Fleksibilni Internet servisi na bazi kontrole kašnjenja i

all incoming traffic. User is not allowed to exceed the peak rate specified by the SLA.
Hence, premium service provided by EF is low-delay, low-jitter, and nearly constant bit
rate service suitable for Internet telephony and video conferencing.
The Assured Forwarding (AF) defines four forwarding classes with three drop
priorities within each class. Each combination of AF service class and drop priority is
associated with distinct DSCP code. In every DiffServ node, certain amount of buffer
space and bandwidth is allocated to each class. In case of congestion, the drop priority of
a packet determines its relative importance within its class. In order to protect packets
with lower drop priority from being discarded, a DiffServ router preferentially discards
packets with higher drop priorities. Hence, in the case of network congestion, the assured
traffic with lower priority may still experience packet losses and high delay as in a best-
effort network.
Even though DiffServ model eliminates certain drawbacks of IntServ, such as the
scalability problem, it has not been widely accepted and deployed. Since DiffServ
provides per-hop QoS differentiation on a class level, it is difficult to ensure end-to-end
performance defined by a SLA contract. From a commercial viewpoint, this is a major
disadvantage because it implies that it is impossible to charge the service defined by the
SLA. Furthermore, DiffServ model cannot be deployed incrementally because all
network nodes are required to support DiffServ mechanisms in order to provide specified
QoS parameters. In 2001, Internet2 QoS Working Group discontinued deployment and
testing of the premium service because of the lack of demand and support from major
router vendors [11].
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