Path Protection in MPLS Networks Using Segment Based Approach

Overview Short Intro to MPLS Introduction to Our work – Protection and the segment Based approach Algorithms for QoS constraints –Switch Over time Algorithm Greedy Approach Consideration of Backup Paths –Conserving protection resources – sharing bw –End-to-End delay and Jitter –Combining the above constraints –Reliability Visualization System Experimental Results Conclusion and work done

Introduction to MPLS Mapping: 0.40 Request: 47.1 Mapping: 0.50 Request: 47.1

Label Switched Path (LSP) IP

MPLS : ROUTE AT EDGE, SWITCH IN CORE IP Forwarding LABEL SWITCHING IP Forwarding IP #L1IP#L2IP#L3 IP  Applies concept of VC routing  Packet forwarding is done based on Label Switching  FEC: Destination address prefix, Traffic Engineering tunnel, Class of Service.

Introduction to Path Protection

Introduction to Path Protection BACKUP PATH

Requirements of Path Protection Should Reroute the traffic satisfying certain QoS constraints Should aim to conserve the amount of protection resources reserved

Global Path Protection Backup Path

Local Path Protection

Segment Based Path Protection  Look at the path as a group of segments – protect each segment separately  Results in fewer backup paths – conserves resources  Meets QoS constraints in a “tight” manner  Gives flexibility Issue : How to segment the path ?

Algorithms for QoS constraints

QoS Constraints Important parameters –Switch-Over Time –End-to-End Delay –Jitter –Reliability –Combination of above Have to conserve protection resources

Bounded Switch Over Time Definition of Switch Over Time

An expression for switch over time Analysis for switch over time RTT( R i, R j ) + T test < 

Example for Segment Based Approach

Here we are able to meet the Switch Over time constraint with 3 backup paths as compared to 7 backup paths in LPP A simple algorithm for segmentation: Greedy Approach

The Resource advantage

Problem with Greedy Approach Need to consider the topology of the network as well

An adaptive Algorithm for segmentation Start from the egress and look for longest possible segment

End-to-End Delay An important parameter

Analysis Max (T + ( t2 – t1 ) ) < EED Bound

Algorithm for end-to-end delay For each backup path, we need to make sure that the end-to-end constraint is satisfied Use shortest path approach for finding a backup path – minimizes end-to-end delay

Algorithm for end-to-end delay d1d1 d2d2 d3d3 d 1 + d 2 + d 3 d3d3 0 d 2 + d 3 Searching for a backup path

Jitter Jitter can be treated as a link property Path Jitter = Σ Link Jitter Algorithm similar to end-to-end delay

Combination of above constraints Approach Dynamic Programming Switch Over Time End-to-End Delay Jitter A combined Algorithm for

Algorithm based on Dynamic Programming Artificial Node RiRi RjRj RkRk

Reliability An important QoS parameter in Computer Networks. Path Reliability : Probability of a path to be in a working state at some instant of time. Link Reliability (p) : Probability of a link to be in working state at some instant of time.

Reliability - Objectives Effect of Path Protection on Reliability Effect of Segment Size on Reliability An O(No. of Links + (No. of Segments) 2 ) Algorithm to find exact path reliability ! Algorithm for Finding most reliable Backup Path Heuristics for SBPP with reliability bounds

Effect of Path Protection on Reliability Total number of links in primary path = n Reliability of a link : p Path Reliability from A to B = p n A B Path Reliability from A to B with backup path = 2p n – p 2n n links

Effect of Path Protection on Reliability

Effect of Segment Size on Reliability Total number of links in primary path = n Reliability of a link : p Size of Segments = k Number of Segments = n/k Size of Backup Path = Size of Segment Reliability of the path = (2p k – p 2k ) n/k

Effect of Segment Size on Reliability

Algorithm to find path reliability Theoretically a path exists between ingress and egress nodes : R1 -> R2 -> R4 -> R5 -> R6 -> R7 No path between ingress and egress nodes in our path switching approach !

Algorithm to find path reliability Probability of Primary path for a particular segment S i to be working Probability of Backup path for Segment S i to be working Probability of S i to S j-1 segments’s primary path to be working & segment S j primary path to have an error

Algorithm for Finding most reliable Backup Path Artificial Node RiRi RjRj

Heuristics for SBPP with reliability bounds Divide any segment into two till the reliability bound is met Find the Segmentation with least number of segments

Visualization System

Visualization of Algorithms A visualization system developed based on POLKA – an algorithm animation toolkit Closely Integrated with the simulator Aids in understanding how the algorithms work Assists in establishing correctness of algorithms and simulations Dynamic Nature of Visualizations

Visualization Two categories of Visualization: –Animation for Adaptive Bounded Switch Over Time Algorithm –Rerouting of packets by SSR in case of failure (packet flow animation) – demonstrates various cases

Topology for Visualization

Visualization Demo

Experimental Results

Implementation Simulator developed in C++ for implemented some algorithms Size of model graph : 100 nodes, 1000 edges RTT of each link = 10 ms BW – 50 to 100 Generated large number of random LSP requests and observed various parameters Results indicate advantages of SBPP

Segment Size vs BW reserved

Segment Size vs Rejection Rate ( for 250 LSPs )

No. of Requested LSPs vs Rejection Rate

Effect of Backup Path Sharing

Crossover - Effects of backup path sharing

Effect of additional constraint

Bandwidth Reserved vs Density

Detection and Notification

A Mechanism for Notification After a fault is detected, notification needs to be sent to the SSR for switching the traffic Some nodes will participate in notification and the SSR will switch the route What information will be passed after a fault occurs ? What changes do we need in the LSR tables for switching? Case of Multiple LSPs : All LSPs using that segment may not pass through the faulty node/link – Only concerned LSPs should be switched

A Mechanism for Notification

Conclusions Fault Tolerance can now be assured to satisfy various QoS constraints Segment Based Algorithms show significant improvement in terms of protection resources used

Work Done Mechanisms for Detection, Notification Algorithms for various QoS constraints –Bounded Switch over time –End-to-End delay –Jitter –Combination of above –Reliability Issues relating to backup path - sharing Simulator developed for above Visualization System