Transport Layer Concepts

Continental Drift Theory. From the discussion of the rock cycle, it has been pointed out that through Earth's external and internal processes. Earth's surface is constantly changing. However, this idea of a changing environment did not conform with the belief of earlier scientists. Rather, they thought that the geographic positions of ocean basins and continents have been static since the beginning of time. It was around the 1500s when Leonardo da Vinci, upon his discovery of fossil seashells found at the high mountains of Italy, first thought of the idea that the areas where mountains are located may have been oceans in the past. Through time, other fossils of marine organisms found far above the current sea level further supported the idea that mountains were uplifted and weathering wore them down. At around the 1800s, most scientists have accepted the idea that Earth's crust is undergoing large vertical movements or uplifting. There was also evidence of possible horizontal movements, but the scientists then were not convinced about it. Alfred Wegener showed evidence of horizontal or lateral movement of the continents in his continental drift theory. According to him, the continents have drifted around the world and have once formed a giant landmass or supercontinent called Pangaea. To support his theory, Alfred Wegener presented a set of geographical, biological, and climatic evidence.Wegener's geographical evidence included the jigsaw puzzle fit of the current continents. He pointed out that the coastlines of South America and Africa seem to fit together. He also pointed the presence of mountain ranges having similar rock types and age but separated by vast oceans, like that of the folded rocks of the Caledonian mountains. The same folded rocks run through West Africa, North America, Newfoundland, Ireland, Wales, Scotland, Greenland, and Norway, all of which are now separated by the Atlantic Ocean. A geographical evidence on the similar rock types in West Africa, North America, Greenland, and Europe is found. The biological evidence came in the discovery of similar plant and animal fossils in different continents separated by oceans. The animal fossils of Mesosaurus and Lystrosaurus indicate that they were not capable of crossing the oceans to reach the other continents. If they were, the fossils should have been more widely distributed Africa, Australia, India, and South America were too large to be carried by wind. This indicates that the areas where the fossils were found were closely linked. It has also been found out that the plant only grew in areas with subpolar climate, which would indicate that the landmasses were located near the South Pole.Lastly, for his climatic evidence, Wegener discovered that a glacial period occurred during the late Paleozoic era in Southern Africa, South America, Australia, and India. The initial explanation for this event was global cooling, but it was rejected because large tropical swamps with so much vegetation were found at the same time in the Northern Hemisphere. This further supported the idea that the supercontinent was indeed near the South Pole, and the continents in Northern Hemisphere were once near the equator. The glacial period also left glacial striations, or the scratches glaciers make as they move across on the underlying bedrock, on the aforementioned continents. For such an event to happen, the continents would have to be connected. SCIENCE PIONEER. Alfred Wegener (1880-1930). Alfred Wegener was a German polar researcher, geophysicist, and meteorologist. He was known for his work on the continental drift theory. In his effort to defend his work, he went to the Greenland ice sheet where he died.Even with all the compelling evidence, the continental drift theory hardly convinced the scientific community at that time because Wegener was unable to identify a credible mechanism that drives the continental drift. He was unable to clearly explain how the continents moved and how the larger continents broke through the ocean floor. Eventually, critics of the continental drift began to accept the theory when new evidence supporting the theory was discovered. The new evidence led to a more encompassing theory the theory of plate tectonics. This theory provided a more convincing explanation as to how the continents moved. The evidence that paved the way for the theory of plate tectonics was the idea of wandering poles. Scientists began studying volcanic rocks to determine the location of the magnetic poles. When volcanic rocks crystallize, the minerals with magnetic properties align themselves parallel to Earth's magnetic field at the time the minerals were formed. This finding allowed scientists to determine the polarity of Earth's magnetic field and the magnetic inclination that showed the location of the poles. Upon studying the paleomagnetism of the rocks, geophysicists found out that