Any Questions?

1. Any Questions?

2. Chapter 9 Class of Service • Main focus of exam • What IP CoS is and why it is needed • IP differentiated services primer • DiffServ-based CoS deployment and verification • Reference materials if you are interested • RFC 2474, “Definition of the Differentiated Services Field in the IPv4 and IPv6 Headers” • RFC 2597, “Assured Forwarding PHB Group” • RFC 2598, “An Expedited Forwarding PHB” • RFC 2698, “A Two Rate Three Color Marker” Pg 464

3. What is QOS and why do I need it • CoS provides a mechanism by which certain packets are afforded preferred treatment in an effort to provide the associated application with a level of performance required for proper operation • Modern networks need a consistent application of QoS Pg 464

4. Why IP Networks need CoS • IP networks use statistical multiplexing and packet switching • Resources on an as needed basis • Originally best-effort based • Since traffic is “bursty” chances are the network will be free when you need it Pg 465

5. Why IP Networks need CoS • Some degree of buffering (queuing) was needed in cases where network is busy when traffic gets sent • Flow control or discards were used when there was lots of congestion • More buffers just changes from dropped packets to delay and jitter Pg 465

6. Why IP Networks need CoS • Converged Networks (VoIP) have different requirements • Some traffic is much more sensitive to drops and delays • Traditional Circuit Switched networks • provided (once connected) minimal and fixed delays, freedom from congestion, guaranteed bandwidth, in-sequence delivery, and low loss. Pg 465

7. Packet Switching and Bandwidth • Bandwidth can solve some problems • Cheaper solution with less overhead • Bandwidth alone does not provide QoS/CoS Pg 465

8. Circuit Switching Issues • Blocking during congestion • Dedicated resources • Fixed bandwidth allocation • Poor survivability Pg 466

9. Any Questions?

10. Current IP Networks • Not QoS/CoS enabled • Too much overhead • Older routers were faster without QoS • QoS isn’t an issue until usage goes to about 80% • No queue to fill before then, as traffic goes right out the interface • Mission Critical applications need more than just “overbuild” • QoS and Bandwidth give you the quality of Service you need Pg 466

11. CoS Terms and Concepts • Focus on QoS concepts for IP networks • Network QoS parameters • Classification • Packet marking • Forwarding classes, queues, and schedulers • Congestion management • Policing and shaping • Typical CoS processing stages in a Juniper router Pg 468

12. Network QoS parameters • Qos and Cos used interchangeable • QoS for network parameters • CoS for combined effect of QoS on packet stream • To get best results, applications should be QoS aware • Be able to mark traffic and request levels of service Pg 468

13. Network QoS parameters • Bandwidth • Bandwidth is a measure of each link’s information-carrying capacity. It is limited by the lesser of the bandwidth supported by each link crossed between two endpoints. • Delay • Delay is a measure of the time taken to move a packet from one point to another. End-to-end delay is a cumulative function of serialization delays, propagation delays, and any queuing delays (buffering) that the packet may experience. • Delay variation (jitter) • Delay variation, often called jitter, is a measure of the variance in transfer delays between packets that make up a stream. Jitter is significant to real-time applications because the receiver must dimension its jitter buffer based on maximum jitter, which adds delays for all packets and causes eventual loss when jitter values exceed buffer capacity. • Loss • Loss measures the percentage of packets not delivered. Loss can stem from transmission errors or discard stemming from congestion in packet-based networks. • Loss pattern • The loss pattern defines the nature of a loss event as either bursty (short duration) or chronic, which is sometimes called a dribble error. Pg 469

14. Classification • Associating received packets with a forwarding class, which maps to a queue • Critical to CoS deployment • Allows different packets to be treated differently Pg 470

15. Classification • As packets leave, they are put in the correct queue/scheduler profile • Classification can drain router resources Pg 470

16. Classification • Two main kinds of classification • Multifield classification • Multifield classifiers are the most flexible and therefore the most computationally burdensome type of classifier. As the name suggests, a multifield classifier is based on matches against multiple fields with the IP packet, including source and destination addresses, protocol type, ports, and so on. • Behavior aggregate (BA) • A BA classifier uses a fixed field in the packet header to make classification decisions. This is highly efficient because of the fixed position, length, and meaning of the bits used in the BA classification field. Classifications based on IP precedence or Differentiated Services code points (DSCPs) are examples of BA classification. Pg 470

17. Classification Deployment • Multifield classifiers close to the edge • Closest to traffic source • Once classified, traffic is remarked with a BA type • More efficient • Juniper uses firewall filters to do multifield classification and BA classification Pg 470

18. Loss Priority • Multifield classifiers close to the edge • Closest to traffic source • Once classified, traffic is remarked with a BA type • More efficient • Juniper uses firewall filters to do multifield classification and BA classification Pg 471