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In opportunistic networks, the availability of an end-to-end path is no longer required. Instead opportunistic networks may take advantage of temporary connectivity opportunities. Opportunistic networks present a demanding environment for network emulation as the traditional emulation setup, where application/transport endpoints only send and receive packets from the network following a black box approach, is no longer applicable. Opportunistic networking protocols and applications additionally need to react to the dynamics of the underlying network beyond what is conveyed through the exchange of packets. In order to support IP-level emulation evaluations of applications and protocols that react to lower layer events, we have proposed the use of emulation triggers. Emulation triggers can emulate arbitrary cross-layer feedback and can be synchronized with other emulation effects. After introducing the design and implementation of triggers in the KauNet emulator, we describe the integration of triggers with the DTN2 reference implementation and illustrate how the functionality can be used to emulate a classical DTN data-mule scenario.

When files are deleted, their information is not removed from the storage media. This is a well known fact, and there exist numerous undelete utilities to recover newly deleted files. When deleted files have been partly overwritten, the data from the part of the file that remains in unallocated space can be readily extracted by file carving. Such carving is often performed in forensic investigations. Furthermore, as a consequence of file system implementation specifics, there additionally exist small remains of the previous files in the space at the end of new files. In this paper we focus on these small remains of previous files, or micro-fragments, that exist even after all the space allocated to the previous file has been reallocated to new files. We derive expressions for modeling the number of micro-fragments that can be expected to be found, and perform experiments to evaluate the analytical model. The obtained results indicate good correspondence between the analytical predictions and the measured results.

In current forensic practice it is regularly needed to determine whether some set of files have been present on a storage medium or not. File carving techniques are readily used as a tool in such examinations. However, if all clusters holding the files searched for have been overwritten, remains of the previous files only resides in the cluster slack. In this work we elaborate on the factors that influence how many such cluster slack ¿micro-fragments¿ that can be expected to be detected. We identify a set of factors that influence the micro-fragment retention characteristics. One such characteristic is the file size distribution of the files overwriting the original files. We derive analytical expressions for three different file size distributions, which allows us to examine the retention characteristics even if the overwriting files come from different sources.

Distributed applications and transport protocolscommunicating over a satellite link may react very strongly to conditions specific to that kind of link. Providing an evaluation framework to allow tests of real implementations of such software in that context is quite a challenging task. In this paper we show how the use of the general-purpose KauNet IP-level emulator combined with satellite-specific packet loss patterns can help by reproducing losses and delays experienced on a satellite link with a simple Ethernet LAN setup. We also describe a simple experimentation platform and how a typical demonstration is carried out. Such a platform is an essential tool for developers performing continuous testing as they provide new features for e.g. video codecs or transport-level software like DCCP and its congestion control components

This user requirements report collects the results from a comprehensive on-line end-user survey that were conducted by the FIVES project. The survey was composed of 50 questions divided into a number of topical areas. In addition to the user survey results, this report also provides guidelines for Human-Computer Interaction (HCI) aspects of systems with a special focus on issues relevant to the task of large volume image classification, which is a major task in many investigations. Furthermore, the aspect of Graphical User Interface (GUI) design is also discussed from the context of FIVES needs.

KauNet is an emulation system that allows deterministic placement of packet losses and bit-errors as well as more precise control over bandwidth and delay changes. KauNet is an extension to the well-known Dummynet emulator in FreeBSD and allows the use of pattern and scenario files to increase control and repeatability. This report provides a comprehensive description of the usage of KauNet, as well as a technical description of the design and implementation of KauNet

This paper presents a DVB-RCS satellite emulation system built using the NPBox programmable network emulation system. NPBox allows system components to be modeled both at a higher abstraction level using a finite-state-machine like abstraction, and also at a lower level using customized event guards and actions. Comparison experiments show that the emulated performance is similar to that of a complex low-level emulator.

The Transmission Control Protocol (TCP) has been the dominant transport protocol within IP-based networks for many years, mainly due to the reliability it provides to its users and the congestion control it employs. However, as the amount of signaling traffic within IP-based networks have increased significantly in recent years, it has become clear that TCP is not suited for this kind of traffic. In order to meet the requirements of signaling traffic the Stream Control Transmission Protocol (SCTP) was developed by the Internet Engineering Task Force (IETF). SCTP is heavily influenced by TCP and is therefore similar to TCP in many ways. One example is the SCTP loss recovery and congestion control mechanisms which are almost identical to those of TCP. The primary purpose of this work is to study the performance and behavior of the TCP/SCTP loss recovery mechanisms for short flows. Using a simple client/server model, we evaluate the performance of these mechanism over a wide range of bandwidths, link delays and packet loss patterns. The experiments evaluate one TCP implementation and two SCTP implementations, and were conducted using network emulation. The experimental results show that there exist strong dependencies between the position of packet loss and the actual transmission time of the corresponding flow. In addition to these dependencies, we also found a number of implementation mistakes in the examined protocol implementations