rocks from various locations point to different magnetic north poles, suggesting that the poles have wandered. Since movement of magnetic poles is very unlikely, scientists have accepted the idea that the continents are indeed moving. And if the continents are moving, scientists thought that maybe the ocean basins are moving too. They also discovered that some rocks showed magnetic reversals, which led them to believe that the magnetic north pole now was not always the magnetic north pole. Seafloor Spreading. After World War II, exploration on the ocean floor became the focus of many geologic studies. It was only then that the ocean ridge system was discovered. A geologist in Princeton University named Harry Hess, along with other scientists, studied this ocean ridge system and hypothesized that the oceanic crust was moving away from the ridge. His hypothesis, known as seafloor spreading, showed that the ocean floor is split along the ridge where the magma rises to form the new ocean floor.Because of this, rocks located near the ridge are younger than those that are located magnetic polarity of Earth is also preserved in those rocks. Withe ridge scientists were able to see the magnetic reversals in the ocean floor, and they were able to make use of information to determine that the ocean floor is moving at a rate of about 10 cm per year. Plate Tectonics. Confirmation of the seafloor spreading hypothesis proved that continents are not moving above the ocean floor. Rather, it is the fragments of the lithosphere. The lithosphere is the rigid layer that is composed of the uppermost mantle and the crust that carry the continents and the ocean basins along. These fragments of the lithosphere are called plates. Underneath the lithosphere is a weaker region in the mantle known as asthenosphere that behaves like a fluid. Thus, the lithosphere floats above the asthenosphere, making it detached and free to move. This became the basis of the theory of plate tectonics. Now that it has been made clear that it is the plates which are moving, the question as to how they move remained. Sir Arthur Holmes proposed the driving force for this plate movement in 1919. He suggested that the movement in the mantle carries the plates along. It was previously discussed that Earth's interior is very hot due to the heat produced by radioactive decay. Convection takes place in the mantle, keeping the asthenosphere hot and weak. The convection currents produced in the asthenosphere are the ones carrying the lithospheric plates and making them move. However, convection currents are not enough. Mechanisms such as ridge push and slab pull aid the convection currents to slowly move the lithospheric plates. Ridge push occurs at mid ocean ridges which are higher in elevation than the surrounding trenches and abyssal plains. The new ocean floor from the ridge is hot and relatively thin. As it moves away from the ridge, it cools down and gets denser, heavier, and thicker. Below this cooling ocean floor is the asthenosphere, which is less dense. This area becomes a massive shear zone and the new ocean floor will effectively slide down the slope of the asthenosphere. When the plate collides with another plate with lesser density, the denser plate sinks and a subduction zone is formed. When the subducting plate sinks, it pulls on the rest of the plate behind it. These mechanisms explain the movement of the plates.Earth has seven major lithospheric plates that account for 94% of Earth's surface. These are the North American Plate, South American Plate, Pacific Plate, African Plate, Eurasian Plate, Indo-Australian Plate, and Antarctic Plate. These plates are constantly moving relative to the other plates. Thus, the interaction of plates occurs mostly along the boundaries. These movements are plotted using information from earthquakes and volcanic activities. There are three main types of plate boundaries: convergent, divergent, and transform boundaries Convergent boundaries are boundaries where two plates move towards each other A convergent boundary is also known as destructive margin since this is where the collision between two plates occhins. There are three types of convergence-oceanic oceanic, oceanic-continental, and continental-continental. Trenches are features of the ocean floor that are present in both oceanic-oceanic boundary and oceanic-continental boundary. Subduction occurs at the trenches, therefore, these are characterized as the deepest parts of Earth. A divergent boundary is the opposite of convergent boundary: two plates move away from each other. Divergent boundaries create new crust; thus, they are also known as constructive margins. The ocean ridge system is a divergent boundary where new ocean floor is produced as magma rises, pushing the older rocks aside.Transform boundary is also known as conservative plate margin since two plates just move past one another, neither creating