optical burst switched networks part 2
. ilh outgoing data channel.-LAƯTịi LAUT of the ith data channel, i = 1,2, ...,1V, for non-void filling scheduling algorithms.-and Starting and endingChapter 6CHANNEL SCHEDULINGWhen a burst arrives to a node, it must be assigned a wavelength on the appropriate outgoing link. In this problem, all-opt Optical burst switched networks part 2 fference between tub and LAƯTị for scheduling algorithms without void filling, and is the difference between tub and E(t,j) of previous scheduled burst, j, for scheduling algorithms with void tilling. If the channel is busy. Gapi is set to 0. Gap information is useful to select a channel for the cas Optical burst switched networks part 2 e in which more than one channel is free.Data channel scheduling algorithms can be broadly classified into two categories: with and without void filliOptical burst switched networks part 2
ng. The algorithms primarily differ based on the type and amount of state information that is maintained at a node about every channel. In data channeChapter 6CHANNEL SCHEDULINGWhen a burst arrives to a node, it must be assigned a wavelength on the appropriate outgoing link. In this problem, all-opt Optical burst switched networks part 2 algorithms, the starting time, S(ij) and ending time. are maintained for each burst on every data channel, where, i = 0,1,..., IV, is the ith data channel and j = 0,1,..., Nby is the jth burst on channel i.Let the initial data channel assignment for the channel scheduling algorithms without void fi Optical burst switched networks part 2 lling and with void filling be as shown in Fig. 6.1(a) and (b), respectively. In Fig. 6.1(a). the LAƯTị on every data channel i = 0,1,...,IV, is maintOptical burst switched networks part 2
ained by the scheduler. In Fig. 6.1(b). the starting time. S(tj) and the ending time, F(ij), where i refer to the ilh data channel and j is the jth buChapter 6CHANNEL SCHEDULINGWhen a burst arrives to a node, it must be assigned a wavelength on the appropriate outgoing link. In this problem, all-opt Optical burst switched networks part 2 ing scheduling algorithms, such as First Fit Unscheduled Channel (FFUC) and Latest Available Unscheduled Channel (LAUC), and traditional void-filling scheduling algorithms, such as First Fit Unscheduled Channel with VoidChannel Sc'heduling•S3Figure 6.1. Initial data channel status (a) without void f Optical burst switched networks part 2 illing (b) with void filling.Filling(FFUC-VF)and Latest Available Unscheduled Channel with Void Filling (LAUC-VF).First Fit Unscheduled Channel (FFUC)Optical burst switched networks part 2
:The FFUC scheduling algorithm keeps track of the LAUT (or horizon) on every data channel. A wavelength is considered for each arriving burst when theChapter 6CHANNEL SCHEDULINGWhen a burst arrives to a node, it must be assigned a wavelength on the appropriate outgoing link. In this problem, all-opt Optical burst switched networks part 2 ssigns the first available channel for the new arriving burst. The primary advantage ofFFUC is the simplicity of the algorithm and that the algorithm needs to maintain only one value (LAU'J'i) for each channel. The FFUC algorithm can be illustrated in Fig. 6.2(a). Based on the LAUTi, data channels D Optical burst switched networks part 2 ỵ and z>2 arc available for the duration of the unscheduled burst. If the channels arc ordered based on the index of the wavelengths (£>0, Pl, ..., PiOptical burst switched networks part 2
v), the arriving burst is scheduled on outgoing data channel D]. The time complexity of the84Channel SchedulingFigure 6.2. Channel assignment after usChapter 6CHANNEL SCHEDULINGWhen a burst arrives to a node, it must be assigned a wavelength on the appropriate outgoing link. In this problem, all-opt Optical burst switched networks part 2 awback of FFUC is the high burst dropping probability as a trade-off for simplicity in scheduling. The following algorithms aim at reducing the burst dropping probability at the expense of increased algorithm complexity.Horizon or Latest Available Unscheduled Channel (LAUC):The LAƯC or Horizon [1Ị s Optical burst switched networks part 2 cheduling algorithm keeps track of the LAƯT (or horizon) on every data channel and assigns the data burst to the latest available unscheduled data chaOptical burst switched networks part 2
nnel. The LAƯC algorithm can be illustrated in Fig. 6.1(a). Based on the LAƯTịy data channels D\ and D-2 are available for the duration of the unschedChapter 6CHANNEL SCHEDULINGWhen a burst arrives to a node, it must be assigned a wavelength on the appropriate outgoing link. In this problem, all-opt Optical burst switched networks part 2 complexity of the LAƯC algorithm is ơ(log VV).First Fit Unscheduled Channel with Void Filling (FFUC-VF):Channel Scheduling85The FFUC-VF scheduling algorithm maintains the starting and ending times for each scheduled data burst on every data channel. The goal of this algorithm is to utilize voids be Optical burst switched networks part 2 tween two data burst assignments. The first channel with a suitable void is chosen. The FFUC-VF algorithm is illustrated on Fig. 6.1(b). Based on theOptical burst switched networks part 2
Sij and Djj, all the data channels Do, Dỵ, D2, and D3 are available for the duration of the unscheduled burst. If the channels are ordered based on thChapter 6CHANNEL SCHEDULINGWhen a burst arrives to a node, it must be assigned a wavelength on the appropriate outgoing link. In this problem, all-opt Optical burst switched networks part 2 eduled on every data channel, then a binary search algorithm can be used to check if a data channel is eligible. Thus, the time complexity of the LAUC-VF algorithm is O(log(WWt)).Latest Available Unscheduled Channel with Void Filling (LAUC-VF):The LAUC-VF [2] scheduling algorithm maintains the start Optical burst switched networks part 2 ing and ending times for each scheduled data burst on every data channel. The goal of this algorithm is to utilize voids between two data burst assignOptical burst switched networks part 2
ments. The channel with a void that minimizes the gap is chosen. The LAUC-VF algorithm is illustrated on Fig. 6.1(b). Based on the Sij and Eij) all thChapter 6CHANNEL SCHEDULINGWhen a burst arrives to a node, it must be assigned a wavelength on the appropriate outgoing link. In this problem, all-opt Optical burst switched networks part 2 he arriving burst is scheduled on D3. If Nị) is the number of bursts currently scheduled on every data channel, then a binary search algorithm can be used to check if a data channel is eligible. Thus, the time complexity of the LAUC-VF algorithm is O(log(WAk)). Optical burst switched networks part 2 Chapter 6CHANNEL SCHEDULINGWhen a burst arrives to a node, it must be assigned a wavelength on the appropriate outgoing link. In this problem, all-optGọi ngay
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