OSI 7 Layer Reference Model

•Physical – transmission of raw bits over a communication channel, e.g. RS-232-C

•Data Link – reliable transmission of a block of data (frame)‏

•Put as special bit pattern on the start and end of each frame.

•Compute a checksum by adding up all the bytes in the frame.

Discussion between a receiver and a sender in the data link layer.

•Network – describes how packets in a network of computers are to be routed.

•IP (Internet Protocol) is a connectionless protocol.

•The virtual channel in ATM (asynchronous transfer mode) is a connection-oriented network layer protocol.

•Transport – logical communication channel between processes (message)‏

•TCP (Transmission Control Protocol): connection-oriented, reliable communication.

•UDP (Universal Datagram Protocol): connection-less unreliable (best-effort) datagram communication.

•TCP for transactions (T/TCP): A TCP protocol combines setting up a connection with immediately sending the request, and sending an answer with closing the connection.

•RTP (Real-time Transport Protocol) is used to support real-time data transfer.

a) Normal operation of TCP.
b) Transactional TCP.

•Session – dialog control between end applications

•Presentation – data format translation

•Application – e.g. ftp, telnet, Web browser, and etc.

•FTP (File Transfer Protocol)‏

•HTTP (HyperText Transfer Protocol)‏

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