PAHON: Power-Aware Hybrid Optical Network

J. Parallel Distrib. Comput. 117 (2018) 1–16

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PAHON: Power-Aware Hybrid Optical Network Lida Ghaemi Dizaji, Akbar Ghaffarpour Rahbar * Computer Networks Research Lab, Electrical Engineering Technologies Research Center, Sahand University of Technology, Sahand New Town, Tabriz, Iran

highlights • • • • •

Propose a novel integrated hybrid optical network called PAHON (Power-Aware Hybrid Optical Network). Under PAHON, OPS packets are sent between OCS packets. PAHON optimizes the network resource utilization. PAHON reduces packet loss rate and connection blocking rate without using any additional hardware. PAHON decreases energy consumption of the network.

article

info

Article history: Received 12 February 2017 Received in revised form 2 December 2017 Accepted 22 January 2018 Available online 3 February 2018 Keywords: Green optical networks Hybrid optical networks OCS OBS OPS PAHON

a b s t r a c t Power consumption of a network, as one of the important concerns in network design, increases when the size and traffic load of the network raises. In this article, a green hybrid optical network namely Power Aware Hybrid Optical Network (PAHON) is proposed. PAHON considers some implementation criteria including proper level of QoS, the optimal use of network resources, domain of network performance, and power consumption of the network. The proposed method considers four switching mechanisms (OCS, long-OBS, short-OBS and OPS) for providing desirable QoS and it could reach to high domain of performance by providing the ability for edge and core nodes to select the proper switching mechanism. PAHON can also decrease the power consumption of the network in comparison with electronic-optical networks and all electronic networks by using optical switches in core nodes. The results of simulations justify the optimal resource utilization and efficient power consumption of our proposed method. © 2018 Elsevier Inc. All rights reserved.

1. Introduction Providing sufficient bandwidth for different network applications that generate huge traffic is one of the main concerns in the Internet. However, the huge amount of bandwidth is achievable with the emergence of optical networks and their rapid developments. Although Optical networks provide huge amount of bandwidth, they have significant power consumption [18]. Growing needs for more network resources and variety of applications have led to some concerns in the optical networks. Some of the concerns include decreasing power consumption of the network, providing Quality of Services (QoS), increasing performance domain, and optimal use of existing resources. Network bandwidth and wavelength converters are the examples of network resources. In other words, an optimal method should behave optimally in both bandwidth and wavelength converter utilization as two valuable resources in networks.

* Corresponding author.

E-mail addresses: [email protected] (L. Ghaemi Dizaji), [email protected] (A. Ghaffarpour Rahbar). https://doi.org/10.1016/j.jpdc.2018.01.007 0743-7315/© 2018 Elsevier Inc. All rights reserved.

For providing QoS in optical networks, different switching mechanisms, including Optical Circuit Switching (OCS) [4,21], Optical Burst Switching (OBS) [25] and Optical Packet Switching (OPS) [16] can be used. Each of these switching mechanisms has advantages besides their disadvantages; which solving their disadvantages makes them more affordable. There are two kinds of nodes in the network model of optical networks as edge nodes and core nodes. Edge nodes are responsible for the communication between the core network and the legacy networks. The core network contains the core nodes that switch OCS, OBS and OPS traffics. At least one edge node is connected to each core node in the optical network. In the OCS mechanism, a path (called a lightpath/circuit) is created between a source and destination pair nodes using a control packet. The lightpath reserves the path for a specific time which is equal to the connection duration. The OCS mechanism is appropriate for long and stable traffic flows, but it may waste bandwidth when a lightpath is not completely used in some intervals. In OBS, bursts are made by assembling the small packets in each ingress edge node. Then, prior to sending the burst, a control packet sets a path from the source to the destination for a specific time according

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L. Ghaemi Dizaji, A. Ghaffarpour Rahbar / J. Parallel Distrib. Comput. 117 (2018) 1–16

to the burst length. Also, sending the burst will be delayed up to a fixed offset time. OBS is appropriate for constant and bursty traffic flows, but it has high loss rate at the core nodes and contention resolution schemes are used for avoiding bursts loss rate in core nodes [1,8,23,31]. On the other hand, the OPS mechanism does not need any prior path reservation and it has high bandwidth utilization. But on the other side, it has high power consumption and high loss rate at the core nodes. In OPS, packet headers are used for their routing. Hybrid optical networks can provide QoS for different types of traffic in an optical network by combining merits of different switching mechanisms [15]. In other words, these networks use the advantages of different switching mechanisms simultaneously in order to obtain the desired performance. Hybrid optical networks can be used for connecting data centers. According to the type and the degree of the combination of different switching mechanisms, hybrid optical networks in general are classified into three classes [15]:

• Client–Server Hybrid Optical Networks: These networks are implemented by creating a server layer and a client layer [15]. Different methods have been introduced for client–server hybrid optical networks [3,20]. In [20], the combination of OCS, OBS, and OPS is considered as a client– server hybrid optical network. In the proposed combination, OCS is considered as the server layer, and either OBS or OPS as the client layer. • Parallel Hybrid Optical Networks: In these networks, only edge nodes could select the proper switching mechanisms for received traffic from legacy networks, and core nodes do not participate in this selection [14,17]. In [17], the OCS and OPS mechanisms are combined as parallel networks in which traffic flows that need guaranteed bandwidth use the OCS mechanism, and the remaining flows are switched according to the OPS mechanism. • Integrated Hybrid Optical Networks: In these networks, selecting the proper switching mechanism is not limited to the edge nodes; this means that, core nodes could have this option to select the proper switching mechanism [15]. Different methods can be used for integrating the different switching mechanisms [9,11–13,19]. The HOS [11–13] is one of the methods that integrates the OCS, long-OBS, shortOBS and OPS switching mechanisms. In HOS, packets are switched via the proper switching mechanism according to their degrees of tolerance to loss, delay, and jitter. According to HOS, – the OCS traffic flows could be sent by other switching mechanisms (such as long-OBS, short-OBS and OPS) when there is not any proper lightpath/circuit in OCS. In other words in HOS, it is assumed that if the traffic belonging to the OCS mechanism could not be sent by the OCS mechanism, it will be sent by long-OBS. If it is not possible, it will be sent by short-OBS, and if it is still not possible, it will be sent by OPS. Although, this issue will lead to zero circuit block rate in OCS, but it will cause some other problems. For instance, increasing the traffic load of other switching mechanisms is a problem that can result in increasing their loss rate, delay and jitter. Moreover, OCS traffic flows (the flows sent in each time slot of time-slotted circuits) sent by other switching mechanisms will not receive required QoS. – the OPS packets could be sent via OCS mechanism in the case of having the same destination address with the OCS circuits.

