RFC 1821 (rfc1821) - Page 3 of 24

Integration of Real-time Services in an IP-ATM Network Architecture

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