Journal papers1998 |
Conference papers1996 1997 1998 1999 2001 |
ThesisMasters Thesis Licentiate Thesis |
This paper was in Computer Communications 21 (13), 1998. Vol. 21, nro 13, s. 1184 - 1194.
There are ATM nodes from several vendors in the market and some operators even are offering public ATM services. However, in order to really make a breakthrough of ATM we must develop ATM applications which are acceptable also by others than computer-wizards. Our paper gives an outline of the ATM evolution from separate nodes to real and practical services utilizing ATM technology. One of the most prominent experiences of current situation is continuously evolving standards. First adopters have faced a dilemma of never ending software and hardware updates. Although we may except that Internet will be upgraded to ATM because of increasing capacity and quality requirements, the definitive role of ATM in the whole network architecture is still shrouded in mystery, and a lot of practical and theoretical questions are open.
This paper is available in PDF-format.
This paper investigates performance evaluation of Asynchronous Transfer Mode (ATM) switching systems: Private Branch Exchanges (PBX), switches and cross-connects. To evaluate performance of a ATM switching systems is not a straightforward as one might expect. This is due to the fact that performance can be seen from different angles. Measurements presented in this paper include: throughput, switching delay, switching delay variation, buffer size, accuracy of the Usage Parameter Control (UPC) procedure and cell discarding under overload situation. These properties have been evaluated through a series of measurements. Measurements are quite general although they have been carried out only against Fore Systems ASX-200 PBX. The main value of this presentation is in comparison of different measurement techniques rather than in the actual results. The results depend on the environment but the techniques are valid in general.
This paper is available in PDF-format.
In this paper, several performance measurements of ATM (Asynchronous Transfer Mode) networks are performed and analysed. Especially, measurement of the buffer size, the traffic management functions and the cell transfer delay in a switching system are studied as a function of various traffic patterns and loading levels. These values have great importance for establishing reliable media for broadband traffic and contributing to the implementation of services in ATM networks.
This paper is available in PDF-format.
Key issues in the current development of Internet seem to be its capability to scale and to support new real-time or near real-time applications like video- and audio conferencing. There are two factors that affect these qualities: one is the ability to distinguish which connections should be switched and the other is the effective control over network resources. ATM is a serious attempt to standardize global multiservice networks. This attempt seems to suit well for the future Internet. ATM was originally meant to be an easy and an efficient protocol but it is now turning to be yet another ISDN. More and more features are implemented to ATM resulting in the overloading of the network with management procedures. Therefore a new approach needs to be taken. In this approach a strong reminder of what is necessary needs to be kept in mind. This paper presents an alternative, simpler approach to the ATM traffic management and introduces some suggestions how to map Internet applications to simplified ATM environment using an advanced IP switching concept.
This paper is available in PDF-format and in PS-format.
ATM has been under a thorough standardization process for more than ten years. Looking at it now, what have we achieved during this time period? Originally ATM was meant to be an easy and an efficient protocol enabling varying services over a single network. What it is turning to be is yet another ISDN-- network full of hopes and promises but too difficult to implement and expensive to market. The fact is that more and more nice features are implemented on the cost of overloading network with hard management procedures. Therefore we need to adopt a new approach. This approach keeps a strong reminds on what is necessary. This paper presents starting points for an alternative approach to the traffic management. We refer to this approach as the minimum management principle. Choosing of the suitable service classes for the ATM network is made difficult by the fact that the more services one implements the more management he needs. This is especially true for the variable bit rate connections that are usually treated based on the stochastic models. Stochastic model, at its best, can only reveal momentary characteristics in the traffic stream not the long range behavior of it. Our assumption is that ATM will move towards Internet in the sense that strict values for quality make little or no sense in the future. Therefore stochastic modeling of variable bit rate connections seems to be useless. Nevertheless we see that some traffic needs to have strict guarantees and that only economic way of doing so is to use PCR allocation.
This paper is available in PDF-format and in PS-format.
One of the most important network elements in the Internet are the routers which do relaying of IP packets. Because of growth of the Internet routers currently experience serious problems in relaying traffic in a satisfying speed. The idea of switching Internet traffic flows has recently been introduced and a new technology called IP switching has emerged. Several differing technological solutions have been suggested. In this paper we describe and compare two methods in flow-based IP switching to make the decisions whether to switch internet traffic flows to separate ATM-connections. Traffic measurements are made in two networks of varying size and based on a specific three-stage flow analysis we suggest that the decision to switch should be made as flexible as possible due to the expected diversity of traffic profiles in different parts of the network. This way the optimal service cluster could be switched and router resources could be optimally utilized. A simple model to determine workload to an IP switch is introduced. Using this model we see that the workload of the flow setup component and the routing component may be optimized, if we use flexible methods to determine the flows that are to be separately switched.
