Routing and Wavelegth Assignment in Optical Networks

1. Routing and Wavelegth Assignment in Optical Networks Xavi Masip, Sergi Sánchez, Eva Marín and Josep Solé (UPC)

2. Outline • Introduction • Routing in OTN • Signalling in OTN • Wavelength conversion • QoS in OTN • New routing proposals • The Routing Inaccuracy Problem • The Routing Inaccuracy Problem in hierarchical networks • Open issues

3. Introduction • Control Plane • Routing issues: compute the lightpath • Signalling issues: establish the lightpath • GMPLS1 is a strong candidate • Routing protocols • Constraint-based routing • Signalling protocols • RSVP-TE2 • CR-LDP3 1L.Berger, “Generalized Multi-Protocol Label Switching (GMPLS): Signaling Functional Description”, IETF, RFC3471, Jan., 2003. 2 “GMPLS signalling resources reservation protocol-traffic engineering (RSVP-TE) extensions”, IETF, RFC3473, Jan. 2003. 3 P.Ashwood-Smith et al, “GMPLS signalling constraint-based routed label distribution protocol (CR-LDP) extensions”, IETF, RFC3472, Jan.2003.

4. Introduction QoS Routing • Routing in IP networks • QoS constraints • Source routing (CBR) BW, delay, jitter, loses,… Network state information ?

5. Introduction • Routing target • Establish a lightpath between source-destination node pair • Routing open issues • Depends on network: • Circuit-switched (ASON) • Burst-switched (OBS) • Packet-switched (OPS) • Depends on wavelength conversion capabilities • Depends on control plane • Centralized lightpath establishment • Distributed lightpath establishment (source/destination-based) • QoS routing: what does it mean in OTN? • Network parameters • Update policies • …

6. Introduction Cables Fibras Bandas de Longitudes de Onda Longitudes De Onda {l..l}1 l TimeSlots Paquetes t0 t1 t2

7. Outline • Introduction • Routing in OTN • Routing constraints • The RWA problem • Signalling in OTN • Wavelength conversion • QoS in OTN • New routing proposals • The Routing Inaccuracy Problem • The Routing Inaccuracy Problem in hierarchical networks • Open issues

8. Routing in OTN ASON, OBS, OPS • Routing and wavelength assignment problem • Determine both: physical route and wavelength/s to be assigned • Connection management protocol Physical path, wavelength assignment

9. Routing constraints • Routing depends on connection management • In legacy backbone networks traffic is generally static • In next-generation optical networks traffic is more dynamic • OBS • Connection requests arriving at high rates • Average duration about several tens or hundreds of milliseconds • New dynamic lightpath provisioning schemes • Control plane is required: GMPLS

10. Routing constraints • Wavelength continuity-constraint • Wavelength converters are expensive (at least for the next 5 years) • Wavelength Selective networks (WS): • There are not wavelength conversion devices • Same wavelength on all the route • Wavelength Interchangeable networks (WI): • There are wavelength conversion devices • Different wavelengths in the end-to-end path

11. Routing constraints • Traffic in a wavelength-routed network • Static traffic pattern • Lightpaths set up all at once • Remain in the network for a long period of time • Dynamic traffic pattern • Lightpath is set up reacting to an incoming request • Lightpaths take down dynamically • Dynamic lightpath (on-demand) is foreseen to best accommodate current and future Internet traffic • Big challenge • Develop efficient algorithms and protocols for establishing lightpaths

12. The RWA problem • Dynamic lightpath establishment • Routing and wavelength assignment problem (RWA) • It is NP-complete to find the optimal solution for the two problems1 • Addressed separately • Through heuristic algorithms • Routing decomposed into: • Routing problem • Wavelength assignment problem 1A.Mokhtar, M.Azizoglu, “Adaptive Wavelength Routing in all-optical networks”, IEEE/ACM Trans.Netw., 1998

13. The RWA problem • Routing subproblem • Static approaches • Fixed routing • A single fixed route is precomputed • Ex: Shortest Path • Fixed-alternate routing • Multiple fixed routes are precomputed • Ex: Fixed shortest-path routing1, Least-Loaded Routing 1 • Adaptive (dynamic) approaches • Ex: Link state approach2, distributed routing approach3 • Adaptive routing based on global information • Adaptive routing based on neighbourhood information • Adaptive routing based on local information 1 E.Karasan, E.Ayanoglu, “Effects of wavelength routing and selection algorithms on wavelength conversion gain in WDM optical networks”, IEEE/ACM Trans.Netw., 1998 2 B.Muhherjee, “WDM Optical Communication Networks: Progress and Challenges”, IEEE JSAC, 2000 3 H.Zang, et al, “Connection management for wavelength-routed WDM networks”, Globecom 1999

