What Kind of QoS Can I Request with RSVP?
The types of QoS that can be reserved by RSVP are consistent with the Internet
Integrated Services Model.These types are controlled-load and guaranteed-rate.
According to the Intserv definition, controlled-load gives applications service as if
they were traversing an unloaded network. Applications requesting controlledload
can expect low latency and a low number of packet drops.These applications
are usually considered tolerant real-time applications. An example could be an
adaptive real-time application like the playback of a recorded conference call. On
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232 Chapter 8 • Advanced QoS for AVVID Environments
Cisco routers, controlled-load services are implemented primarily with weighted
random early detection.We will discuss WRED later in this chapter.
RSVP can also request guaranteed-rate services. According to the Intserv definition,
guaranteed-rate delivers assured bandwidth with consistent delay.
Applications that require this service to function well are usually considered intolerant
real-time applications. An example would be delay-sensitive applications like
VoIP. On Cisco routers, guaranteed-rate services are implemented primarily with
weighted fair queuing.
NOTE
Although WFQ can provide guaranteed-rate services to applications, it
alone may not be sufficient to assure low latency to delay-sensitive applications
such as VoIP during periods of congestion. IOS versions 12.1(3)T
and later provide support for LLQ to RSVP.