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MPLS
Traffic Engineering
George Swallow


Traffic Engineering

© 1999, Cisco Systems, Inc.

1


What is Traffic Engineering

Taking control of how traffic flows in your
network in order to Improve overall network performance
Offer premium services
As a tactical tool to deal with network design
issues when the longer range solution are not
deployed
Traffic Eng.

© 1999, Cisco Systems, Inc.

Cisco Systems

2


Voice Traffic Engineering
• Telco’s noticed that demands vary

widely by time of day
• Began “engineering the traffic”
long ago
• Evolved over time
• Now fully automated
Traffic Eng.

© 1999, Cisco Systems, Inc.

Cisco Systems

3


Reasons for Traffic Engineering

•
•
•
•

Traffic Eng.

Economics – more packets, fewer $$$
Address deficiencies of IP routing
Tactical tool for network operations
Class-of-service routing

© 1999, Cisco Systems, Inc.

Cisco Systems

4


Economics of Traffic Engineering

“The efficacy with which one uses the
available bandwidth in the transmission
fabric directly drives the fundamental
‘manufacturing efficiency’ of the
business and its cost structure.”
Mike O’Dell, UUnet

Savings can be dramatic. Studies have shown that
transmission costs can be reduced by 40%.
Traffic Eng.

© 1999, Cisco Systems, Inc.

Cisco Systems

5


The “Fish” Problem
a deficiency in IP routing
R8

R3

R4
R2

R5

R1
R6

R7

IP uses shortest path destination based routing
Shortest path may not be the only path
Alternate paths may be under-utilized while the
shortest path is over-utilized
Traffic Eng.

© 1999, Cisco Systems, Inc.

Cisco Systems

6


Deficiencies in IP Routing

• Chronic local congestion
• Load balancing
Across long haul links

• Size of links

Difficult to get IP to make good use unequal size
links without overloading the lower speed link

Traffic Eng.

© 1999, Cisco Systems, Inc.

Cisco Systems

7


Load Balancing

Making good use of expensive links simply by
adjusting IGP metrics can be a frustrating exercise!
Traffic Eng.

© 1999, Cisco Systems, Inc.

Cisco Systems

8


Overlay Motivation
Separate Layer 2 Network
(Frame Relay or ATM)
“The use of the explicit Layer 2 transit layer
gives us very exacting control of how

traffic uses the available bandwidth in
ways not currently possible by tinkering
with Layer 3-only metrics.”
Mike O’Dell
UUnet, November 17, 1996

Traffic Eng.

© 1999, Cisco Systems, Inc.

Cisco Systems

9


The Overlay Solution
L3

L3
L2

L3

L2

L2
L2

L3

L2
L3

L2

L3

L3

L3

L3
L3

L3

L3

Physical

Logical

• Layer 2 network used to manage
the bandwidth
• Layer 3 sees a complete mesh
Traffic Eng.

© 1999, Cisco Systems, Inc.

Cisco Systems

10


Overlay Drawbacks
• Extra network devices (cost)
• More complex network management
Two-level network without integrated NM
Additional training, technical support,
field engineering

• IGP routing doesn’t scale for meshes
Number of LSPs generated for a failed router is
O(n3); n = number of routers
Traffic Eng.

© 1999, Cisco Systems, Inc.

Cisco Systems

11


Traffic Engineering & MPLS

+
Router

ATM Switch

or

=
MPLS
Router

ATM MPLS
Router

• MPLS fuses Layer 2 and Layer 3
• Layer 2 capabilities of MPLS can
be exploited for IP traffic engineering
• Single box / network solution
Traffic Eng.

© 1999, Cisco Systems, Inc.

Cisco Systems

12


An LSP Tunnel
R8

R3
R4
R2

R5

R1
R6

R7

Labels, like VCIs can be used to establish virtual
circuits
Normal Route R1->R2->R3->R4->R5
Tunnel: R1->R2->R6->R7->R4
Traffic Eng.

