Optical Hub Network –proposal and implementation- Jun-ichi Mizusawa(mizu@it.aoyama.ac.jp)

Aoyama Gakuin University, 5-10-1 Fuchinobe Sagamihara-shi Kanagawa-ken Japan 229-8558 Takayuki Sugeta(sugeta@e-lambdanet.com)

E-LambdaNet Corporation, 2-12-24 Yaei Sagamihara-shi Kanagawa-ken Japan 229-0029

Abstract: FTTH is now being rapidly introduced in Japan. NTT is

planning to demonstrate NGN test services. Neither service meets Cyber Hospital requirements. We are a co-operative working group combining two universities and a small venture company. Working with a research grant from MIC (Ministry of Internal Affairs and Communications), we are now developing a fiber based high speed network tentatively named the “Optical Hub Network”. Requirements, specification, network operation and test bed data are described. 1. INTRODUCTION

The purpose of the Optical Hub Network is to implement a new type of city area network using dark fibers, and to provide a service which until now has been difficult to provide with FTTH or NGN. We expect it will be a good example of a city or metropolitan area network infrastructure in the near future.

Our group is composed of three members: a technical department of Aoyama Gakuin University, a medical system research department of Kitasato Medical University and a small venture company: E-LambdaNet Corporation.

The specification requirement comes from the medical university. Japan is now facing an increasingly aging population. The national social security budget is increasing every year, so improved hospital services are required. The medical university has a plan to implement a so-called Cyber Hospital. The idea is to have networking among several big main hospitals and many small hospitals over one city area “Sagamihara-city” where two universities are located. 2. REQUIREMENTS

If a small hospital can have better medical advice from a medical specialist group working in a big hospital, it will contribute to improved medical services. The question is what types of network services are required. Here are three vital areas: (1) High volume medical contents should be smoothly transferred through a network. (2) Low latency network transmission for a high definition digital camera moving images. (3) High speed radio transmission to a hospital from an ambulance.

To solve these problems, applying the up-coming NGN service might be one solution. For the moment, however, a hospital system application is not expected as an NGN killer application. It seems that no NGN services provider is currently expecting such high speed

city area networking to play a major role in Japan. 3. DESIGN ISSUES

Conventional FTTH, i.e., PON system has the following issues to be solved. (1) Media access methods are not equal for all users as we see in Ethernet, so system enhancement depends on a carrier’s investment. (2) PON applies a time-share scheme and it is strictly controlled from the head end. This means it limits the flexibility for communication speed selection, that is, a client cannot select communication speed. (3) Where a large capacity link is required, CWDM technology is applied to a FTTH fiber because the cost is considered reasonable. But, a new light wave channel has been added independently from the PON scheme. So a PON system that has the possibility of plural wave channels selection has not yet been introduced commercially. This results in a PON client’s communication capacity increase being limited.

Our proposed Optical Hub Network meets the challenge of solving these issues using the following design principles: (a) Introduce an equal media access scheme via an Optical Hub which delivers all optical inputs to all outputs equally. (b) The network scale could be extended by applying plural Optical Hub connections. This requires the introduction of SOA to compensate optical signal losses. (c) CWDM or DWDM is introduced to provide high speed communication. (d) The Optical Hub Network has two access modes, i.e., DA (Dedicated Access) and MA (Multiple Access). (e) The MA mode allows all terminals to share the Optical Hub Network based on the Ethernet 1000BASE-T process. (f) The DA mode assigns a connection between terminals by means of a time slot and a wavelength allocation. 4. TEST BED DESIGN

