e present an enhancement to the IP best effort service, alternative best effort (ABE), which relies on the idea of providing low delay at the expense of maybe less throughput. The motivation for such a service is twofold. First, there now exist interactive multimedia applications that perform well across a wide range of loss and throughput conditions [1, 2] , but for which delay often remains the major impediment [3] . Second, unlike differentiated services, we would like to design a service where it is not required to police how much traffic uses the low delay capability, in order to retain the operational simplicity of a single-class network. The article is organized as follows. We define the ABE service and analyze its implications. In particular, we identify and discuss the central issue, called green does not hurt blue. We also discuss migration issues from the traditional IP service (flat best effort) to ABE. As a proof of concept, a router implementation is described; it is based on the combination of a scheduler called duplicate scheduling with deadlines (DSD) and a traditional control loop. Implementations were done in the Linux kernel, in the Dummynet network emulator, and in the ns-2 simulator [4] . Simulation results of the ns-2 implementation are shown. We review related work and position ABE with respect to other proposals in differentiated services. ABE is defined as follows: • ABE packets are marked either green or blue. 1 • Green packets receive a low bounded delay at every hop. Realistic values of the per-hop delay bound are discussed later in this section. • Green does not hurt blue: If some source decides to mark some of its packets green rather than blue, the quality of the service(delay and throughput) received by sources that mark all their packets blue remains the same or becomes better. This definition is made more specific later. • All ABE packets belong to one single best effort class. If the total load is high, every source may receive little throughput. However, entirely blue sources experience more throughput than entirely green sources sharing the same network resources.  We propose alternative best effort (ABE), a novel service for IP networks, which relies on the idea of providing low delay at the expense of maybe less throughput. The objective is to retain the simplicity of the original Internet single-class best-effort service while providing low delay to interactive adaptive applications. With ABE, every best effort packet is marked as either green or blue. Green packets are guaranteed a low bounded delay in every router. In exchange, green packets are more likely to be dropped (or marked using congestion notification) during periods of congestion than blue packets. For every packet, the choice of color is made by the application based on the nature of its traffic and on global traffic conditions. Typically, an interactive application with real-time deadlines, such as audio, will mark most of its packets as green, as long as the network conditions offer large enough throughput. In contrast, an application that transfers binary data such as bulk data transfer will seek to minimize overall transfer time and send blue traffic. We propose router requirements that aim at enforcing benefits for all types of traffic, namely that green traffic achieves low delay and blue traffic receives at least as much throughput as it would in a flat (legacy) best effort network. ABE is different from differentiated or integrated services in that neither packet color can be said to receive better treatment; thus, flat rate pricing may be maintained, and there is no need for reservations or profiles. In this article we define the ABE service, its requirements, properties, and usage. We discuss the implications of replacing the existing IP best effort service by the ABE service. We propose and analyze an implementation based on a new scheduling method called duplicate scheduling with deadlines. It supports any mixture of TCP, TCP-friendly, and non-TCP-friendly traffic.
Duplicate Scheduling with Deadlines REF is used to guarantee a low bounded delay in the transmission of packets sent in a connection carrying traffic with diverse requirements.
ABE: Providing a Low-Delay Service within Best Effort
IEEE Network
Computer Science