14. The RWA problem • Adaptive routing based on global information • Routing decisions based on network state information • Full information about wavelength availability • Implemented in: • Centralized manner • Distributed manner: • Standardized by GMPLS • Different implementations • Link state approach • Distance-vector approach (or distributed routing approach) • Least-congested path algorithm

15. The RWA problem • Centralized manner • A single device maintains complete network state information • A single device finds routes and establishes the lightpaths • No huge coordination between nodes is required • Critical point of failure • Distributed manner • Decisions are distributed to different network nodes • GMPLS-based network: • Routes are computed by any routing (RWA) algorithm • A signalling (connection management) scheme is responsible for establishing the lightpath • Signalling candidates: • RSVP-TE • CR-LDP • There is not any guarantee that the updated global information with respect to wavelength availability on each link will be available in a distributed environment

16. The RWA problem • Distributed manner • Link state approach: • Each node maintains complete network state information • Each node finds the route in a distributed manner • Network state updating whenever network state changes • Signalling overhead vs outdated information • Distance-vector approach (or distributed routing approach): • Each node does not maintain global network state information • Each node maintains a routing table indicating the next hop and the distance to the destination • Updating is also required • Least-congested path algorithm: • Congestion on a link = number of available wavelengths • Links with fewer available wavelengths = links more congested • Congestion on a path = congestion on the most congested link on the path • Selects a set of sequence of routes for each source-destination pair • The least congested is selected • Using SP + LCP performs better than only using LCP

17. The RWA problem • Summary • Routing schemes based on global network state information perform better whenever update network state information • Suitable for networks where lightpaths do not change much with time • Small optical networks • Static traffic (not bursty) • Good updating procedure (signalling protocol) • New routing schemes assuming outdated network state information

18. The RWA problem • Adaptive routing based on neighbourhood information • In the LCP all links on all paths must be examined in choosing the least congested one • Network state information must be either: • Maintained by each node • Gathered in real time when establishing the lightpath • LCP variant: • Only examines the first k-links on each path (neighbourhood information) • K = 2 behaves similar than fixed-alternate routing

19. The RWA problem • Adaptive routing based on local information (deflection routing) • Also named alternate link routing • Another approach to adaptive routing with limited information • Selects from alternate links on a hop-by-hop basis instead of alternate routes on a end-to-end basis • Each node maintains a routing table indicating one or more outgoing links to each destination • The outgoing links are precomputed and can be properly ordered • A link is selected depending on its wavelength availability • Each node only maintains information regarding the wavelength availability on its outgoing links • No update messages are required

20. The RWA problem • Dynamic routing seems better than static routing: • Considers network state information when selecting lightpaths • BUT • Traditional dynamic routing algorithms selects the path maximizing the number of available wavelengths • the length of the routes and the wavelength distribution must be jointly considered in the lightpath selection process • Dynamic routing + global information = routing inaccuracy • Shortest path selects routes only based on hop length • Fixed-alternate routing is a trade-off mechanism

21. The RWA problem • Wavelength Assignment subproblem • Random, First-Fit, Least-Used, Most-Used, Min-Product, Least-Loaded, Max-Sum, Relative Capacity Loss1 • The literature results show that the First-Fit2: • Very good performance • Is very simple to implement • Examples: • Fixed-alternate routing and first-fit wavelength assignment (FAR-FF) • Least-Loaded routing and first-fit wavelength assignment (LLR-FF) • Fixed-alternate vs dynamic • LLR-FF performs better • LLR-FF longer setup delays and higher control overheads 1H.Zang, et al., “A Review of Routing and Wavelength Assignment Approaches for Wavelength-Routed Optical WDM Networks”, ONM, 2000 2 Y.Zhu, et al, “A Comparison of Allocation Policies in Wavelength Routing Networks”, Photon. Net. Commun.J., 20000

22. Outline • Introduction • Routing in OTN • Signalling in OTN • Signalling schemes • Updating procedure • Wavelength conversion • QoS in OTN • New routing proposals • The Routing Inaccuracy Problem • The Routing Inaccuracy Problem in hierarchical networks • Open issues

23. Signalling schemes • A signalling protocol is required to reserve resources along the selected route • Three signalling schemes • Source initiated reservation (SIR) • Wavelength resources are reserved as the control messages traverses along the forward path to the destination • Destination initiated reservation (DIR) • Connection request collecting wavelength availability on each link • Based on this information the destination node will select an available wavelength along the path • Intermediate-node initiated reservation (IIR) • Some intermediate nodes can initiate the wavelength reservation

24. Signalling schemes • SIR • Source routing (IP networks) • Wavelength/s are reserved as setup message is forwarded to the end • Wavelength number = f (wavelength information accuracy) • If source node has complete network state information: • May reserve only one wavelength • Complete network state information is not usual • Reserve all possible or a group of wavelengths • SIR problem: OVER-RESERVATION • Consequence: blocking of simultaneous connections

