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Restoration Routing in MPLS Networks

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provides restoration for a primary LSP that traverses (i, j), if (i, j) fails. i. j ... traversing through (i, j) Buv:= Set of all nhop paths traversing through ... – PowerPoint PPT presentation

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Title: 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
6
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?

12
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
13
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)

16
oAIS versus AIS Example
  • LSP Request-1 (src, dst, bw) (A, C, 4)

D
E
F
GAF4
FAB4
A
B
C
HAB4
G
17
oAIS Example
LSP Request-2 (src, dst, bw) (A, C, 5)
D
E
F
GAF4
FAB9
FAB4
A
B
C
HAB5
HAB4
GAG5
G
18
oAIS Example
LSP Request-3 (src, dst, bw) (D, E, 7)
FDE7
D
E
F
GAF4
GAF7
FAB9
A
B
C
HAB5
GAG5
G
19
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)

22
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

25
Single Link Protection Network 1
26
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
31
  • 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
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