Abstract
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.
Highlights
The demands of the growing Internet are often satisfied by adding more routers, more or faster links, and more switching capacity [1]
Lemma 6: The three-stage SCS1 switching fabric presented in Fig. 2 is strict-sense nonblocking for connection C(i, j, m), 1 mmin m mmax min{fin; fout }/2, if and only if the number of middle-stage switches is pSSNB (m, me) pb (m, me) + 1, (38)
Theorem 1: The three-stage asymmetrical SCS1 switching fabric presented in Fig. 2 is strict-sense nonblocking for any connection C(i, j, m), 1 mmin m mmax min{fin; fout }/2, if and only if the number of middle-stage switches is pSSNB pb (m, me) + 1, (51)
Summary
The demands of the growing Internet are often satisfied by adding more routers, more or faster links, and more switching capacity [1]. In view of the prediction of the Compound Annual Growth Rate (CAGR, years 2015-2020) that IP traffic will be equal to 22% [2], such an approach to sustaining the IP core network expansion might not be enough. The annual global IP traffic at the end of 2016 already exceeded the zettabyte threshold [2]; new ways of increasing network throughput are required. Optical networks (EONs) are a new approach to using the available bandwidth more intelligently and more efficiently [3]. EONs are an example of signal multiplexing, and multiplexing is a method of transmission of multiple signals over a shared medium [4]–[7].
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