25. Signalling schemes • SIR

26. Signalling schemes • DIR • Blocking produced by outdated information • DIR outperforms SIR (no wavelength conversion)

27. Signalling schemes • SIR problem • Over-reservation (many wavelengths are reserved) • DIR problem • Outdated information (only one wavelength is reserved) • IIR: proposed solution • Allows reservations to be initiated by a set of intermediate nodes before connection request arrives at the destination node • Reduces the over-reservation • Reduces the vulnerable period = outdated information

28. Signalling schemes • IIR without last link conflict

29. Signalling schemes • IIR with last link conflict

30. Updating procedure • Update in OTN • Updating is needed to refresh network changes • Information about topology and resource availability • Done by LSAs (link state advertisements) based on flooding • Dynamic network = huge amount of update messages = congestion • Triggering policies: • Update reduction • Inaccurate network state information • Triggering policies • Periodical updating • Relative change based triggers • Current link state – past link state > th (%) • Absolute change based triggers • Number of changes > th • Lazy flooding (not published yet) • Threshold, exponential, fibonacci

31. Outline • Introduction • Routing in OTN • Signalling in OTN • Wavelength conversion • Wavelength conversion schemes • Wavelength conversion trade-off • Wavelength converters placement • Signalling schemes and wavelength conversion • QoS in OTN • New routing proposals • The Routing Inaccuracy Problem • The Routing Inaccuracy Problem in hierarchical networks • Open issues

32. Wavelength conversion schemes • A lightpath connection could be blocked by • A route with a free available wavelength from s-d cannot be found • A wavelength cannot be found between s-d although there is free capacity on every hop of the path • Wavelength continuity constraint (WCC) • Blocking due to the WCC is dominant in the global blocking • Solution: Remove the WCC • Introducing wavelength converters • Problem: Wavelengths converters are expensive • It is not feasible to include a wavelength converters on all the network nodes • Not affordable in the next 5 years (CISCO said)

33. Wavelength conversion schemes l1 Fibra #1 Fibra #1 l100 lp l1 Fibra #N Fibra #N l100 The labels indicate wavelengths (or frequencies)

34. Wavelength conversion schemes Fiber #1 Fibra #1 Fibra #1 lp {l..l}10 Fibra #N Fibra #N {l..l}10 The labels indicate wavelength bands

35. Wavelength conversion trade-off • Solution • Sparse wavelength conversion • Limited wavelength conversion • Sparse wavelength conversion • Wavelength conversion is available only on a set of nodes • New converters placement schemes must be developed • Limited wavelength conversion • Limits the range of conversion by a fixed value k • Translation degree D • Λ is the total number of wavelengths on a link

36. Wavelength conversion trade-off • In short • In WDM networks with centralized wavelength provisioning, sparse conversion could achieve nearly the same performance as full wavelength conversion • The question is: • Given a network topology, a certain number of wavelength converters, and traffic statistics • How can the wavelength converters be placed into the network in order to minimize the overall blocking probability?

37. Wavelength converters placement • Easy way • Analyze nodes more congested • These nodes are candidates to get conversion capabilities • Best way: • There are many converter placement algorithms for simple topologies (bus, ring) • The complex the topology the complex the algorithm • Many heuristics are currently defined for static routing + random • It has been demonstrated that any converter placement algorithm does not work on any RWA1 • Both issues must be tackled together 1X.Chu, B.Li, I.Chlamtac, “Wavelength Converter Placement under Different RWA Algorithms in Wavelength-Routed All-Optical Networks”, IEEE ToN, vol51, nº4, April 2003

38. Wavelength converters placement • Target: • Place the wavelength converters in those nodes so that blocking decreases • Proposals1 • Minimum blocking probability first (MBPF) • To be applied to the FAR-FF (fixed-alternate routing) • Weighted Maximum Segment Length (WMSL) • To be applied to the LLC-FF (dynamic routing) • Boths solutions assume: • Sparse wavelength conversion • Full range conversion (not limited) • Based on placing converters one by one sequentially 1X.Chu, B.Li, I.Chlamtac, “Wavelength Converter Placement under Different RWA Algorithms in Wavelength-Routed All-Optical Networks”, IEEE ToN, vol51, nº4, April 2003

39. Wavelength converter placement • MBPF: • Find the N feasible paths according to the FAR • Define candidate nodes as those nodes without conversion capabilities • Assume a WC on all candidate nodes (one by one) • Compute blocking based on a mathematical model • Place a WC in that node minimizing the blocking • Repeat the process till the M WC are placed • WMSL: • Assign a weight to each candidate node indicating the impact of this node on the blocking • Assume that the hop length significantly contributes to the blocking for WS networks • Introduce WC so that the end-to-end paths are divided into several “WS” segments. • Blocking is fully dependent on the segment length

