CN534B

CN534B

以太網(wǎng)技術的zui初進展來自于施樂帕洛阿爾托研究中心的許多先鋒技術項目中的一個。人們通常認為以太網(wǎng)發(fā)明于1973年，當年羅伯特·梅特卡夫(Robert Metcalfe）給他PARC的老板寫了一篇有關以太網(wǎng)潛力的備忘錄。但是梅特卡夫本人認為以太網(wǎng)是之后幾年才出現(xiàn)的。在1976年，梅特卡夫和他的助手David Boggs發(fā)表了一篇名為《以太網(wǎng)：局域計算機網(wǎng)絡的分布式包交換技術》的文章。1977年底，梅特卡夫和他的合作者獲得了“具有沖突檢測的多點數(shù)據(jù)通信系統(tǒng)"的。多點傳輸系統(tǒng)被稱為CSMA/CD（帶沖突檢測的載波偵聽多路訪問），從此標志以太網(wǎng)的誕生。

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1979年，梅特卡夫為了開發(fā)個人電腦和局域網(wǎng)離開了施樂，成立了3Com公司。3com對迪吉多，英特爾，和

以太網(wǎng)插頭

施樂進行游說，希望與他們一起將以太網(wǎng)標準化、規(guī)范化。這個通用的以太網(wǎng)標準于1980年9月30日出臺，當時業(yè)界有兩個流行的非公有網(wǎng)絡標準令牌環(huán)網(wǎng)和ARCNET，在以太網(wǎng)大潮的沖擊下他們很快萎縮并被取代。而在此過程中，3Com也成了一個化的大公司。

梅特卡夫曾經(jīng)開玩笑說，Jerry Saltzer為3Com的成功作出了貢獻。Saltzer在一篇與他人合著的很有影響力的論文中指出，在理論上令牌環(huán)網(wǎng)要比以太網(wǎng)*。受到此結論的影響，很多電腦廠商或猶豫不決或決定不把以太網(wǎng)接口做為機器的標準配置，這樣3com才有機會從銷售以太網(wǎng)網(wǎng)卡大賺。這種情況也導致了另一種說法“以太網(wǎng)不適合在理論中研究，只適合在實際中應用"。也許只是句玩笑話，但這說明了這樣一個技術觀點：通常情況下，網(wǎng)絡中實際的數(shù)據(jù)流特性與人們在局域網(wǎng)普及之前的估計不同，而正是因為以太網(wǎng)簡單的結構才使局域網(wǎng)得以普及。梅特卡夫和Saltzer曾經(jīng)在麻省理工學院 MAC項目（Project MAC）的同一層樓里工作，當時他正在做自己的哈佛大學畢業(yè)論文，在此期間奠定了以太網(wǎng)技術的理論基礎。

