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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 20, Iss. 16 — Jul. 30, 2012
  • pp: 17421–17439
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Performance benchmarking of core optical networking paradigms

Andreas Drakos, Theofanis G. Orphanoudakis, and Alexandros Stavdas  »View Author Affiliations


Optics Express, Vol. 20, Issue 16, pp. 17421-17439 (2012)
http://dx.doi.org/10.1364/OE.20.017421


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Abstract

The sustainability of Future Internet critically depends on networking paradigms able to provide optimum and balanced performance over an extended set of efficiency and Quality of Service (QoS) metrics. In this work we benchmark the most established networking modes through appropriate performance metrics for three network topologies. The results demonstrate that the static reservation of WDM channels, as used in IP/WDM schemes, is severely limiting scalability, since it cannot efficiently adapt to the dynamic traffic fluctuations that are frequently observed in today’s networks. Optical Burst Switching (OBS) schemes do provide dynamic resource reservation but their performance is compromised due to high burst loss. It is shown that the CANON (Clustered Architecture for Nodes in an Optical Network) architecture exploiting statistical multiplexing over a large scale core optical network and efficient grooming at appropriate granularity levels could be a viable alternative to existing static as well as dynamic wavelength reservation schemes. Through extensive simulation results we quantify performance gains and we show that CANON demonstrates the highest efficiency achieving both targets for statistical multiplexing gains and QoS guarantees.

© 2012 OSA

1. Introduction

Under the above framework, the advances of optical transmission technologies are profound and evident [1

1. J.-X. Cai, Y. Cai, C. R. Davidson, D. G. Foursa, A. J. Lucero, O. V. Sinkin, W. W. Patterson, A. N. Pilipetskii, G. Mohs, and N. S. Bergano, “Transmission of 96 × 100-Gb/s bandwidth-constrained PDM-RZ-QPSK channels with 300% spectral efficiency over 10610 km and 400% spectral efficiency over 4370 km,” J. Lightwave Technol. 29(4), 491–498 (2011) . [CrossRef]

,2

2. J.-X. Cai, Y. Cai, C. Davidson, A. Lucero, H. Zhang, D. Foursa, O. Sinkin, W. Patterson, A. Pilipetskii, G. Mohs, and N. Bergano, “20 Tbit/s capacity transmission over 6,860 km,” In Proceedings of Optical Fiber Communication Conference (OFC), OSA Technical Digest (CD) (Optical Society of America, 2011), paper PDPB4.

]. In striking contrast, the identification of an efficient switching mode is still an open issue raising considerable controversy. This controversy is part of a much broader skepticism: is it reasonable to believe that existing networking paradigms could guarantee the end-to-end QoS performance across a core network under acceptable CAPEX (capital expenditure) figures? If not, we need to have a major rethinking with respect to the existing premises.

Today, all developments are aiming at the proliferation of the Internet. A necessary step to safeguard the sustainability of Future Internet is the identification of networking modes performing equally well across an extended set of parameters that include traditional QoS like (i) capacity and throughput, (ii) end-to-end packet loss, (iii) end-to-end packet delay and jitter, plus a set of additional parameters like (iv) degree of resource utilization, (v) availability, (vi) physical layer performance (Q-factor, BER), (vii) power consumption. Obviously, interest is on solutions offering a balanced performance across all indexes. Additionally, each solution should be investigated in conjunction with the associated switching mode for it is exactly this interplay that makes feasible to attain the requested performance.

Apparently, a stumbling block in achieving these objectives is that the most established optical networking modes/paradigms fail to provide either mechanisms for efficient and coherent traffic grooming facilitating the transportation and switching of different granularities ranging from an IP packet to a WDM waveband, or mechanisms achieving statistical multiplexing gains (the main feature of packet switching) equivalent to the robust two-way resource reservation (the main feature of circuit switching). Historically telecommunication networks have evolved following two distinct approaches, namely the connection-oriented and connectionless communication modes. Today’s existing offspring solutions (pure IP, MPLS-TP, PBT-TE, etc.), have the characteristics of one of these modes i.e. they are in essence either circuits or packets in their origin and they are trying to embrace the features of the complementary mode (i.e. statistical multiplexing and guaranteed performance, respectively). Unfortunately, they fail to do so because of the inherent granularity mismatch between the transmission granularity of the electronic layer and that of the WDM channel: the maximum identifiable bandwidth granularity stemming from the “electronic layer” is too small (compared to the round trip time in a Metro/Core network) to allow for an efficient two-way reservation. Moreover, this granularity mismatch has a secondary effect: IP-over-WDM networks are bound to frequent transitions between the optical and electronic layer (o/e-e/o conversions) followed by OTN aggregation in order to minimize the total amount of resources used i.e. the number of WDM channels and the number of optical switching ports. This incurs the penalty of excessive information processing leading to complex, high-CAPEX, solutions requiring considerable power consumption.

In this work, we benchmark the performance of the main networking modes in core networks against the extended set of QoS parameters. The networking modes under consideration include Optical Circuit Switching (OCS), Optical Burst Switching (OBS), Optical Fast Circuit Switching (OFCS) which can also be understood as dynamic OCS, and a new core optical networking architecture we have proposed named Clustered Architecture of Nodes in Optical Networks (CANON). The mode of operation of the aforementioned networking paradigms are described and analyzed in the following section (Section 2). The rest of the paper is organized as follows: in Section 3 we discuss the network dimensioning and operational parameters that affect performance in each case, define the performance metrics of interest and elaborate our benchmarking methodology aiming to have a consistent, coherent and fair way to simulate the essential aspects of these mechanisms. In Section 4 the results of the performance benchmarking over several figures of merit are presented. Through extensive simulation results we quantify performance gains and we show that CANON demonstrates the highest efficiency achieving both targets for statistical multiplexing gains and QoS guarantees. Finally Section 5 concludes our work.

2. Overview of dynamic and static resource reservation schemes and related work

OCS provides the equivalent of circuits in legacy telecommunication networks. “Optical circuits” are established through lightpaths [3

3. I. Chlamtac, A. Ganz, and G. Karmi, “Lightpath communications: an approach to high bandwidth optical WAN’s,” IEEE Trans. Commun. 40(7), 1171–1182 (1992). [CrossRef]

] and are classified to transparent, translucent, opaque or hybrid. For future reference in this work, transparent is the configuration where a lightpath is not wavelength converted when cross-connected in intermediate nodes, translucent is the configuration with intermediate wavelength conversion [4

4. C. Chu and L. B. Li, “Dynamic routing and wavelength assignment in the presence of wavelength conversion for all-optical networks,” IEEE/ACM Trans. Netw. 13(3), 704–715 (2005). [CrossRef]

] but no traffic grooming, and opaque is as before including OTN traffic grooming. Finally, a hybrid mode is the case where there could be traffic grooming in a selected number of nodes (to be decided during the planning phase) whilst in other network paths optical bypassing is deployed (off-loading). Optical bypassing [5

5. G. Hill, “A wavelength routing approach to optical communication networks,” Br. Telecommun. Technol. J. 6, 24–31 (1988).

