MPLS and Traffic Engineering

Ji-Hoon Yun

Computer Communications and Switching Systems Lab.

scc C om pu ter C om m u n ica tion s& S w itch in g S ystem s L ab

Table of contents

Introduction What is ‘traffic engineering’ ? Traffic handling in the current Internet MPLS and traffic engineering Signaling protocol Examples Conclusion

scc C om pu ter C om m u n ica tion s& S w itch in g S ystem s L ab

Traffic engineering

The process of arranging how traffic flows through the network

Central goal : minimizing congestion Congestion scenarios

Network resources are insufficient Augmenting network capacity, or modulating, conditioning, or

throttling the demand Inefficient mapping of traffic onto resources

Efficient resources allocation : Traffic engineering

Another goal : reliable network operation Failure recovery

scc C om pu ter C om m u n ica tion s& S w itch in g S ystem s L ab

Traffic engineering process model

Performance monitorsFault monitors

Analytical models

Formulation of control policy

Observation of network state

Characterization of traffic and network state

Performanceoptimization ?

Revisecontrol policy?

Optimize network

performance

Performance monitorsFault monitors

Analytical modelsPerformance monitors

Fault monitors

Performance monitorsFault monitors

Analytical models

Performance monitorsFault monitors

Analytical models

Capacity planningNetwork design

Network operations control

Performance monitorsFault monitors

Analytical models

Performance monitorsFault monitors

Analytical modelsCapacity augmentationConfiguration control

Yes

No

No

Yes

scc C om pu ter C om m u n ica tion s& S w itch in g S ystem s L ab

Basic components of T.E.

Distribution of topology information

Path selection

Directing traffic along the computed paths

Traffic management

scc C om pu ter C om m u n ica tion s& S w itch in g S ystem s L ab

Traffic handling in the current Internet

Inadequacy of measurement functions Even a traffic matrix is difficult to estimate

Limited intradomain routing control functions Destination-based Each router makes independent routing decisions Mostly shortest path routing

Drawbacks Imbalance of network load Lack of traffic management

scc C om pu ter C om m u n ica tion s& S w itch in g S ystem s L ab

“the fish picture” example

scc C om pu ter C om m u n ica tion s& S w itch in g S ystem s L ab

T.E. with the classical overlay model

scc C om pu ter C om m u n ica tion s& S w itch in g S ystem s L ab

Eliminating a full mesh of adjacencies using label switching

scc C om pu ter C om m u n ica tion s& S w itch in g S ystem s L ab

Traffic engineering with MPLS

Connection-oriented forwarding in an IP network Label Switched Path(LSP) Label Switched Router(LSR) Provides a method to set up explicit paths and

forward traffic on them

No addressing of how to find paths with constraints

scc C om pu ter C om m u n ica tion s& S w itch in g S ystem s L ab

What does ‘multiprotocol’ mean ?

IPv6 AppleTalkIPv4 IPX

Label switching

Eth

ern

et

Fram

e R

ela

y

FD

DI

ATM

Poin

t-to-p

oin

t

Network layerprotocols

Link layerprotocols

scc C om pu ter C om m u n ica tion s& S w itch in g S ystem s L ab

Connection-oriented Networks

QoS features are much easier to support All data traveling along a specific connection can be treated

similarly No special analysis needs to be done on each data packet

Each connection can be delivered along a unique path

Useful in traffic engineering Useful as a policy tool

scc C om pu ter C om m u n ica tion s& S w itch in g S ystem s L ab

Connection-oriented Networks(cont’d)

High-speed service restoration for loss-sensitive services

Traffic can be redirected to other alternate connections in a very rapid fashion

In an IP network, the routing protocol must converge before service will be restored

scc C om pu ter C om m u n ica tion s& S w itch in g S ystem s L ab

Components of the MPLS Traffic Engineering Model

Path management Path selection

The source router computes the complete path pruning the database to remove links that are ineligible A shortest path algorithm is then run on the pruned topology

Specifies the explicit route for an LSP tunnel Path placement

Instantiate LSP tunnels using a signaling protocol RSVP, constraint-based routed LDP(CR-LDP)

Path maintenance Sustains and terminates already established LSP tunnels

scc C om pu ter C om m u n ica tion s& S w itch in g S ystem s L ab

Components of the MPLS Traffic Engineering Model (cont’d)

Traffic Assignment Partitioning ingress traffic Apportionment the partitioned traffic

Network State Information Dissemination Extension of IGP(Interior Gateway Protocol) Maximum link bandwidth, maximum reservable bandwidth,

current bandwidth reservation, resource class or color of the link, etc.

Used by constraint-based routing entities

scc C om pu ter C om m u n ica tion s& S w itch in g S ystem s L ab

Components of the MPLS Traffic Engineering Model (cont’d)

Network Management Configuration management functions, performance and

accounting management functions, fault management functions

Monitoring the state of LSP and controlling their characteristics

scc C om pu ter C om m u n ica tion s& S w itch in g S ystem s L ab

MPLS signaling protocols

Control-driven LSP Next hop is determined based on IP forwarding table Label Distribution Protocol (LDP)

Constraint-based Routed LSP (CR-LSP) The route is specified in the setup message May be used for traffic engineering Constraint-based routed LDP (CR-LDP), extension of RSVP

scc C om pu ter C om m u n ica tion s& S w itch in g S ystem s L ab

Requirements for a Signaling Protocol

Robustness Scalability Specification of QoS LSP establishment / teardown / maintenance LSP priority / preemption Flexibility in path setup options Alternative path setup and rerouting capability

scc C om pu ter C om m u n ica tion s& S w itch in g S ystem s L ab

CR-LDP vs. RSVP

CR-LDP Extension of RSVP

Transport mechanism Transport in TCP (reliable)

Raw IP packets (unreliable)

State management Hard state Soft state; needs per-flow refresh management

Messages required for LSP setup and maintenance

Request and Mapping

Path, Resv and ResvConf

Base architecture Based on LDP developed for MPLS

Based on RSVP, but may require major changes to the basic protocol to improve its scalability

scc C om pu ter C om m u n ica tion s& S w itch in g S ystem s L ab

Establishing LSP with CR-LDP

scc C om pu ter C om m u n ica tion s& S w itch in g S ystem s L ab

Establishing LSP with RSVP

scc C om pu ter C om m u n ica tion s& S w itch in g S ystem s L ab

Mapping packets into LSPs - example

scc C om pu ter C om m u n ica tion s& S w itch in g S ystem s L ab

Forwarding topology with LSPs

scc C om pu ter C om m u n ica tion s& S w itch in g S ystem s L ab

Using an alternative path for reroute in IP networks

scc C om pu ter C om m u n ica tion s& S w itch in g S ystem s L ab

Protection LSP

scc C om pu ter C om m u n ica tion s& S w itch in g S ystem s L ab

Steady state path

scc C om pu ter C om m u n ica tion s& S w itch in g S ystem s L ab

Forwarding over the protection LSP

scc C om pu ter C om m u n ica tion s& S w itch in g S ystem s L ab

Conclusion

Inadequacies of present-day IP networks

The MPLS-based solution for traffic engineering

Comparison of the two signaling protocol, RSVP and CR-LDP

MPLS coupled with the extensions of existing routing protocol and signaling protocols can provide powerful traffic engineering in ISP networks