Frequency Slot Units Research Articles

Simulation Studies of Link Group in Elastic Optical Networks Used in Internet of Things Solutions

Abstract The elastic optical network (EON) solution is the most flexible in terms of allocation of resources for various traffic streams transported in core part (edge-cloud) of Internet of Things (IoT) networks. This paper presents the results of a study on the determination of the occupancy distribution and the loss probability for particular traffic flows offered in EONs supporting IoT systems. The purpose of the research was to determine the impact of: the number of links making up a group, the numbers of frequency slot units (FSUs) in individual EON link, the traffic intensity of individual traffic flows, the capacity of the EON link (number of FSUs) and the number of FSUs requested by different traffic streams. The developed simulation program of link group of EON allows the calculation of the values of the occupancy distribution and loss probability. The results obtained from the simulation are presented on the graphs in the form of points with confidence intervals.

Rearrangeable Nonblocking Conditions for Four Elastic Optical Data Center Networks

Four variants of elastic optical data center network (DCN) architectures based on optical circuit switching were proposed in an earlier study. The necessary and sufficient values of frequency slot units (FSUs) per fiber required for these four DCNs in the sense of there being strictly nonblocking (SNB) were derived, but no results in the sense of being rearrangeable nonblocking (RNB) were presented. In reality, only limited bandwidths are available, and reducing the value of FSUs per fiber has become a critical task to realize nonblocking optical DCN architectures in practice. In this paper, we derive the sufficient value of FSUs per fiber required for the four DCNs to be RNB by two multigraph approaches. Our results show that the proposed RNB conditions in terms of FSUs per fiber for a certain two of the four DCNs reduce their SNB results down to at least half for most cases, and even down to one-third.

New upper bound for a rearrangeable non‐blocking WSW architecture

An optical network based on elastic optical switches allows requests using different spectrum widths to improve utilisation efficiency. This study considers one three-stage WSW (waveband switching-space switching-waveband switching), optical node architecture for elastic optical networks. A sufficient condition for a rearrangeable non-blocking WSW architecture with limited input/output links has been derived in an earlier work. In this study, the author improves the upper bound by adopting a new interstage link partition scheme associated with a tricky routing algorithm. Suppose a WSW architecture has r input/output links each of which has n frequency slot units (FSUs). Compared with earlier results, the results of the proposed scheme show that s − 1 (or 3s − 4) FSUs per interstage link can be reduced for even (or odd) min{r, n}, where s = min{⌈r/2⌉, ⌈n/2⌉}. The reduction gain is at least 3.5% (or 10%) for even (or odd) min{r, n} if r = n ≤ 26, even achieving 23.3% for limited odd r = n.

Generic Dijkstra for optical networks

We present the generic Dijkstra shortest path algorithm: an efficient algorithm for finding a shortest path in an optical network, both in a wavelength-division multiplexed network, and an elastic optical network (EON). The proposed algorithm is an enabler of real-time softwarized control of large-scale networks, and is not limited to optical networks. The Dijkstra algorithm is a generalization of the breadth-first search, and we generalize the Dijkstra algorithm further to resolve the continuity and contiguity constraints of the frequency slot units required in EONs. Specifically, we generalize the notion of a label, change what we iterate with, and reformulate the edge relaxation so that vertices are revisited, loops avoided, and worse labels discarded. We also used the typical constriction during edge relaxation to take care of the signal modulation constraints. The algorithm can be used with various spectrum allocation policies. We motivate and discuss the algorithm design, and provide our free, reliable, and generic implementation using the Boost Graph Library. We carried out 85000 simulation runs for realistic and random networks (Gabriel graphs) of 75 vertices with about a billion shortest-path searches, and found that the proposed algorithm outperforms considerably three other competing optimal algorithms that are frequently used.

Rearrangeable 2 times 2 elastic optical switch with two connection rates and spectrum conversion capability

In this study, we consider simultaneous connection routing in the three-stage switching fabric of the wavelength-space-wavelength architecture for elastic optical switches, which serve connections that can occupy different spectrum widths. Recently, the upper bound of the rearrangeability conditions was derived and proved for a switching fabric serving a limited number of connection rates. A control algorithm based on matrix decomposition was also proposed. In addition, the necessary and sufficient conditions were derived and proved for a switching fabric with a size of 2 times 2 serving only two connection rates, but only when the ratios between the connection rates and link capacity are integers. In this study, we extend these results to an arbitrary ratio between the connection rates and link capacity. The number of frequency slot units required in the interstage links is much lower than that in the strict-sense nonblocking switching fabrics. We also propose modifications to the control algorithm, which further reduces the number of frequency slot units required in many cases. Finally, we extend the results for 2 times 2 switching fabrics to those with a size of r times r.

