社団法人 電子情報通信学会THE INSTITUTE OF ELECTRONICS,INFORMATION AND COMMUNICATION ENGINEERS

信学技報TECHNICAL REPORT OF IEICE.

ハイブリッド型光Add/Dropリングネットワークにおける交換ノードの初期的検証実験

李 慧† 今泉 英明† 種村 拓夫†

中野 義昭† 森川 博之†

†東京大学〒 153–8904東京都目黒区駒場 4–6–1

E-mail: †lihui@mlab.t.u-tokyo.ac.jp

あらまし 本稿では，メトロエリアにおいて将来の多彩なアプリケーションを支援することを目的とし，光回線交換

(OCS)方式と多波長光パケット交換 (MW-OPS)方式を組み合わせたハイブリッド型光 Add/Dropリングネットワーク技

術を提案する．現在メトロエリアでは，OCS方式を基礎とする ROADM (Reconfigurable Optical Add/Drop Multiplexer)

技術を用いたリングネットワークが広く利用されている．ROADM技術では，OCS方式の特徴により QoSを容易に

保証できるが，帯域利用効率の低さが問題となる．一方で，近年登場したバースト交換方式を基礎とするリングバー

スト技術では，高い帯域利用効率を提供できるが，QoS保証を行うにはスロット割当を非常に高い精度で行わなけれ

ばならない．本稿では，双方の利点を同時に実現するために，OCS方式と MW-OPS方式を組み合わせたリングネッ

トワークアーキテクチャを提案し，交換ノードを設計する．120 (12波長× 10) Gb/s交換ノードを実装し，初期的検

証実験を行う．

キーワード メトロエリアリングネットワーク，ハイブリッド光ネットワークアーキテクチャ，多波長光パケット

Preliminarily Demonstration of Hybrid Optical Add/Drop Ring Network

Combining Circuit Switching and Multi-Wavelength Packet Switching

Hui LI †, Hideaki IMAIZUMI †, Takuo TANEMURA†,

Yoshiaki NAKANO†, and Hiroyuki MORIKAWA†

† The University of Tokyo

Komaba 4–6–1, Meguro-ku, Tokyo, 153–8904 Japan

E-mail: †lihui@mlab.t.u-tokyo.ac.jp

Abstract In order to perform an optical network which offers various services for future applications in metro area, this paper

proposes a hybrid optical ring network architecture combing two forwarding paradigms, optical circuit switching (OCS) and

multi-wavelength optical packet switching (MW-OPS). Nowadays, ring networks adapting reconfigurable optical add/drop

multiplexer (ROADM) technology based on OCS are widely used in metro area. Although it can provide QoS-guranteed

communication, ROADM has the drawback of low bandwidth utilization due to the nature of circuit switching. On the other

hand, while recently appeared ring burst technologies based on optical burst switching technology can provide high bandwidth

utilization, very high accuracy for time slot allocation is needed to provide QoS-guaranteed communication. In this paper,

we propose a hybrid ring network architecture combining OCS and MW-OPS to utilize the merits of the both two forwarding

paradigms. We design a hybrid switching node and preliminarily demonstrate the switching node in 120 (12λ × 10) Gb/s

testbed.

Key words Metro Area Ring Network，Hybrid Optical Architecture，Multi-Wavelength Optical Switching

— 1 —

1. Introduction

Nowadays, Internet could be viewed as a three-level hierarchy

consisting of core networks, metro area networks (MANs) and lo-

cal access networks (LANs) [1]. Core networks provide abundant

bandwidth by employing wavelength division multiplexing (WDM)

technology which provides tremendous capacity that can exceed 30

Tb/s nowadays [2]. Metro area networks interconnect core networks

with local access networks. Local access networks connect to indi-

vidual users. By employing advanced access networks technolo-

gies, such as the IEEE 802.3av 10 Gigabit Ethernet PON (10GE-

PON) which provides the transmission rate of 10Gb/s [3], access

networks provide increasing amounts of bandwidth.

Besides, Internet is supposed to be able to support newly emerg-

ing various applications as well as current IP-centric services in

future. Especially, bandwidth-intensive applications such as super

high-definition 4K/8K video broadcast services will bring new re-

quirements to the Internet, which are greatly different from the ones

that current IP-centric services ask for. Moreover, as the trend of

these bandwidth-intensive broadcasting and streaming services be-

come a commercial service, QoS-guaranteed transport will be re-

quired in Internet. These new requirements are driving the deploy-

ment of high-performance networks with the properties of high ca-

pacity, high bandwidth utilization, and QoS-guaranteed transport.