This paper is available in PDF-format and in PS-format.
New services come at cost to the Internet community, therefore determining the needed level of QoS for the services is important. This due to the fact that guaranteeing quality demands extra functionality and extra cost for equipment in the network. We have chosen voice transmission over IP network as a candidate service for the study of QoS issues. We wanted to see what is the difference in perceived quality of service in following cases: a network with conventional forwarding and a similar network using a layer 3 switching (IP-switching). We present measurements with a commercial embedded microprocessor system and a public domain software in a general purpose computer. From experiences we can say that the present general purpose computer architecture is no means optimal for providing controlled quality of service for a real-time communication. We conclude that routers offering real-time services need prioritized traffic handling.
This paper is available in PDF-format and in PS-format.
This paper is available in conference proceedings pp 3017-3022.
Differentiated services (DS) is a mechanism by which network service providers can offer differing levels of network service to different traffic, and in doing so they provide quality of service (QoS) to their customers. The advantage of DS is that many traffic flows can be aggregated to a small number of classes, thereby simplifying the processing and storage associated with packet classiffication and conditioning. In addition, there is no signaling state or related processing required in the DS network since QoS is invoked on a packet-by-packet basis. To succeed in differentiation, router must somehow decide which packet should go into which class. This decision can be based on inherent characteristics of traffic source or application or some other networking perspective. Traffic in Internet can be broadly categorized into two different classes: interactive and bulk. Interactive traffic is seen to be formed from conversational applications needing continuos attention from the user like IP telephony, video conferencing, collaborative application (shared white board etc) and applications forming a group of which some have interactive nature as an application (web, remote shell) or require some level consistency in delivery time like streaming audio and video. Bulk category takes all what is left from previous ones. These left overs are usually related to background processes like le transfer (FTP) or messaging (email). In this paper we will present a survey of ways to do quality differentiation and packet classiffication. A group of classiffication mechanisms are investigated more closely, namely measurement based classiffiers.
This paper is available in PDF-format and in PS-format.
This paper is available in PDF-format and in PS-format.
Internet is moving towards the time of Quality of Service (QoS) networking. This move is taking place through the application of Differentiated Services (DiffServ) architecture. DiffServ offers low overhead tools to implement class based differentiation for the traffic. Decision of differentiation is, however, left as an open matter, to be settled between service provider and customer. Majority of customers are, based on our assumption, not ready to say what should be the quality or class for their traffic. This leaves space for provider intervention - service, to do this classification for the customer. Service provider is dealing with three problems which need to be solved concurrently: (1)Deciding the proper forwarding class for the application data stream (2)Separation of application ows from the packet stream (3)Constructing proper forwarding treatments. If successful with this operation, operator has direct control over the resource utilization within different classes and therefore service level provided to the customer. In order to cope with this service, tools for analyzing network traffic and forming suitable traffic groups are required. We present algorithms and methodologies which do differentiation of traffic based on the activity/traffic characteristics of applications. These values are determined from the flow analysis of packet lengths and inter-sending times.
This paper was presented in SPIE´s International Symposium ITCom, Denver Colorado USA, 19-24 August 2001.
This paper is available in PDF-format and in PS-format.
ATM and ATM measurements are rather new area in the telecommunications technology. So far ATM measurements have been apcomblished as a part of product development. This has lead the view to the very narrow area of ATM measurements. This largely due to the fact that there is no clear picture about the ATM traffic and how to model and implement it to the measurement tools. There have been some performance tests between different ATM switching systems but their perspective have been more or less in the area of data communications. This thesis tries to give larger perspective to the problem we are dealing with the traffic management and performance.
From the performance measurements, parameters which have relation to the information transfer are presented and respective ways to measure them. Parameters considered here are transfer delay, usage parameter control and buffering. All of these measurements have been done in manner that they give short insight to the idea.
Keywords: ATM, B-ISDN, QoS, TRAFFIC MEASUREMENT, UPC
This thesis is available in PDF-version.
DiffServ is based on the conceptual formulation of mechanisms. It does not cover implementation or services. Implementation of DiffServ compliant devices is left to the resposibility of individual implementers, which may add other functionalities beyond those described in DiffServ RFCs. This leads easily to non-interoperable services, as there is a great possibility of having different types of services and implementations of same services.
This work serves as an introduction to the service problems of QoS networking in the Internet. It presents Best Effort, Integrated Services and Differentiated Services architectures, and tries to pinpoint their strengths and weaknesses. Simulations of DiffServ provide some insight to the problems of mixed implementations of same service. In addition, difficulties of service provisioning become apparent from the results.
Keywords: Differentiated Services, Internet, Simulation
This thesis is available in PDF-version.
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