Performance of New Dynamic Benefit-Weighted Scheduling Scheme in DiffServ Networks

In this paper, we design a new dynamic packet scheduling scheme suitable for differentiated service (DiffServ) network. Designed dynamic benefit weighted scheduling (DBWS) uses a dynamic weighted computation scheme loosely based on weighted round robin (WRR) policy. It predicts the weight required by expedited forwarding (EF) service for the current time slot (t) based on two criteria; (i) previous weight allocated to it at time (t-1), and (ii) the average increase in the queue length of EF buffer. This prediction provides smooth bandwidth allocation to all the services by avoiding overbooking of resources for EF service and still providing guaranteed services for it. The performance is analyzed for various scenarios at high, medium and low traffic conditions. The results show that packet loss is minimized, end to end delay is minimized and jitter is reduced and therefore meet quality of service (QoS) requirement of a network.

Analysis of Heterogeneous IP Traffic in Wireless Environment

Wireless access is expected to play a crucial role in the future of the Internet. The demands of the wireless environment are not always compatible with the assumptions that were made on the era of the wired links. At the same time, new services that take advantage of the advances in many areas of technology are invented. These services include delivery of mass media like television and radio, Internet phone calls, and video conferencing. The network must be able to deliver these services with acceptable performance and quality to the end user. This thesis presents an experimental study to measure the performance of bulk data TCP transfers, streaming audio flows, and HTTP transfers which compete the limited bandwidth of the GPRS/UMTS-like wireless link. The wireless link characteristics are modeled with a wireless network emulator. We analyze how different competing workload types behave with regular TPC and how the active queue management, the Differentiated services (DiffServ), and a combination of TCP enhancements affect the performance and the quality of service. We test on four link types including an error-free link and the links with different Automatic Repeat reQuest (ARQ) persistency. The analysis consists of comparing the resulting performance in different configurations based on defined metrics. We observed that DiffServ and Random Early Detection (RED) with Explicit Congestion Notification (ECN) are useful, and in some conditions necessary, for quality of service and fairness because a long queuing delay and congestion related packet losses cause problems without DiffServ and RED. However, we observed situations, where there is still room for significant improvements if the link-level is aware of the quality of service. Only very error-prone link diminishes the benefits to nil. The combination of TCP enhancements improves performance. These include initial window of four, Control Block Interdependence (CBI) and Forward RTO recovery (F-RTO). The initial window of four helps a later starting TCP flow to start faster but generates congestion under some conditions. CBI prevents slow-start overshoot and balances slow start in the presence of error drops, and F-RTO reduces unnecessary retransmissions successfully.

Providing Soft Bandwidth Guarantees Using Elastic TCP-based Tunnels

The best-effort nature of the Internet poses a significant obstacle to the deployment of many applications that require guaranteed bandwidth. In this paper, we present a novel approach that enables two edge/border routers-which we call Internet Traffic Managers (ITM)-to use an adaptive number of TCP connections to set up a tunnel of desirable bandwidth between them. The number of TCP connections that comprise this tunnel is elastic in the sense that it increases/decreases in tandem with competing cross traffic to maintain a target bandwidth. An origin ITM would then schedule incoming packets from an application requiring guaranteed bandwidth over that elastic tunnel. Unlike many proposed solutions that aim to deliver soft QoS guarantees, our elastic-tunnel approach does not require any support from core routers (as with IntServ and DiffServ); it is scalable in the sense that core routers do not have to maintain per-flow state (as with IntServ); and it is readily deployable within a single ISP or across multiple ISPs. To evaluate our approach, we develop a flow-level control-theoretic model to study the transient behavior of established elastic TCP-based tunnels. The model captures the effect of cross-traffic connections on our bandwidth allocation policies. Through extensive simulations, we confirm the effectiveness of our approach in providing soft bandwidth guarantees. We also outline our kernel-level ITM prototype implementation.

