RINGOSTAR

1. RINGOSTAR By : VahidGholizadeh School of Engineering Emerging Technologies University of Tabriz Monday, July 27, 2009

2. WDM rings vs. augmented rings • WDM rings appear to be natural candidates to multichannel upgrade optical single-channel ring networks (e.g., RPR) • Pros & cons of WDM rings • Existing fiber infrastructure is exploited without requiring additional fiber links & modifications of ring topology • At the downside, all ring nodes need to be WDM upgraded at the same time (e.g., with transceiver array or wavelength (de)multiplexer) • Furthermore, WDM rings are able to survive only a single link or node failure similar to their single-channel counterparts • Alternatively, optical single-channel rings can be multi-channel upgraded by means of topological enhancements => augmented rings • RINGOSTAR is a novel augmented optical ring network with a hybrid ring-star topology

3. RINGOSTAR • As opposed to WDM rings, RINGOSTAR requires additional fiber links to build star subnetwork • Unlike WDM rings, however, RINGOSTAR does not require all ring nodes to be WDM upgraded at the same time • RINGOSTAR provides an evolutionary multichannel upgrade path of optical single-channel ring networks • Only a subset of ring nodes need to be WDM upgraded & attached to star WDM subnetwork according to given traffic demands and/or cost constraints • Furthermore, star subnetwork & two novel performance-enhancing techniques (proxy stripping, protectoration) • render RINGOSTAR survivable against multiple link & node failures • let RINGOSTAR clearly outperform WDM rings in terms of network capacity & network lifetime

4. Architecture

5. Network architecture • Subset of ring nodes is connected to single-hop star sub-network, preferably by bidirectional pairs of dark fiber • Using dark (i.e., unlit) fibers provides promising way to upgrade network capacity & reduce network costs • Ring nodes are attached to star subnetwork one at a time in a pay-as-you-grow manner according to given traffic patterns • N ring nodes are subdivided into • P = D.S ≤ N ring-and-star homed nodes and • Nr = N – D.S ring homed nodes (where D, S ≥ 1) • Single-hop star subnetwork • Offers minimum-hop short-cuts • Hub may be a wavelength-broadcasting PSC, a wavelength-routing AWG, or a combination of both, depending on given capacity requirements

6. Node architecture • All N nodes are attached to bidirectional dual-fiber ring by means of two pairs of FT-FR • Ring-and-star homed nodes are equipped with additional tunable transceiver • Tunable transmitter is connected to a combiner input port • Tunable receiver is connected to opposite splitter output port • Node structure • FT2-FR2 for ring homed node • FT2-TT-FR2-TR for ring-and-star homed node • Each node performs OEO conversion & has separate electrical transit and station queues for either fiber ring

7. Ring homed node architecture • Similar to RPR, each ring homed node is equipped with two transit queues • Primary transit queue (PTQ) for high-priority traffic • Secondary transit queue (STQ) for low-priority traffic • Plus, one receive & one transmit station queue

8. Ring-and-star homed node architecture

9. Proxy stripping • To exploit short-cuts of star subnetwork, each ring-and-star homed node performs proxy stripping

10. Proxy stripping • The following variables can be used to formally describe proxy stripping for a given pair of source node s & destination node d • hrs(s): hop distance between s and its closest proxy stripping node • hrs(d): hop distance between d and its closest proxy stripping node • hring(s,d): minimum hop distance between s and d on ring (i.e., without proxy stripping) • hstar(s,d): minimum hop distance between s and d via short-cuts of star subnetwork (i.e., with proxy stripping) • Note that hstar(s,d) = hrs(s) + 1 + hrs(d)

11. Proxy stripping • Formal description of proxy stripping • If hring(s,d) ≤ hstar(s,d) • Source node s sends data packet(s) along ring on shortest path to destination stripping node d (no proxy stripping) • If hring(s,d) > hstar(s,d) • Source node s sends data packet(s) to its closest proxy stripping node (this implies that all ring nodes need to be aware of presence & location of proxy stripping nodes) • Alternatively, transparent proxy stripping can be deployed • Ring homed nodes do not have to be aware of presence & location of proxy stripping nodes • Source node s sends data packet(s) in same direction as done in shortest path routing bidirectional ring • In general, transparent proxy stripping results in larger mean hop distance

12. Proxy stripping • Special case hrs(s) = 0 (i.e., source node s is a ring-and-star homed node that performs proxy stripping) • If hring(s,d) ≤ hstar(s,d) • Proxy stripping source node s sends its generated data packet(s) along ring on shortest path to destination stripping node d (no proxy stripping) • If hring(s,d) > hstar(s,d) • Proxy stripping source node s sends its generated data packet(s) across star subnetwork to corresponding proxy stripping node which is either destination itself or close to destination stripping node d

