Support QoS in IP over ATM
Introduction
The asynchronous transfer mode, commonly given the acronym ATM, is the most widely studied and implemented form of cell networking [1]. ATM began as a technology designed specifically to address the needs of the international telecommunications carrier community. It has evolved over the past few years, and the various protocols and interfaces are defined in a set of standards created by the International Telecommunications Union (ITU). This gives network designers a solid base on which to build ATM networks. ATM is the underlying transmission system for the ITU's next-generation ISDN, broadband (B) ISDN. B-ISDN is designed to provide subscriber communications services over a wide range of bit rates from a few megabits to several gigabits. The current ATM standards are designed to allow subscribers access to the telephone networks at speeds of up to 622 Mbits s−1, and it is expected that eventually, gigabit speeds will also be supported as the underlying ATM transmission system is clearly capable of these speeds.
The major selling point of ATM is that it is the first technology that can deliver different types of traffic, such as voice, video and data, over a single digital transport mechanism. ATM can also handle scalable amounts of bandwidth as a result of its switching architecture, which can support multimedia applications and network growth for years to come. As the Internet integrated service (IIS) is becoming important, the ATM will play an important role as a backbone network technology for the Internet.
However, in a very competitive market, ATM cannot be the sole technology used; it is going to cooperate with existing network technologies in the Internet environment. It is hoped that the combined networks will provide quarantees of quality of service (QoS), which is required by network users and for the performance of the Internet. These QoS guarantees, however, come at a price. Contrary to common misconceptions, ATM is a very complex technology [2], perhaps the most complex ever developed by the networking industry. While the structure of ATM cells and cell switching do facilitate the development of hardwired and high-performance ATM switches, the deployment of ATM networks requires an infrastructure which consists of layers of highly complex protocols and softwares. Therefore, one of the challenges that ATM faces is to interoperate with the vast number of TCP/IP networks. Using IP and ATM together presents some interesting problems because they differ in fundamental ways, from their respective models of data forwarding (connectionless vs. connection-oriented) to support for the preferential treatment of packets (no support vs. the potential for support guarantees). In this paper, we will introduce some strategies and propose a priority scheme to support QoS for IP datagrams carried over the interconnected ATM and TCP/IP networks in IETF IP over ATM [3], [4], [5]. The implications of various IP-over-ATM strategies on network performance, particularly the aspects relating to QoS, virtual circuit (VC) multiplexing, and VC management are also addressed.
The paper is structured as follows. In Section 2, the concept of IP over ATM is introduced along with some related work. The protocol design principles are described in Section 3. In Section 4, protocol implementation using ATM VCs with guarantee of performance to carry IP datagrams is shown. Finally, conclusions are given and further studies are discussed in Section 5.
Section snippets
The concepts of IP over ATM
In the current Internet, the solution to forward data through an heterogeneous internetwork is provided by the Internet protocol (IP). The IP is almost entirely independent of the subnet technology used—it just makes a few assumptions about the nature of individual subnets. IP packets can traverse many different types of subnets (including ATM networks) without either the senders or the receivers being aware of the details of the networks encountered along the path. Unlike the ATM, the IP is a
Protocol design principles
Our goal is to extend the QoS features of an ATM network to IP applications. Although the IP in its current form has no provision for QoS support, the underlying ATM subnet has the capability to offer performance guarantees. We would therefore like Internet applications to gain some of the benefits of ATM performance guarantees, without the end-hosts or applications necessarily being aware of this capability.
As shown in Fig. 4, there is only one SVC between each host pair in classical IP over
Protocol implementation
In this section, we introduce the proposed priority scheme. It uses the TOS [12] field in the IP datagram header and is backward-compatible with existing IP implementation. These newer options need only be implemented on the end systems that wish to take advantage of them.
Conclusions and future work
In this paper, we have proposed a priority scheme (named the User Priority) by extending the IP datagram header. The goal is to enable a better packet delivery performance in traditional IP over ATM networks with QoS guarantees. Today's networks consist of mostly IP traffic. They can be benefited by application of the method when passing through ATM networks.
Currently, the User Priority scheme does not support a dynamic change of the QoS. There are several commonly mentioned reasons for a
Acknowledgements
This research is supported in part by the NSC under contract numbers NSC86-2622-E-007-001 and NSC86-2213-E-011-056.
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