Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
Optical Packet/Burst Switchingbased on : “Optical Packet and Burst Switching Technologies for the Future Photonic Internet” S.J. Ben Yoo Raimena Veisllari
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
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
Optical Networks Evolution Wei et. al.“High-Performance Hybrid-Switching Optical Router for IP over WDM Integration”
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
OBS Control Protocols • Based on the reservatio/contention resolution schemes employed. Differentiate between: • Setting the switching matrix : Sending the control packet in advance/not in advance (Toffset) • Releasing the switching matrix: Giving the payload length in advance/use release packet after the burst • 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).
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)
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
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
Optical Switching Fabrics (2) Optical switching technologies for OCS, OBS, and OPS
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
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.
OPS for packet switching (1) • Guard time : longer than the longest transition time but short for efficient switching • Space Switching (KEOPS example Broadcast and select or NxN OXS with SOA)
OPS for packet switching (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. • Wavelength Routing Switching Fabric • KW x KW AWGRs with F shared recirculating FDLs; Switching in time, space and wavelength
OPS for packet switching (3) • 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 • TDM and CDM OPS • Research is less active due to the difficulties of producing ultrafast mux/dmux in optical TDM and optical CDM technologies • OPS using CMOS/RAM • Switch with high speed OE converters parallel to serial -> CMOS RAM -> serial to parallel (Is it still OPS all-optical?)
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. • Discarding Store-and-forward, • 4 classes of labels 40 bits long: • 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 • Error-free 101 hop-cascaded OLS router operations have been demonstrated with rapid clock recovery 1ns and guard time 2-3ns
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??