MPLS cisco QOS VPN full mpls advanced

Advanced Developments
in MPLS QoS
Bruce Davie


MPLS NW Internal 05/01

© 2001, Cisco Systems, Inc.

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Agenda

• DS-TE
Diffserv-aware traffic engineering &
MPLS Guaranteed Bandwidth services

• “QoS Transparency”

© 2001, Cisco Systems, Inc.
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Diffserv-aware Traffic
Engineering (DS-TE)

2302
Presentation_ID
2000, Cisco Systems,
Inc.Systems, Inc.

MPLS NW Internal ©
05/01
© 2001, Cisco

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Terminology
• DS-TE: Diffserv-aware Traffic Engineering
A set of protocol extensions to existing MPLS TE
purely in the control plane - no new data plane QoS
mechanisms (e.g. no per-label queueing)
does NOT achieve QoS “guarantee” by itself

• Guaranteed Bandwidth Services
End-end (or edge-edge) services
Built using DS-TE and existing MPLS QoS features (MPLS
Diffserv, QPPB,..)

© 2001, Cisco Systems, Inc.
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MPLS Traffic Engineering
Find route & set-up tunnel for 20 Mb/s from POP1 to POP4
Find route & set-up tunnel for 10 Mb/s from POP2 to POP4

WAN area

POP4

POP1
POP

POP2
POP
POP
© 2001, Cisco Systems, Inc.
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Relationship between MPLS TE and
QoS
• MPLS TE designed to improve backbone efficiency
independently of QoS:
MPLS TE compute routes for aggregates across all PHBs
MPLS TE performs admission control using “global” bandwidth pool
unaware of bandwidth allocated to each queue

• MPLS TE and MPLS Diff-Serv:
can run simultaneously & independently
TE distributes aggregate load
Diff-Serv provides QoS differentiation
are unaware of each other (e.g., no per-class admission control in TE)

© 2001, Cisco Systems, Inc.
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Delay/Load Trade-Off

Delay
Good
Best-Effort
Target
Data
Premium
Target
Voice
Target

Utilization
0%

α%

β % 100%

If I can keep EF traffic < α % , I will keep EF delay under M1 ms
If I can keep AF1 traffic < β % , I will keep AF1 delay under M2 ms
© 2001, Cisco Systems, Inc.
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Motivation for DS-aware TE
• Additional constraints to ensure QoS of each
class:
Good EF behavior requires EF load < α % of link
Good AF behavior requires AF load < β % of link

• Cannot be enforced by current aggregate TE

• Requires Diff-Serv-aware TE
Constraint Based Routing per Class with different
bandwidth constraints
Admission Control per Class over different bandwidth
pools (reflecting bandwidth allocated to class queue)
© 2001, Cisco Systems, Inc.
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Bandwidth Pools
Global TE Bandwidth Pool
reflects total link capacity

A per-class pool
reflects queue capacity
A second per-class pool

© 2001, Cisco Systems, Inc.
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When is DS-aware TE needed?
• Not in uniformly over-provisioned networks
Aggregate load is small percentage of link
⇒ EF load will be less than α %;
AF1 load will be less than β %

• In networks where some parts are not
over-provisioned
ensures (through routing and admission control) that per-class

loads targets are met (e.g. EF < α %)
example: Global (transcontinental) ISPs

• Note: does not “create” bandwidth
Use resources on non SPF-path
Reject establishment of excess tunnels
© 2001, Cisco Systems, Inc.
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Diff-Serv aware TE:
protocol Components
• Current IGP (OSPF/ISIS) extensions for TE:
advertise “unreserved TE bandwidth” (at each
preemption level)

• Proposed IGP extensions for DS aware TE:
Class-Type: a group of Diff-Serv classes sharing the
same bandwidth constraint (e.g. AF1x and AF2x)
advertise “unreserved TE bandwidth” (at each
preemption level) for each Class-Type

© 2001, Cisco Systems, Inc.
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Diff-Serv aware TE:
protocol Components (2)
• Current LSP-signalling* extensions for TE:
at LSP establishment signal TE tunnel parameters

(label, explicit route, affinity, preemption,…)

• Proposed LSP-signalling* extensions for DS
aware TE:
also signal the Class-Type
perform Class-Type aware admission control

* RSVP-TE and CRLDP
© 2001, Cisco Systems, Inc.
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Diff-Serv aware TE:
protocol Components
• Current Constraint Based Routing for TE:
compute shortest path over links with
sufficient “unreserved TE bandwidth”

• Proposed Constraint Based Routing for DS
aware TE:
same algorithm but compute path over links
with sufficient “unreserved bandwidth for the
relevant Class-Type”

