Restoration Routing in MPLS Networks

1
Restoration Routing in MPLS Networks

• Zartash Afzal Uzmi
• Computer Science and Engineering
• Lahore University of Management Sciences

2
Outline

• Background Quick overview of MPLS
• Introduction to restoration routing
• QoS Requirements Why restoration routing?
• Local Restoration Types of Backup Paths
• Local Restoration Fault Models
• Backup Bandwidth Sharing
• Activation sets
• Typical example of restoration routing frameworks
• Optimized aggregate information scenario (oAIS)
• Experiments, simulations, and results

3
IP versus MPLS

• In IP Routing, each router makes its own routing
  and forwarding decisions
• In MPLS, source router makes the routing decision
• Intermediate routers make forwarding decisions
• A path is computed and a virtual circuit is
  established from ingress router to egress router
• An MPLS path or virtual circuit from source to
  destination is called an LSP (label switched path)

4
Restoration in IP network

• In traditional IP, what happens when a link or
  node fails?
• Information needs to be disseminated in the
  network
• During this time, packets may go in loops
• Restoration latency is in the order of seconds
• We look for restoration possibilities in an MPLS
  network

5
QoS Requirements

• Bandwidth Guaranteed Primary Paths
• Bandwidth Guaranteed Backup Paths
• BW remains provisioned in case of network failure
• Minimal Restoration Latency
• Restoration latency is the time that elapses
  between the occurrence of a failure and the
  diversion of network traffic on a new path

Path Restoration ? More Latency Local Restoration
? Less Latency
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Restoration in MPLS
Path Protection
S
1
2
3
D
This type of path Protection still takes 100s
of ms.
We need to explore Local Protection to quickly
switch onto backup paths!
Primary Path
Backup Path
7
Types of Backup Paths

• A next hop (nhop) path that spans a link (i, j)
  is a backup path which
• originates at node i, and
• provides restoration for a primary LSP that
  traverses (i, j), if (i, j) fails.

i
j
nhop path that spans (i, j)
PLR Point of Local Repair
8
Types of Backup Paths

• A next next hop (nnhop) path that spans a link
  (i, j) is a backup path which
• originates at node i, and
• provides restoration for a primary LSP that
  traverses (i, j), if either (i, j) or node j
  fails.

nnhop path that spans (i, j)
j
i
PLR Point of Local Repair
9
Local Restoration Fault Models
Link Protection
Node Protection
A
B
C
D
Element Protection
A
B
C
D
10
nhop and nnhop paths
nnhop
A
B
D
C
E
nhop
PLR Point of Local Repair
All links and all nodes are protected!
11
Opportunity cost of backup paths

• Local Protection requires that backup paths are
  setup in advance
• Upon failure, traffic is promptly switched onto
  preset backup paths
• Bandwidth must be reserved for all backup paths
• This results in a reduction in the number of
  Primary LSPs that can otherwise be placed on the
  network
• Can we reduce the amount of backup bandwidth
  but still provide guaranteed backups?

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BW Sharing in backup Paths

• Example

L1
BW X
A
B
X
X
max(X, Y)
X
E
G
F
XY
Y
Y
C
D
BW Y
L2
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Activation Sets
A
A
E
E
B
B
C
C
D
D
Activation set for node B
Activation set for link (A,B)
14
Restoration Routing Frameworks

• We look to answer the following questions?
• Who computes the primary path?
• What is the fault model (link, node, or element
  protection)?
• Where do the backup paths originate?
• Who computes the backup path?
• At what point do the backup paths merge back with
  the primary path
• What information is stored locally in the
  nodes/routers
• What information is propagated through routing
  protocols
• What if a primary path can not be fully protected
• The goal is almost always to maximize bandwidth
  sharing
• Performance criteria is almost always the maximum
  number of LSPs that can be placed on the network

15
Extent of BW Sharing oAIS
More Information propagated ? More potential for
BW sharing

• Aggregate Information Scenario (AIS)
• Fij Bandwidth reserved on link (i, j) for all
  primary LSPs
• Gij Bandwidth reserved on link (i, j) for all
  backup LSPs
• Optimized AIS (oAIS) (Hij instead of Fij)
• Hij Maximum bandwidth reserved on any one link
  by all backup paths spanning link (i, j)

