1. December 20, 2004MPLS: TE and Restoration1 MPLS: Traffic Engineering and Restoration Routing Zartash Afzal Uzmi Computer Science and Engineering Lahore University of Management Sciences

2. December 20, 2004MPLS: TE and Restoration2 Outline Background IP Routing and related problems MPLS Routing Labels and label switched paths Traffic Engineering Restoration Routing Our Research

3. December 20, 2004MPLS: TE and Restoration3 Application Scenario A service provider (ISP) with geographically distributed points of presence (PoPs) ISP provisions applications with “strict” network requirements (e.g., VoIP service) Two major requirements: Guaranteed minimum bandwidth between a source and a destination Less then 50ms recovery time in the event of any network element failure

4. December 20, 2004MPLS: TE and Restoration4 Traditional (IP) Routing Individual nodes (routers) take A routing decision, and A forwarding decision Forwarding is destination based When routers forward packets, they only look at the destination address May lead to congestion in some parts of the network

5. December 20, 2004MPLS: TE and Restoration5 IP Routing Example Packet 1: Destination A Packet 2: Destination B S computes shortest paths to A and B; finds D as next hop Both packets will follow the same path Leads to IP hotspots! Solution? Try to divert the traffic onto alternate paths 11 12 A B C A B S D

6. December 20, 2004MPLS: TE and Restoration6 IP Routing Example Increase the cost of link DA from 1 to 4 Traffic is diverted away from node D A new IP hotspot is created! Solution(?): Network Engineering Put more bandwidth where the traffic is! Leads to underutilized links; not suitable for large networks 14 12 A B C S A B D

7. December 20, 2004MPLS: TE and Restoration7 IP Routing Vs MPLS Traditional IP Routing Multiprotocol Label Switching (MPLS) SD 54 3 21 MPLS allows overriding shortest paths!

8. December 20, 2004MPLS: TE and Restoration8 Routing Along Explicit Paths Idea: Let the source make the complete routing decision; source decides the complete path for each flow How this may be accomplished? Attach a label to the IP packets; let everyone make forwarding decision on that label On what basis should you choose different paths for different flows? Define some constraints and hope that the constraints will take “some” traffic away from the hotspot! Use CSPF instead of SPF (shortest path first)

9. December 20, 2004MPLS: TE and Restoration9 MPLS: Basics How did they route along parallel paths? They decided to use a label They also decided to use a new label at each hop to save on label space Terminology LSP: Label switched path LSR: Label switch router IP DatagramLabel

10. December 20, 2004MPLS: TE and Restoration10 MPLS Flow Progress LSR1 LSR2 LSR3 LSR5 LSR6 R1R2LSR4 D 1 - R1 receives a packet for destination D connected to R2 R1 and R2 are regular routers D destination

11. December 20, 2004MPLS: TE and Restoration11 MPLS Flow Progress LSR1 LSR2 LSR3 LSR5 LSR6 R1R2LSR4 D 2 - R1 determines the next hop as LSR1 and forwards the packet (Makes a routing as well as a forwarding decision) D destination

12. December 20, 2004MPLS: TE and Restoration12 MPLS Flow Progress LSR1 LSR2 LSR3 LSR5 LSR6 R1R2LSR4 D 3 – LSR1 establishes a path to LSR6 and “PUSHES” a label (Makes a routing as well as a forwarding decision) D destination 31

13. December 20, 2004MPLS: TE and Restoration13 MPLS Flow Progress LSR1 LSR2 LSR3 LSR5 LSR6 R1R2LSR4 D 4 – LSR3 just looks at the incoming label LSR3 “SWAPS” with another label before forwarding D destination 17 Labels have local signifacance!

