Restoration Routing in MPLS Networks Zartash Afzal Uzmi Computer Science and Engineering Lahore University of Management Sciences

Sept 17, 2005Lahore University of Management Sciences2 Outline Background: Quick overview of MPLS Introduction to restoration routing QoS Requirements: Why restoration routing? Local Restoration: Types of Backup Paths Local Restoration: Fault Models Backup Bandwidth Sharing Activation sets Typical example of restoration routing frameworks Optimized aggregate information scenario (oAIS) Experiments, simulations, and results

Sept 17, 2005Lahore University of Management Sciences3 IP versus MPLS In IP Routing, each router makes its own routing and forwarding decisions In MPLS, source router makes the routing decision Intermediate routers make forwarding decisions A path is computed and a “virtual circuit” is established from ingress router to egress router An MPLS path or virtual circuit from source to destination is called an LSP (label switched path)

Sept 17, 2005Lahore University of Management Sciences4 Restoration in IP network In traditional IP, what happens when a link or node fails? Information needs to be disseminated in the network During this time, packets may go in loops Restoration latency is in the order of seconds We look for restoration possibilities in an MPLS network

Sept 17, 2005Lahore University of Management Sciences5 QoS Requirements Bandwidth Guaranteed Primary Paths Bandwidth Guaranteed Backup Paths BW remains provisioned in case of network failure Minimal “Restoration Latency” Restoration latency is the time that elapses between the occurrence of a failure and the diversion of network traffic on a new path Path Restoration  More Latency Local Restoration  Less Latency

Sept 17, 2005Lahore University of Management Sciences6 Restoration in MPLS S123D Primary Path Backup Path Path Protection This type of “path Protection” still takes 100s of ms. We need to explore “Local Protection” to quickly switch onto backup paths!

Sept 17, 2005Lahore University of Management Sciences7 Types of Backup Paths A next hop (nhop) path that spans a link (i, j) is a backup path which: originates at node i, and provides restoration for a primary LSP that traverses (i, j), if (i, j) fails. i j PLR: Point of Local Repair nhop path that spans (i, j)

Sept 17, 2005Lahore University of Management Sciences8 Types of Backup Paths A next next hop (nnhop) path that spans a link (i, j) is a backup path which: originates at node i, and provides restoration for a primary LSP that traverses (i, j), if either (i, j) or node j fails. i j PLR: Point of Local Repair nnhop path that spans (i, j)

Sept 17, 2005Lahore University of Management Sciences9 Local Restoration: Fault Models ABCD Link Protection ABCD ABCD Node Protection Element Protection

Sept 17, 2005Lahore University of Management Sciences10 nhop and nnhop paths Primary Path Backup Path All links and all nodes are protected! AB C D E PLR: Point of Local Repair nnhop nhop

Sept 17, 2005Lahore University of Management Sciences11 Opportunity cost of backup paths Local Protection requires that backup paths are setup in advance Upon failure, traffic is promptly switched onto preset backup paths Bandwidth must be reserved for all backup paths This results in a reduction in the number of Primary LSPs that can otherwise be placed on the network Can we reduce the amount of “backup bandwidth” but still provide guaranteed backups?

Sept 17, 2005Lahore University of Management Sciences12 BW Sharing in backup Paths Example: max(X, Y) BW: Y AB CD E F G L1 L2 BW: X Primary Path Backup Path X X X YY X+YX+YSharing

Sept 17, 2005Lahore University of Management Sciences13 Activation Sets A B C D E Activation set for node BActivation set for link (A,B) A B C D E

Sept 17, 2005Lahore University of Management Sciences14 Restoration Routing Frameworks We look to answer the following questions? Who computes the primary path? What is the fault model (link, node, or element protection)? Where do the backup paths originate? Who computes the backup path? At what point do the backup paths merge back with the primary path What information is stored locally in the nodes/routers What information is propagated through routing protocols What if a primary path can not be fully protected The goal is almost always to maximize bandwidth sharing Performance criteria is almost always the maximum number of LSPs that can be placed on the network

Sept 17, 2005Lahore University of Management Sciences15 Extent of BW Sharing: oAIS Aggregate Information Scenario (AIS) F ij : Bandwidth reserved on link (i, j) for all primary LSPs G ij : Bandwidth reserved on link (i, j) for all backup LSPs Optimized AIS (oAIS) – (H ij instead of F ij ) Hij : Maximum bandwidth reserved on any one link by all backup paths spanning link (i, j) More Information propagated  More potential for BW sharing

Sept 17, 2005Lahore University of Management Sciences16 oAIS versus AIS: Example LSP Request-1 (src, dst, bw) = (A, C, 4) A F D E BC G F AB =4 H AB =4 G AF =4

