The Photonic Technologies Impact on the Next Generation Network

Wireless Personal Communications17: 311–322, 2001.© 2001Kluwer Academic Publishers. Printed in the Netherlands.

The Photonic Technologies Impacton the Next Generation Network

YUKOU MOCHIDA, TOSHITAKA TSUDA and HIDEO KUWAHARANetwork Systems Laboratories, Fujitsu Laboratories Ltd., Kamikodanaka 4-1-1, Nakahara-Ku, Kawasaki,211-8588, JapanE-mail: [email protected]

Abstract. This paper describes the possible impact of photonic technologies on the next-generation network.With the explosion of the Internet (IP), the capacity demand is increasing exponentially, which exceeds Moor’slaw. The next-generation IP network should sustain this increase. This paper shows the possible node processingbottleneck even the transmission capacity can be supported by the use of WDM technology. Based on this analysis,the paper proposes a virtual router network as a solution, which applies a logical full-mesh connection based onsalient features of photonic network technology. Development of the WDM technology sets the target at 1000wavelengths on a fiber so that a dynamic wavelength routing function is becoming available. The increase inwavelengths, transparency among wavelengths, and the wavelength routing function can provide an optical path,which forms the base of a logical full-mesh structure and also provides an easy migration scenario from the currentnetwork to the next-generation IP network. The possibility is examined by calculation using a bi-directional loopnetwork as an example. As the foundation of the proposal, the current status of photonic network technologies isdescribed with future projection.

Keywords: photonic network, next-generation network, routing, label switching, virtual router view network, edgenode, node cut-through, WDM transport, wavelength channel, optical add/drop, optical cross-connect, wavelengthrouting, AOTF, tunable LD.

1. Background

Because of the explosive increase in internet (IP) traffic, the network for the 21st century needsto be tailored to IP traffic. Among the many requirements for such a network, a cost-efficientbroadband packet transmission and the provision of an appropriate QoS (Quality of Service)for different services are necessary conditions.

Photonic networking technology based on WDM (Wavelength Division Multiplex) isshowing rapid progress. WDM achieves a transmission capacity increase linearly dependenton the wavelength number, provides wavelength transparency which enables transmission ofdifferent transport formats with different bit rates on a fiber, and also provides a switchingfunction with wavelength as the key information. These salient features can be a powerfultool to achieve a next-generation network requiring low cost, wide bandwidth, and QoS.

This paper describes the possible impact of photonic technology on next-generation net-works and the current status of photonic technology. Section 2 describes the trend of trafficincrease and transmission technology in comparison with Moor’s law, and shows the possibleprocessing bottleneck at the node. In Section 3, we propose a virtual router network structureas a countermeasure, which utilizes logical full-mesh connections based on photonic networkfeatures. To show the possibility of constructing a fully meshed network, some calculation

312 Yukou Mochida et al.

Figure 1. Traffic in Japan.

Figure 2. Technology development.

results will be shown based on a bi-directional ring network. In Section 4, the latest status andfuture projection of photonic technologies are described.

2. Traffic Increase and Technology Trend

The total amount of information in Japan estimated by Nikkei is shown in Figure 1. The dottedline indicates Moor’s law, which is the technology advancement index of a semi-conductorachieving 1.6 times improvement every year. Due to the expansion of IP traffic, the totalamount of information is estimated to grow exponentially, showing a good match with Moor’slaw or even larger. Figure 2 shows our optical transmission R&D, again in comparison withMoor’s law. Owing to the technology, the transmission capacity increase in an optical fibermade a jump which exceeds Moor’s law and is good enough to cover the capacity demand.

The Photonic Technologies Impact on the Next Generation Network313

Figure 3. Virtual router view network.

Even the transmission capacity is ready for the capacity demand; since the capacity demanditself exceeds Moor’s law, one of the key problems in constructing the next-generation networkis switching/routing node implementation. The node implementation cannot be achieved if itdepends on the semi-conductor technology progress. Another factor that makes the situationmore critical is that processing at the node is becoming more complex, such as layer 4 routing,and the required processing power improvement is more than the ratio of the increase in thetraffic. A fundamental change in network architecture is necessary to solve the problem. Ourproposal is to make a network paradigm shift toward a virtual router view network, fullyutilizing the salient features of photonic networking technology. This is described in detail inthe next section.

3. Virtual Router View Network Based on Photonic Technology

Figure 3 shows a virtual router network as a paradigm of the next-generation network. It is oneapproach to making the total public network seen as a virtual single router. The IP packet isterminated and processed at the ingress and egress edge node, and the internal transfer of theIP packet is done in a more efficient manner, like layer 2 label switching or layer 1 wavelengthrouting, then releasing the IP data from the hop-by-hop processing. The Best effort path andthe Guaranteed path are prepared, and each IP packet is properly assigned to the appropriatepath at the edge node. The guaranteed path may be provided by IP QoS routing, but the use


Figure 4. Round trip delay.

of different transport mechanisms, such as using ATM, is another possibility. The photonicnetwork forms the foundation of the transport network.

