Wireless Ad Hoc and Sensor Networks

Background on Networking 5loss rate that must closely approximate the basic packet error rate of thetransmission medium. CLS traffic is also characterized by (optional) peakrate, token bucket parameters, and maximum packet size. The CLS doesnot accept or make use of specific target values for control parameterssuch as delay or loss. It uses loose admission control and simple queuemechanisms, and is essentially for adaptive real-time communications.Thus, it does not provide a worst-case delay bound like the GS.Intserv requires packet scheduling and buffer management on a perflow basis. As the number of flows and line rate increase, it becomes verydifficult and costly for the routers to provide Intserv. A solution calledDiffserv can provide QoS control on a service class basis. It is more feasibleand cost-effective than the Intserv.1.1.2 Differentiated Services (Diffserv)Service differentiation is desired to accommodate heterogeneous applicationrequirements and user expectations, and to permit differentiatedpricing of Internet services. DS, or Diffserv (Stallings 2002), are intendedto provide scalable service discrimination in the Internet without the needfor per flow state and signaling at every hop, as with the Intserv. The DSapproach to providing QoS in networks employs a small, well-defined setof building blocks from which a variety of services may be built. Theservices may be either end-to-end or intradomain. A wide range of servicescan be provided by a combination of the following:• Setting bits in the type of service (ToS) byte at network edges andadministrative boundaries• Using those bits to determine how packets are treated by therouters inside the network• Conditioning the marked packets at network boundaries in accordancewith the requirements of each serviceAccording to this model, network traffic is classified and conditionedat the entry to a network and assigned to different behavior aggregates.Each such aggregate is assigned a single DS codepoint (i.e., one of themarkups possible with the DS bits). Different DS codepoints signify thatthe packet should be handled differently by the interior routers. Eachdifferent type of processing that can be provided to the packets is calleda different per-hop behavior (PHB). In the core of the network, packetsare forwarded according to the PHBs associated with the codepoints. ThePHB to be applied is indicated by a Diffserv codepoint (DSCP) in the IPheader of each packet. The DSCP markings are applied either by a trustedcustomer or by the boundary routers on entry to the DS network.