Joachim Sachs

Ambient networks: an architecture for communication networks beyond 3G

In this article we present a new networking concept referred to as ambient networks, which aims to enable the cooperation of heterogeneous networks belonging to different operator or technology domains. We aim to provide a domain-structured edge-to-edge view for the network control to embrace the heterogeneity arising from the different network control technologies. In this way, it appears as homogeneous to the users of the network services. We aim for an instant network composition to allow rapid adaptation of the network domain topology as required for moving networks. This new view of network composition allows us to treat the communication endpoints as a special case of network domains as well. We introduce the ambient control space, which enables the ambient networks concept and introduce its main features. Two ambient control space functions, media delivery and generic link layer, are presented in more detail. AMBIENT NETWORKS: AN ARCHITECTURE FOR COMMUNICATION NETWORKS BEYOND 3G

Performance evaluation of a TCP proxy in WCDMA networks

The article addresses the end-to-end performance of TCP in a scenario where WCDMA is used as the access link. In particular, the performance gain that can be achieved by placing a TCP split connection proxy in the WCDMA core network is examined. It is well known that performance enhancing proxies are able to improve the performance of TCP over wireless links that suffer from impairments. However, while previous work on TCP proxies for wireless systems either focused on other wireless systems, like wireless LAN or satellites, or provided a more generic framework, we address in detail the characteristics of a WCDMA access scenario supported by a TCP proxy. The characteristics of WCDMA as perceived by TCP are discussed thoroughly. We argue that the motivation for introducing a proxy is only to overcome problems stemming from a large bandwidth delay product and not to assist local transport layer error recovery at the wireless link. Based on simulations that consider both link layer protocols and TCP, the end-to-end performance for file downloads is investigated. Simulation results show that a proxy can significantly improve performance in the case of high data rates like 384 kb/s. For lower data rates, like 64 and 128 kb/s, it is sufficient to use a well configured TCP implementation.