Work within Department 6 of NEWCOM is organized into the areas transport protocols, architectures and cross-layer aspects, and modelling. In this deliverable we provide a second report on the frameworks/models used to support research integration within the Department. The integration approach and the defined models/frameworks are described for each one of the three areas of the department. The deliverable also includes an updated report on tools, software libraries and traces that can be shared between the partners

The Fourth Newcom Department 6 Technical Workshop was organized in Toulouse, France, on September 13-14, 2006. The workshop program contained 6 presentations and contained reports on ongoing integrated research activities as well as presentation intended to initiate additional joint research activities between the partners. All of the three areas of the department, transport protocols, architectures and cross-layer aspects, and modelling were represented with presentations. This deliverable contains the presentation material from the workshop. The included presentations are: - P2P Video Transmission over Heterogeneous Wired/Wireless Networks: A Starting Point for Integrated Research - DCCP Overview and First Experiments - Estimation of the SCTP Failover Time - Improving End to End Goodput of Ad Hoc Networks with SCTP Multihoming - A Taxonomy and Survey of SCTP Research - Integrating KAUnet and SWINE Where available the presentation notes are also included with the presentations

The Third Newcom Department 6 Technical Workshop was organized in Catania, Italy, on February 2, 2006. The workshop program contained 4 presentations and contained reports on ongoing integrated research activities as well as presentation intended to initiate additional joint research within the department. All of the three areas of the department, transport protocols, architectures and cross-layer aspects, and modelling were represented with presentations. This deliverable contains the presentation material from the workshop. The included presentations are: - P2P-based Video transmission in wireless networks - Transport Layer Handover using SCTP - WIPEMU 4G System Emulation and Sample Results - Wireless Networks Emulation Where available the presentation notes are also included with the presentations

The Second Newcom Department 6 Technical Workshop was organized in Barcelona on September 16-17, 2005. The workshop program contained 6 presentations and provided a good overview of ongoing research integration activities within the department. All of the three areas of the department, transport protocols, architectures and cross-layer aspects, and modelling were represented with presentations. This deliverable contains the presentation material from the workshop. The included presentations are: - Westwood-SCTP: A Transport Protocol for Traffic Balancing on Multihomed Hosts - Transport Layer Handover using SCTP - The Optimization of Transport Protocol over Ad-Hoc Networks - Wireless Networks Emulation - An Analytical Model of Rate-Controlled MPEG Video Sources in a UMTS Network - An Analytical Model of a Rate-controlled MPEG-4 Video Source Capturing both Intra-frame and Inter-frame Correlation As an option, a supporting paper for the presentation could also be supplied by the authors. The deliverable contains supporting articles for two of the presentations

During the first phase of NEWCOM the focus areas of Department 6 were identified and refined. A number of relevant knowledge gaps were identified for the areas transport protocols, architectures and cross-layer aspects, and modelling. In this deliverable we describe a first set of frameworks/models to support research integration within the Department. The integration approach and the defined models/frameworks are described for each one of the selected knowledge gaps. The deliverable also includes a report on tools, software libraries and traces that can be shared between the partners

The evolution of computer communications and the Internet has led to the emergence of a large number of communication technologies with widely different capabilities and characteristics. While this multitude of technologies provides a wide array of possibilities it also creates a complex and heterogeneous environment for higher-layer communication protocols. Specific link technologies, as well as overall network heterogeneity, can hamper user-perceived performance or impede end-to-end throughput. In this thesis we examine two transport layer centered approaches to improve performance. The first approach addresses the decrease in user satisfaction that occurs when web waiting times become too long. Increased transport layer flexibility with regards to reliability, together with error-resilient image coding, is used to enable a new trade-off. The user is given the possibility to reduce waiting times, at the expense of image fidelity. An experimental examination of this new functionality is provided, with a focus on image-coding aspects. The results show that reduced waiting times can be achieved, and user studies indicate the usefulness of this new trade-off. The second approach concerns the throughput degradations that can occur as a consequence of link and transport layer interactions. An experimental evaluation of the GSM environment shows that when negative interactions do occur, they are coupled to large variability in link layer round-trip times rather than simply to poor radio conditions. Another type of interaction can occur for link layers which expose higher layers to residual bit errors. Residual bit-errors create an ambiguity problem for congestion controlled transport layer protocols which cannot correctly determine the cause for a loss. This ambiguity leads to an unnecessary throughput degradation. To mitigate this degradation, loss differentiation and notification mechanisms are proposed and experimentally evaluated, Distrubution: Karlstads Universitet, , Datavetenskap, , 65188 Karlstad

