Transcript Traffic Engineering - Suraj @ LUMS

Introduction to MPLS
and Traffic Engineering
Zartash Afzal Uzmi
First slide…
Questions?
Ask when you have them!
Jan 11, 2006
Lahore University of Management Sciences
2
Outline

Traditional IP Routing




MPLS Terminology and Operation




Forwarding and routing
Problems with IP routing
Motivations behind MPLS
MPLS Label, LSR and LSP, LFIB Vs FIB
Transport of an IP packet over MPLS
More MPLS terminology
Traffic Engineering [with MPLS]



Nomenclature
Requirements
Examples
Jan 11, 2006
Lahore University of Management Sciences
3
Outline

Traditional IP Routing




MPLS Terminology and Operation




Forwarding and routing
Problems with IP routing
Motivations behind MPLS
MPLS Label, LSR and LSP, LFIB Vs FIB
Transport of an IP packet over MPLS
More MPLS terminology
Traffic Engineering [with MPLS]



Nomenclature
Requirements
Examples
Jan 11, 2006
Lahore University of Management Sciences
4
Forwarding and routing

Forwarding:


Routing:


Computing the “best” path to the destination
IP routing – includes routing and forwarding



Passing a packet to the next hop router
Each router makes the forwarding decision
Each router makes the routing decision
MPLS routing


Only one router (source) makes the routing decision
Intermediate router make the forwarding decision
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IP versus MPLS routing

IP routing


Each IP datagram is routed independently
Routing and forwarding is destination-based



Routers look at the destination addresses
May lead to congestion in parts of the network
MPLS routing


A path is computed “in advance” and a “virtual
circuit” is established from ingress to egress
An MPLS path from ingress to egress node is
called a label switched path (LSP)
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How IP routing works
Searching
Longest
Prefix Match
in FIB (Too
Slow)
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Problems with IP routing

Too slow



Too rigid – no flexibility


IP lookup (longest prefix matching) “was” a
major bottleneck in high performance routers
This was made worse by the fact that IP
forwarding requires complex lookup operation
at every hop along the path
Routing decisions are destination-based
Not scalable in some desirable applications

When mapping IP traffic onto ATM
Jan 11, 2006
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IP routing rigidity example
D
1
A
1
S
B




1
C
B
2
Packet 1: Destination A
Packet 2: Destination B
S computes shortest paths to A and B; finds D as next hop
Both packets will follow the same path


A
Leads to IP hotspots!
Solution?

Try to divert the traffic onto alternate paths
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IP routing rigidity example
D
1
A
4
S
B




A
1
C
B
2
Increase the cost of link DA from 1 to 4
Traffic is diverted away from node D
A new IP hotspot is created!
Solution(?): Network Engineering


Put more bandwidth where the traffic is!
Leads to underutilized links; not suitable for large networks
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Motivations behind MPLS

Avoid [slow] IP lookup



Provide some scalability for IP over ATM
Evolve routing functionality


Led to the development of IP switching in 1996
Control was too closely tied to forwarding
Evolution of routing functionality led to some
other benefits


Explicit path routing
Provision of service differentiation (QoS)
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IP routing versus MPLS routing
Traditional IP Label
Routing
Multiprotocol
Switching (MPLS)
1
2
S
D
3
4
5
MPLS allows overriding shortest paths!
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Outline

Traditional IP Routing




MPLS Terminology and Operation




Forwarding and routing
Problems with IP routing
Motivations behind MPLS
MPLS Label, LSR and LSP, LFIB Vs FIB
Transport of an IP packet over MPLS
More MPLS terminology
Traffic Engineering [with MPLS]



Nomenclature
Requirements
Examples
Jan 11, 2006
Lahore University of Management Sciences
13
MPLS label


To avoid IP lookup MPLS packets carry
extra information called “Label”
Packet forwarding decision is made using
label-based lookups
Label


IP Datagram
Labels have local significance only!
How routing along explicit path works?
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Routing along explicit paths


Idea: Let the source make the complete routing
decision
How is this accomplished?