14. December 20, 2004MPLS: TE and Restoration14 MPLS Flow Progress LSR1 LSR2 LSR3 LSR5 LSR6 R1R2LSR4 D 5 – LSR6 looks at the incoming label LSR6 “POPS” the label before forwarding to R2 D destination 17 Path within MPLS cloud is pre-established: LSP (label-switched path)

15. December 20, 2004MPLS: TE and Restoration15 TE Capability Recap Who establishes the LSPs in advance? Ingress routers How do ingress routers decide not to always take the shortest path? Ingress routers use CSPF (constrained shortest path first) instead of SPF Examples of constraints: Do not use links left with less than 7Mb/s bandwidth Do not use links with blue color for this request Use a path with delay less than 130ms

16. December 20, 2004MPLS: TE and Restoration16 IP versus MPLS: Summary In IP Routing, each router makes its own routing and forwarding decisions In MPLS, source makes the routing decision Intermediate routers make forwarding decisions In IP Routing, packets usually follow the SPF In MPLS packets follow the CSPF In IP Routing, restoration takes few seconds In MPLS, restoration can be of the order of 10ms

17. December 20, 2004MPLS: TE and Restoration17 CSPF What is the mechanism? First prune all links not fulfilling constrains Now find shortest path on the rest of the topology Requires some Reservation mechanism Changing state of the network must also be recorded and propagated For example, ingress needs to know how much bandwidth is left on links The information is propagated by means of routing protocols and their extensions

18. December 20, 2004MPLS: TE and Restoration18 Restoration Routing Application of Traffic Engineering

19. December 20, 2004MPLS: TE and Restoration19 Restoration in IP network In traditional IP, what happens when a link or node fails? Failure information must be disseminated in the network During this time, packets may go in loops Restoration latency is in the order of seconds

20. December 20, 2004MPLS: TE and Restoration20 Restoration in MPLS S123D Primary Path Backup Path Path Protection This type of “path Protection” still takes 100s of ms.

21. December 20, 2004MPLS: TE and Restoration21 Restoration in MPLS S123D Primary Path Backup Path Element Local Protection Local Protection takes order of 10ms

22. December 20, 2004MPLS: TE and Restoration22 Opportunity Cost Fast restoration requires that backup paths are established “in advance” Backup provisioning requires bandwidth reservation along the backup paths Backup bandwidth is taken from the primary bandwidth Fewer primary LSPs can be accommodated Can we do something to avoid “wasting” so much bandwidth in backup paths? Try to share the backup bandwidth!

23. December 20, 2004MPLS: TE and Restoration23 BW Sharing in Backup Paths Assumption: Two primary paths, whose backups are sharing bandwidth, must not fail together Is this assumption realistic? Failure is a low probability event Once failure occurs, new primary paths with new backups are computed Failure of another element in that time is unlikely

24. December 20, 2004MPLS: TE and Restoration24 BW Sharing in Backup Paths Example S1D1 S2D2 453 b1 b2 max(b1, b2) = LSR

25. December 20, 2004MPLS: TE and Restoration25 Activation Sets When an element fails, a number of backups are activated “simultaneously” Such backups are in the activation set of that protected element Backups in a single activation set can not share the bandwidth Backups in different activation sets may share the bandwidth

26. December 20, 2004MPLS: TE and Restoration26 Activation Set for node j

27. December 20, 2004MPLS: TE and Restoration27 Activation Set for link(i,j)

28. December 20, 2004MPLS: TE and Restoration28 Considerations What constitutes a backup sharing scheme? How much information is propagated through routing protocols Who propagates that information Who maintains that information Design an algorithm which provides Maximum bandwidth sharing Minimum information propagation

29. December 20, 2004MPLS: TE and Restoration29 Simulation Parameters 20 node ISP network Each link with capacity 120 units 380 possible pairs LSP requests arrive one by one Ingress/Egress chosen randomly Bandwidth demand for each request is uniformly distributed between 1 and 6 Call holding time is infinite 100 experiments with randomly selected ingress/egress pairs and traffic demands

30. December 20, 2004MPLS: TE and Restoration30 Schemes Compared Kini’s scheme Signaled path is suboptimal Reservations made are corrective Facility Optimal path is signaled Static pools for primary and backups NPP Primary and backups dynamically allocated Optimal path is signaled

31. December 20, 2004MPLS: TE and Restoration31 Results

32. December 20, 2004MPLS: TE and Restoration32 Results