Layer 1 Physical • Physical channel • To move bits of data between systems • Hubs • Passive • Repeater • 1 and 0 • cabling Layer 2 Data Link Layer • Sub layers • Logical Link Layer • Media Access Control • Media Access Control • Remembers NICs MAC address • communicates with the adapter card • controls the type of media being used: • 802.3 CSMA/CD (Ethernet) Layer 2 Data Link Layer • Logical Link Layer • NIC talks to the operating system • Places data from the software into frames • Bridge • Switch • NIC Layer 3 Network • translates logical network address and names to their physical address (e.g. computername ==> MAC address) • responsible for • addressing • determining routes for sending • managing network problems such as packet switching, data congestion and routing • if router can’t send data frame as large as the source computer sends, the network layer compensates by breaking the data into smaller units. At the receiving end, the network layer reassembles the data • Routers • brouters Layer 4 Transport • Transport layer manages end to end message delivery in a network and also provides the error checking and hence guarantees that no duplication or errors are occurring in the data transfers across the network. • Transport layer also provides the acknowledgement of the successful data transmission and retransmits the data if no error free data was transferred. • It also provides and error handling and connectionless oriented data deliver in the network. Layer 6 Session • Session layer establish and manages the session between the two users at different ends in a network. • Session layer also manages who can transfer the data in a certain amount of time and for how long. • The examples of session layers and the interactive logins and file transfer sessions. • Session layer reconnect the session if it disconnects. It also reports and logs and upper layer errors. Layer 5 Presentation • The presentation layer presents the data into a uniform format and masks the difference of data format between two dissimilar systems. • It also translates the data from application to the network format. • Presentation layer is also responsible for the protocol conversion, encryption, decryption and data compression. Layer 7 Application • The application layer defines the interfaces for communication and data transfer. • This layer also provides and support services such as job transfer, handles network access, e-mail, supports user applications and error recovery. • Protocols: FTP, DNS, SMTP, FINGER, Network Devices: Gateway network device is operated on the application layer.
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