– the OBS traffic can be sent via two mechanisms. In long-OBS mechanism of HOS, for creating long-OBS bursts, a mixed timer-length assembly algorithm is used. In the burst assembly algorithm, the length of a long-OBS burst (L′B ) is chosen randomly in range [LLB1 , LLB2 ] when a new client packet arrives at an edge switch and is saved in the relevant buffer. Parameter Lmin is considered as a minimum threshold for a longOBS burst size, where Lmin < (L′B ). When the length of a long-OBS burst reaches Lmin , a timer will start. If the length of the long-OBS burst reaches (L′B ) before the timer ends, that long-OBS burst will be sent to the core node after the offset time; but if the timer expires and the length of the long-OBS burst is smaller than (L′B ), the long-OBS burst will be sent to the core node (with smaller length than (L′B )) after the offset time. LongOBS bursts are switched in core nodes via slow switch fabrics, with several milliseconds switching times. For creating long-OBS burst in each edge node, there are x (equal to the number of destination addresses) buffers for accumulating client packets and creating long-OBS bursts. For creating short-OBS bursts, another mixed timer-length assembly algorithm is used; where the length of short-OBS bursts (LB ) is selected randomly in range [LSB1 , LSB2 ] when a new client packet arrives at an edge switch and is saved in the relevant short-OBS buffer. A timer is started simultaneously by entering the new client packet. After starting the timer, the operation of the short-OBS assembly algorithm will be the same as the long-OBS assembly algorithm after starting the timer. Short-OBS bursts are switched via fast switch fabrics in core nodes. Again there are x additional buffers in the edge node for creating shortOBS bursts. EISM [9] is another integration of four switching mechanisms (as OCS, long-OBS, short-OBS and OPS). In EISM, circuits that use the time slots of the same circuit in a fiber could have different destination addresses. As a result, fast switch fabrics are used in core nodes for the OCS mechanism. The big difference between EISM and HOS is in the OCS and OPS switching mechanisms. In HOS, the circuits that want to use time slots of a TDM-circuit should have the same destination address; however, in EISM, this restriction has been omitted. The same method is used in the OPS switching mechanism; therefor OPS packets using free time slots of a TDM-circuit could have different destination addresses. FTM [19], another integrated hybrid optical method, integrates continuous streaming mode, periodic streaming mode, burst mode and packet mode. The FTM method uses a control packet in all of the mentioned switching modes for reserving resources before sending the main data. Continuous streaming mode is used for applications with huge bandwidth and longer periods of time requirements. It also has high priority for reserving the network resources. In periodic streaming mode, a lightpath is created between a source–destination pair by sending a control packet and traffic is sent in separate time slots on the lightpath. Periodic streaming mode is used for switching medium priority traffic flow. The gap between time slots of a circuit in this streaming mode is kept equal to inter-arrival time of the first packet. Burst mode traffic has low priority in reserving the network resources and the operation of the burst mode is only similar to the operation of short-OBS in HOS. Packet mode is very similar to OPS with the difference of sending a control packet beforehand for each OPS packet. Packet mode has very low priority in reserving the network resources.

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In FTM, pre-emptive dropping technique is used in core nodes. According to the pre-emptive dropping technique, an already scheduled traffic with medium priority or low priority or very low priority will be dropped by entering the high priority traffic in the case of not existing free bandwidth for reserving. Accordingly, the high priority traffic first tries to drop a very low priority packet; but if it could not find an overlapping very low priority packet, it tries to find a low priority burst. In the case of not finding even an overlapping low priority burst, the search continues for finding on overlapping medium priority traffic. Eventually, if the scheduler could not find any overlapping very low or low or medium priority traffic for reserving, the high priority traffic will be dropped. Comparing the hybrid optical networks, parallel networks have lower implementation complexity than integrated networks; but on the other hand, they have low performance domain; where the performance domain is the ability of edge nodes and core nodes in selecting the proper switching mechanisms for the received traffic flows. Integrated networks operate differently; they have high implementation complexity and high performance domain than parallel networks. Client–server hybrid optical networks have poor resource utilization (as bandwidth and wavelength converters) in comparison with parallel and integrated networks; this is because of creating the server layer in client–server networks with establishing circuit between every two core nodes in the network. Different methods have been presented for hybrid optical networks, but most of them have limited criteria in implementing hybrid optical networks. For having a practical network which could be implemented in real world, we should consider various criteria. Our objective in this paper is to improve the performance of hybrid optical networks by considering a number of criteria; which leads to propose a method namely PAHON (Power Aware Hybrid Optical Network). For providing QoS in the proposed methods, the OCS, long-OBS, short-OBS and OPS switching mechanisms are used. In HOS [13], the combination of four switching mechanisms (OCS, long-OBS, short-OBS and OPS) is also used; but in HOS all the circuits which use the time slots of one TDM-circuit, should have the same destination address; but in the proposed PAHON method, this constraint is reduced and the circuits could have different destinations. This option is extended to the operation of the OPS switching mechanism. In other words, OPS packets in our method could use the time slots of a TDM-circuit without considering TDM-circuit destination address. In addition, in PAHON, intermediate core nodes could avoid the drop of OPS packets by changing their modes from the non-slotted to the slotted mode and using free time slots of TDM-circuit. As the result, the network resources (bandwidth and wavelength converters) could be used optimally in PAHON in comparison with HOS [13] while also the power consumption of the network is considered in our proposed method. PAHON could reduce power consumption of the network in comparison with our previous proposed EISM method [9] by using slow optical switches instead of fast optical switches for OCS traffic. As a result, the performance of OCS and OPS mechanisms will be changed; but the performance of the long-OBS and shortOBS mechanisms will remain the same as in EISM [9]. In EISM [9], the same destination address restriction necessary in HOS [13], is omitted entirely; but in PAHON, this restriction is reduced in a way that same destination restriction is converted to same output fiber in core nodes (detailed in Section 3). PAHON could reach this reduction while considering the power consumption of the network. Our contribution in this article is the proposal of PAHON method in which, four switching mechanisms (OCS, long-OBS,

Fig. 1. An example of the network model.

short-OBS and OPS) are integrated together in a way that network resources can be optimally used. In addition in order to reach a green optical network, PAHON decreases power consumption of the optical network to less than the power consumption in electronic-optical and all electronic networks. The network model of the proposed method is introduced in Section 2. Section 3 is devoted to the proposed PAHON method. Performance evaluation of the proposed method is discussed in Section 4, and Section 5 summarizes the main conclusions of this article. 2. Network model In this section, the network model of PAHON is discussed in detail. A mesh network model is used for the proposed method; where each node is composed of an edge node and a core node. Distance between each two core nodes is assumed to be multiple times of a time-slot’s length of TDM-circuits (detailed in Section 3). Fig. 1 displays an example of the network model with three nodes; where it is assumed that each edge node is connected to the corresponding core node with an optical fiber and also there are W wavelengths per fiber. For providing QoS for the network traffic, first of all, edge nodes should select a proper switching mechanism for the received client network traffic, according to their QoS requirements. The client network traffic, having very low tolerance to loss, delay, and jitter parameters can use the OCS switching mechanism. The client network traffic that is sensitive to the jitter and loss parameters uses the long-OBS mechanism. The client network traffic that is sensitive to the jitter parameter uses the short-OBS mechanism. Finally, the OPS mechanism is used for the traffic that is tolerant to loss, delay, and jitter parameters. The proposed method in this paper makes use of OCS, long-OBS, short-OBS, and OPS as the switching mechanisms for providing a wide range of QoS. According to the supported level of QoS by different switching mechanisms, the OCS mechanism has the highest priority in reserving the network resources and after that, long-OBS, shortOBS and OPS are prioritized in order. The high priority of longOBS bursts in comparison with short-OBS bursts in reserving the network resources is because of long-OBS bursts’ length and also long offset time of long-OBS bursts. In order to avoid the network resources to be preempted by the OCS mechanism, we consider a limit in reserving the resources by the OCS mechanism.

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Fig. 2. Core node architecture of PAHON.

