RFC 1821 (rfc1821) - Page 3 of 24
Integration of Real-time Services in an IP-ATM Network Architecture
Alternative Format: Original Text Document
RFC 1821 Real-time Service in IP-ATM Networks August 1995
In the IP-over-ATM environment, as in many others, multicast routing
adds an additional set of challenges. While the major focus of this
paper is quality of service (QoS) issues, it is unwise at best to
ignore multicast when considering these issues, especially since so
many of the applications that motivate the provision of real time QoS
also require efficient multicast support. We will therefore try to
keep considerations of multicast in the foreground in the following
discussion.
One of the primary motivations for this document is a belief by the
authors that ATM should, if possible, be used as more than a leased
line replacement. That is to say, while it is possible for the
Internet to be overlaid on constant bit rate (CBR), permanent virtual
circuits (PVCs), thus reducing IP over ATM to a previously solved
problem, we believe that this is unlikely to be the most efficient
way to use ATM services as they are offered by carriers or as they
appear in LANs. For example, a carrier offering a CBR service must
assume that the peak bit rate can be used continuously with no
degradation in quality and so resources must be allocated to the
connection to provide that service, even if the peak rate is in fact
rarely used. This is likely to make a CBR service more expensive that
a variable bit rate service of the same peak capacity. Another way
to view this is that the new IP service model will allow us to
associate information about the bandwidth requirements of
applications with individual flows; surely it is not wise to discard
this information when we request a service from an ATM subnet.
While we believe that there is a range of capabilities in ATM
networks that can be effectively used by a real-time Internet, we do
not believe that just because ATM has a capability, the Internet must
use it. Thus, our goal in this RFC is to begin to explore how an
Internet with real time service capability might make most effective
use of ATM networks. Since there are a number of problems to be
resolved to achieve this effective use, our major goal at this point
is to describe the scope of the problems that need to be addressed.
2.0 Problem Space Overview
In this section we aim to describe in high level terms the scope of
the problem that will be explored in more detail in later sections.
2.1 Initial Assumptions
We begin by assuming that an Integrated Services Internet, i.e., an
Internet with a range of qualities of service to support both real-
time and non-real-time applications, will eventually happen. A number
of working groups are trying to make this happen, notably
Borden, et al Informational