IDEAL 85491 RG-58 BNC PLUG TWIST-ON PLUG PVC, BAG OF 5, NEW IN BAG
 
HUBBELL 120/277VAC 20A SINGLE POLE TOGGLE SWITCH, HBL1221GY *NEW*
 
RELIANCE ELECTRIC 115VAC/DC DUAL INPUT MODULE 45C40
 
MICRO SWITCH 15A ROLLER PLUNGER MICRO SWITCH BZ-2RQ18-A2 *NEW*
 
PEPPERL + FUCHS 24-240/250VAC, 12-240VDC PHOTOELECTRIC SENSOR FE7D-RPR7 *NEW*
 
TAPER SHANK HIGH SPEED STEEL BLACK OXIDE PTD 27/32 HSS BRAZIL
 
ABB CIRCUIT BREAKER S281 K 20A
 
ACME 2000VA 240 X 480PR 60HZ DRY TYPE DISTRIBUTION TRANSFORMER T 2-53012-S *NIB*
 
COOPER CROUSE-HINDS 600V 8A 6P 6' FEMALE PLUG CORDSET, X8987-4C *NEW*
 
MENCOM * 3-PIN/F CABLE ASSEMBLY NIB * MAC-3FP-12
 
FUJI ELECTRIC CIRCUIT PROTECTOR 15A 250V 1KA 41-20112
 
TURCK 20-250VAC/DC PROXIMITY SWITCH Bi2-CRS260-ADZ3?0X2-B1131/S34
 
FABCO AIR THE PANCAKE LINE AIR VALVE 14SP-3
 
ACCUSPEC CAPACITOR 020190 220 Ohm 1/2WATT 104X122CA-002
 
FLAME RESPONSE 3 SEC R7023 B 1003
 
DELTA CONTROLS MODEL 852 LEVEL TRANSMITTER 852D-1-4X-LE
 
TPC WIRE & CABLE 4 POLE MALE 90° DC MICRO CONNECTORS, 39700 *NEW LOT OF 9*
 
LUMBERG CONNECTOR RSF50-677/1FT NNB LOT OF 8
 
SHOPLOGIX INC. RELAY ISN-075-DEV3-00?0005
 
HIRSCHMANN RS2-TX 8 PORT ETHERNET RAIL SWITCH
 
ROBOTRON ROBOTRON ROLLER HEAD LIMIT SWITCH T-GWA 1 R
 
IDEC 10AMP 300V 8PIN RELAY SOCKET BASE LOT OF 4 SH2B-05
 
ALLEN BRADLEY WHITE PUSHBUTTON W/ TRANSFORMER AND CONTACTORS 800E-2T5
 
CKD VALVE AB21-D2-2-2
 
ATLAS COPCO 5/8" DRIVE NUTRUNNER 4220 3752 11 / QMR62-46-RT / QRT 62-200
 
TURCK 250V 4A 4PIN STRAIGHT MALE/FEMALE CORDSET, RKC 4.4T-2-RSC 4.4T *NEW*
 
SCC STATIC CONTROLS CORPORATION OPERATOR INTERFACE 1080-P4-14-128-?C-FN
 
UB TAP PIPE TAPER HSS 1/4-18NPT
 
ALLEN BRADLEY 1 AMP 3 POLE CIRCUIT BREAKER LOT OF 7 1492-ACB SER B
 
FESTO 8 PIN DISTRIBUTOR PORT MPV-E/A-08-M8 NIB
 
YOKOGAWA 0-600 DC AMPERES GAUGE 251300DRDR7JLA
 
SOLO ELECTRIC GS TRANSFORMER 83--24-260-2
 
DORMEYER LAMINATED SOLENOID 2006-M-1 NNB
 
ENLIN FLANGE END CAP A/SA182 F316L/316 150B16.5 4 8L3J0
 
ALLEN BRADLEY * DEVICENET CORDSET * 1485R-P5M5-C SER. A
 
ALLEN BRADLEY 3 POSITION SELECTOR SWITCH 800T-J2KU7 SER T
 
RADISYS 85-250V INPUT 1.0A POWER SUPPLY, EMC-PS5-AC *NEW*
 
SICK PHOTOELECTRIC REFLEX SWITCH EL3-P2428 1044704 NIB
 
GENERAL ELECTRIC 200A 3P 600VAC FUSIBLE INTERRUPTER QMR364
 
HAROWE HAROSYN-RW RESOLVER 11BRW-300-M-10B
 
16A 690V ON/OFF SWITCH IEC/ EN 60947-3
 
HUBBELL 3/4" STRAIN RELIEF CONDUIT GRIP NIB 074093513
 
MODICON CABLE ASSEMBLY AS-W804-006 *NEW IN BOX*
 
TURCK * 3-PIN M/F 22AWG CABLE ASSEMBLY NIB * KB 3T-6-SB 3T
 
UNITED ABRASIVES TYPE 1 BENCH GRINDER WHEEL SAIT 28023
 