In the proposed network model, two modes are considered for the wavelengths: slotted mode and non-slotted mode. The traffic, supposed to be sent via slotted wavelengths, should be sent on specified times by both edge and core nodes. The traffic sent via non-slotted wavelengths, could be switched arbitrarily by edge and core nodes. For synchronizing received traffic from slotted wavelengths in core nodes, a synchronization method is used; which could be a calibrated set of optical delay lines [22]. The amount of devoted wavelengths to each mode (slotted or nonslotted) is specified according to the request of different switching mechanisms and their traffic loads. The architecture of each core node of PAHON is depicted in Fig. 2. According to Fig. 2, Optical Amplifiers (OAs) are used in both input and output of the core node for amplifying the received signals from the fibers. Each input fiber with W wavelengths enters a Wavelength Division Multiplexing Demultiplexer (WDM Demux) for separating its wavelengths. For separating control information and sending it to the control unit, control information extraction (CIE) units are used. For reinserting control information, control information reinsertion (CIR) units are used. For each input fiber in core nodes, a limited number of Tunable Wavelength Converters (TWCs) are used for converting the wavelength of the received packets/bursts/flows. For example, if n denotes the number of TWCs for each input fiber, then we will have N × n TWCs for a core node with N input fibers. TWCs are shared between all four switching mechanisms, i.e., OCS, long-OBS, short-OBS, and OPS. The control unit of the core node is used for configuring the Switching Elements (SEs) of the slow and fast switch fabrics. Slow switch fabrics are made of SEs with switching time in the order of milliseconds. Hence, slow switch fabrics are not suitable for OPS and short-OBS mechanisms with packets/bursts length in the order of microseconds. An example of slow switch fabrics, is MicroElectro-Mechanical System (MEMS); in which SEs are miniature movable mirrors made of silicon. Switching time of fast switch fabrics is in the order of nanoseconds. Semiconductor Optical Amplifier or SOA is a kind of fast switch fabric. Power consumption of fast switch fabrics is many folds of slow switch fabrics; therefore, when it is possible, it should be avoided using fast switch fabrics for switching flows/bursts in core nodes. The synchronization unit (SYN) is used for synchronizing flows/packets in slotted wavelengths [22]. According to the explanation of PAHON method (see

Section 3), slow switch fabrics are used for switching TDM-circuit flows in PAHON. Therefore, the synchronization unit is located before the slow switch fabric (see Fig. 2). A Wavelength Division Multiplexing Multiplexer (WDM Mux) is used for each output fiber for multiplexing W wavelengths on a fiber. 3. The PAHON method In the proposed PAHON method, different implementation criteria including QoS, resource optimization, performance domain, and power consumption are considered. In the following, PAHON method is explained in more detail. In OCS, Time Division Multiplexed (TDM) circuit is used and OCS connection setup packets are used for establishing circuits. In TDMcircuits, wavelengths are divided into frames as a function of the time; in other words, they are supposed in the slotted mode. In TDM-circuit, each frame contains a fixed number of time slots and each time slot can be used by a circuit. In this case, having g time slots in a frame, is equal to having g circuits in that wavelength. In the PAHON method circuits, although using time slots of a same frame, can have different destination addresses. The operation of the long-OBS and short-OBS mechanisms is as the same as what is explained in Section 1. Different algorithms, including ’’First-Fit Unscheduled Channel with Void Filling’’ (FFUCVF) [10] and ’’Best Fit with Void Filling’’ (BF-VF) [5], can be used for reserving free wavelengths on fibers for OBS bursts. In the PAHON method, the FFUC-VF algorithm is used for reserving the free wavelengths of fibers. In FFUC-VF, the first unscheduled wavelength is reserved for sending the received OBS bursts. The time needed to reserve a wavelength is according to ‘‘just enough time reservation mechanism’’ [30]; which reserves the wavelength just for the time, needed for sending the received OBS bursts. In PAHON, the OPS packets could use free time slots of TDMcircuits; which are devoted to the OCS mechanism. This approach will result in the reduction of the packet loss probability in OPS. In addition, resource optimization will be reached. For this purpose, some of the slots of TDM-circuits of OCS are reserved for OPS packets, say m time slots. Using free time slots of TDM-circuits by OPS packets depends on having proper length of OPS packets according to the free slot length. In PAHON, long-OBS, short-OBS and OPS traffic enter the core network in the non-slotted mode.

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Fig. 3. Flowchart of the OPS mechanism in PAHON.

On the other hand, OCS traffic is switched in the slotted mode. According to these options, OPS packets that want to use free slots of TDM-circuits should be sent to the core nodes in slotted mode. One of the solutions for converting OPS packets from non-slotted to slotted mode is to use the optical buffers in the core nodes, where OPS packets are delayed until the next free time slot reaches. However, using optical buffers has some problems that make them undesirable. In PAHON, a core node that decides to send an OPS packet through a free time slot sends the packet to its connected edge node (called intermediate edge node) for converting the OPS packet mode from non-slotted to slotted mode. The electronic buffers of the edge node are used for this purpose. The OPS packet is stored in the electronic buffers until it could be sent to the connected core node at the beginning of the following time slot. In the case of no free time slot, the packet will still be stored until the beginning of the next time slot. In PAHON, free time slots of a TDM-Circuit are stored in a linked list, as the result the complexity of finding a free time slot is O(1). In order to avoid the long delay of the OPS packet, a timer is started by entering the OPS packet to the intermediate edge node. The duration of the timer is multiples of a time slot length. For example, if a time slot length is T seconds, the timer length will be G × T seconds; where G is an arbitrary integer number. If the intermediate edge node cannot find a free time slot until the timer expires, then the OPS packet will be resent in non-slotted mode to the core node; this will be possible if there is a free non-slotted wavelength in the intermediate edge node. In some cases, non-slotted wavelengths may be released in a core

node in the interval between sending an OPS packet from the core node to the intermediate edge node. If the OPS packet could not be returned to the core node, neither in the slotted mode nor in the non-slotted mode, it will be dropped in the intermediate edge node. On the other hand, if an OPS packet which is in the slotted mode, could not find a free time slot in the core node, it will be sent via a non-slotted wavelength (in the case of existing wavelength converter), but the OPS packet still stays in the slotted mode. In this way, if the next core node wants to switch the OPS packet to slotted mode, there is no need for sending it to the intermediate edge node for changing its mode from non-slotted to slotted mode. This issue could reduce the OPS packet delay. To avoid loop between core nodes and the intermediate edge nodes, a non-slotted OPS packet is marked in an intermediate edge node before returning back to the core node. This way, a core node will not send a marked OPS packet to the intermediate edge node for converting its mode from non-slotted to slotted mode. In PAHON, if OPS packets are sent via free time slots of TDMcircuits, they will be switched with slow switch fabrics. But in the case of not using TDM-circuits, considering the small length of OPS packets, fast switch fabrics with small switching times should be used for the optimal usage of the existing bandwidth. The summary of the OPS mechanism is presented in Fig. 3. In PAHON, we want to decrease constraints in reserving the time slots of TDM-circuit in OCS; this means that we can have circuits with different destinations in the same frame. As a result, the switch fabric in core nodes should be adjustable in each time

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Fig. 4. A scenario in a core node. (a) The core node before switch configuration; in which two OCS connection setup packets, entering from the same input fiber on the same wavelength, want to go to the output fibers #1 and #3 respectively. (b) The core node after switch configuration, where the connection setup packets have passed to the output fibers #1 and #3 respectively on different wavelengths.

