Computer Science Notes

protocols have to be implemented. Compare and contrast OSI vs TCP/IP styles of defining what it is the parts of a network should do. OSI The ISO 7-layer reference model of a network, defined by committee. 1. Physical Layer. Hardware that implements a commlink. 2. Data Link Layer. Framing mechanism, e.g. EtherNet. 3. Network Layer. Packet routing, e.g. IP. 4. Transport Layer. End-to-end messaging, e.g. TCP, UDP. 5. Session Layer. (Application datastream multiplexing?) 6. Presentation Layer. (Data Format, e.g. endianness, ASCII vs UTF8) 7. Application Layer. (The application proper) TCP/IP The IETF 4-layer model. This was never really formally defined: it just happened this way. 1. Network. Hardware + Data Link. e.g., NIC + 802.3 2. IP. routing for packet-switched data 3. TCP, UDP. transport for packet-switched data. 4. Application. End-user apps. In the TCP/IP model, applications may access any of the the lower layers, not just the transport layer of TCP and UDP. 7.2 Physically conne..