Applying Bidirectional Crossbar Switches with Extra Sets of Inlets and Outlets to Three-Stage Clos Networks


Labson Koloko,Graduate School of Engineering Science, Akita University, Japan
Hitoshi Obara*,Graduate School of Engineering Science, Akita University, Japan


In scaling up optical network capacity in space-division multiplexing, the three stage Clos network has been used for building high port count switches with reduced Crosspoint. This paper presents a new three stage Clos architecture with extra internal routes yielding a smaller number of crossbar switches. The three-stage Clos network, denoted by C(n, m, r), where n, m, and r represent the number of input (output) ports of the input (output) switches, the number of middle switches, and the number of input and output switches, respectively, is widely used. Here, we consider Clos networks that include conventional crossbar switch elements, which are composed of 22 basic cells often used in optical networks. First, we point out that the crossbar switches have a number of idle ports unused, and discuss how they can be employed to improve the network performance. We then introduce a new type of Clos network in which the middle stage is composed of bidirectional crossbar switches with extra sets of inlets and outlets. This is done by utilizing the idle ports on the crossbar switches. Second, we elaborate on the non-blocking performance of this network and show that the theoretical lower bound of m for rearrangeable non-blocking capability can be reduced by 25% of the original Clos network when idle ports are used. We also demonstrate that when m = n, the number of rearrangements is reduced to one at most, regardless of the values of n and r, while typical Clos networks require r  1 rearrangement in worst-case scenarios. Finally, we show that m in the wide-sense non-blocking bidirectional Clos network can be approximately 25% lower than in the conventional strictly non-blocking Clos network. With this result, the architecture can be applicable to three stage clos networks where the size of the middle switches is larger than that of inputs and outputs stages.



Switch network, Three-stage clos network, Non-blocking condition, Bidirectional switches, Rearrangeable non-blocking switch, Wide-sense non-blocking switch


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  • APA:
    Koloko,L.& Obara*,H.(2021). Applying Bidirectional Crossbar Switches with Extra Sets of Inlets and Outlets to Three-Stage Clos Networks. International Journal of Energy, Information and Communications, 12(1), 1-14. 10.21742/IJEIC.2021.12.1.01
  • Harvard:
    Koloko,L., Obara*,H.(2021). "Applying Bidirectional Crossbar Switches with Extra Sets of Inlets and Outlets to Three-Stage Clos Networks". International Journal of Energy, Information and Communications, 12(1), pp.1-14. doi:10.21742/IJEIC.2021.12.1.01
  • IEEE:
    [1] L.Koloko, H.Obara*, "Applying Bidirectional Crossbar Switches with Extra Sets of Inlets and Outlets to Three-Stage Clos Networks". International Journal of Energy, Information and Communications, vol.12, no.1, pp.1-14, Nov. 2021
  • MLA:
    Koloko Labson and Obara* Hitoshi. "Applying Bidirectional Crossbar Switches with Extra Sets of Inlets and Outlets to Three-Stage Clos Networks". International Journal of Energy, Information and Communications, vol.12, no.1, Nov. 2021, pp.1-14, doi:10.21742/IJEIC.2021.12.1.01


  • Volume 12, No. 1, 2021
  • ISSN(p):2093-9655
  • ISSN(e):2652-1989
  • Published:Nov. 2021