13. Proxy stripping • Proxy stripping may be applied in both single-queue & dual-queue modes • Single-queue mode • Proxy-stripped packets are put in additional star transmit queue at corresponding proxy stripping node • Receiving proxy stripping node forwards packets by putting them into corresponding ring transit queue, if necessary • Dual-queue mode • Each proxy stripping node has two additional star transmit queues, one for high-priority and one for low-priority proxy-stripped packets • Receiving proxy stripping node forwards packets by putting them into corresponding ring transit queue according to their priority, if necessary

14. Access & fairness control • As an evolutionary WDM upgrade, RINGOSTAR builds on access & fairness control protocols used in original single-channel ring network (e.g., RPR) • No protocol modifications are required for data trans-missions on bidirectional ring • For data transmissions on star subnetwork, modifications are required for • Access control protocol • Reservation on star subnetwork • Fairness control protocol • Adaptation of distributed virtual-time scheduling in rings (DVSR)

15. Reservation on star subnetwork • Access on AWG-based star subnetwork can be controlled via reservation protocol with pretransmission coordination • Prior to data transmission, ring-and-star homed node broadcasts control packet on either fiber ring by means of source stripping • Control packet consists of three fields • Address of source ring-and-star homed node • Address of ring-and-star homed node closest to destination node • Length of data packet • Control packet is sent using RPR’s high-priority traffic class service => constant latency equal to ring RTT • As a result, all P ring-and-star homed nodes are able to acquire & maintain global knowledge in synchronized manner • Based on global knowledge, all P nodes schedule transmission & reception on star subnetwork

16. Reservation on star subnetwork • Aforementioned reservation on ring suffers from inefficiencies • Each control packet traverses all N nodes • As a consequence, each control packet consumes bandwidth of entire ring & needs to be processed also by ring homed nodes • To mitigate wasted bandwidth & nodal processing resources, control packets may be sent across star subnetwork • To enable broadcasting, wavelength-insensitive PSC is deployed in parallel with AWG • Operating PSC & AWG in parallel also avoids single point of failure of star network & improves fault tolerance of RINGOSTAR (to be discussed later)

17. Spatial reuse • In single-channel & WDM rings, spatial reuse of wavelength channels is limited due to missing alternate physical paths • In RINGOSTAR, spatial reuse factor of wavelength channels is given by physical degree D of AWG • In principle, D can be chosen arbitrarily large => RINGOSTAR provides better multichannel upgrade than conventional WDM upgrades • Parameter D together with physical degree S of combiners/splitters determine • Number of ring-and-star homed nodes P = D S • Degree of spatial wavelength reuse on ring • Improved spatial reuse translates into increased capacity • Clearly, there is a tradeoff between spatial wavelength reuse & nodal WDM upgrade costs

18. Adaptation of DVSR • So-called distributed virtual-time scheduling in rings (DVSR) fairness protocol was initially proposed for RPR • DVSR can be extended to incorporate proxy stripping & provide fairness control in RINGOSTAR • Packets arriving at transit queue(s) & station queues are FIFO queued at each node • One fairness control packet circulates upstream on each ring • Each fairness control packet consists of N + DS/2 fields • N fields contain fair rates of ring links • DS/2 fields contain fair rates of star links • One control packet carries fair rates of even-numbered star links • The other control packet carries fair rates of odd-numbered star links

19. Adaptation of DVSR • Each node monitors both fairness control packets & writes its local fair rates in corresponding fields of control packets • Calculation of local fair rates • Each node measures number of bytes, lk, arriving from node k, including the station itself, during time interval T between previous & actual arrival of control packet • Each node performs separate measurements for either ring using two separate time windows • Proxy stripping nodes additionally count number of bytes arriving from star for each node & use time window of fairness control packet that carries fair rate of corresponding proxy stripping node • Fair rate F of a given link is equal to max-min fair share among all measured link rates lk/T with respect to link capacity C currently available for fairness-eligible traffic

20. Adaptation of DVSR • Each node limits data rate of its N-1 ingress flows by using token buckets whose refill rates are set to current fair rates of corresponding destinations • Each node i counts bytes ρij sent to destination j during the two aforementioned time windows • There are two sets of N-1 byte counters, one for each time window • Upon arrival of fairness control packet, a given node calculates fair rate of each ingress flow as follows • Capacity available to given node on a certain link equals fair rate F which is shared among all its ingress flows crossing that link • Based on measured ingress rate ρij/T of these flows & available capacity F, max-min fair share f is calculated for each crossed link & refill rate of each token bucket is set to minimum fair share f of these links

