Packet-by-packet contention resolution in an optical-label switching system with 2R regeneration

Abstract

We demonstrate packet-by-packet contention resolution in wavelength, time and space domains in an optical-label switching system using tunable wavelength conversion, arrayed-waveguide grating router and fiber delay-line, and with 2R regeneration.

Full text

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Packet-by-packet contention resolution in an optical-
label switching system with 2R regeneration

Zhong Pan, Min Yong Jeon, Yash Bansal, Jing Cao, Julie Taylor, S. J. B. Yoo, and Venkatesh Akella
Department of Electrical and Computer Engineering, University of California, Davis, CA 95616
yoo@ece.ucdavis.edu

Katsunari Okamoto
Okamoto Laboratory, NEL, 6705-2 Naka-machi, Naka-gun, Ibaraki Pref., 311-0122, Japan
okamoto@photo.nel.co.jp

Shin Kamei
NTT Photonics Laboratories, 162 Tokai, Naka-gun, Ibaraki-pref, 319-1193 Japan

Abstract: We demonstrate packet-by-packet contention resolution in wavelength, time
and space domains in an optical-label switching system using tunable wavelength
conversion, arrayed-waveguide grating router and fiber delay-line, and with 2R
regeneration.
© 2003 Optical Society of America
OCIS codes: (060.4510) Optical communications; (060.4250) Networks


1. Introduction

Electronic routers rely on random access memory (RAM) to resolve contentions. Without a practical
optical RAM, all-optical packet-switching routers can exploit contention resolution in wavelength, time and
space domains. Previous network simulations [1] and experiments [2] show excellent performance in
optical-label switching systems. We further demonstrate packet-by-packet contention resolution with 2R
regeneration.

2. Experiment Description

Optical-label switching with sub-carrier label has been reported [3], and will not be covered here. Fig. 1
shows the experiment setup. (m,n)in represents wavelength n on input fiber m. Likewise, (m,n)out represents
wavelength n on output fiber m. Two packet streams arrive at (1,1)in and (2,1)in aligning to a fixed-sized
time slot T (T=819 ns), with the former arriving 50 ns earlier than the latter. Three scenarios demonstrate
wavelength, time and space domain contention resolutions respectively. In each scenario contentious and
non-contentious time slots alternate to show packet-by-packet operation. For all scenarios, at 0T packet P1
with label L1 (L1 means that the destination is any wavelength on output fiber 1, denoted by (1,*)out)
arrives at (1,1)in and obtains its preferred path (1,1)out. After 50 ns, P1’ with L1 arrives at (2,1)in. The
controller finds (1,1)out occupied, thus contention happens. The controller resolves the contention either in
wavelength domain by converting the packet to another wavelength on the same output fiber (1,2)out, or in
time domain by sending the packet to a fiber delay-line (4,1)out, or in space domain by sending the packet to
a deflecting route (3,1)out. For all scenarios, at 1T, P2 with L2 (destination (2,*)out) arrives at (1,1)in and gets
its preferred path (2,1)out. 50 ns later, P2’ with L1 arrives at (2,1)in and gets its preferred path (1,1)out
without contention. For the wavelength and space domain scenarios packet patterns repeat from here. For
the time domain scenario, at 2T the packet previously sent to the delay-line comes back at (4,1)in and goes
to (1,1)out, while P3 with L2 arrives at (1,1)in and goes to (2,1)out, P3’ with L3 arrives at (2,1)in and goes to
(3,1)out. Then the packet pattern repeats.
To be concise, only the results from the wavelength domain contention resolution are presented. Fig. 1
shows the input and output packet streams. Fig. 2(a) shows the traces at output ports, proving the successful
operation. Comparing the bottom trace to the top one, the extinction ratio is improved, and the logic
inversion due to cross-gain modulation is reversed. Fig. 2(b) shows the BER measurement and eye-
CThS1 CThS2CThS3CThS4CThT1 CThT2CThT3 CThT4CThT5 CThT6 CThT7CThU1CThU2CThU3CThU4CThU5CThU6CThV1CThV2CThV3CThV4CThV5CThV6CThW1CThW2CThW3CThW4CThW5CThW6CThW7CThX1CThX2CThX3CThX4CThX5CThX6

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diagrams. Negative power penalty is achieved by 2R regeneration from cross-phase modulation in the fixed
wavelength conversion.

