Differentiated Services or DiffServ

5.1 QoS Architectures

IETF has proposed two QoS architectures:

  • Integrated Services (IntServ):
  • Differentiated Services (DiffServ): DiffServ network

IntServ reserves resources based on per application flow, using RSVP (discussed in previous chapter).

IntServ can provide guaranteed end-to-end QoS but is only suitable for small/medium sized networks since the amount of state information to be stored and processed for each application flow would become unwieldy for large/backbone networks. Hence, a more scalable option was proposed, namely DiffServ.


5.2 Ensuring QoS in DiffServ

While discussing Diffserv a lot of acronyms are extensively used, but here are the three most important ones necessary [7]:

Behavior Aggregate (BA): a collection of packets with the same DS codepoint crossing a link in a particular direction.

DS codepoint (DSCP): a specific value of the DSCP portion of the DS field, used to select a PHB. The six most significant digits of the Type of Service (ToS) field in IP header are considered as DSCP; the last two digits are currently unused.

Per Hop Behavior (PHB): the externally observable forwarding behavior applied at a DS-compliant node to a DS behavior aggregate.

Diffserv provides QoS assurances to aggregate flows by employing traffic classification and conditioning at the edge and PHB inside the DS-domain.