MPLS Protection Routing: A Tutorial Zartash Afzal Uzmi

Jan 13, 2006Lahore University of Management Sciences2 First slide… Questions? Ask when you have them!

Jan 13, 2006Lahore University of Management Sciences3 Outline Background Network Services and QoS Architectural Requirements IP and MPLS Introduction to protection and restoration routing Terminology Local Protection: Types of Backup Paths Fault Models Backup Bandwidth Sharing Activation sets Protection routing framework Components Typical example Evaluation and Experimentation

Jan 13, 2006Lahore University of Management Sciences4 Outline Background Network Services and QoS Architectural Requirements IP and MPLS Introduction to protection and restoration routing Terminology Local Protection: Types of Backup Paths Fault Models Backup Bandwidth Sharing Activation sets Protection routing framework Components Typical example Evaluation and Experimentation

Jan 13, 2006Lahore University of Management Sciences5 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!

Jan 13, 2006Lahore University of Management Sciences6 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

Jan 13, 2006Lahore University of Management Sciences7 Architectural Requirements Emerging applications Two-way interactive communications One-way streaming media type applications Under normal conditions We are worried about the buffers used in 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

Jan 13, 2006Lahore University of Management Sciences8 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 aggregation Example: 100x100 project Edge network is packet-switched Core network is virtual-circuits

Jan 13, 2006Lahore University of Management Sciences9 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)

Jan 13, 2006Lahore University of Management Sciences10 Outline Background Network Services and QoS Architectural Requirements IP and MPLS Introduction to protection and restoration routing Terminology Local Protection: Types of Backup Paths Fault Models Backup Bandwidth Sharing Activation sets Protection routing framework Components Typical example Evaluation and Experimentation

Jan 13, 2006Lahore University of Management Sciences11 Protection and Restoration Restoration On-demand recovery – no preset backup paths Example: existing recovery in IP networks Protection Pre-determined recovery – backup paths “in advance” Primary and backup are provisioned at the same time IP supports restoration Because it is datagram service MPLS supports restoration as well as protection Because it is virtual-circuit service

Jan 13, 2006Lahore University of Management Sciences12 Restoration in IP network In traditional IP, what happens when a link or node fails? Failure 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 protection possibilities in an MPLS network, but… First we need to look at the QoS requirements

Jan 13, 2006Lahore University of Management Sciences13 QoS Requirements Bandwidth Guaranteed Primary Paths Bandwidth Guaranteed Backup Paths BW remains provisioned in case of network failure Minimal “Protection or Restoration Latency” Protection/Restoration latency is the time that elapses between: “the occurrence of a failure”, and “the diversion of network traffic on a new path” Restoration is generally SLOWER than protection

Jan 13, 2006Lahore University of Management Sciences14 Protection in MPLS First we define Protection level Path protection Also called end-to-end protection For each primary LSP, a node-disjoint backup LSP is set up Upon failure, ingress node diverts traffic on the backup path Local Protection Upon failure, node immediately upstream the failed element diverts the traffic on a “local” backup path Path Protection  More Latency Local Protection  Less Latency

Jan 13, 2006Lahore University of Management Sciences15 Protection 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!

Jan 13, 2006Lahore University of Management Sciences16 Local Protection: Fault Models ABCD Link Protection ABCD ABCD Node Protection Element Protection

Jan 13, 2006Lahore University of Management Sciences17 Protection Modes 1+1 protection Flow sent on two separate disjoint paths Receiver responsible for choosing one of the two 1:1 protection A backup path protects a single LSP (or a portion of a single LSP) N:1 protection A backup path protects one link or one node or both Overlapping portions of many LSPs are protected by a single backup path Applicable for local protection only N:M protection (M<N)

Jan 13, 2006Lahore University of Management Sciences18 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 LOCAL PROTECTION

Jan 13, 2006Lahore University of Management Sciences19 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?

Jan 13, 2006Lahore University of Management Sciences20 BW Sharing in backup Paths Example: max(X, Y) BW: Y AB CD E F G LSP1 LSP2 BW: X Primary Path Backup Path X X X YY X+YX+Y Sharing

Jan 13, 2006Lahore University of Management Sciences21 Activation Sets A B C D E Activation set for node BActivation set for link (A,B) A B C D E

Jan 13, 2006Lahore University of Management Sciences22 Outline Background Network Services and QoS Architectural Requirements IP and MPLS Introduction to protection and restoration routing Terminology Local Protection: Types of Backup Paths Fault Models Backup Bandwidth Sharing Activation sets Protection routing framework Components Typical example Evaluation and Experimentation

Jan 13, 2006Lahore University of Management Sciences23 Protection 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 primary LSPs that can be placed on the network

Jan 13, 2006Lahore University of Management Sciences24 Evaluation & Experimentation Traffic Generation Use existing or emerging traffic models Consider call holding times and multi-service traffic Rejected Requests Experiments Generate a set of LSP requests 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 LSP requests Simulate on various topologies

Jan 13, 2006Lahore University of Management Sciences25 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)

Jan 13, 2006Lahore University of Management Sciences26 We are not done, yet… Questions & Answers

Jan 13, 2006Lahore University of Management Sciences27 Extra Stuff! Example: A Protection Routing Architecture

Jan 13, 2006Lahore University of Management Sciences28 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 Rij : Bandwidth remaining on link (i, j) 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) Also propagate G ij and Rij More Information propagated  More potential for BW sharing

Jan 13, 2006Lahore University of Management Sciences29 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

Jan 13, 2006Lahore University of Management Sciences30 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

Jan 13, 2006Lahore University of Management Sciences31 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

Jan 13, 2006Lahore University of Management Sciences32 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

Jan 13, 2006Lahore University of Management Sciences33 Single Link Protection: Network 1

Jan 13, 2006Lahore University of Management Sciences34 Single Link Protection: Network 1

Jan 13, 2006Lahore University of Management Sciences35 Single Link Protection: Network 2

Jan 13, 2006Lahore University of Management Sciences36 Single Link Protection: Network 2

Jan 13, 2006Lahore University of Management Sciences37 Single Node Protection: Network 1

Jan 13, 2006Lahore University of Management Sciences38 Single Element Protection: Network 1

Jan 13, 2006Lahore University of Management Sciences39 More Extra Stuff! Bandwidth Sharing Model for oAIS

Jan 13, 2006Lahore University of Management Sciences40 A Bandwidth Sharing Model Primary Path Backup Path All links are protected! (Simplified for the Link Protection Fault Model) Recall the definition of nhop paths ABCD Link Protection

Jan 13, 2006Lahore University of Management Sciences41 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)

Jan 13, 2006Lahore University of Management Sciences42 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

Jan 13, 2006Lahore University of Management Sciences43 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

Jan 13, 2006Lahore University of Management Sciences44 Last slide… Thank you! Questions?