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L3 QoS Standards

L3 QoS Standards. CIT 443. Differentiated Services. DiffServ IETF Standard RFC 2474 & 2475. DiffServ. Priority is set in DS CodePoint (DSCP) byte of the IP Header IPv4 Type of Service field IPv6 Traffic Class field 8 bits – hence the DSCP byte Two bits are reserved

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L3 QoS Standards

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  1. L3 QoS Standards CIT 443

  2. Differentiated Services • DiffServ • IETF Standard • RFC 2474 & 2475

  3. DiffServ • Priority is set in DS CodePoint (DSCP) byte of the IP Header • IPv4 Type of Service field • IPv6 Traffic Class field • 8 bits – hence the DSCP byte • Two bits are reserved • Six bits (64 values) are used for priority levels • 32 are reserved for testing

  4. DiffServ Image from Cisco Systems Inc: http://www.cisco.com/en/US/technologies/tk543/tk766/technologies_white_paper09186a00800a3e2f.html

  5. DiffServ Image from Cisco Systems Inc: http://www.cisco.com/en/US/technologies/tk543/tk766/technologies_white_paper09186a00800a3e2f.html

  6. DiffServ • Each network device: • Must support DiffServ • Must agree on the treatment for each CodePoint value (policy) • Queues and forwards based on ToS priority

  7. DiffServ • Per hop forwarding policies • Expedited Forwarding (EF) RFC 3246 • Maximum priority • Packets matching the EF CodePoint are immediately forwarded • Egress rate exceeds the ingress rate on these packets • Must be kept to a small fraction of overall traffic • Assured Forwarding (AF) • Four priorities • Gold, Silver, Bronze, Best Available

  8. DiffServ • Limitations • Requires advance provisioning and bandwidth reservation • All network devices must agree on the prioritization scheme • Including the source, destination, and all intermediate networks

  9. For Next Time • Find and document the table of all DiffServ Code Points (DSCP) • Identify which DSCP values would be applicable to the service(s) you are deploying in lab *Be sure to include all necessary references

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