We present a novel approach to building and deploying network protocols. The approach is based on mobile code, demand loading, and caching techniques. The architecture of our system allows new protocols to be dynamically deployed at both routers and end systems, without the need forcoordination and without unwanted interaction between co-existing protocols. In this paper, we describe our architecture and its realization in a prototype implementation. To demonstrate how to exploit our architecture, we present two simple protocols that operate within our prototype to introduce multicast and mobility services into a network that initially lacks them. 1

In this article we present a framework for the emerging Internet quality of service (QoS). All the important components of this framework --- integrated services, RSVP, differentiated services, multiprotocol label switching (MPLS), and constraintbased routing --- are covered. We describe what integrated services and differentiated services are, how they can be implemented, and the problems they have. We then describe why MPLS and constraint-based routing have been introduced into this framework, how they differ from and relate to each other, and where they fit into the differentiated services architecture. Two likely service architectures are presented, and the end-to-end service deliveries in these two architectures are illustrated. We also compare ATM networks to router networks with differentiated services and MPLS. Putting all these together, we give the readers a grasp of the big picture of the emerging Internet QoS. 12 IEEE Network . March/April 1999 9 and differenti...

Many real-time application domains can benefit from flexible and open distributed architectures, such as those defined by the CORBA specification. CORBA is an architecture for distributed object computing being standardized by the OMG. Although CORBA is well-suited for conventional request/response applications, CORBA implementations are not yet suited for real-time applications due to the lack of key quality of service (QoS) features and performance optimizations. This paper makes three contributions to the design of realtime CORBA systems. First, the paper describes the design of TAO, which is our high-performance, real-time CORBAcompliant implementation that runs on a range of OS platforms with real-time features including VxWorks, Chorus, Solaris 2.x, and Windows NT. Second, it presents TAO’s realtime scheduling service that can provide QoS guarantees for deterministic real-time CORBA applications. Finally, the paper presents performance measurements that demonstrate the effects of priority inversion and non-determinism in conventional CORBA implementations and how these hazards are avoided in TAO. 1

To be an effective platform for performance-sensitive real-time systems, distributed object computing middleware must support application quality of service (QoS) requirements end-toend. This article describes how the OMG's Real-time CORBA specification defines standard policies and mechanisms that permit the specification and enforcement of end-to-end QoS.

We discuss the architecture and technical viability of transporting real-time voice over packet-switched networks such as the Internet. The value of integrating voice and data networks onto a common platform is well known. The telephony industry has proposed the ATM standard as a means of upgrading the Internet to provide both real-time and data services. In contrast, voice services may be added to traditional IP networks that were originally designed for data transmission alone. Here, we consider the feasibility and expected quality of service of audio applications over IP networks such as the Internet. In particular, we examine possible architectures for voice over IP and discuss measured Internet delay and loss characteristics. 12 IEEE Network . January/February 1998 19 provide any QoS guarantees, but does specify that a reliable transport protocol, such as TCP, be used for transmitting control information. The Voice Over IP (VoIP) standards committee is proposing a subset...

Active networks permit applications to inject programs into the nodes of local and, more importantly, wide area networks. This supports faster service innovation by making it easier to deploy new network services. In this paper, we discuss both the potential impact of active network services on applications and how such services can be built and deployed. We explore the impact by suggesting sample uses and arguing how such uses would improve application performance. We explore the design of active networks by presenting a novel architecture, ants, that adds extensibility at the network layer and allows for incremental deployment of active nodes within the Internet. In doing so, ants tackles the challenges of ensuring that the exibility o ered by active networks does not adversely impact performance orsecurity. Finally, we demonstrate how a new network service may be expressed in ants.

ith the advent of the World Wide Web, the Internet has seen enormous growth from its roots as a network of modest proportions, mostly used by the research and academic community, to a large public data network. Several thousands of corporate users and several millions of dialin residential users have gone online in the last few years, making the Internet a true public data network. This accelerated growth in subscription has led to a surge of data in the Internet backbone. In order to keep up with this demand in service and bandwidth, all Internet service providers (ISPs) have scaled their networks severalfold, in both size and bandwidth. The forecast for this continuing growth is even more astounding [1, 2]. With fast emerging technologies, such as voice over IP and electronic commerce, the need to scale the

This article reviews the key differences between traditional IP routing and the emerging MPLS approach, and identifies where MPLS adds value to IP networking. In various corners of the industry MPLS has been held up as the solution to IP QoS, gigabit forwarding, network scaling, and traffic engineering. Each of these expectations is critically considered in the light of developments in conventional gigabit IP routers. It is shown that MPLS adds the ability to forward packets over arbitrary non-shortest paths, and emulate high-speed "tunnels" between IP-only domains --- capabilities critical to service providers who need to better manage resources around their backbones, or who are planning IP VPN services. However, it is also argued that the technology required to support IP QoS and gigabit forwarding is not unique to MPLS. A network of gigabit IP routers or switches may be entirely sufficient for QoS and performance if traffic engineering is not a requirement.

With the growth of the Internet and intranets, QoS technology that has been developed over a span of several years is quickly becoming more relevant. This article first defines QoS and introduces a taxonomy for QoS mechanisms. The evolution of several major QoS mechanisms is described with a special focus on RSVP and differentiated services. Special attention is paid to the role of the IETF in developing QoS mechanisms. We describe a QoS network that combines RSVP and differentiated services in a manner that realizes the benefits of each. We show that, in general, the adoption of increasingly sophisticated QoS mechanisms can enhance the ability of a network to offer high-quality service guarantees while simultaneously making efficient use of raw network resources. These mechanisms carry a cost in the form of increased overhead, which must be weighed against the benefits of the mechanism.

Many types of applications can benefit from flexible and open middleware. CORBA is an emerging middleware standard for Object Request Brokers (ORBs) that simplifies the development of distributed applications and services. Experience with CORBA demonstrates that it is suitable for traditional RPC-style applications. However, the lack of performance optimizations and quality of service (QoS) features in conventional CORBA implementations make them unsuited for highperformance and real-time applications. This paper makes four contributions to the design of CORBA ORBs for applications with high-performance and real-time requirements. First, it describes the design of TAO, which is our high-performance, real-time CORBA-compliant ORB. Second, it presents TAO's Real-time Scheduling Service, which provides QoS guarantees for deterministic realtime CORBA applications. Third, empirically evaluates the effects of priority inversion and non-determinism in conventional ORBs and shows how these ha...