slot. Because of the small length of time slots, fast switch fabrics with several nanoseconds switching time should be used in core nodes for OCS traffic. However, power consumption of fast switch fabrics is considerably more than the power consumption of the slow switch fabrics, i.e., many folds. Therefore, the PAHON method must use slow switch fabrics for OCS traffic in core nodes. By using slow switch fabrics in core nodes for OCS traffic, it will not be possible to configure the switches in each time slot because of the small length of the time slots. For solving this problem, a constraint for reserving time slots of a frame is considered in core nodes in both OCS and OPS mechanisms. The constraint is that, if a wavelength of an input fiber is mapped to a special output by a slow switch fabric, the OCS and OPS traffic, which should use the same output according to their destination addresses, can use the same input wavelength in the same input fiber. However, if their destinations are different, they should use Wavelength Converter (WC) for converting the input wavelength. For clarifying this constraint, we consider a scenario in Fig. 4. According to Fig. 4(a), two OCS connection setup packets, where each one want to establish a circuit according to the OCS mechanism, enters to a core node with three input and three output fibers. Assume that, there are two wavelengths on each optical fiber. The labels written on each OCS connection setup packet shows its output fiber number according to its destination. According to Fig. 4-(a), OCS connection setup packets enter from the same input fiber on the same wavelength, but their output fibers are different. OCS connection setup packets enter the core node sequentially as shown in Fig. 4-(a). At the first, OCS connection setup packet enters to the core node with the destination output fiber #1, the first wavelength of input fiber #1 will be connected to the first wavelength of output fiber #1 (as shown in Fig. 4(b)); therefore, the first time slot of the first wavelength in both fibers will be dedicated to the first request. The second OCS connection setup packet wants to go to output fiber #3, but because of the configuration time of the slow switch fabric by the previous OCS connection setup packet to output fiber #1, this request cannot be guaranteed; in this case a WC will be used first for converting the input wavelength of the OCS connection setup packet to an empty input wavelength (say wavelength #2 in Fig. 4-(b)) and then switching it to output fiber #3. In the PAHON method, OPS packets that want to use the dedicated wavelengths to OCS, should consider this constraint too. In PAHON, selecting the proper switching mechanisms is not restricted to edge nodes; i.e., core nodes participate in this selection as well. Therefore, PAHON can be considered as an example of integrated hybrid optical networks, having high performance domain.

4. Performance evaluation In this section, the performance of the proposed PAHON method is evaluated according to different parameters including:

• OPS packet delay: time between receiving an OPS packet in • •

• •

•

• •

a source edge node and delivering it to a destination edge node. Maximum Packet Delay (MPD): maximum delay of OPS packets. OBS burst delay: sum of the time required for creating an OBS burst in an edge node, the offset time of the OBS burst and its waiting time in the buffer of the edge node. Maximum Burst Delay (MBD): maximum delay of the OBS bursts. Worst Case Jitter (WCJ): difference between the maximum and minimum OPS packets/OBS bursts delay. Note that the propagation delay of OPS packets/OBS bursts is not added to the delay performance of OPS packets/OBS bursts, thus it is possible that the minimum OPS packet delay becomes equal to zero during the simulations and as the result, WCJ equals to MPD in the OPS mechanism. Packet/Burst Loss Rate (PLR/BLR) (of long-OBS, short-OBS and OPS packets): proportion of the lost OPS packets/OBS bursts to the total number of received and dropped OPS packets/OBS bursts. Block Rate (BR) (of OCS): proportion of blocked circuits to total number of established and blocked circuits. Power consumption of the network.

For evaluating the performance of PAHON, we have compared it with HOS [13], EISM [9] and FTM [19]. It will be more fair to compare PAHON with methods with the same switching mechanisms as HOS and EISM. In order to provide more comparisons, we have compared it with the FTM method, which has different switching mechanisms but with the same cost (i.e., the same fast and slow switches). 4.1. Power consumption As the power consumption of the networks is so important for evaluating the network performance, in this subsection power consumption analysis is used according to the analytical methods detailed in [11–13]. Assuming that, a node in a network is composed of an edge node and a core node, the power consumption of a node (PC ) will be calculated according to Eq. (1): PC = PEdge + PCore ,

(1)

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Table 1 Power consumption of an edge node and a core node. Edge node Variable

Description (Power consumption of)

Power (W)

PEdge PGEF PLC at10 Gbps(1 × w av elength) [2] PRP (1 × 16 w av elength) PSwitch (1 × w av elength) PTA PTCC (1 × w av elength) PAssem (1 × w av elength) PRA (1 × node) PPE (1 × w av elength)

Edge node General Edge Function block Input Line Cards Route Processor Switch Traffic Aggregation block Traffic Classifier and traffic Conditioner Traffic Assembler Resource allocator Packet Extractor

2653.12 1425.12 74.57 200 2 1228 62 62 72 25

Core node Variable

Description (power consumption of)

Power (W)

PCore PCL (1 × node) PGMPLS POffline POnline PSearchEngine PScheduler PTransceiver PSF PPort (1 × w av elength) POAC PSC PCIE /R POA PTWC PSYN

Core node Control logic GMPLS control plane Routing, signaling and link management Label processing, table lookup and forwarding Search Engine used for table lookup Sum of the OPS packet, OBS burst and circuit Scheduler Receiving/transmitting control information Slow/Fast switching fabric Single slow/fast switch Port Other Active Component Switch Control unit Control Information Extraction and Reinsertion Optical Amplifier Tunable WC Synchronization Unit

609.75 486 150 40 4.5 40 + 40 + 40 1.25 9.29 × NSOA + 0.1 × NMEMS SOA:9.29 ; MEMS: 0.1 1200 + NTWC × 1.69 300 17 14 1.69 20

where PEdge shows the power consumption of the edge node and PCore shows the power consumption of the core node, which will be discussed in more details in the following. 4.1.1. Power consumption of an edge node (PEdge ) Power consumption of the edge node (PEdge ) is calculated by Eq. (2). It is assumed that, each edge node is connected to the corresponding core node with a fiber and there are W wavelengths on each fiber. The descriptions of the variables in Eqs. (2)–(4) are summarized as Table 1. PEdge = PGEF + PTA , PGEF = W × (PLC + PTA =

W 2

In order to evaluate the performance of our proposed PAHON method with 10 Gbps data rate of each wavelength, the so-called HOS method with 40 Gbps data rate on each wavelength is considered. According to [6,7], by quadruplicating data rate of each wavelength, the power consumption of each switch port will be quadruplicated; hence for calculating the value of some variables in Eq. (3) and Eq. (4) that depend on the data rate, the values in [13] (for 40 Gbps) are divided by four (for 10 Gbps). The amount of variables for 10 Gbps (needed for our simulations) are given in Table 1.

(2) PRP 16

+ PSwitch ),

× (PTCC + PAssem +

PRA W

+ PPE ),

PCore = PCL + PSF + POAC ,

(3)

4.2. Cost model

(4)

In this subsection, the cost model of PAHON method is presented. It is worthy to remind that a node in a network is composed of an edge node and a core node; therefore, the cost of a node (CN ) is sum of the edge node cost and the core node cost as Eq. (10); where CEdge shows the cost of the edge node and CCore shows the cost of the core node. More details are as the following.

(5)

PCL = PGMPLS + PScheduler + N × W × PTransceiver ,

(6)

PGMPLS = POffline + N × POnline + N × W × PSearchEngine ,

(7)

PSF = PPort × NAP , and

(8)

POAC = PSC + N × W × PCIE /R + 2 × N × POA

+ NTWC × PTWC + PSYN .

