TCOM 513 Optical Communications Networks

1. TCOM 513Optical Communications Networks Spring, 2006 Thomas B. Fowler, Sc.D. Senior Principal Engineer Mitretek Systems

2. Topics for TCOM 513 • Week 1:Wave Division Multiplexing • Week 2: Opto-electronic networks • Week 3: Fiber optic system design • Week 4: MPLS and Quality of Service • Week 5: Heavy tails, Optical control planes • Week 6: The business of optical networking: economics and finance • Week 7: Future directions in optical networking

3. Heavy-tailed Distributions • For large x values, cumulative distribution function F(x) has property that its complementary distribution and where Setting b=2 and differentiating above equation,

4. Heavy-tailed Distributions (continued) • Recall from calculus that only if p > 1

5. Heavy-tailed Distributions (continued) • Since is fixed, so then the variance is determined by • If in addition b< 1, then for the mean, since

6. Physical Significance of Infinite Variance • Consider finite variance on expanding time scales:

7. Physical Significance of Infinite Variance (continued) • Infinite variance case 0 -20 20 0 -5 5 5 0 -5 -50 50 0

8. Network session or connection size (length in bytes) • Empirical data from 220,000 connections at www site: Source: Willinger & Paxson, 1998

9. Network session or connection size (length in bytes) (continued) • Use points to calculate F(x), then plot 1-F(x) against corresponding session size • Behavior agrees with Pareto distribution • Yields • Corresponds to infinite variance • Aggregate property of traffic source

10. Heavy-tailed distributions (continued) • Upper tail declines like power law with exponent < 2 • Appears as lack of convergence of sample variance as function of sample size • Pareto distribution is simplest heavy-tailed distribution • Effect increases as a decreases

11. Heavy-tailed Distributions (continued) Pareto distribution, a=0.5, k=1 Pareto distribution, a=1, k=1

12. Heavy-tailed Distributions (continued)

13. Heavy-tailed Distributions (continued)

14. Relationship of Key Traffic Concepts Heavy tails Files, transmission times Order of discovery Infinite variance Transmission times Self-similarity Packets, sessions Long-range dependence Packets, sessions Order of explanation Burstiness on multiple scales Packets

15. Analyzing networks in terms of planes Management Deploys and manages services Minimal in standard IP networks Control Network-level coordination State information management Decision-making Action invocation Best effort utilizing h/w and s/w in components in standard IP networks Data or bearer Physical transmission of data through network

16. Traditional approaches to integration

18. Problems of traditional approach

19. Steps in the evolution of network architectures (continued) • Dynamic IP Optical Overlay Control Plane • Ring replaced by mesh using DWDM • Dynamic wavelength provisioning • Easier, more scalable control • Enhanced restoration capabilities • Integrated IP Optical Peer Control Plane • Integrate dynamic wavelength provisioning processes of Optical Transport Network (OTN) into IP network routing • Make OTN visible to IP network

20. “Old World” networks • Utilize SONET for delivering reliable WAN connectivity at layer 1 • Large, interconnecting rings • Lots of expensive hardware, e.g., ADMs • Utilize ATM for provisioning data services • Connection oriented • Can assure QoS, VPN • High operational cost for high reliability • High overhead (~25%)

21. “New World” networks • Eliminate SONET, ATM • Still need to provide layer 2 functionality Source: Tomsu & Schmutzer

22. IP/Optical adaptation Packet over SONET (POS) Ref. p. 91 PPP does L2 functions Dynamic Packet Transport (DPT) SRP=spatial reuse protocol; Intended for ring architecture Ref. p. 105 Gigabit Ethernet ATM Simple Data Link (SDL) Source: Tomsu & Schmutzer

23. Two-layer architecture IP edge routers aggregatetraffic and multiplex it onto“Big Fat Pipes” Source: Tomsu & Schmutzer

24. Two-layer architecture (continued) • Ingress traffic multiplexed onto “big fat pipes” (BFPs) • Provided by optical layer • Optical layer functions as cloud for interconnecting attached devices • Key point is that configuration within optical layer controlled at same time that service layer is configured (common management) • May use either DWDM or dark fiber • Can be point-to-point, ring, or mesh • Similar to ATM networks because any logical connectivity between IP nodes can be implemented

25. “New World”: Overlay and Peer Models • Main distinction in “New World” models is between overlay and peer models • Overlay • OTN (Optical Transport Network) or bearer plane is opaque to IP network • OTN merely provides connections to IP network above • Has its own control plane • Peer • Common control plane for both OTN and IP networks • Optical connections derived from IP routing knowledge (paths)

26. Overlay and Peer Models (continued) IP Network IP + Optical Network Peer Model Optical Transport Network Overlay Model Source: Tomsu & Schmutzer

27. MPlS overlay model • Two separate control planes • Interaction minimized • IP network routing and signaling protocols independent of corresponding optical network protocols • Edge devices see only lightpaths, not topology • Similar to IP over ATM • Client/Server model: IP ~ client, optical network ~ server • Two versions • Static • Signaled

