QoS in MPLS

Strategy

• To support end-to-end QoS as in IP• MPLS not an end-to-end protocol• Efficient ways of mapping QoS to LSPs• Traffic Engineering key to QoS

QoS Models

• Best effort – Original IP service

• Int-serv.– Fist IP effort to support QoS

• Diff-serv.– Simple, scalable

• Future– Int+ Diff+ TE with e2e SLAs

Integrated Services and RSVP

• Service Classes– Guaranteed service– Controlled load

• MPLS support of RSVP– New object (label object) carried inside RSVP RESV

message– Down-stream label allocation– Once the label binding is over, only the edge router

concerned with which packets belong to the reserved flow

– Can aggregate multiple micro-flows to realize pipes between sites

• New RSVP object carried in the PATH message (LABEL REQUEST)

RSVP Scalability

• Micro-flow reservations scale badly (Not RSVP by itself)

• Aggregation will help reduction of complexity• RSVP Refresh reduction

– RSVP a soft state protocol and hence need refresh– Unreliable and hence need high frequency refresh– Solutions

• Reliable delivery through ACKS – reduced refresh rate once the ACK received

• Summary refresh – send the IDs instead of the whole message; can combine multiple message IDs

Differential Services

• Need to map DSCP to labels– How to set the right value?– Who sets the DSCP value?– What does a router do when a packet with a DSCP value arrives?

• DSCP defines PHB (Per Hop Behavior)– Default – equivalent to best effort as in IP– Expedited Forwarding (EF)

• Should be forwarded with minimal delay• All the packets with EF marking put in a dedicated EF queue• Arrival rate less than the service rate

– Assured Forwarding• Defined in the form of AFxy – x defines the class and y specifies the drop

preference• Example AF11, AF12, AF13 …

• Who sets the values– Based on the application, hosts do it– Router sets it based on locally configured policies – arrival interface, BW

etc.

MPLS Support for DS

• Map the DSCP to label– Map into the 3-bit EXP field (E-LSP)

• Limits the PHBs to 8 (as opposed to 64 possibilities)

• Requires Shim-label support• No additional signaling required

– What if more than 8 PHBs• Use explicit LSP (hence label distribution)to

represent PHBs (L-LSP)

E-LSP vs. L-LSP

R1 R2 R3

R1 R2 R3

AF1y packets

Default packets

L-LSP for AF1y

L-LSP for Default

E-LSP vs. L-LSP (Cont’d)

– E-LSP• Minimal label usage• Conforms to classical DS model

– L-LSP• Arbitrarily large no. of PHBs• Possibility engineer different paths for various

PHBs

– Combinations are also possible

Explicit Congestion Notification (ECN)

• Congestion control vs. avoidance– Drop the packet vs. CE (Congestion experienced) bit

set

• Accommodation nodes with varying capabilities– In IP use the two bits left in the TOS field

• ECT – ECN capable transport• CE

– How to do it in MPLS• May have maximum 1-bit available• Code the possible three states into two states and do

the corresponding mapping

CISCO QoS Framework

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VPNsVPNsMultimediaVideo Conference,

Collaborative Computing

MultimediaVideo Conference,

Collaborative Computing

Mission Critical Services

Mission Critical ServicesVoIPVoIP

HybridHybridMPLSMPLSDiffServDiffServIntServIntServ

Signaling Techniques (RSVP, DSCP*, ATM (UNI/NNI))Signaling Techniques (RSVP, DSCP*, ATM (UNI/NNI))

Link Efficiency Mechanisms (Compression, Fragmentation)Link Efficiency Mechanisms (Compression, Fragmentation)

Congestion Avoidance Techniques (WRED)Congestion Avoidance Techniques (WRED)

Congestion Management Techniques (WFQ, CBWFQ, LLQ)Congestion Management Techniques (WFQ, CBWFQ, LLQ)

Classification & Marking Techniques (DSCP, MPLS EXP, NBAR, etc.)Classification & Marking Techniques (DSCP, MPLS EXP, NBAR, etc.)

FrameRelay

FrameRelay

PPPHDLC

PPPHDLC SDLC

SDLCATM, POSATM, POS FE,Gig.E

10GE

FE,Gig.E 10GE

WirelessFixed,Mobile

WirelessFixed,Mobile

BroadBandCable,xDSL

BroadBandCable,xDSL

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Traffic Conditioners (Policing, Shaping)Traffic Conditioners (Policing, Shaping)