7 OSI Layer

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7 OSI Layer
2014-03-27 18:15:17
Application Layer
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  1. 7 - Application
    Provides services to lower layers. Enables program-to-program communication and determines whether sufficient resources exist for communication. Examples are e-mail, gateways, (SMTP), TFTP, FTP, SNMP
  2. 6 - Presentation Layer
    Presents information to the Application Layer. Compression, data conversion,  encryption, decryption and standard formatting occur here. Contains data formats JPEG, MPEG, MIDI, and TIFF
  3. 5 - Session Layer
    Establishes and maintains communication 'sessions' between applications (dialogue control) Sessions can be simplex (One direction only), half duplex (One direction at a time), or full duplex (both ways simultaneously). Session Layer keeps different applications data separate from other applications. Protocols include: NFS, SQL, X Windows, RPC, ASP, and NetBios Names
  4. 4 - Transport Layer
    Responsible for end-to-end integrity of data transmission and establishes a logical connection between sending and receiving hosts via 'virtual circuits' Windowing works at this level to control how much information is transferred before acknowledgement is required. Data is segmented and reassembled at this layer. Port numbers are used to keep track of different conversations crossing the network at the same time. Supports TCP, UDP, SPX, and NBP. Segmentation works here (Segments) and error correction (not detection)
  5. 3 - Network Layer
    Routes data from one node to another and determines the best path to take. Routers operate at this level. Network addresses are used here, which are used for routing (packets). Routing tables, subnetting, and control of network congestion occur here. Routing protocols, regardless of which protocol they run over, reside here: IPX, ARP, IGRP, and Appletalk
  6. 2 - Data Link Layer
    • Sometimes referred to as the LAN layer. Responsible for the physical transmission of data from one node to another. Error detection occurs here. Packets are translated into frames here and hardware address is added. Bridges and switches operate at this layer
    • (LLC ad MAC) Logical link Control sublayer manages comms between devices over a single link on a network. Uses service access point(SAP's) to help lower layers talk to the network layer
    • Media access Control sublayer (MAC) 802.3: Builds frames from 1s and 0s that the Physical Layer (address = 6 byte/48 bit) picks up from the wire as a digital signal and runs a Cyclic Redundancy Check(CRC) to assure no bits were lost or corrupted
  7. 1 - Physical Layer
    Puts data onto the wire and takes it off. Physical Layer specifications, such as the connectors, voltage, physical data rates, and DTE/DCE interfaces. Some common implementations include Ethernet/IEEE 802.3, FastEthernet, and Token Ring/IEEE 802.5