21. Adaptation of DVSR

22. Limitations of RPR protection • RPR’s two protection techniques (wrapping & steering) result in rather inefficient use of bandwidth • Wrapped traffic continues to travel from source node to wrapping node until failure notification arrives at source node • Steering avoids this problem, but does not eliminate increased bandwidth consumption incurred on secondary (longer) path • Both wrapping & steering are able to protect traffic only against single link or node failure • In case of multiple failures, full connectivity of RPR is lost => RPR is divided into two or more disjoint subrings • As a consequence, RPR poorly meets survivability requirements of metro networks & important metro applications without built-in adequate survivability, e.g., storage networking protocols

23. SRR • Pre-standard RPR solutions exist which provide advanced resilience solutions in addition to wrapping & steering • For example, so-called single ring recovery (SRR) protocol • SRR is an extension to spatial reuse protocol (SRP) of dynamic packet transport (DPT) rings • In SRR, wrapping & steering take place in case of single link/node failure on either ring, similar to RPR • If on one of both rings multiple failures occur, wrapping is not deployed & all nodes use only other failure-free ring • Failed ring may have multiple failures without losing full network connectivity, provided other ring is failure free • Note that SRR affects entire ring network in that all nodes must support SRR

24. PROTECTORATION • Unlike SRR, protectoration is a novel multi-failure recovery technique which affects only a subset of ring nodes • Protectoration is able to guarantee full network connectivity also in presence of multiple failures on both fiber rings, as opposed to SRR • Protectoration aims at combining recovery time of protection & bandwidth efficiency of restoration

25. PROTECTORATION: Architecture

26. PROTECTORATION: Architecture • Hub of star subnetwork • D x D AWG in parallel with D x D PSC, where D ≥ 1 • Ring-and-star homed node i, where i = 1, …, P and P = D.S • Dedicated home channel λi on PSC • PSC waveband ΛPSC • P home channels • One control wavelength channel λc • AWG waveband ΛAWG • D.R contiguous data wavelength channels, where R ≥ 1 denotes free spectral range (FSR) of AWG • Total number of contiguous wavelength channels operated in star subnetwork equals Λ = ΛAWG + ΛPSC = D(R + S) + 1

27. PROTECTORATION: Node architecture • Ring homed node • Same architecture as conventional RPR node • Ring-and-star homed node • Same number & type of transceivers and queues as ring homed node for transmission & reception on both rings • In addition, each ring-and-star home node has several transceivers attached to star subnetwork

28. PROTECTORATION: Node architecture • Ring-and-star homed node architecture for both rings

29. PROTECTORATION: Node architecture • Ring-and-star homed node buffer structure for either ring

30. PROTECTORATION: Operation • Wavelength channel allocation in star subnetwork

31. PROTECTORATION: Operation • Wavelength access • Ring-and-star homed node puts data packet(s) pulled from ring in one of its two star transit queues according to priority • Service among star transit queues & star transmit queue is arbitrated by applying same scheduling algorithms as on ring • Correspondingly, ring-to-star in-transit traffic is given priority over locally generated star traffic • Star transit queues provide lossless path for in-transit traffic • Prior to transmitting a data packet, ring-and-star homed node broadcasts a control packet to all P ring-and-star homed nodes on λc in its assigned slot • Control packet has three fields • Address of ring-and-star homed node closest to destination • Length of data packet • Priority of data packet

32. PROTECTORATION: Operation • Wavelength access • After sending control packet, ring-and-star home node transmits data packet on home channel of addressed ring-and-star home node in subsequent L slots • L denotes length of data packet in number of slots • Data packet is sent within same frame as corresponding control packet • Size of data packet is 1 ≤ L ≤ F – DS • Data packet is successfully received unless one or more other ring-and-star homed nodes transmit data packets in at least one of the L slots • Collided data packets are kept in queues until retransmission is successful • Due to the fact that control packets are sent collision-free all P nodes are aware of original order => in-order packet delivery

33. PROTECTORATION: Operation • Retransmission • No control packets have to be retransmitted for collided data packets • By processing collision-free control packets each ring-and-star homed node is able to find out which data packets have collided • Index j, 1 ≤ j ≤ DS, of used control slot and destination & length fields of control packet are used to determine whether corresponding data packet has collided or not • Collided data packets are retransmitted across AWG • Index j of control slot uniquely identifies not only source ring-and-star homed node but also its input port of AWG • Based on index j together with destination field of control packet, all P nodes are able to determine appropriate wavelength(s) on AWG • Retransmission on chosen wavelength is scheduled in distributed collision-free fashion