ABB CA7-40K W/ ABB TBC25
 
ROSS 3/2 NORMALLY CLOSED SINGLE SOLENOID PILOT 2773B6011

    
REAL POWER 115/230VAC 60/50Hz POWER SUPPLY RPS-7230
 
SUMITOMO HEAVY INDUSTRIESBACKP?LANE CHASSIS WITH BPIS SA765265AD/SA76?5266AX
 
FANUC PERTRONICS 0.1KVA TRANSFORMER A80L-0010-0071-?02
 
VICTAULIC PIPE HOUSING 10" ID STYLE 995
 
UNKNOWN MFG * 208/220V 60CYC COIL NIB * TB10-2
 
UNION BUTTERFIELD TAP 5/16-18 H3 2F PLUG SP PT
 
KASUGA TRANSFORMER 500 VA DVSE500
 
HEIDENHAIN CONNECTING CABLE 298400-07
 
NACHI TEACHING CONTROLLER RTC221
 
GENERAL ELECTRIC PANEL METER 50-255320RXRX1J?AF
 
TWECO POSITIVE-CAM CABLE CONNECTOR COMPLETE 2-MPC
 
PARKER 1" ROD SEAL KIT RK2AHL0101
 
MOELLER MANUFACTURING CO. CIRCUIT BREAKER FAZNS1
 
APPLETON 1 1/2 X UNILET FORM 35
 
WESTINGHOUSE PPD VOLTAGE TRANSFORMER 7526A05G04
 
BINDICATOR BIN-LEVEL INDICATOR A-1-MN
 
WEISS PRESSURE GAUGE 0-150 F
 
RELIANCE ELECTRIC 3.38V 100A TRANSMITTER 600595-13AD *NEW*
 
2" VALVE T250G
 
ALLEN BRADLEY 509-TOA SER B NEMA SIZE 00
 
BARNES 1/2 HUB SIZE CONDUIT CONNECTOR BAG OF 2 17441
 
ELECTRICAL CONNECTOR 0-250VAC LOT OF 2 TYPE 2508
 
LITFUSE 6-1/4A 600V POWR-GARD FUSE FLSR 6-1/4 *LOT OF 6*
 
WESTINGHOUSE 300V BF CONTROL RELAY BF22F NIB
 
MOORE CIRCUIT BOARD 15936-11-3
 
TURCK UPROX 4-PIN PROXIMITY SENSOR Bi6U-EM18H-AN6X?-H1141
 
WESTINGHOUSE RELAY MOTOR PROTECTOR CONTROL IQ-1000
 
ALLEN BRADLEY 600V 200A 3-POLE FUSEHOLDER SET X-410743 & X-402237
 
RELIANCE ELECTRIC 24VOLTS 1.90W FLIGHT II FAN ASSEMBLY 615196-SR *NEW NO BOX*
 
ELECTROMOTOREN 24VDC 5A ACTUATOR LINEAR DRIVE MAX30-A300515A2?510A-000 *CUT CABLE
 
GE 3POLE 60AMP 600 VAC FLEX-A-PLUG BROKEN PLUG COVER FVK362R
 
MEASUREX CP+ TRANSITION 05427000 REV A
 
ALLEN BRADLEY * TRANSFORMER TYPE M * X-343858
 
TURCK * SENSOR * BI2-G12-YO
 
SMC SOLENOID VALVE EVT307V
 
GE DIELEKTROL VII FLUID 2400V 3PH 60KV CAPACITOR 54L303WS60
 
ITT 120V 60HZ CLASS-A SOLENOID COIL, C225A02A18 *NEW*
 
ADVANCE 120V CORE AND COIL BALLAST REPLACEMENT KIT T1B061 *NEW*
 
SIC HEATING ELEMENT RC049 0052
 
ASHCROFT 0-100PSI INDUSTRIAL DURALIFE GAUGE 35-109-AW-2B-10?0
 
ALLEN BRADLEY AC RELAY 700-N200A1 SER. B
 
TDK 250VAC 20A NOISE FILTER ZAG2220-11S
 
BACO 12A 600VAC 2 POSITION MAINTAINED SWITCH PR12
 
FESTO MANIFOLD BLOCK PRS-ME-1/8-3
 
ALLEN BRADLEY CONTACT BLOCK 800T-XD2 SER D
 
HONEYWELL PRECISION LIMIT SWITCH 51ML2 8642
 
ALLEN BRADLEY PILOT LAMP KIT CLEAR LENS 125 VOLTS SER A NIB 1699-N71

    
ORIENTAL INDUCTION MOTOR 3IK15GN-AW W/ GEARHEAD 3GN5KA
 
ALLEN BRADLEY BLUE MUSHROOM PUSH BUTTON LOT OF 2 800T-D... SER T 99073
 
