1
Optical Packet/Burst Switching
based on : “Optical Packet and Burst Switching
Technologies for the Future Photonic Internet” S.J.
Ben Yoo
Raimena Veisllari
2
Content
•
•
•
•
•
•
•
•
•
Short Introduction
Optical Burst Switching (reservation, contention resolution)
Optical Switches Fabrics/Technologies
Optical Header Processing
Optical Packet Synchronization/Time Switch
Optical Packet Switches
Optical Label Switching
Testbed demonstration of edge/core OLR
Summary
3
Optical Networks
evolution
• WDM ptp first-generation
– The true benefit of optical networking
may rise from avoiding electronics in the data plane
• All-optical second generation
– Format and protocol transparency
– Simplifies hardware requirements in the
data plane?
– ROADM and OXC
• OPS/OBS
– True IP over WDM
– Statistically
Multiplexing
4
Optical Networks Evolution
Wei et. al.“High-Performance Hybrid-Switching Optical Router for IP over WDM Integration”
5
6
OBS principles
•
•
Quickly transport large amount of data without provisioning long-lasting
circuits.
Burst Header Cell (BHC) or BCP
• Depends on the reservation scheme (one-way or two-way
signalling), Usually Hdr info + burst length
• If no resources available->contention resolution based on local
node
7
OBS Control Protocols
•
Based on the reservatio/contention resolution schemes employed.
Differentiate between:
1. Setting the switching matrix : Sending the control packet in
advance/not in advance (Toffset)
2. Releasing the switching matrix: Giving the payload length in
advance/use release packet after the burst
3. One-way reservation (no ACK) or two-way reservation
•
Compare the low latency of one-way and the guaranteed delivery of two-way
– TAG-based OBS (No ACK out-of-band) to achieve both datagram
and VC switching
•
•
JET signalling (No FDL)
Built-in-offset Toffset=0 (FDL)
– Other schemes available like fixed or limited duration and two-way
signalling schemes based on RWA algorithms with practical
limitation on number of nodes (not discussed).
8
Just Enough Time (JET)
9
OBS (2)
•
Requires a careful precomputation of T to avoid possible burst loss by
compensating the total latency experienced by BHC.
•
Research on varying the QoS (CoS) by varying the offset time T.
•
Limitation: The burst blocking probability related to the number of
wavelegths and the traffic load.
•
The built-in TAG-OBS uses OPS schemes
– The built-in optical buffer (FDL) allows the burst to be «queued» for the time it takes
to process BHC and set the switching matrix
•
Usually a low offset time + FDLs are employed throughout the
network! (OPS-like OBS)
10
OBS Contention Resolution
• Contention: Burst requiring the same output, same
wavelength at the same time in one node -> use
alternative forwarding path
– Wavelength domain
• The most effective solution because it does not require additional latency
while maintaining the shortest path or minimum hop.
– Time domain
• FDL (FIFO) and all inherited problems of such queueing and FDL size
– Space domain
• Hot-potato, forward to another output and let the network itself be a buffer.
– Out-of-order sequencing
– Delay/jitter
11
Optical Switching Fabrics (1)
• OBS vs. OPS
– Subwavelength granularity
– Fast switching speeds (us, ms) vs. nanoseconds in OPS
– Other considerations?
• Optical Switching fabrics carachteristics
– Signal Quality Issues : Crosstalk, Jitter, Chirp, attenuation, OSNR
– Configuration Issues: Scalability, blocking/nonblocking,
promptness, switching domain, optical transparency, practical
implementation
– Performance issues: Switching speed, PLD, Insertion loss, level of
transparency
12
Optical Switching Fabrics (2)
Optical switching technologies for OCS, OBS, and OPS
13
OPS Technologies (1)
• Categorizing based on the combination of:
– Synchronous/Asynchronous pkt switching
– Fixed/Variable packet length
– Store and forward vs cut-through pkt switching
• WDM, TDM and Optical CDM (difficulties in developing
multiplexing devices for TDM and CDM)
Synchronous
fixed length
Asynchronous
Variable length
14
Optical Hdr Processing
15
Optical Hdr Techniques
16
Optical Packet
Synchronizer/Time Switch
• In a system with N time granularity, K ports and W
wavelengths there are needed NxKxW modules
(Scalability? Complexity compared with the OPS itself?)
• One possible solution is shared or loopback buffering.
17
OPS for packet switching (1)
• Guard time : longer than the longest transition time but
short for efficient switching
1. Space Switching (KEOPS example Broadcast and select
or NxN OXS with SOA)
18
OPS for packet switching (2)
2. Optical Phase Array
– Like a phased-array radar, the OPA components select wavelength
paths across a 64 × 64 cross-point switch via an optical interference
mechanism that operates by changing the waveguides’ refractive
indices. 64 non-blocking 1x64 switches, the switching time 30ns.
3. Wavelength Routing Switching Fabric
– KW x KW AWGRs with F shared
recirculating FDLs; Switching in time,
space and wavelength
19
OPS for packet switching (3)
4. Store and Forward OPS and Optical Buffers
– The lack of the optical buffer is the main problem in the OPS research so
far mainly because of this switching paradigm.
– TCP congestion control algorithm determines the size of the buffer
• RTT x (data rate of the link) -> For OPS 25Mb for 10Gbps link
• PLR vs systems scalability
– Pipelined router architecture
5. TDM and CDM OPS
– Research is less active due to the difficulties of producing ultrafast
mux/dmux in optical TDM and optical CDM technologies
6. OPS using CMOS/RAM
– Switch with high speed OE converters parallel to serial -> CMOS RAM ->
serial to parallel (Is it still OPS all-optical?)
20
Optical Label Switching (OLS)
• DARPA proposal and patent (optical-tag switching)
interoperable with MPLambdaS through GMPLS extension. It
facilitates interoperability between OCS, OBS and OPS.
A. Discarding Store-and-forward,
I.
4 classes of labels 40 bits long:
1.
2.
3.
4.
II.
Class A label dst oriented similar to IP hdr ( dst, src, QoS, CoS, optical TTL, exp bits)
Class B = Class A plus TE in the exp bits
Class C for label based forwarding similar to MPLS
Class D for Circuit Switching
Use a unified and pipelined contention resolution scheme in the
wavelength, time and space domains
III. Error-free 101 hop-cascaded OLS router operations have been
demonstrated with rapid clock recovery 1ns and guard time 2-3ns
21
Optical Label Switching (OLS)
22
Summary
• OPS and OBS research on the combination of the vast
optical bandwidth and subwavelength granularity by
switching/routing packets and burst in the optical layer.
• OBS offers BE with one-way signalling with milli to
microseconds switching time
• OPS needs faster switching times up to nanoseconds to be
effective
• Optical Label (Hdr) Processing and switching in times, space
and wavelength domains provide the nanosecond speeds.
• OLS facilitates the interoperability between OCS, OPS and
OBS with less power requirement and reduced complexity??