【正文】 Sx = Pr (Rr Pr) or (Pm Pr) amp。1 Ring Networks Ring Networks ? All rights reserved. No part of this publication and file may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without prior written permission of Professor NenFu Huang (Email: ). 2 Ring Networks Ring Network ?Active Repeater ?PointtoPoint Connections ?Unidirectional Transmission 3 Ring Networks Ring Network ?Functions of the Repeater ?Frame Insertion: Medium Access Control Dependent ?Frame Reception: Address Recognition ?Frame Removal: Close Loop without Terminators ? By Source: Automatic Acknowledgement Multicast and Broadcast Addressing ? By Destination: Increase Channel Utilization (for HighSpeed Network) 4 Ring Networks Ring Network Configuration 訊標(biāo) Token 網(wǎng)路卡 工作站 網(wǎng)路卡 工作站 網(wǎng)路卡 工作站 網(wǎng)路卡 工作站 網(wǎng)路卡 工作站 5 Ring Networks Repeater States ?Listen State: Retransmission with a small delay to allow the repeater to perform necessary functions ? Scan passing bit stream and pattern identification ? Copy ining bit to the station while retransmit each bit ? Modify a bit as it passes by 6 Ring Networks Repeater States ?Transmit State: Transmit the frame and receive bit from the ining link ?Receive its own bit: if the bit length of the ring is shorter than the frame ?Buffer others bits for retransmission later 7 Ring Networks Repeater States ?Bypass State: If station falls or its powered off ?Provide a better work reliability ?Eliminate unnecessary repeater delay 延遲一個位元時間 工作站 工作站 工作站 8 Ring Networks Bit Length ?Total number of bits can reside in the ring simultaneously ?Example ?100 repeaters (repeater delay = 1 bit) ?Distance between two repeaters: 10 meters ?Data rate: 10 Mbps ?Propagation Velocity: 2x108 m/s ?Bit Length Between two stations ((10 m)/(2x108 m/s)) x (107 bit/s) = bit ?Total Bit Length 100 + 100 x = 150 bits 9 Ring Networks Medium Access Control Method Token Ring ?Freetoken A special bit pattern (., 11111111) ?Busytoken The last bit of the free token is changed (., 11111110) ?Any station gets the freetoken may change it to a busytoken and followed by the frame to be transmitted. 10 Ring Networks ?Bit stuffing may be used to avoid data confusing with the token. ?The source station will remove the frame from the ring ?A new freetoken will be regenerated if the station has pleted transmission of its frame. ?If the frame is short, multiple tokens are possible. However, single token simplifies priority and error recovery functions Medium Access Control Method Token Ring 11 Ring Networks ?Only one frame can reside on the ring at a time. In single token, a free