nor destroying land. Earthquake epicenters are usually detected at transform boundaries because the rocks tend to break and not fold or sink, like in convergent boundaries. Evolution of the Ocean Basins. Both the movement of the plates and seafloor are responsible for the evolution of ocean basins. Along the divergent boundary where ocean ridge systems are found, magma is released and new ocean floor is created. Along convergent boundaries, the ocean floor is being destroyed. The evolution of the ocean basins started during the time when Pangaea was still present and was surrounded by the vast ocean or superocean known as Panthalassa, also called Paleo-Pacific or "old Pacific." Upon the initial break up of Pangaea into Laurasia and Gondwanaland, the Tethys Sea began to form. Then, the Eurasian and North about, forming the North Atlantic. The South Atlantic only started to form when the African Plate and South American Plate separated. The continued movement of the plates created the Himalayas at one side and separated the Pacific Ocean and Atlantic Ocean at the other side, which consequently formed the current ocean basins. Both the movement of the plates and seafloor are responsible for the evolution of ocean basins. Along the divergent boundary where ocean ridge systems are found, magma is released and new ocean floor is created. Along convergent boundaries, the ocean floor is being destroyed. The evolution of the ocean basins started during the time when Pangaea was still present and was surrounded by the vast ocean or superocean known as Panthalassa, also called Paleo-Pacific or "old Pacific." Upon the initial break up of Pangaea into Laurasia and Gondwanaland, the Tethys Sea began to form. Then, the Eurasian and North about, forming the North Atlantic. The South Atlantic only started to form when the African Plate and South American Plate separated. The continued movement of the plates created the Himalayas at one side and separated the Pacific Ocean and Atlantic Ocean at the other side, which consequently formed the current ocean basins.Continents do not immediately end at the point where the ocean meets the land. They may extend slightly into the oceans. The portion of the continent that is submerged is called continental margin. There are two types of continental margin: passive margin and active margin. A passive continental margin consists of a continental shelf, continental slope, and continental rise. It is not associated with plate boundaries; thus, there are very little tectonic activities. An active continental margin only has a continental shelf and a continental slope. It is associated with plate boundaries; thus, a main feature of this boundary is a trench. The different features of a continental margin are the following: 1. The continental shelf is the gently-sloping submerged portion of the continent. 2. The continental slope is the steep slope after the continental shelf. It is still part of the continent. 3. The continental rise is the gently-sloping area after the continental slope and before the ocean floor. 4. The trenches are the deepest parts of the ocean. These are narrow depressions caused by the subduction of the ocean floor along the convergent boundaries. 5. The mid-oceanic ridge is the mountain range system in the ocean. It is responsible for the production of new ocean floor. This is the region where new magma constantly emerges from. SCIENCE CAREER. A scientific illustrator uses art to inform and communicate complex details and concepts of science. He/She makes use of scientifically informed observations and research along with his/her technical art and aesthetic skills to make accurate representations. In Natural History, the scientific illustrators recreate how the extinct species look like by working with scientists and fossil records. Moreover, with the advances in technology, illustrators are now into 3D modelling, animation, and video making. Earth's History. All the processes that have been discussed require long periods of time to create a noticeable change on Earth's surface. You can just imagine how long it would take to create an oceanas vast as the Pacific Ocean if the ocean floor moves only at about 10 cm/year. It is then important to know the history of Earth to learn the complexities of its past and be able to use it to understand the present. Just like learning the history of a country that requires one to read a lot of books, learning the history of Earth involves studying a lot of rocks. Rocks, especially sedimentary rocks, contain a lot of information about Earth's past. It holds the key to most of the geologic processes that happened on Earth and the key to uncovering how life on Earth evolved. But these discoveries are worthless if there is no time perspective. Thus, one of the most important contributions of geologists to mankind is the geologic time scale, which holds a history that is exceedingly long.

