In this chapter, we introduced a lot of QoS mechanisms of various natures and
explained how they can be used effectively to plan an overall QoS strategy for
your AVVID environment. It is apparent that there is no single mechanism that is
a cure-all for every situation. On the contrary, the power of these mechanisms lies
in their capacity to work together. Each of the mechanisms has its own particular
place in the network and its own particular function. Classification, simply put, can
help to divide your traffic into classes of service, marking them so that other
mechanisms can deliver differentiated QoS.With Congestion Management mechanisms,
you can determine which packets get dropped and which ones get priority
through the network. Congestion Avoidance works to prevent congestion by notifying
senders to slow down when the network is busy. Policing and Shaping techniques
regulate traffic flow according to set parameters, dropping traffic that does
not conform, to avoid congestion situations downstream. Signaling can be used by
clients to request end-to-end QoS across a network. Finally, Link Efficiency mechanisms
can make the most efficient use of available bandwidth by using compression
techniques and by binding small links into one logical pipe.The following
list arranges the mechanisms discussed in this chapter by type and usage:
Classification/Marking Used primarily at the edge of the network
(ACLs, IP precedence)
Congestion Management Used on serial interfaces (PQ, CQ,WFQ,
CBWFQ, LLQ)
Congestion Avoidance Used on Frame Relay interfaces and aggregating
interfaces (RED,WRED, BECN, Foresight)
Policing and Shaping Used on data-rate mismatched interfaces (GTS,
FRTS, CAR)
Signaling Used end-to-end between clients and on intermediate nodes
(RSVP)
Link Efficiency Used on low-speed and multilink interfaces (CRTP,
MLP, LFI, FRF.12)
To help consolidate the information presented in this chapter, Figure 8.9
shows a small network indicating where each of these mechanisms would be
applicable.
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