ALLEN BRADLEY * SIZE 2 TYPE 4 AC AUTOMATIC STARTER * 709-CCA SER. L
 
ADVANCE INSTANT START ELECTRONIC 120V 60HZ REL2P60S
 
GAST 115V, 1725RPM, 1-PHASE, 60CYCLE PISTON AIR COMPRESSOR 3LBA-10-M300X *NEW*
 
OHMITE 25 WATTS 10K OHMS VITREOUS ENAMELED RESISTORS, 0215 *NEW LOT OF 6*
 
TAPER SHANK HIGH SPEED STEEL BLACK OXIDE PTD 13/16 HSS
 
GENERAL ELECTRIC PURPOSE CONTACTOR 24V CR7RB
 
POWER TEAM ENERPAC HYDRAULIC HAND PUMP REPAIR KIT
 
BELL & HOWELL M-SERIES PRESSURE TRANSMITTER 4-373-0107
 
SPEED-RAIL LOT OF 2 31-18
 
MIDWEST ELECTRIC CURRENT TRANSFORMER 3CT13-B
 
VALBIA SR-085 SET05 PNEUMATIC ROTARY ACTUATOR
 
EATON CUTLER-HAMMER CSMS3F3CY1604 600 VOLT 13 AMP 3PIN 13FT CORDSET, NEW IN BAG
 
ALLEN BRADLEY DEVICENET 5 PIN MALE PATCHCORD 1485G-P5D5-N5 SER. B *NEW*
 
TURCK 4 PIN PROXIMITY SENSOR BI16-EM30H-AP6X?-H1141/S1589
 
ABB CIRCUIT BREAKER S 221 K10A LOT OF 2
 
PANAMETRICS 26DL PLUS UNTRASONIC THICKNESS GAUGE
 
HARTING TOP ENTRY METAL HOOD, *NEW SEALED*
 
PARKER 3/8"NPT, 110/120V, 10W, 50/60HZ SOLENOID VALVE 74332BN3RNJ1N0D?1D1P3 *NEW*
 
OMRON 24VDC SAFETY RELAY UNIT, G9S-301
 
SMC * FITTINGS LOT OF 10 * KQW07-34S
 
FERRAZ SHAWMUT 600V, 30A 3 POLE FUSEHOLDER USCC3 M217522
 
TURCK * 18 AWG, 4 CONNECTOR CABLE NIB * RKG 4.4T-5-RSG 4.4T/S600
 
ALLEN-BRADLEY GENERAL PURPOSE MOUNTING BRACKET ASSEMBLY 60-1479 *NEW*
 
DYNA-QUIP CONTROLS DM4 LOT OF 7 BRASS - 1/4" MPT
 
BRAD HARRISON * 4-PIN/F 22AWG MICRO-CHANGE CABLE NIB * 804000A09M020
 
ORIENTAL COMPUTER FAN * MD1208PTS3
 
Newly listedSQUARE D THERMAL-MAGNETI?C CIRCUIT BREAKER SERIES 2 KAL262251021
 
UFM TYPE 4 FLOW METER MM-NSF16GM-4-32?V1.0-M3WR-PC4M-?DC-C-Z86-8U
 
ALLEN PRODUCTS, INC AT 210-4 COMMUNICATION CIRCUIT ACCESSORY, LOT OF 43, NEW
 
FUJI ELECTRIC * CONTACT BLOCK * 2DI30Z-100
 
GOULD SHAWMUT 600V 3-POLE POWER DISTRIBUTION BLOCK 68083
 
HONEYWELL * PROXIMITY SWITCH * 923AA2HM-A7T-L
 
KEYENCE STATIC ELIMINATOR CONTROLLER POWER SUPPLY UNIT ONLY SJ-S020
 
ALLEN BRADLEY BULLETIN 700 SUPPRESSOR FILTER BAG OF 3 700-AV3R
 
VICTAULIC PIPE JOINING SYSTEM S'/163.3MM STYLE 920
 
MAH NEER STEEL CONDUIT LOCKNUTS100 IN BOX 3/4 " L-200 NIB
 
FUJI ELECTRIC BLACK PUSH BUTTON LOT OF 7 AR22F0R
 
BLACK SELECTOR SWITCH 99656
 
BEI 3/8" SHAFT DIA. ENCODER, H25D-SS-180-ABZ?-7406R-EM16
 
EMECANIQUE CLUSTER GREEN LIGHT SET NIB XVBKEQ37433G3
 
APPLETON 1 1/4" MALL IRON CONDUIT HUBS STRAIGHT HUB-125 NIB
 
ALLEN BRADLEY OVERLOAD RELAY 193-A4C1 SER A
 
NEER PLASTIC INSULATING CONDUIT BUSHING PB-500 1/1/2" LOT OF 20
 
UNKNOWN MFG * CABLE * E-18621-7
 
