Cabletron Systems manual BRIM-A6 User’s Guide B-7

Page 45

ATM Protocol

ATM provides the function of the first three layers of the OSI model, but performs all the information routing (cell switching) in only the Physical and Data Link Layer.

Performing the information routing functions in the Physical and Data Link layers essentially bypasses the Network Layer. This allows ATM to process cells much quicker and more efficiently than packet-based routing.

Since ATM differs with the OSI model in only its bottom three layers, a direct comparison of each layer provides the best method for understanding where these changes exist.

Layer 1: Physical Layer

In both models, the Physical Layer defines how information is transported over a network. This information includes all the physical connectors, pinouts, voltage levels, media type, and so on, that are considered valid for the network.

The major difference between each model in the Physical Layer, is in the type of media considered suitable for transmission. While PTM transmission protocols specify certain media types, ATM is not limited to any particular media. Due to its fixed-cell construction, ATM is only limited to the media type it uses. For example, if ATM is operating over coaxial cable, it only performs at the level that coaxial cable allows.

Layer 2: The Data Link Layer vs. The ATM Layer

In the OSI model, the Data Link Layer is involved with data transmission, error detection, and flow control. The data link layer acts as a shield for higher network model layers by controlling transmission and reception.

In the ATM model, the ATM layer defines the format of the ATM cell, and how it is transmitted over an ATM network. In addition, this layer defines the negotiated quality of service (QOS) and Traffic Management. This information is contained within the Header field of the cell.

BRIM-A6 User’s Guide

Page B-7

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Page 44 Page 46
Contents BRIM-A6 USER’S Guide BRIM-A6 User’s Guide FCC Notice DOC NoticeVcci Notice Exclusion of Warranty and Disclaimer of Liability Cabletron SYSTEMS, INC. Program License AgreementCabletron Software Program License United States Government Restricted Rights Declaration of Conformity Contents Viii BRIM-A6 User’s Guide Chapter Introduction Using this ManualFollowing conventions are used throughout this document Document ConventionsBRIM-A6 Overview BRIM-A6 FeaturesRelated Manuals BRIM-A6 SpecificationsEMI EMCGetting Help Unpacking the Brim Chapter InstallationInstalling an Apim Installing ApimsInstalling a Brim in a MIM Installing BrimsRemoving the Brim Coverplate Installing a Brim in a Hub BRIM-A6 User’s Guide Chapter Local Management Keyboard Conventions Function Local Management Keyboard ConventionsATM Connection Tables Screen Using LIM to Create PVCsATM Connection Tables Screen Fields Using ATM Connection Tables Screen Commands ATM Connection Tables Screen CommandsDeleting PVCs from the Connection Tables Screen Adding PVCs to the Connection Tables ScreenBRIM-A6 Setup Screen Using LM to Create PvcsBRIM-A6 Setup Screen Fields VPIVCI BRIM-A6 Setup Screen Commands Accessing the BRIM-A6 Add/Delete Entry Screen Using BRIM-A6 Setup Screen CommandsBRIM-A6 Add/Delete Entry Screen Fields Adding a PVC BRIM-A6 Add/Delete Entry Screen CommandsModifying a PVC Deleting a PVC BRIM-A6 LEDs ChapterDescribes each of the Apim LEDs Apim LEDsAppendix a Apim Specifications APIM-11 SpecificationsAPIM-21 Specifications APIM-29 Specifications APIM-22 SpecificationsBNC APIM-67 SpecificationsATM Basics Appendix B ATM OverviewFigure B-1 ATM Cells ATM CellBRIM-A6 User’s Guide B-3 Virtual Channels and Virtual Paths ATM NetworkATM Protocol Permanent and Switched Virtual ChannelsB-6 BRIM-A6 User’s Guide BRIM-A6 User’s Guide B-7 B-8 BRIM-A6 User’s Guide
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