The Invention of the Automobile An automobile, or car, is a wheeled vehicle that carries its own motor and transports passengers. The automobile as we know it was not invented in a single day by a single inventor. In 1769, the French engineer Nicolas-Joseph Cagnon devised the first self-propelled road vehicle, a military tractor powered by a steam engine. One year later, Cagnon built a steam-driven tricycle that could carry four passengers, but steam engines were very heavy and they proved a poor design for road vehicles. Around 1830, the Scotsman Robert Anderson built the first electric carriage. Both steam and electric road vehicles were soon abandoned in favour of petrol-powered vehicles. In 1876, Nicolaus August Otto built the first practical four-stroke internal combustion engine. In an internal combustion engine, the fuel is burnt inside the engine, while in a steam engine, the fuel is burnt outside. The most common internal combustion engine type is petrol-powered. The first petrol-powered vehicles were developed by Gottlieb Daimler and Karl Benz. In 1885, Karl Benz designed the first three-wheeler powered by an internal combustion engine. In 1891, Benz built the first four-wheeler. The first automobile to be mass-produced in the USA was the 1901 curved-dashed Oldsmobile built by Ransom L.E. Odds. Odds devised the basic concept of the assembly line and started the Detroit-area automobile industry. Henry Ford installed the first conveyor belt-based assembly line in his car factory in Michigan in 1913. The assembly line reduced production costs for cars by reducing assembling time. Ford's famous Model T was assembled in 93 minutes. The Ford Motor Company was launched in 1903, and by 1927, 15 million Model Ts have been manufactured. The modern era of automobiles had begun. The assembly line During the period known as the Industrial Revolution (1760-1850) machines changed people’s lives as well as their methods of manufacturing. Most products people in the industrialized nations use today are manufactured by the process of mass production, that is by people and robots that use power-driven machines. Through the use of mass pro-duction methods and the assembly line, a larger amount of goods can be produced in a given period of time, usually at a lower cost.The assembly line developed at the Ford Motor Com-pany in 1913 had immense influence on the automo-tive industry and on other industrial branches. Henry Ford, founder of the company, had built his first car in 1896 and was unique among automobile inventors. In Ford’s early assembly line, cars were pulled by rope from one worker to the next. This new technique allowed individual workers to stay in one place and perform the same task repeatedly on vehi-cles as they passed by. This reduced production timeby about one-half. Ford later employed the use of conveyor belts to move the parts down the line.

I Le contrat de vente classique 1. L’intérêt pour la PMI de connaître la diversité des contrats commerciaux Les PME-PMI sont régulièrement amenées à conclure des contrats commerciaux. Il est donc nécessaire pour l’assistant(e) de gestion de connaître les différents contrats et les règles qui les régissent. 2. Le transfert de propriété Dès qu’il y a accord entre le vendeur et l’acheteur, il y a transfert de propriété. L’acheteur doit donc assumer les risques dès le transfert de propriété. Pour pallier ce risque, il peut prévoir dans le contrat une clause de réserve en propriété, qui a pour effet de différer le transfert de la propriété et des risques qu’il entraine jusqu'à conclusion totale du contrat. 3. Les obligations des parties Les garanties dans le contrat de vente se décomposent ainsi :  Les garanties obligatoires : o la garantie légale de conformité permettant au client d’obtenir la réparation, le remboursement ou le remplacement du produit défectueux o la garantie contre les vices cachés : se sont des défauts non visibles au moment de l’achat qui rendent le bien inutilisable  Les garanties complémentaires ou commerciales : elles sont facultatives pour le client. Elles peuvent être gratuites (mise à disposition d’un produit au client durant une réparation) ou payantes (extension de garantie pour l’achat d’une machine à laver) Exercice d’application 4. Les recours possibles Lorsqu’une procédure est engagée, la juridiction compétente pour statuer l’affaire est le tribunal de commerce du défendeur si le client et l’entreprise sont des commerçants. Les sanctions les plus courantes sont : - infliger des pénalités de retard - obtenir une réduction de prix - faire exécuter le contrat par une autre entreprise - obtenir des dommages et intérêts II Les particularités du contrat de vente commerciale Le contrat présente certaines particularités que la PME doit connaitre : On peut donc considérer qu’un bon de commande est un contrat de vente commerciale, dans la mesure où il réunit ses clauses. Enfin, il existe des situations ou les engagements peuvent différés. C’est le cas : - de la vente à distance : le client dispose d’un délai de rétractation de 14 jours - la vente avec arrhes : si le client verse des arrhes, il pourra annuler le contrat mais perdra le montant versé à l’entreprise. III