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Optical Packet/Burst Switching

based on : “Optical Packet and Burst Switching Technologies for the Future Photonic Internet” S.J. Ben Yoo

Raimena Veisllari

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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

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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”

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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

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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 burst3. 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).

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Just Enough Time (JET)

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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)

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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

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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

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Optical Switching Fabrics (2)Optical switching technologies for OCS, OBS, and OPS

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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

AsynchronousVariable length

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Optical Hdr Processing

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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.

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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)

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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

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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?)

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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. Class A label dst oriented similar to IP hdr ( dst, src, QoS, CoS, optical TTL, exp bits)

2. Class B = Class A plus TE in the exp bits

3. Class C for label based forwarding similar to MPLS

4. Class D for Circuit Switching

II. 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

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Optical Label Switching (OLS)

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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??