A survey of performance enhancement of transmission control protocol (TCP) in wireless ad hoc networks

This Article is provided by the Brunel Open Access Publishing Fund - Copyright @ 2011 Springer OpenTransmission control protocol (TCP), which provides reliable end-to-end data delivery, performs well in traditional wired network environments, while in wireless ad hoc networks, it does not perform well. Compared to wired networks, wireless ad hoc networks have some specific characteristics such as node mobility and a shared medium. Owing to these specific characteristics of wireless ad hoc networks, TCP faces particular problems with, for example, route failure, channel contention and high bit error rates. These factors are responsible for the performance degradation of TCP in wireless ad hoc networks. The research community has produced a wide range of proposals to improve the performance of TCP in wireless ad hoc networks. This article presents a survey of these proposals (approaches). A classification of TCP improvement proposals for wireless ad hoc networks is presented, which makes it easy to compare the proposals falling under the same category. Tables which summarize the approaches for quick overview are provided. Possible directions for further improvements in this area are suggested in the conclusions. The aim of the article is to enable the reader to quickly acquire an overview of the state of TCP in wireless ad hoc networks.This study is partly funded by Kohat University of Science & Technology (KUST), Pakistan, and the Higher Education Commission, Pakistan

Decisive analysis of current state of the art in congestion aware and control routing models in ad hoc networks

An important aspect that portrays a crucial position in the ad hoc network routing is congestion. Almost every research analysis is en-route in adapting this key factor in addressing congestion. This problem cannot be totally addressed by the regular TCP protocol based networks, keeping in view the special assets which include multi hop sharing etc, which is difficult to ascertain in ad hoc networks. Many attempts have been made and are in progress by researchers to provide unique solutions to the above mentioned problems. This paper projects a vital study on jamming aware and different routing standards that have been dealt with in recent times

Reliable Transport Method for Hybrid Networks

Nykyaikaisten tietoverkkojen monipuolistuessa käytettyjen teknologioiden määrä tulee lisääntymään. Langattomista ja langallisista komponenteista rakentuvat liityntäverkot ovat entistä laajemmassa käytössä jo nykyään. Tämä asettaa tavoitteita paitsi laitteiden yhteistoiminnalle, myös tiedonsiirron luotettavuudelle. Erityisesti langattomalla siirtotiellä esiintyvät häiriöt ja niistä johtuvat pakettihukat ovat uhka luotettavalle tiedonsiirrolle. Näiden pakettihukkien estäminen ja niistä palautuminen ovat tärkeitä keinoja luotettavuuden parantamiseksi. Tässä työssä on mallinnettu ja simuloitu eräs menetelmä luotettavan tiedonsiirron toteuttamiseksi. Menetelmä on nimeltään HBH, ja se on hyppykohtaisiin negatiivisiin kuittauksiin perustuva menetelmä. Sen tarkoituksena on varmistaa luotettava tiedonsiirto korjaamalla linkillä tapahtuvat pakettihukat nopeasti ja tehokkaasti. Mallinnukseen on käytetty OPNET Modeler -ohjelmaa. Simulaatioiden perusteella saatiin selville, että menetelmä parantaa linkkikohtaista luotettavuutta huomattavasti. Erityisesti 10-30% pakettihukilla toiminta tehostuu huomattavasti verrattuna varmistamattomaan tilanteeseen. Kvalitatiivinen analyysi TCP:n toiminnasta menetelmän kanssa antoi erittäin lupaavia tuloksia suorituskyvyn parantumisesta erityisesti kun pakettihukkaa alkoi esiintyä huomattavasti.As modern communication networks become more diverse, the amount of utilised technologies will increase in the future. Access networks comprised of wireless and wired components are in even wider use than before. This sets goals not only for device interoperability, but also for transmission reliability. Especially wireless medium interference and packet loss caused by it is a threat to reliable communication in environments using those technologies. Avoidance of and recovery from these packet losses are key methods to improve reliability. In this Thesis a method for reliable transmission is modeled and simulated. The method is called HBH (hop-by-hop) and it is a method based on hop-by-hop negative acknowledgements. Its purpose is to secure reliable transmission by repairing link-based packet losses quickly and efficiently. The method is modeled using OPNET Modeler. Based on simulations we discovered that the method improves link-based reliability significantly. Especially when experiencing packet loss of 10 to 30 percent the communication is substantially improved compared to the case without any reliability support. Qualitative analysis on TCP operation gives very promising results on improving performance, especially when significant packet loss is present

