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11-29-2011, 09:06 PM
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cs601 helping material for preparation
The International Standards Organization created a model called the Open Systems Interconnection, which allows diverse systems to communicate.
The seven-layer OSI model provides guidelines for the development of universally compatible networking protocols. The physical, data link, and network layers are the network support layers. The session, presentation, and application layers are the user support layers. The transport layer links the network support layers and the user support layers. The physical layer coordinates the functions required to transmit a bit stream over a physical medium. The data link layer is responsible for delivering data units from one station to the next without errors. The network layer is responsible for the source-to-destination delivery of a packet across multiple network links. The transport layer is responsible for the process-to-process delivery of the entire message. The session layer establishes, maintains, and synchronizes the interactions between communicating devices. The presentation layer ensures interoperability between communicating devices through transformation of' data into a mutually agreed upon format. The application layer enables the users to access the network TCP/IP is a five-layer hierarchical protocol suite developed before the OSI model. The TCP/IP application layer is equivalent to the combined session, presentation, and application layers of the OS! model. Four levels of addresses are used in an internet following the TCP/IP protocols: phys-ical (link) addresses, logical (IP) addresses, port addresses, and specific addresses. The physical address, also known as the link address, is the address of a node as defined by its LAN or WAN. The IP address uniquely defines a host on the Internet. The port address identifies a process on a host. A specific address is a user-friendly address. 
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