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

Dec 20, 2005Lahore University of Management Sciences2 Outline Background Network Services and QoS Architectural Requirements IP and MPLS Introduction to restoration routing Local Restoration: Types of Backup Paths Local Restoration: Fault Models Backup Bandwidth Sharing Activation sets Restoration routing framework Components Typical example Evaluation and Experimentation

Dec 20, 2005Lahore University of Management Sciences3 Outline Background Network Services and QoS Architectural Requirements IP and MPLS Introduction to restoration routing Local Restoration: Types of Backup Paths Local Restoration: Fault Models Backup Bandwidth Sharing Activation sets Restoration routing framework Components Typical example Evaluation and Experimentation

Dec 20, 2005Lahore University of Management Sciences4 Network Traffic and Services Network Traffic today Not what it was 10 years ago Multimedia intensive New and interactive applications are emerging Internet telephony Videoconferencing Streaming media (voice and video) Remote collaboration (e.g., remote desktop) Many new applications are real-time More and more users of these applications Burstiness behavior has changed over the years!

Dec 20, 2005Lahore University of Management Sciences5 Current Network Architecture Internet is popular because It is inexpensive Internet is inexpensive because It uses resource sharing by means of statistical multiplexing Current Internet architecture Uses packet switches with buffers Required buffer size is primarily determined by a random traffic pattern Buffer size optimization Too low  High drop rate Too high  High delay

Dec 20, 2005Lahore University of Management Sciences6 Architectural Requirements Emerging applications Two-way interactive communications One-way streaming media type applications Under normal conditions We are worried about the two-way interactive applications When resources fail We are also worried about the one-way applications Current Internet architecture is not suitable for new and emerging applications New architectures are being researched

Dec 20, 2005Lahore University of Management Sciences7 Architectural Requirements New network architectures All circuit-switched? Mix of packet-switch and “circuit-switch-like” Experience with networks Bigger buffers are required when there is more randomness and more aggregation Should use circuits at places where we see more randomness Example: 100x100 project Edge network is packet-switched Core network is virtual-circuits

Dec 20, 2005Lahore University of Management Sciences8 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)

Dec 20, 2005Lahore University of Management Sciences9 Outline Background Network Services and QoS Architectural Requirements IP and MPLS Introduction to restoration routing Local Restoration: Types of Backup Paths Local Restoration: Fault Models Backup Bandwidth Sharing Activation sets Restoration routing framework Components Typical example Evaluation and Experimentation

Dec 20, 2005Lahore University of Management Sciences10 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

Dec 20, 2005Lahore University of Management Sciences11 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

Dec 20, 2005Lahore University of Management Sciences12 Restoration in MPLS S123D Primary Path Backup Path Path Protection This type of “path Protection” still takes 100s of ms. We may explore “Local Protection” to quickly switch onto backup paths!

Dec 20, 2005Lahore University of Management Sciences13 Local Restoration: Fault Models ABCD Link Protection ABCD ABCD Node Protection Element Protection

Dec 20, 2005Lahore University of Management Sciences14 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

Dec 20, 2005Lahore University of Management Sciences15 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?

Dec 20, 2005Lahore University of Management Sciences16 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

Dec 20, 2005Lahore University of Management Sciences17 Activation Sets A B C D E Activation set for node BActivation set for link (A,B) A B C D E

Dec 20, 2005Lahore University of Management Sciences18 Outline Background Network Services and QoS Architectural Requirements IP and MPLS Introduction to restoration routing Local Restoration: Types of Backup Paths Local Restoration: Fault Models Backup Bandwidth Sharing Activation sets Restoration routing framework Components Typical example Evaluation and Experimentation

Dec 20, 2005Lahore University of Management Sciences19 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

Dec 20, 2005Lahore University of Management Sciences20 Evaluation & Experimentation Traffic Generation Use existing or emerging traffic models Consider call holding times and multi-service traffic Rejected Requests Experiments Measure the number of rejected requests Simulate on various topologies Network Loading Experiments Set link capacities to infinity Measure the total bandwidth required to service a given set of requests Simulate on various topologies

Dec 20, 2005Lahore University of Management Sciences21 Recent Trends Preemption of lower class traffic Multilayer recovery We can “almost” deal with recovery at a single protocol layer What if we intend to provide recovery at multiple protocol layers? For multilayer recovery, we need to consider these additional issues: Interworking of layers Local information stored at each node of each layer Recovery provided by each individual layer Signaling mechanism from one layer to another Effects on bandwidth sharing (if sharing is used)

Dec 20, 2005Lahore University of Management Sciences22 Thank You! Questions & Answers

Dec 20, 2005Lahore University of Management Sciences23 Extra Stuff!

Dec 20, 2005Lahore University of Management Sciences24 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

Dec 20, 2005Lahore University of Management Sciences25 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

Dec 20, 2005Lahore University of Management Sciences26 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

Dec 20, 2005Lahore University of Management Sciences27 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

Dec 20, 2005Lahore University of Management Sciences28 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

Dec 20, 2005Lahore University of Management Sciences29 Single Link Protection: Network 1

Dec 20, 2005Lahore University of Management Sciences30 Single Link Protection: Network 1

Dec 20, 2005Lahore University of Management Sciences31 Single Link Protection: Network 2

Dec 20, 2005Lahore University of Management Sciences32 Single Link Protection: Network 2

Dec 20, 2005Lahore University of Management Sciences33 Single Node Protection: Network 1

Dec 20, 2005Lahore University of Management Sciences34 Single Element Protection: Network 1

Dec 20, 2005Lahore University of Management Sciences35 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

Dec 20, 2005Lahore University of Management Sciences36 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)

Dec 20, 2005Lahore University of Management Sciences37 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

Dec 20, 2005Lahore University of Management Sciences38 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

Dec 20, 2005Lahore University of Management Sciences39 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