MANETs: Internet Connectivity and Transport Protocols

A Mobile Ad hoc Network (MANET) is a collection of mobile nodes connected together over a wireless medium, which self-organize into an autonomous multi-hop wireless network. This kind of networks allows people and devices to seamlessly internetwork in areas with no pre-existing communication infrastructure, e.g., disaster recovery environments. Ad hoc networking is not a new concept, having been around in various forms for over 20 years. However, in the past only tactical networks followed the ad hoc networking paradigm. Recently, the introduction of new technologies such as IEEE 802.11, are moved the application field of MANETs to a more commercial field. These evolutions have been generating a renewed and growing interest in the research and development of MANETs. It is widely recognized that a prerequisite for the commercial penetration of the ad hoc networking technologies is the integration with existing wired/wireless infrastructure-based networks to provide an easy and transparent access to the Internet and its services. However, most of the existing solutions for enabling the interconnection between MANETs and the Internet are based on complex and inefficient mechanisms, as Mobile-IP and IP tunnelling. This thesis describes an alternative approach to build multi-hop and heterogeneous proactive ad hoc networks, which can be used as flexible and low-cost extensions of traditional wired LANs. The proposed architecture provides transparent global Internet connectivity and address autocofiguration capabilities to mobile nodes without requiring configuration changes in the pre-existing wired LAN, and relying on basic layer-2 functionalities. This thesis also includes an experimental evaluation of the proposed architecture and a comparison between this architecture with a well-known alternative NAT-based solution. The experimental outcomes confirm that the proposed technique ensures higher per-connection throughputs than the NAT-based solution. This thesis also examines the problems encountered by TCP over multi-hop ad hoc networks. Research on efficient transport protocols for ad hoc networks is one of the most active topics in the MANET community. Such a great interest is basically motivated by numerous observations showing that, in general, TCP is not able to efficiently deal with the unstable and very dynamic environment provided by multi-hop ad hoc networks. This is because some assumptions, in TCP design, are clearly inspired by the characteristics of wired networks dominant at the time when it was conceived. More specifically, TCP implicitly assumes that packet loss is almost always due to congestion phenomena causing buffer overflows at intermediate routers. Furthermore, it also assumes that nodes are static (i.e., they do not change their position over time). Unfortunately, these assumptions do not hold in MANETs, since in this kind of networks packet losses due to interference and link-layer contentions are largely predominant, and nodes may be mobile. The typical approach to solve these problems is patching TCP to fix its inefficiencies while preserving compatibility with the original protocol. This thesis explores a different approach. Specifically, this thesis presents a new transport protocol (TPA) designed from scratch, and address TCP interoperability at a late design stage. In this way, TPA can include all desired features in a neat and coherent way. This thesis also includes an experimental, as well as, a simulative evaluation of TPA, and a comparison between TCP and TPA performance (in terms of throughput, number of unnecessary transmissions and fairness). The presented analysis considers several of possible configurations of the protocols parameters, different routing protocols, and various networking scenarios. In all the cases taken into consideration TPA significantly outperforms TCP

Adaptive protocols for mobile ad hoc networks

Recent advances in low-power technologies have resulted in the proliferation of inexpensive handheld mobile computing devices. Soon, just like the Internet empow- ered a whole new world of applications for personal computers, the development and deployment of robust ubiquitous wireless networks will enable many new and exciting futuristic applications. Certain to be an important part of this future is a class of networks known as "mobile ad hoc networks." Mobile ad hoc networks (or simply "ad hoc networks") are local-area networks formed "on the spot" between collocated wireless devices. These devices self-organize by sharing information with their neigh- bors to establish communication pathways whenever and wherever they are. For ad hoc networks to succeed, however, new protocols must be developed that are capable of adapting to their dynamic nature. In this dissertation, we present a number of adaptive protocols that are designed for this purpose. We investigate new link layer mechanisms that dynamically monitor and adapt to changes in link quality, including a protocol that uses common control messages to form a tight feedback control loop for adaptation of the link data rate to best match the channel conditions perceived by the receiver. We also investigate routing protocols that adapt route selection according to network characteristics. In particular, we present two on-demand routing protocols that are designed to take advantage of the presence of multirate links. We then investigate the performance of TCP, showing how communication outages caused by link failures and routing delays can be very detrimental to its performance. In response, we present a solution to this problem that uses explicit feedback messages from the link layer about link failures to adapt TCP's behavior. Finally, we show how link failures in heterogeneous networks containing links with widely varying bandwidth and delay can cause repeated "modal" changes in capacity that TCP is slow to detect. We then present a modifed version of TCP that is capable of more rapidly detecting and adapting to these changes