(9)

4.1.2. Power consumption of a core node (PCore ) The analytical model of evaluating PCore is introduced in this section according to the analytical methods detailed in [11–13]. Parameter PCore is calculated by summing the power of active components of the core node, which is shown by Eq. (5). In equations number (6)–(9), N is the number of input/output fibers to/from the core node, NAP is the number of active ports of a slow or fast switch fabric in core nodes, and NTWC is the number of active TWCs. The descriptions of remaining variables in Eqs. (5)–(9) are also summarized in Table 1.

CN = CEdge + CCore .

(10)

4.2.1. Cost of an edge node (CEdge ) Cost of an edge node (CEdge ) is calculated by Eq. (11). It is assumed that each edge node is connected to the corresponding core node with a fiber with W wavelengths. The descriptions of the variables in Eqs. (11)–(13) are presented in Table 2. CEdge = CGEF + CTA , CGEF = W × (CLC + CTA =

W 2

(11) CRP 16

+ CSwitch ),

× (CTCC + CAssem +

CRA W

(12)

+ CPE ).

(13)

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L. Ghaemi Dizaji, A. Ghaffarpour Rahbar / J. Parallel Distrib. Comput. 117 (2018) 1–16

Table 2 Cost of an edge node and a core node. Edge node Variable

Description (Cost of)

Cost ($)

CEdge CGEF CLC at10 Gbps (1 × w av elength) CRP (1 × 16 w av elength) CSwitch (1 × w av elength) CTA CTCC (1 × w av elength) CAssem (1 × w av elength) CRA (1 × node) CPE (1 × w av elength)

Edge node General Edge Function block Input Line Cards Route Processor Switch Traffic Aggregation block Traffic Classifier and traffic Conditioner Traffic Assembler Resource allocator Packet Extractor

8 + 28 × W 20 × W 16 48 1 8+8×W 7 6 16 3

Core node Variable

Description (Cost of)

Cost ($)

CCore CCL (1 × node) CGMPLS COffline COnline CSearchEngine CScheduler CTransceiver CSF CPort (1 × w av elength) COAC CSC CCIE /R COA CTWC CSYN

Core node Control logic GMPLS control plane Routing, signaling and link management Label processing, table lookup and forwarding Search Engine used for table lookup Sum of the OPS packet, OBS burst and circuit Scheduler Receiving/transmitting control information Slow/Fast switching fabric Single slow/fast switch Port Other Active Component Switch Control unit Control Information Extraction and Reinsertion Optical Amplifier Tunable WC Synchronization Unit

115 + 6 × W 85 + 3 × W 40 15 1 30 1 40 × NSOA + 20 × NMEMS SOA: 40; MEMS: 20 189 + 4.5 × W 70 1.5 10 1 11

4.2.2. Cost of a core node (CCore ) The analytical model of evaluating CCore is introduced in this section by Eq. (14). In Eqs. (15)–(18), N is the number of input/output fibers to/from the core node, NP is the number of ports of a slow or fast switch fabric in core nodes, and NTWC is the number of TWCs. The descriptions of remaining variables in Eqs. (14)–(18) are also presented in Table 2. CCore = CCL + CSF + COAC ,

(14)

CCL = CGMPLS + CScheduler + N × W × CTransceiver ,

(15)

CGMPLS = COffline + N × COnline + N × W × CSearchEngine ,

(16)

CSF = N × W × CPort , and

half of the wavelengths of a fiber use fast switch and the remaining half use slow switch. As it is clear from Fig. 5(b), increasing the usage proportion of fast switches results in an increase in the cost of the core node, which increases the overall cost of a node. In Fig. 5(b), the cost of the node for the case that both fast and slow switches are used for all wavelengths of a fiber, is also reported as the fourth column. In this case, all of the wavelengths can be used for switching all kinds of the switching mechanisms (i.e., OCS, longOBS, short-OBS and OPS) in PAHON. Note that Fig. 5(a) is plotted according to the last setting, in which both fast and slow switches are used for all the wavelengths.

(17) 4.3. Performance evaluation assumptions

COAC = CSC + N × W × CCIE /R + 2 × N × COA

+ NTWC × CTWC + CSYN .

ρ = 0, slow MEMS switch is used in the core node and traffic is routed through slow switches only. Similarly, ρ = 0.5 means that

(18)

4.2.3. Cost analysis of the PAHON method According to Eqs. (12)–(18), the cost of a node depends on W, N, and NTWC ; by considering constant values for N (i.e. N = 3) and NTWC (i.e. NTWC = 4), the cost of a node will only depend on the number of wavelengths in each fiber (i.e., W ). The costs of the components of both edge node and core node are not real costs in this cost model. In addition, the cost of the fast SOA switch port is considered twice the cost of the slow MEMS switch port (i.e., CPort of SOA = 2 × (CPort of MEMS )). Fig. 5(a) shows the cost of a node; where four values are considered for the number of wavelengths in each fiber (W ) as 16, 24, 32, and 40. According to Fig. 5(a), by increasing the number of wavelengths, the cost of a node increases too. In order to analyze the effect of fast and slow switches on the cost of a node, we have provided Fig. 5(b); in which the cost of a node is reported according to three different values for ρ ; where ρ shows the usage proportion of fast switches in a core node. In fact, if ρ = 1, just fast SOA switch is used in the core node and if

There are W = 16 wavelengths on each fiber and data rate of each wavelength has been set to 10 Gbps for our simulations. The edge nodes in PAHON, EISM, and HOS generate the network traffic according to the following pattern: 37.5% OCS, 20.83% long-OBS, 20.83% short-OBS, and 20.83% OPS. In FTM, traffic pattern is as the following: 25% continuous streaming mode, 25% periodic streaming mode, 25% burst mode, and 25% packet mode. For evaluating the effect of the number of Tunable Wavelength Converters (TWCs) on the network performance, two different number of TWCs as 4 and 8 are considered for each fiber in the simulations. We have the following configurations in HOS [13], EISM [9] and PAHON. The OCS traffic is generated according to the Erlang distribution with inputs 50 or 100 for variable k in k = λ × h (λ: number of connection requests per second, h: holding time of the connections in seconds), and a circuit request will be blocked if there is not any free time slot or a free wavelength for establishing the circuit. The holding time (h) of the connections in OCS is according to the exponential distribution with mean 2 s. LongOBS, short-OBS and OPS packets are generated according to the exponential distribution. The number of slots in TDM-circuit has been set to 10 slots and each slot length has been set to 4 KBytes.

L. Ghaemi Dizaji, A. Ghaffarpour Rahbar / J. Parallel Distrib. Comput. 117 (2018) 1–16

9

Fig. 5. Cost of PAHON node in different situations. (a) Cost of a node with different number of wavelengths and 4 TWCs. (b) Cost of a node with different proportion of fast and slow switches.