Sept 17, 2005Lahore University of Management Sciences17 oAIS Example LSP Request-2 (src, dst, bw) = (A, C, 5) A F D E BC G F AB =9 H AB =5 G AF =4 G AG =5 F AB =4 H AB =4

Sept 17, 2005Lahore University of Management Sciences18 oAIS Example LSP Request-3 (src, dst, bw) = (D, E, 7) A F D E BC G F AB =9 H AB =5 G AF =4 G AG =5 F DE =7 G AF =7

Sept 17, 2005Lahore University of Management Sciences19 oAIS Example LSP Request-4 (src, dst, bw) = (A, C, 6) A F D E BC G F AB =9 G AF =7 G AG =5 F DE =7 Need to Evaluate cost of all possible backup paths? How much BW is shareable on (A, F)? AIS: Shareable = max(0, G AF - F AB ) = G AF - min(G AF, F AB ) = 0 Additional resv = 6 oAIS: (H AB ≤ F AB ) Shareable = G AF - min(G AF, H AB ) = 2 Additional resv = = 4 CIS: (link (A,B) knows BW red ) Shareable = G AF - BW red = = 3 Additional resv = = 3 H AB =5

Sept 17, 2005Lahore University of Management Sciences20 A Bandwidth Sharing Model Primary Path Backup Path All links and all nodes are protected! (Simplified for the Link Protection Fault Model) Recall the definition of nhop paths ABCD Link Protection

Sept 17, 2005Lahore University of Management Sciences21 Bandwidth Sharing Model Previous: A ij := Set of all primaries traversing through (i, j) B uv := Set of all backups traversing through (u, v) New definition (specialized for link protection case): A ij := Set of all primaries traversing through (i, j) B uv := Set of all nhop paths traversing through (u, v) µ ij := Set of all nhop paths that span (i, j)  ij uv := B uv ∩ µ ij (set of paths falling on (u,v) if (i,j) fails)

Sept 17, 2005Lahore University of Management Sciences22 Bandwidth Sharing Model i uv j k RED=7 BLU=2 3 OLD MODEL: A ij = {R, B} B uv = {R, B, …} A ij ∩ B uv = {R, B} || A ij ∩ B uv || = 2+7 = 9 Un-shareable = 9 Shareable = = 1 GRN=3 (New Request) Guv = 10 NEW MODEL: A ij = {R, B} B uv = {nh ij r, nh ij b, …}(nhops through (u, v)) µ ij = {nh ij r, nh ij b, …}(nhops spanning (i, j))  ij uv = µ ij ∩ B uv = {nh ij r, nh ij b } ||  ij uv || = = 9(Un-shareable) Shareable = G uv - ||  ij uv || = = 1

Sept 17, 2005Lahore University of Management Sciences23 Bandwidth Sharing Model i uv j k RED=7 BLU=2 3 OLD MODEL: A ij = {R, B} B uv = {R, B, …} A ij ∩ B uv = {R, B} || A ij ∩ B uv || = 2+7 = 9 Un-shareable = 9 Shareable = = 1 NEW MODEL: A ij = {R, B} B uv = {nh ij r, nh jk b, …}(nhops through (u, v)) µ ij = {nh ij r, nh ij b, …}(nhops spanning (i, j))  ij uv = µ ij ∩ B uv = {nh ij r } ||  ij uv || = 7(Un-shareable) Shareable = G uv - ||  ij uv || = = 3 GRN=3 (New Request) Guv = 10

Sept 17, 2005Lahore University of Management Sciences24 Simulation Experiments Rejected Requests Experiments Measure the number of rejected LSPs for each information scenario Simulated on two topologies Network Loading Experiments Link capacities set to infinity Measure the total bandwidth required to service a given set of LSPs for each information scenario Simulated on two topologies

Sept 17, 2005Lahore University of Management Sciences25 Single Link Protection: Network 1

Sept 17, 2005Lahore University of Management Sciences26 Single Link Protection: Network 1

Sept 17, 2005Lahore University of Management Sciences27 Single Link Protection: Network 2

Sept 17, 2005Lahore University of Management Sciences28 Single Link Protection: Network 2

Sept 17, 2005Lahore University of Management Sciences29 Single Node Protection: Network 1

Sept 17, 2005Lahore University of Management Sciences30 Single Element Protection: Network 1

Sept 17, 2005Lahore University of Management Sciences31 Questions & Answers

Sept 17, 2005Lahore University of Management Sciences32 Restoration in MPLS Primary Path Backup Path Path Protection MPLS path Protection may take 100s of ms, whereas MPLS Local protection takes less than 10 ms. AB CDE