Especially considering metro area networks, most existing MANs

are based on WDM ring networks using Reconfigurable Optical

Add/Drop Multiplexers (ROADMs) [4], which is based on circuit

switching networks. Although these ROADM technologies can pro-

vide QoS-guaranteed communications, they are not suitable to sat-

isfy the new requirements for the Internet such as high bandwidth

utilization due to the nature of circuit switching. On the other hand,

optical packet switching (OPS) technology becomes a very attrac-

tive technology to realize high bandwidth utilization and fine gran-

ularity to support various applications for high-performance net-

works [5], [6]. Besides, Matisse Networks Inc. has already devel-

oped an etherburst optical carrier ethernet system based upon ring

optical burst switching (Ring OBS) and now produces it as mer-

chandise for the first time in the world [7]. This etherburst optical

ring network can provide high bandwidth utilization services. How-

ever, the drawback of this network is that high accuracy for time slot

allocation is needed to provide QoS-guaranteed services.

As a result, we are considering hybrid optical network architec-

ture combining two or more forwarding paradigms instead of net-

work architectures with only one forwarding paradigm such as OCS

or OPS [8] in order to provide multi-granularity forwarding services

in metro area networks.

In this paper, we design the optical ring network architecture as

well as the hybrid switching node and preliminarily demonstrate the

switching node in 120 (12λ × 10) Gb/s testbed. The remainder of

this paper is organized as follows: Section 2 discusses the relate

works on Metro Area Networks. Section 3 proposes our design of

the hybrid optical ring switching architecture. Section 4 describes

the preliminarily demonstration of the hybrid optical ring switching

node. Section 5 presidents the experimental results. Section 6 con-

cludes the paper.

2. Related Works

In recent years, several kinds of ring network architectures for

metro area networks have been proposed.

Nord [9] proposes an hybrid optical ring network architectures

for the MAN, combining SWRON (static wavelength routed optical

network) and OPSRN (OPS ring network) node architectures. This

network architecture aims to improve the performance-complexity

ratio in MAN networks. The wavelength resources are separated

into an SWRON and an OPSRN waveband.

Chiaroni et al. [11] consider an optical network combining packet

optical add/drop multiplex (POADM) and wavelength-selective

switch (WSS) based reconfigurable optical add/drop multiplex

(ROADM) together, in order to introduce packet granularity to op-

timize bandwidth utilization. This work provides packet optical

add/drop multiplex services by processing packets consisting of

header and payload encoded into a same wavelength. This prop-

erty makes the number of optical devices such as packet optical

add/drop multiplexers be proportional to the number of the wave-

lengths available in the WDM network.

Kataoka et al. [10] propose an optical ring network employ-

ing acousto-optic wavelength-tunable filters (AOTFs) and optical

packet add/drop multiplexers to provide fine-granularity packet

add/drop multiplexing in ROADM network. The packet add/drop

multiplexers in this network also process the packets encoded the

header and the payload into a same wavelength.

Taking the total power consumption, total network cost and phys-

ical complexity of the switching node into account, we are con-

sidering the proposal of multi-wavelength optical packet switching

(MW-OPS) [12] technology to provide the similar network services

with lower number of optical devices. Because the MW-OPS is

capable of reducing the number of optical devices by switching a

wavelength-multiplexed optical packet with a single wideband op-

tical switch.

3. Design of the Hybrid Optical Ring SwitchingArchitecture

In this section, we introduce our proposed ring network and the

node switching architecture.

In the network, each node is connected to adjacent node with two

fibers: one is primary and the other is backup as shown in the left-

hand side on the top of Fig.1.

Optical circuits and multi-wavelength optical packet (MW-

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demux muxFBG

Pass-Through Circuits

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MW-Packet

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SOA Label

Detector

(label)

SOAλc

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trl

RX

2x2

MEMS

λ0

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(label)λ0

Label

Generator

λc2

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trl

TX

λ1λ2 λn...User RX Channels

λ1λ2 λn...User TX Channels

2x2

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1x5 WSS

Incoming Signal

Backup Fiber

Outgoing Signal

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Fig. 1 Hybrid Optical Ring Switching Architecture

Packet) utilize the same wavelengths available in the fiber. The

basic policy is that wavelengths are dedicated for optical circuits

and only free wavelengths can be used for MW-Packet as illustrated

in the right-hand side on the top of Fig.1. Moreover, the wavelength

resource allocation ratio could be dynamically changed between the

two forwarding paradigms, in order to achieve higher wavelength

resource utilization.