] is proposed as a means to provide WDM channel routing while obviating expensive electronic switching. In this case, lightpaths are pre-provisioned resulting in semi-static network connections making use of, mature, slowly reconfigurable WDM technology i.e. Reconfigurable Add-Drop Multiplexers (ROADMs) and/or Optical Cross-Connects (OXCs). Their set-up/release procedure can be either centralized or distributed since the interconnection patterns do change but on a very large time scale.

Regarding OCS, several studies have shown that over-provisioning of lightpaths is essential to guarantee QoS mandating a considerable number of transceivers and large port-count switches [6

6. A. Stavdas, T. Orphanoudakis, and A. Drakos, “QoS performance benchmarking of networking paradigms in core networks,” European Conference and Exhibition on Optical Communication (ECOC) (Turin, Italy, 2010).

10

10. C. Qiao, M. A. Gonzalez-Ortega, A. Suarez-Gonzalez, X. Liu, and J. C. Lopez-Ardao, “On the benefit of fast switching in optical networks,” in Proceedings of Optical Fiber Communication Conference (OFC), OSA Technical Digest (CD) (Optical Society of America, 2010), paper OWR2.

]. Thus, the requested performance is attained at the expense of a high overall cost and poor resource utilization.

In order to overcome the scalability limitations of OCS, schemes allowing for a) statistical multiplexing gains enabling sharing of resources and b) traffic grooming at sub-wavelength granularity, are sought. So far, various dynamic resource allocation schemes like Optical Burst/Packet Switching (OBS/OPS) were studied as an alternative to OCS. In OBS presented in [11

11. C. Qiao and M. Yoo, “Optical burst switching (OBS) - A new paradigm for an optical internet,” J. High Speed Netw. 8, 69–84 (1999).

] and [12

12. J. S. Turner, “Terabit burst switching,” J. High Speed Netw. 8, 3–16 (1999).

], the incoming packets are queued at edge nodes. Each node aggregates traffic towards a particular destination node and casts it into a burst after transmitting a reservation message informing the intermediate nodes for the upcoming burst transmission. Burst generation (also called “burstification process”) is performed based on local queue status information. Burst switching nodes rely on a more mature technology than OPS [13

13. S. Yao, B. Mukherjee, and S. Dixit, “Advances in photonic packet switching: an overview,” IEEE Commun. Mag. 38(2), 84–94 (2000). [CrossRef]

] and for this reason, in this work we focus on OBS rather than OPS. However, there are serious concerns regarding OBS and specifically that the one-way reservation scheme may lead to high burst loss probabilities at high loads [14

14. A. Zalesky, “To burst or circuit switch?” IEEE/ACM Trans. Netw. 17(1), 305–318 (2009). [CrossRef]

20

20. Z. Zhang, L. Liu, and Y. Yang, “Slotted Optical Burst Switching (SOBS) networks,” Comput. Commun. 30(18), 3471–3479 (2007). [CrossRef]

].

In [21

21. T. Orphanoudakis, A. Drakos, C. T. Politi, A. Stavdas, G. Zervas, and D. Simeonidou, “A hybrid reservation mode for optical fast circuit switching,” in Proceedings of 15th Eur. Conf. on Netw. and Optical Commun. (NOC), (Faro, Portugal, 2010).

] a mechanism termed Optical Fast Circuit Switching (OFCS) employs a time-limited wavelength reservation, a process that is disassociated from the time-frame needed for forming-up the transportation unit (packet/burst). Thus, OFCS is implementing a two-way reservation protocol (e.g. RSVP) where each reservation lasts for an unknown period and, hence, it may serve a number of consecutive number of packets/bursts (Fig. 1
Fig. 1 Wavelength reservation and data transmission (a) OFCS (b) OBS.
).

In [22

22. A. Stavdas, H. C. Leligou, K. Kanonakis, C. Linardakis, and J. Angelopoulos, “A novel scheme for performing statistical multiplexing in the optical layer,” J. Opt. Netw. 4(5), 237–247 (2005). [CrossRef]

24

24. A. Stavdas, T. G. Orphanoudakis, H. C. Leligou, K. Kanonakis, C. Matrakidis, A. Drakos, J. D. Angelopoulos, and A. Lord, “Dynamic CANON: A scalable multi-domain core network,” IEEE Commun. Mag. 46(6), 138–144 (2008). [CrossRef]

], we have proposed CANON as a solution for networks exhibiting considerable spatial and temporal traffic asymmetry. As it is shown in this work, CANON demonstrates (a) efficient grooming at the optical layer via a distributed multiplexing based on ring topology networks (obviating any electronic grooming), (b) a balanced deployment of dynamic resource allocation with two-way reservation mechanisms and (c) statistical multiplexing gains per network segment (as opposed to the achievable gains per single node).

With reference to Fig. 2
Fig. 2 Clustered Architecture for Nodes in an Optical Network (CANON).
, we consider a partially-mesh connectivity core network (upper right). Following CANON, a Core/Metro network is decomposed into a number of geographically limited areas (clusters). The partitioning is based on various criteria like administrative domains, topological characteristics, traffic patterns, legacy infrastructure, and so on. An important consideration is that each of these clusters comprises a group of nodes in geographical proximity. We have developed a formal methodology for clustering original mesh-topology networks but the details of this algorithm are outside the scope of this paper.

