The abstract system design and a prototype implementation of an admission control system is described. The system exploits the load signal generated by low complexity active queue management schemes at internal nodes to carry out flow admission control at edge gateways. The location of functional components is studied and appropriate signalling extensions to exchange load information are presented. The suitability of such signalling extensions for admission control and traffic regulation are discussed in the context of RSVP signalling. A number of questions of detail which are usually ignored by existing theory and simulation work, are examined and solutions are presented. Certain modifications to traffic control algorithms at both internal packet marking nodes and edge gateways are proposed and discussed. The functionality and correct system operation are demonstrated by experiments using the software prototype. Further, a variety of marking algorithms is compared experimentally to assess the suitability of their respective load signal for admission control of inelastic traffic and load-adaptive traffic regulation.

This paper introduces a framework for answering questions regarding the conditions on the network load that allow a best-effort network like the Internet to support connections of given duration that require a certain quality of service. Such quality of service is expressed in terms of the percentage of time the bandwidth allocated to a connection may drop below a certain level or the maximum allowable delay in placing the call through the network waiting for more favorable loading conditions. The call-acceptance conditions, which depend on the behavior of the system over the lifetime of accepted calls, are thus based on transient models for the congestion (instead of looking at the average behavior) and attempt to exploit the time-scales of the fluctuations of the number of connections competing for bandwidth. Extensions of the model consider the case of dynamic pricing which allows connections that pay more to get larger shares of the bandwidth, and investigate the trade-off between quality of service, the size of the acceptance region, and the charge to be paid by the connection. One potential use of this methodology is towards developing a simple admission control mechanism for placing voice calls through an IP network, where the decisions can be taken by edge devices.

There is an increasing demand for supporting real-time audiovisual services over next-generation wired and wireless networks. Various link/network characteristics make the deployment of such demanding services more challenging than traditional data applications like e-mail and the Web. These audiovisual applications are bandwidth adaptive but have stringent delay, jitter, and packet loss requirements. Consequently, one of the major requirements for the successful and wide deployment of such services is the efficient transmission of sensitive content (audio, video, image) over a broad range of bandwidth-constrained access networks. These media will be typically compressed according to the emerging ISO/IEC MPEG-4 standard to achieve high bandwidth efficiency and content-based interactivity. MPEG-4 provides an integrated object-oriented representation and coding of natural and synthetic audiovisual content for its

Connection acceptance control is a mechanism which can be used to moderate the load placed on a network by turning away connection requests during times of overload. Traditionally these mechanisms have been implemented by setting up state within a network using signalling protocols, such as the IETF's Resource Reservation Protocol. There have been recent proposals for admission control based on end-systems probing the network to infer network load. These distributed algorithms often have less router state and hence scale more easily. This paper discusses an ECN (Explicit Congestion Notification) probe-based admission control protocol that is fast, scalable and robust. The protocol's performance is then studied through simulation. It is concluded that probe-based admission control is viable in both partitioned and integrated networks, but more research is needed to understand the implications for network policy control. 1.

Roberts, Massoulié and co-authors have introduced and studied a flow level model of Internet congestion control, that represents the randomly varying number of flows present in a network where bandwidth is dynamically shared between elastic file transfers. In this paper we consider a generalization of the model to include streaming traffic as well as file transfers, under a fairness assumption that includes TCP-friendliness as a special case. We establish stability, under conditions, for a fluid model of the system. We also assess the impact of each traffic type on the other: file transfers are seen by streaming traffic as reducing the available capacity, whereas for file transfers the presence of streaming traffic amounts to replacing sharp capacity constraints by relaxed constraints. The integration of streaming traffic and file transfers has a stabilizing effect on the variability of the number of flows present in the system.

Quality of Service (QoS) has been touted as a technological requirement for many different networks at many different times. However, very few (if any) schemes for providing it have ever been successful, despite a huge amount of research in the area of QoS provision. In this position paper we analyze some of the reasons why so many QoS mechanisms have failed to be widely deployed. We suggest two factors in this failure: the timeliness of QoS mechanisms (they rarely arrive when they are needed), and the inherent contradiction of layering QoS mechanisms over a best-effort network. We also give some thoughts on how future QoS research might increase its chances of successful deployment by better positioning itself relative to other developments in networking.

Pre-congestion notification (PCN) in IP networks uses packet metering and marking within a PCN domain to notify its egress nodes whether link-specific admissible or supportable rate thresholds have been exceeded by high priority traffic. Based on this information simple admission control and flow termination is implemented. The latter is a new flow control function and useful in case of overload through high priority traffic which can occur in spite of admission control, e.g., when traffic is rerouted in failure cases. Resilient admission control admits only so much traffic that admitted traffic can be rerouted without causing congestion on backup paths in case of a likely failures, e.g., single link failures. We propose algorithms to configure the link-specific PCN rate thresholds such that resources are utilized efficiently and fairly by competing traffic aggregates while meeting resilience constraints. This is done for the single and dual marking PCN architecture whereby the single marking case is more demanding since it requires that the supportable rate is a fixed multiple of the admissible rate on all links within a single PCN domain. Furthermore, we derive objective functions to optimize the underlying routing system for both cases. Our performance results for various network types show that the dual marking PCN architecture leads to significantly better resource efficiency than the single marking PCN architecture.

large and small scale systems

In this paper we describe a novel Endpoint Admission Control scheme (EAC) for IP telephony. EAC mechanisms are driven by independent measurements taken by the edge nodes on a flow of packets injected in the network to probe the source to destination path. Our scheme is characterized by two fundamental features. First, it does not rely on any additional procedure in internal network routers other than the capability to apply di#erent service priorities to probing and data packets. Second, the connection admission decision is based on the analysis of the probing flow delay variation statistics. Simulation results, which focus on a IP telephony scenario, show that, despite the lack of core routers cooperation, toll-quality performance figures (99th delay percentiles not greater than few ms per router) can be obtained even in severe overload conditions. Finally, a comparison with an EAC scheme driven by probe losses only, shows that the use of delay variation statistics as endpoint decision criterion is a key factor for EAC e#ectiveness.

uni-wuerzburg.de The PCN working group of the IETF discusses the use of pre-congestion notification (PCN) to implement flow admission control. Packet meters and markers are used on all network links and packet markings are recorded as congestion level estimates (CLEs) the egress nodes. The working group currently discusses the pros and cons of possible marking algorithms that play a major role in this new architecture. This paper provides a detailed description of threshold and ramp marking based on a virtual queue formulation. We investigate the impact of the marking threshold and the virtual queue size on the marking behavior and develop different marking strategies. We test the robustness of the CLEs obtained for both marking schemes against different CLE parameters and traffic characteristics. Furthermore, we show that ramp marking can be well approximated by appropriately configured threshold marking. 1