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TCOM 513 Optical Communications Networks

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TCOM 513 Optical Communications Networks

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  1. TCOM 513Optical Communications Networks Spring, 2005 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: Optical control planes • Week 6: The business of optical networking: economics and finance • Week 7: Future directions in optical networking

  3. Resources • www.sorrentonetworks.com/whitepapers.asp • Get their “IP over Optical” presentation • www.tellium.com/optical/presentations.html • Get “Convergence of IP and Optics” • Other presentations useful as well • www.nanog.org/mtg-9905/mpls.html • Right click and you can get the slides (Nortel) • www.cellstream.com/prod08.htm • Multiprotocol Label Switching • You’ll have to pay for this one: $27.95 • www.itprc.com • Info about various routing protocols

  4. Resources (continued) • www.cis.ohio-state.edu/~jain/ • Tutorials and papers on various networking subjects from Raj Jain • www.cisco.com/warp/public/503/2.html • Cisco networking icons in various formats • www.iec.org • Download MPLS tutorial from Trillium

  5. Topics • Switching problem and label switching • MPLS • MPlS • Current Network Problems • Enhancing Internet Protocol (IP) Networks To Support A Variety of Applications • Quality of Service (QoS) As A Solution • Real-time Application Protocols • Two Locations for QoS: Access And Backbone • Diffserv and QoS • Cyber Security and QoS

  6. Economic reality: Carrier’s dilemma

  7. How can carriers find new high-margin service offerings?

  8. Network reality—SONET infrastructure

  9. Network reality: DWDM • Most packet data networks are meshed

  10. How to best marry these three…

  11. Fundamental conflicts • Topology and technology • Data networks on SONET and DWDM • Some services still require SONET 50 msec restoration • Economics • Packet data networks are naturally resilient • May not justify cost for SONET redundancy in order to collect lower revenue for “best effort” service • Providers are looking for network to support voice, private line, data with same infrastructure

  12. How to deal with problem and retain (or improve) profitability • Migrate to intelligent optical networking • Offer new services • Higher bandwidth services • Optical VPNs: Public services that act like private networks • Migrate to mesh when and where appropriate • Dedicated 50msec restoration for those services requiring it (and willing to pay for it) • Shared mesh restoration for resilient packet services (FR, ATM, IP) • May save up to 60% in costs • Send IP and Optical to marriage mediation • Must learn to live together • Divorce is not an option

  13. General approach • Virtualization • Virtual: has same functionality as a particular physical network, but does it through emulation (essentially software) • Make physical networks more virtual • To speed provisioning • To allow faster upgrades • Make virtual networks more physical • To reduce overhead

  14. Problem: routers have limited visibility • Routers do not naturally see • Rings • Connections • Native IP is connectionless protocol • Routers do see • Ports and addresses (i.e., routing tables) • Proprietary QoS queues

  15. Brief historical background • Early Internet was concerned only with mechanics of reliable data transfer • Simple applications such as FTP, remote login • Used software-based routers • Later devices that could switch in hardware at levels 2 and 3 had to be deployed • Layer 2 switching: addressed bottlenecks in LANs • Layer 3 switching: addressed bottlenecks in layer 3 routing by moving route lookup to high-speed hardware • Issues • Did not address service requirements for info in packets • Based on shortest path only • No consideration of jitter, delay, congestion • Best effort utilizing algorithms in network components • Little or no global control or optimization

  16. The switching problem OSI Reference Model Application Presentation Session Transport Route/ Switch Network Knows about other workgroups Router Workgroup Switch Hub Data Link Knows about local workgroup Physical Repeater Doesn’t know anything

  17. The switching problem (continued) • What does a switch do? • Establishes a path through a network end-end (“connection”) • Example: circuit switch used in telephony • No need for decisions at each point along the way

  18. The switching problem (continued) • What does a router do? • Looks at incoming packet address and looks it up in table to find outgoing port • No dedicated paths established (“connectionless”) • Router does not know total path • Dynamic paths • Path for subsequent packets going to same destination may change due to congestion or other problems • Requires seach • Complexity ~ O(log2 n), where n is number of entries in routing table

  19. The switching problem (continued) • IP traffic: primarily routed • ATM traffic: primarily switched • Permanent virtual circuit (PVC) — fixed • Switched virtual circuit (SVC) — dynamic

  20. The switching problem (continued) • How to switch (route) packets with least expenditure of processing? • How to allow different services to coexist on same IP network? • At present, isochronous traffic (e.g., voice) does not work if network utilization greater than about 25% • Requires QOS (quality of service) or COS (class of service) • How to allow different protocols on same network? • IP • ATM • FR

  21. The switching problem (continued) • How to have a single packet forwarding method or paradigm while still allowing for different routing paradigms • OSPF: Open Shortest Path First • PNNI: Private Network to Node Interface or Private Network to Network Interface • An ATM routing protocol

  22. Desired solution elements • Combine best of switching and routing • Do routing once to find a path • Record path elements • Apply tag to subsequent packets with path information • No need for looking into these packets to fetch addresses and do lookups at each router • Complexity ~ O(1), because indexing is used • Initially called “Tag switching” or “Label switching” • Similar (but not identical) to Post Office method • Do handwriting recognition on a letter once • Encode address info at bottom of envelope with bar code • Use bar code to route letter through mail system

  23. One of the many ways of getting from A to B: • BROADCAST: Go everywhere, stop when you get to B, never ask for directions. • HOP BY HOP ROUTING: Continually ask who’s closer to B go there, repeat … stop when you get to B. “Going to B? You’d better go to X, its on the way”. • SOURCE ROUTING: Ask for a list (that you carry with you) of places to go that eventually lead you to B. “Going to B? Go straight 5 blocks, take the next left, 6 more blocks and take a right at the lights”. Source: Nortel