SCM
Tx1Tx1
TLD1TLD1
SCM
Tx2Tx2
TLD2TLD2
SOA2SOA2
(1,1)out
(1,1)out
(1,2)out
(1,2)out
(2,1)out
(2,1)out
(2,2)out
(2,2)out
(3,1)out
(3,1)out
(3,2)out
(3,2)out
(4,1)out
(4,1)out
(4,2)out
(4,2)out
(1,1)in
(1,1)in
(1,2)in
(1,2)in
(2,1)in
(2,1)in
(2,2)in
(2,2)in
(3,1)in
(3,1)in
(3,2)in
(3,2)in
(4,1)in
(4,1)in
(4,2)in
(4,2)in
time time
wavelengthwavelength
spacespace
1542.6 nm
1546.0 nm
1546.0 nm
1554.0 nm
1563.7 nm
1552.2 nm
AWGRAWGR
1552.2 nm
MZI WCMZI WCMZI WC
TLD
ModuleModuleModule
330m330m
BMRX1BMRX1
BMRX2BMRX2
Forwarding Table
and Controllerand Controllerand Controller
P2 P2P2
L2L2L2
P1P1 P1
L1L1L1
P2’P2’
L1L1
P1’P1’
L1L1
50 ns50 ns
P2’ P2’
P1P1
P1’P1’
P2P2
LELESOA1SOA1
LELE
Optical path Optical path
Electrical path Electrical path
Fixed Wavelength Converter
(FWC) (FWC)
SCM
SCM
1542.6 nm
1546.0 nm
1546.0 nm
1554.0 nm
1563.7 nm
1552.2 nm
1552.2 nm
TLD TLD
Forwarding Table Forwarding Table
Fixed Wavelength Converter

Fig. 1 Setup and the scenario of wavelength domain contention resolution. SCM Tx=Sub-carrier Transmitter;
LE=Label Extractor; BMR =Burst-mode Receiver; TLD=Tunable Laser Diode; SOA=Semiconductor Optical
Amplifier; AWGR=Arrayed Waveguide Grating Router; MZI WC=Mach-Zehnder Interferometer Wavelength
Converter

(1,1)out
(1,1)out
(1,2)out
(1,2)out
500 ns/div500 ns/div
P1P1
P1’P1’
P1P1
P1P1
P2’P2’
P2’P2’
P2P2P2P2
P1’P1’P1’P1’
(2,1)out
(2,1)out
P1 P1P1P1
P1P1
P2’P2’
P2’P2’
(1,1)out
after
FWCFWC
(1,1)out
after
-30-28-26
Received Power ( dBm)
-24-22-20 -18
1E-3
1E-4
1E-5
1E-6
1E-7
1E-8
1E-9
1E-10
1E-11
1E-12
BER
P1 Back-to-back
P1 at (1,1)out after FWCP1 at (1,1)out after FWC
P1 Back-to-back
P1 at (1,1)out after FWC
P1 Back-to-back
100 ps/div
100 ps/div

(a) (b)
Fig. 2 Results for wavelength-domain contention resolution. (a) Traces at output ports. (b) BER and eye-diagrams.

3. Conclusion

We demonstrate contention resolution in wavelength, time and space domains using optical-label switching.
Experimental results show successful packet-by-packet forwarding with contention resolution and 2R
regeneration with improved extinction ratio. .

[1] Shun Yao, et. al., "A comparison study between slotted and unslotted all-optical packet-switched
network with priority-based routing," OFC, Anaheim, CA, 2001.
[2] S. J. B. Yoo, et. al., "Optical-Label Switching based Packet Routing System with Contention
Resolution Capabilities in Wavelength, Time, and Space Domains," paper #WO2, OFC, Anaheim,
CA, 2002.
[3] S. J. B. Yoo, et. al., "Optical-label switching and routing by rapidly tunable wavelength
conversion and uniform loss cyclic frequency array-waveguide grating," paper #WO2, OFC,
Anaheim, CA, 2001.
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