This document discusses enhancing fault tolerance and rerouting strategies in MPLS networks. It begins with an introduction to MPLS including its goals, architecture, labels, and label distribution. It then discusses fault tolerance in MPLS, including protection switching and rerouting. Specific fault tolerance techniques discussed include path protection, local protection with different protection modes, and the cost of backup paths. The motivation for the research is then provided, focusing on reducing backup bandwidth, increasing network capacity, and enhancing fault tolerance performance without affecting normal traffic. Related work on fast path recovery, single link failure recovery, threshold sharing schemes, and utilizing failure-free LSPs is also summarized.

1. ENHANCING FAULT TOLERANCE AND
REROUTING STRATEGIES IN MPLS NETWORKS
Rajiv Gandhi Proudyogiki Vishwavidyalaya, Bhopal
Supervisor
Dr. Kanak Saxena
Professor
Department of Computer Applications
Samrat Ashok Technological Institute
Vidisha (M.P.)
Research Scholar
Ravindra Kumar Singh
*

2. MULTI-PROTOCOL LABEL SWITCHING
GOALS OF MPLS
▪ Scalability of network layer routing.
▪ Using labels as a means to aggregate forwarding
information, while working in the presence of routing
hierarchies.
▪ Greater flexibility in delivering routing services.
▪ Using labels to identify particular traffic which are to
receive special services, e.g. QoS.
▪ Increased performance.
▪ Using the label-swapping paradigm to optimize network
performance.

3. GOALS OF MPLS CONT…
▪ Simplify integration of routers with cell switching based
technologies.
▪ Making cell switches behave as routers.
▪ By making information about physical topology
available to network layer routing procedures.

4. MULTI-PROTOCOL LABEL SWITCHING
INTRODUCTION TO MPLS
▪ MPLS improves internet scalability by eliminating the need
for each router and switch in a packet's path to perform
traditionally redundant address lookups and route
calculation.
▪ Improves scalability through better traffic engineering.
▪ MPLS also permits explicit backbone routing, which
specifies in advance the hops that a packet will take across
the network.
▪ This should allow more deterministic, or predictable,
performance that can be used to guarantee QoS.
▪ These paths function at layer 3 or can even be mapped
directly to layer 2 transport such as ATM or frame relay.

5. INTRODUCTION TO MPLS CONT…
▪ Explicit routing will give IP traffic a semblance of end-to-
end connections over the backbone.
▪ The MPLS definition of IP QoS parameters is limited.
▪ Out of 32 bits total, an MPLS label reserves just three bits
for specifying QoS.
▪ Label-switching routers (LSRs) will examine these bits and
forward packets over paths that provide the appropriate
QoS levels. But the exact values and functions of these so-
called 'experimental bits‘ remain to be defined.
▪ The MPLS label could specify whether traffic requires
constant bit rate (CBR) or variable bit rate (VBR) service,
and the ATM network will ensure that guarantees are met.

6. MULTI-PROTOCOL LABEL SWITCHING
ARCHITECTURE

7. MULTI-PROTOCOL LABEL SWITCHING
LABELS
▪ A label is short, fixed length physically continuous identifier
which is used to identify a FEC ( forwarding equivalence
class), usually of local significance.
▪ Ru can transmits a packet labeled L to Rd, if they can agree
to a binding between label L and FEC F for packets moving
from Ru to Rd.
▪ Ru (upstream LSR) → Rd (downstream LSR with
respect to a given binding).
▪ L becomes Ru’s “outgoing label” representing FEC F,
and L becomes rd’s “incoming label” representing FEC
F.
▪ Rd must make sure that the binding from label to FEC is
one-to-one.

8. MULTI-PROTOCOL LABEL SWITCHING
LABELS CONT…
▪ Rd must not agree with Ru1 to bind L to FEC F1, while
agreeing with some other LSR Ru2 to bind L to a different
FEC F2, unless rd can always tell, when it receives a packet
with incoming label L, whether the label was put on the
packet by Ru1 or Ru2.
L for FEC F1
L for FEC F2
Ru1
Ru2
Rd

9. MULTI-PROTOCOL LABEL SWITCHING
LABELED PACKET
▪ A packet into which a label has been encoded.
▪ The label resides in an encapsulation header which exists
specifically for this purpose.
▪ Or the label may reside in a existing data link or network
layer header.
▪ The particular encoding technique which is used must be
agreed to by both the entities which encodes the label and
the entity which decodes the label.

10. MULTI-PROTOCOL LABEL SWITCHING
LABEL DISTRIBUTION
▪ It is set of procedures by which one LSR informs another
LSRs of the bindings (label/FEC) it has made.
▪ Two LSRs which use a distribution protocol to exchange
label/FEC binding information are known as “label
distributing peers” with respect to the binding information
they exchange.
▪ There exists many different distribution protocols ( [MPLS-
BGP], [MPLS-RSVP], [MPLS-RVSP-TUNNELS],
[MPLS-CR-LDP]).

11. 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).

12. FAULT TOLERANCE IN MPLS
▪ In MPLS two basic models are used to recover from faults
▪ Protection Switching
▪ Rerouting

13. PROTECTION SWITCHING AND REROUTING
▪ Rerouting
▪ On-demand recovery – no preset backup paths.
▪ Example: existing recovery in IP networks.
▪ Protection
▪ Pre-determined recovery – backup paths “in advance”.
▪ Primary and backup are provisioned at the same time.
▪ IP supports rerouting .
▪ Because it is datagram service.
▪ MPLS supports rerouting as well as protection.
▪ Because it is virtual-circuit service.