34. PROTECTORATION: Operation with failures • Aside from link & node failures, other network elements may fail, e.g., • Splitter, amplifier, combiner, waveband (de)partitioner, PSC, or AWG • Various failures affect network differently, e.g., • Fiber cut between a ring-and-star homed node & attached combiner disconnects only a single node from star subnetwork • If both AWG & PSC fail, entire star subnetwork goes down and affects all ring-and-star homed nodes • A number of techniques exist to be used for fault detection in ring & star subnetwork

35. PROTECTORATION: Operation with failures • Single ring failure

36. PROTECTORATION: Operation with failures • Single ring failure • In the event of fiber cut, wrapped traffic neither makes round-trip between source & destination nodes nor takes any long secondary path • As a result, wrapped traffic consumes significantly fewer bandwidth resources on ring • After learning about fiber cut, source node sends data packets along different path with smaller hop count, if available • Ring-and-star homed nodes use source & destination MAC addresses of packet together with direction it comes from to determine whether packet has undergone wrapping or not • If wrapping has taken place, corresponding ring-and-star homed node recomputes shortest path taking link failure into account • In the case of a failed ring-and-star homed node, neighboring proxy-stripping nodes take over role of proxy stripping traffic

37. PROTECTORATION: Operation with failures • Multiple ring failures • Nodes can use intact star subnetwork to bypass multiple ring failures without losing full connectivity • Full connectivity in event of multiple ring failures is guaranteed only if no more than one link or node failure occurs between each pair of neighboring ring-and-star homed nodes • Otherwise, one or more nodes between a given pair of neighboring ring-and-star homed nodes are disconnected from network

38. PROTECTORATION: Operation with failures • Star failures • Star failures include fiber cuts & nonfunctional devices • Depending on failure, only one, subset, or all ring-and-star homed nodes are disconnected from star subnetwork • Fiber cut between a given ring-and-star homed node & attached combiner/splitter port disconnects only ring-and-star homed node • If a given combiner/splitter, amplifier, waveband (de)partitioner, or any fiber between these devices goes down, all S corresponding ring-and-star homed nodes are disconnected • If central hub (AWG & PSC) goes down, connectivity of star subnetwork is entirely lost => conventional RPR ring • After detecting disconnection, affected ring-and-star homed nodes inform all remaining nodes & act subsequently as conventional ring homed nodes

39. Impact on RPR • Protectoration is a multiple-failure recovery technique that combines fast recovery time of protection (wrapping) & bandwidth efficiency of restoration (steering) • It does not change scheduling algorithms of RPR • In-transit traffic is given priority over station traffic on both ring & star subnetwork • In-transit traffic coming from star subnetwork is forwarded with ring in-transit traffic in round-robin fashion • It maintains lossless property of RPR • It supports service differentiation of dual-queue mode RPR • It can be used for both strict packet mode (default mode in IEEE 802 protocols) & relaxed packet mode of RPR • To guarantee in-order packet delivery, source nodes must apply strict-mode steering while intermediate nodes perform proxy stripping of both wrapped & steered traffic

40. Traffic forecasting • Traffic forecasting is an important means to predict when & where network bottlenecks emerge & capacity upgrades are needed • Current forecasting techniques allow prediction of required capacity upgrades over several months into the future within reasonable error bounds • However, traffic forecasting techniques typically don’t take into account events that are hard to predict (e.g., breaking news, flash crowd events, denial-of-service attacks, or link failures) • Those events are in general hard to predict & may be typically short lived, but they occur frequently & have significant impact on network traffic load

41. Unpredictable traffic • Amount of unpredictable traffic is expected to increase due to aforementioned short-lived events & the fact that server farms with popular Internet services may be located anywhere on the network • As a result, changes & shifts in traffic load are expected to occur more frequently & more suddenly than in the past • Ability of a network to sustain unexpected changes & shifts in traffic load is becoming increasingly important • So-called network lifetime predicts the ability of a network to survive unpredicted traffic changes

42. Network lifetime • Network lifetime is a measure of the growth & shifts in traffic load that a network can sustain & largely depends on assumed initial traffic matrix • Network lifetime ψ*(U) • Quantitative measure of maximum uniform growth & shifts (perturbations) in a given initial traffic matrix that network can sustain without exceeding link capacities & violating routing constraints • Function of U, where U ≥ 0 denotes unexpected traffic growth in a traffic distribution • Amount of traffic between node pair (i,j) or at single node i in a given initial traffic matrix increases by U while total amount of traffic remains constant • For any value of U ε [0, Umax], ψ*(U) denotes maximum uniform growth factor • RINGOSTAR dramatically improves network lifetime of rings

43. Thank you for your attention