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Exploiting AWG Free Spectral Range Periodicity in Distributed Multicast Architectures

Kamran Keykhosravi, Houman Rastegarfar, Nasser Peyghambarian, Erik Agrell

TL;DR

This paper tackles interdomain bottlenecks in AWG-based distributed multicast switches by exploiting multiple AWG free spectral ranges (FSRs) with a multi-FSR scheduling approach. It develops a general analytical framework to estimate blocking probabilities and validates it against Monte Carlo simulations, demonstrating significant interdomain BP improvements when increasing the FSR count up to about $F=4$. A cross-layer analysis incorporating pulse amplitude modulation (PAM) and rate-adaptive forward error correction (FEC) shows that higher FSR counts reduce bit-error rates and increase effective throughput, with 4-PAM often delivering the best performance. The work provides a path toward scalable, wavelength-reuse optical interconnects for data centers and 5G fronthaul by addressing interdomain capacity while quantifying the trade-offs between hardware complexity and performance.

Abstract

Modular optical switch architectures combining wavelength routing based on arrayed waveguide grating (AWG) devices and multicasting based on star couplers hold promise for flexibly addressing the exponentially growing traffic demands in a cost- and power-efficient fashion. In a default switching scenario, an input port of the AWG is connected to an output port via a single wavelength. This can severely limit the capacity between broadcast domains, resulting in interdomain traffic switching bottlenecks. In this paper, we examine the possibility of resolving capacity bottlenecks by exploiting multiple AWG free spectral ranges (FSRs), i.e., setting up multiple parallel connections between each pair of broadcast domains. To this end, we introduce a multi-FSR scheduling algorithm for interconnecting broadcast domains by fairly distributing the wavelength resources among them. We develop a general-purpose analytical framework to study the blocking probabilities in a multistage switching scenario and compare our results with Monte Carlo simulations. Our study points to significant improvements with a moderate increase in the number of FSRs. We show that an FSR count beyond four results in diminishing returns. Furthermore, to investigate the trade-offs between the network- and physical-layer effects, we conduct a cross-layer analysis, taking into account pulse amplitude modulation (PAM) and rate-adaptive forward error correction (FEC). We illustrate how the effective bit rate per port increases with an increase in the number of FSRs. %We also look at the advantages of an impairment-aware scheduling strategy in a multi-FSR switching scenario.

Exploiting AWG Free Spectral Range Periodicity in Distributed Multicast Architectures

TL;DR

This paper tackles interdomain bottlenecks in AWG-based distributed multicast switches by exploiting multiple AWG free spectral ranges (FSRs) with a multi-FSR scheduling approach. It develops a general analytical framework to estimate blocking probabilities and validates it against Monte Carlo simulations, demonstrating significant interdomain BP improvements when increasing the FSR count up to about . A cross-layer analysis incorporating pulse amplitude modulation (PAM) and rate-adaptive forward error correction (FEC) shows that higher FSR counts reduce bit-error rates and increase effective throughput, with 4-PAM often delivering the best performance. The work provides a path toward scalable, wavelength-reuse optical interconnects for data centers and 5G fronthaul by addressing interdomain capacity while quantifying the trade-offs between hardware complexity and performance.

Abstract

Modular optical switch architectures combining wavelength routing based on arrayed waveguide grating (AWG) devices and multicasting based on star couplers hold promise for flexibly addressing the exponentially growing traffic demands in a cost- and power-efficient fashion. In a default switching scenario, an input port of the AWG is connected to an output port via a single wavelength. This can severely limit the capacity between broadcast domains, resulting in interdomain traffic switching bottlenecks. In this paper, we examine the possibility of resolving capacity bottlenecks by exploiting multiple AWG free spectral ranges (FSRs), i.e., setting up multiple parallel connections between each pair of broadcast domains. To this end, we introduce a multi-FSR scheduling algorithm for interconnecting broadcast domains by fairly distributing the wavelength resources among them. We develop a general-purpose analytical framework to study the blocking probabilities in a multistage switching scenario and compare our results with Monte Carlo simulations. Our study points to significant improvements with a moderate increase in the number of FSRs. We show that an FSR count beyond four results in diminishing returns. Furthermore, to investigate the trade-offs between the network- and physical-layer effects, we conduct a cross-layer analysis, taking into account pulse amplitude modulation (PAM) and rate-adaptive forward error correction (FEC). We illustrate how the effective bit rate per port increases with an increase in the number of FSRs. %We also look at the advantages of an impairment-aware scheduling strategy in a multi-FSR switching scenario.

Paper Structure

This paper contains 10 sections, 1 theorem, 19 equations, 6 figures, 2 tables.

Table of Contents

  1. Introduction
  2. A Multi-FSR Scheduling Algorithm
  3. Blocking Probability Analysis
  4. Blocking probability in a star coupler
  5. Interdomain blocking probability with $F=1$
  6. Interdomain blocking probability with $F=2$
  7. Intradomain blocking probability
  8. Numerical validation
  9. Cross-Layer Performance Analysis
  10. Conclusion

Key Result

Lemma 1

Each of the $K_{\mathrm{in}}$ connection requests is blocked with probability Here, the random variable $\mathbf{n}_{\mathrm{idle}}$ is the number of idle output ports, whose average is

Figures (6)

  • Figure 1: A distributed multicast architecture based on star couplers and AWG rastegarfar2017PAM. SOA: semiconductor optical amplifier. EDFA: erbium-doped fiber amplifier. WSS: wavelength selective switch.
  • Figure 2: Interdomain BP $b_{\mathrm{inter}}$ of the switch in Fig. \ref{['fig:Top']} for $F\in\{1 , 2 , 4 , 8 \}$. Analytical approximations for $F=1$ and $F=2$ are plotted based on \ref{['btotal_FSR1']} and \ref{['btotal_FSR2']}, respectively. The BP for a single coupler with $64$ ports, evaluated via simulations and Lemma \ref{['lemma:1']}, is also included for comparison.
  • Figure 3: Intradomain BP $b_{\mathrm{intra}}$ of the switch in Fig. \ref{['fig:Top']} for $F\in\{1 , 2 , 4 , 8 \}$. Analytical approximations for $F=1$, $F=2$ as well as for $F\geq 8$ are also plotted.
  • Figure 4: Transmission path of (a) interdomain and (b) intradomain traffic for the switch in Fig. \ref{['fig:Top']}.
  • Figure 5: BER for (a) 2-PAM, (b) 4-PAM, and (c) 8-PAM for $F = 1 , 2 , 4 , 8$.
  • ...and 1 more figures

Theorems & Definitions (2)

  • Lemma 1
  • proof