Across the Oceans : Development of Overseas Business Information Transmission, 1815-1875

Earlier studies have shown that the speed of information transmission developed radically during the 19th century. The fast development was mainly due to the change from sailing ships and horse-driven coaches to steamers and railways, as well as the telegraph. Speed of information transmission has normally been measured by calculating the duration between writing and receiving a letter, or between an important event and the time when the news was published elsewhere. As overseas mail was generally carried by ships, the history of communications and maritime history are closely related. This study also brings a postal historical aspect to the academic discussion. Additionally, there is another new aspect included. In business enterprises, information flows generally consisted of multiple transactions. Although fast one-way information was often crucial, e.g. news of a changing market situation, at least equally important was that there was a possibility to react rapidly. To examine the development of business information transmission, the duration of mail transport has been measured by a systematic and commensurable method, using consecutive information circles per year as the principal tool for measurement. The study covers a period of six decades, several of the world's most important trade routes and different mail-carrying systems operated by merchant ships, sailing packets and several nations' steamship services. The main sources have been the sailing data of mail-carrying ships and correspondence of several merchant houses in England. As the world's main trade routes had their specific historical backgrounds with different businesses, interests and needs, the systems for information transmission did not develop similarly or simultaneously. It was a process lasting several decades, initiated by the idea of organizing sailings in a regular line system. The evolution proceeded generally as follows: originally there was a more or less irregular system, then a regular system and finally a more frequent regular system of mail services. The trend was from sail to steam, but both these means of communication improved following the same scheme. Faster sailings alone did not radically improve the number of consecutive information circles per year, if the communication was not frequent enough. Neither did improved frequency advance the information circulation if the trip was very long or if the sailings were overlapping instead of complementing each other. The speed of information transmission could be improved by speeding up the voyage itself (technological improvements, minimizing the waiting time at ports of call, etc.) but especially by organizing sailings so that the recipients had the possibility to reply to arriving mails without unnecessary delay. It took two to three decades before the mail-carrying shipping companies were able to organize their sailings in an optimal way. Strategic shortcuts over isthmuses (e.g. Panama, Suez) together with the cooperation between steamships and railways enabled the most effective improvements in global communications before the introduction of the telegraph.

Cross-layer Assisted TCP Algorithms for Vertical Handoff

The ever expanding growth of the wireless access to the Internet in recent years has led to the proliferation of wireless and mobile devices to connect to the Internet. This has created the possibility of mobile devices equipped with multiple radio interfaces to connect to the Internet using any of several wireless access network technologies such as GPRS, WLAN and WiMAX in order to get the connectivity best suited for the application. These access networks are highly heterogeneous and they vary widely in their characteristics such as bandwidth, propagation delay and geographical coverage. The mechanism by which a mobile device switches between these access networks during an ongoing connection is referred to as vertical handoff and it often results in an abrupt and significant change in the access link characteristics. The most common Internet applications such as Web browsing and e-mail make use of the Transmission Control Protocol (TCP) as their transport protocol and the behaviour of TCP depends on the end-to-end path characteristics such as bandwidth and round-trip time (RTT). As the wireless access link is most likely the bottleneck of a TCP end-to-end path, the abrupt changes in the link characteristics due to a vertical handoff may affect TCP behaviour adversely degrading the performance of the application. The focus of this thesis is to study the effect of a vertical handoff on TCP behaviour and to propose algorithms that improve the handoff behaviour of TCP using cross-layer information about the changes in the access link characteristics. We begin this study by identifying the various problems of TCP due to a vertical handoff based on extensive simulation experiments. We use this study as a basis to develop cross-layer assisted TCP algorithms in handoff scenarios involving GPRS and WLAN access networks. We then extend the scope of the study by developing cross-layer assisted TCP algorithms in a broader context applicable to a wide range of bandwidth and delay changes during a handoff. And finally, the algorithms developed here are shown to be easily extendable to the multiple-TCP flow scenario. We evaluate the proposed algorithms by comparison with standard TCP (TCP SACK) and show that the proposed algorithms are effective in improving TCP behavior in vertical handoff involving a wide range of bandwidth and delay of the access networks. Our algorithms are easy to implement in real systems and they involve modifications to the TCP sender algorithm only. The proposed algorithms are conservative in nature and they do not adversely affect the performance of TCP in the absence of cross-layer information.