40. Signalling schemes and wavelength conversion • DIR for networks with sparse wavelength conversion

41. Signalling schemes and wavelength conversion • IIR for networks with sparse wavelength conversion

42. Outline • Introduction • Routing in OTN • Signalling in OTN • Wavelength conversion • QoS in OTN • New routing proposals • The Routing Inaccuracy Problem • The Routing Inaccuracy Problem in hierarchical networks • Open issues

43. QoS in OTN • What does QoS mean in OTN? • The answer is not easy at all • What we know is how network performance can be evaluated • The blocking probability • Look at: • Customer needs • Applications requirements • Operator technical requirements • Service classes

44. QoS in OTN • Usability Requirements • blocking probability • network availability • application set-up time • connection set-up time • network robustness • throughput • delay • jitter • packet loss rate • BER (bit error rate) • bandwidth requirements • security requirements • nomadism • connectivity (number of senders/receivers) • naming and numbering • Operator Requirements (fulfill user requirements with the lowest possible quantity of resources and in the most efficent way) • business roles • elasticity (level of modification of original traffic shape) • interactivity • availability • nature of bidirectional traffic (symmetric or asymmetric) • provisioning of network resources • naming and numbering • supervision of network performance and faults (monitoring) • AAA (Authentication, Authorization, Accounting)

45. QoS in OTN • QoS classes • emergency („strict“ real-time) • conversational (real-time) • streaming („almost“ real-time) • prioritized elastic (business non-real-time) • best effort (non-real-time) • Selection of QoS parameters • required optical network service • max. and min. holding times • connection set-up and tear-down time • blocking probability • bandwidth requirements • latency • BER • routing stability • controlling and signalling delay • load overhead for admin, mgmt etc. • service availability • in case of OBS service: burst aggregation mechanism, burst loss and blocking probability • physical parameters in case of analogue optical network service • Optical network services • connection-oriented analogue • connection-oriented with wavelength switching • connection-oriented burst switching • connectionless burst switching • connectionless packet switching • transparent or opaque lightpaths • dedicated or shared lightpaths

46. Outline • Introduction • Routing in OTN • Signalling in OTN • Wavelength conversion • QoS in OTN • New routing proposals • MICORA (Minimum Coincidence Routing Algorithm) • PBR • The Routing Inaccuracy Problem • The Routing Inaccuracy Problem in hierarchical networks • Open issues

47. MICORA • Dynamic routing seems better than static routing: BUT • Traditional dynamic routing algorithms selects the path maximizing the number of available wavelengths • the length of the routes and the wavelength distribution must be jointly considered in the lightpath selection process • Dynamic routing + global information = routing inaccuracy • Shortest path selects routes only based on hop length • Fixed-alternate routing is a trade-off mechanism • New proposal • Trade-off between network performance and complexity • Fixed-alternate routing + wavelength assignment • MICORA (Minimum Coincidence Routing Algorithm) • Aims to optimize the physical route selection • Aims to reduce effects of selecting paths regardless network state • Does not select the k-shortest paths • Selects paths with minimum “coincidences”

48. MICORA • MICORA1 • Selects the k-(shortest & minimum coincident) paths • Computes the end to end paths considering the routes that have less shared links and minimum number of hops • Looks for the k-routes in two iterative basic steps • MICORA steps to compute k-routes • Selects the shortest path • Computes the Minimum Shared Link (MSL) MSL =NH * SL • NH: number of hops • SL: number of links shared between each path and the previous selected path • Select the path with minimum MSL • Repeat the last two steps (k-2) times 1S.Sánchez-López, X.Masip-Bruin, J.Solé-Pareta, “The Minimum Coincidence Routing in Optical Networks”, Workshop on G/MPLS, Girona, March 2006

49. MICORA: Illustrative example Shortest paths Selected paths 1-7-12-13 1-2-8-12-13 1-7-12-13 1-6-8-12-13 1-2-8-5-9-11-14-12-13 1-6-8-5-9-11-14-12-13 • Incoming request from node 1 to node 13 • K = 3 • MICORA steps: • Selects the shortest path as the first path

50. MICORA: Illustrative example Path = 1-7-12-13 SL MSL Selected paths 1-2-8-12-13 1 4 * 1 = 4 1-7-12-13 1-6-8-12-13 1 4 * 1 = 4 1-2-8-12-13 1-2-8-5-9-11-14-12-13 1 8 * 1 = 8 1-6-8-5-9-11-14-12-13 1 8 * 1 = 8 • MICORA steps: • Computes the MSL parameter • Selects the path minimizing the MSL value • First iteration to compute the second path • Second iteration to compute the third path