Nortel ISDN Signaling Link, Описание, установка и эксплуатация

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Page 126 of 378 ITG Engineering Guidelines
553-3001-202 Standard 1.00 April 2000
Implement QoS in IP networks
Today’s corporate intranets developed because of the need to support data
services, services which for the most part a “best effort” IP delivery
mechanism suffices. Standard intranets are designed to support a set of
Quality of Service (QoS) objectives dictated by these data services.
When an intranet takes on a real-time service, the users of that service will
impose additional QoS objectives in the intranet; some of these targets may
be less stringent compared with those imposed by current services, while
other targets would be more stringent. For intranets not exposed to real-time
services in the past but now need to deliver ITG traffic, it is likely that the
QoS objectives pertaining to delay will impose an additional design
constraint on the intranet.
One approach is to simply subject all intranet traffic to additional QoS
constraints, and design the network to the strictest QoS objectives, essentially
a “best-of-breed” solution. This for example would improve the quality of
data services, even though most applications may not perceive a reduction of
say 50ms in delay. Improving the network results in one that would be
adequately engineered for voice, but over-engineered for data services.
Another approach is to consider using QoS mechanisms in the intranet, the
goal of which is to provide a more cost-effective solution to engineering the
intranet for non-homogenous traffic types. Unfortunately IP QoS
mechanisms are still relatively recent technology, hardly implemented on
intranets, and difficult to predict the consequences.
This section outlines what QoS mechanisms can work in conjunction with the
ITG node, and with what new intranet-wide consequences if implemented.
Traffic mix
Before implementing QoS mechanisms in the network, the technician needs
to assess the traffic mix of the network. QoS mechanisms depend on the
process and ability to distinguish traffic (by class) so as to provide
differentiated services.
If an intranet is designed solely to deliver ITG traffic, and all traffic flows are
equal priority, then there is no need to consider QoS mechanisms. This
network would only have one class of traffic.