TCP-Friendly Rate Control (TFRC) is a congestion control mechanism that is proposed to be used together with the new DCCP protocol. This paper provides an overview of the issues surrounding the use of TFRC for interactive media applications. Most issues are related to speci_c TFRC mechanisms, and to the use of smaller-than-MSS packets. An analytical examination of TFRCs behavior in the presence of wireless bit errors is also presented. The results show that DCCP's builtin loss differentiation can potentially be disabled for resourceconstrained devices in order to reduce overhead

This paper examines the effects of non-congestion related wireless link errors on transport protocol performance. Although link-level retransmissions to a large extent can alleviate this problem for TCP, delay-sensitive applications using DCCP may not be well served by link-level retransmissions. The loss differentiation and loss notification mechanisms in DCCP are discussed, and the TFRC congestion control is numerically evaluated for wireless loss sensitivity. The results show that the use of loss differentiation can be critical for high rate senders. The results, however, also show that the blind use of DCCP loss differentiation for low rate senders may be inefficient considering the communications and computational overheads involved. Further, a TCP implementation modified to provide loss differentiation and loss notification is experimentally examined. As expected there are considerable gains from using loss differentiation.

The EU FP6 network of excellence in wireless communication, Newcom, is a large network that covers most areas of wireless communication. The research work within Newcom is organized into a number of departments and projects where Department 6 addresses Protocols and Architectures, and Traffic Modelling for (Reconfigurable/ Adaptive) Wireless Networks. The scope of Department 6 is quite broad making it important to further identify and refine the focus areas of the department. This document summarizes research areas that fall within the competence of and are of interest for the members of Department 6 and also describes the background of the partners within these areas. A set of knowledge gaps that will be addressed within the department are identified. A number of integrating activities that can be used to coordinate the efforts of the partners are described and an action plan for the continued work within the department is provided

In certain wireless environments the common transport protocol assumption that all packet losses are due to congestion may not hold true. If transport protocols react identically to both congestion and non-congestion related losses, performance will degrade. To avoid this performance problem, transport protocols must be able to differentiate between losses that are due to congestion and losses that are due to wireless link errors. Various loss differentiation techniques exist, some based on the sender side and some on the receiver side. If the loss differentiation is performed at the receiver, loss notification is needed to inform the sender of the loss cause. The sender use the loss notification information to adapt its retransmission and congestion avoidance behavior. The work in this paper examines the effectiveness of two different notification schemes that are to be used in conjunction with receiver based loss differentiation. The first scheme uses a TCP option to explicitly convey the a loss counter and the sequence number of the last corrupted packet. The second scheme uses the generation of additional dup-acks as a way to implicitly influence the retransmission and congestion behavior of the sender. The advantage of the second scheme is that it requires no changes at the sender side TCP implementation. However, since the second scheme can not change the basic loss behavior of halving the congestion window of TCP, its performance is reduced in relation to the first scheme. This paper provides a description of the design of these two loss notification schemes. Additionally, an experimental evaluation is presented, based on a FreeBSD kernel implementation of the two notification schemes in conjunction with checksum based loss differentiation

In a wireless environment the common transport protocol assumption that all packet losses are due to congestion no longer holds true. If the transport protocols react identically to both congestion and noncongestion related losses, performance will degrade. To avoid this performance problem, transport protocols must be able to differentiate between losses that are due to congestion and losses that are due to wireless link errors. Suitable congestion avoidance behavior can then be applied as appropriate. This paper overviews previous work on loss differentiation, and proposes a checksumbased scheme. The proposed scheme reuses the checksums already available at various layers in the receiver endhost protocol stack. It is an endtoend solution for the case where the lossy link is the last hop. Header decoding, data integrity and other issues related to the implementation of our cecksumbased scheme are also discussed

This paper reports on experiments with a web-browsing application using PRTP, a new TCP-based protocol. With PRTP it is possible for an application to specify, and receive, a more flexible transport service than with TCP or UDP. A web application using PRTP is presented, and experiments examining the performance implications of using PRTP instead of TCP are discussed. The experiments used actual implementations of TCP and PRTP to conduct web page transfers over a network capable of emulating different network characteristics. The JPEG part of the web pages were recoded using a robust JPEG coding and transmitted using the partially reliable transport service made possible by PRTP. A novelty in these experiments was that the packet loss could be controlled in detail, allowing specific packets in a stream to be lost as opposed to losing packets with a certain probability. The experiments were performed for five different network characteristics each at six different loss ratios using three different web pages. The results show that using a partially reliable transport service in conjunction with the presented application provides throughput gains in the majority of cases, at the expense of slightly degraded image quality. The gains relative to TCP are up to 41% with a mean of 7.2%.