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MPLS Protection Routing: A Tutorial. Zartash Afzal Uzmi. First slide…. Questions? Ask when you have them!. Outline. Background Network Services and QoS Architectural Requirements IP and MPLS Introduction to protection and restoration routing Terminology
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MPLS Protection Routing: A Tutorial Zartash Afzal Uzmi
First slide… Questions? Ask when you have them! Lahore University of Management Sciences
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 Lahore University of Management Sciences
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 Lahore University of Management Sciences
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! Lahore University of Management Sciences
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 Lahore University of Management Sciences
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 Lahore University of Management Sciences
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 Lahore University of Management Sciences
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) Lahore University of Management Sciences
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 Lahore University of Management Sciences
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 Lahore University of Management Sciences
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 Lahore University of Management Sciences
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 Lahore University of Management Sciences
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 Lahore University of Management Sciences
Protection in MPLS Path Protection S 1 2 3 D This type of “path Protection” still takes 100s of ms. We may explore “Local Protection” to quickly switch onto backup paths! Primary Path Backup Path Lahore University of Management Sciences
A B C D Local Protection: Fault Models Link Protection Node Protection A B C D Element Protection A B C D Lahore University of Management Sciences
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) Lahore University of Management Sciences
Primary Path Backup Path nhop and nnhop paths LOCAL PROTECTION nnhop A B D C E nhop PLR: Point of Local Repair All links and all nodes are protected! Lahore University of Management Sciences
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? Lahore University of Management Sciences
Sharing Primary Path Backup Path BW Sharing in backup Paths • Example: LSP1 BW: X A B X X max(X, Y) X E G F X+Y Y Y C D BW: Y LSP2 Lahore University of Management Sciences
Activation Sets A A E E B B C C D D Activation set for node B Activation set for link (A,B) Lahore University of Management Sciences
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 Lahore University of Management Sciences
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 Lahore University of Management Sciences
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 Lahore University of Management Sciences
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) Lahore University of Management Sciences
We are not done, yet… Questions & Answers Lahore University of Management Sciences
Extra Stuff! Example: A Protection Routing Architecture Lahore University of Management Sciences
Extent of BW Sharing: oAIS • Aggregate Information Scenario (AIS) • Fij: Bandwidth reserved on link (i, j) for all primary LSPs • Gij: Bandwidth reserved on link (i, j) for all backup LSPs • Rij: Bandwidth remaining on link (i, j) • Optimized AIS (oAIS) – (Hij instead of Fij) • Hij: Maximum bandwidth reserved on any one link by all backup paths spanning link (i, j) • Also propagate Gij and Rij More Information propagated More potential for BW sharing Lahore University of Management Sciences
oAIS versus AIS: Example LSP Request-1 (src, dst, bw) = (A, C, 4) D E F GAF=4 FAB=4 A B C HAB=4 G Lahore University of Management Sciences
oAIS Example LSP Request-2 (src, dst, bw) = (A, C, 5) D E F GAF=4 FAB=9 FAB=4 A B C HAB=5 HAB=4 GAG=5 G Lahore University of Management Sciences
oAIS Example LSP Request-3 (src, dst, bw) = (D, E, 7) FDE=7 D E F GAF=4 GAF=7 FAB=9 A B C HAB=5 GAG=5 G Lahore University of Management Sciences
oAIS Example LSP Request-4 (src, dst, bw) = (A, C, 6) Need to Evaluate cost of all possible backup paths? FDE=7 How much BW is shareable on (A, F)? D E AIS: Shareable = max(0, GAF - FAB) = GAF - min(GAF, FAB) = 0 Additional resv = 6 F GAF=7 oAIS: (HAB≤ FAB) Shareable = GAF - min(GAF, HAB) = 2 Additional resv = 6 - 2 = 4 FAB=9 A B C HAB=5 CIS: (link (A,B) knows BWred) Shareable = GAF - BWred = 7 - 4 = 3 Additional resv = 6 - 3 = 3 GAG=5 G Lahore University of Management Sciences
Single Link Protection: Network 1 Lahore University of Management Sciences
Single Link Protection: Network 1 Lahore University of Management Sciences
Single Link Protection: Network 2 Lahore University of Management Sciences
Single Link Protection: Network 2 Lahore University of Management Sciences
Single Node Protection: Network 1 Lahore University of Management Sciences
Single Element Protection: Network 1 Lahore University of Management Sciences
More Extra Stuff! Bandwidth Sharing Model for oAIS Lahore University of Management Sciences
A B C D Primary Path Backup Path A Bandwidth Sharing Model (Simplified for the Link Protection Fault Model) Recall the definition of nhop paths Link Protection All links are protected! Lahore University of Management Sciences
Bandwidth Sharing Model • Previous: • Aij:= Set of all primaries traversing through (i, j) • Buv:= Set of all backups traversing through (u, v) • New definition (specialized for link protection case): • Aij:= Set of all primaries traversing through (i, j) • Buv:= Set of all nhop paths traversing through (u, v) • µij:= Set of all nhop paths that span (i, j) • ijuv:= Buv ∩ µij (set of paths falling on (u,v) if (i,j) fails) Lahore University of Management Sciences
Bandwidth Sharing Model RED=7 BLU=2 u v GRN=3 (New Request) Guv = 10 3 k i j NEW MODEL: Aij = {R, B} Buv = {nhijr, nhijb, …} (nhops through (u, v)) µij = {nhijr, nhijb, …} (nhops spanning (i, j)) ijuv = µij ∩ Buv= {nhijr, nhijb} || ijuv || = 2 + 7 = 9 (Un-shareable) Shareable = Guv - || ijuv || = 10 - 9 = 1 OLD MODEL: Aij = {R, B} Buv = {R, B, …} Aij ∩ Buv= {R, B} || Aij ∩ Buv || = 2+7 = 9 Un-shareable = 9 Shareable = 10 - 9 = 1 Lahore University of Management Sciences
Bandwidth Sharing Model RED=7 BLU=2 u v GRN=3 (New Request) Guv = 10 3 k i j OLD MODEL: Aij = {R, B} Buv = {R, B, …} Aij ∩ Buv= {R, B} || Aij ∩ Buv || = 2+7 = 9 Un-shareable = 9 Shareable = 10 - 9 = 1 NEW MODEL: Aij = {R, B} Buv = {nhijr, nhjkb, …} (nhops through (u, v)) µij = {nhijr, nhijb, …} (nhops spanning (i, j)) ijuv = µij ∩ Buv= {nhijr} || ijuv || = 7 (Un-shareable) Shareable = Guv - || ijuv || = 10 - 7 = 3 Lahore University of Management Sciences
Last slide… Thank you! Questions? Lahore University of Management Sciences