The War Between Mice and Elephants

Recent measurement based studies reveal that most of the Internet connections are short in terms of the amount of traffic they carry (mice), while a small fraction of the connections are carrying a large portion of the traffic (elephants). A careful study of the TCP protocol shows that without help from an Active Queue Management (AQM) policy, short connections tend to lose to long connections in their competition for bandwidth. This is because short connections do not gain detailed knowledge of the network state, and therefore they are doomed to be less competitive due to the conservative nature of the TCP congestion control algorithm. Inspired by the Differentiated Services (Diffserv) architecture, we propose to give preferential treatment to short connections inside the bottleneck queue, so that short connections experience less packet drop rate than long connections. This is done by employing the RIO (RED with In and Out) queue management policy which uses different drop functions for different classes of traffic. Our simulation results show that: (1) in a highly loaded network, preferential treatment is necessary to provide short TCP connections with better response time and fairness without hurting the performance of long TCP connections; (2) the proposed scheme still delivers packets in FIFO manner at each link, thus it maintains statistical multiplexing gain and does not misorder packets; (3) choosing a smaller default initial timeout value for TCP can help enhance the performance of short TCP flows, however not as effectively as our scheme and at the risk of congestion collapse; (4) in the worst case, our proposal works as well as a regular RED scheme, in terms of response time and goodput.

On Class-based Isolation of UDP, Short-lived and Long-lived TCP Flows

The congestion control mechanisms of TCP make it vulnerable in an environment where flows with different congestion-sensitivity compete for scarce resources. With the increasing amount of unresponsive UDP traffic in today's Internet, new mechanisms are needed to enforce fairness in the core of the network. We propose a scalable Diffserv-like architecture, where flows with different characteristics are classified into separate service queues at the routers. Such class-based isolation provides protection so that flows with different characteristics do not negatively impact one another. In this study, we examine different aspects of UDP and TCP interaction and possible gains from segregating UDP and TCP into different classes. We also investigate the utility of further segregating TCP flows into two classes, which are class of short and class of long flows. Results are obtained analytically for both Tail-drop and Random Early Drop (RED) routers. Class-based isolation have the following salient features: (1) better fairness, (2) improved predictability for all kinds of flows, (3) lower transmission delay for delay-sensitive flows, and (4) better control over Quality of Service (QoS) of a particular traffic type.

Differentiated Control of Web Traffic: A Numerical Analysis

Internet measurements show that the size distribution of Web-based transactions is usually very skewed; a few large requests constitute most of the total traffic. Motivated by the advantages of scheduling algorithms which favor short jobs, we propose to perform differentiated control over Web-based transactions to give preferential service to short web requests. The control is realized through service semantics provided by Internet Traffic Managers, a Diffserv-like architecture. To evaluate the performance of such a control system, it is necessary to have a fast but accurate analytical method. To this end, we model the Internet as a time-shared system and propose a numerical approach which utilizes Kleinrock's conservation law to solve the model. The numerical results are shown to match well those obtained by packet-level simulation, which runs orders of magnitude slower than our numerical method.

A programmable architecture for layered multimedia streams in IPv6 networks

A new configurable architecture is presented that offers multiple levels of video playback by accommodating variable levels of network utilization and bandwidth. By utilizing scalable MPEG-4 encoding at the network edge and using specific video delivery protocols, media streaming components are merged to fully optimize video playback for IPv6 networks, thus improving QoS. This is achieved by introducing “programmable network functionality” (PNF) which splits layered video transmission and distributes it evenly over available bandwidth, reducing packet loss and delay caused by out-of-profile DiffServ classes. An FPGA design is given which gives improved performance, e.g. link utilization, end-to-end delay, and that during congestion, improves on-time delivery of video frames by up to 80% when compared to current “static” DiffServ.