The bottom of the figure illustrates our proposed hybrid optical

ring switching node architecture. There are five main components

in the node: 2x2 MEMS, 1x5 WSS, SOA, FBG, and Label Detec-

tors.

2x2 MEMS provides recovery for impairment of fiber or node by

switching to the backup fiber and keeping the ring state.

1x5 WSS distributes the incoming optical signal into five sets of

wavelengths: (1) Pass-Through optical circuits, (2) Drop optical cir-

cuits, (3) Multicast optical circuits, (4) MW-Packet, and (5) an op-

tical circuit connection with the neighbor for exchanging control

information. Pass-through optical circuits means the wavelengths

which are not received by the local node. Therefore, they are just

forwarded to the next node. Drop optical circuits are the wave-

lengths that the local node receives and terminates. They will be

demultiplexed at the demultiplexer notated as demux and received

by optical receivers. Multicast optical circuits represent the multi-

cast optical circuits that the local node receives and does not ter-

minate. These wavelengths are split at the coupler right after the

WSS. One is received by the local node and the other is merged into

Path-Through optical circuits.

The wavelengths for MW-packet are split at the coupler right after

the WSS into two SOA gates which are controlled by the label de-

tector. The label detector controls the SOA switches in accordance

with the label of the MW-packet. The label is examined by the label

detector after the FBG extractsλ0 dedicated for the label. The two

SOA gates provide multicasting capability for MW-OPS.

The through optical signals are merged into the new optical cir-

cuits and MW-packets inserted to the node at the coupler and then

forwarded to the next node.

Two wavelengths,λc1 andλc2 are dedicated for a control channel

for exchanging control information with two adjacent nodes. Due

to the fact that these control channels will not consume such wide

bandwidth as optical circuits, some arrangement will be required for

allocating free wavelengths.

Besides, in order to connect two hybrid optical ring networks de-

scribed above, our proposed switching node can be exploited. The

details could be referred to [8].

4. Implementation and Demonstration

In order to verify the feasibility of the hybrid switching based

on our proposed architecture design described above, we imple-

mented a hybrid optical ring switching testbed and demonstrated

hybrid drop/through mechanism of 40 (4λ×10)Gb/s MW-OPS and

80 (8λ × 10)Gb/s OCS. Wavelength select switch(WSS) is used

to select the right wavelengths used for MW-OPS or OCS in this

demonstration.

— 3 —

Table. 1 Experimental Parammeters (a)

Label Payload Multicast Path Drop path Through Path

Number ofLamdas 1 4 2 3 3

Range of Wavelength1551.72nm 1553.33 - 1555.75nm1556.55 - 1557.36nm1558.17 - 1559.79nm1560.61 - 1562.23nm

Number of Channels Ch0 Ch1-Ch4 Ch5-Ch6 Ch7-Ch9 Ch10-Ch12

In this experiment, the number of maximum wavelength available

for MW-optical payload and optical paths is 12 (Max=12), the num-

ber of wavelengths used for MW-payload, multi-cast paths, drop

paths and pass-through paths is 4, 2, 3 and 3, respectively. The de-

tails of the parameters in this experiment are showed in the Table. 1

and Table. 2.

Fig.2 depicts the experimental setup of the testbed. This testbed

mainly consists of a signal generator as a subsystem and a hybrid

optical Add/Drop node without the add mechanism.

Table. 2 Experimental Parammeters (b)

Label Payload Path

Bit Rate 25Mb/s NRZ 4 × 10Gb/s NRZ 8 × 10Gb/s NRZ

Data Length 120ns 300ns Continous

Data Signal ”111” or ”101” 231 − 1 PRBS 231 − 1 PRBS

Fig. 2 Experiment Testbed

In the signal generator, the input hybrid optical signal is gener-

ated through the following process. First, 13 optical signals on dif-

ferent sources are generated by the light source. One of the wave-

lengths (1551.72 nm:CH0) is modulated to a 25Mb/s NRZ signal

(‘111” or “101”) by the PLZT switch as labels. The other 10 wave-

lengths from 1553.3 to 1562.23 nm with 100 GHz spacing are multi-

plexed at the multiplexer (Mux) and the multiplexed signal is modu-

lated to 10Gb/s PRBS signal (231 − 1) by theLiNbO3(LN) Mod-

ulator with the PPG (Pulse Pattern Generator). Then, two AWGs

and twelve FDLs of different lengths remove bit-level correlations

among the twelve wavelengths. In this experiment, we use 8 wave-

lengths (1556.55 nm - 1562.23 nm) for optical paths and these 8

wavelengths avoid the following packet generation process. The

other 4 wavelengths (1553.33 nm - 1555.75nm) are multiplexed and

then cut into 300ns envelopes by the AOM (Acoustic Optical Modu-

lator). These envelopes are used as the4×10Gb/s multi-wavelength

payload (MW-payload) in this experiment. The label, path and MW-

payload are merged at the couplers and sent to the input ports as an

optical signal containing both optical paths and MW-optical pack-

ets.

