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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. Integrated Services (IntServ) • Developed by IETF in early 90’s • The 1st significant attempt at QoS • Actually, a collection of services • Developed, in part, from work performed on MBONE

  10. Resource Reservation Protocol • RSVP • Reserves the required amount of resources from each router in path • Periodically renews reservations

  11. RSVP Process • Sender must describe the needs of the application • Defined in characteristics of the flow • Sources send a special PATH message to the destination • Each RSVP enabled router establishes a “path state” for the data flow that includes the next upstream (closer to the source) router address • The Sender Traffic Specification (TSpec) • After the path has been set the receiver sends a RESV message back up the path containing • TSpec • The reservation specification (RSpec) • The filter specification • Src/dest port

  12. RSVP Process • Reservations are “soft” in the network devices memory • The source must periodically renew the reservation • A RESV message is used to tear down the reservation

  13. RSVP Process • Each router along the path authenticates the request and either accepts or rejects the reservation • Rejections are sent to the source immediately • Only the initial router will send an acceptance to the source • Data can now be forwarded within the flow

  14. RSVP Process

  15. IntServ • Each network device must: • Support IntServ • Agree upon RSVP operations • Access Control • Hold resources for reserved flow

  16. IntServ Limitations • All devices must support RSVP • Reservations can cross non-RSVP enabled routers, but the flow reverts to best available for this portion of the trip • Overhead intensive • Designed for long-lasting flows • Limited Scalability • All packets within flow must follow the same path • Lack of direct support from routing protocols • Resource intensive on backbone routers

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