DCN386 - 1(2 marks Identify four Data Communications...

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1. (2 marks) Identify four Data Communications Standards Organization and describe what each does. Most official computer standards are set by one of the following organizations: o ANSI (American National Standards Institute) ITU (International Telecommunication Union) o IEEE (Institute of Electrical and Electronic Engineers) ISO (International Standards Organization) o VESA (Video Electronics Standards Association) 2. (8 marks) Provide a COMPLETE description of the activity in each of the OSI Model layers (remember to split the data link layer into two sublayers) Application (layer 7) This layer supports application and end-user processes. Communication partners are identified, quality of service is identified, user authentication and privacy are considered, and any constraints on data syntax are identified. Everything at this layer is application-specific. This layer provides application services for file transfers, e-mail , and other network software services. Telnet and ftp are applications that exist entirely in the application level. Tiered application architectures are part of this layer. Presentation (layer 6) This layer provides independence from differences in data representation (e.g., encryption ) by translating from application to network format, and vice versa. The presentation layer works to transform data into the form that the application layer can accept. This layer formats and encrypts data to be sent across a network, providing freedom from compatibility problems. It is sometimes called the syntax layer . Session (layer 5) This layer establishes, manages and terminates connections between applications. The session layer sets up, coordinates, and terminates conversations, exchanges, and dialogues between the applications at each end. It deals with session and connection coordination. Transport (layer 4) This layer provides transparent transfer of data between end systems, or hosts, and is responsible for end-to-end error recovery and flow control . It ensures complete data transfer. Network (layer 3) This layer provides switching and routing technologies, creating logical paths, known as virtual circuits , for transmitting data from node to node. Routing and forwarding are functions of this layer, as well as addressing, internetworking , error handling, congestion control and packet sequencing. Data link (layer 2) At this layer, data packets are encoded and decoded into bits . It furnishes transmission protocol knowledge and management and handles errors in the physical layer, flow control and frame synchronization. The data link layer is divided into two sublayers: the media access control (mac) layer and the logical link control (llc) layer. The mac sublayer controls how a computer on the network gains access to the data and permission to transmit it. The llc layer controls frame synchronization, flow control and error checking. Physical
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This note was uploaded on 03/21/2011 for the course DCN 386 taught by Professor Allison during the Winter '10 term at Seneca.

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DCN386 - 1(2 marks Identify four Data Communications...

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