The node cut-through by wavelength routing and the accommodation of different transportsystems by wavelength transparency are used. Wavelength transparency is the nature that theWDM system can provide, keeping independence among different wavelengths. With thisnature, different transport systems, different bit rates, and different QoS class paths can berealized by assigning different wavelengths and can be accommodated in a single fiber.

Most of the intelligence is moved to the edge node and the core consists of a simple, veryhigh-capacity data transport mechanism.

To examine the possible performance improvement obtained with this architecture, we car-ried out a preliminary study. Figure 4 shows the result of the round-trip delay time measuredby PIN command. Linear increase and large variation are observed with the increase in thenumber of hops for the current hop-by-hop network. In the virtual router network, as wasexpected, the delay time stays small. The variation is also small owing to the cut-througheffect.

The node cut-through technology based on the wavelength can also release the node fromthe increase in processing power requirement, because this technology off-loads the unnec-essary routing processing. The node cut-through can be realized by making a network witha logical full-mesh structure. Then, only the traffic terminated at the node is processed andthe transfer traffic just cuts through the node without applying any routing processing. Thisapproach has been considered economically impractical. However, WDM technology has


Table 1. Number of nodes as a function of wave number.

Number of wves 128 256 512 1024

Nodes is a loop 32 45 64 90

Nodes in double layered loop 1024 2025 4096 8100

changed the situation. Because of the independent nature among different wavelengths calledtransparency, multiple independent optical wavelength channels can be provided on one fiber.A total of 256 optical wavelength channels are within reach, and the target is set at 1000. Inaddition, the optical add/drop function and the cross-connection function are available, whichroute optical wavelength channels using wavelength information as a routing key. These en-able wavelength path provisioning on a fiber, which drops only necessary optical wavelengthchannels for termination at the node by way of optical wavelength routing.

Table 1 shows the possible number of full-mesh configured nodes on the double-loop net-work shown in Figure 5. The calculation assumes a bi-directional transmission and wavelengthreuse. When the 1024 wavelength becomes available, even the simple double-loop structurecan construct a full-mesh network having 90 nodes and the two-layered loop network structurecan construct a network having more than 8000 nodes, with each layer having a full-meshstructure.

When more nodes are requested, a space-division technique using more fibers can be ap-plied. Therefore, a logical full-mesh configuration is a technically realistic solution and helpsmake the network simple and the node implementation feasible and economical.

Another impact that photonic technology can have is that the multi-service network whichsupports multiple transport and switching systems becomes feasible on one fiber. This isbecause of the wavelength transparency.

Figure 6 shows a concept of a photonic network.The multi-service network gives flexibility in two ways; the first being that the most suit-

able transmission/routing system for the required QoS can be used, and the second being tohelp the smooth migration of the network. Because of the expansion of IP services, servicessuch as mission-critical application and real-time stream service require different servicequality than the best effort. This may be accomplished by improving the router, althoughthe use of a multi-service network is another candidate for a public network solution. Figure 7shows the evolutionary steps of a photonic network. It started with WDM transmission, thenOADM was deployed to make an optical loop. The optical cross-connect will be the next stepand will connect optical loops to configure a large-scale network. The final step will be anoptical router starting with wavelength routing, and followed by optical packet switching asthe ultimate solution.

4. Photonic Network R&D Status

4.1. WDM TRANSPORT

Amplifier technology is the basis of a photonic network. The first-generation Erbium-dopedfiber amplifier (EDFA) has a gain in the so-called “conventional” (C) band of 1,530 to1,570 nm. The second-generation amplifier, gain-shifted EDFA, extends available bandwidth


Figure 5. Water reuse.

Figure 6. Photonic network.


Figure 7. Evolutionary steps.

Figure 8. C + L band amplifier.

to the longer wavelength region of 1,570 to 1,610 nm, which is often called the “L-band”. Acombined C + L band was then developed, an example of which is shown in Figure 8. Thisexample shows WDM with 64 wavelengths having 0.8 nm spacing. It has been reported,however, that 170 wavelengths are possible if 0.4 nm spacing is used. R&Ds are aimingtowards 1000 wavelengths by further narrowing the wavelength spacing and also developingan optical amplifier which can cover a shorter wavelength band with Raman amplifiers. The256 wavelength WDM is already within reach, and the 1000 wavelength will become availablewithin a few years.

4.2. WAVELENGTH ROUTING TECHNOLOGIES

The OADM (Optical Add Drop Multiplexer) is the functional block which drops the desiredwavelengths from received WDM signals, and makes the remaining wavelengths go throughfor further transmission. At the same time, using the dropped wavelengths, new signals fromthat node are added to WDM signals. This function helps realize our proposed full-mesh


Figure 9. AOTF configuration and main characteristics.

optical path network. The fixed wavelength type OADM, which adds and drops the predeter-mined wavelengths, is already on the market, and dynamic type OADMs, which can changethe add and drop wavelengths, are under development. The key devices are a tunable filter anda tunable Laser Diode (LD). We are developing the Acousto-Optic Tunable Filter (AOTF),which appears to be a promising device. Figure 9 shows the structure and the key parametersof the AOTF. With the AOFT, by adding a high-frequency control signal around 170 MHz,the corresponding wavelength to control signal is selected to come out from the drop port,while the remaining wavelengths come out from the through port. By adding multiple controlsignals, multiple wavelengths are selected. Figure 9 shows the operation by adding 16 controlsignals. The performance parameters show good filter performance, which is applicable to thereal system. Wide tunable range is good enough to cover both the C and L bands.