Rearrangeable W-S-W Elastic Optical Networks Generated by Graph Approaches: erratum

In elastic optical networks, a connection uses different spectrum widths that spread over adjacent frequency slot units (FSUs) to improve utilization efficiency. A three-stage wavelength-space-wavelength (W-S-W) optical node architecture for elastic optical networks employs wavelength switching in the first and third stages and space switching in the second stage. This paper considers twoW-S-Warchitectures, calledWSW1andWSW2networks. In an earlier study, a matrix decomposition approach was used to derive a condition that was sufficient for rearrangeable nonblocking (RNB), but only for a WSW1 network with a limited number of connection rates. In this paper, instead of using a matrix decomposition approach, we use a graph approach to derive the same result. Furthermore, we adopt different graph approaches to derive two sufficient conditions, which benefit limited connection rates and limited input/output fibers of an RNB WSW1 (or WSW2) network. Specifically, the former is better than the latter if the number of connection rates is less than the minimum ceiling value of half the number of 1) input/output switches and 2) FSUs in each input and output fiber, and vice versa if the number of input/output switches is less than the minimum value of 1) twice the maximum FSUs occupied by a single connection and 2) FSUs in each input and output fiber. Note that limited input/output switches lead to limited input/output fibers. The graph approaches proposed in this paper can be applied to various other elastic optical networks for further study

Asymmetrical Space-Conversion-Space SCS1 Strict-Sense and Wide-Sense Nonblocking Switching Fabrics for Continuous Multislot Connections

Recently, Danilewicz et al. have proposed two strict-sense nonblocking structures of switching fabrics, called Space-Wavelength-Space 1 and Space-Wavelength-Space 2, for elastic optical network nodes. This paper considers one of the two previously presented structures. The node uses a three-stage switching fabric that applies space switching in the first and third stages and wavelength switching in the second stage (an S-W-S switching fabric). In elastic optical networks, an optical path can use a frequency slot spread over m adjacent frequency slot units. Such a connection is called an m-slot connection. In this paper, a more general case is presented in which conversion in the middle-stage switches can be made for one of the different domains (frequency, time, etc.). However, the m-slot connections are a basis for the presented theory. This theory concerns space-conversion-space (S-C-S) switching fabrics in which conversion can be performed for different domains. Danilewicz et al. considered S-W-S switching fabrics in which 1 ≤ m ≤ m max . For the S-C-S switching fabrics discussed in this paper, we derive and prove strict-sense nonblocking conditions when m-slot connections are set up, in which m min ≤ m ≤ m max . Strict-sense nonblocking conditions are derived for asymmetrical S-C-S switching fabrics. In addition, wide-sense nonblocking conditions for switching fabrics with functional decomposition of center-stage switches are presented. It is shown that the wide-sense nonblocking switching fabrics may require less than a half of the switches in the middle-stage compared with the strict-sense nonblocking switching fabrics.

Rearrangeability of 2×2 W-S-W Elastic Switching Fabrics with Two Connection Rate

The rearreangeable conditions for the 2×2 three-stage switching fabric of a W-S-W architecture for elastic optical switches are considered in this paper. Analogies between the switching fabric considered and the three-stage Clos network are shown. On the other hand, differences are also shown, which presented the modifications required in the control algorithm used in rearrangeable networks. The rearrangeable conditions and the control algorithm are presented and proved. Operation of the proposed control algorithm is shown based on a few examples. The required number of frequency slot units in interstage links of rearrangeable switching fabrics is much lower than in the strict-sense non-blocking switching fabrics characterized by the same parameters.

Strict-Sense Nonblocking Space-Wavelength-Space Switching Fabrics for Elastic Optical Network Nodes

In elastic optical networks, a connection may occupy a frequency slot that spreads over m adjacent frequency slot units (FSUs). Such connection (called m-slot connection) also must be realized in optical nodes used in these networks. The paper considers two architectures of the three-stage switching fabric that can be used in such network nodes. The switching fabric applies space switching in the first and the third stages and wavelength switching in the second stage [the space-wavelength-space (S-W-S) switching fabric]. For both architectures, denoted by SWS1 and SWS2, we derived and proved the strict-sense nonblocking conditions when m-slot connections are set up. The number of center stage wavelength switches is calculated and evaluated. The switching fabrics are compared with the strict-sense nonblocking wavelength-space-wavelength (W-S-W) switching fabric. It is shown that the number of center stage switches does not depend on the number of FSUs available in input and output fibers but only on the maximum number of FSUs, which can be used by one connection and the number of input/output fibers in one input/output space switch. When the number of FSUs in one connection is, for instance, limited to 5, only 11 center stage switches are needed for nonblocking operation in one of the architectures. Moreover, for switching fabrics with a greater number of maximum FSUs in one connection and a greater number of FSUs in one input or output fiber, the S-W-S switching fabrics can be practically realized, unlike the W-S-W switching fabric.

Strict-Sense Nonblocking W-S-W Node Architectures for Elastic Optical Networks

The paper considers optical node architectures for elastic optical networks. They use switching fabric topologies which are similar to the three-stage Clos switching networks. These architectures employ wavelength switching in the first and the third stages, and space switching in the second stage, and are also called W-S-W switching fabrics. In elastic optical networks, the optical spectrum is divided into frequency slot units. One frequency slot unit uses 12.5 GHz of bandwidth and an optical path may use m adjacent frequency slot units. Such connection is called an m-slot connection. For each architecture, strict-sense nonblocking conditions are derived and proved for such m-slot connections. The number of center stage switches and the number of frequency slot units in interstage links are calculated and evaluated. The considered architectures are compared to each other. When the maximum number of frequency slot units that may be used by one connection, is not too high, these architectures can be implemented in practice.