Bidirectional Optical Ring Network Having Enhanced Load Balancing and Protection Dzmitry Kliazovich, Fabrizio Granelli, University of Trento, Italy Copenhagen, Denmark May 22, 2006 Hagen Woesner CREATE-NET ONDM 2006

Hagen Woesner May 22, 2005 Outline Introduction  Last Mile and Metropolitan Networks Traffic Aggregation Core  Network and node architectures  MAC Protocol Candidates  Resilience and Load Balancing Strategies Comparison and Conclusions

ONDM 2006 Hagen Woesner May 22, 2005 Last Mile Networks Which technology will drive Access in networks? FTTx became economically feasible  Up to 100 Mb/s per user Passive Optical Networks  PON (A/B/E/GPON): total bitrate 155 Mb/s and 2.5 Gb/s  SuperPON: 10 or 40 Gb/s Optical transmission is required Switching inside OLT can be done electronically

ONDM 2006 Hagen Woesner May 22, 2005 Metropolitan Area Network (MAN) Traffic Aggregation in Metro Area  Switching and Routing becomes a Communication and Computing Bottleneck!

ONDM 2006 Hagen Woesner May 22, 2005 Traffic Aggregation Core Perform Distributed Switching Shared medium (bandwidth) Drop-and-Continue principle to avoid OEO conversion and corresponding processing Bidirectional Communications Ref.: A. Gumaste and I. Chlamtac, "Light-trails: a novel solution for IP-centric communication," in Workshop on High Performance Switching and Routing (IEEE, New York, 2003). Ref.: D. Kliazovich, F. Granelli, H. Woesner, and I. Chlamtac, “Bidirectional Light- Trails for Synchronous Communications in WDM Networks”, GLOBECOM'05, St. Louis, US, December 2005.

ONDM 2006 Hagen Woesner May 22, 2005 Traffic Aggregation Core Bidirectional Optical Ring Client Node Drop-and-Continue using Optical Couplers

ONDM 2006 Hagen Woesner May 22, 2005 Traffic Aggregation Core Hub-and-spoke Architecture Virtual Link Break creates Two Dual Buses on a bidirectional optical ring allowing spatial reuse Each bus is running OTDM  HUB communicates at full bus speed (100 or 160 Mb/s)  Client node receives/transmits in a single time slot (10 Mb/s) Downstream: point-to-multipoint Upstream: multipoint-to-point Terminates eastern bus downstream Terminates western bus downstream

ONDM 2006 Hagen Woesner May 22, 2005 Hub Node Architecture High-speed transmitters and receivers  Implemented using Short Pulse Lasers ( us)

ONDM 2006 Hagen Woesner May 22, 2005 Client Node Architecture Low-cost requirement  Minimum number of transmitters and receivers

ONDM 2006 Hagen Woesner May 22, 2005 Network Initialization Discovery Topology  Hub goes around the ring configuring client nodes in “path-through” mode Place Virtual Link Break  Assume uniform network load initially  Divide ring into two equal by the number of nodes dual buses Assign Home Channels  Client node listens a certain OTDM channel in downstream  Several nodes can share a single channel

ONDM 2006 Hagen Woesner May 22, 2005 Network Communications Point-to-multipoint Downstream reserved for reception Multipoint-to-point Upstream requires contention resolution to ensure collision-free medium access No node is allowed to transmit if the bus is not idle (medium sensing module) – CSMA/CA However CSMA/CA in light trails leads to Unfairness  It always favors the nodes located closer to the beginning of the upstream bus

ONDM 2006 Hagen Woesner May 22, 2005 MAC Protocol Candidates Reservation-based MAC  Client sends bandwidth request in the upstream  Hub computes a fair share  Bandwidth is granted via downstream Good Fairness (depends on scheduler) Large Reservation-Grant Delay  At least double propagation time between Hub and Client node  Depends of the node relative position with the bus A good candidate for constant bandwidth provisioning  Example: dedicated channels for ISPs

ONDM 2006 Hagen Woesner May 22, 2005 MAC Protocol Candidates Token-rotation MAC  Tokens generated by Hub in the downstream are rotated into the upstream  Token detection requires optical correlator  Token extraction is done using overwrite operation Medium Access Delay tradeoffs with Round-trip propagation delay, Token rotation and Token holding time Network size defines Utilization and Performance Backpressure Control  CSMA/CA in Medium Access  Hub monitors node’s sending rates  Hub sends backpressure signal to the nodes sending above a fair share On-demand Medium Access

ONDM 2006 Hagen Woesner May 22, 2005 Resilience and Load Balancing Key: Shift Virtual Link Break Single Link Failure or Node Malfunction Robustness  Complete shut down of optical functionality is considered  Distributed algorithm with no Hub coordination Load Balancing between busses  Triggered by Hub based on the bus utilization level

ONDM 2006 Hagen Woesner May 22, 2005 Resilience and Load Balancing 1. Downstream clock and no upstream clock – turn into “loopback” mode 2. No downstream clock – join another bus by flipping optical switches. Then, send signal on the upstream 3. Being in “loopback” switch to “path-through” upon incoming signal on the upstream Tree rules of Distributed Resilience algorithm followed by nodes:

ONDM 2006 Hagen Woesner May 22, 2005 Resilience and Load Balancing Link Failure CN 1 hearing clock on the downstream and no clock on the upstream closes western bus; Being isolated CN 2 and CN 3 try to join eastern bus and send in the upstream; CN 4 hearing an upstream signal turns off light terminator opening the downstream for CN 3 and CN 2 ;

ONDM 2006 Hagen Woesner May 22, 2005 Related Works and Comparison

ONDM 2006 Hagen Woesner May 22, 2005 Conclusions Optical Network Architecture for traffic aggregation in Metropolitan Area Network (MAN) which consists of two dual buses on a bidirectional ring fiber Low-cost Client node architecture MAC candidates: reservation-based, token- rotation or CSMA/CA with backpressure control Resilience strategy able to resolve single link break or node malfunction

ONDM 2006 Hagen Woesner May 22, 2005 Thank you!