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Current metropolitan area networks (MANs) based on the SONET transport are not developing at the rate required to support the phenomenal increase in data traffic. To address the needs of future MANs, the Optical Communications Research Laboratory at Stanford University and Sprint Advanced Technology Laboratories are building HORNET (Hybrid Optoelectronic Ring NETwork). HORNET has a multiple access architecture, in which nodes access any WDM channel using a novel media access control protocol and fast tunable laser transmitters. HORNET transports data packets directly over the WDM ring, eliminating the SONET transport. This paper presents the HORNET architecture, the node design consisting of novel packet-over-WDM components, and the experimental testbed with results.

To cost-effectively address the phenomenal demand for bandwidth in the metropolitan area, the Optical Communications Research Laboratory at Stanford University and Sprint Advanced Technology Laboratories have developed a novel architecture for a large-scale metropolitan area network (MAN). The network, which is called HORNET, is a packet-over-WDM multiple-access network featuring the use of fast-tunable transmitters and a novel “CSMA/CA” media access protocol to improve network efficiency well beyond that of today’s solution. This paper presents the design and implementation of the network architecture and gives an analytical discussion of its advantages.

Hybrid opto-electronic ring network (HORNET) is a novel packet-over-WDM multiple-access network designed by the Stanford Optical Communications Research Laboratory (OCRL) to provide efficient bandwidth sharing among a large number of access points (APs) in a metropolitan area. The HORNET network eliminates the cost and complexity of SONET equipment by transmitting IP/ATM packets directly over the wavelength division multiplexing (WDM) layer. To improve performance above that of a conventional ring network, HORNET employs a multiple-access architecture using fast tunable transmitters and a novel carrier-sense multiple-access with collision avoidance (CSMA/CA) media access control (MAC) protocol. The OCRL has constructed a testbed to demonstrate the ability of a HORNET AP to transmit packets using a fast-tunable transmitter and a novel MAC protocol and to asynchronously receive packets in the packet-over-WDM architecture. The experimental results confirm that HORNET successfully achieves the following functions: 1) fast (low overhead) wavelength tuning using a fast-tunable transmitter; 2) collision-free packet transmission over a multiple-access network via the CSMA/CA MAC protocol; and 3) fast clock and data recovery using the embedded clock tone (ECT) technique.

The hybrid optoelectronic ring network (HORNET) is a novel packet-switched wavelength-division-multiplexed metropolitan area network (MAN). HORNET uses a combination of optical and electronic packet-switching and an optical carrier sense multiple access with collision avoidance (CSMA/CA) media access scheme to efficiently provide large bandwidth to many users. The HORNET optical packets consist of 2.5-Gb/s payload data, an embedded 2.5-GHz clock tone, and a subcarrier-multiplexed (SCM) header for CSMA/CA. We are constructing an experimental testbed to demonstrate the ability of HORNET nodes to transmit and receive packets, to recover the destination node address carried by the SCM header, and to perform fast clock and data recovery with minimal overhead within the HORNET packet receiver.

The bursty nature of traffic in metropolitan area networks results in underutilized and inefficient SONET networks. The hybrid optoelectronic ring network (HORNET) is a network being developed at the Optical Communications Research Laboratory at Stanford University to address the problems of SONET transport in metropolitan area networks (MAN's). HORNET performs packet switching using a fast-tunable wavelength transmitter, which hops to different wavelengths on a packet-by-packet basis. In this letter, we present simulation results which quantify the benefits of a wavelength tunable transmitter in a packet switched wavelength-division-multiplexed MAN. We show that a tunable transmitter is able to take advantage of imbalances in wavelength utilization, and provides a 45% improvement in packet latency characteristics. We also show that in order to maintain these benefits the tuning time of the transmitter cannot exceed 10% of the packet transmit time.

The impact of crosstalk in an arrayed-waveguide (AWG) router on the performance of an N-channel optical add-drop multiplexer (OADM), with m add/drop channels and n-pass channels is theoretically investigated. A single arrayed-waveguide router is simultaneously used for multiplexing and demultiplexing. This results in crosstalk not only from the incoming channels, but from the outgoing channels as well. We show that the performance of the OADM degrades as either N or m are increased, suggesting that the number of channels in a network based on OADM's is limited by crosstalk in the AWG router. When an optical filter is added at the output of the OADM the digital signal-to-noise ratio Q is independent of N and m, and within a few tenths of a decibel of the perfect filtering case.

The Stanford OCRL has designed HORNET-a novel optical packet-switched WDM MAN. The key advantages of HORNET are efficient bandwidth sharing among a large number of users and lower equipment cost than SONET. We are constructing an experimental testbed to investigate the capabilities of HORNET. The experimental results confirm the HORNET node's ability to transmit and receive optical packets with better than 10/sup -9/ BER, to correctly route packets according to their recovered destination node address carried by subcarrier signals, and to effectively handle data clock recovery on a packet-by-packet basis. The network simulation results on the queue depth and the packet latency prove the benefits of the VOQ over the single FIFO queue at heavy traffic load.

