Workshop Mensch-Computer-Vernetzung Vergabe der IP-Adressen

Workshop Mensch-Computer-Vernetzung Stand und Perspektiven des Einsatzes einer "Voice over IP"-Lösung für die Telefonie am URZ der TU Chemnitz auf Grundlage der VOCAL-Server-Suite

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: Loss; TFRC; AIMD; TCP. Includes bibliographical references (p. 147-155).

In general, rural areas in Africa are seen as unprofitable by operators and hence these areas do not benefit from typical wired Internet access. Due to the cost involved, only a small number of people in Africa benefit from the Internet. On the other hand, the Global System for Mobile communications (GSM) has thoroughly penetrated Africa and in many cases unutilized capacity exists in rural areas. Since the cost of GSM services is still extremely high when compared to the average income of African communities, many organizations are now considering alternative business models for the provision of Internet access to disadvantaged populations. To try to bridge the digital divide, the aim of this contribution is to show that basic but affordable Internet Protocol (IP) connectivity can be provided to rural communities by using spare capacity on GSM networks to carry Wireless Local Area Network (WLAN) traffic. Since the main problem with WLAN in Africa is not the last mile, but rather finding a way to connect the wireless access point to an existing backbone network, a solution to integrate WLAN with GSM is proposed.

Η παρούσα διπλωματική εργασία παρουσιάζει το πρόβλημα της εξάντλησης των IPv4 διευθύνσεων καθώς και τη διαδικασία μετάβαση στο IPv6. Πιο συγκεκριμένα, παρουσιάζονται τεχνολογίες και τεχνικές που έχουν προταθεί σε διεθνή forum για την μετάβαση από IPv4 σε IPv6 και αφορούν MPLS δίκτυα telecom provider. Στο 5ο κεφάλαιο δημιουργείται ένα περιβάλλον εξομοίωσης δικτυακών συσκευών και προσομοιώνονται βέλτιστες πρακτικές. Πολλοί providers έχουν επενδύσει τα τελευταία χρόνια στην εγκατάσταση IPv4-MPLS για τα δίκτυα κορμού τους. Από μια τέτοια μακροχρόνια επένδυση είναι λογικό μία επιχείρηση να περιμένει οφέλη. Η υποστήριξη IPv6 πάνω από το ήδη υπάρχον IPv4-MPLS θα απέδιδε τα μέγιστα οφέλη για μια τέτοια επιχείρηση. Έτσι μια τέτοια μετάβαση αποτελεί στρατηγική κίνηση που ουσιαστικά σκοπεύει στην αύξηση των κερδών του καθώς και την προετοιμασία του για το μέλλον. / This thesis aims to present the issue of constantly-decreasing available IPv4 addresses as well as the related transition process to IPv6, before the fully elimination of IPv4. More specifically, in this thesis there will be presented technologies and techniques which have been recommended in several international forums in relation to transition from IPv4 to IPv6 and which concern the MPLS networks for telecom providers. In the fifth chapter, an emulation environment for network devices will be “created”, through which some of the most appropriate transition implementation practices will be simulated. During the last years several providers have invested in installing IPv4-MPLS for their core networks. From such a long-term investment is sensible that one business expects profits. According to Chapter 5, the transition to IPv6 in conjunction with the full utilization of existing IPv4-MPLS equipment would have significant benefits for any business decided to proceed with this option. In particular, such a transition (from IPv4 to IPv6) could be part of a business strategy since not only contributes to the technological upgrading of a company’s systems and the production of more reliable services, but also to create synergies and economies of scale.

