Demonstration of Simultaneous Multiplexing/Demultiplexing ...

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Demonstration of Simultaneous Multiplexing/Demultiplexing Operation of an All-Optical 2x2 Packet Switch with Asynchronous Variable-length Optically Labeled 40Gbps Packets H. N. Poulsen (1), W. Donat(1), V. Lal(1), M. L. Masanovic(1) and D. J. Blumenthal(1) G. Epps(2), D. Civello(2), G. Fish(3) and C. Coldren(3) (1) ECE Department, University of California, Santa Barbara, CA 93106, U.S.A., [email protected] (2) Cisco Systems, Inc. (3) JDSU

Abstract We demonstrate simultaneous multiplexing/demultiplexing operation of a 2x2 all-optical packet switch loaded with a random iMix stream of asynchronous variable-length 40Gbps optically-labelled packets. Layer-2 performance shows >95% optical label and >90% packet throughput for both ports. Introduction All-optical packet switching is a promising approach to address the scalability, power and space limitations of electronic router architectures [1, 2]. In order to build packet switches that can operate in real network environments, optical packet switching technology needs to be advanced to address the higher-level functions including statistical de-multiplexing and performance multiplexing. Additionally, measurements must go beyond simple PRBS BER used for transmission systems and full payload and header recovery must be performed to correctly determine that packets are routed to their correct destination with correct payloads. Previously we reported statistical de-multiplexing operation of a 2x2 switch, where each input port was shown capable of demultiplexing an asynchronous stream of variable length packets to both output ports [3]. We also utilized layer-2 measurements to quantify the optical label recovery loss, correct re-written labels detected and correct payloads detected. However, this work did not address the more complex problem of multiplexing asynchronous packet streams from multiple input ports merged onto one output port. In this paper, we report for the first time, to the best of our knowledge, simultaneous multiplexing and demultiplexing operation of a 2x2 all-optical packet switch and measurement of layer-2 performance. The measurements and operation reported here are at a much higher level of difficulty than what has been demonstrated before. As illustrated in Figure 1 (top), both input ports are loaded with variable length asynchronous 40Gbps optically labelled packets which are individually switched (based on asynchronously recovered 1OGbps optical labels) between the two output ports. Since both input ports are active, packets are both being merged from multiple inputs to a common output (multiplexing) and switched from one input to multiple outputs (demultiplexing). Full burst-mode recovery of lOG optical labels and 400 payloads is performed in order to determine the error rate of recovered optical labels (which can lead to misrouted packets) and the

percentage of correctly routed payloads after the forwarding process and the error rate in the re-written optical labels. The 2x2 switch is shown in Figure 1 (bottom). The packet stream is optically tapped and the optical headers asynchronously recovered using a burst mode clock and data recovery (CDR). After optical header recovery/processing a correctly timed erase signal gates a blanking SOA for optical label erasure. The new packet X and a new optical header are computed and sent to the Packet Forwarding Chip (PFC), an InP-based Mach Zehnder Interferometric wavelength converter with on-chip fast tuneable CW laser and header re-write modulator described in [4].

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The electronic processing time in the Electronic Route Processor (ERP) is accounted for by a fixed optical delay (-60m fiber = -300ns). An Arrayed Waveguide Grating Router (AWGR) is used in combination with the PFC to forward the optical packets to the correct egress port on a per-packet basis. Experimental setup The optical packet transmitter generates variable length 40Gbps RZ payloads (40-,1500) bytes with 10Gbps NRZ headers (128 bits). We use a repeating 60 packet long packet stream with a 7:4:1 (iMix "Internet Mixture") packet payload size ratio of 7X40 byte payloads (8ns), 4X570 byte payloads (114ns), and 1X1500 byte long payloads (300ns). The label fields in the optical headers are programmed for packets from ingress port A to be alternately

forwarded to egress ports A and B, and packets from ingress port B to be alternately forwarded to egress ports B and A. A total guard band of lOOns accommodates uncertainty in optical and electrical signal processing times. The focus of this experiment was not to minimize the guard bands and the current values are not representative of a lower limit.

slightly worse with ~-90% being recovered. The main reason for this discrepancy is due to the performance variation between PEG A and B (also seen in the payload performance graphs in Figure 5). The performance of PEG A alone is almost 50% of the combined performance and that of PEG B almost 40%. No additional penalty is incurred when are

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Results and discussion

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The quality of the routed packets is evaluated using80 Layer 2 measurements. Individual packets were recovered, and the number of switched and received the number transmitted. The optical headers are uniquely identified by a 64 bit field and the payloads similarly tagged with a unique identifier. A SHE 50Gbps BERT (10000 series) with 128 Mbit of RAM stores captured data, which is then transferred to a 80 PG for packet by packet comparison. Eigure 2 60 illustrates the variable length optical packet stream conversion after payload and header rewrite at the output of egress port A and B before and after multiplexing the routed packets from ingress ports A and B. There is an extinction ratio inequality between egress ports A and B that originates from the PEG in path B which performed worse than the PEG in path A. This in turn degraded the multiplexed streams from the two PEGs. Egress port A

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VVe have demonstrated for the first time to our knowledge, simultaneous multiplexing/demultiplexing

operation of a 2x2 all-optical packet switch. A random iMix stream of asynchronous variable-length 40Gbps 100ps/diV optically-labelled packets were on-a-per-packet-basis fobnd Combihedotput uptrwarded to the egress ports based on burst mode label detection and processing. Erom each egress port, packets and re-written optical labels are recovered and Layer-2 performance is evaluated Fig. 2. Pulse traces before and after being combined. showing very small packet loss with >95% correctly re-written optical labels and -90% payloads It should be stressed that to achieve these results, the measured for both ports. PEG has successfully performed the following tasks simultaneously: i) wavelength conversion of RZ Acknowledgments payloads at 40Gbps, ii) re-write of NRZ headers at This work is supported by LASOR award #W91IINE10Gbps and iii) switched the wavelength on a per04-9-0001 under the DARPA/MTO DoD-N program. packet basis. Error free packet BER for the PEG has been previously reported [3] and Eigure 4 shows the References corresponding Layer 2 header and payload recovery 1 Blumenthal, D. J, et al., Scientific American, 284 measurements as a function of the input power to the (1), pp. 79-83, (2001) receiver. Back-to-back measurements packet (packet 2 Blumenthal, D. J., in Proc. of EGOG 2005, paper transmitter connected directly to the receiver) as well We2.1.1, Glasgow, Scotland, (2005). as measurements without combining the streams at 3 D. Wolfson et al., in Proc. of EGOG 2005, paper the egress ports are included in the graphs. Eor the Th4.5. 1, Glasgow, Scotland, (2005). latter, the measured input power was adjusted by 3dB FrmIngressPortB

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