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DiffServ uses the scheduling at both edge and core of the network
4) Queue Management: Queue control can accurately con-trol packets (including
packet discarding) during congestion. As the Queue Control uses a packet priority
discarding mech-anism, it can differentiate traffic and provide different loss and delay
characteristics to the packets belonging to different service classes of the same queue. The
common queue control systems include the Random Early Detection (RED).When the
queue length reaches the preset threshold, the RED
randomly discards packets and this
discard rate is decided by the function of queue length. Packets are discarded in
proportion to the flow before the tail packet discarding occurs due to queue overflow.
E. Basic Network QoS Technologies
This section explains basic QoS technologies that are avail-able which are IntServ (RSVP),
DiffServ,MPLS.
1) IntServ Networks: IntServ is the architecture that re-serves the flow all along the
network end-to-end as requested by the application or user and thus, provides guaranteed
QoS. RSVP is the signalling protocol that requests bandwidth and other resources for the
IntServ architecture. Intserv defines 2 service models: Guaranteed Service
andControlled load. Guaranteed Service is for applications requiring strict QoS and
provides the mathematical upper limit on the queuing delay. Control load controls load
using multiplex statistics and for applications with higher flexibility that guaranteed
service. [Wan] gives a good overview on Intserv and RSVP. More details on IntServ
and RSVP can be found out from [RCS], [Bea], [Wrob], [Wroa] and [SPG].
2) DiffServ Networks: There is a difficulty in implementing and deploying Integrated
Services and RSVP and there are critical issues like scalablity in IntServ. And to overcome
these issues and to assure simplicity, Differentiated Services (DS) was introduced.
Customers can mark DS fields of individual packets to indicate the desired
service or have them marked by the leaf router based on MF classification.At the ingress
of the ISP networks, packets are classified, policed and bpossibly shaped. The
classification, policing and shaping rules used at the ingress routers are derived from
the SLAs. The amount of buffering space needed for these operations is also derived
from the SLAs. When a packet enters one domain from another domain, its DS field
may be re-marked, as determined by the SLA between the two domains.
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