University of Helsinki Department of Computer Science

Department of Computer Science

Department information


IIP Cross Project

Predecessor projects
IIP Mixture
IIP Mobile & IIP Wireless

In collaboration with

- Brief project description

The standardization body for the Internet protocols, the Internet Engineering Task Force (IETF), is specifying various performance enhancements to TCP and has documented the impact of problematic link-layer characteristics to the Internet protocols. In addition, mitigations to the performance implications of problematic link characteristics and approaches to enhance the performance that the Internet protocols, particularly TCP, attain in the face of particular link characteristics have being documented and a number of further proposals are work in progress.

The research projects IIP Mobile and IIP Wireless addressed primarily issues on TCP behavior and TCP performance enhancements over wireless links. The focus in IIP Mixture project was shifted towards Internet solutions that are able to handle heterogeneous traffic smoothly over wireless links. The key areas of interest included studies on how different types of competing traffic (traffic mixtures) behave and how the behaviour could be affected with IP-QoS mechanisms such as differentiated packet treatment (DiffServ) and active queue management (e.g., RED).

The IIP Cross project studies how the Internet transport protocol performance could be improved in mobile and wireless networks with an appropriate co-operation across the different protocol layers (transport, network, and link layer).

The current Internet architecture and protocols adhere to the quite strict division of the data communication functions into different protocol layers. Introducing additional co-operation across protocol layers enables a new set of transport protocol performance improvements. The focus of the project is on studying how the TCP protocol behaves in a mobile environment with vertical handovers, where the end user terminal moves and the link characteristics of the access link may change dramatically after the handover. Various enhancements to the TCP protocol and algorithms are studied, including TCP sender algorithms that adjust the TCP retransmission timeout and congestion control parameters after a vertical handover as well as the TCP Quick Start mechanism for better estimating the available end-to-end network capacity after the handover. In addition, the project studies how explicit loss notifications from the link layer can be used in improving TCP performance and how an appropriate co-operation between IP and link-level QoS mechanisms improves the behavior of heterogeneous traffic loads in a wireless environment.

- Project members

Kimmo Raatikainen
Markku Kojo

Davide Astuti
Laila Daniel
Lauri Hyttinen
Ilpo Järvinen
Aki Nyrhinen
Pasi Sarolahti

Markku Kojo -