TCP/IP Tutorial and Technical Overview - IBM Redbooks

Although RSVP can be used to request resources from the network, Integrated
Services defines the needed service types, quantifying resource requirements
and determining the availability of the requested resource.
There are some factors that have prevented the deployment of RSVP and, thus,
Integrated Services in the Internet. These include:
► Only a small number of hosts currently generate RSVP signalling. Although
the number is expected to grow in the near future, many applications cannot
generate RSVP signalling.
► Integrated Services is based on flow-state and flow-processing. If
flow-processing rises dramatically, it might become a scalabiltiy concern for
large networks.
► The necessary policy control mechanisms, such as access control
authentication and accounting, have only recently become available.
The requirements of the market will determine if Integrated Services with RSVP
will inspire service providers to use these protocols. But this requires that
network devices (for example, routers) need the required software support.
Another aspect also needs to be considered. Support of Integrated Services
running over Differentiated Services networks is a possibility. This solution
provides:
► End-to-end QoS for applications, such as IP telephony and video on demand.
► Intserv enables hosts to request per-flow and quantify able resources along
the end-to-end path, including feedback about admission to the resources.
► Diffserv eliminates the need for per-flow state and per-flow processing, and
therefore enables the scalability across large networks.
8.3 Differentiated Services
The Differentiated Services (DS) concept is currently under development at the
IETF DS working group. The DS specifications are defined in some IETF Internet
drafts. There is no RFC available yet. This section gives an overview of the
basics and ideas to provide service differentiation in the Internet. Because the
concept is still under development, some of the specifications mentioned in this
book might be changed in the final definition of differentiated services.
The goal of DS development is to provide differentiated classes of service for
Internet traffic to support various types of applications and meet specific
business requirements. DS offers predictable performance (delay, throughput,
packet loss, and so on) for a given load at a given time. The difference between
Chapter 8. Quality of service 309