The lengths of long-OBS, short-OBS bursts, and OPS packet, are random integers in the ranges [LLB1 , LLB2 ] = [2500, 5000] KBytes, [LSB1 , LSB2 ] = [50, 125] KBytes, and [1, 4] KBytes, respectively. The deadline for receiving the acknowledge for OCS connection setup packets (i.e., the time required for establishing connections) is set to 1.5 ms in our simulations. The offset time of long-OBS (D′off ) and short-OBS (Doff ) bursts are set to 1 ms and 20 µs, respectively. The timer of the long-OBS bursts has been set to 17 ms and it has been set to 7.4 ms for short-OBS bursts. The minimum length of longOBS bursts has been set to (Lmin ) = 2500 KBytes. The timer of OPS packets (see Section 3) in intermediate edge nodes is as the same as the time slot length of OCS mechanism (i.e., G = 1). All these parameter settings are the same for the HOS, EISM and the proposed PAHON method. In FTM, traffic of the continuous streaming mode, periodic streaming mode, burst mode and packet mode are generated according to the exponential distribution. The length of continuous streaming mode packets are set to 1 MB and each circuit in periodic streaming mode, should send 20 packets with average size of 50 KBytes and gap between time slots of a circuit is kept equal to inter-arrival time of the first packet. The length of the bursts in burst mode, and also the length of the packets in the packet mode are random integers in the ranges [50, 125] KBytes, and [1, 4] KByte, respectively. The offset time of continuous streaming mode, periodic streaming mode, burst mode and packet mode are set to 800 µs, 400 µs, 20 µs and 0.8 µs respectively. The timer of burst mode has been set to 7.4 ms. 4.4. Numerical results and analysis In all of the simulations, the NSF network topology is used as the network model for HOS, EISM, FTM and the proposed PAHON method. OPNET 14.5 is used as our simulation modeler. We have obtained 95% level of confidence interval, at worst within 5% of the mean values shown. In this article, in HOS, EISM, and PAHON, network traffic load is referred to the traffic load of long-OBS, shortOBS and OPS switching mechanisms. We have used the load of 50 Erlang and 100 Erlang for the OCS mechanism. In FTM, network traffic load is referred to the traffic load of the four mentioned modes (continuous streaming mode, periodic streaming mode, burst mode and packet mode). The performances of HOS [13], EISM [9], FTM [19] and PAHON, under different simulation conditions are compared with each other in the following sections. In all of the diagrams, the performances of HOS, EISM and PAHON methods under a Erlang traffic are displayed with HOS-a, EISM-a and PAHON-a, respectively. Similarly, they are displayed with HOS-b C, EISM-b C, FTMb C and PAHON-b C symbols, respectively; where b refers to the number of TWCs in every core node. In the following, at first the comparison of HOS, EISM and the proposed PAHON method, all

Fig. 6. BR of OCS with 4 TWCs at 50 and 100 Erlangs.

having the same type of switching mechanisms, will be presented; then, Section 4.4.2 is devoted to the comparison of the PAHON and FTM methods, which have two types of switching mechanisms in common. 4.4.1. Comparison of HOS, EISM and the proposed PAHON method In all HOS, EISM and PAHON methods, four switching mechanisms as OPS, short-OBS, long-OBS and OCS are used. In the following, the influence of OCS traffic loads and the number of TWCs on the performance of mentioned methods will be evaluated. 4.4.1.1. The influence of OCS traffic loads. In the following, the influence of OCS traffic loads on the performance of HOS, EISM and PAHON is evaluated. For this need, we have considered a scenario in which, four TWCs are considered for each input fiber in each core node and OCS traffic load increases from 50 Erlang to 100 Erlang. As it is shown in Fig. 6, in EISM, the BR of OCS is zero for both OCS traffic loads because of omitting the restrictions of HOS in reserving the time-slots of each frame. But in both HOS and PAHON methods, BR increases as the OCS traffic increases from 50 Erlang to 100 Erlang. PAHON has better performance than HOS under both 50 and 100 Erlangs. Due to the fact that time-slots of a frame in PAHON, in contrast to HOS, can be used by circuits with different destination addresses, PAHON could use the resources optimally and can provide low BR than HOS. Therefore, PAHON could decrease BR about 4.5 times at 50 Erlang and about 4.99 times at 100 Erlang in comparison with HOS. Fig. 6 shows the BR as a function of the network traffic load (long-OBS, short-OBS, and OPS switching mechanisms). As it is shown in Fig. 6, increasing the traffic load of network does not have any effect on BR; this is because of the high priority of the OCS traffic in reserving the network resources in comparison with other switching mechanisms.

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(a) PLR of OPS packets.

(b) MPD and WCJ of OPS packets.

Fig. 7. PLR, MPD and WCJ of OPS packets with 4 TWCs at 50 and 100 Erlangs.

(a) BLR of short-OBS bursts.

(b) BLR of long-OBS bursts.

Fig. 8. BLR of short-OBS and long-OBS bursts with 4 TWCs at 50 and 100 Erlangs.

Table 3 Progress of MPD and WCJ of OPS packets in PAHON. Traffic load

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Progress

6.72

55.3

72

87

99.8

113.53

126.23

128.6

Fig. 7(a) and (b) show the PLR and MPD/WCJ of the OPS mechanism, respectively as a function of the network traffic load. According to Fig. 7(a), in HOS, increasing the established circuits means increasing the probability of sending OPS packets via free timeslots of TDM-circuits; in other words, increasing the number of established circuits decreases OPS PLR. But, PLR of OPS in EISM and PAHON is almost the same at both 50 and 100 Erlangs. This is because of optimum use of time slots of a frame in EISM and PAHON that causes to ignorable increase in PLR of OPS even with doubling the OCS traffic. EISM has the lowest PLR of the OPS packets in comparison with HOS and PAHON; this is because of eliminating the restrictions of reserving the time-slots, which increases the power consumption of the network. As it is obvious from Fig. 7(a), PLR of HOS is lower than PLR of PAHON. On the other hand, according to Fig. 7(b), OPS packets in PAHON have very low MPD and WCJ in comparison with HOS. For example at traffic load 0.1, this difference is about 6.7 times, and it is about 128.6 times at load 0.8. These results are shown in Table 3. To sum up, according to Fig. 7(a) and (b), PAHON could insert more OPS packets to the core network than HOS. On the other hand, PAHON has ignorable increase in PLR of OPS packets than HOS; because of the optimal use of the network resources in PAHON. It should be noted that increasing OPS packet loss rate by 27%

(in PAHON) under almost all traffic loads could be ignored when considering a decrease of 86 times in MPD and WCJ on average. As it is obvious in Fig. 7(a), MPD and WCJ of OPS packets are almost the same and they both are low in PAHON and EISM; this is because of the optimum use of time slots of a frame and sending OPS packets via free time slots of TDM-circuits. The WCJ of OPS packets in EISM and PAHON stays approximately constant by increasing the network traffic load. Hence, the need for electronic buffers in edge nodes will be decreased. Fig. 8(a) and (b) show BLR of the short-OBS and long-OBS mechanisms, respectively. According to the optimum use of network resources by PAHON, the BLR of short-OBS and long-OBS is almost the same at both 50 and 100 Erlangs, and it is lower than the BLR in HOS. According to Fig. 8(a) and (b), BLRs of both short-OBS and long-OBS mechanisms in PAHON are lower than EISM. As EISM could establish more circuits than PAHON and circuits have the highest priority in reserving the network resources, bursts (shortOBS and long-OBS) in EISM possess less network resources for reserving than PAHON. In PAHON, EISM and HOS, only OPS packets could be sent in free time slots of TDM-circuits and PAHON and EISM could insert more OPS packets into the core network in comparison with HOS via optimum use of network resources; therefore, the traffic loads

L. Ghaemi Dizaji, A. Ghaffarpour Rahbar / J. Parallel Distrib. Comput. 117 (2018) 1–16

(a) MBD of short-OBS bursts.

(c) MBD of long-OBS bursts.

11

(b) WCJ of short-OBS bursts.

(d) WCJ of long-OBS bursts.

