CCIE Practical Studies, Volume I

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Appendix B. The 'Abridged' OSI Reference Model

Almost every book on networking has some reference to the OSI reference model; this one will be no exception. However, instead of repeating the same text that you've probably already read 50 times, I would like to offer a new twist on the model in Table B-1. This information is presented here in less then 10 words per level, as an "abridged" OSI reference model. To read "unabridged" versions, refer to Interconnections, Second Edition: Bridges, Routers, Switches, and Internetworking Protocols by Radia Perlman or Networking Standards a Guide to OSI ISDN, LAN, and MAN Standards by William Stallings.

Table B-1. OSI Reference Model Quick Reference

OSI Layer "10-Word Description"
Application layer Governs end- user applications and services; FTP, WWW browsers, Telnet, SMTP
Presentation layer Handles data formats, encoding, and transfer; GIF, JPEG, ASCII, EBCDIC, HTML
Session layer Handles application dialogue control, data grouping, and recovery; NFS, SQL, NetBIOS
Transport layer Manages network connections; reliable (TCP and SPX) and unreliable(UDP) transport
Network layer Addresses and routes packets, packet fragmentation; IP, IPX, AppleTalk
Data link layer Controls physical layer data flow; Frame Relay, ATM, PPP, IEEE 802.x
Physical layer Defines electrical and physical specifications; EIA/TIA-232, V.35, 10Basex, B8ZS, NRZI
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