The hybrid optical add/drop node mainly consists of a1×5 WSS,

a label detector and a MW-packet switch. The1×5 WSS selects the

wavelengths for drop paths, for multicast paths, for through paths

and for MW-packets and sent them into each port respectively. Then

a 3dB coupler splits the multicast path signals for both drop port and

through port. The MW-packet signals are sent into the MW-packet

switch. In the MW-packet switch, the incoming packet signal is

switched based on broadcast and selection by the coupler and SOA

gate switches. The MW-packet signals splitted for drop port are sent

into the label detector. In the label detector, the FBG extracts label

from the MW-packets and then the PD converts the label into elec-

tric signal and sends it to the FPGA. The FPGA operates the SOA

switches in MW-packet switch in accordance with the labels. Both

signals of MW-packets and optical paths to either output drop port

or output through port are merged at the couplers.

This is a preliminarily demonstration because we just demon-

strate the switching feasibility of the node. The feasibility of insert

new optical signals containing both optical paths and MW-packets

is not demonstrated.

Packets with labels “111” and “101” are switched into output

drop port and through port, respectively.

5. Experimental Result

Fig.3 shows the waveform results and Fig.4 shows the spectrum

results at points (a) to (f) as shown in Fig.2. The waveform and

spectrum results of (e) and (f) show MW-OPS and OCS functions

work correctly in accordance with the labels and the channel num-

bers. The spectrum results (a), (b), (c) and (d) show the output of

WSS, we can see that signals for drop paths, through paths, multi-

cast paths and MW-packets are switched corrected to the right ports

in accordance with the channel numbers by the WSS. In addition,

we measured eye diagrams and BER (Bit Error Rate) to evaluate the

transmission quality of this switching node. Fig.5 and Fig.6 show

the results of eye diagrams and BER results. The eye-diagrams for

all twelve wavelengths were clear enough and1 × 10−9 BER are

achieved with power penalty of approximately 4dB or less. The rea-

— 4 —

son of 4dB power penalty is considered as the parameters of SOA

switch we used this time did not achieve optimum. We believe that

BER results could be improve if we use a better SOA switch or

consider the SOA parameters such as SOA gain more carefully.

InputPacket Ch1Ch2Ch3Ch4Ch5Ch6Ch7Ch8Ch9Ch10Ch11Ch12

101MW-PayloadLabel(CH0)

MW-PayloadMulticast pathDrop path

Throughpath

111 111101 101111 111101Drop Port Through Port

GND GNDGNDGNDGNDGNDGNDGNDGND

GNDGNDGNDGNDGNDGND GNDGNDGNDGNDGNDGNDGNDGNDGNDGNDGNDGNDGND

Fig. 3 Experimental Result of Waveform

Resolution: 0.1nm2nm/div1551.72 1557.36 1562.22(e)

Resolution: 0.1nm2nm/div1551.72 1557.36 1562.22(d)

0dBm-40dBm-20dBm1551.72Resolution: 0.1nm2nm/div

1557.36 1562.22(b) (c)Resolution: 0.1nm2nm/div1551.72 1557.36 1562.22

-20dBm-60dBm-40dBm(a)1551.72 1557.36 1562.22

Resolution: 0.1nm2nm/div

1551.72 1557.36 1562.22(f)Resolution: 0.1nm

2nm/divFig. 4 Experimental Result of Spectrum

6. Conclusion

We applied a hybrid optical architecture combining OCS and

MW-OPS to metro area ring networks. In this paper, we designed

a hybrid optical add/drop ring switching node and the feasibility of

the hybrid switching has been demonstrated. The results showed

error-free transmission in the switching node. Future work includes

complete demonstration of the add/drop node and network perfor-

mance evaluation of the whole ring network.

Acknowledgements

This paper is supported by National Institute of Information and

Communication Technology(NICT).

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-32-31-30-29-28-27-26-25-24-23

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