he Internet was simply designed for packet delivery. However recent developments such as commercialization and the diversity of application requirements make it obvious that a more concrete definition of the type of service delivered to the user is needed. This description of the service delivered by the network is called the service model and documents the commitments the network makes to the clients that request service. It describes a set of end-toend services and it is up to the network to ensure that the services offered at each link along a path combine meaningfully to support the end-to-end service.Traditionally, in the Internet all packets are treated the same without any discrimination or explicit delivery guarantees. This is known as the best effort service model; all the network promises is to exert its best effort to deliver the packets injected into it without committing to any quantitative performance (quality of service, QoS) bounds. 1 Users do not request permission before transmitting, and therefore perceived performance is determined not only by the network itself, but also from other users' offered load, resulting in a complete lack of isolation and protection. The best effort service model has no formal specification; rather, it is specified operationally; packet delivery should be an expectation rather than an exception. The traditional applications and protocols were flexible, adaptive, and robust enough to operate under a wide range of network conditions without requiring any particularly welldefined service. The Problem of CongestionCongestion is the state of sustained network overload where the demand for network resources is close to or exceeds capacity. Network resources, namely link bandwidth and buffer space in the routers, are both finite and in many cases still expensive. The Internet has suffered from the problem of congestion which is inherent in best effort datagram networks due to uncoordinated resource sharing. It is possible for several IP packets to arrive at the router simultaneously, needing to be forwarded on the same output link. Clearly, not all of them can be forwarded simultaneously; there must be a service order. In the interim buffer space must be provided as temporary storage for the packets still awaiting transmission.Sources that transmit simultaneously can create a demand for network resources (arrival rate) higher than the network can handle at a certain link. The buffer space in the routers offers a first level of protection against an increase in traffic arrival rate. However, if the situation persists, the buffer space is exhausted and the router has to start dropping packets. Traditionally Internet routers have used the first come first served (FCFS) service order, typically implemented by a first in first out (FIFO) queue, and drop from the tail at buffer overflow as their queue management strategy.The problem of congestion cannot be solved by introducing "infinite" buffer space inside the network; the queues would then grow without bound, and the end-to-e...
Recently we have witnessed an increasing interest in providing differentiated Internet services, departing from the traditional notion of fairness in the best effort service model. However research efforts have almost exclusively focused on routers, by enhancing their scheduling and queue management capabilities in order to treat flows according to policies. There has been much less work on transport level approaches to differentiated services. MulTCP [1], is the only piece of work in this direction known to the authors. In this paper we briefly describe the MulTCP modifications in TCP's congestion control mechanism, its implementation in a BSD networking stack and present some experiences from a series of experiments over real networks comparing its performance when implemented on different TCP variants. Our results were particularly interesting in the case of RED gateways. We comment on the effectiveness and scalability of the differentiation mechanism and conclude that in certain popular environments the proposed method for transport level differentiation can be both feasible and effective.
The use of scheduling mechanisms like Class Based Queueing (CBQ) is expected to play a key role in next generation multiservice IP networks. In this paper we attempt an experimental evaluation of ALTQ/CBQ demonstrating its sensitivity to a wide range of parameters and link layer driver design issues. We pay attention to several CBQ internal parameters that affect performance drastically and particularly to "borrowing", a key feature for flexible and efficient link sharing. We are also investigating cases where the link sharing rules are violated, explaining and correcting these effects wheneverpossible. Finally we evaluate CBQ performance and make suggestions for effective deployment in real networks.
No abstract
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.