Let the ingress attach a label to the IP packet and let
intermediate routers make forwarding decisions only
On what basis should you choose different paths
for different flows?


Define some constraints and hope that the constraints
will take “some” traffic away from the hotspot!
Use CSPF instead of SPF (shortest path first)
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Label, LSP and LSR

Label
01234567890123456789012345678901
Label
| Exp|S|
TTL
Label = 20 bits
Exp = Experimental, 3 bits
S = Bottom of stack, 1bit
TTL = Time to live, 8 bits



Router that supports MPLS is known as label
switching router (LSR)
An “Edge” LSR is also known as LER (edge router)
Path which is followed using labels is called LSP
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LFIB versus FIB


Labels are searched in LFIB whereas normal IP
Routing uses FIB to search longest prefix match
for a destination IP address
Why switching based on labels is faster?




LFIB has fewer entries
Routing table FIB has very large number of entries
In LFIB, label is an exact match
In FIB, IP is longest prefix match
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Mpls Flow Progress
D
R1
LSR4
R2
LSR1
D
LSR6
destination
LSR3
LSR2
R1 and R2 are
regular routers
LSR5
1 - R1 receives a packet for destination D connected to R2
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Mpls Flow Progress
R1
D
LSR4
R2
LSR1
D
LSR6
destination
LSR3
LSR2
LSR5
2 - R1 determines the next hop as LSR1 and forwards the packet
(Makes a routing as well as a forwarding decision)
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Mpls Flow Progress
R1
LSR4
LSR1
31
R2
D
D
LSR6
destination
LSR3
LSR2
LSR5
3 – LSR1 establishes a path to LSR6 and “PUSHES” a label
(Makes a routing as well as a forwarding decision)
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Mpls Flow Progress
R1
LSR4
R2
LSR1
D
LSR6
LSR3
17
destination
D
LSR2
LSR5
Labels have local
signifacance!
4 – LSR3 just looks at the incoming label
LSR3 “SWAPS” with another label before forwarding
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MPLS Flow Progress
R1
LSR4
R2
LSR1
D
LSR6
LSR3
17
destination
D
LSR2
LSR5
Path within MPLS cloud
is pre-established:
LSP (label-switched path)
5 – LSR6 looks at the incoming label
LSR6 “POPS” the label before forwarding to R2
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MPLS and explicit routing recap

Who establishes the LSPs in advance?


Ingress routers
How do ingress routers decide not to always take
the shortest path?


Ingress routers use CSPF (constrained shortest path
first) instead of SPF
Examples of constraints:
 Do not use links left with less than 7Mb/s bandwidth
 Do not use blue-colored links for this request
 Use a path with delay less than 130ms
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CSPF

What is the mechanism?




First prune all links not fulfilling constrains
Now find shortest path on the rest of the topology
Requires some reservation mechanism
Changing state of the network must also be
recorded and propagated


For example, ingress needs to know how much
bandwidth is left on links
The information is propagated by means of routing
protocols and their extensions
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More MPLS terminology
Upstream
Downstream
172.68.10/24
LSR1
LSR2
Data
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Label advertisement

Always downstream to upstream label
advertisement and distribution
Upstream
Use label 5 for destination
171.68.32/24
Downstream
171.68.32/24
LSR1
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MPLS Data Packet
with label 5 travels
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LSR2
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Label advertisement

Label advertisement can be downstream
unsolicited or downstream on-demand
Upstream
Sends label
Without any Request
Downstream
171.68.32/24
LSR2
LSR1
Upstream
Sends label ONLY after
receiving request
Downstream
171.68.32/24
LSR1
Jan 11, 2006
Request For label
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LSR2
27
Label distribution


Label distribution can be ordered or unordered
First we see an example of ordered label distribution
Label
Egress LSR
Ingress LSR
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Label distribution


