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QoS in MPLS

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

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QoS in MPLS

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  1. QoS in MPLS CSE 8344

  2. 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 CSE 8344

  3. 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 CSE 8344

  4. 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) CSE 8344

  5. 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 CSE 8344

  6. 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. CSE 8344

  7. 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) CSE 8344

  8. E-LSP vs. L-LSP R2 R3 R1 L-LSP for AF1y L-LSP for Default AF1y packets R1 R2 R3 Default packets CSE 8344

  9. 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 CSE 8344

  10. 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 CSE 8344

  11. VoIP Mission Critical Services Multimedia Video Conference, Collaborative Computing VPNs IntServ DiffServ MPLS Hybrid Frame Relay PPP HDLC SDLC ATM, POS FE,Gig.E 10GE Wireless Fixed,Mobile BroadBand Cable,xDSL CISCO QoS Framework POLICY-BASED NETWORKING PROVISIONING & MONITORING Signaling Techniques (RSVP, DSCP*, ATM (UNI/NNI)) Classification & Marking Techniques (DSCP, MPLS EXP, NBAR, etc.) Congestion Avoidance Techniques (WRED) Traffic Conditioners (Policing, Shaping) Congestion Management Techniques (WFQ, CBWFQ, LLQ) Link Efficiency Mechanisms (Compression, Fragmentation) CSE 8344

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