28. MPlS overlay model PXC Core Optical Network GigE OC12 PXC PXC Metro optical network (Access Ring) DWDM Core optical network (Regional Ring) DWDM Metro optical network (Access Ring) DWDM PXC OC12/ OC48 OC12/ OC48 Optical Network UNI Source: Cellstream

29. MPlS overlay model—another view

30. Dynamic Optical Control Plane • Central problem: wavelength provisioning • Optical cross-connects (OXCs) combined with IP routing intelligence to control wavelength allocation, setup, and teardown • Done dynamically • Allows same elements to be reconfigured rapidly to improve utilization • Other benefits • Expedited provisioning • Enhanced restoration • Any virtual topology can be provided

31. Implementing dynamic optical control plane: Wavelength routing • IP routing protocols (e.g., OSPF) adapted to create routing protocol used by wavelength routers (WRs) in optical layer • Connections can be dynamically provisioned to interconnect IP routers • Wavelength routing protocol only protocol running on WRs • IP network does not participate in wavelength routing process • IP network interacts with OTN on client/server relationship • Overlay model • Typical use: OTN owned by optical interexchange carrier, other service providers buy lightpaths to establish their own IP networks

32. Overlay model: wavelength routing IP Router B IP Router A IP Network Wavelength RoutingNetwork Lightpath (IP Connectivitybetween A and B) WavelengthRouter WavelengthRouter Source: Tomsu & Schmutzer

33. Wavelength routing control plane • Responsible for establishing end-end connection or lightpath • Two methods of implementing IP-based control plane • Attach external IP routers to each OXC • Integrate IP routing functionality into OXC Source: Tomsu & Schmutzer

34. Method 1: details • Routers with control interface called wavelength routing controllers (WRCs) • WRCs provide needed functions • Resource management • Configuration and capacity management • Addressing • Routing • Traffic engineering • Topology discovery • Restoration

35. Method 1: details (continued) • Control interface specifies primitives used by WRC • Connect: cross connect input, output channels • Disconnect: remove connection • Switch: change incoming channel/link combination • OXC communicates with WRC • Alarm: failure condition

36. Cross-connect tables illustration Source: Tomsu & Schmutzer

37. Digital communication network • Control plane exchanges control traffic through Digital Communications Network (DCN) • In band • Default-routed lightpath used • Out of band • Routers and leased lines used to set up completely separate IP network interconnecting all WRs

38. Operation of control plane • WRs exchange info about network topology and status of OTN across DCN • All elements have unique IP addresses • Routers • Amplifiers • Interfaces • MPlS used for lightpath routing and service provisioning in OTN • Provisions LSPs in service layer

39. Route calculation for lightpaths • Centralized • Distributed

40. Centralized lightpath routing • Uses traffic engineering control server • Server maintains information database • Topology • Inventory of physical resources • Current allocations • WRs request lightpath to be set up • Server checks resource availability and initiates resource allocation at each hop

41. Centralized lightpath routing (continued) Source: Tomsu & Schmutzer

42. Distributed lightpath routing • Each WR maintains information database and set of routing algorithms • Perform neighbor discovery after bootup • Builds topology map • Creates resource hierarchies • Constraint-based routing used to define appropriate path through network

43. Distributed lightpath routing (continued) Source: Tomsu & Schmutzer

44. Distributed lightpath routing (continued) Source: Tomsu & Schmutzer

45. Comparing WRs and LSRs • Similar in architecture and functionality • LSR (Label Switched Router) provides unidirectional point-to-point connections (LSPs=Label Switched Paths) • Traffic aggregated in FECs (Forwarding Equivalence Classes) • WR (Wavelength Router) provides unidirectional optical point-to-point connections (lightpaths) • Used to transmit traffic aggregated by service layer • Two key differences • LSR must process packets (do label lookup) • WR does not do any packet level processing • Switching info for WR is lightpath ID, not any packet label

46. Comparing WRs and LSRs (continued) • Lightpaths are very similar to LSP • Unidirectional, point-to-point virtual paths between ingress and egress node • LSPs define virtual topology over data network, as do lightpaths over OTN • Allocating label  allocating channel to a lightpath Source: Tomsu & Schmutzer

47. Comparing WRs and LSRs (continued) • MPLS label = fixed length value in packet header • MPlS label = certain wavelength over fiber span • Label space is significant • In MPLS, may be thousands of FECs • Won’t work in MPlS, because only 40-128 labels (ls) available • Must aggregate traffic into traffictrunks ~ lightpath • Suitable for core use

48. Integrated Optical Peer Control Plane • Second of the methods of integrating IP and optical • Differs from overlay model in that there is a single control plane rather than two separate control planes • IP network sees optical network • Uses MPLS Traffic Engineering (MPLS-TE) to implement control plane and provision lightpaths across OTN and service layer

49. MPlS peer model (continued) • Single control plane spans entire network • IP, Optical networks treated as single network • OXCs treated as IP routers with assigned IP addresses • Edge devices see entire network • No distinction between NNI, UNI • Single routing protocol over both domains • Topology and link state information maintained by IP and optical routers is same • Reuses existing MPLS framework

50. Control Plane Functions • Control Channels • May be on dedicated fiber(s) • Could also be Ethernet connection or IP tunnel • Bi-directional • Manage links • Restoration • Establish LSPs