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

Diffserv Architecture Two types of components:  edge routers  classification, marking, and shaping  core routers  forwarding according to classification and marking

Classification, Marking, and Shaping  packet mark in Differentiated Services (DS) field in IP pkt (supersedes type of service field)  classifier and marker DSCPCU 6 bits classifier marker shaper/ dropper forward drop profile meter packets

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 priority WFQ WFQ  assured forwarding

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.

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:

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