The test bed (named APN2; Aoyama Gakuin Univ. Network2) has four routers interfacing with our campus network. The purpose of an overlay network structure is to carry high bit rate streams such as HDV on APN2, and internet access via the campus network. The router, located between APN2 and the campus network, identifies these traffic types for routing. So APN2 routers run by FreeBSD and some part of the routing algorithm

has been modified. Still we need further research for a better routing operation. The APN2 framework is as follows: (1) An Optical Hub Network has 2 key components: an Optical Hub (OHUB) and an Optical Network Interface Card (ONIC). For the moment, this is a box rather than a card. (2) The test bed has one OHUB and four ONICs. Four ONICs are connected to each other via an OHUB and optical fibers as Figure 1 shows. (3) The OHUB has 4 in-ports and 4 out-ports. One light signal entered to an in-port is distributed equally to 4 out-ports as Figure 2, right, shows. (4) The ONIC has the functions of E/O, O/E, and input/output electronic signal line selection. It also has a function of a timeslot and wavelength allocation for OHUB fiber lines. For the test convenience, the allocation order comes from Scheduler which provides a time and wavelength matrix to ONIC.

The Test Bed operation is designed as follows: (1) There are two domain axes: “time” and “optical wave length”. Here, the minimum switching time between timeslots is one millisecond. Time synchronization is controlled by having a GPS 1ms signal when necessary. Four wavelengths, 1.53, 1.55, 1.57, 1.59 microns, are selected from a CWDM. Each wavelength has the capacity for 2.5Gbps transmission. (2) When the ONIC receives an information transfer request from a client terminal, it selects one available slot between a source ONIC and a destination ONIC. The slot could be one wavelength, one time slot, or a combination of time and wavelength. (3) Here “the time and wave matrix (TWM)” is the key network routing information, i.e., it allocates Optical Hub Network resources for all source/destination connections. (4) In the case of the Test Bed, TWM is given from Scheduler at present. We plan to implement a distributed processing algorithm as the Ethernet provides ARP among all joining terminals. (5) The Test Bed has MA and DA modes. (6) MA is an access to a slot where multiple ONICs are allowed access. Access control is performed on an optical level at ONIC fiber input/output. So an optical signal does not transfer on a fiber between ONICs/OHUB when no data signal transmission is

necessary. (7) DA allows access to a slot where access is dedicated to a pair of ONICs by TWM.

The Optical Hub Network is physically an optical broadcast network. The Test Bed applies 1000BASE-T to provide both broadcast and unicast services on it by means of an ONIC control. 5. TEST BED RESULTS

We have confirmed that two types of DA connections, i.e., the high speed transmissions are available as Figure 1 shows. (1) HDMI transmission (2) HDV IEEE1394 transmission We are half way to implementing MA connection. The key issue which limits the network capacity is the optical signal loss budget. The design parameters are as follows. -OHUB has 4 ports. Insertion loss=12dB -ONIC LD; Pout=0.0 to 5.0 dBm, -ONIC PIN-PD Pmin< -18dBm

So, a one stage OHUB connection between ONICs does not require optical signal amplification.

When we consider tandem connection of OHUBs, an optical amplifier is indispensable for OHUB. We are currently evaluating SOA capability [1]. Our tentative data shows it has approximately 20dB gain. Further study is necessary for successful Optical Hub Network design. 6. CONCLUSION

We have proposed an Optical Hub Network. It consists of two major components, an Optical Network Interface Card and an Optical Hub. Our Test Bed APN2 is presented in terms of a network structure and an operation design. It has two access modes, multiple access (MA) and dedicated access (DA). APN2 is now possible to demonstrate two types of high speed stream transmission. The critical design parameter is the optical loss budget and we are working on how to apply SOA to solve the problem. REFERENCES [1] Iannone, P.P., Reichmann, K.C., and Spiekman, L.H., 2003b. “Amplified CWDM Systems”, Proc. Lasers and Electro-Optics Society Annual Meeting 2003, vol.2, pp.678-679 [2]M.Akiyama, K.Tada, J.Mizusawa ”Photonic Switching System”, IEICE. Trans. Vol.E74. No.1, pp84-92,1991 Acknowledgement: This research is funded by SCOPE (Ministry of Internal Affairs and Communications, Japan

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