Path Protection in MPLS Networks

1
Path Protection in MPLS Networks
Design and Evaluation of Fault Tolerance
Algorithms with Performance Constraints

• Ashish Gupta
• Ashish Gupta

2
Our Work

• Fault Tolerance in MPLS Networks
• Issues
• QoS Constraints
• Expeditious Path Restoration
• Bandwidth Efficiency
• There is a tradeoff

3
QoS Parameters

• Important parameters
• Packet Loss Time
• Jitter
• End-to-End Delay
• Reliability
• Have to minimize bandwidth usage

MPLS
ADVANCED NETWORKING LAB
PATH PROTECTION
4
QOS Parameters
Packet Loss Time Packet Loss time is the time
for which the packets will be dropped in case a
failure along the LSP Jitter Jitter is the
deviation from the ideal timing of receiving a
packet at the destination End-to-End Delay The
transmission time of a packet to reach the
destination node from the source Reliability
The probabilistic measure of reachability of the
destination from the source
5
Path Protection

• A disjoint backup path is allocated along with
  the primary path
• Local Path Protection
• Global Path Protection
• Segment Based Approach A General Approach to
  Path Protection

MPLS
ADVANCED NETWORKING LAB
PATH PROTECTION
6
Segment Protection

• 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

7
Optimization Problem
The structure of backup path(s) and its peering
relationship with the primary path affects the
QoS Constrains
The Design of backup LSPs must address both BW
efficiency and expeditious path restoration
8
Explanation of QoS Parameters
9
Expressions

• Ensure
• Packet Loss time
• RTT( Si , Si1 ) Ttest lt delta
• Where delta is maximum permissible packet loss
  time
• Jitter
• t2 t1 lt Jitter Bound ( See diagram )
• In worst case user doesnt receive packets for
• Max (RTT( Si , Si1 ) Ttest (t2 t1) )

10
End-to-End Delay
11
End-to-End delay

• Ensure
• Max (T ( t2 t1 ) ) lt EED Bound

12
Problem Statements
13
Theoretical Model

• Let G (R,L,B,pB,bB,D) describe the given
  network where
• R set of routers
• L set of links
• B Bandwidth of the Links
• pB Primary Path bw reserved
• bB Backup Path bw reserved
• D Delays of the Links

14
Packet Loss Time

• General Problem Statement
• Input
• A Network G and Packet Loss time bound delta. An
  ingress Node a and an egress node b between which
  a connection of bandwidth y has to be routed.
• Output
• A primary path between a and b , a set of segment
  switch routers S and set of backup paths BP.
• Such that
• S0 a
• In case of a fault, the max packet loss time
  while rerouting is lt delta
• RTT ( Si , Si1 ) Ttest lt delta
• Bandwidth resources are conserved
• No of segments is minimized or S is minimum(
  Transformation )

15
Jitter

• General Problem Statement
• Input
• A Network G and Packet Loss time bound delta and
  jitter bound deltaj . an ingress Node a and an
  egress node b between which a connection of
  bandwidth y has to be routed.
• Output
• A primary path between a and b , a set of segment
  switch routers S and set of backup paths BP.
• Such that
• S0 a
• In case of a fault, maximum jitter bound is
  deltaj
• Max ( t2 t1 ) lt deltaj
• RTT ( Si , Si1 ) Ttest lt delta
• Bandwidth resources are conserved
• No of segments is minimized or S is minimum(
  Transformation )

16
End-to-End Delay

• General Problem Statement
• Input
• A Network G and end-to-end delay bound deltaeed .
  An ingress Node a and an egress node b between
  which a connection of bandwidth y has to be
  routed.
• Output
• A primary path between a and b , a set of segment
  switch routers S and set of backup paths BP.
• Such that
• S0 a
• In case of a fault, EED does not exceed delteeed
• Max ( T (t2 t1) ) lt deltaeed
• Bandwidth resources are conserved
• No of segments is minimized or S is minimum (
  Transformation )

17
Reliability

• General Problem Statement
• Input
• A Network G and set of reliabilities of each node
  and link in G . A lower bound of acceptable
  reliability p , an ingress Node a and an egress
  node b between which a connection of bandwidth y
  has to be routed.
• Output
• A primary path between a and b , a set of segment
  switch routers S and set of backup paths BP.
• Such that
• S0 a
• The reliability of the LSP from a to b is greater
  than a certain reliability value p
• The bandwidth used is minimum
• No of segments is minimized or S is minimum (
  Transformation )

18
RELIABILITY - 1

• How Backup Path Improves Reliability

Link Reliability pe n links each in the
primary and backup paths. Reliability from A to B
without a backup path p Reliability from A to B
with backup path 2 p p2
19
RELIABILITY - 2
20
RELIABILITY - 3

• How Backup Path Improves Reliability

A
B
Link Reliability pe n links each in the
primary and backup paths. Reliability from A to B
without a backup path pn Reliability from A to
B with backup path 2 pn p2n
21
RELIABILITY - 4
Total number of links in primary path n Size of
Backup Path Size of Segment Size of Segments
k Assume no sharing of backup paths
22
RELIABILITY - 5

• Reliability of a link p
• Reliability of a segment 2pk p2k
• Number of Segments n/k
• Reliability of the path (2pk p2k)n/k

23
RELIABILITY 6
24
How to Calculate Reliability?

• NP-Complete problem, even when failure
  probability is same for all links.
• For a graph G with edge reliability pe for edge
  e,

where O is the set of operational states.
Therefore we will have to estimate reliability of
a path by using upper and lower bounds.
25
Graph Transformations

• Node to Link Reliability

• Merging
• Serial
• Parallel

pe
pe pf - pe pf
pf
26
Approximating Reliability

• Consider a path from link A to B
• Total number of links in primary and backup paths
  n
• Reliability of a link p
• Probability ( failure of k links )
• nck pn-k (1-p)k

27
Probability of k links failing
Probability that 0 or 1 or 2 links failed
0.9861819
28
Approximating Reliability
29
Approximating Reliability

• Number of States with 0 link failure nc0
• Probability of occurrence of this state pn
• Probability that a path exist 1
• Number of States with 1 link failure nc1
• Probability of occurrence of this state
  pn-1(1-p)
• Probability that a path exist 1
• Number of States with 2 link failure nc2
• Probability of occurrence of this state
  pn-2(1-p)2
• Probability that a path exist From
  Simulation(say q)

30
Approximating Reliability

• Lower Bound
• nc0 pn 1.0 nc1 pn-1(1-p) 1.0 nc2
  pn-2(1-p)2 q
• Upper Bound
• 1 - nc2 pn-2(1-p)2 (1-q)
• Reliability
• (Upper Bound Lower Bound)/2

31
Lower Upper Bounds
32
Maximum Difference between Actual Approximated
Reliability