Showing papers by "Markku Kojo published in 2001"

Performance Enhancing Proxies Intended to Mitigate Link-Related Degradations

Abstract: This document is a survey of Performance Enhancing Proxies (PEPs) often employed to improve degraded TCP performance caused by characteristics of specific link environments, for example, in satellite, wireless WAN, and wireless LAN environments. Different types of Performance Enhancing Proxies are described as well as the mechanisms used to improve performance. Emphasis is put on proxies operating with TCP. In addition, motivations for their development and use are described along with some of the consequences of using them, especially in the context of the Internet.

Seawind: a Wireless Network Emulator .

Abstract: Wide area wireless networks are being studied worldwide in order to provide better network service with good performance to customers. The Software Emulator for Analyzing Wireless Network Data Transfers (Seawind) is a real-time network simulator that allows researchers to measure the performance of real network applications over an emulated network that follows the user specified wireless network behavior model. Using an emulator in network performance tests has several benefits. It allows constructing and repeating specific test scenarios that are interesting to the researcher. The researcher has full control over the parameters affecting the network behavior and he can run performance tests on future networks that are not yet available for testing. By using emulator the performance tests are faster and cheaper to carry out than real field tests. A benefit of real-time emulation over simulators running in virtual time is that we can study the actual protocol implementations of different operating systems and applications.

End-to-end Performance Implications of Links with Errors

Abstract: This document discusses the specific TCP mechanisms that are problematic in environments with high uncorrected error rates, and discusses what can be done to mitigate the problems without introducing intermediate devices into the connection.

End-to-end Performance Implications of Slow Links

Abstract: This document makes performance-related recommendations for users of network paths that traverse "very low bit-rate" links.

Exploitation of wireless link QoS mechanisms in IP QoS architectures

Abstract: TCP/IP protocols make minimal assumptions about the capabilities of a link layer used to carry IP packets between nodes. The recent evolution of IP-based mobile and wireless communication has driven the design of wireless link layers and new features, including support for different QoS levels, are being included in the new link layer designs. The current IP QoS architectures are based purely on IP-layer decision making, packet buffering and scheduling through a single link-layer service access point. However, mobile wireless networks pose new challenges for IP QoS architecture implementations. In this paper, we introduce a generic convergence layer interface for controlling the capabilities of wireless network interfaces. Emphasis is on discovering the link layer functionalities and mapping IP QoS mechanisms to the available link layer features. Issues such as packet buffering and scheduling are discussed.