Ashish GuptaAshish Gupta

Under Guidance ofProf. B.N. JainDepartment of Computer

Science and Engineering

Advanced Networking Laboratory

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BACKUP PATH

Should provide quick recovery after a failure

Optimal Use of Backup Resources

Backup Path

Primary Path

The solutions are fixed No assurance for various QoS

constraints

We need guarantees that in case of failure, we will not lose packets for more than 50 ms

Or even in case of failure, the end to end delay will not

exceed 150 ms

Results in fewer backup paths – conserves resources

Can meet QoS constraints in a “tight” manner

Gives flexibility – How ?

The Main Idea

Look at the path as a sequence of segments and protect each segment separately

How to divide the path into segments such that ?

If any segment fails, specified QoS constraints can be guaranteed

A Segment is a set of nodes which consists of:

1. Segment Switch Router – protects the segment

2. Protected Nodes

Main Focus

Various QoS constraints considered:–Bounded Switch-Over Time–End-to-End Delay–Jitter–Reliability–Combination of above

Algorithms have to use backup resources effectively

Switch over time : The time for which the packets are lost between the failure and recovery

Using Timing Analysis, we derived a limit to the possible segment size

RTT( Ri , Rj ) + Ttest <

Divide the path into minimum number of segments such that the inequality is satisfied for each segment

Intuitive choice: Greedy Algorithm

Problems with Greedy Algorithm

A new Adaptive Algorithm for Bounded Switch over time has been developed

Takes into account the topology and bandwidth reservation in the network

Assures QoS satisfaction

Proved to be optimal

Robust

We have implemented it using the LSP Admission Control Simulator and tested it

Results indicate its efficiency

In this analysis, we need to consider backup paths also.

Max (T + ( T2 – T1 ) ) <

We need to satisfy the inequality for each possible path

• For each segment (found using previous algorithm), find the shortest possible backup path

• Will give the minimum value of end-to-end delay

• Check if inequality is satisfied, otherwise reject the current segment

Jitter – similar to End-to-End delay

Multiple QoS constraints

Bounded Switch Over time

End-to-End Delay

Jitter

Developed an algorithm using

Dynamic Programming Approach

Finding Reliability between two nodes : An NP complete problem

Earlier we were engaged in finding bounds

But turns out, Segment Based Approach allows for simpler analysis !

An O(No. of Links + (No. of Segments)2 ) Algorithm to find exact path reliability !

Algorithm for finding the most reliable backup path

A heuristic Algorithm has been developed for meeting bounds on Reliability for the protection configuration

Probability of Primary path for a particular segment Si to be working

Probability of Backup path for Segment Si to be working

Probability of Si to Sj-1 segments’s

primary path to be working & segment Sj primary path to have an error

A visualization system developed for the Segment based Algorithms: based on POLKA

Closely Integrated with LSP Admission Control Simulator Visualizations are Dynamic not Static

Aids in understanding how the algorithms work Assists in establishing correctness of algorithms and simulations

Topology Used

Aim of the Experiments

To evaluate the resource related advantages of Segment based Approach, while assuring QoS constraints

An LSP Admission Control Simulator has been developed in C++

Simulates multiple networks with different reservation policies and compares results

We implement the Segment Based Algorithm for Bounded Switch over time for providing Protection to LSPs generated

BW Sharing Mechanisms also implemented

Simulation Setup Topology with 50 routers and 82 links

LSPs setup using Djiktra’s Algorithm

BW of each link: 3000 to 10000 units

Delay of each link : 8 to 12 ms

BW requirements of each LSP : 20 to 70 units

LSP requests were generated with different QoS parameters

Today major networking companies are quickly shifting towards MPLS-based networks

Major Players:Cisco , AT&T, Level 3, Hewlett Packard,

UUNet, MCI World Com

“Within an MPLS-enabled network, even packet voice services such as voice over IP will benefit from reduced latency and congestion control”

Ranjeet Sudan, MPLS product manager at Cisco

Efficient Fault Tolerance in such services is a major concern

For providing reliability to such services we now have Fault Tolerance Schemes which:

1. Guarantee satisfaction of various QoS constraints in case of failure

2. Use backup resources in an optimal manner

Mechanisms for Detection and 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… Admission Control Simulator developed for above Visualization System

Paper being submitted to

Being held in Mumbai this year