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A General approach to MPLS Path Protection using Segments

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Flexibility in creating segments - flexibility in Path Protection ( delay and backup paths ) ... Fault can be detected by periodically sending liveness ... – PowerPoint PPT presentation

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Title: A General approach to MPLS Path Protection using Segments


1
A General approach to MPLS Path Protection using
Segments
  • Ashish Gupta Ashish Gupta

2
Overview
  • Intro to MPLS
  • Difference from IP
  • Why Path Protection ?
  • Existing Schemes
  • Segment Based Approach
  • Its Mechanisms
  • Algorithm for segment setup
  • Simulation Results
  • Detection , Notification and Path Switching

3
MPLS Label Distribution
1
47.1
3
3
2
1
1
2
47.3
3
47.2
2
4
Label Switched Path (LSP)
1
47.1
3
3
2
1
1
2
47.3
3
47.2
2
5
The Need for Path Protection
  • What happens if fault occurs in a network element
    ?
  • For traffic with critical QOS requirements , fast
    rerouting is required
  • IP rerouting can take order of seconds
  • Solution Protect the path with another backup
    path

6
Existing Schemes
  • Global Path Protection
  • Local Path Protection
  • Link Failure
  • Node Failure

Backup LSP
  • Drawback No flexibility in providing path
    protection for a MPLS network
  • Segment Based Approach A General Scheme for
    Path Protection

7
Segment Based Approach
  • Protect each segment separately Each segment
    seen as a single unit of failure
  • SSR Segment Switching router
  • Flexibility in creating segments -gt flexibility
    in Path Protection ( delay and backup paths )
  • SBPP Segment Based Path Protection

8
Steps in SBPP
  • Creation of LSP
  • Creation of segments - Greedy Algorithm
  • Reservation of Backup Paths
  • Backup paths as tunnels
  • A new combined Algorithm
  • Advantages
  • Label Management in SBPP
  • Changes required in LSR
  • Label Distribution Mechanisms
  • Signaling mechanisms
  • Buffering to avoid packet loss and reordering
  • Steps in recovery
  • Fault Detection and Localization
  • Fault Notification How does it work in MPLS ?
  • Switching the path
  • Backup Path recovery
  • Experimental Results

9
Fault Detection , Localization and Notification
  • Fault can be detected by periodically sending
    liveness messages Absence of response indicates
    link/node failure
  • For faster detection , each node sends periodic
    messages to its neighbors
  • Timing Analysis for Detection and Notification

10
Fault Detection , Localization and Notification
11
Creation of Segments
  • Created according to QOS criteria
  • Delay , Reliability , Bandwidth
  • Just ensure each segment individually meets the
    criteria
  • Example - Bounded Delay on switching
  • Greedy Algorithm

Some Problems - Experiments
12
Issues in Reservation of Backup Paths
  • Avoiding Loops
  • Sharing of backup paths important
  • Cases
  • 1. Multiple LSPs , Multiple Segments
  • 2. Multiple LSPs, Same Segment
  • Assumptions Only one failure at a time
  • Problem with the previous approach see figure

13
Loops in Backup Paths
14
Problem with Greedy Algorithm
15
A New Combined Algorithm
  • Possible approaches
  • Exhaustive search for a suitable path
    computationally exhaustive need a heuristic
  • The Combined Path Setup Algorithm
  • 1. Setup a primary path ( based on a constraint
    e.g. min delay)
  • 2. Start from egress node and find the largest
    possible segment which satisfies bounded delay
    switching time constraint ( call the SSR of this
    segment S1 )
  • 3. Find a backup path for this segment starting
    from S1
  • 4. If no backup path can be found , shrink the
    segment and try to find the backup path from the
    new SSR. If no further shrinking is possible then
    Reject request( or try another primary path -
    see below)
  • 5. Repeat Step 4 until a segment with a backup
    path is found.
  • 6. Repeat from step 2 for creating the next
    segment
  • 7. Do this until the complete LSP is segmented.

16
Advantages of this algorithm
  • Ensures that if segmentation is possible on the
    primary path, then it will be performed.
  • Here we have multiple starting nodes possible for
    finding the backup paths , so possibility of
    finding backup paths is more
  • Can add more flexibility for the choice of SSR in
    forming segments e.g. case of overloaded LSR
    wont be made a SSR

17
Description of Simulation Setup
  • An MPLS network of was created
  • 100 Nodes
  • 200 Edges
  • RTT of each link 10 ms
  • Periodicity of Liveness message 2 ms
  • BW 50 to 100
  • Generated large number of random LSPs requests
    and observed various parameters
  • Results indicate advantages of SBPP

18
Segment Size vs BW reserved
19
Segment Size vs BW reserved
20
Segment Size vs Rejection Rate ( for 250 LSPs )
21
No. of Requested LSPs vs Rejection Rate
22
Effect of Backup Path Sharing
23
Bandwidth reserved vs No. of LSPs setup
24
Crossover - Effects of backup path sharing
25
Further Analysis More possibilities
  • End-to-end delay of Backup Path also affects
    switching time !
  • Long backup paths Higher end-to-end delay
    Higher Switching time so have to constrain backup
    path construction also
  • New expression for switching time
  • Tp RTT (t2-t1) lt max. switching delay
  • Can help in providing bound in other performance
    metrics like jitter

26
Steps in Rerouting
27
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

28
A Mechanism for Notification
29
Other work
  • Creating Backup paths using tunnels
  • Analysis of Liveness message periodicity

30
Future Work
  • Label Management and Distribution Issues
  • Formal Definition of Protocol and Signaling
    Mechanisms required for detection, notification
    and other parts of our scheme
  • Use of buffering to reduce packet loss during
    switchover
  • Recovery Issues
  • Implementation of our scheme in MPLS emulator.

31
Targets specified in Mid-sem
  • December 1st 2001
  • Error detection and notification issues in
    Segment based protection (SBP)
  • Work out example scenarios using SBP
  • An algorithm for SBP
  • Label management issues in SBP
  • May 1st 2002
  • Simulations to test performance and resource
    usage vs. other schemes
  • Explore other issues like Buffering
  • Documenting our work

32
Thank You
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