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Open systems interconnection model papers
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Abstract
The Physical Layer is the lowest layer of the Open Source Interconnect Model (OSI). It is the layer that deals with all the measurable, physical entities associated with the network. At this layer it is specified how much bandwidth (Baseband or Broadband) will be used in the transmission of data on the network. This layer also includes the physical topology (physical lay out) of the network such as: Bus, Star, Ring or Mesh. The Physical Layer includes these devices: Network Interface Cards (NICs), Transceivers, Hubs, Multistation Access Units (MAUs), Repeaters and Cables. It is at this layer that frames received from the Data Link layer are converted to bits for transmission over the network media to the receiving machines Physical Layer.
The Physical Layer defines all electrical and physical specifications for devices. This includes the layout of pins, voltages, and cable specifications. The major functions and services performed by the Physical Layer are: establishment and termination of a connection to a communications medium, participation in the process whereby the communication resources are effectively shared among multiple users, modulation, or conversion between the representation of digital data in user equipment and the corresponding signals transmitted over a communications channel. These are signals operating over the physical cabling copper and fiber optic. ("OSI Model", 2005)
"The Physical Layer is special compared to the other layers of the model, because it is the only one where data is physically moved across the network interface. All of the other layers perform useful functions to create messages to be sent, but they must all be transmitted down the protocol stack to the Physical Layer, where they are actually sent out over the network."(Kozierok, 2004)
Physical Layer also specifies how much of the media will be used during the data transmission referred to as Baseband or Broadband signaling.
1. Baseband Signaling: Technology in which a network uses all available signal frequencies or the entire bandwidth i.e., Most LAN technologies like Ethernet.
2. Broadband Signaling: Technology in which a network uses only one frequency or a part of the entire bandwidth i.e., multiple signals can be transmitted over a media simultaneously like TV signals, where you have various channels like CNBC, MTV, BBC, each on a different frequency and hence each occupies a part of the bandwidth. (Chandrasekaran, 2002)
The Physical Layer also deals with the way a network is laid out which is referred to as the topology of a network.
Multiplexing will gather the data from the source host and give that data some header information. This data will be created into segments by demultiplexing and then be sent to the 3rd layer (Network layer). So to summarize multiplexing will gather data and give it header information and demultiplexing will create segments and sent them to the network layer. Now with flow control that will relate with multiplexing, mainly because it can take multiple data streams and combine them into one shared stream, making that a form of data flow control. Now as far as error checking that will relate to the frames of the data. The logical link control will use a frame check sequence (FCS) to check the frame to see if there is any problems with it. If it detects an error during the frame check sequence then the frame will be discarded and the data will be passed on to the network layer. With this all being said this will mainly be used in the OSI model since the logical link control is the sub-layer for the data link layer. (The other sub layer being MAC) Without the logical link control or 802.2 then the data link layer wouldn’t function
“Network topology is the arrangement of the various network elements such as node, link, of computer network. Basically, it is topological structure of a network which ether be physically or logically.”
Internal schema at the internal level to describe physical storage structures and access paths, typically uses a physical data model.
Wireless networks – While the term wireless network may technically be used to refer to any type of network that is wireless, the term is most commonly used to refer to a telecommunications network whose interconnection between nodes is implemented without the use of wires, such as a computer network. Wireless telecommunication networks are generally implemented with some type of remote information transmission system that uses electromagnetic waves, such as radio waves, for the carrier and this implementation usually takes place at the physical level or “layer” network.
OSI – Open Systems Interconnection - is reference model for how applications can communicate over a network. A reference model is a conceptual framework for understanding relationships.
To attempt to define a network in a few sentences would be a fool’s errand. A network could be seen as simply a grid of interconnecting connections between multiple bodies. However when this vision is applied to real-world systems, they all start to differ. There is not anything that exists in the universe that is not part of a network. A network is the result of different parts or members which have similarities in parts of their identity. This similarity that they have in common, they will also have with other bodies forming a network between them. Most of these factors of identity are different from those of most others. As a result, each factor will be in common with different other members of different networks. Each factor includes this body in a multitude of networks. This means that no one thing is in one and only one network, but is included in many.
Secondly, the seven layers proposed by OSI are completely out of touch with reality. The defacto networking standard is TCP/IP. TCP/IP is the grandaddy of XNS, IPX/SPX, Banyan, AppleTalk, and a host of other protocols and pre-dates that seven layer thing because it was funded by the largest organization in the world devoted to maintaining Eurocentric socioeconomic domination; the US Military. And for some reason, that makes it better. Yeah.
Multiplexing, by definition, is the process where multiple channels are combined for transmission over a common transmission path. In the early 1990s, fiber could only carry one wavelength, or color, of light at a time. Lasers were used by quickly turning them on and off. By the mid 1990s wave division multiplexing could split the light into two colors. The number of colors rapidly grew and today as many as 160 colors can be carved out by using the most advanced systems, in what is now called dense wave division multiplexing (DWDM). In other words, DWDM combines multiple optical signals so that they can be amplified and transported over a single fiber. An example would be a DWDM network with a mix of SONET signals operating at OC-48 (2.5 Gbps) and OC-192 (10 Gbps) over a DWDM infrastructure can achieve capabilities of over 40Gbps. The reliability of the system is maintained throughout this process. DWDM networks are self-regulated at the bit-rate and format level. They can also accept any combination of interface rates on the same fiber at the same time. This greatly increases the flexibility of the system. The communication industry can become fully integrated, using multiple vendor interfaces with distinct technologies into one physical infrastructure. The fiber itself would remain transparent to the protocol or type of information. If a carrier operates both ATM and SONET networks, it is not required that the ATM signal be multiplexed up to the SONET rate.
Cyber physical systems combine communications,
It just doesn't get much simpler than the physical bus topology when it comes to connecting nodes on a Local Area Network (LAN). The most common implementation of a linear bus topology is IEEE 802.3 Ethernet. All devices in a bus topology are connected to a single cable called the bus, backbone, or ether. The transmission medium has a physical beginning and an end. All connections must be terminated with a resistor to keep data transmissions from being mistaken as network traffic. The terminating resistor must match the impedance of the cable.
A communications network can provide many types of service. The most basic type of service is known as simplex. This service provides one-way communication. Examples of this type of service are TV distribution, and the transmission of burglar alarm messages.
The next modulation technique is Direct-Sequence Spread Spectrum (DSSS) which applies the (PN) code directly to the data entering the carrier modulator. The baseband signal is spread out into a much larger bandwidth greater than the minimum bandwidth required to transmit the information.
Asynchronous Transmission: The asynchronous signaling methods use only 1 signal. The receiver uses changes on that signal to figure out the rate and timing of the transmitter, and then synchronizes a clock to the proper timing with the transmission rate. A pulse from the local clock indicates when another bit is ready. Asynchronous transmission is a slower but less expensive and effective for low-speed data communication.
The architecture of a neural network is the specific arrangement and connections of the neurons that make up the network. One of the most common neural network architectures has three layers. The first layer is called the input layer and is the only layer exposed to external signals. The input layer transmits signals to the neurons in the next layer, which is called a hidden layer. The hidden layer extracts relevant features or patterns from the received signals. Those features or patterns that are considered important are then directed to the output layer, the final layer of the network. Sophisticated neural networks may have several hidden layers, feedback loops, and time-delay elements, which are designed to make the network as efficient as possible in discriminating relevant features or patterns from the input layer.
The term Topology refers to the physical or logical shape or layout of a network. Communication between different nodes within a network is determined by its topology. Mesh, Bus, Ring and Star are four of the most common network topologies, each with advantages and disadvantages in relation to each other.