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Temat artykułu: OSI Model
Tekst napisał pitt2k dnia 08-01-2004
OSI Reference
The OSI Model is the most important concept in the entire study guide, memorize it!! Many of the test questions will probably be based upon your knowledge about what happens at the different layers.
OSI MODEL
Layer Name Function
7 Application Layer Provides network services to user applications. Establishes program-toprogram communication. Identifies and establishes the availability of the intended communication partner, and determines if sufficient resources exist for the communication.
6 Presentation Layer Manages data conversion, compression, decompression, encryption, and decryption. Provides a common representation of application data while the data is in transit between systems. Standards include MPEG, MIDI, PICT, TIFF, JPEG, ASCII, and EBCDIC.
5 Session Layer Responsible for establishing and maintaining communication sessions between applications. In practice, this layer is often combined with the Transport Layer. Organizes the communication through simplex, half and full duplex modes. Protocols include NFS, SQL, RPC, AppleTalk Session Protocol (ASP) and XWindows.
4 Transport Layer Responsible for end-to-end integrity of data transmission. Hides details of network dependent info from the higher layers by providing transparent data transfer. The "window" works at this level to control how much information is transferred before an acknowledgement is required. This layer segments and reassembles data for upper level applications into a data stream. Port numbers are used to keep track for different conversations crossing the network at the same time. Uses both connection-oriented and connectionless protocols. Supports TCP, UDP and SPX.
3 Network Layer Routes data from one node to another. Sends data from the source network to the destination network. This level uses a 2 part address to establish and manages addressing, track device locations, and determines the best path to use for moving data on the internetwork. Responsible for maintaining routing tables. Routers operate at this level.
2 Data Link Layer Responsible for physically transmission of data from one node to another. Handles error notification, network topology, flow control. Translates messages from the upper layers into data frames and adds customized headers containing the hardware destination and source address. Bridges and switches operate at this layer.
Logical Link Control Sublayer - Acts as a managing buffer between the upper layers and the lower layers. Uses Source Service Access Points (SSAPs) and Destination Service Access Points (DSAPs) to help the lower layers talk to the Network layer. Responsible for timing, and flow control.
Media Access Control Sublayer - Builds frames from the 1's and 0's that the Physical layer picks up from the wire as a digital signal, and runs Cyclic Redundancy Checksum (CRC) to assure that nothing was damaged in transit. 1 Physical Layer Manages putting data onto the network media and taking the data off. Sends and receives bits. Communicates directly with communication media. Provides electrical and mechanical transmission capability.
REMEMBER THIS !!!
Know the above OSI model definitions backward and forward.
Know that the OSI model was originally developed so different vendor networks could work with each other.
Know the 2 sublayers of the Data Link Layer and the function of each.
Know that the Network Layer devices have 4 characteristics: 1) Two-part addresses, 2) Use routing tables, 3) Use broadcast addresses, and 4) provide path selection.
Opracowanie na podstawie materiałów TroyTech (www.troytech.com).
Temat artykułu: OSI Model
Tekst napisał pitt2k dnia 08-01-2004
OSI Reference
The OSI Model is the most important concept in the entire study guide, memorize it!! Many of the test questions will probably be based upon your knowledge about what happens at the different layers.
OSI MODEL
Layer Name Function
7 Application Layer Provides network services to user applications. Establishes program-toprogram communication. Identifies and establishes the availability of the intended communication partner, and determines if sufficient resources exist for the communication.
6 Presentation Layer Manages data conversion, compression, decompression, encryption, and decryption. Provides a common representation of application data while the data is in transit between systems. Standards include MPEG, MIDI, PICT, TIFF, JPEG, ASCII, and EBCDIC.
5 Session Layer Responsible for establishing and maintaining communication sessions between applications. In practice, this layer is often combined with the Transport Layer. Organizes the communication through simplex, half and full duplex modes. Protocols include NFS, SQL, RPC, AppleTalk Session Protocol (ASP) and XWindows.
4 Transport Layer Responsible for end-to-end integrity of data transmission. Hides details of network dependent info from the higher layers by providing transparent data transfer. The "window" works at this level to control how much information is transferred before an acknowledgement is required. This layer segments and reassembles data for upper level applications into a data stream. Port numbers are used to keep track for different conversations crossing the network at the same time. Uses both connection-oriented and connectionless protocols. Supports TCP, UDP and SPX.
3 Network Layer Routes data from one node to another. Sends data from the source network to the destination network. This level uses a 2 part address to establish and manages addressing, track device locations, and determines the best path to use for moving data on the internetwork. Responsible for maintaining routing tables. Routers operate at this level.
2 Data Link Layer Responsible for physically transmission of data from one node to another. Handles error notification, network topology, flow control. Translates messages from the upper layers into data frames and adds customized headers containing the hardware destination and source address. Bridges and switches operate at this layer.
Logical Link Control Sublayer - Acts as a managing buffer between the upper layers and the lower layers. Uses Source Service Access Points (SSAPs) and Destination Service Access Points (DSAPs) to help the lower layers talk to the Network layer. Responsible for timing, and flow control.
Media Access Control Sublayer - Builds frames from the 1's and 0's that the Physical layer picks up from the wire as a digital signal, and runs Cyclic Redundancy Checksum (CRC) to assure that nothing was damaged in transit. 1 Physical Layer Manages putting data onto the network media and taking the data off. Sends and receives bits. Communicates directly with communication media. Provides electrical and mechanical transmission capability.
REMEMBER THIS !!!
Know the above OSI model definitions backward and forward.
Know that the OSI model was originally developed so different vendor networks could work with each other.
Know the 2 sublayers of the Data Link Layer and the function of each.
Know that the Network Layer devices have 4 characteristics: 1) Two-part addresses, 2) Use routing tables, 3) Use broadcast addresses, and 4) provide path selection.
Opracowanie na podstawie materiałów TroyTech (www.troytech.com).