Title: A General approach to MPLS Path Protection using Segments
1A General approachto MPLS Path Protectionusing
Segments
2Overview
- 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
3MPLS Label Distribution
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4Label Switched Path (LSP)
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5The 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
6Existing 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
7Segment 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
8Steps 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
9Fault 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
10Fault Detection , Localization and Notification
11Creation 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
12Issues 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
13Loops in Backup Paths
14Problem with Greedy Algorithm
15A 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.
16Advantages 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
17Description 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
18Segment Size vs BW reserved
19Segment Size vs BW reserved
20Segment Size vs Rejection Rate ( for 250 LSPs )
21No. of Requested LSPs vs Rejection Rate
22Effect of Backup Path Sharing
23Bandwidth reserved vs No. of LSPs setup
24Crossover - Effects of backup path sharing
25Further 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
26Steps in Rerouting
27A 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
28A Mechanism for Notification
29Other work
- Creating Backup paths using tunnels
- Analysis of Liveness message periodicity
30Future 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.
31Targets 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
32Thank You