Fig. 9. MBD and WCJ of short-OBS and long OBS bursts with 4 TWCs at 50 and 100 Erlangs.

of long-OBS and short-OBS will be the same as in PAHON, EISM and HOS; and PAHON could decrease the BLR of long-OBS and shortOBS in comparison with HOS via the optimum use of the network resources. Therefore, MBD and WCJ of long-OBS and short-OBS bursts will be the same in PAHON, EISM and HOS (as shown in Fig. 9). The MBD of short-OBS is depicted in Fig. 9(a). According to Fig. 9(a), the MBD at traffic load 0.1 is high, but it decreases as the traffic load increases; this behavior of short-OBS bursts is due to the time needed for aggregating small packets in order to make OBS bursts. As the traffic load increases from 0.1 to 0.4, the required time for constructing OBS bursts decreases and this will decrease the MBD of short-OBS bursts. However, as the traffic load goes higher than 0.4, the delay for storing bursts in buffers of edge nodes will be added to the bursts delay, which increases MBD. As it is obvious from Fig. 9(a), MBD values of short-OBS in HOS, EISM and PAHON are approximately the same. This is because of inserting the same loads of short-OBS traffic into the core network via the edge nodes in three methods. Fig. 9(b) depicts WCJ of short-OBS bursts in HOS, EISM and PAHON. As it is obvious, the behavior of WCJ is as the same as the behavior of MBD at different traffic loads. Fig. 9(c) and (d) show MBD and WCJ of long-OBS bursts, respectively. Because of the length of long bursts in this mechanism, the time needed for constructing burst decreases with an increase in the network traffic load; this itself leads to a decrease in the MBD of long-OBS bursts. The WCJ of the long-OBS bursts behaves as the same as the short-OBS bursts, but the increase in WCJ of long-OBS from traffic load 0.4 to 0.8 is noticeable. As mentioned before the MBD and WCJ of OBS bursts are the same in HOS, EISM and PAHON. This is because of feeding of the core nodes with the same loads of OBS bursts; i.e., the waiting time of OBS bursts is the same in edge nodes in all the three methods.

Fig. 10. Power consumption of HOS [13] and PAHON with 4 TWCs at 50 and 100 Erlangs.

Fig. 10 shows the power consumption of HOS and the proposed PAHON. Due to the fact that PAHON could support more OCS and OPS traffic than HOS via optimum use of the network resources, PAHON has more active components (such as SEs or TWCs) than HOS. This means that its power consumption is more than HOS. According to Eqs. (1)–(9) and Table 1, coefficients of active components in the equations of network power consumption are low; hence power consumption of PAHON with more active components does not have noticeable increase in comparison with HOS. In other words, PAHON has a close power consumption to HOS and because HOS could decrease the network power consumption several times in comparison with optical-electronic (in which fast

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L. Ghaemi Dizaji, A. Ghaffarpour Rahbar / J. Parallel Distrib. Comput. 117 (2018) 1–16

of power consumption of PAHON and HOS, it has not been plotted in Fig. 10. Although BR of OCS circuits in EISM is zero and PLR of OPS packets is 19 times less than PAHON; BLR of the short-OBS and long-OBS mechanisms in EISM are higher than PAHON and power consumption of EISM is many folds of power consumption of PAHON.

Fig. 11. BR of OCS at 50 Erlang with 4 and 8 TWCs.

electronic switches are used for the OPS and short-OBS mechanisms and slow optical switch fabrics are used for the long-OBS and OCS mechanisms in core nodes) and all electronic networks (in which only fast electronic switches are used for switching in core nodes); therefore, PAHON has less power consumption than optical-electronic and all electronic networks. EISM could use the network resources optimally in comparison with the PAHON and HOS methods. Moreover, it has more power consumption than both PAHON and HOS. As power consumption of EISM is many folds

(a) PLR of OPS packets.

4.4.1.2. Effect of the number of TWCs. In this section, the number of TWCs is increased from 4 to 8 at 50 Erlang and the effect of this increase on the network performance of PAHON and HOS is evaluated in Figs 11–14. According to Fig. 11, increasing the number of TWCs decreases the BR of both HOS and PAHON methods. Increasing the number of TWCs also decreases the OPS PLR in both HOS and PAHON as shown in Fig. 12(a). As it is mentioned in Section 4.4.1.1, PAHON can send more OPS packets to the core network than HOS. Hence, in PAHON, increasing the number of TWCs has more effect on OPS PLR. On the other hand, this ability of PAHON (sending more OPS packets to the core network) could decrease the MPD of OPS mechanism in comparison with HOS method by reducing the waiting time of OPS packets in edge nodes; this is obvious in Fig. 12(b). But in both HOS and PAHON, increasing the number of TWCs does not have any effect on maximum delay of OPS packets, short-OBS and long-OBS bursts. This is due to the fact that increasing the number of TWCs is related to the core network and this increase has no effect on edge nodes’ traffic load which enters to the core network by edge nodes.

(b) MPD and WCJ of the OPS packets.

Fig. 12. PLR, MPD and WCJ of OPS packets at 50 Erlang with 4 and 8 TWCs.

(a) BLR of short-OBS.

(b) BLR of long-OBS.

Fig. 13. BLR of short-OBS and long-OBS at 50 Erlang with 4 and 8 TWCs.

L. Ghaemi Dizaji, A. Ghaffarpour Rahbar / J. Parallel Distrib. Comput. 117 (2018) 1–16

Fig. 14. Power Consumption of HOS [13] and PAHON at 50 Erlang with 4 and 8 TWCs.

Fig. 13(a) and (b) illustrate BLR of the short-OBS and the long-OBS methods, respectively. Increasing the number of TWCs decreases BLR of both switching mechanisms in both HOS and PAHON. According to Eq. (9), increasing the number of TWCs in each input fiber increases the power consumption of a network; this is obvious in Fig. 14. Power consumption of PAHON has an ignorable increase in comparison with HOS because of the low coefficients of active components in the equations used for computing network power consumption (see Section 4.1.2). 4.4.2. Comparison of FTM and the proposed PAHON method According to the operation of different switching mechanisms in FTM and PAHON, burst mode of FTM has similar operation to

13

short-OBS in PAHON, and packet mode in FTM is similar to OPS in PAHON. Accordingly in the following, performance evaluations of the FTM and PAHON methods are illustrated as the function of short-OBS (or burst mode) and OPS (or packet mode) mechanisms. As it is obvious from Fig. 15(a), PLR of PAHON is on average 6 times lower than the PLR of FTM. While FTM uses control packet in OPS, it cannot have better PLR than PAHON. The reason is that PAHON can use free time slots of OCS mechanism for sending OPS packets. According to Fig. 15(b), maximum packet delay (MPD) of OPS packets in FTM is lower than PAHON under loads 0.1 and 0.2. However, for loads more than 0.2 MPD in FTM is higher than PAHON; the performance of PAHON for load 0.8 is significantly better than FTM. As the result, PAHON could decrease PLR of OPS packets and simultaneously it could decrease MPD at most of the loads by using the network resources optimally. Fig. 15(c) and (d) illustrate BLR and MBD of short-OBS. According to the simulation results, MBD of bursts in FTM is lower than PAHON; it shows that FTM prevents bursts from gathering in the queues of edge nodes and this causes the MBD to be decreased. On the other hand, BLR in FTM is higher than PAHON; this means that although FTM could decrease MBD and it inserts more bursts to the core network, but it could not handle them well enough and as the result most of the bursts are dropped at the core nodes. PAHON decreases BLR 4.5 times in average in comparison with FTM. It is worthy to note that high delay is tolerable under bursty traffic by considering the assembly time of the bursts, therefore having less drop is preferable than having low delay in shortOBS. In conclusion, PAHON method outperforms the FTM method. According to Fig. 16, because both FTM and HOS use the same kinds of the switches for switching the received traffic i.e., slow optical switches for two kind of traffic (OCS and long-OBS in PAHON, continuous streaming mode and periodic streaming mode in FTM) and fast optical switches for the two remaining ones (short-OBS

(a) PLR of OPS packets with 8 TWCs.