Qualidade de serviço em redes IP serviços diferenciados

Este trabalho tem como finalidade apresentar uma visão geral dos assuntos relacionados à definição, configuração e gerenciamento dos serviços habilitados pela arquitetura de Serviços Diferenciados em relação à priorização de tráfego. Nele, descrevemos as necessidades por QoS nas redes atuais e futuras, bem como o direcionamento da Internet 2 em relação ao QoS, mais especificamente voltada ao mecanismo DiffServ. Também são destacados os mecanismos de QoS para redes IP do fornecedor Cisco Systems, o qual possui a maior gama de mecanismos já implantados pelos fornecedores. Por fim, identificamos as características necessárias para participar do QBone, um testbed para Serviços Diferenciados.

Adicionando qualidade de serviço para um ambiente de colaboração visual baseado em H.323.

A colaboração visual, recurso que permite a troca de informações de forma remota, é construída em cima de uma combinação de diversas ferramentas, na qual estão incluídos: videoconferência, “streaming de vídeo”, compartilhamento e transferência de informações e imagens (colaboração em cima de dados) entre outros. Estas soluções, vêm utilizando cada vez mais, o protocolo IP e a Internet para o transporte dos sinais. Com este objetivo, o ITU-T lançou a recomendação H.323, que definiu um padrão confiável, que permite a troca de sinais multimídia em redes de pacotes sem qualidade de serviço. Entretanto, com o passar dos anos percebeu-se que aplicações que manipulam voz e vídeo, precisam que as redes de pacotes tenham capacidade de prover características semelhantes às oferecidas por redes de comutação por circuito, para o transporte dos sinais multimídia. Neste sentido, redes IP podem utilizar mecanismos de qualidade de serviço como o DiffServ, para prover tratamento adequado dos sinais de áudio e vídeo e assim, aumentar a qualidade percebida pelos usuários. As aplicações de colaboração visual são notáveis candidatas a utilização de mecanismos de QoS da rede. Neste caso é desejável que estas aplicações estejam aptas a especificar o nível de qualidade de serviço desejado e requisitem este nível de serviço para a rede. Neste contexto, o trabalho apresenta um modelo para o desenvolvimento de um terminal H.323 capaz de requisitar qualidade de serviço para a rede IP, visando aumentar a qualidade percebida pelo usuário em relação aos sinais de mídia. Neste terminal foi incluída uma entidade chamada de EPQoSE, responsável pela sinalização de QoS em benefício do terminal. Além disso, o modelo proposto neste texto apresenta um sistema de gerenciamento baseado em políticas, responsável por controlar as requisições de QoS dos terminais H.323, dentro de um domínio. Como o terminal precisa se comunicar com estas entidades, apresentamos no trabalho, a maneira como ele faz isso e definimos um conjunto de funções que devem ser implementadas pelo QoSM no terminal.

Apresentação multimédia com garantias de qualidade de serviço: QoSMedEval (Quality of Service Media Evaluation Tool)

Orientador: Paulo Nazareno Maia Sampaio

Especificação de uma rede MPLS fim-a-fim com diferenciação de serviços

New multimedia applications that use the Internet as a communication media are pressing for the development of new technologies, such as: MPLS (Multiprotocol Label Switching) and DiffServ. These technologies introduce new and powerful features to the Internet backbone, as the provision of QoS (Quality of Service) capabilities. However, to obtain a true end-to-end QoS, it is not enough to implement such technologies in the network core, it becomes indispensable to extend such improvements to the access networks, what is the aim of the several works presently under development. To contribute to this process, this Thesis presents the RSVP-SVC (Resource Reservation Protocol Switched Virtual Connection) that consists in an extension of RSVP-TE. The RSVP-SVC is presented herein as a mean to support a true end-to-end QoS, through the extension of MPLS scope. Thus, it is specified a Switched Virtual Connection (SVC) service to be used in the context of a MPLS User-to-Network Interface (MPLS UNI), that is able to efficiently establish and activate Label Switched Paths (LSP), starting from the access routers that satisfy the QoS requirements demanded by the applications. The RSVP-SVC was specified in Estelle, a Formal Description Technique (FDT) standardized by ISO. The edition, compilation, verification and simulation of RSVP-SVC were made by the EDT (Estelle Development Toolset) software. The benefits and most important issues to be considered when using the proposed protocol are also included