MPLS: The Magic Behind the
Myths
Grenville Armitage
Lucent Technologies
Introduction
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Reviews key differences (and similarities)
between IP routing and emerging MPLS
approach
Article highlights MPLS does not offer much as
once portrayed – e.g. gigabit forwarding
Fails to point out flaws in vision
Contribution related to traffic engineering
Scalability Issues
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MPLS provides traffic engineering capabilities
– agreed
Benefits of MPLS extend only as far as its
deployment
End-to-end solution possible only if entire
network MPLS enabled
MPLS is domain specific!
Scalability Issues (contd.)
VoIP
packet
Supports
MPLS
No
MPLS
No QoS
guarantee
MPLS is domain specific!!
Stateful Routers
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LSR (label-switching routers) keep info about
different labels
Labels correspond to states stored in router
Routers that keep information are bad
Does not mention how to deal with failures
Stateful Routers
P
1
4
P
2 ??
3
Lose label
information
Loss of Label makes packet Unroutable!
Control and Management
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Unclear how QoS characteristics of each LSP
managed
Unclear how non-shortest paths for traffic
engineering obtained
Human intervention required for router
configuration
Complex and error-prone
MPLS not for QoS
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Domain specificity and scalability issues in
deployment
No standards to designate Type of Service
(TOS) bits
MPLS has no end-to-end solution
MPLS suffers from static routing problems
Static Routing Problem
P
4
1
3
P
P
2
MPLS offers static routing only!
P
MPLS not for QoS (contd.)
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Internet is a significant and rapidly growing
carrier of voice traffic
Ineffective and impractical for fluctuating
demands of VoIP
MPLS nothing but domain-specific circuit
switching
MPLS for VPNs
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No automatic encryption of data
Susceptible to data leak if a connection is
disrupted
Potential for administrator doing wrong
provisioning causing loss of privacy
Not clear how MPLS will make use of
encryption for security
ISPs must manage routing table for each VPN
Where does MPLS fit ??
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Aims to perform a useful function at the wrong
layer – not universally useful
LSR, according to IETF specs, expects to
speak IP
No strategy for evolving an existing ATM
network into MPLS network
No Application-level Routing
Intelligence

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Need to distinguish different packets on the
network
QoS requirements statically determined in
MPLS
Can’t make use of application specific
knowledge and requirements
MPLS unfit for VoIP
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MPLS unaware of application requirements
No alternate routing to prevent latency, delay,
packet loss, jitter
Static and domain-specificity hurts in long run
Conclusions
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MPLS static and non-application aware
Suited to core of major networks
Can be deployed only in single-domain
environment where all routers are MPLS
enabled
No end-to-end solution
Guaranteed QoS still elusive
MPLS – No Magic, All Myth!!