© 1999, Cisco Systems, Inc.

Cisco Systems

13


Comprehensive Traffic
Engineering
• Network design
Engineer the topology to fit the traffic

• Traffic engineering
Engineer the traffic to fit the topology
Given a fixed topology and a traffic matrix, what set
of explicit routes offers the best overall network
performance?

Traffic Eng.

© 1999, Cisco Systems, Inc.

Cisco Systems

14


The Traffic Engineering System
Statistics
Collection
Traffic Analysis
Traffic Engineering
Design and Modeling

CLI
TE Tunnel

Router Network
Traffic Eng.

© 1999, Cisco Systems, Inc.

Configuration

Traffic Engineering Tools
Cisco Systems

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Topology

Approaches to Traffic
Engineering

Comprehensive Comprehensive
for
TE
Premium Flows

Tactical
for
Premium Flows

Tactical
TE

Type of Traffic
Traffic Eng.

© 1999, Cisco Systems, Inc.

Cisco Systems

16


Tactical Traffic Engineering

• Links not available
Infrastructure doesn’t exist
Lead times too long

• Failure scenarios
• Unanticipated growth and
shifts in traffic
Traffic Eng.

© 1999, Cisco Systems, Inc.

Cisco Systems

17


Tactical TE
An Example
Major US ISP
 New web site appears
Within weeks becomes the largest traffic source on their
network
One of their PoPs becomes completely congested

 Once the problem was identified
TE tunnels were established to route away any traffic passing
through that PoP, but not destined or sourced there
Congestion was completely resolved in 5 minutes

Traffic Eng.

© 1999, Cisco Systems, Inc.

Cisco Systems

18


System Block Diagram
Traffic
Engineering
Control
Path
Selection

TE Topology
Database

RSVP

TE Link
Adm Ctl

IS-IS/OSPF
Routing

Flooding

Forwarding Engine

Traffic Eng.

© 1999, Cisco Systems, Inc.

Cisco Systems

19


TE Tunnel Attributes
• Bandwidth
• Setup & Holding priorities
Used for Admission Control

• Resource class affinity
Simple policy routing

• Path Options
Input to route selection
Traffic Eng.

© 1999, Cisco Systems, Inc.

Cisco Systems

20


LSP Tunnel Setup
R9

R8
R3
R4
R2

Pop

R5

R1

32
49
17

R6

R7
22

Setup: Path (R1->R2->R6->R7->R4->R9) Tunnel ID 5, Path ID 1
Reply: Communicates Labels and Label Operations
Reserves bandwidth on each link
Traffic Eng.

© 1999, Cisco Systems, Inc.

Cisco Systems

21


Multiple Parallel Tunnels
• Automatically load shared
• Weighted by bandwidth
to nearest part in 16

• Traffic assigned by either
Source-Destination hash
Round robin

Traffic Eng.

© 1999, Cisco Systems, Inc.

Cisco Systems

22


Automatic Load Balancing

New York
#1
New York
#2

LSP Tunnel #1
Link #1

LSP Tunnel #2
Link #2

Stockholm
London
#1
Frankfurt
London
#2
Amsterdam

Brussels
Washington

Traffic Eng.

© 1999, Cisco Systems, Inc.

LSP Tunnel #3
Link #3

Cisco Systems

Paris

Munich

23

Additional Features
• Adjusting to failures
Requires rapid notification

• Adjusting to improvements
• Need to account for
Global optimality
Network stability
Traffic Eng.

© 1999, Cisco Systems, Inc.

Cisco Systems

24


Protection Strategy
Two pronged approach:
• Local protection
Repair made at the point of failure us to keep critical
applications going
Fast - O(milliseconds)
Sub-optimal

• Path protection
An optimized long term repair
Slower - O(seconds)

Traffic Eng.

© 1999, Cisco Systems, Inc.

Cisco Systems

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