Fleksibilni Internet servisi na bazi kontrole kašnjenja i

Fig. 1. Traffic control mechanisms employed in a QoS capable router.
Admission control implements a decision algorithm that a router employs to
determine whether an incoming request for service can be accepted without disrupting the
service guarantees to established data flows. Unlike in a best-effort network, where a new
connection request is accepted from any source anytime, a Call Admission Control
(CAC) algorithm is executed in a QoS-enabled network. It decides whether to accept or
reject a new connection. The CAC algorithm estimates whether the available resources
meet the set of QoS parameters requested by the connection [32].
Traffic policing ensures that an accepted connection conforms to the QoS
parameters negotiated during the admission control phase. For each packet entering the
network, the policing mechanism detects whether it conforms to the “QoS contract”. If
conforming, the packet is admitted to the router. Otherwise, the policing mechanism can
either drop the packet or decide to accept it as a lower priority packet that will be dropped
if congestion occurs. Policing is necessary only in access routers. There is no need to
police the traffic in core routers [33].
Traffic shaping is used to smooth out packets bursts in cases when incoming
traffic does not conform to negotiated “QoS contract”. Unlike policing mechanisms,
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