A cluster consists of a number of nodes and the resultant structure is further decomposed to a number of ring topology networks; the ring topology becomes a building block for network engineering purposes. Thus, a single –hierarchically flat- core network is now seen as an assembly of clusters generating a single inter-cluster and a number of intra-cluster sub-networks. Since the objective is the ring nodes to share the same wavelength(s) in TDMA fashion, there is no shortest path routing in the intra-cluster segment. In each cluster there is a single node with a dual purpose: it acts as a gateway between the particular cluster and other clusters and it coordinates the transmission of all other nodes of its own cluster. Consequently, two distinctive node classes are identified: a number of Metro-Core Edge Nodes (MENs; called Regular Nodes in [23

23. J. D. Angelopoulos, K. Kanonakis, G. Koukouvakis, H. C. Leligou, C. Matrakidis, T. Orphanoudakis, and A. Stavdas, “An optical network architecture with distributed switching inside node clusters features improved loss, efficiency and cost,” J. Lightwave Technol. 25(5), 1138–1146 (2007). [CrossRef]

]) with a ROADM in the optical section and a single Core Transit Node (CTN; called Master Node in [23

23. J. D. Angelopoulos, K. Kanonakis, G. Koukouvakis, H. C. Leligou, C. Matrakidis, T. Orphanoudakis, and A. Stavdas, “An optical network architecture with distributed switching inside node clusters features improved loss, efficiency and cost,” J. Lightwave Technol. 25(5), 1138–1146 (2007). [CrossRef]

]) that is an OXC and is the gateway node. Moreover, CANON postulates two new sub-wavelength granularities in the optical layer, namely, the optical slot and the optical frame (Fig. 3
Fig. 3 CANON layering and transmission granularities.
). Having defined these, the end-to-end operation is as follows: in a given MEN, the incoming traffic is classified per class-of-service (CoS) and it is groomed (under the CoS priorities) into fixed size containers called Optical Slots (slots, hereafter) based on MEN destination criteria; contiguous slots are also envisaged. The details of this process are discussed in length in [23

23. J. D. Angelopoulos, K. Kanonakis, G. Koukouvakis, H. C. Leligou, C. Matrakidis, T. Orphanoudakis, and A. Stavdas, “An optical network architecture with distributed switching inside node clusters features improved loss, efficiency and cost,” J. Lightwave Technol. 25(5), 1138–1146 (2007). [CrossRef]

]. Under the supervision of a Medium Access Control (MAC) protocol executed at the CTN, a given MEN would launch slots in the ring. The slots from different MENs in a ring destined towards nodes residing in a specific remote cluster are transported towards the CTN over the same wavelength channel(s). Hence, the role of the CTN is twofold: (i) to arbitrate, by means of a central scheduler, the collision-free introduction of the slots from all MENs in the ring like in [25

25. L. Dittmann, C. Develder, D. Chiaroni, F. Neri, F. Callegati, W. Koerber, A. Stavdas, M. Renaud, A. Rafel, J. Sole-Pareta, W. Cerroni, N. Leligou, L. Dembeck, B. Mortensen, M. Pickavet, N. Le Sauze, M. Mahony, B. Berde, and G. Eilenberger, “The European IST project DAVID: A viable approach toward optical packet switching,” IEEE J. Sel. Areas Comm. 21(7), 1026–1040 (2003). [CrossRef]

] acting as a distributed multiplexer, and (ii) to handle the transportation in the inter-cluster network segment of the generated frames towards their destination cluster. A long cascade of slots effectively forms a larger container called Optical Frame (frame, hereafter). To accommodate for traffic variations the process is repeated in a time-frame equal to the duration of the frame. Based on fairness SLA constraints etc. one MEN may add more slots than another leading to statistical multiplexing gains over the ring under spatial and temporal traffic asymmetries.

To schematically illustrate the operation, in Fig. 3 the size L of the slots is in the order of several microseconds and could be standardized e.g. to accommodate one or more OTN G.709 [26

26. ITU-T G.709, “Interfaces for the Optical Transport Network” (2003).

] frames. A frame (of size F in the order of several milliseconds) is a container that is formed up when slots are casted together towards specific distant clusters. For example, in Fig. 3, two wavelength channels are supposed to transport traffic from Cluster 1 to Cluster 2 and one channel from Cluster 1 to Cluster 3. The upper part of Fig. 3 is showing the grooming hierarchy in CANON in both electronic and optical domains. Efficient grooming is achieved, per node, by means of standard electronic L2/L3 systems whilst the CANON intra-cluster operation, similar to “distributed multiplexer”, as said, is leading to statistical multiplexing gains across the ring. It is pointed out that this is a collective effect, having its origin in the coordinated operation of many network nodes, and not the outcome of an individual node; thus, allowing for gains that are not feasible using schemes like OBS/OPS etc.

In the inter-cluster segment (between CTNs), a wavelength channel may transport either a single frame or a cascade of frames to a distant cluster. This wavelength channel may be statically [23

23. J. D. Angelopoulos, K. Kanonakis, G. Koukouvakis, H. C. Leligou, C. Matrakidis, T. Orphanoudakis, and A. Stavdas, “An optical network architecture with distributed switching inside node clusters features improved loss, efficiency and cost,” J. Lightwave Technol. 25(5), 1138–1146 (2007). [CrossRef]

] or dynamically reserved as a response to traffic fluctuations [24

24. A. Stavdas, T. G. Orphanoudakis, H. C. Leligou, K. Kanonakis, C. Matrakidis, A. Drakos, J. D. Angelopoulos, and A. Lord, “Dynamic CANON: A scalable multi-domain core network,” IEEE Commun. Mag. 46(6), 138–144 (2008). [CrossRef]

] so the communication mode between CTNs may exploit OCS, OFCS or OBS. To avoid confusion, for the rest of this work when the communication mode is OCS, OFCS or OBS between edge nodes this will be designated as “mesh” hereafter, and when it refers to the inter-cluster segment transportation it will be designated as “CANON”.

Overall, in the intra-cluster segment where the optical slots are short in duration compared to the round trip time the lossless transportation of slots is based on a MAC protocol which has proved to be an efficient arbitration mechanism in access networks. Due to the distributed slot multiplexing and the statistical multiplexing gains achieved we will show that the traffic profile is smoothed-out which means that optical slots are well-groomed in optical frames.

3. Benchmarking methodology

Regarding the switching granularity, it is worth pointing out that OCS and OFCS employ static and dynamic, respectively, two-way channel reservations before data transmission between any two nodes. OBS and CANON on the other hand employ burst data transmission on a burst or frame level, respectively. While OBS has been initially conceived to operate based on variable length bursts [6

6. A. Stavdas, T. Orphanoudakis, and A. Drakos, “QoS performance benchmarking of networking paradigms in core networks,” European Conference and Exhibition on Optical Communication (ECOC) (Turin, Italy, 2010).