  24. LANE#1 TURN RIGHT USE LANE#2 Label Switching • Have a friend go to B ahead of you using one of the previous two techniques. At every road they reserve a lane just for you. At every intersection they post a big sign that says for a given lane which way to turn and what new lane to take. LANE#1 LANE#2 Source: Nortel

  25. Basic idea behind label switching • Set up “virtual circuit” between source and destination • Assign numbers to each path element • Copy numbers to packets • Switch packet based on number • Ingress router or host applies label • Exit router strips it off

  26. Basic idea behind label switching (continued) • Forwarding of packets done using a short, fixed-length label rather than disassembly of complete address • Addressing scheme different for different protocols (ATM, FR, IP, etc) • Labels identify streams of traffic • Label table much smaller than routing table • Each label represents a set of destination addresses • Packets with same label treated as a group, not individually • Utilizes Time-To-Live (TTL) counter accurately maintained • Idea is similar to PVCs and SVCs

  27. Solution: Multiprotocol Label Switching (MPLS) • Layer 3 technology • Works with any protocol, but primarily used for IP traffic • Glues connectionless IP to connection-oriented networks • IP to ATM • IP to optical networks • Referred to as “shim layer” • Something between layer 2 and layer 3 to make them fit better

  28. Solution (continued) • Addresses problems of modern networks • Speed • Scalability • Quality of Service (QoS) management • Traffic engineering (TE) • Multiprotocol

  29. MPLS functions • Mechanisms to manage traffic flows of various granularities • Independent of layer 2 and layer 3 specs • But serves as “glue” • Maps IP addresses to fixed length labels to speed forwarding • Interfaces to existing routing protocols such as OSPF • Supports IP, FR, ATM layer 2 protocols

  30. MPLS paths • Utilizes label-switched paths (LSPs) • Sequence of labels at every node from source to destination • Each label represents a path between two nodes • Set up in two ways • Hop-by-hop • Explicit routing • Label establishment • Prior to packet transmission (control-driven) • Upon detection of a certain flow (data-driven)

  31. MPLS devices • LSR: Label Switched Router • High speed router (switch) in core of MPLS network • Participates in establishment of LSPs • LER: Label Edge Router • Operates at edge of access network and MPLS network • Forwards traffic to MPLS network after establishing paths and attaching labels

  32. Aggregating addresses in one label • Aggregating addresses may be done in different ways • Flow direction • Traffic priority • Traffic type • Source address Label Switched Path 225 Part of Label Information Base Source: Cellstream

  33. There are many examples of label substitution protocols already in existence • ATM - label is called VPI/VCI and travels with cell. • Frame Relay - label is called a DLCI and travels with frame. • TDM - label is called a timeslot its implied, like a lane. • X25 - a label is an LCN • Proprietary PORS, TAG etc.. • One day perhaps Frequency substitution where label is a light frequency (or wavelength)?

  34. Route at edge, switch in core Source: Nortel

  35. Label creation methods • Topology-based • Uses normal processing of routing protocols • Request-based • Uses processing of request-based control traffic • Traffic-based • Uses reception of packet to trigger assignment and distribution of label

  36. MPLS terminology • Label: short, fixed length, contiguous bits, locally significant (i.e., on a single link) • Label switching router (LSR): Routers that use labels • Traditional router • ATM switch • FR switch • Optical switch • Forwarding equivalence class (FEC): Same path and same treatment => same label • Label switched path (LSP): Particular path through network • MPLS domain: contiguous set of MPLS nodes in one administrative domain

  37. MPLS terminology (continued) • MPLS edge node: ingress or egress node • Label information base (LIB): label tables in each MPLS node which contain path information associated with labels • Label distribution protocol (LDP): Method for distributing label information • Flow: flow of data from one application to another • Stream: Aggregate of one or more flows

  38. Label switched path (vanilla)

  39. Standard IP network

  40. Normal routing of packet

  41. Label distribution by MPLS

  42. MPLS switching through network

  43. Shim label for PPP traffic (most common in IP networks) • Packet structure Link layer Header SHIM Network (IP) Layer Header Payload MPLS label (Mlabel) Exper. S TTL 0 19 20 22 23 24 31 Exper.=experimental; COS TTL = time to live S= Bottom of stack (for multiple labels) Source: Cellstream

  44. Labels can be stacked Labels popped 225 Exper. 0 10 33 Exper. 0 7 105 Exper. 1 3

  45. What happens when label looked up • Next destination to which packet to be forwarded is found • The correct operation required to be performed on packet before forwarding • Replace top label stack entry with a new one • Pop entry off stack (exposing next one down) • Replace top label stack, push one or more new entries onto stack

  46. Forwarding results of lookup LSP 33 Label Switched Path 225 LSP 196 LSP 75

  47. Labels can be merged Label Switched Path 33 LSP 196 Label Switched Path 225

  48. Labels can also be tunneled LSP 33 LSP 33 LSP 99 LSP 225 LSP 225

  49. Routing protocols in MPLS • OSPF: Open Shortest Path First • Intended to yield better routing • Based on link-state technology • Allows Variable Length Subnet Masks (VLSM) • Other enhancements • BGP: Border Gateway Protocol • Purpose is to advertise to other routers what your network can route to (internally) • IS-IS: Intermediate System to Intermediate System • Authentication between routers

  50. Summary of motivations for MPLS • Simplified forwarding based on exact match of fixed length label • Initial drive for MPLS was based on existence of cheap, fast ATM switches • Separation of routing and forwarding in IP networks • Facilitates evolution of routing techniques by fixing the forwarding method • New routing functionality can be deployed without changing the forwarding techniques of every router in the Internet • Facilitates the integration of ATM and IP • Allows carriers to leverage their large investment of ATM equipment