Les contrats de maintenance et de sous6traitance 1. Le contrat de maintenance C’est un contrat par lequel une entreprise se charge de vérifier, d’entretenir ou de réparer un appareil technique ou une installation complexe. Il doit donc spécifier : - la définition de la prestation et le lieu de réalisation - la durée du contrat - le prix unitaire ou forfaitaire 2. Le contrat de sous-traitance Il permet à une entreprise appelée « donneur d’ordre » de confier la réalisation d’une prestation à une autre entreprise appelée « sous traitant ». L’entreprise s’engage à payer le sous traitant selon les modalités prévues dans le contrat et reste donc responsable de la réalisation de la prestation devant le client. Avantages et inconvénients de la sous-traitance : IV Créer un contrat via un réseau de franchise Afin de développer son activité, l’assistant(e) de gestion peut conclure des contrats commerciaux avec des partenaires étrangers La franchise est une méthode de collaboration entre, d’une part, une entreprise, le franchiseur, et, d’autre part, une ou plusieurs entreprises, les franchisés. Son objet est d’exploiter un concept de franchise mis au point par le franchiseur. Tous sont porteurs de la même enseigne, symbole de l’identité et de la réputation du réseau. La garantie de qualité est assurée par la transmission et le contrôle du respect du savoir-faire et par la mise à disposition d’une gamme homogène de produits, de services et/ou de technologies. a. Le franchiseur C’est un entrepreneur indépendant qui a mis au point et exploité avec succès un concept original dans plusieurs unités pilotes. Il apporte à ses franchisés une formation initiale et permanente pour leur permettre d’appliquer son concept et consacre à la promotion de sa marque, à la recherche et à l’innovation, les moyens humains et financiers permettant d’assurer le développement et la pérennité de son concept. b. Le franchisé C’est un entrepreneur indépendant sélectionné par le franchiseur. Il doit avoir la volonté de collaborer loyalement à la réussite du réseau de franchise en adhérant au principe d’homogénéité de ce réseau, tel que défini par le franchiseur. Il engage des moyens financiers, afin de rétribuer le franchiseur pour ses apports (paiement d’un droit d’entrée et d’un pourcentage sur le chiffre d’affaires). c. Les avantages et les inconvénients du contrat de franchise pour le franchiseur et pour le franchisé. Avantages Inconvénients Franchiseur – Développer son réseau à moindres frais. – Faire des économies d’échelle. – Maîtriser le développement de son concept. – Développer son image, sa notoriété. – Augmenter ses parts de marché. – Accroître son chiffre d’affaires. – Organiser des campagnes publicitaires à l’échelon national. – Transmettre son savoir-faire à des commerçants indépendants. – Assurer une assistance technique et des formations. – Avoir des franchisés qui déprécient l’image de l’entreprise. Franchisé – Avoir une notoriété dès l’ouverture du commerce. – Rester un commerçant indépendant et être responsable de son entreprise. – Bénéficier du savoir-faire du franchiseur. – Bénéficier d’une assistance technique, de formations, d’une logistique d’approvisionnements, etc. – Respecter la charte et les normes du franchiseur, ce qui limite sa liberté de commerçant indépendant. – S’acquitter des droits d’entrée et de redevance. – Avoir une obligation d’approvisionnement exclusif chez le franchiseur. d. Les clés de la réussite de cette forme de commerce Les clés de la réussite sont : – la collaboration commerciale et technique ; – l’association du savoir-faire du franchiseur et de l’esprit entrepreneurial du franchisé ; – les structures organisationnelles sont plus simples et plus économiques qu’en succursalisme car un bon franchisé est motivé et n’a pas besoin d’être poussé ; – c’est un système rapide et évolutif pour couvrir un marché car investissements et compétences sont partagées. e. Les chiffres clés de la franchise en 2019 f. La typologie des franchisés • 60% des franchisés sont des hommes • 50% des franchisés ont entre 35 et 49 ans • 66% des franchisés sont d’anciens salariés du privé • Chaque franchisé emploie en moyenne 7 salariés • 84% des réseaux sont toujours la propriété de leur fondateur • Chaque réseau crée en moyenne 8 nouveaux points de vente par an • 29% des réseaux ont des points de vente à l’étranger

Transport Layer

Quiz on Transport Layer (ACT2D) - Group 4

Understanding of network and internet, network core, Understanding of Delay, Loss and Throughput in the packet switching network, Network Models- OSI Reference Model, TCP/IP Model,Introduction to data link layer services, error-detection and correction techniques, Multiple access protocols, addressing, Ethernet, switches, Virtual LAN,Introduction to forwarding and routing, Network Service models, Virtual and Datagram networks, study of router, IP protocol, IPV4 and IPV6 addressing in the Internet, Routing algorithms, Broadcast and Multicast routing,Introduction and transport layer services, Multiplexing and Demultiplexing, Connectionless transport (UDP), Principles of reliable data transfer, Connection- oriented transport (TCP), Congestion control, TCP congestion control.

