Module B - Assignment 4

OSI is a model that defines a networking framework for implementing protocols in seven layers. Control is passed from layer to layer starting at the application layer (layer 7) and working its way down to the physical layer (layer 1). Then going to the next station over the channel and back up the layers.

The initial layer is the seventh layer, which is known as the application layer. This layer supports application and end-user processes. Everything at this layer is application-specific. The communication partners, any constraits on data syntax, as well as the quality of service are identified. While the user authentication and privacy are considered. Provided by htis layer are application services for file transfers, e-mail, as well as other software services. Some applications that entirely exist on this layer are Telnet and FTP. Also tierd application architectures are part of this layer.

The next layer is the sixth layer, which is known as the presentation layer. Less frequently it is also known as the syntax layer. Provided by this layer is the independence from differences in data representation. An example of thjis is encryption. This occurs by translating from network to application format, and vice versa. This layer works to transform data into a form that will be accepted by the apllication layer. This layer formats as well as encrypts data so that it can be sent across a network. This providing freedom from compatibility problems.

The fixth layer is known as the session layer. It establishes, manages and terminates connections between applications. Also it sets up, terminates and coordinates exchanges, conversations and dialogues between the applications at each end. This layer deals with the coordination of sessions and connections.

The fourth layer is known as the transport layer. It provides the transparent tranferring of data between end systems (or hosts), and is also responsible for end-to-end error recovery and flow control. This layer primary function is to ensure the complete transfer of data.

The third layer is known as the network layer. It provides switching and routing technologies, creating logical paths. These paths are known as virtual circuits, and are used for transmitting data from node to node. Functions of this layer include routing and forwarding as well as addressing, internetworking, congestion control, error handling, and packet sequencing.

The second layer is known as the data link layer. This layer encodes and decodeds data packets into bits. This llayer is divided into two sublayers: the Media Access Control (MAC) layer and the Logical Link Control (LLC) layer. How a computer on the network gains access to the data and obtaining permission to transmit it is controlled by thre MAC sublayer. The LLC layer, on the other hand, controls frame synchronization, flow control and error checking.

The final layer is the first layer which is physical layer. It is responsible for conveying the bit stream (electrical impulse, light or radio signal) through the network at the electrical and mechanical level. Provided by it is also the hardware means of sending and receiving data on a carrier. This including defining cables, cards as well as physical aspects. Protocols of this layer's components include Fast Ethernet, RS232 and ATM.

The relevance of the ethernet to OSI is as follows, it defines a number of wiring and signalling standards for the physical layer (the first layer). This occurs through means of network access at the sublayer MAC/Data Link layer (the second layer) and also through a common addressing format.

Bibliography

http://en.wikipedia.org/wiki/Ethernet

http://en.wikipedia.org/wiki/Open_Systems_Interconnection
http://www.webopedia.com/quick_ref/OSI_Layers.asp

Module B Assignment 2

Topic # 1

Part A:

- Police Radio Jammer: Blocks radar gun readings, and accidentally blocks wireless signals. It is not permanent because you can move it around.

- Signal Jammer: Hospitals use them so they don't mess up any chemotherapy by having someone's cell phone go off. They're like... permanent fixtures.

- Concrete Blocks: Due to its thickness it blocks signals, used for building concrete walls, like the walls found in schools or in basements.

- Microwaves: the particles emitted by a microwave while it is in the process of cooking/thawing food can cause signals to be lost...

Part B

-Signal Jammer: To avoid EMI from a signal jammer simply move away from the unit.

-Police Radio Jammer: By turning a radio jammer off, you avoid EMI. By doing so you also risk getting caught by the police for speeding.

-Concrete Blocks: To avoid the EMI from concrete blocks, you have to either re-build the wall using a materail that won't emit EMI or by a signal booster.

-Microwave: To avoid EMI from micowaves you must make sure that the router isn't near the microwave, or between your computer and the router if you use a wireless connection.