(b) MPD of OPS packets with 8 TWCs.

(c) BLR of short-OBS with 8 TWCs.

(d) MBD of short-OBS with 8 TWCs.

Fig. 15. Comparison of FTM [19] and PAHON.

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L. Ghaemi Dizaji, A. Ghaffarpour Rahbar / J. Parallel Distrib. Comput. 117 (2018) 1–16

all three switching mechanisms (OPS, short-OBS, and long-OBS) are high in the netbench [26] real Internet traffic, while the loss rates of them are low in the redundant-stream [27], BC-pAug89 [24], and tcp-ethereal-file [28] real Internet traffic. Fig. 18(a), 18(b), and 18(c) show maximum delay of the OPS packets, short-OBS and long-OBS bursts, respectively. Both OPS packets and short-OBS bursts have high delay only in the nfs-bad-stalls [29] real Internet traffic but long-OBS bursts’ delays are high in the three redundantstream [27], iperf-mptcp [27], and nfs-bad-stalls [29] real traffic. 5. Conclusion

Fig. 16. Power Consumption of FTM [19] and PAHON with 8 TWCs.

and OPS in PAHON, burst mode and packet mode in FTM), they have almost the same power consumption. 4.4.3. PAHON under real internet traffic In this section, the behavior of the proposed PAHON method under real Internet traffic is evaluated. Accordingly, six different real data sets obtained from [24,26–29] are used in the simulations for the traffic of OPS, short-OBS, and long-OBS mechanisms. For the OCS mechanism in this scenario, we do as before and generate 100 Erlang of OCS traffic. We consider that many resources with the proposed real Internet traffic are connected to each edge node of the NSF network topology. The loss rate of OPS packets, shortOBS and long-OBS bursts are illustrated in Fig. 17(a), (b), and (c), respectively. According to the simulation results, the loss rates of

In this article, a power efficient green hybrid optical network namely PAHON (Power Aware Hybrid Optical Network) has been introduced. For providing QoS in the proposed method, the OCS, long-OBS, short-OBS and OPS switching mechanisms are used. Sending OPS packets among OCS traffic flows can optimize the network resource utilization in PAHON. In addition, using time slots of a same frame via circuits with different destinations further optimizes the network resource utilization. According to the performance of the proposed method, there is no need for optical buffers in core nodes for reaching optimized resource usage. In PAHON, other implementation criteria are also considered such as increasing the performance domain and decreasing power consumption of the network. As PAHON is an integrated hybrid optical network, it has high performance domain by providing the ability for edge and core nodes to select the proper switching mechanism. PAHON can also decrease the network power consumption several times in comparison with optical-electronic and all electronic networks. Performance of the proposed PAHON method is evaluated according to different parameters. According to the simulation results, the proposed method has better performance than the HOS

(a) PLR of OPS packets.

(b) BLR of short-OBS bursts.

(c) BLR of long-OBS bursts.

Fig. 17. Loss rate of different switching mechanisms in PAHON under real Internet traffic.

L. Ghaemi Dizaji, A. Ghaffarpour Rahbar / J. Parallel Distrib. Comput. 117 (2018) 1–16

(a) MPD of OPS packets.

15

(b) MBD of short-OBS bursts.

(c) MBD of long-OBS bursts.

Fig. 18. Maximum delay of different switching mechanisms in PAHON under real Internet traffic.

method in many criteria. For example, its good performance is in BR of OCS and also MPD and WCJ of OPS packets. PAHON outperforms the FTM method in PLR and MPD of OPS mechanism and BLR of short-OBS mechanism. Because of a little increase of WCJ for OPS packets by increasing the network traffic load, the need for electronic buffers in edge nodes could be decreased in PAHON. Also, in this article, we have provided cost analysis of the proposed PAHON method. According to the cost model, increasing the number of wavelengths increases the cost of the node. At the end, the behavior of the PAHON method is investigated under six real Internet traffic. References [1] Anna Agusti, Cristina Cervello-Pastor, Miquel A. Fiol, Performance analysis of the sent-but-sure strategy for optical burst and packet switched networks, Perform. Eval. 68 (1) (2011) 1–20. [2] Slavisa Aleksic, Analysis of power consumption in future high-capacity network nodes, J. Opt. Commun. Netw. 1 (3) (2009) 245–258. [3] Mohamed Mostafa Azim, Xiaohong Jiang, Pin-Han Ho, Susumu Horiguchi, A new hybrid architecture for optical burst switching networks, in: Springer in High Performance Computing and Communications, First International Conference, Sorrento, Italy, September 21-23, 2005, pp. 196–202. [4] Kevin J. Barker, Alan Benner, Ray Hoare, Adolfy Hoisie, Alex K. Jones, Darren J. Kerbyson, Dan Li, Rami Melhem, Ram Rajamony, Eugen Schenfeld, Shuyi Shao, Craig Stunkel, Peter Walker, On the feasibility of optical circuit switching for high performance computing systems, in: Proceedings of the 2005 ACM/IEEE conference on Supercomputing, Washington, USA, November, 2005. [5] Yang Chen, Chunming Qiao, Xiang Yu, Optical burst switching: a new area in optical networking research, IEEE Netw. 18 (3) (2004) 16–23. [6] Cisco Nexus 9508 Switch Power and Performance, [cited 2015 2015/12/7], Available from: http://www.cisco.com/c/en/us/products/collateral/switches/ nexus-9000-series-switches/solution-brief-c22-730049.html. [7] Cisco Nexus 5600 Platform 40-Gbps Switches Data Sheet, [cited 2015 2015/12/7], Available from: http://www.cisco.com/c/en/us/products/collater al/switches/nexus-5624q-switch/datasheet-c78-733100.html.

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Lida Ghaemi Dizaji received her B.Sc. degree in Information Technology Engineering from the University of Tabriz, Tabriz, Iran, in 2012. She received her M.Sc. degree in Computer Networks from the Sahand University of Technology, Sahand New Town, Tabriz, Iran, in 2015. Her research interests include hybrid optical switching, power consumption in optical networks, wireless networks, computer network attacks, and network modeling.

Akbar Ghaffarpour Rahbar received the B.Sc. and M.Sc. degrees in computer hardware and computer architecture from the Iran University of Science and Technology, Tehran, Iran, in 1992 and 1995, respectively, and the Ph.D. degree in computer science from the University of Ottawa, Ottawa, Canada, in 2006. He is currently a Professor with the Electrical Engineering Department, Sahand University of Technology, Sahand New Town, Tabriz, Iran. He is the director of the Computer Networks Research Laboratory, Sahand University. Dr. Rahbar is a senior member of the IEEE. His current research interests include optical networks, optical packet switching, scheduling, PON, IPTV, network modeling, analysis and performance evaluation, the results of which can be found in over 120 technical papers (see http://ee.sut.ac.ir/showcvdetail.aspx?id=13).