ALL-OPTICAL PACKET HEADER PROCESSING SCHEME
BASED ON PULSE POSITION MODULATION
IN PACKET-SWITCHED NETWORKS
Z. Ghassemlooy, H. Le Minh, Wai Pang Ng
Optical Communications Research Group
Northumbria University, UK http://soe.unn.ac.uk/ocr/

Contents
 Overview of header processing in optical networks
 Header processing based on pulse-position modulation (PPM)
 Proposed node architecture
 Simulation results
 Summary

Optical Communication Network (OCN)
Demand traffic
[bit/s]
1P
NEC-2001
100T
10T
1T
100G
Total
Data
10G
Voice
1G
100M
1995 2000 2005 2010
Year
- Future OCNs: faster signal processing and switching to cope with the increase of the demanding network traffic
- Existing OCNs: depends on electronic devices for processing the packet address to obtain the routing path.
However, the limitation of electronic response will cause the speed bottleneck
 Solution: All-optical processing & switching

Future OCNs
Optical transparent path
- Future OCN will have the processing and switching data packets entirely in optical domain, i.e. generate optical transparent path for routing data packets
 Require: compact and scalable processing scheme

Current All-optical Processing Schemes
Example: N = 4, node with M = 3
N -bit
?
Port 1
Port 2


All-optical logic gates
All-optical correlators
Port 3
Problems:
• Large size routing table  increased processing time
• Optical device complexity  poor scalability
Solution:
• To reduce the size of the routing table
1 0 0 1
1 0 1 0
1 0 1 1
1 1 0 0
1 1 0 1
1 1 1 0
1 1 1 1
Address patterns
0 0 0 0
0 0 0 1
0 0 1 0
0 0 1 1
0 1 0 0
0 1 0 1
0 1 1 0
0 1 1 1
1 0 0 0
Output ports
Port 2
Port 1
Port 3
Port 1
Port 3
Port 2
Port 2
Port 1
Port 3
Port 2
Port 2
Port 3
Port 1
Port 1
Port 2
Port 1
Decimal value
0
1
4
5
6
2
3
7
8
12
13
14
15
9
10
11

PPM - Operation
Data packet payload a
0 a
1 a
2 a
3
Clk
Header
( packet address )
Address extraction
(a)
PPM
(b)
(a) (b)

PPM Based Routing Table
Pulse-position routing table (N = 4, M = 3)
 Grouping address patterns having the same output ports
 Each new pulse-position routing table ( PPRT ) entry has optical pulses at the positions corresponding to the decimal values of group’s patterns

Header Correlation
 Single AND operation is required for matching PPM-address and multiple address patterns (PPRT entry)
 Processing-time gain:

Proposed Node with PPM Processing
Data H Clk
Data H Clk
All-optical switch
SW1
SW2
SWM
1
...
2
M
H
S-P
Converter
...
PPM-ACM
Clock extraction
& 1
& 2
& M
...
PPRT
Entry 1
Entry M
...
Header processing unit






Clock extraction : synchronize the arrival of data packet and the node processing
S-P converter : convert the serial address bits to parallel bits
PPM-ACM : (PPM address conversion module): convert binary address to the PPM-converted address
PPRT : store M entries ( M PPM frames)
Switch synchronisation : synchronise SW with data packet
All-optical switch : controlled by matching signals to open the correct SW

PPRT with Multimode Transmission
Pulse-position routing table (N = 4, M = 3)
 Same address pattern can appear at multiple PPRT entries
 Modes: unicast, multicast, broadcast and deletion

Node with Multicast Tx Mode
Data H Clk
Data H Clk
H
S-P
Converter
...
PPM-ACM
Clock extraction
PPRT
Entry 1
Entry M
...
Header processing unit
& 1
& 2
& M
All-optical switch
SW1
SW2
Data
SWM
1
H Clk
...
2
M
...

Optical PPM Generation Circuit
N -bit address-codeword: A = [ a i

{0,1}], i = 0, …, N – 1
PPM-format address: y ( t ) = x ( t +
 i a i

2 i

T s
)

PPRT Generation
 Is self-initialised with the extracted clock pulse. The M entries are filled by:
– Single optical pulse + Array of 2 N optical delay lines; Or,
– M pattern generators + M optical modulators.

Ultrafast Optical AND Gate
A/B 0
0 0
1 0
1
0
1
A
B
Implementation:
Using optical interferometer configuration
+ optical nonlinear devices
SOA1
A × B
SOA2
Symmetric Mach-Zehnder Interferometer
(SMZI)

All-Optical Switch
1

M
CP 1
SMZ1
CP 2
SMZ2
CPM
SMZM
1
2
M

Simulation Results
For an all-optical core network up to 2 5 = 32 nodes
32 node network
00000
0
0001
1
01000
...
8
10001
17
01111
15
11101
29
Simulation parameters Values
Address length N 5
Number of outputs M
Bit rate
3
50 Gb/s
Payload
Packet gap
Pulse width FWHM
Pulse’s power peak
Wavelength
PPM slot duration T s
16 bits
2 ns
1 ps
2 mW
1554 nm
5 ps

Simulation Results
Demonstrate the PPM processing and Tx modes
PPRT with 3 entries:

Simulation Results
Input
Output 1
Output 2
Output 3

Simulation Results
0 1 1 1 0
Packet with address 01110
PPM-converted address
PPRT entry 1
Synchronized matching pulse

Conclusions
 PPM processing scheme
–
–
Reduces the required processing time
Provides the scalability: adding/dropping network nodes and node outputs
 Applications:
–
–
All-optical core/backbone networks (N >> M ~ 3-6)
Optical bypass router (electrical router + optical bypass router)
 Challenges:
–
–
Optical switch with long and variable switching window
Timing jitter and received pulse dispersion

Publications
 H. Le-Minh, Z. Ghassemlooy, and W. P. Ng., “ A novel node architecture for all-optical packet switched network ”, proceeding of
10 th European Conference on Networks and Optical
Communications 2005 (NOC2005), pp. 209-216, London, UK, Jul.
2005
 H. Le-Minh, Z. Ghassemlooy, and W. P. Ng., ” Ultrafast header processing in all-optical packet switched-network ” proceeding of
7 th International Conference on Transparent Optical Networks
2005 (ICTON2005), Vol. 2, pp. 50-53, Barcelona, Spain, Jul. 2005

Acknowledgements
 Northumbria University for sponsoring the research work