A General approach to MPLS Path Protection using Segments

1
A General approachto MPLS Path Protectionusing
Segments

• Ashish GuptaAshish 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