TCP/IP Tutorial and Technical Overview - IBM Redbooks

For example, a flow might consist of one video stream between a given host pair.
To establish the video connection in both directions, two flows are necessary.
Each application that initiates data flows can specify which QoSs are required for
this flow. If the videoconferencing tool needs a minimum bandwidth of 128 kbps
and a minimum packet delay of 100 ms to assure a continuous video display,
such a QoS can be reserved for this connection.
Differentiated Services
Differentiated Services mechanisms do not use per-flow signaling, and as a
result, do not consume per-flow state within the routing infrastructure. Different
service levels can be allocated to different groups of users, which means that all
traffic is distributed into groups or classes with different QoS parameters. This
reduces the amount of maintenance required in comparison to Integrated
Services.
8.2 Integrated Services
The Integrated Services (IS) model was defined by an IETF working group to be
the keystone of the planned IS Internet. This Internet architecture model includes
the currently used best-effort service and the new real-time service that provides
functions to reserve bandwidth on the Internet and internetworks. IS was
developed to optimize network and resource utilization for new applications, such
as real-time multimedia, which requires QoS guarantees. Because of routing
delays and congestion losses, real-time applications do not work very well on the
current best-effort Internet. Video conferencing, video broadcast, and audio
conferencing software need guaranteed bandwidth to provide video and audio of
acceptable quality. Integrated Services makes it possible to divide the Internet
traffic into the standard best-effort traffic for traditional uses and application data
flows with guaranteed QoS.
To support the Integrated Services model, an Internet router must be able to
provide an appropriate QoS for each flow, in accordance with the service model.
The router function that provides different qualities of service is called traffic
control. It consists of the following components:
Packet scheduler The packet scheduler manages the forwarding of different
packet streams in hosts and routers, based on their
service class, using queue management and various
scheduling algorithms. The packet scheduler must ensure
that the packet delivery corresponds to the QoS
parameter for each flow. A scheduler can also police or
shape the traffic to conform to a certain level of service.
The packet scheduler must be implemented at the point
Chapter 8. Quality of service 289