], it has also been studied in [12

12. J. S. Turner, “Terabit burst switching,” J. High Speed Netw. 8, 3–16 (1999).

,20

20. Z. Zhang, L. Liu, and Y. Yang, “Slotted Optical Burst Switching (SOBS) networks,” Comput. Commun. 30(18), 3471–3479 (2007). [CrossRef]

] in its slotted variant. Slotted OBS (S-OBS) is an OBS solution where all bursts are constrained to be of a fixed size and all control plane messages are transmitted under a specific time relation with respect to data units creating a slotted system. Apparently, S-OBS offers many advantages not only due to a smaller burst collision probability [20

20. Z. Zhang, L. Liu, and Y. Yang, “Slotted Optical Burst Switching (SOBS) networks,” Comput. Commun. 30(18), 3471–3479 (2007). [CrossRef]

] but also due to the reduced switching node control and scheduling complexity, when variable slot allocations need to be scheduled in real-time (only at the cost of synchronization at each port, which is not considered to have a critical impact). Following the above remarks and in order to allow for direct comparison with CANON, our benchmarking uses this OBS variant. Hence, the S-OBS burstification and the CANON frame generation processes share some common features described below.

For each destination node/cluster (OBS/CANON respectively) upon receipt of the first packet (at the local queue of an OBS edge node) or request (at the CTN in CANON) to reach this destination, a timer Tk is set. Whenever the timer reaches a maximum acceptable delay value TMAX (variable queues and thresholds could be implemented depending on the required QoS) burst/frame generation is triggered irrespective of the total amount of accumulated packets/requests. In case, during the time interval between setting Tk and its expiration after TMAX, the sum of the packets/requests expressed by Rtot exceeds the burst/frame capacity F i.e. Rtot > F, a burst/frame (of fixed size F) generation procedure is initiated. Finally in case Rtot exceeds a minimum acceptable burst/frame fill level UMIN, after a reasonable waiting time TMIN again a burst/frame generation is triggered, in order to expedite data forwarding at the cost of an acceptable level of burst/frame underutilization (in which case Uloss = F- UMIN).

Figure 4(a)
Fig. 4 Pan-European network in a mesh and clustered (CANON) configuration (a), Ideal equidistant 16 node network following a 4x4 Torus (mesh) and clustered (CANON) topology (b), Telecom Italia mesh and clustered network (c).
depicts the Pan-European network topology for both partially-meshed node connectivity and CANON. As discussed in [31

31. A. Drakos, T. G. Orphanoudakis, C. T. Politi, A. Stavdas, and A. Lord, “Evaluation of optical core networks based on the CANON architecture,” Photonic Netw. Commun. 20(1), 75–82 (2010). [CrossRef]

], the latter introduces a node connectivity modification shown in the inset of Fig. 4(a). The (ideal) equidistant node topology is illustrated in Fig. 4(b). In this case, to simulate OCS, OFCS and S-OBS a Torus network connectivity is assumed, while to simulate CANON the selected node connectivity follows the argumentation of [31

31. A. Drakos, T. G. Orphanoudakis, C. T. Politi, A. Stavdas, and A. Lord, “Evaluation of optical core networks based on the CANON architecture,” Photonic Netw. Commun. 20(1), 75–82 (2010). [CrossRef]

]. Finally the original mesh topology TI network is shown in Fig. 4(c) (lower part). In order to modify the node connectivity following CANON, we performed node clustering resulting in the (asymmetric) clustered network shown in Fig. 4(c) (upper part). For the inter-cluster segment, the partial-mesh connectivity of CTNs exclusively uses existing links. The implicit assumption has been made that each CTN is connected with at least 2 CTNs while the inter-cluster network retains the original average nodal degree.

Performance evaluation was conducted by means of an event-driven network simulator. All simulations were run for sufficient time to obtain steady-state results. In general, thirty million time units were simulated per point in each curve. Model validation followed the variance reduction technique with 40 replicated simulations using different seeds obtaining results with 95% confidence.

4. Performance metrics and simulation results

In this work, the aforementioned networking modes are benchmarked against the extended set of QoS parameters which are used as “figures of merit”. Although the definition of parameters like loss and delay is straightforward, parameters like network utilization and efficiency, that correlate traffic performance with CAPEX, overall network resources and their utilization level, need further elaboration. The merit functions we used are the following:

- Packet or Slot Loss Probability (SLP) measures the percentage of the lost L3/L2 packets that arrive at ingress nodes which are then transmitted either as they are (i.e. with no further L2 processing like in OCS, OFCS) or they are aggregated into burst/frames (OBS, CANON). It is pointed out that in our work SLP reflects the fraction of the incoming packets to the edge node that are lost and not the percentage of burst (OBS case) or optical frame (CANON) losses. The origin of these losses is either due to collisions (output port blocking in an intermediate network node) or buffer overflows at edge nodes.

- Delay measures the average end-to-end time needed for the packets (at the input of an ingress node) to arrive to the final recipient node. The delay is a collective event including the queuing delay at the ingress node and the propagation delay. The retransmission delay, which is important in OBS due to collisions, is not taken into account.

- Reserved capacity/Total Network Capacity (R/C) provides a useful insight into the way the resource reservation mechanisms operate and demonstrates the long term average capacity they require as a ratio of the total installed capacity C. Obviously static solutions like OCS reserve available resources at the highest level to service the peak rate demand.

- Used capacity/Reserved capacity (S/R) provides a useful insight into the effectiveness of the corresponding networking architecture since it shows the long-term average of the transmitted data units for the reserved resources. Obviously framing mechanisms that allow transmission of partially filled frames/bursts or predictive reservation schemes (like OCS and OFCS) allowing transmission of empty/idle frames in case of absence of data (assuming synchronous operation) result in lower values of this factor.

Conclusively, OCS outperforms the other networking modes but it does this at an unacceptably high cost that severely limits the scalability of this solution. It should be pointed out here that even though OCS appears to have excellent performance, in the extreme cases where the traffic rate increases close to the service rate, packet losses would inevitably occur. Actually, the system for dedicated capacity under the Poisson arrival pattern can be modeled as an M/D/1 queuing system (if we assume an ideal system with infinite buffering capability). It is well known from queuing theory [32

32. L. Kleinrock, Queueing Systems: Volume I – Theory (Wiley Interscience, 1975).

] that M/D/1 performs reversely proportional to (1-ρ) where ρ = λ/μ is the system utilization factor, λ is the average arrival rate of the Poisson process and μ is the service rate. Thus, congestion (queue size and delay) is expected to worsen (actually tending to infinity or – practically – high SLP) when λμ. However, in our case a dedicated wavepath served by one WDM channel is more than enough to accommodate the traffic matrix we have assumed leading to guaranteed robust performance at the cost of underutilization: the data of Table 1 indicate U = 0.1/0.15/0.13 for the Pan-European, Torus and TI cases, respectively, whilst R/C = 1 meaning that all available wavelengths are reserved but they are poorly utilized since S/R = 0.27/0.27/0.26. Last but not least, the lower number of transceivers for the ideal Torus network is due to the higher connectivity pattern (larger average nodal degree) of this topology mandating fewer wavepaths for node interconnection.