Figure 10 shows an example of a tunable LD. In this example, 8 LD Array, optical coupler,and semiconductor optical amplifier are monolithically integrated on one chip. Each LD has atunable range of more than 400 GHz, which is equivalent to 4 wavelengths of 100 GHz span,and the total module can cover 32 wavelengths.

An optical cross-connect switch (OXC), which exchanges wavelength path among manyfibers, is another important wavelength routing functional block.

In the OXC, the input signal in each port is wavelength-demultiplexed and then switched ina spatial switch to change the route and multiplexed again into the output port for transmission.OXCs are commercially available, but at present the number of ports is limited around 32 by32 or 64 by 64. We have demonstrated a 32 by 32 port OXC using PILOSS optical switch,and are now expanding the scale to 256 by 256.

In summary, the projection of photonic network technology progress is shown in Figure 11.


Figure 10. Tunable LD.

Figure 11. Optical technology road map.

5. Conclusion

Based on the analysis, this paper pointed out a possible bottleneck of the node-processingpower for the next-generation IP network. We proposed a virtual router view network, whichuses a logical full-mesh network configuration based on the WDM photonic network. Weshowed that the simple bi-directional double-loop can accommodate 90 nodes when 1000wavelengths become available. The latest R&D status of photonic network technologies wasalso described as the foundation of the proposal. More work is needed to make the proposala reality; however, as proposed in this paper, but we are at the stage of taking new steps inpreparing for the explosion of IP traffic in the 21st century. Photonic technology will be thepowerful tool.


References

1. H. Kuwahara et al., “Photonic Network Architecture towards 1000 Wavelengths”, inTelecomm’99 Forum,Oct. 1999.

2. Y. Mochida, “Recent Achievements in Advanced Optical Networking Technology and Forward View”, inPlenary, NOC’98, 1998, p. 11.

3. “Special Issue on Photonic Networks”,Fujitsu Scientific and Technical Journal, Vol. 35, No. 1, 1999.4. T. Naito et al., “1 Terabit/s WDM Transmission over 10,000 km”, inPost Deadline Paper, OECC’99, Sept.

1999.5. T. Nakazawa et al., “Ti:LiNbO3 AOTF for 0.8 nm Channel Spaced WDM”,Post Deadline Paper PD-1,

OFC’98.

Yukou Mochida received his B.S. and Ph.D. degrees from the University of Tokyo in 1964and 1988, respectively. He joined Fujitsu Laboratories in 1964 and developed digital trans-mission and processing systems, including Gbit/s DWDM systems. Dr. Mochida is a seniorvice president of Fujitsu Laboratories Ltd. His responsibilities include next-generation inter-net, photonic networks, and mobile systems. He is a member of IEEE and the Institute ofElectronics, Information and Communication Engineers of Japan.


Toshitaka Tsuda was born in 1947 in Fukuoka, Japan. He received his B.S., M.S., andPh.D. degrees in electrical engineering from the University of Tokyo in 1979, 1972, and1975, respectively. He joined Fujitsu Laboratories Ltd. in 1975, where he was engaged inR&D of digital signal processing, picture coding, ISDN transmission, optical transmission,packet switching, and computer architecture. From 1978 to 1979, he was with the Universityof California, Berkeley, as a research associate. Currently, he is a member of the board ofFujitsu Laboratories Ltd. He is also a senior member of IEEE and a member of IEIEC.

Hideo Kuwahara was born in 1948. He received his B.S., M.S., and Ph.D. degrees in electri-cal engineering from the University of Tokyo in 1972, 1974, and 1984, respectively. In 1974he joined Fujitsu Laboratories where he was engaged in R&D of fiber, semiconductor lasers,ISDN, subscriber loop systems, coherent transmission systems, optical amplifier technology,high-speed gigabit systems, submarine systems, optical amplifier systems, WDM systems,and next-generation photonic networks. Currently, he is a senior vice president of PhotonicNetwok Laboratory, Fujitsu Network Communications, Inc.

Dr. Kuwahara is a senior member of the Institute of Electrical and Electronics Engineers(IEEE) and a member of the Institute of Electronics, Information and Communication Engi-neers (IEICE) of Japan. He received the Sakurai Memorial Award from the OptoelectronicIndustry and Technology Development Association (OITDA) in 1990 and the Achievement


Award from IEICE of Japan in 1998 with his experimental realization of optical terabit trans-mission. He is serving as a technical program committee member of the European Conferenceon Networks & Optical Communications (NOC) and as an organizing committee member ofthe Optoelectronics and Communications Conference (OECC).

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The Photonic Technologies Impact on the Next Generation Network