[工學(xué)]07-datalinkcontrol-展示頁
2025-01-28 10:31本頁面
【正文】 z信道利用率（ Utilization (efficiency)） 指出某信道有百分之幾的時間是被利用的（有數(shù)據(jù)通過）。 傳輸時延 = 數(shù)據(jù)塊長度（ 比特 ）數(shù)據(jù)的傳輸速率（ 比特 /秒 ）Transmission time： Time taken to emit all bits into medium時延 (delay 或 latency)z傳播時延 電磁波在信道中需要傳播一定的距離而花費(fèi)的時間。10Polynomials( 生成 多項(xiàng)式 ） P183For P=110011, P(X)=X5+X4+X+1常用的生成多項(xiàng)式：CRC12 = x12 + x11 + x3 + x2 + x + 1CRC16 = x16 + x15 + x2 + 1CRCCCITT = x16 + x12 + x5 + 111 Flow Control P209zFlow control: Assuring the sending entity does not overwhelm the receiving entity with datayPreventing buffer overflow12Model of Frame Transmission混淆13Stop and Wait flow control 停等流量控制 P210zSource transmits framezDestination receives frame and replies with acknowledgementzSource waits for ACK before sending next framezDestination can stop flow by not send ACKStop and waitA BDATADATAACK傳播時延 tp處理時間 tpr傳播時延 tp處理時間 tprtT時間兩個成功發(fā)送的數(shù)據(jù)幀之間的最小時間間隔數(shù)據(jù)幀的發(fā)送時間 tf設(shè)置的重傳時間tout時延 (delay 或 latency)z傳輸時延 （發(fā)送時延 ） 發(fā)送數(shù)據(jù)時，數(shù)據(jù)塊從結(jié)點(diǎn)進(jìn)入到傳輸媒體所需要的時間。沒有余數(shù)。（ 4）（ 5） 根據(jù)公式（ 2），可化簡為公式（ 5）。1 Error Detection (see chapter6 P177)zAdditional bits added by transmitter for error detection codezParity checkzCyclic Redundancy Check(循環(huán)冗余 )2Parity check 奇偶校驗(yàn) P179zAppend a parity bit to the end of a block of datazIf use odd parity(奇校驗(yàn) ), to transmit 1110001, append a 1 and transmit 11110001zThe receiver examines zValue of parity bit is such that character has even (even parity) or odd (odd parity) number of oneszEven number of bit errors goes undetected3Cyclic Redundancy Check(循環(huán)冗余 ) P179zFor a block of k bits message, transmitter generates n bit sequence as a frame check sequence (FCS)幀檢驗(yàn)序列zTransmit k+n bits which is exactly divisible by some numberzReceiver divides frame by that numberyIf no remainder, assume no error4Modulo 2 Arithmetic （模 2運(yùn)算）zUses binary addition with no carries (進(jìn)位 ), just the exclusive OR (異或 ) operation. 做加減運(yùn)算時：相同為 0，相異為 15CyclicRedundancy CheckRemainderAt the receiver:Trans
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