Progetto e realizzazione di un protocollo di trasporto per reti Ad Hoc Multi-Hop

A Mobile Ad hoc Network (MANET) is a collection of mobile nodes connected together over a wireless medium, which self-organize into an autonomous multi-hop wireless network. This kind of networks allows devices to seamlessly internetwork in areas with no pre-existing communication infrastructure, e.g., disaster recovery environments. This thesis examines the problems encountered by TCP over multi-hop ad hoc networks. TCP is not able to efficiently deal with the unstable and very dynamic environment provided by multi-hop ad hoc networks. This is because TCP implicitly assumes that packet loss is almost always due to congestion phenomena causing buffer overflows at intermediate routers. Furthermore, it also assumes that nodes are static (i.e., they do not change their position over time). Unfortunately, these assumptions do not hold in MANETs, since in this kind of networks packet losses due to interference and link-layer contentions are largely predominant, and nodes may be mobile. This thesis presents a new lightweight transport protocol (TPA) designed from scratch, that provides a connection-oriented, reliable type of service. TPA differs from TCP in a number of ways. Specifically, the data transfer and the congestion control algorithms have been re-designed. Furthermore, TPA explicitly detects and deals with both route failures and route changes and it can also leverage cross-layer interactions with the routing protocol, when available. This thesis also includes a preliminary simulative evaluation of TPA

Distributed services for mobile ad hoc networks

A mobile ad hoc network consists of certain nodes that communicate only through wireless medium and can move arbitrarily. The key feature of a mobile ad hoc network is the mobility of the nodes. Because of the mobility, communication links form and disappear as nodes come into and go out of each other's communica- tion range. Mobile ad hoc networks are particularly useful in situations like disaster recovery and search, military operations, etc. Research on mobile ad hoc networks has drawn a huge amount of attention recently. The main challenges for mobile ad hoc networks are the sparse resources and frequent mobility. Most of the research work has been focused on the MAC and routing layer. In this work, we focus on distributed services for mobile ad hoc networks. These services will provide some fundamental functions in developing various applications for mobile ad hoc networks. In particular, we focus on the clock synchronization, connected dominating set, and k-mutual exclusion problems in mobile ad hoc networks

The Bologna Process and Its Impact in Europe: It\u27s So Much More than Degree Changes

The Bologna Process is a massive, multi-year project designed to create the European Higher Education Area by the year 2010. It began ten years ago, when four European Union(EU) countries signed a relatively vague declaration. It has grown to include forty-six countries, including all of the EU Member States and nineteen non-EU countries. The Bologna Process countries have agreed on ten action lines for restructuring European higher education. These action lines are nothing short of revolutionary--they address everything from a three-cycle degree system (e.g., bachelor-master\u27s-doctorate degrees), European-wide quality assurance efforts, mobility of higher education students and staff, recognition in one European country of studies undertaken in another European country, and the suitability of education for the marketplace. Because of the number of countries participating in the Bologna Process, its ambitious goals, and its demonstrated commitment to achieving those goals, the Bologna Process is an extremely significant development that will be important not only in Europe but elsewhere in the world. This Article is designed to provide one-stop shopping for understanding the Bologna Process, which will allow the reader to learn about all of its initiatives and action lines, and to understand and place in context future developments. This Article covers developments through the May 2007 London Ministerial meeting. It concludes with an examination of the impact of the Bologna Process on European higher education, including legal education

The Bologna Process and Its Impact in Europe: It\u27s so Much More than Degree Changes

The Bologna Process is a massive, multi-year project designed to create the European Higher Education Area by the year 2010. it began ten eyars ago, when four European Union (EU) countries signed a relatively vague declaration. It has grown to include forty-six countries, including all of the EU Member States and nineteen non-EU countries. The Bologna Process countries have agreed on ten action lines for restructuring European higher education. These action lines are nothing short of revolutionary - they address everything from a three-cycle degree system (e.g., bachelor-master\u27s-doctorate degrees), European-wide quality assurance efforts, mobility of higher education students and staff, recognition in one European country of studies undertaken in another European country, and the suitability of education for the marketplace. Because of the number of countries participating in the Bologna Process, its ambitious goals, and its demonstrated commitment to achieving those goals, the Bologna Process is an extremely significant development that will be important not only in Europe but elsewhere in the world. This Article is designed to provide one-stop shopping for understanding the Bologna Process, which will allow the reader to learn about all of its initiatives and action lines, and to understand and place in context future developments. This Article covers developments through the May 2007 Ministerial meeting. It concludes with an examination of the impact of the Bologna Process on European higher education, including legal education