1. QoS in MPLS
SMU
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
SMU
CSE 8344

3. QoS Models Best effort Int-serv. Diff-serv. Future Original IP service
Fist IP effort to support QoS
Diff-serv.
Simple, scalable
Future
Int+ Diff+ TE with e2e SLAs
SMU
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)
SMU
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
SMU
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.
SMU
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)
SMU
CSE 8344

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

9. E-LSP vs. L-LSP (Cont’d)
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
SMU
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
SMU
CSE 8344

11. POLICY-BASED NETWORKING
CISCO QoS Framework
POLICY-BASED NETWORKING
VPNs
Multimedia
Video Conference,
Collaborative Computing
Mission Critical
Services
VoIP
PROVISIONING & MONITORING
Hybrid
MPLS
DiffServ
IntServ
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)
Frame
Relay
PPP
HDLC
SDLC
ATM, POS
FE,Gig.E
10GE
Wireless
Fixed,Mobile
BroadBand
Cable,xDSL
SMU
CSE 8344