Given that OCS trades network performance with high CAPEX under time-varying traffic patterns, dynamic reservation schemes like S-OBS and OFCS aim to exploit statistical multiplexing, per single node, to set a lower figure on the required resources as well as to limit resource under-utilization. Certain conditions under which OBS can achieve improved utilization figures are reported in [7

7. F. Xue, S. J. Ben Yoo, H. Yokoyama, and Y. Horiuchi, “Performance comparison of optical burst and circuit switched networks,” in Proceedings of Optical Fiber Communication Conference (OFC), Technical Digest (CD) (Optical Society of America, 2005), paper OWC1.

16

16. M. Düser and P. Bayvel, “Analysis of a dynamically wavelength-routed optical burst switched network architecture,” J. Lightwave Technol. 20(4), 574–585 (2002). [CrossRef]

].

The burst size F directly affects the transmission efficiency (due to physical layer overheads) but more important it affects the control channel load since the control plane protocol overhead in OBS is directly proportional to the number of bursts transported over the network. This overhead is shown for different values of the average message load (across all links) per node in the network (expressed as a percentage of the channel capacity) in Fig. 7
Fig. 7 S-OBS and OFCS total average message load per node.
, where one can observe the inversely proportional relation between F and control channel load.

This could become critical in networks with high numbers of nodes and many WDM channels per link, leading to severe congestion and, eventually, SLP degradation [33

33. N. Barakat and T. E. Darcie, “Control-plane congestion in Optical-Burst-Switched Networks,” J. Opt. Netw. 1(3), B98–B110 (2009). [CrossRef]

]. Thus, we can conclude that S-OBS in a meshed connectivity network trades one QoS performance parameter for another; overall, it has a very poor performance unless the network capacity is significantly over-provisioned, while the utilization of the available resources is modest at best (Fig. 6 / Table 2).

The QoS performance of the Pan-European mesh connectivity network topology employing the OFCS solution is shown in Fig. 8
Fig. 8 OFCS performance in terms of: SLP (a), Average end-to-end delay (b) and resource utilization expressed as R/C (c) and S/R (d).
. Similarly to S-OBS, the performance of a network adopting the OFCS mode is affected by the sensitivity of the sampling period TS, during which the decisions for channel reservation or release are taken, and a threshold Th for rounding to the closest number of VWPs [21

21. T. Orphanoudakis, A. Drakos, C. T. Politi, A. Stavdas, G. Zervas, and D. Simeonidou, “A hybrid reservation mode for optical fast circuit switching,” in Proceedings of 15th Eur. Conf. on Netw. and Optical Commun. (NOC), (Faro, Portugal, 2010).

]. For a direct comparison with S-OBS, the QoS indexes are parameterized against the same set of values. However, their actual impact on OFCS performance is lower than that of the corresponding parameters in S-OBS. What is important to point out is that OFCS, unlike S-OBS, actually improves the SLP performance (Fig. 8(a)). Specifically, when C = 0.75∙ COCS, the Pan-European network under the OFCS mode exhibits lossless performance. However, this performance is attained at the expense of significantly higher end-to-end delay as it is indicated in Fig. 8(b) that may exceed 100 msec (average value) in extreme cases (i.e. at higher loads and limited capacity). This is an unavoidable outcome due to the delay introduced by to the capacity estimation process. OFCS utilizes as many resources as possible to prevent losses due to buffer overflow at edge nodes and, as a result, it demonstrates a much better utilization performance compared to S-OBS as observed in Figs. 8(c)-8(d) and in Table 3

Table 3. Throughput/ Total Network Capacity (T/C) for OFCS

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.

Conclusively, the simulation results for S-OBS and OFCS show that both networking paradigms trade the performance of one QoS parameter for the other. This is inevitable since statistical multiplexing and resource reservation are carried out at a single node level.

CANON on the other hand demonstrates an almost lossless operation in all cases as shown in Fig. 9(a)
Fig. 9 CANON performance in terms of SLP (a) Average end-to-end delay (b) and resource utilization expressed as R/C (c) and S/R (d).
. Losses are observed only at very high loads and only for a dynamic inter-cluster network (based on OFCS or S-OBS). CANON has a higher end-to-end delay (Fig. 9(b)) compared to OCS and S-OBS but lower than that of OFCS; the delay remains bounded to acceptable limits in all cases. The number of transceivers in CANON is slightly higher than OFCS and S-OBS but still remains much lower than that of OCS. On the other hand, it is very important to point out that although in “mesh” networking solutions the number of transceivers coincides to the number of the number of WDM channels in the network (in reality, the product of number of fibers times the WDM channels per fiber), in CANON the number of WDM channels is significantly reduced due to the statistical multiplexing on network level and not per node, as will be shown below.

Having, reached the above conclusions we evaluate for the scenario (set of parameters) giving the best results for S-OBS and OFCS presenting in Figs. 10(a)
Fig. 10 S-OBS, OFCS and CANON performance for the Torus network and OFCS and CANON performance for the TI network in terms of SLP (a, d) average end-to-end delay (b, e) and resource utilization expressed as U = T/C (c, f).
10(c) comparatively the benchmarking results in terms of SLP, delay and utilization U = T/C for S-OBS, OFCS and CANON when the ideal network of Fig. 4(b) is used (Torus mesh and clustered respectively).

Finally, under the same conditions we evaluate the case of the larger TI network of Fig. 4(c). Since S-OBS performance has been shown in many studies to degrade with the size of the network (e.g. [17

17. R. Parthiban, R. S. Tucker, C. Leckie, A. Zalesky, and A. V. Tran, “Does optical burst switching have a role in the core network?” in Proceedings of Optical Fiber Communication Conference (OFC), Technical Digest (CD) (Optical Society of America, 2005), paper OWC2.

,20

20. Z. Zhang, L. Liu, and Y. Yang, “Slotted Optical Burst Switching (SOBS) networks,” Comput. Commun. 30(18), 3471–3479 (2007). [CrossRef]

,34

34. J. P. C. Rodrigues and M. Freire, ICOIN 2004, LNCS 3090 (Springer-Verlag, 2004), pp. 750–759.

]) we only focus on the performance of OFCS and CANON presenting the results in Figs. 10(d)-10(f). As we observe from Fig. 10(d) the impact of the size of the network on SLP is minimal under the same dimensioning, yielding only a lower T/C ratio due to the large number of links, which in turn result in longer multi-hop VWPs. Thus, we can confirm that our observations above hold for any network size and topology.

