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RJ45/MDI-X/568A/568B

InfoTech
2012年3月14日 / 149次阅读
标签:以太网

什么是8P8C Contact

其实很简单,就是这个:

水晶头,8p8c contact

水晶头,8p8c contact

 

水晶头有8个铜片用来连接线缆。

还记得以前家里的电话线吗,那个水晶头只有2个铜片。

RJ45 Jack

rj45-jack

rj45-jack

 

水晶头那一端的称呼是connector。

MDI

A 10BASE-T or 100BASE-TX node such as a PC, with a connector called medium dependent interfaces (MDI), transmits on pin 1 and 2 and receives on pin 3 and 6 to a network device using a "straight-through" (pin 1 to pin 1, pin 2 to pin 2 and so on) cable. 10BASE-T and 100BASE-TX only require two pairs to operate.

以前MDI

Hosts (all devices except switch and hub) transmit on Pins 1 and 2;

Switches/Hubs listen on Pins 1 and 2 and transmit on Pins 3 and 6;

PCSwitch连用straight-through线缆;

SwitchSwitch连用crossover线缆;

SwitchHub是一组,其它设备是一组,组内crossover,组间straight-through

这两种线的差别非常小,就是一条内线的链接不一样;

crossover连接方法,以前做网线需要用到。

crossover连接方法,以前做网线需要用到。

 

MDI-X

MDI-X口,就是在接口内进行crossover,还是使用straight-through线缆;以前这种口常常被称为Uplink。现在已经全自动了。Many modern Ethernet host adapters can automatically detect another computer connected with a straight-through cable and then automatically introduce the required crossover, if needed; if neither of the adapters has this capability, then a crossover cable is required. Most newer switches have automatic crossover ("auto MDI-X" or "auto-uplink") on all ports, eliminating the uplink port and the MDI/MDI-X switch, and allowing all connections to be made with straight-through cables. If both devices being connected support 1000BASE-T according to the standards, they will connect regardless of the cable being used or how it is wired.

GE口的时代,已经不存在这个问题了,标准已经定义;(straight-through and cross-over cables are still applicable, but most of device have supported the Mdix. So, it’s not a big issue anymore.

FE口还配置在很多CPE和企业级小Router上,所有还能在标书中看到这个。

Cisco设备接口下有个命令mdix auto,默认使能。

straight-through的两个标准568A/568B

straight-through的两个标准568A/568B

straight-through的两个标准568A/568B

RJ11

还有一种小的水晶头,插在电话机后面的,叫RJ11.

通常只有一对线。

本文链接:http://www.maixj.net/ict/rj45-mdi-x-568a-568b-3508
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