Viivesietoisten verkkojen nykytila ja tulevaisuuden haasteet

Delay and disruption tolerant networks (DTNs) are computer networks where round trip delays and error rates are high and disconnections frequent. Examples of these extreme networks are space communications, sensor networks, connecting rural villages to the Internet and even interconnecting commodity portable wireless devices and mobile phones. Basic elements of delay tolerant networks are a store-and-forward message transfer resembling traditional mail delivery, an opportunistic and intermittent routing, and an extensible cross-region resource naming service. Individual nodes of the network take an active part in routing the traffic and provide in-network data storage for application data that flows through the network. Application architecture for delay tolerant networks differs also from those used in traditional networks. It has become feasible to design applications that are network-aware and opportunistic, taking an advantage of different network connection speeds and capabilities. This might change some of the basic paradigms of network application design. DTN protocols will also support in designing applications which depend on processes to be persistent over reboots and power failures. DTN protocols could also be applicable to traditional networks in cases where high tolerance to delays or errors would be desired. It is apparent that challenged networks also challenge the traditional strictly layered model of network application design. This thesis provides an extensive introduction to delay tolerant networking concepts and applications. Most attention is given to challenging problems of routing and application architecture. Finally, future prospects of DTN applications and implementations are envisioned through recent research results and an interview with an active researcher of DTN networks.

TCP Performance with Vertical Handoff

With the proliferation of wireless and mobile devices equipped with multiple radio interfaces to connect to the Internet, vertical handoff involving different wireless access technologies will enable users to get the best of connectivity and service quality during the lifetime of a TCP connection. A vertical handoff may introduce an abrupt, significant change in the access link characteristics and as a result the end-to-end path characteristics such as the bandwidth and the round-trip time (RTT) of a TCP connection may change considerably. TCP may take several RTTs to adapt to these changes in path characteristics and during this interval there may be packet losses and / or inefficient utilization of the available bandwidth. In this thesis we study the behaviour and performance of TCP in the presence of a vertical handoff. We identify the different handoff scenarios that adversely affect TCP performance. We propose several enhancements to the TCP sender algorithm that are specific to the different handoff scenarios to adapt TCP better to a vertical handoff. Our algorithms are conservative in nature and make use of cross-layer information obtained from the lower layers regarding the characteristics of the access links involved in a handoff. We evaluate the proposed algorithms by extensive simulation of the various handoff scenarios involving access links with a wide range of bandwidth and delay. We show that the proposed algorithms are effective in improving the TCP behaviour in various handoff scenarios and do not adversely affect the performance of TCP in the absence of cross-layer information.

Jatrophanviljely ja maankäyttö Vietnamissa

Biofuels are under discussion all over the world today. There are fears that the farming of biofuel plants hurts food production and weakens the food security of the poor. On the other hand, biofuel production could lessen the green house gas emissions caused by transportation, and it could also spread the profits from fuel markets more evenly between countries. The aim of this thesis is to find out how an oil plant called jatropha curcas L., which is used for biodiesel production, can affect the sustainability of livelihoods in Vietnam from the point of view of land use. Special attention is given to the effects of jatropha farming on food production, land productivity, natural resources of livelihoods and global livelihood. Jatropha belongs to the family Euphorbiaceae, and it grows naturally in tropical and subtropical areas. It can be grown on poor soils, its seeds have high oil content, and it cannot be eaten due to its toxicity. The plant grows naturally in Vietnam, and during the past few years it has also begun to be farmed for making biodiesel. Population growth in Vietnam has slowed down, but the population's standard of living and energy consumption are still rising quickly. An interest in the international biodiesel markets has awoken following Vietnam's opening up to international trade. Jatropha diesel plays a significant part in Vietnam’s clean fuel strategy, and many companies have set up jatropha plantations to produce raw material for biodiesel. Diesel made from jatropha is planned to be used both locally and for export. This thesis uses a theoretical concept of sustainable livelihoods. According to the theory, the resources that people have shape their livelihood possibilities. Farming of jatropha affects the livelihoods of people especially through land use, as land use changes have effects on many of the livelihood resources. In addition to the written sources, the material of the thesis is based on 14 interviews in Vietnam and Finland, and on observation during a field trip to Northern Vietnam in the spring of 2008. The results of the thesis show that jatropha diesel can support the sustainability of livelihoods at different scales if it is produced with deliberation. However, positive results are only possible if decisions are made carefully and more experience is collected. The possibilities of sustainable jatropha farming depend mainly on the previous land use methods and ways of production. Farming of jatropha does not threaten food production in Vietnam if the farming plans are implemented as planned. Jatropha may take some land from cassava, but at the same time, food production can be increased if mixed farming is used on some farms. Plenty of new research information and practical experiences on jatropha farming has to be collected before results of the real sustainability of the farming are ready. Carefully considered continuation and documentation of present and future projects would help to understand the possibilities of jatropha diesel in Vietnam and elsewhere.