1. © 2006 Cisco Systems, Inc. All rights reserved. 3.3: Selecting an Appropriate QoS Policy Model

2. © 2006 Cisco Systems, Inc. All rights reserved. Objectives  Describe 3 QoS models: best effort, IntServ and Diffserv.  Identify the strengths and weaknesses of each of the 3 QoS models.  Describe the purpose and functionality of RSVP.

3. © 2006 Cisco Systems, Inc. All rights reserved. Three QoS Models ModelCharacteristics Best effortNo QoS is applied to packets. If it is not important when or how packets arrive, the best- effort model is appropriate. Integrated Services (IntServ) Applications signal to the network that the applications require certain QoS parameters. Differentiated Services (DiffServ) The network recognizes classes that require QoS.

4. © 2006 Cisco Systems, Inc. All rights reserved. Best-Effort Model  Internet was initially based on a best-effort packet delivery service.  Best-effort is the default mode for all traffic.  There is no differentiation among types of traffic.  Best-effort model is similar to using standard mail— “The mail will arrive when the mail arrives.”  Benefits: Highly scalable No special mechanisms required  Drawbacks: No service guarantees No service differentiation

5. © 2006 Cisco Systems, Inc. All rights reserved. Integrated Services (IntServ) Model Operation  Ensures guaranteed delivery and predictable behavior of the network for applications.  Provides multiple service levels.  RSVP is a signaling protocol to reserve resources for specified QoS parameters.  The requested QoS parameters are then linked to a packet stream.  Streams are not established if the required QoS parameters cannot be met.  Intelligent queuing mechanisms needed to provide resource reservation in terms of: Guaranteed rate Controlled load (low delay, high throughput)

6. © 2006 Cisco Systems, Inc. All rights reserved. IntServ Functions Flow IdentificationPacket Scheduler Data Plane Routing Selection Admission Control Reservation Setup Control Plane Reservation Table

7. © 2006 Cisco Systems, Inc. All rights reserved. Benefits and Drawbacks of the IntServ Model  Benefits: Explicit resource admission control (end to end) Per-request policy admission control (authorization object, policy object) Signaling of dynamic port numbers (for example, H.323)  Drawbacks: Continuous signaling because of stateful architecture Flow-based approach not scalable to large implementations, such as the public Internet

8. © 2006 Cisco Systems, Inc. All rights reserved. Resource Reservation Protocol (RSVP)  Is carried in IP—protocol ID 46  Can use both TCP and UDP port 3455  Is a signaling protocol and works with existing routing protocols  Requests QoS parameters from all devices between the source and destination Sending Host RSVP Receivers RSVP Tunnel  Provides divergent performance requirements for multimedia applications: Rate-sensitive traffic Delay-sensitive traffic

9. © 2006 Cisco Systems, Inc. All rights reserved. RSVP Daemon Policy Control Admission Control Packet Classifier Packet Scheduler Routing RSVP Daemon Reservation Data

10. © 2006 Cisco Systems, Inc. All rights reserved. Reservation Merging  R1, R2 and R3 all request the same reservation.  The R2 and R3 request merges at R4.  The R1 request merges with the combined R2 and R3 request at R5.  RSVP reservation merging provides scalability. R5 R4 R3 R5 R4 R1 R2 Sender

11. © 2006 Cisco Systems, Inc. All rights reserved. RSVP in Action  RSVP sets up a path through the network with the requested QoS.  RSVP is used for CAC in Cisco Unified CallManager 5.0.

12. © 2006 Cisco Systems, Inc. All rights reserved. The Differentiated Services Model  Overcomes many of the limitations best-effort and IntServ models  Uses the soft QoS provisioned-QoS model rather than the hard QoS signaled-QoS model  Classifies flows into aggregates (classes) and provides appropriate QoS for the classes  Minimizes signaling and state maintenance requirements on each network node  Manages QoS characteristics on the basis of per-hop behavior (PHB)  You choose the level of service for each traffic class Edge Interior Edge DiffServ Domain End Station

13. © 2006 Cisco Systems, Inc. All rights reserved. Self Check 1.Which of the QoS models is more scalable, yet still provides QoS for sensitive traffic? 2.Which QoS model relies on RSVP? 3.What are some drawbacks of using IntServ for QoS? 4.What is admission control? 5.What are the drawbacks of using Diffserv?

14. © 2006 Cisco Systems, Inc. All rights reserved. Summary  Best effort QoS is appropriate where sensitive traffic does not have to be services. When sensitive traffic must be services, IntServ or Diffserv should be used to provide QoS.  IntServ uses RSVP to guarantee end to end services for a traffic flow. RSVP has significant signaling overhead and is not highly scalable.  Diffserv uses classes to identify traffic and then provides QoS to those classes. Diffserv is highly scalable, but does not provide a service guarantee.