While today’s computer networks support only best-effort service, future packet-switching integrated-services networks will have to support real-time communication services that allow clients to transport information with performance guarantees expressed in terms of delay, delay jitter, throughput, and loss rate. An important issue in providing guaranteed performance service is the choice of the packet service discipline at switching nodes. In this paper, we survey several service disciplines that are proposed in the literature to provide per-connection end-to-end peqormance guarantees in packet-switching networks. We describe their mechanisms, their similarities and differences, and the performance guarantees they can provide. Various issues and tradeoffs in designing service disciplines for guaranteed performance service are discussed, and a general framework for studying and comparing these disciplines are presented. I.

Existing approaches for providing guaranteed services require routers to manage per ow states and perform per ow operations [9, 21]. Such a stateful network architecture is less scalable and robust than stateless network architectures like the original IP and the recently proposed Di serv [3]. However, services provided with current stateless solutions, Di serv included, have lower exibility, utilization, and/or assurance level as compared to the services that can be provided with per ow mechanisms. In this paper, we propose techniques that do not require per ow management (either control or data planes) at core routers, but can implement guaranteed services with levels of exibility, utilization, and assurance similar to those that can be provided with per ow mechanisms. In this way we can simultaneously achieve high quality of service, high scalability and robustness. The key technique we use is called Dynamic Packet State (DPS), which provides a lightweight and robust mechanism for routers to coordinate actions and implement distributed algorithms. We present an implementation of the proposed algorithms that has minimum incompatibility with IPv4.

We present and prove a delay guarantee for the Virtual Clock service discipline. The guarantee has several desirable properties, including the following firewall property: The guarantee to a flow is unaffected by the behavior of other flows sharing the same server. There is no assumption that sources are flow-controlled or well-behaved. In this paper, we first introduce and define the concept of an active flow. The delay guarantee is then formally stated as a theorem. We show how to obtain delay bounds from the delay guarantee for a single server. Derivations of end-to-end delay bounds for various networks and source specifications are presented elsewhere. Keywords: virtual clock, rate-based service discipline, priority queue, throughput guarantee, delay guarantee, packet switching. Research supported in part by National Science Foundation grants no. NCR-9004464 and NCR9506048, and in part by NSA INFOSEC University Research Program. This paper was presented at the 9th IEEE Workshop ...

this paper we present a class of scheduling algorithms --- called Rate-Proportional Servers (RPS) --- with bounds on end-to-end delays, buffer requirements and internal traffic burstiness equal to those of Weighted Fair Queueing. This class of algorithms is based on the notion of the potential

Today’s Internet provides one simple service: best effort datagram delivery. This minimalist service allows the Internet to be stateless, that is, routers do not need to maintain any fine grained information about traffic. As a result of this stateless architecture, the Internet is both highly scalable and robust. However, as the Internet evolves into a global commercial infrastructure that is expected to support a plethora of new applications such as IP telephony, interactive TV, and e-commerce, the existing best effort service will no longer be sufficient. In consequence, there is an urgent need to provide more powerful services such as guaranteed services, differentiated services, and flow protection. Over the past decade, there has been intense research toward achieving this goal. Two classes of solutions have been proposed: those maintaining the stateless property of the original Internet (e.g., Differentiated Services), and those requiring a new stateful architecture (e.g., Integrated Services). While stateful solutions can provide more powerful and flexible services such as per flow bandwidth and delay guarantees, they are less scalable than stateless solutions. In particular, stateful solutions require each router to maintain and manage per flow state on the control path, and to perform per flow classification, scheduling, and buffer management on the data path. Since today’s routers can

Leave-in-Time is a new rate-based service discipline for packet-switching nodes in a connection-oriented data network. Leave-in-Time provides sessions with upper bounds on end-to-end delay, delay jitter, buffer space requirements, and an upper bound on the probability distribution of end-to-end delays. A Leave-inTime session's guarantees are completely determined by the dynamic traffic behavior of that session, without influence from other sessions. This results in the desirable property that these guarantees are expressed as functions derivable simply from a single fixed-rate server (with rate equal to the session's reserved rate) serving only that session. Leave-in-Time has a non-work-conserving mode of operation for sessions desiring low end-to-end delay jitter. Finally, Leave-in-Time supports the notion of delay shifting, whereby the delay bounds of some sessions may be decreased at the expense of increasihg those of other sessions. We present a set of admission control algorithms which support the ability to do delay shifting in a systematic way.

Fair queuing is a well-studied problem in modern computer networks. However, there remains a gap between scheduling algorithms that have provably good performance, and those that are feasible and practical to implement in highspeed routers. In this paper, we propose a novel packet scheduler called Stratified Round Robin, which has low complexity, and is amenable to a simple hardware implementation. Stratified Robin Robin exhibits good fairness and delay properties that are demonstrated through both analytical results and simulations. In particular, it provides a single packet delay bound that is independent of the number of flows. This property is unique to Stratified Round Robin among all other schedulers of comparable complexity.

We propose and develop a novel virtual time reference system as a unifying scheduling framework to provide scalable support for guaranteed services. This virtual time reference system is designed as a conceptual framework upon which guaranteed services can be implemented in a scalable manner using the DiffServ paradigm. The key construct in the proposed virtual time reference system is the notion of packet virtual time stamps, whose computation is core stateless, i.e., no per-flow states are required for its computation. In this paper, we lay the theoretical foundation for the definition and construction of packet virtual time stamps. We describe how per-hop behavior of a core router (or rather its scheduling mechanism) can be characterized via packet virtual time stamps, and based on this characterization, establish end-to-end per-flow delay bounds. Consequently, we demonstrate that, in terms of its ability to support guaranteed services, the proposed virtual time reference system has the same expressive power and generality as the IntServ model. Furthermore, we show that the notion of packet virtual time stamps leads to the design of new core stateless scheduling algorithms, especially work-conserving ones. In addition, our framework does not exclude the use of existing scheduling algorithms such as stateful fair queuing algorithms to support guaranteed services.

We develop a simple theory of flows to study the flow of data in real-time computing networks. Flow Theory is based on discrete and nondeterministic mathematics, rather than the customary continuous or probabilistic mathematics. The theory features two types of flows: smooth and uniform, and eight types of flow operators. We prove that, if the input flow to any of these operators is smooth or uniform, then both the internal buffer and delay of that operator are bounded. Linear networks of flow operators are introduced, and their internal buffers and delays are derived from the internal buffers and delays of their constituent operators. We extend Flow Theory so that it can be used in analyzing cyclic networks and networks of multiflows. Since many rate-reservation protocols can be represented as linear networks of flow operators, we use Flow Theory to prove that a number of these protocols (Stop-and-Go, Hierarchical Round-Robin, Weighted Fair Queueing, Self-Clocking Fair Queueing, and Virtual Clock) require bounded buffering and introduce bounded delay.

We present a scheduling protocol, called Time-Shift scheduling, to forward data packets from multiple input flows to a single output channel. Each input flow is guaranteed a predetermined forwarding rate and an upper bound on packet delay. The protocol is an improvement over existing protocols because it satisfies the properties of low delay, fairness, and efficiency, while existing protocols fail to satisfy at least one of these properties. In Time-Shift scheduling, each flow is assigned an increasing timestamp, and the packet chosen for transmission is taken from the flow with the least timestamp. The protocol features the novel technique of time shifting, in which the scheduler's real-time clock is adjusted to prevent flow timestamps from increasing faster than the real-time clock. This bounds the difference between any pair of flow timestamps, thus ensuring the fair scheduling of flows. 1.