© 2001, Cisco Systems, Inc.
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DS-TE Standardisation

• Standardization effort initiated in mid-2000
• Internet Drafts:
draft-ietf-tewg-diff-te-reqts-00.txt
draft-ietf-mpls-diff-te-ext-01.txt
draft-ietf-ospf-diff-te-00.txt
draft-ietf-isis-diff-te-00.txt
© 2001, Cisco Systems, Inc.
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Aggregate TE in Best Effort
Network
Find route & set-up tunnel for 20 Mb/s from POP1 to POP4
Find route & set-up tunnel for 10 Mb/s from POP2 to POP4

WAN area

POP4

POP1
POP

POP2
POP
POP
© 2001, Cisco Systems, Inc.
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Aggregate TE in Diff-Serv Net

Find route & set-up tunnel for 20 Mb/s (aggregate) from POP1 to POP4
Find route & set-up tunnel for 10 Mb/s (aggregate) from POP2 to POP4

WAN area

POP4

POP1
POP

POP2
POP
POP

© 2001, Cisco Systems, Inc.
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Per-Class Traffic Engineering
Find route & set-up tunnel for 5 Mb/s of EF from POP1 to POP4
Find route & set-up tunnel for 3 Mb/s of EF from POP2 to POP4

WAN area

POP4

POP1
POP

POP2

Find route & set-up tunnel for 7 Mb/s of BE from POP2 to POP4

POP

Find route & set-up tunnel for 15 Mb/s of BE from POP1 to POP4

POP

© 2001, Cisco Systems, Inc.
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Guaranteed Bandwidth
Services
Applying DS-TE

2302
Presentation_ID
2000, Cisco Systems,
Inc.Systems, Inc.
MPLS NW Internal ©
05/01
© 2001, Cisco

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The Trouble With Diff-serv

• As currently formulated, Diff-serv is strong on

simplicity and weak on guarantees
• “Virtual Wire” using EF is quite firm, but how
much can be deployed?
No topology-aware admission control
mechanism
• Example: How do I reject the “last straw” VOIP
call that will degrade service of calls in progress?
© 2001, Cisco Systems, Inc.
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MPLS Guaranteed Bandwidth
• Combining MPLS Diff-Serv & Diff-Serv-TE to
achieve strict point-to-point QoS guarantees
• A new “sweet-spot” on QoS spectrum
Aggregated State (DS)
Aggregate Admission Control (DSTE)
Aggregate Constraint Based Routing (DSTE)
No state

Best effort

Aggregated
state

Per-flow state
MPLS Diffserv
+ MPLS DS-TE

Diffserv

MPLS
Guaranteed
Bandwidth

RSVP v1/
Intserv

© 2001, Cisco Systems, Inc.
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MPLS Guaranteed Bandwidth
• A Guaranteed Bandwidth “service” is a unidirectional point-to-point BW
guarantee from Site A to Site B
“The Pipe Model”

• “Site” may include a single host, a “pooling point”, etc.

N2 Mb/s
Guarantee
CE
10.2

CE

11.5

N1 Mb/s Guarantee

CE

11.6

CE 10.1

© 2001, Cisco Systems, Inc.
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MPLS Guaranteed Bandwidth:
QoS Recipe
• Each service is delivered using 3 ingredients:
per-service input policing at edge
per-LSP admission control at every hop
→ Aggregated admission control: one LSP may carry
many individual “Guaranteed Bandwidth” services
per-class scheduling (one queue for all traffic of a given
PHB)
→ Aggregated scheduling: a class queue carries many
LSPs.

• Admission control + policing at edge + dedicated
queue → guaranteed BW
© 2001, Cisco Systems, Inc.
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GB Service: Edge Behavior
• Edge Behaviors
determine which packets go onto a tunnel (classification)
perform marking & policing of those packets

forward packets onto tunnels (label imposition)

• Example: to provide guaranteed BW of 5 Mbps to
all packets from site A to site B
identify all packets matching a prefix located at B as they
arrive from A
Apply a 5 Mbps token bucket policer
mark conforming packets to AF11, non-conformers to
AF12, send all down guaranteed LSP
© 2001, Cisco Systems, Inc.
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VoMPLS using Diff-Serv EF
PSTN
Call
Agent
EF/PQ

PSTN

Voice

BE
Data

If EF load obviously very small compared to every link
capacity then just works fine. That’s it!

© 2001, Cisco Systems, Inc.

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DS-TE Applications:
Voice Trunks
PSTN
Call
Agent
EF/PQ

PSTN
Voice

BE
Data

MPLS TE Tunnel for EF (one direction)

© 2001, Cisco Systems, Inc.
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