1

Advanced QOS for MPLS Based
Metro Networks
MPLS Japan 2005
David Zelig
Corrigent Systems
davidz@corrigent.com

2Content

MPLS QOS today

Metro QOS req.

QOS building blocks



Fitting MPLS for the metro req.

Interoperability between the approaches

3MPLS QOS Today

MPLS-TE is widely used in core networks• Rough congestion hot-spot avoidance• VoIP bypass• Tunnel is a virtual pipe

QOS based on DiffServ model• Connectivity and QOS handling are treated as independent entities:• Queue configuration seperated from tunnel set-up• Complicated and manual queue tuning



E-LSP is widely used for priority queuing between applications

4

The E-LSP model

EXP to queuemapping

MPLSNetwork

FEC to LSP mapping
DSCP to EXP mapping
Single BW profile

5

Metro QOS Requirements
High number of individually guaranteed services• Should be operationally manageable

Optimize network cost by migrating to over-subscribed networks insteadof over-engineered networks

PIR is important• The access market principle• Low pricing of PIR services, but user experience should be good

Guaranteed services under network failure scenarios

6The QOS TriangleCACMarkingQueuing

7

CAC – Call Admission Control

CAC avoids creating services that would negatively impact existing
services QoS• Local CAC verifies availability of resources in each node along thepathShould be on a per COS basis

In MPLS, CAC requests are propagated along the path by RSVP-TE,
each node verifies its local resources

Current MPLS implementations have various levels of COS awarenesslevels, from one level to multiple levels.

8QueuingEnforce the relative priority of traffic on a per packet level

Define the scheduling scheme between various COS

Existing tools typically ensure strict priority and simple weighting
between the queues, combined with WRED (Weighted Random EarlyDetection)

AF1xAF2xBE

SchedulingEFInterface

9Marking

Enforce the CIR to EIR partitioning on a per packet basis



Since CIR is always taken into considerations in queue configuration,
wrong marking can lead to violation of CIR for other servicesMarking is the key to enable sharing of a queue between different users

RateM

EIRThreshold

EIRMQueueCIRM

DropOver PIRMarkPassCAC

Marking

CIR
Threshold

Queuing

10

Fitting MPLS for the metro requirements
MPLS has the right building blocks to meet the metro networks
requirements

However, the tools provided by MPLS should be better used in order toeffectively built an economic and operational QOS scheme

CAC

Marking

CAC

QueuingMarkingQueuing

11

The Importance of PIRThe residential access market relies today exclusively on “BE like”
serviceHowever some guarantee is needed – user expects an “always on”
service with reasonable throughput at any timeThis traffic is combined with true guaranteed traffic on the same network• Which has also it’s own EIR component in addition to CIRThe evolution toward statistical multiplexing metro networks

12The Importance of PIR
Key components to enable this feature:• Always reserve network bandwidth for BE – CAC guarantee forPIR share• Fairness between BE users• Queuing and RPR• PIR signaling to gain fairness based on PIR ratio

13Queuing scheme for PIR guarantee and fairness

EFEF

SP1
CIR
RR

AF1
CIR

AF2

SP2EIREIRBEW2WFQ

W1W3
W3 = EIR(BE)/[EIR(BE)+EIR(AF1)+EIR(AF2)]

SP3Interface

14

RPR - Fairness at the network level

RPR fairness enables sharing of ring excess bandwidth fairly by allstations

Each station weight is proportional to it’s services’ EIR

Ring-wide statistical multiplexing gains, compared to other approaches
where it occurs locallyThis in addition to other RPR properties• Sub 50-msec protection at the MAC layer• Spatial reuse of BW• Native multicast support

15

Example of RPR fairness
Assume 3 stations competing on 10Mbps Excess traffic

10M available• S1 services EIR = 5M, sending 6M• S2 services EIR = 4M, sending 5M

S1S2• S3 services EIR = 1M, sending 2M

10Mbpsavailable
capacity

Unfairness

Equal Fairness

Weighted Fairness

S3

16

Operational ScalabilityLarge number of circuits dictates automatic queue
configurations

Queuing cannot be a separate configuration
domain, and should be tightly related to the MPLS
connections that are established

CAC

MPLS already carries CIR/PIR•

Only CIR can be actually configured inexisting implementations•

Use both parameters to adjust the queues
parameters on the fly•Automatically adjust at failures that affect theconnection route

MarkingQueuing17CAC Enhancements

PIR is part of the queue configurations



If the PIR portion has to be guaranteed, it should be taken into
consideration as part of the CAC

EF limit

EF+ CIR
EF+ CIR+limit
EIR/factor
limitInterfacerate

18

The need for L-LSP

L-LSP has a single COS (Ordered Aggregate) per tunnel

It is the key to enable the automatic per connection CAC and queues
settingHowever, L-LSP is not widely supported in packet based platformThe solution:• Use a single tunnel per COS• Each COS will be assigned the applicable EXP Bits

19

L-LSP and the co-existence with E-LSP core

EXP to queue
mapping
LSP->EXP mapping
MPLS
NetworkFEC+DSCP to LSP mapping
BW profile per (FEC+DSCP)

20

Summary

The metro QOS scheme should negotiate between two engineering
tradeoffs: scalability and capacity management

The solution:• Bind all QOS building blocks together• Automate the relationship between the blocks

Co-existence with MPLS core DiffServ networks is possible

21Thank YouQuestions?