5. Concluding remarks

An extensive benchmarking of several networking modes has been presented for three networking topologies and over a range of operation parameters and conditions. The conclusion of these studies is that OBS and OFCS require a considerable number of WDM channels just to avoid collisions/blocking. On the other hand, CANON not only keeps loss quite low in all cases, even when employing an OBS-like solution over the inter-cluster network, but also it efficiently grooms slots into frames allowing for statistical multiplexing of data over a larger number of contributing nodes, increasing resource utilization as shown in Fig. 9 and Table 4. The same conclusions hold in all topologies and, as also shown in [30

30. P. Pagnan and M. Schiano, “A λ switched photonic network for the new transport backbone of Telecom Italia,” International Conference on Photonics in Switching, PS '09, (2009).

] for the clustered topology of Fig. 4(a), the improved performance cannot be attributed to the topology transformation alone. On the contrary, it is the interplay of the hierarchical aggregation, reservation and switching mechanisms that reduce collision domains (a cause of high loss probability) while they are leading to the efficient utilization of available resources and a limited end-to-end delay. CANON outperforms other solutions even when OCS is employed over the inter-cluster network, under the traffic conditions examined in this study, and provides optimal loss and delay performance with a minor increase of the required capacity compared to S-OBS, yielding though high utilization and reduced overall network cost. However, for better scalability both in larger node count network topologies and higher traffic volumes, CANON with OFCS in the inter-cluster network may prove a more cost-effective solution.

Acknowledgment

This work was carried out with the support of STRONGEST, an Integrated Project funded by the European Commission through the 7th ICT-Framework Program. The authors are extremely grateful to two unknown reviewers that greatly helped to improve the accuracy of the manuscript.

References and links

1.

J.-X. Cai, Y. Cai, C. R. Davidson, D. G. Foursa, A. J. Lucero, O. V. Sinkin, W. W. Patterson, A. N. Pilipetskii, G. Mohs, and N. S. Bergano, “Transmission of 96 × 100-Gb/s bandwidth-constrained PDM-RZ-QPSK channels with 300% spectral efficiency over 10610 km and 400% spectral efficiency over 4370 km,” J. Lightwave Technol. 29(4), 491–498 (2011) . [CrossRef]

2.

J.-X. Cai, Y. Cai, C. Davidson, A. Lucero, H. Zhang, D. Foursa, O. Sinkin, W. Patterson, A. Pilipetskii, G. Mohs, and N. Bergano, “20 Tbit/s capacity transmission over 6,860 km,” In Proceedings of Optical Fiber Communication Conference (OFC), OSA Technical Digest (CD) (Optical Society of America, 2011), paper PDPB4.

3.

I. Chlamtac, A. Ganz, and G. Karmi, “Lightpath communications: an approach to high bandwidth optical WAN’s,” IEEE Trans. Commun. 40(7), 1171–1182 (1992). [CrossRef]

4.

C. Chu and L. B. Li, “Dynamic routing and wavelength assignment in the presence of wavelength conversion for all-optical networks,” IEEE/ACM Trans. Netw. 13(3), 704–715 (2005). [CrossRef]

5.

G. Hill, “A wavelength routing approach to optical communication networks,” Br. Telecommun. Technol. J. 6, 24–31 (1988).

6.

A. Stavdas, T. Orphanoudakis, and A. Drakos, “QoS performance benchmarking of networking paradigms in core networks,” European Conference and Exhibition on Optical Communication (ECOC) (Turin, Italy, 2010).

7.

F. Xue, S. J. Ben Yoo, H. Yokoyama, and Y. Horiuchi, “Performance comparison of optical burst and circuit switched networks,” in Proceedings of Optical Fiber Communication Conference (OFC), Technical Digest (CD) (Optical Society of America, 2005), paper OWC1.

8.

X. Liu and C. Qiao, Xiang. Yu, and W. Gong, “A fair packet-level performance comparison of OBS and OCS,” in Proceedings of Optical Fiber Communication Conference (OFC), Technical Digest (CD) (Optical Society of America, 2006), paper JThB48.

9.

C. Qiao, W. Wei, and X. Liu, “Extending generalized multiprotocol label switching (GMPLS) for polymorphous, agile, and transparent optical networks (PATON),” IEEE Commun. Mag. 44(12), 104–114 (2006). [CrossRef]

10.

C. Qiao, M. A. Gonzalez-Ortega, A. Suarez-Gonzalez, X. Liu, and J. C. Lopez-Ardao, “On the benefit of fast switching in optical networks,” in Proceedings of Optical Fiber Communication Conference (OFC), OSA Technical Digest (CD) (Optical Society of America, 2010), paper OWR2.

11.

C. Qiao and M. Yoo, “Optical burst switching (OBS) - A new paradigm for an optical internet,” J. High Speed Netw. 8, 69–84 (1999).

12.

J. S. Turner, “Terabit burst switching,” J. High Speed Netw. 8, 3–16 (1999).

13.

S. Yao, B. Mukherjee, and S. Dixit, “Advances in photonic packet switching: an overview,” IEEE Commun. Mag. 38(2), 84–94 (2000). [CrossRef]

14.

A. Zalesky, “To burst or circuit switch?” IEEE/ACM Trans. Netw. 17(1), 305–318 (2009). [CrossRef]

15.

A. Zapata-Beghelli and P. Bayvel, “Dynamic versus static wavelength-routed optical networks,” J. Lightwave Technol. 26(20), 3403–3415 (2008). [CrossRef]

16.

M. Düser and P. Bayvel, “Analysis of a dynamically wavelength-routed optical burst switched network architecture,” J. Lightwave Technol. 20(4), 574–585 (2002). [CrossRef]

17.

R. Parthiban, R. S. Tucker, C. Leckie, A. Zalesky, and A. V. Tran, “Does optical burst switching have a role in the core network?” in Proceedings of Optical Fiber Communication Conference (OFC), Technical Digest (CD) (Optical Society of America, 2005), paper OWC2.

18.

P. Pavon-Marino and F. Neri, “On the myths of Optical Burst Switching,” IEEE Trans. Commun. 59(9), 2574–2584 (2011). [CrossRef]

19.

