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Understanding the network.pdf - Back to Home

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presents data in a common and universally acceptable form that can be transported<br />

and exchanged without concern for <strong>the</strong> terminal used for displaying <strong>the</strong> data.<br />

Pro<strong>to</strong>cols associated with this layer are <strong>the</strong> following:<br />

• ISO—Connection-oriented presentation pro<strong>to</strong>col<br />

• TCP/IP—Network Virtual Terminal (NVT)<br />

• AppleTalk—AppleTalk Filing Pro<strong>to</strong>col (AFP)<br />

Adobe PostScript<br />

• IPX—NetWare File Service Pro<strong>to</strong>col (NFSP)<br />

• Server Message Block (SMB)<br />

Layer 5: Session<br />

Layer 5 manages <strong>the</strong> exchange of data between application processes. Session<br />

interposes communication, flow control, and error checking services. Most <strong>network</strong><br />

operating systems (AppleTalk, Novell NetWare, and Microsoft Networking) provide<br />

service activities at this level. The variety of pro<strong>to</strong>cols used <strong>to</strong> provide session<br />

services are as follows:<br />

• ISO—Connection-oriented session pro<strong>to</strong>col<br />

• TCP/IP—Berkeley socket service<br />

System V streams service<br />

• AppleTalk—AppleTalk Data Stream Pro<strong>to</strong>col (ADSP)<br />

AppleTalk Session Pro<strong>to</strong>col (ASP)<br />

Printer Access Pro<strong>to</strong>col (PAP)<br />

Zone Information Pro<strong>to</strong>col (ZIP)<br />

• IPX—NetBIOS<br />

Layer 4: Transport<br />

Layer 5 checks <strong>the</strong> data for integrity and keeps <strong>the</strong> application program apprised of<br />

<strong>the</strong> communications process, but Layer 4 is concernedwith end-<strong>to</strong>-end data<br />

transport. This transport can be managed as ei<strong>the</strong>r connection-oriented or<br />

connectionless. Connection-oriented data transmission is needed for reliable

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