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A General approach to MPLS Path Protection using Segments

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Applies concept of VC routing. Packet forwarding is done based on Label Switching ... delay : Higher Switching time so have to constrain backup path construction also ... – 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 BUILT ON STANDARD IP
47.1
1
2
1
3
2
1
47.2
3
47.3
2
  • Destination based forwarding tables as built by
    OSPF, IS-IS, RIP, etc.

4
IP FORWARDING USED BY HOP-BY-HOP CONTROL
47.1
1
IP 47.1.1.1
2
IP 47.1.1.1
1
3
2
IP 47.1.1.1
1
47.2
3
47.3
2
5
MPLS Label Distribution
1
47.1
3
3
2
1
1
2
47.3
3
47.2
2
6
Label Switched Path (LSP)
1
47.1
3
3
2
1
1
2
47.3
3
47.2
2
7
MPLS ROUTE AT EDGE, SWITCH IN CORE
IP
IP
IP Forwarding
IP Forwarding
LABEL SWITCHING
  • Applies concept of VC routing
  • Packet forwarding is done based on Label
    Switching
  • FEC Destination address prefix, Traffic
    Engineering tunnel, Class of Service.

8
WHY MPLS ?
  • Ultra fast forwarding
  • IP Traffic Engineering
  • Constraint-based Routing
  • Virtual Private Networks
  • Controllable tunneling mechanism
  • Voice/Video on IP
  • Delay variation QoS constraints

9
BEST OF BOTH WORLDS
CIRCUIT SWITCHING
PACKET ROUTING
HYBRID
  • MPLS IP form a middle ground that combines the
    best of IP and the best of circuit switching
    technologies.

10
Path Protection and its Purpose
  • 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

11
Existing Schemes
  • Global Path Protection
  • Local Path Protection
  • Link Failure
  • Node Failure
  • 11 Path Protection
  • Sharing Modes - 1 1, 1 N, M N

Backup LSP
No flexibility in providing path protection for a
MPLS network
Segment Based Approach A General Scheme for
Path Protection
12
Example
  • Global Path Protection Large Notification
    Delay
  • Local Path Protection Small delay but large
    number of backup paths
  • These solutions lie at two extremes.
  • Segment Based Approach A General Scheme for
    Path Protection

13
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

14
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
  • Label Distribution Mechanisms
  • Signaling mechanisms
  • Buffering to avoid packet loss and reordering
  • Steps in recovery
  • Fault Detection and Location
  • Fault Notification How does it work in MPLS ?
  • Switching the path
  • Backup Path recovery
  • Experimental Results

15
Steps in SBPP
  • For setting up a path request - Local Computation
  • Information needed
  • Topology
  • Link Delays and congestion information
  • Bandwidth of each link primary , backup , free
  • After computation Label information disseminated

16
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17
Fault Detection , Location 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

18
Fault Detection , Localization and Notification
19
Creation of Segments
  • Created according to QOS criteria
  • Delay or Reliability or a combination
  • Ensure each segment individually meets the
    criteria
  • Example - Bounded Delay on switching
  • Greedy Algorithm

Some Problems - Experiments
20
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21
Reservation of Backup Paths
  • Advantage of SBPP Flexibility in reservation of
    backup paths, not rigid
  • Issues
  • 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

22
Loops in Backup Paths
23
Problem with Greedy Algorithm
24
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.

25
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

26
Description of Simulation Setup
  • An MPLS network with
  • 100 Nodes
  • 200 Edges
  • RTT of each link 10 ms
  • Periodicity of Liveness messages 2 ms
  • BW 50 to 100
  • Generated large number of random LSP requests and
    observed various parameters
  • Results indicate advantages of SBPP

27
Segment Size vs BW reserved
28
Segment Size vs BW reserved
29
Segment Size vs Rejection Rate ( for 250 LSPs )
30
No. of Requested LSPs vs Rejection Rate
31
Effect of Backup Path Sharing
32
Bandwidth reserved vs No. of LSPs setup
33
Crossover - Effects of backup path sharing
34
Further Analysis Improvement to Algorithm
  • Delay over Backup Path also affects jitter !
  • 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
  • Improvements to our Algorithm due to this

35
Steps in Rerouting
36
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

37
A Mechanism for Notification
38
Other work
  • Creating Backup paths using tunnels
  • Analysis of Liveness message periodicity

39
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.

40
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

41
Thank You
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