Plăcile de rețea (Network Interface Cards-NICs) conectează un echipament la rețea. Plăcile de rețea Ethernet sunt folosite pentru o conexiune cablată, în timp ce plăcile de rețea WLAN (Wireless Local Area Network) sunt folosite pentru wireless. Un echipament cu utilizator final ar putea include unul sau ambele tipuri de plăci de rețea. De exemplu, o imprimantă de rețea poate avea doar o placă de rețea Ethernet, așadar, trebuie să se conecteze la rețea printr-un cablu Ethernet. Alte echipamente, precum tabletele sau telefoanele pot conține o placă de rețea WLAN și trebuie să folosească o conexiune wireless. Layer-ul Fizic Layer-ul fizic de la OSI furnizează mijloacele de transport a biților care realizează un frame de data link în mediul de rețea. Acest layer acceptă un frame complet de la layer-ul data link și îl codifică sub forma unor serii de semnale care sunt transmise în mediul local. Biții codificați care comprimă un frame sunt primiți fie de un echipament final, fie de unul intermediar. Procesul prin care trec datele de la nodul sursă la nodus destinație este: • Datele utilizatorului sunt segmentate de layer-ul transport, plasate în pachete de către layer-ul rețea, iar apoi încapsulate sub formă de frame-uri de către layer-ul data link. • Layer-ul fizic codifică frame-urile și creează semnalele undelor electrice, optice și radio care reprezintă biții în fiecare frame. • Aceste semnale sunt trimise în mediu pe rând. • Nodul destinație preia aceste semnale individuale de la nivelul fizic, le transformă în reprezentare binară și transmit biții la nivelul superior, data link, sub forma unui frame. Mediul layer-ului Fizic Există trei forme de bază ale mediului de rețea. Layer-ul fizic produce reprezentarea și gruparea biților pentru fiecare mediu, după cum urmează: • Cablu de cupru: Semnalele sunt modele ale pulsurilor electrice. • Cablul cu fibră optică: Semnalele sunt modele de lumină. • Wireless: Semnalele sunt modele ale transmisiunilor cu microunde. Figura afișează exemple de semnalizare pentru cupru, fibră optică și wireless. Pentru a activa interoperabilitatea layer-ului fizic, toate aspectele acestor funcții sunt guvernate de organizațiile de standardizare. Standardele Layer-ului Fizic Protocoalele și operațiile layerelor superioare din OSI sunt efectuate în software proiectat de ingineri și oameni de știință. De exemplu, serviciile și protocoalele din suita TCP/IP sunt definite de Internet Engineering Task Force (IETF) în RFC-uri așa cum se arată în Figura 1. Layer-ul fizic constă în circuite electronice, mediu și conectori dezvoltați de ingineri. Așadar, este corespunzător ca standardele care guvernează acest hardware să fie definite de orgnizațiile relevante din domeniul ingineriei și electronicii. Există mai multe organizații naționale și internaționale diferite, organizații guvernamentale de reglementare și companii private implicate în stabilirea și menținerea standardelor layer-ului fizic. De exemplu, hardware-ul layer-ului fizic, mediul, codificarea și standardele de semnalizare sunt definite și guvernate de către: • International Organization for Standardization (ISO) • Telecommunications Industry Association/Electronic Industries Association (TIA/EIA) • International Telecommunication Union (ITU) • American National Standards Institute (ANSI) • Institute of Electrical and Electronics Engineers (IEEE) • Autoritățile de reglementare națională a telecomunicațiilor, inclusiv Federal Communication Commission (FCC) din USA și European Telecommunications Standards Institute (ESTI) Pe lângă acestea, există grupuri de standardizare a cablărilor regionale precum CSA (Canadian Standards Association), CENELEC (European Committee for Electrotechnical Standardization) și JSA/JSI (Japanese Standards Association), care dezvoltă specificații locale. Figura 2 listează contribuitorii principali și câteva standarde relevante ale layer-ului fizic.

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