Post on 19-Dec-2015
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