G. Weichenberg, V. W. S. Chan, and M. Médard, “Design and analysis of optically flow switched networks,” J. Opt. Commun. Netw. 1(3), B81–B97 (2009). [CrossRef]

20.

Z. Zhang, L. Liu, and Y. Yang, “Slotted Optical Burst Switching (SOBS) networks,” Comput. Commun. 30(18), 3471–3479 (2007). [CrossRef]

21.

T. Orphanoudakis, A. Drakos, C. T. Politi, A. Stavdas, G. Zervas, and D. Simeonidou, “A hybrid reservation mode for optical fast circuit switching,” in Proceedings of 15th Eur. Conf. on Netw. and Optical Commun. (NOC), (Faro, Portugal, 2010).

22.

A. Stavdas, H. C. Leligou, K. Kanonakis, C. Linardakis, and J. Angelopoulos, “A novel scheme for performing statistical multiplexing in the optical layer,” J. Opt. Netw. 4(5), 237–247 (2005). [CrossRef]

23.

J. D. Angelopoulos, K. Kanonakis, G. Koukouvakis, H. C. Leligou, C. Matrakidis, T. Orphanoudakis, and A. Stavdas, “An optical network architecture with distributed switching inside node clusters features improved loss, efficiency and cost,” J. Lightwave Technol. 25(5), 1138–1146 (2007). [CrossRef]

24.

A. Stavdas, T. G. Orphanoudakis, H. C. Leligou, K. Kanonakis, C. Matrakidis, A. Drakos, J. D. Angelopoulos, and A. Lord, “Dynamic CANON: A scalable multi-domain core network,” IEEE Commun. Mag. 46(6), 138–144 (2008). [CrossRef]

25.

L. Dittmann, C. Develder, D. Chiaroni, F. Neri, F. Callegati, W. Koerber, A. Stavdas, M. Renaud, A. Rafel, J. Sole-Pareta, W. Cerroni, N. Leligou, L. Dembeck, B. Mortensen, M. Pickavet, N. Le Sauze, M. Mahony, B. Berde, and G. Eilenberger, “The European IST project DAVID: A viable approach toward optical packet switching,” IEEE J. Sel. Areas Comm. 21(7), 1026–1040 (2003). [CrossRef]

26.

ITU-T G.709, “Interfaces for the Optical Transport Network” (2003).

27.

A. Stavdas, C. T. Politi, T. Orphanoudakis, and A. Drakos, “Optical packet routers: how they can efficiently and cost-effectively scale to petabits per second,” J. Opt. Netw. 7(10), 876–894 (2008). [CrossRef]

28.

A. Stavdas, T. Orphanoudakis, C. T. Politi, A. Drakos, and A. Lord, “Design, performance evaluation and energy efficiency of optical core networks based on the CANON architecture,” Optical Fiber Communication Conference (OFC), 22–26 March 2009.

29.

S. D. Maesschalck, D. Colle, I. Lievens, M. Pickavet, P. Demeester, C. Mauz, M. Jaeger, R. Inkret, B. Mikac, and J. Derkacz, “Pan-European optical transport networks: An availability-based comparison,” Photonic Netw. Commun. 5(3), 203–225 (2003). [CrossRef]

30.

P. Pagnan and M. Schiano, “A λ switched photonic network for the new transport backbone of Telecom Italia,” International Conference on Photonics in Switching, PS '09, (2009).

31.

A. Drakos, T. G. Orphanoudakis, C. T. Politi, A. Stavdas, and A. Lord, “Evaluation of optical core networks based on the CANON architecture,” Photonic Netw. Commun. 20(1), 75–82 (2010). [CrossRef]

32.

L. Kleinrock, Queueing Systems: Volume I – Theory (Wiley Interscience, 1975).

33.

N. Barakat and T. E. Darcie, “Control-plane congestion in Optical-Burst-Switched Networks,” J. Opt. Netw. 1(3), B98–B110 (2009). [CrossRef]

34.

J. P. C. Rodrigues and M. Freire, ICOIN 2004, LNCS 3090 (Springer-Verlag, 2004), pp. 750–759.

OCIS Codes
(060.4250) Fiber optics and optical communications : Networks
(060.4510) Fiber optics and optical communications : Optical communications

ToC Category:
Fiber Optics and Optical Communications

History
Original Manuscript: February 24, 2012
Revised Manuscript: May 6, 2012
Manuscript Accepted: June 18, 2012
Published: July 17, 2012

Citation
Andreas Drakos, Theofanis G. Orphanoudakis, and Alexandros Stavdas, "Performance benchmarking of core optical networking paradigms," Opt. Express 20, 17421-17439 (2012)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-20-16-17421