Co-immunoprecipitation (co-IP) followed by proteomic analysis was employed to examine the phosphoenolpyruvate carboxylase (PEPC) interactome of developing castor oil seed (COS) endosperm. Earlier studies suggested that immunologically unrelated 107-kDa plant-type and 118-kDa bacterial-type PEPCs (p107/PTPC and p118/BTPC, respectively) are subunits of an unusual ~910-kDa hetero-octameric Class-2 PEPC complex of developing COS. The current results confirm that a tight physical interaction occurs between p118 and p107 since p118 quantitatively co-IP’d with p107 following elution of COS extracts through an anti-p107-IgG immunoaffinity column. No PEPC activity or immunoreactive PTPC or BTPC polypeptides were detected in the corresponding flow-through fractions. Although BTPCs lack the N-terminal phosphorylation site characteristic of PTPCs, Pro-Q Diamond Phosphoprotein staining, immunoblotting with phospho-(Ser/Thr) Akt substrate IgG, and phosphate-affinity PAGE demonstrated that the co-IP’d p118 was significantly phosphorylated at unique Ser and/or Thr residue(s). The co-IP of p118 and p107 was not influenced by their phosphorylation status. As p118 phosphorylation appeared unchanged 48 h following elimination of photosynthate supply due to COS depodding, the signaling mechanisms responsible for photosynthate-dependent p107 phosphorylation differ from those controlling p118’s in vivo phosphorylation. A third PEPC polypeptide of ~110-kDa (p110; RcPPC1) co-IP’d with p118 and p107 when depodded COS was used. Analysis of RcPpc1’s full-length cDNA sequence revealed p110’s identity with PTPCs, but that a pair of unique amino-acid substitutions occurs in its N-terminal sequence that may render p110 non-phosphorylatable in vivo. The plastidial pyruvate dehydrogenase complex (PDCpl) was identified as a novel PEPC interactor. Subcellular fractionation indicated that p118 and p107 are strictly cytosolic, but that PDCpl is targeted to both the cytosol and leucoplast of developing COS. Thus, a putative cytosolic metabolon involving PEPC and PDCpl could function to channel carbon from phosphoenolpyruvate to acetyl-CoA and/or to recycle CO2 from PDCpl to PEPC. / Thesis (Master, Biology) -- Queen's University, 2007-09-26 15:57:52.216

Al igual que la telefonía rural en los países en vía de desarrollo, donde las compañías operadoras de telefonía no invierten porque la demanda de abonados no es suficiente para cubrir los estándares de equipamiento y operación y el costo de mantenimiento es muy alto por el desplazamiento del capital de trabajo a zonas alejadas. En el primer cordón del Gran Buenos Aires, existe una situación similar, en la que las principales compañías operadoras de telefonía de la Argentina, no hacen inversión para extender su red de cobertura a esta zona: razones como las antes expuestas, sumadas el robo continuo de cables de cobre o fibra óptica, con los que se transmite la telefonía convencional, impiden que estas compañías lleguen al lugar. Además de esto, se detecto que en la zona, existe una marcada presencia de comunidades inmigrantes, que integran un segmento de mercado que demanda servicios de llamadas internacionales para comunicarse con sus familiares en el exterior. Esto conllevó al diseño de una estrategia de marketing para comercializar servicios de telefonía IP e internet, llegando a la zona a través de enlaces wireles que permite evadir el problema de robo de cables de cobre y/o fibra óptica. Esta estrategia comprende un análisis del mercado en el que sobresalen las características, necesidades, tendencias, evolución prevista, competidores y posibles productos sustitutos. Un análisis FODA que permitió elaborar un diagnostico de la situación, y detectar los factores externos (Oportunidades y Amenazas) e Internos (Fortalezas y Debilidades) del negocio y adecuar los factores internos a los factores externos con el fin de obtener la mejor posición competitiva, y el desarrollo de una estrategia conjunta de segmentación, diferenciación, penetración y fidelización que permita además de brindar un beneficio financiero, generar un beneficio social para la población del primer cordón del Gran Buenos Aires, ofreciendo mayor acceso al conocimiento, formación e inclusión de estas personas.

