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Class-based QoS

Class-based QoS. Internet QoS model requires per session state at each router 1000s - 1000000s of flows per session RSVP is complex => reluctance on part of network admins to accept intserv Differentiated services (diffserv) scalable and flexible service differentiation.

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Class-based QoS

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  1. Class-based QoS • Internet QoS model requires per session state at each router • 1000s - 1000000s of flows • per session RSVP is complex => reluctance on part of network admins to accept intserv Differentiated services (diffserv) • scalable and flexible service differentiation

  2. Diffserv Architecture Two types of components: • edge routers • classification, marking, and shaping • core routers • forwarding according to classification and marking

  3. DSCP CU 6 bits Classification, Marking, and Shaping • packet mark inDifferentiated Services (DS) field in IP pkt (supersedes type of service field) • classifier and marker profile meter packets forward shaper/dropper classifier marker drop

  4. Per-Hops Behavior • per-hop behavior results in deifferent service classes receiving different measurable performance • two PHBs • expedited forwarding: departure rate of an aggregate class must exceed a configured rate • policies that can provide this: • priority • WFQ • assured forwarding

  5. Assured Forwarding • four classes of service • ordering among delays between classes at router, i.e., delay of a class 1 packet no greater than for class 2 packet • within each class three “drop preference” categories • ordering among categories, i.e., packet with drop preference 1 is less likely t be dropped than packet with drop preference 2.

  6. Where is Diffserv going? • PHBs are on their way to definition • several marking schemes have been proposed • two color • three color • services combining PHBs and marking schemes yet to be defined • the hottest Internet topic around IETF Diffserv home page: http://www.ietf.org/html.charters/diffserv-charter.html

  7. Quality of Service Guarantees: Summary • various applications need QoS guarantees to be effective • QoS touches almost all layers of network architecture: • API, application • transport (end system policing, smoothing) • network • data link • call admission, blocking • call setup protocol need to actively engage switches • importance of packet-level scheduling • area of active research

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