Andreas Schorr

Adaptive media streaming in heterogeneous wireless networks

In this paper we present a system for IP based networks which adapts media streams to the respective characteristics of different (wireless) access networks. Inside the mobile node, an interface selection subsystem monitors characteristics of network interfaces and triggers vertical handovers based on policies supplied by the operator. A service subsystem initiates media stream adaptation to match network resource availability and provider constraints. A media subsystem on mobile and correspondent node transmits the media streams and applies appropriate error correction mechanisms (like FEC, ARQ) depending on network characteristics. We evaluate vertical handover behaviour of our system in a combined GPRS - WLAN testbed and analyze the impact of several error correction mechanisms on the perceived video quality.

A Session-Initiation-Protocol-Based Middleware for Multi-Application Management

The deployment of multimedia services in next- generation networks is a challenge due to the high configuration complexity of the streaming process in different stationary and mobile sub-networks and for various user devices. The session initiation protocol (SIP) has proven to be a suitable mechanism to handle the control of multimedia services in such networks. However, the current standardization and implementation of SIP do not allow the simultaneous coordination of multiple concurrent applications on a single device, as the prescribed realization of the SIP state machines (transactions) does not consider mutual access of applications to a single SIP stack. This paper presents a SIP- based mechanism for synchronized management of services in a shared environment. We have developed a middleware that facilitates the uniform access of multiple applications towards one or multiple SIP stacks to enable prioritization of services and centralized resource coordination of concurrent SIP applications on a single terminal or server.