14. REROUTING IN IP NETWORKS
▪ In traditional IP, what happens when a link or node fails?
▪ Failure information needs to be disseminated in the
network.
▪ During this time, packets may go in loops.
▪ Rerouting latency is in the order of seconds.
▪ We look for protection possibilities in an MPLS network,
but…
▪ First we need to look at the QoS requirements

15. QoS REQUIREMENTS
▪ Bandwidth Guaranteed Primary Paths
▪ Bandwidth Guaranteed Backup Paths
▪ BW remains provisioned in case of network failure
▪ Minimal “Protection or rerouting Latency”
▪ Protection/rerouting latency is the time that elapses
between:
▪ “the occurrence of a failure”, and
▪ “the diversion of network traffic on a new path”
rerouting is generally SLOWER than protection

16. PROTECTION IN MPLS
▪ First we define Protection level.
▪ Path protection
▪ Also called end-to-end protection.
▪ For each primary LSP, a node-disjoint backup LSP is set up.
▪ Upon failure, ingress node diverts traffic on the backup path.
▪ Local Protection
▪ Upon failure, node immediately upstream the failed element
diverts the traffic on a “local” backup path.
Path Protection ➔ More Latency
Local Protection ➔ Less Latency

17. PROTECTION IN MPLS CONT…
PATH PROTECTION
S 1 2 3 D
Primary Path
Backup Path
This type of “path Protection”
still takes 100s of ms.
We may explore “Local Protection” to
quickly switch onto backup paths!

18. PROTECTION IN MPLS CONT…
LOCAL PROTECTION: FAULT MODELS
A B C D
Link
Protection
A B C D
A B C D
Node
Protection
Element
Protection

19. PROTECTION IN MPLS CONT…
PROTECTION MODES
▪ 1+1 protection
▪ Flow sent on two separate disjoint paths
▪ Receiver responsible for choosing one of the two
▪ 1:1 protection
▪ A backup path protects a single LSP (or a portion of a
single LSP)
▪ N:1 protection
▪ A backup path protects one link or one node or both
▪ Overlapping portions of many LSPs are protected by a
single backup path
▪ Applicable for local protection only
▪ N:M protection (M<N)

20. COST OF THE BACKUP PATH
▪ 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?

21. MOTIVATION FOR THE RESEARCH
▪ We First 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?

22. MOTIVATION FOR THE RESEARCH CONT…
▪ Then we try to solve the following unsolved problems and
hence motivations:
▪ How can we reduce the amount of “backup bandwidth” but
still provide guaranteed backups? Thus maximizing the
bandwidth sharing.
▪ How to increase the maximum number of primary LSPs
that can be placed on the network?
▪ How to maintain the survivability of network by recovering
from failure with in the acceptable delay and minimum
packet loss while efficiently utilizing the network
resources?

23. MOTIVATION FOR THE RESEARCH CONT…
▪ How to enhance the fault-tolerance performance without
affecting the fault free traffic?
▪ How to solve the packet disorder problem while
rerouting the affected traffic?

24. RELATED WORK
▪ Jenhui Chen et al. in [26] proposed a fast path recovery mechanism,
which employs the Enhanced Interior Gateway Routing Protocol
(EIGRP) and the Diffusing Update Algorithm (DUAL) together, to
find the working and backup paths simultaneously and modify the
LDP to establish the LSP by using the routing table of EIGRP.
▪ S Sae Lor et al. in [25] proposed a novel technique for fast re-route in
hop-by-hop routing in case of single link failures. It offers full repair
coverage without requiring additional mechanisms such as tunneling
or interface-specific operations. The technique handles the failures
without jeopardizing the operable parts of a network.
▪ Sahel Alouneh et al. in [27] present a novel approach for fault
tolerance in MPLS networks using a modified (k, n) threshold
sharing scheme with multi-path routing.

25. RELATED WORK CONT…
▪ Jenn-Wei Lin et al. in [28] enhanced the fault-tolerant performance
of the two recovery mechanisms (protection switching and
rerouting). The proposed approach utilizes the failure free LSPs to
transmit the traffic of the failed LSP (the affected traffic).
▪ Ravindra Kumar Singh et al. in [30] proposed a new algorithm for
an optimum LSP pair selection from multiple parallel LSP pairs. It
minimizes the probability of network congestion, packet loss and
request loss by selecting the LSP which is lightly loaded and
possess upward and downward bandwidth proportional to the
service request.

26. RESEARCH METHODOLOGY
▪ Survey of literature, Study of various algorithms/ models/
methods of the Fault Tolerance and Rerouting currently
available.
▪ Comparison between existing algorithms/ models based on
their efficiency and methodology, complexity.
▪ Analysis of pros and cons of different Fault Tolerance and
Rerouting methods exist in the literature.
▪ Criteria for evaluating the performance factors.
▪ Creation of new algorithms/ models which removes
drawbacks of existing methods

27. EXPECTED OUTCOMES
▪ Implementation model for proposed work.
▪ Complete analysis of various factors affecting performances of
fault tolerance algorithm.
▪ Implementation/ simulation of newly developed algorithms/
models/ methods.
▪ Comparison of newly developed algorithms/ models/ methods
with the existing algorithms/ models/ methods.
▪ Testing & maintenance of the newly developed algorithms/
models Necessary optimization models to be designed and / or
simulated.
▪ Experiments with real world networks are reported to
demonstrate the optimality of the algorithm / model / methods.

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