Ever had an experience of forgetting to do something very important on a place you just past?. Remembering, on arrival at your destination afterward, requires an action to return to the task location. This can be unproductive and perhaps result to frustration. The purpose of this thesis is to develop a “Location Task-To-Do manager” an android mobile application that will efficiently organizes task-to-do list and remind an individual to perform a task at a pre-defined location through notification and alert messages. The methods used includes,  investigation of pre-existing systems, requirement elicitation survey technique, three-tier architecture design pattern, iterative development life-cycle model, acceptance test plan and a sets of other technology such as  Java SDK, Android APIs, TCP/IP protocol, object oriented programing techniques and MySql relational database. The result showed that, installed “Location Task-To-Do manager” application on individual mobile devices/smartphones were capable of creating task, adding task, editing task, deleting task, sharing task and setting task location through its user friendly graphical interfaces. Users are able to receive notification to perform a task within a minimum distance of 1km to the exact task location.

Wireless networks introduce a whole range of challenges to the traditional TCP/IP network, especially Virtual Private Network (VPN). Changing IP address is a difficult issue for VPNs in wireless networks because IP addresses are used as one of the identifiers of a VPN connection and the change of IP addresses will break the original connection. The current solution to this problem is to run VPN tunnels over Mobile IP (MIP). However, Mobile IP itself has significant problems in performance and security and that solution is inefficient due to double tunneling. This thesis proposes and implements a new and novel solution on simulators and real devices to solve the mobility problem in a VPN. The new solution adds mobility support to existing L2TP/IPsec (Layer 2 Tunneling Protocol/IP Security) tunnels. The new solution tunnels Layer 2 packets between VPN clients and a VPN server without using Mobile IP, without incurring tunnel-re-establishment at handoff, without losing packets during handoff, achieves better security than current mobility solutions for VPN, and supports fast handoff in IPv4 networks. Experimental results on a VMware simulation showed the handoff time for the VPN tunnel to be 0.08 seconds, much better than the current method which requires a new tunnel establishment at a cost of 1.56 seconds. Experimental results with a real network of computers showed the handoff time for the VPN tunnel to be 4.8 seconds. This delay was mainly caused by getting an IP address from DHCP servers via wireless access points (4.6 seconds). The time for VPN negotiation was only 0.2 seconds. The experimental result proves that the proposed mobility solution greatly reduces the VPN negotiation time but getting an IP address from DHCP servers is a large delay which obstructs the real world application. This problem can be solved by introducing fast DHCP or supplying an IP address from a new wireless access point with a strong signal while the current Internet connection is weak. Currently, there is little work on fast DHCP and this may open a range of new research opportunities.

A research area that has recently gained great interest is the development of network architectures relating to the tracking of wireless VoIP devices. This is particularly so for architectures based on the popular Session Initiation Protocol (SIP). Previous work, however, in this area does not consider the impact of combined VoIP and tracking on the capacity and call set-up time of the architectures. Previous work also assumes that location information is always available from sources such as GPS, a scenario that rarely is found in practice. The inclusion of multiple positioning systems in tracking architectures has not been hitherto explored. It is the purpose of this thesis to design and test SIP-based architectures that address these key issues. Our first main contribution is the development of a tracking-only SIP based architecture. This architecture is designed for intermittent GPS availability, with wireless network tracking as the back-up positioning technology. Such a combined tracking system is more conducive with deployment in real-world environments. Our second main contribution is the development of SIP based tracking architectures that are specifically aimed at mobile wireless VoIP systems. A key aspect we investigate is the quantification of the capacity constraints imposed on VoIP-tracking architectures. We identify such capacity limits in terms of SIP call setup time and VoIP QoS metrics, and determine these limits through experimental measurement and theoretical analyses. Our third main contribution is the development of a novel SIP based location tracking architecture in which the VoIP application is modified. The key aspect of this architecture is the factor of two increase in capacity that it can accommodate relative to architectures utilizing standard VoIP. An important aspect of all our tracking architectures is the Tracking Server. This server supplies the location information in the event of GPS unavailability. A final contribution of this thesis is the development of novel particle-filter based tracking algorithms that specifically address the GPS intermittency issue. We show how these filters interact with other features of our SIP based architectures in a seamless fashion.