Label distribution can be ordered or unordered
Next we see an example of unordered label distribution
Label
Label
Egress LSR
Ingress LSR
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Label retention modes

Label retention can be conservative or liberal
?
Destination
Label
LSR1
Label
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Label operations

Advertisement



Distribution



Downstream unsolicited
Downstream on-demand
Ordered
Unordered
Retention


Liberal
Conservative
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Outline

Traditional IP Routing




MPLS Terminology and Operation




Forwarding and routing
Problems with IP routing
Motivations behind MPLS
MPLS Label, LSR and LSP, LFIB Vs FIB
Transport of an IP packet over MPLS
More MPLS terminology
Traffic Engineering [with MPLS]



Nomenclature
Requirements
Examples
Jan 11, 2006
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Traffic Engineering
Traffic Engineering with MPLS
(Application of CSPF)
What is traffic engineering?



Performance optimization of operational networks
 optimizing resource utilization
 optimizing traffic performance
 reliable network operation
How is traffic engineered?
 measurement, modeling, characterization, and
control of Internet traffic
Why?


high cost of network assets
service differentiation
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Traffic engineering




Recall the IP hotspot problem
The ability to move traffic away from the
shortest path calculated by the IGP (such as
OSPF) to a less congested path
IP: changing a metric will cause ALL the traffic
to divert to the less congested path
MPLS: allows explicit routing (using CSPF) and
setup of such explicitly computed LSPs
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MPLS-TE: How to do it?


LSPs are set up by LSRs based on information
they learn from routing protocols (IGPs)
This defeats the purpose!

If we were to use “shortest path”, IGP was okay
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MPLS TE: How we actually do it?

MPLS TE Requires:

Enhancements to routing protocols



Enhancement to signaling protocols to allow
explicit constraint based routing


OSPF-TE
ISIS-TE
RSVP-TE and CR-LDP
Constraint based routing


Jan 11, 2006
Explicit route selection
Recovery mechanisms defined
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Signaling mechanisms

RSVP-TE


BGP-4


Carrying label information in BGP-4
CR-LDP


Extensions to RSVP for traffic engineering
A label distribution protocol that distributes labels
determined based on constraint based routing
RSVP-TE and CR-LDP both do label distribution
and path reservation – use any one of them!
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RSVP-TE
Basic flow of LSP set-up using RSVP
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RSVP-TE PATH Message


PATH message is used to establish state and
request label assignment
R1 transmits a PATH message addressed to R9
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RSVP-TE RESV Message




RESV is used to distribute labels after reserving resources
R9 transmits a RESV message, with label=3, to R8
R8 and R4 store “outbound” label and allocate an “inbound” label.
They also transmits RESV with inbound label to upstream LSR
R1 binds label to forwarding equivalence class (FEC)
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Rerouting LSP tunnels



When a more “optimal” route/path
becomes available
When a failure of a resource occurs along
a TE LSP
Make-before-break mechanism


Adaptive, smooth rerouting and traffic
transfer before tearing down the old LSP
Not disruptive to traffic
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Recovering LSP tunnels
LSP Set-up
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Protection LSP set up
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Protection LSP
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References





RFC 2702 “Requirements for Traffic
Engineering Over MPLS”
RFC 3031 “Multiprotocol Label Switching
Architecture”
RFC 3272 “Overview and Principles of
Internet Traffic Engineering”
RFC 3346 “Applicability Statement for
Traffic Engineering with MPLS”
MPLS Forum (http://www.mplsforum.org)
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Last slide…
Thank you!
Questions?
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Outline



Background
 Network Services and QoS
 Architectural Requirements
 IP and MPLS
Introduction to restoration routing
 Local Restoration: Types of Backup Paths
 Local Restoration: Fault Models
 Backup Bandwidth Sharing
 Activation sets
Restoration routing framework
 Components
 Typical example
 Evaluation and Experimentation
Jan 11, 2006
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Outline



