Sami Iren

The transport layer: tutorial and survey

Transport layer protocols provide for end-to-end communication between two or more hosts. This paper presents a tutorial on transport layer concepts and terminology, and a survey of transport layer services and protocols. The transport layer protocol TCP is used as a reference point, and compared and contrasted with nineteen other protocols designed over the past two decades. The service and protocol features of twelve of the most important protocols are summarized in both text and tables.

Progressively authenticated image transmission

Network-conscious image compression has been shown to provide faster progressive display than traditional compression algorithms, when images are transmitted over lossy low-bandwidth packet-switched networks. In this paper, we combine the advantages of wavelet-based, network-conscious image compression with a blind digital image signature technique. Together these two approaches investigate progressive display where each progressive image can be authenticated by the receiver in real time.

Network-conscious GIF image transmission over the Internet

Traditional image compression techniques seek the smallest possible file size for a given level of image quality. By contrast, network-conscious image compression techniques take into account the fact that a compressed image will be transmitted over a packet-switched network that may lose and reorder packets. We describe GIFNCa, a network-conscious revision of the popular GIF89a standard. As with GIF89a, GIFNCa compresses an image using LZW encoding, however GIFNCa does so using an Application Level Framing approach. The data is segmented into path MTU-size data units, each of which can be independently decompressed and displayed on its own. Under lossy network conditions, when used in combination with an unordered transport protocol, GIFNCa permits faster progressive display at the receiver than GIF89a over an ordered transport protocol. This advantage comes in exchange for a small penalty in overall compression. This paper defines GIFNCa, and presents preliminary experimental data concerning this tradeoff. The overall goal of this research is to illustrate (1) the value of considering network characteristics in designing image formats, and (2) the value of unordered transport service.

Testing environment for innovative transport protocols

This paper describes the development of a test environment for innovative transport protocols. Central to this work is the development of a universal transport library (UTL). The UTL is a library of transport protocols that provides application programmers the ability to write to a single application programming interface (API), then test their application with many different transport protocols. The UTL also allows for rapid prototyping of transport protocols at the user level. The UTL has been incorporated into two multimedia communication systems designed to provide better performance over lossy networks by using innovative transport protocol features: NETCICATS (a Network-Conscious Image Compression and Transmission System) and ReMDoR (a Remote Multimedia Document Retrieval system). These three tools facilitate the evaluation of flexible transport protocols and compression techniques for multimedia communications over lossy battlefield networks.

Network-Conscious Compressed Images over Wireless Networks

We apply the concept of network-consciousness to image compression, an approach that does not simply optimize compression, but which optimizes overall performance when compressed images are transmitted over a lossy packet-switched network such as the Internet. Using an Application Level Framing philosophy, an image is compressed into path MTU-size Application Data Units (ADUs) at the application layer. Each ADU carries its semantics, that is, it contains enough information to be processed independently of all other ADUs. Therefore each ADU can be delivered to the receiving application out-of-order, thereby enabling faster progressive display of images. We explain why this approach is useful in general and specifically for wireless/heterogeneous environments.

Network-conscious compressed image transmission over battlefield networks

We introduce an image compression and transmission system for battlefield networks. The system is based on network-conscious image compression, an approach to compression that does not simply maximize compression, but which optimizes overall performance when compressed images are transmitted over a lossy, packet-switched battlefield network. Using an application level framing philosophy, an image is compressed into path-maximum transmission unit-size application data units (ADUs) at the application layer. Each ADU is independent of others and carries its own semantics, that is, each ADU is a self-contained unit possessing all information necessary for decoding and displaying the information within that packet. Each independent ADU can be delivered to the receiving application out-of-order, thereby enabling faster progressive display of the image. We combine network-conscious image compression with an embedded focusing feature to provide a system that can be used in battlefield scenarios such as telemedicine or intelligence gathering.

NETCICATS: Network-Conscious Image Compression and Transmission System

NETCICATS is a software system for empirically evaluating network-conscious image compression, an approach that does not simply optimize compression, but which optimizes overall performance when compressed images are transmitted over a lossy packet-switched network such as the Internet. Based on Application Level Framing, an image is compressed into path-MTU-size Application Data Units (ADUs) at the application layer. Each ADU contains enough information to be processed independently of all other ADUs. Each ADU can be delivered to the receiving application out-of-order, thereby enabling faster progressive display of images. NETCICATS allows the empirical investigation of the combination of transport protocol features and compression algorithms that perform best over a lossy packet-switched network. It includes software components from the network layer (e.g., lossy router), transport layer (e.g., innovative transport protocols), and application layer (e.g., compression algorithms, browsers, etc.). We describe each component of the system and explain how the whole system is used. This paper also presents two network-conscious image compression algorithms: network-conscious GIF and wavelet zerotree encoding.

Application level framing applied to image compression

Two well-known wavelet zerotree encoding algorithms, Embedded Zerotree Encoding (Ezw) and Set Partitioning in Hierarchical Trees (Spiht), provide excellent progressive display when images are transmitted over reliable networks. However, both algorithms are state-dependent and can perform poorly over unreliable networks. We apply the concept of network-conscious image compression to theSpiht wavelet zerotree encoding algorithm, to improve its performance over unreliable networks. Experimental results confirm the utility of network-conscious image compression concept.RésuméLe codage par ondelettes avec quantification hiérarchique de type «arbre nul» constitue une façon efficace de comprimer les images. Dans une perspective de transmission d’images, deux algorithmes de codage classiques,Ezw (Embedded Zerotree Encoding) etSpiht (Set Partitioning in Hierarchical Trees), permettent un affichage progressif de bonne qualité lorsque les images sont transmises sur un réseau fiable. Cependant, les deux algorithmes dépendent de l’état du réseau et une erreur introduite par le réseau peut altérer sérieusement le résultat. Nous appliquons le concept de compression d’image consciente du réseau à l’algorithme spiht pour l’amélioration de ses performances dans des environnement réseau non fiables. Nos résultats confirment l’avantage de cette technique dans certaines situations de qualités de service.

SPIHT-NC: network-conscious zerotree encoding

Wavelet zerotree encoding has been proven to be an efficient way of compressing still images. Two well-known zerotree encoding algorithms, embedded zerotree encoding (EZW) and set partitioning in hierarchical trees (SPIHT), provide excellent progressive display when images are transmitted over reliable networks. However, both algorithms are state-dependent and can perform poorly over unreliable networks. In this paper, we apply the concept of network-conscious image compression to the SPIHT wavelet zerotree encoding algorithm, to improve its performance over unreliable networks. Experimental results confirm the utility of network-conscious image compression concept.