Channel crosstalk generates signal beat terms that reduce the digital SNR at the receiver. The digital SNR falls off with the size of the OADM and the number of add/drop channels, suggesting that the number of channels in a network is limited by crosstalk in the AWG router. With an optical filter added at the output of the AWG router the digital SNR is independent of the total number of channels in the network and the number of add/drop channels.

As data traffic increases exponentially, IP over WDM transport will replace conventional SONET transport in metropolitan area networks. Such networks will require new media access control (MAC) protocols to efficiently share network bandwidth among multiple network nodes. This paper describes and evaluates novel and practical carrier sense multiple access with collision avoidance (CSMA/CA) MAC protocols for IP over WDM ring networks that handle variable size IP packets without complex variable optical delays or centralized algorithms. Simulation results show that the proposed IP-MAC protocols are efficient and comparable to our selected benchmark and will be implemented in the IP-HORNET testbed.

Future Internet technologies will cause an evolution in metropolitan area networks throughout the following decades. To keep pace with the development of Internet access technologies and devices, we have created a novel architecture called HORNET. Through the use of ultra-fast tunable transmitters and packet-over-WDM technology, HORNET is optimized for the metro area traffic of the future. We have developed a novel media access protocol and a novel survivability protocol for HORNET that we describe here. Also, we have generated successful experimental results, including a demonstration of the media access protocol and 4-ns wavelength switching durations in the tunable transmitter.

Summary form only given. Over the last years tunable lasers have been developed rapidly due to the advantage they can provide for WDM systems. Traditional 1:1 protection of the systems requires a spare optical transceiver for each working one. Tunable transceivers can reduce total system cost by providing 1:N protection with one tunable transceiver acting as a backup for N working transceivers. At the same time, fast tunable lasers can improve QoS by permitting dynamic wavelength allocation. The two-section DBR (distributed Bragg reflector) laser diode chip is discretely tuned between 7 wavelengths with a nominal channel spacing of 100 GHz over a 5.2 nm range.

Building on well-known Stanford experimental WDM networks — STARNET and CORD — the Optical Communications Research Laboratory (OCRL) at Stanford has continued to investigate future WDM networks. In this paper, we describe two new Stanford experimental networks, LEARN and HORNET. LEARN is a reconfigurable circuit switched WDM experimental network interconnecting the campuses of Sprint Advanced Technology Laboratories (An) in Burlingame, CA and Stanford OCRL in Stanford, CA. HORNET is a hybrid optoelectronic packet-switched WDM networking experiment designed to overcome the limitations of circuit switching. We discuss lessons learned from past Stanford projects and describe challenges to be met in the future concerning WDM metropolitan area networks (MANs). Lastly, we describe the approach of Terabit Networks, Inc. to future WDM MANS. Terabit Networks is a new company building on Stanford technology to provide highly efficient high-bandwidth MAN solutions optimized for data traffic.

HORNET is a metro network designed to better face the challenges offered by next generation metropolitan area networks. HORNET uses a packet-over-WDM transport on a bi-directional ring network. Fast-tunable packet transmitters and wavelength routing enable it to scale cost-effectively to ultra-high capacities. A control-channel-based MAC protocol enables the nodes to share the bandwidth of the network while preventing collisions. The MAC protocol is designed to transport variable-sized IP packets and guaranteed bit-rate circuits while maintaining fairness in the network. Survivability protocols protect circuit and best effort traffic against a fiber cut or node failure. A burst mode receiver, in conjunction with the tunable transmitter and constant gain optical amplifiers make up the essential sub-systems inside a node. This article summarizes the accomplishments of the HORNET project, including the design, analysis, and demonstration of the architecture, protocols, sub-systems and testbed. As this work shows, the HORNET architecture is an excellent candidate for next-generation high-capacity metro networks.

We compare several approaches and their tradeoffs to achieving terabit/s transmission in SMF with 40 km and/or 80 km repeater spacing. Capacity and maximum transmission distances in multiple low-loss windows are discussed.

The Optical Communications Research Laboratory (OCRL) at Stanford University and Sprint Advanced Technology Laboratories have designed and constructed an experimental WDM network called LEARN: Lightwave Exchangeable Add/Drop Ring Network. LEARN employs two optical add/drop multiplexers (OADMs), one optical wavelength translating cross-connect (OWTC), and an out- of-band control channel for network management and topology reconfiguration. The structure of OADM and OWTC using array waveguide (AWG) routers is described in detail. The implementations of the out-of-band control network based on two architectures, the server-client and the broker, are compared. The LEARN testbed has demonstrated format and bit-rate transparency.

A novel technique utilizing both WDM and TDM is proposed to reduce FWM crosstalk in the zero-dispersion wavelength region. The effectiveness of our technique is shown by simulations for a 12-channel 2.5-Gb/s per channel WDM system.