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oAIS versus AIS Example

• LSP Request-1 (src, dst, bw) (A, C, 4)

D
E
F
GAF4
FAB4
A
B
C
HAB4
G
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oAIS Example
LSP Request-2 (src, dst, bw) (A, C, 5)
D
E
F
GAF4
FAB9
FAB4
A
B
C
HAB5
HAB4
GAG5
G
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oAIS Example
LSP Request-3 (src, dst, bw) (D, E, 7)
FDE7
D
E
F
GAF4
GAF7
FAB9
A
B
C
HAB5
GAG5
G
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oAIS Example
LSP Request-4 (src, dst, bw) (A, C, 6)
Need to Evaluate cost of all possible backup
paths?
FDE7
How much BW is shareable on (A, F)?
D
E
AIS Shareable max(0, GAF - FAB)
GAF - min(GAF, FAB) 0 Additional resv 6
F
GAF7
oAIS (HAB FAB) Shareable GAF - min(GAF, HAB)
2 Additional resv 6 - 2 4
FAB9
A
B
C
HAB5
CIS (link (A,B) knows BWred) Shareable GAF -
BWred 7 - 4 3 Additional resv 6 - 3 3
GAG5
G
20
A Bandwidth Sharing Model
(Simplified for the Link Protection Fault
Model) Recall the definition of nhop paths
Link Protection
All links and all nodes are protected!
21
Bandwidth Sharing Model

• Previous
• Aij Set of all primaries traversing through (i,
  j)
• Buv Set of all backups traversing through (u,
  v)
• New definition (specialized for link protection
  case)
• Aij Set of all primaries traversing through (i,
  j)
• Buv Set of all nhop paths traversing through
  (u, v)
• µij Set of all nhop paths that span (i, j)
• ?ijuv Buv n µij (set of paths falling on (u,v)
  if (i,j) fails)

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Bandwidth Sharing Model
RED7 BLU2
u
v
GRN3 (New Request) Guv 10
3
k
i
j
NEW MODEL Aij R, B Buv nhijr, nhijb,
(nhops through (u, v)) µij nhijr, nhijb,
(nhops spanning (i, j)) ?ijuv µij n Buv
nhijr, nhijb ?ijuv 2 7
9 (Un-shareable) Shareable Guv - ?ijuv
10 - 9 1
OLD MODEL Aij R, B Buv R, B, Aij n
Buv R, B Aij n Buv 27
9 Un-shareable 9 Shareable 10 - 9 1
23
Bandwidth Sharing Model
RED7 BLU2
u
v
GRN3 (New Request) Guv 10
3
k
i
j
OLD MODEL Aij R, B Buv R, B, Aij n
Buv R, B Aij n Buv 27
9 Un-shareable 9 Shareable 10 - 9 1
NEW MODEL Aij R, B Buv nhijr, nhjkb,
(nhops through (u, v)) µij nhijr, nhijb,
(nhops spanning (i, j)) ?ijuv µij n Buv
nhijr ?ijuv 7 (Un-shareable) Shareable
Guv - ?ijuv 10 - 7 3
24
Simulation Experiments

• Rejected Requests Experiments
• Measure the number of rejected LSPs for each
  information scenario
• Simulated on two topologies
• Network Loading Experiments
• Link capacities set to infinity
• Measure the total bandwidth required to service a
  given set of LSPs for each information scenario
• Simulated on two topologies

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Single Link Protection Network 1
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Single Link Protection Network 1
27
Single Link Protection Network 2
28
Single Link Protection Network 2
29
Single Node Protection Network 1
30
Single Element Protection Network 1
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• Questions Answers

32
Restoration in MPLS
Path Protection
A
B
C
D
E
MPLS path Protection may take 100s of ms, whereas
MPLS Local protection takes less than 10 ms.
Primary Path
Backup Path