Cabletron Systems BRIM-F6 manual Figure A-4. Token and Frame Formats

Page 32

APPENDIX A: BASIC FDDI NETWORKS

Other functions of the PHY include generation of a 125 Mhz transmit clock, synchronization of the receive clock with an upstream transmitter, encoding and decoding for media control symbols, and in some applications, buffering for the incoming bit stream.

The MAC entity resides on the lower sublayer of the Data Link layer. The upper sublayer, Logical Link Control (LLC) serves as an interface between the OSI model and the FDDI network. The MAC element, under control of Station Management, performs many of the tasks associated with frame preparation and media access: ring scheduling, token generation, timers that monitor ring activity, ring initialization, and beaconing. Other tasks for the MAC entity include assembling data frames, maintaining medium addressing, and generating and checking data check bytes.

The MAC generates two basic message formats, tokens and frames. Figure A-4 shows the layout for each message. Control and format bits within the header define specific types of frames and classes of tokens. The MAC sublayer receives transmittable Data frames from the LLC as Service Data Units (SDUs). MAC uses these SDUs to construct Protocol Data Units (PDUs) that it passes on to PHY. The PDUs consist of a MAC header, the encapsulated SDU, and a Frame Check Sequence (FCS). The MAC generates FCS during transmission.

TOKEN

Preamble

16 Symbols

Starting Frame Ending

Delimiter Control Delimiter

2 Symbols 2 Symbols 2 Symbols

JK

TT

Frame Check

T

Sequence Coverage

 

 

 

FRAME

Preamble

16 Symbols

Starting Frame

Delimiter Control

2 Symbols 2 Symbols

Destination Address

Source Address

Information

4 or 12 Symbols

4 or 12 Symbols

0 Symbol Pairs

Frame Check

Sequence

8 Symbols

Ending

Delimiter

1 Symbols

Frame Status

3 Symbols

Maximum - 9000 Symbols

Figure A-4. Token and Frame Formats

Page A-6

BRIM-F6 User’s Guide

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Contents BRIM-F6 USER’S Guide Page Contents Page Chapter Introduction Using This Manual Getting HelpBRIM-F6 Overview BRIM-F6 FeaturesBRIM-F6 Overview Related Documentation Chapter Installation Unpacking the Brim and the FPIMsInstalling the FPIMs Fpim ScrewsInstalling the BRIM-F6 Installing the BRIM-F6Installing a BRIM-F6 into a MIM Brim Tab Installing a BRIM-F6 into a Hub BRIM-F6 User’s Guide Chapter Using Lanview TWR Twisted Ring Chapter Specifications Fiber Optic InterfaceMultimode Receiver Signal Detect Single Mode Specifications Single Mode ReceiverUnshielded Twisted Pair Receiver Signal Detect Cable Specifications Shielded Twisted Pair Transmitter SpecificationsMultimode Fiber Twisted Pair Pinout Configuration Twisted Pair Cable LengthSafety EnvironmentAppendix a Basic Fddi Networks BRIM-F6 User’s Guide A-1Appendix a Basic Fddi Networks Reliability BRIM-F6 User’s Guide A-3Figure A-2. Wrapping a Broken Ring Ansi Standard X3T9.5 BRIM-F6 User’s Guide A-5Figure A-4. Token and Frame Formats BRIM-F6 User’s Guide A-7 Fddi StationFddi Connection Rules Fddi Devices BRIM-F6 User’s Guide A-9Figure A-7. Valid Station Configurations Figure A-8. Duplex Fiber Optic Receptacles and Connectors BRIM-F6 User’s Guide A-11A-12 BRIM-F6 User’s Guide A-13 Bypass State Operational StateFigure A-10. Fddi Devices Design Considerations For Fddi Networks BRIM-F6 User’s Guide A-15Bandwidth Figure A-11. Physical Device Connections BRIM-F6 User’s Guide A-17
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