Presentation 10 – Quality of Service (QoS)

1. Presentation 10 – Quality of Service (QoS)

2. Objectives At the end of this presentation, you will be able to:

3. List four different definitions of the term Quality of Service (QoS) • List three IETF initiatives related to QoS. • Explain the basic idea behind Integrated Services (IntServ). • Explain the basic idea behind Differentiated Services (DiffServ). • Explain the basic idea behind Multi-Protocol Label Switching (MPLS).

4. General QoS Definitions • Networking – Refers to the probability of the network meeting specified conditions. • Networking – Refers to how well a logical or physical connection is performing. • Telephony – Indicates how well a telephone connection is performing. • Telephony – Refers to the lack of noise, extraneous tones, echoes, etc. on a given circuit. Includes factors like sufficient loudness, appropriate clarity, etc.

5. QoS as Related to VoIP • The capability for preferential handling of different types of packets. • Measurable, objective characteristics of network performance. • Did the experience meet your expectations?

6. Ways to Insure QoS • Over-engineer – Provide enough bandwidth, processing power, etc. to insure that your packets get through even at the busiest of times. • Make reservations ahead of time • Receive preferential treatment

7. IETF Initiatives • Differentiated Services (DiffServ) • Integrated Services (IntServ) • Multiprotocol Label Switching (MPLS)

8. Differentiated Services (DiffServ) • Takes the preferential treatment approach to QoS. • It provides a mechanism whereby different types of network traffic can be divided into classes of service (CoS).

9. Class of Service (CoS) • Indicates the degree of preferential treatment or priority given to a packet. • Classes: • Expedited Forwarding (EF)– Highest Priority • Assured Forwarding (AF) • Class 1 • Class 2 • Class 3 • Class 4

10. EF AF-1 AF-2 AF-3 AF-4

11. EF AF-1 AF-2 AF-3 AF-4

12. EF AF-1 AF-2 AF-3 AF-4

13. Nature of the Priority • Not absolute – EF packets are not automatically sent to the head of the line. • Probabilistic – EF packets are given a higher probability of being sent to the head of the line.

14. EF AF-1 AF-2 AF-3 AF-4

15. Differentiated Services Code Point (DSCP) • Included in the Header of IP packets. • A 6-bit code that can be used to assign a class of service (CoS) to a packet. • Replaces the old and rarely used ToS field.

16. DSCP The IP Header IP Header IHF Length Ver ToS TTL Protocol Check Sum Source Address Destination Address

17. Per Hop Behavior (PHB) • A set of behaviors from which an application can select. • The node’s behavior can be customized on the fly to make it more appropriate for a particular class of service. • The node’s behavior can be tailored to increase its probability of providing no worse than a specified delay, a specified level of jitter, a specified bandwidth, etc.

18. DiffServ Review • “Rob Peter to pay Paul” approach. • Different types of packets are given different priorities. • The higher priority packets are given preferential treatment, often at the expense of lower priority packets. • While it can be used for any application, it is particularly valuable with VoIP because of the time-sensitive nature of real-time packets.

19. Integrated Services (IntServ) • A series of protocols developed by IETF to integrate real-time and voice, video into the classical data streams. • QoS Strategy: Find and reserve the required resources needed for a particular level of QoS.

20. Resource Reservation Protocol(RSVP) • Allows an application (say, VoIP) to request minimum specified resources throughout the path that the session will use. • “Hey, I am about to call ______. Can you give me a bandwidth of X-kbps, with a delay no greater than Y-milliseconds, and jitter no worse than Z- milliseconds?”

21. Router Router Router Sender RSVP PATH Recipient RESV

22. The RSVP Compliant Router • Requires an RSVP Daemon. • Admission Control – Does the node have the resources available? • Policy Control – Does the user have permission to make the reservation?

23. Multi-Protocol Label Switching (MPLS) • QoS Strategy: Increase packet forwarding performance and path selection flexibility. • Adds a “label” between the data link-layer and the network layer headers.

24. 20-Byte IP Header IP Data Ethernet/IP Packet 14-Byte Ethernet Header MPLS Label

25. MPLS Network Label Edge Router (LER) Label Switch Routers (LSR)

26. IETF Initiatives • Differentiated Services (DiffServ) • Integrated Services (IntServ) • Multiprotocol Label Switching (MPLS)

27. Differentiated Services (DiffServ) A service architecture that can select network node behavior, appropriate to the class of service, based on the Differentiated Services field in the header of the IP datagram.

28. Integrated Services (IntServ) A service architecture that can find and reserve resources at each network node in its path appropriate to the class of service being transported for as long as needed to complete a session.

29. Multi-Protocol Label Switching (MPLS) A service architecture that makes forwarding decisions based solely on a label that is added between the data-link and network headers.

30. End