PARKER 60 SERIES BRASS COUPLER BH4-60
 
ALLEN BRADLEY 110/115-120V COIL SIZE 1 REVERSING STARTER 509-BOD SER. A

DONGAN 120X240V 150KVA 3R SINGLE PHASE TRANSFORMER 35-M015
 
ALLEN BRADLEY DISSCONNECT HANDEL 1494F-MI *NEW NO BOX*
 
DEVAR 4-1/2 DIGIT LOOP POWERED INDICATOR 18-LPI-4
 
SIEMENS CABLE A5E02161627
 
BANNER 20-250VAC PHOTOELECTRIC SENSOR S18RW3DLQ
 
ASHCROFT 0-250 DEGREES F -20-120 DEGREES C BIMETAL THERMOMETER 2F034 *NEW*
 
NUMATICS 150PSIG, 24VDC, 6.0W, 1/4"NPT SOLENOID VALVE 11SAD44AB
 
ORIENTAL MOTOR GEAR HEAD 4GN7.5K
 
MILLER SAFETY CLIMBING BELT LARGE 2NA
 
HONEYWELL 305965 30 PSI 1/8" NPT PRESSURE GAUGE, NIB
 
NUMATICS ACTUATOR 1A, 6-24VDC HALL EFFECT SENSOR AH6-002
 
CLE FORGE 1 21/64 HS DRILL BIT 205695
 
RUSSELLSTOLL 250V 50A ONE WAY EVERLOK RECEPTACLE ENCLOSURE 8331 *NEW*
 
BRAD HARRISON * 3 POLE FEMALE 22AWG CABLE NIB * 8030P1D01M050
 
MICRO SWITCH 10-28VDC PHOTOELECTRIC SWITCH, FE8B-TC6GR-M
 
ALLEN BRADLEY 120VAC 10A RELAY LOT OF 4 700-HA32A1-3-4 SER D
 
VEXTA 5-PHASE STEPPING MOTOR UPH599-B2
 
OM OREINTAL MOTOR INDUCTION MOTOR 5IK40GN-AUL
 
OKAYA 250VAC 5A NOISE FILTER SUP-P5H-EPR-4
 
COXREELS * 3/16" CABLE REEL WITH STAINLESS CABLE * SD-35-1
 
GKT 800 REPAIR FLAT GHN 421825-1
 
BALLUFF 35-250VAC 3 PIN PROXIMITY SWITCH BES 515-449-S21-L
 
TURCK 250V, 4A, 4 M OAL CABLE WK 4.2T-4 *NEW*
 
SQUARE D FLUSH HEAD PUSH BUTTON 9001 1SKR1R SER. K *NEW*
 
TURCK CABLE RSMCBC5 5711-4M
 
BANNER FIBER OPTIC CABLE IAT2.53S
 
FESTO FILTER CARTRIDGE LFMBP-1/2-H NIB
 
BANNER * FIBER OPTIC CABLE * IAT13S-17913
 
HONEYWELL 15-30oC, SATIN CHROME, THERMOSTAT COVER 14004406-110 *LOT OF 17, NEW*
 
RELIANCE ELECTRIC * MOTOR BRUSH NIB BOX OF 8 * 416956-4DF
 
BODINE * GEAR MOTOR * 48R6BFC1-F2
 
BANNER POWER BLOCK 2PBA
 
SIEMENS SUBRACK CR2 C-L6B01616
 
SANYO DENKI BRUSHLESS DC FINE ACE 20 109P0424H6D11
 
SHAWMUT AMPTRAP CLASS J 400AMPS FUSE A4J400
 
WESTINGHOUSE SERIES C MOLDED CASE SWITCH 480A 3 POLE 600VAC KD3400KW
 
DYNAMATIC 10HP P/S BOARD 15-871-5
 
PARKER 2.50" STROKE 3." BORE PNEUMATIC CYLINDER 02.50 BB2ANU14 3.00
 
CUTLER HAMMER 3A 600V CONTACTOR CE15AN3 B1
 
TURCK CABLE 9-PIN 4PR/24 NIB RJ45SFKSD841-2M
 
DATA TECHNOLOGY OPTECON ENCODER, ON35-1250-50/5
 
ALLEN BRADLEY 872C-D 3NN12-D4 SERIES C PROXIMITY SENSOR NNB
 
FUJI ELECTRIC 220VAC 5A 2 POLE CIRCUIT BREAKER, SA32B
 
ALLEN BRADLEY CIRCUIT BREAKER 1POLE 4 A LOT OF 7 1492-CB1 H400 SER C
 
SCHMERSAL 24VDC SAFETY RELAY SCR 1R
 
UNKNOWN MFG * SOLENOID COIL * 27-462-1
 
IMO ACTUATED SWITCH VALVE D1H-A150 NNB
 
1/8" BRASS SOCKET PLUG LOT OF 20