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References

  1. J.-X. Cai, Y. Cai, C. R. Davidson, D. G. Foursa, A. J. Lucero, O. V. Sinkin, W. W. Patterson, A. N. Pilipetskii, G. Mohs, and N. S. Bergano, “Transmission of 96 × 100-Gb/s bandwidth-constrained PDM-RZ-QPSK channels with 300% spectral efficiency over 10610 km and 400% spectral efficiency over 4370 km,” J. Lightwave Technol.29(4), 491–498 (2011) . [CrossRef]
  2. J.-X. Cai, Y. Cai, C. Davidson, A. Lucero, H. Zhang, D. Foursa, O. Sinkin, W. Patterson, A. Pilipetskii, G. Mohs, and N. Bergano, “20 Tbit/s capacity transmission over 6,860 km,” In Proceedings of Optical Fiber Communication Conference (OFC), OSA Technical Digest (CD) (Optical Society of America, 2011), paper PDPB4.
  3. I. Chlamtac, A. Ganz, and G. Karmi, “Lightpath communications: an approach to high bandwidth optical WAN’s,” IEEE Trans. Commun.40(7), 1171–1182 (1992). [CrossRef]
  4. C. Chu and L. B. Li, “Dynamic routing and wavelength assignment in the presence of wavelength conversion for all-optical networks,” IEEE/ACM Trans. Netw.13(3), 704–715 (2005). [CrossRef]
  5. G. Hill, “A wavelength routing approach to optical communication networks,” Br. Telecommun. Technol. J.6, 24–31 (1988).
  6. A. Stavdas, T. Orphanoudakis, and A. Drakos, “QoS performance benchmarking of networking paradigms in core networks,” European Conference and Exhibition on Optical Communication (ECOC) (Turin, Italy, 2010).
  7. F. Xue, S. J. Ben Yoo, H. Yokoyama, and Y. Horiuchi, “Performance comparison of optical burst and circuit switched networks,” in Proceedings of Optical Fiber Communication Conference (OFC), Technical Digest (CD) (Optical Society of America, 2005), paper OWC1.
  8. X. Liu and C. Qiao, Xiang. Yu, and W. Gong, “A fair packet-level performance comparison of OBS and OCS,” in Proceedings of Optical Fiber Communication Conference (OFC), Technical Digest (CD) (Optical Society of America, 2006), paper JThB48.
  9. C. Qiao, W. Wei, and X. Liu, “Extending generalized multiprotocol label switching (GMPLS) for polymorphous, agile, and transparent optical networks (PATON),” IEEE Commun. Mag.44(12), 104–114 (2006). [CrossRef]
  10. C. Qiao, M. A. Gonzalez-Ortega, A. Suarez-Gonzalez, X. Liu, and J. C. Lopez-Ardao, “On the benefit of fast switching in optical networks,” in Proceedings of Optical Fiber Communication Conference (OFC), OSA Technical Digest (CD) (Optical Society of America, 2010), paper OWR2.
  11. C. Qiao and M. Yoo, “Optical burst switching (OBS) - A new paradigm for an optical internet,” J. High Speed Netw.8, 69–84 (1999).
  12. J. S. Turner, “Terabit burst switching,” J. High Speed Netw.8, 3–16 (1999).
  13. S. Yao, B. Mukherjee, and S. Dixit, “Advances in photonic packet switching: an overview,” IEEE Commun. Mag.38(2), 84–94 (2000). [CrossRef]
  14. A. Zalesky, “To burst or circuit switch?” IEEE/ACM Trans. Netw.17(1), 305–318 (2009). [CrossRef]
  15. A. Zapata-Beghelli and P. Bayvel, “Dynamic versus static wavelength-routed optical networks,” J. Lightwave Technol.26(20), 3403–3415 (2008). [CrossRef]
  16. M. Düser and P. Bayvel, “Analysis of a dynamically wavelength-routed optical burst switched network architecture,” J. Lightwave Technol.20(4), 574–585 (2002). [CrossRef]
  17. R. Parthiban, R. S. Tucker, C. Leckie, A. Zalesky, and A. V. Tran, “Does optical burst switching have a role in the core network?” in Proceedings of Optical Fiber Communication Conference (OFC), Technical Digest (CD) (Optical Society of America, 2005), paper OWC2.
  18. P. Pavon-Marino and F. Neri, “On the myths of Optical Burst Switching,” IEEE Trans. Commun.59(9), 2574–2584 (2011). [CrossRef]
  19. G. Weichenberg, V. W. S. Chan, and M. Médard, “Design and analysis of optically flow switched networks,” J. Opt. Commun. Netw.1(3), B81–B97 (2009). [CrossRef]
  20. Z. Zhang, L. Liu, and Y. Yang, “Slotted Optical Burst Switching (SOBS) networks,” Comput. Commun.30(18), 3471–3479 (2007). [CrossRef]
  21. T. Orphanoudakis, A. Drakos, C. T. Politi, A. Stavdas, G. Zervas, and D. Simeonidou, “A hybrid reservation mode for optical fast circuit switching,” in Proceedings of 15th Eur. Conf. on Netw. and Optical Commun. (NOC), (Faro, Portugal, 2010).
  22. A. Stavdas, H. C. Leligou, K. Kanonakis, C. Linardakis, and J. Angelopoulos, “A novel scheme for performing statistical multiplexing in the optical layer,” J. Opt. Netw.4(5), 237–247 (2005). [CrossRef]
  23. J. D. Angelopoulos, K. Kanonakis, G. Koukouvakis, H. C. Leligou, C. Matrakidis, T. Orphanoudakis, and A. Stavdas, “An optical network architecture with distributed switching inside node clusters features improved loss, efficiency and cost,” J. Lightwave Technol.25(5), 1138–1146 (2007). [CrossRef]
  24. A. Stavdas, T. G. Orphanoudakis, H. C. Leligou, K. Kanonakis, C. Matrakidis, A. Drakos, J. D. Angelopoulos, and A. Lord, “Dynamic CANON: A scalable multi-domain core network,” IEEE Commun. Mag.46(6), 138–144 (2008). [CrossRef]
  25. L. Dittmann, C. Develder, D. Chiaroni, F. Neri, F. Callegati, W. Koerber, A. Stavdas, M. Renaud, A. Rafel, J. Sole-Pareta, W. Cerroni, N. Leligou, L. Dembeck, B. Mortensen, M. Pickavet, N. Le Sauze, M. Mahony, B. Berde, and G. Eilenberger, “The European IST project DAVID: A viable approach toward optical packet switching,” IEEE J. Sel. Areas Comm.21(7), 1026–1040 (2003). [CrossRef]
  26. ITU-T G.709, “Interfaces for the Optical Transport Network” (2003).
  27. A. Stavdas, C. T. Politi, T. Orphanoudakis, and A. Drakos, “Optical packet routers: how they can efficiently and cost-effectively scale to petabits per second,” J. Opt. Netw.7(10), 876–894 (2008). [CrossRef]
  28. A. Stavdas, T. Orphanoudakis, C. T. Politi, A. Drakos, and A. Lord, “Design, performance evaluation and energy efficiency of optical core networks based on the CANON architecture,” Optical Fiber Communication Conference (OFC), 22–26 March 2009.
  29. S. D. Maesschalck, D. Colle, I. Lievens, M. Pickavet, P. Demeester, C. Mauz, M. Jaeger, R. Inkret, B. Mikac, and J. Derkacz, “Pan-European optical transport networks: An availability-based comparison,” Photonic Netw. Commun.5(3), 203–225 (2003). [CrossRef]
  30. P. Pagnan and M. Schiano, “A λ switched photonic network for the new transport backbone of Telecom Italia,” International Conference on Photonics in Switching, PS '09, (2009).
  31. A. Drakos, T. G. Orphanoudakis, C. T. Politi, A. Stavdas, and A. Lord, “Evaluation of optical core networks based on the CANON architecture,” Photonic Netw. Commun.20(1), 75–82 (2010). [CrossRef]
  32. L. Kleinrock, Queueing Systems: Volume I – Theory (Wiley Interscience, 1975).
  33. N. Barakat and T. E. Darcie, “Control-plane congestion in Optical-Burst-Switched Networks,” J. Opt. Netw.1(3), B98–B110 (2009). [CrossRef]
  34. J. P. C. Rodrigues and M. Freire, ICOIN 2004, LNCS 3090 (Springer-Verlag, 2004), pp. 750–759.

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