Background
 Network Services and QoS
 Architectural Requirements
 IP and MPLS
Introduction to restoration routing
 Local Restoration: Types of Backup Paths
 Local Restoration: Fault Models
 Backup Bandwidth Sharing
 Activation sets
Restoration routing framework
 Components
 Typical example
 Evaluation and Experimentation
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Network Traffic and Services

Network Traffic today



New and interactive applications are emerging





Not what it was 10 years ago
Multimedia intensive
Internet telephony
Videoconferencing
Streaming media (voice and video)
Remote collaboration (e.g., remote desktop)
Many new applications are real-time

More and more users of these applications
Burstiness behavior has changed over the years!
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Current Network Architecture

Internet is popular because


Internet is inexpensive because


It uses resource sharing
 by means of statistical multiplexing
Current Internet architecture



It is inexpensive
Uses packet switches with buffers
Required buffer size is primarily determined by a
random traffic pattern
Buffer size optimization


Too low  High drop rate
Too high  High delay
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Architectural Requirements

Emerging applications



Under normal conditions


We are worried about the two-way interactive
applications
When resources fail


Two-way interactive communications
One-way streaming media type applications
We are also worried about the one-way applications
Current Internet architecture is not suitable for
new and emerging applications

New architectures are being researched
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Architectural Requirements

New network architectures



Experience with networks



All circuit-switched?
Mix of packet-switch and “circuit-switch-like”
Bigger buffers are required when there is more
randomness and more aggregation
Should use circuits at places where we see more
randomness
Example: 100x100 project


Edge network is packet-switched
Core network is virtual-circuits
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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)
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Outline



Background
 Network Services and QoS
 Architectural Requirements
 IP and MPLS
Introduction to restoration routing
 Local Restoration: Types of Backup Paths
 Local Restoration: Fault Models
 Backup Bandwidth Sharing
 Activation sets
Restoration routing framework
 Components
 Typical example
 Evaluation and Experimentation
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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
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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.
Primary Path
We may explore “Local Protection” to
quickly switch onto backup paths!
Backup Path
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Local Restoration: Fault Models
Link
Protection
Node
Protection
Element
Protection
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A
B
C
D
A
B
C
D
A
B
C
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59
nhop and nnhop paths
nnhop
A
B
D
C
E
nhop
PLR: Point of Local Repair
Primary Path
Backup Path
Jan 11, 2006
All links and all nodes are protected!
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Opportunity cost of backup paths

Local Protection requires that backup paths are
setup in advance


Bandwidth must be reserved for all backup
paths


Upon failure, traffic is promptly switched onto
preset 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:
Sharing
L1
A
BW: X
B
X
X
E
G
F
X+Y
Y
C
X
max(X, Y)
L2
BW: Y
Y
D
Primary Path
Backup Path
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Activation Sets
A
A
E
B
C
C
D
D
Activation set for node B
Jan 11, 2006
E
B
Activation set for link (A,B)
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Outline



Background
 Network Services and QoS
 Architectural Requirements
 IP and MPLS
Introduction to restoration routing
 Local Restoration: Types of Backup Paths
 Local Restoration: Fault Models
 Backup Bandwidth Sharing
 Activation sets
Restoration routing framework
 Components
 Typical example
 Evaluation and Experimentation
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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
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Evaluation & Experimentation

Traffic Generation



Rejected Requests Experiments



Use existing or emerging traffic models
Consider call holding times and multi-service traffic
Measure the number of rejected requests
Simulate on various topologies
Network Loading Experiments



Set link capacities to infinity
Measure the total bandwidth required to service a given
set of requests
Simulate on various topologies
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Recent Trends


Preemption of lower class traffic
Multilayer recovery



We can “almost” deal with recovery at a single protocol
layer
What if we intend to provide recovery at multiple
protocol layers?
For multilayer recovery, we need to consider
these additional issues:





Interworking of layers
Local information stored at each node of each layer
Recovery provided by each individual layer
Signaling mechanism from one layer to another
Effects on bandwidth sharing (if sharing is used)
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Thank You!
Questions & Answers
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Extra Stuff!
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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)

Jan 11, 2006
Hij:
Maximum bandwidth reserved on any one link by all
backup paths spanning
link (i,Sciences
j)
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oAIS versus AIS: Example
LSP Request-1 (src, dst, bw) = (A, C,
4)
D
GAF=4
E
F
FAB=4
A
HAB=4
B
C
G
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oAIS Example
LSP Request-2 (src, dst, bw) = (A, C, 5)
D
GAF=4
E
F
FAB=4
=9
A
B
C
HAB=4
=5
GAG=5
G
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oAIS Example
LSP Request-3 (src, dst, bw) = (D, E, 7)
FDE=7
D
GAF=7
=4
E
F
FAB=9
A
B
C
HAB=5
GAG=5
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?
How much BW is shareable on (A, F)?
D
AIS:
Shareable = max(0, GAF - FAB)
= GAF - min(GAF, FAB) = 0
Additional resv = 6
oAIS: (HAB ≤ FAB)
Shareable = GAF - min(GAF, HAB) = 2
Additional resv = 6 - 2 = 4
CIS: (link (A,B) knows BWred)
Shareable = GAF - BWred = 7 - 4 = 3
Additional resv = 6 - 3 = 3
Jan 11, 2006
GAF=7
FDE=7
E
F
FAB=9
A
B
C
HAB=5
GAG=5
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Single Link Protection: Network 1
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Single Link Protection: Network 1
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Single Link Protection: Network 2
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Single Link Protection: Network 2
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Single Node Protection: Network 1
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Single Element Protection: Network 1
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A Bandwidth Sharing Model
(Simplified for the Link Protection Fault Model)
Recall the definition of nhop paths
Link
Protection
A
B
C
D
Primary Path
Backup Path
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All links and all nodes are protected!
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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 ∩ µij (set of paths falling on (u,v) if (i,j) fails)
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Bandwidth Sharing Model
u
3
i
OLD MODEL:
Aij = {R, B}
Buv = {R, B, …}
Aij ∩ Buv= {R, B}
|| Aij ∩ Buv || = 2+7 = 9
Un-shareable = 9
Shareable = 10 - 9 = 1
Jan 11, 2006
v
j
RED=7
BLU=2
GRN=3 (New Request)
Guv = 10
k
NEW MODEL:
Aij = {R, B}
Buv = {nhijr, nhijb, …}
(nhops through (u, v))
µij = {nhijr, nhijb, …}
(nhops spanning (i, j))
ijuv = µij ∩ Buv= {nhijr, nhijb}
|| ijuv || = 2 + 7 = 9
(Un-shareable)
Shareable = Guv - || ijuv || = 10 - 9 = 1
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Bandwidth Sharing Model
u
3
i
OLD MODEL:
Aij = {R, B}
Buv = {R, B, …}
Aij ∩ Buv= {R, B}
|| Aij ∩ Buv || = 2+7 = 9
Un-shareable = 9
Shareable = 10 - 9 = 1
Jan 11, 2006
v
j
RED=7
BLU=2
GRN=3 (New Request)
Guv = 10
k
NEW MODEL:
Aij = {R, B}
Buv = {nhijr, nhjkb, …}
(nhops through (u, v))
µij = {nhijr, nhijb, …}
(nhops spanning (i, j))
ijuv = µij ∩ Buv= {nhijr}
|| ijuv || = 7
(Un-shareable)
Shareable = Guv - || ijuv || = 10 - 7 = 3
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Restoration in MPLS
Path Protection
A
Primary Path
B
C
D
E
MPLS path Protection may take
100s of ms, whereas MPLS Local
protection takes less than 10 ms.
Backup Path
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