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楼主: 电子乌托邦
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21
sinanjj| | 2010-1-9 16:27 | 只看该作者 回帖奖励 |倒序浏览
Auto-MDIX (automatic medium-dependent interface crossover) is a computer networking technology that automatically detects the required cable connection type (straight-through or crossover) and configures the connection appropriately, thereby removing the need for crossover cables to interconnect switches or connecting PCs peer-to-peer.

When it is enabled, either type of cable can be used and the interface automatically corrects any incorrect cabling. For Auto-MDIX to operate correctly, the speed on the interface and duplex setting must be set to "auto". Auto-MDIX was developed by HP engineers Dan Dove and Bruce Melvin.

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22
sinanjj| | 2010-1-9 16:35 | 只看该作者
Many local area network (LAN) products use a medium consisting of twisted pair copper wire pairs for the transmission and reception of data. It is generally a requirement that one or more pairs be used for transmission of data in one direction and one or more other pairs to receive data in the opposite direction. The connection between two node devices is a link. Many LAN devices, which employ a full-duplex medium, have different pairs for transmission than for reception and require, therefore, that each end of the link use a defined assignment for its twisted pair connector to a particular pair of wires. If the transmit pair of wires of one device is connected to the transmit connectors of another, obviously the communication link will fail.

Most LAN standards address this problem by assigning different connector pins to the wires in the twisted pair at the RJ-45, which is often referred to as the Media Dependent Interface (MDI). In switched networks, Network Interface Devices (NIC) may be directly connected to another NIC, or a repeater may be connected to another repeater, or a repeater may alternately be connected to a switch. Depending upon the assignment of pins in the network interface, it is sometimes necessary to use a crossover cable to address the problem that both products use the same pin designations on their interfaces. Determining whether the interface requires this cable can cause confusion and frustration if the customer lacks the necessary cable.

To get around this problem, some products use a manual "MDIX" switch. But that still requires user intervention. The need arose, then, for automatically ensuring viable connections among MDIs in complex LANs. HP's Auto-MDIX technology effectively solves the problem of lock step interaction among devices having MDIs from various well-known manufacturers.

HP扯了一堆蛋也没提原理.

继续查

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23
sinanjj| | 2010-1-9 16:46 | 只看该作者
Link Up Time

                    Auto-MDIX Legacy
Break_link_timer      1500     1500  ms
mdix_time              700       0   ms
ability_match           72       72  ms
ack_match               72       72  ms
complete_ack           192      192  ms
flp_link_good_check   1000     1000  ms
Total                 3.536    2.836 second


mdix_time              700       0   ms

mdix需要格外700ms时间

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24
sinanjj| | 2010-1-9 16:55 | 只看该作者
17楼说法有误:

Ethernet MDI/MDIX Auto Cross

Normally, Twisted Pair ports must be connected so that the Transmit pair on one end is connected to the Receive pair on the other end, and vice versa. If the cabling is done so that Transmit on one end is wired to Transmit on the other, and Receive is wired to Receive, the link will not come up.

Hubs and switches are deliberately wired opposite the way end stations are wired, so that when a hub or switch is connected to an end station, a "straight through" ethernet cable can be used and the pairs will match up properly. When two hub/switches are connected to each other, or two end stations are connected to each other, a "crossover" cable is used to make sure that the correct pairs are connected.

The standard wiring for end stations is known as "MDI" (Media Dependent Interface), and the standard wiring for hubs and switches is known as "MDIX" (Media Dependent Interface with Crossover).

On certain devices, it is possible for hardware to automatically correct errors in cable selection, making the distinction between a "straight through" cable and a "crossover" cable unimportant. This capability is known as Auto Cross.

On some products, including the CFETF100 Media Converter, Auto Cross is simply either enabled(1) or disabled(2). When disabled, the port reverts to MDI mode.

On other products, like the CBFTF100 Switch, Auto Cross on Twisted Pair switch ports can be set to auto(1), MDI(2), or MDIX(3). For fiber switch ports, Auto Cross has a read-only value of notApplicable(4).


就是说: MDI和MDIX是一种线序规定. MDI通常是到端的, MDIX是连接交换机/路由器的.

那么Auto Cross功能的原理...........啊, 差了查也没查到.........

哪位造过路由器的朋友给说一说.

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25
电子乌托邦|  楼主 | 2010-1-9 17:03 | 只看该作者
哈哈,sinanjj这么热心啊!

造过路由器的也不一定知道啊,这是物理层解决的问题,应该是造过以太网物理层芯片的说说。

网上说:原先的电脑以太网物理层芯片用MDI,路由器交换机物理层芯片用MDIX,不过现在的物理层芯片都auto了,用一种发现网络不通后,转到另一种接口线序。

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26
sinanjj| | 2010-1-9 17:09 | 只看该作者
这个是HP的专利, 从IEEE上看好像还要密码.
HP1999年做出的.
肯定有原理图的.

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27
xinzha| | 2010-1-9 17:09 | 只看该作者
当然是一种线序有关规定,MDI必须是用指定线序的,而MDIX是接口可以在四对线中切换,直到找到能够正确建立电气连接的一种组合。
你还是查802.3吧,关于以太网10/100/1000的有线网络内容都是以这个为基准,查这些厂商的文档没有看协议来得清晰。
我倒是没造过路由器,不过核心网媒体网关以及企业级路由器的MAC/PHY曾经是我的工作,除非这几年MDIX功能又变了。

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28
sinanjj| | 2010-1-9 17:15 | 只看该作者
http://en.wikipedia.org/wiki/Medium_dependent_interface

Medium dependent interface crossover (MDIX) (the “X” representing “crossover”) is a female 8P8C port connection on a computer, router, hub, or switch.
MDIX是一种连接电脑, 路由器, 交换机的8针母头连接方式

Straight through cables connect pins 1 & 2 (transmit) on an MDI device to pins 1 & 2 (receive) on an MDIX device. Similarly pins 3 & 6 are receive on an MDI device and transmit on an MDIX device. The X refers to the fact that transmit wires on an MDI device must be connected to receive wires on an MDIX device. As a rule, end stations (i.e., PCs or workstations) and routers use an MDI interface, hubs and switches use MDIX interfaces. Newer routers, hubs and switches (including some 10/100, and all 1 Gigabit or 10 Gigabit devices) use Auto MDI/MDIX to automatically switch to the proper configuration once a cable is connected. The other four wires are used but are not crossed since Auto MDI/MDIX is mandatory at the higher speeds. See Ethernet over twisted pair for more details on cables and standards. Some Routers and other devices have an uplink switch to go back and forth between MDI and MDIX on a specific port.

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29
sinanjj| | 2010-1-9 17:17 | 只看该作者
"在四对线中切换,直到找到能够正确建立电气连接的一种组合。"

这个叫   Auto-MDIX  或者是 Auto Cross

http://en.wikipedia.org/wiki/Auto-MDIX

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30
yewuyi| | 2010-1-9 17:19 | 只看该作者
直接用两台PC测试一下看看不就知道了吗?!

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31
yewuyi| | 2010-1-9 17:19 | 只看该作者
用新一点的PC测试就是了,哈哈,行不行,一湿就知道。。。

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32
xinzha| | 2010-1-9 17:20 | 只看该作者
谢谢17楼朋友,简介明了,直入重点,原来是这个功能啊!看见PHY芯片手册说有MDIX功能,一直也没明白,多谢,多谢,以后选phy芯片要选有这个功能的。

再次感谢。 ...
电子乌托邦 发表于 2010-1-9 15:48

LZ,这个也是要有选择的,不见得PHY芯片带MDIX功能就是好。
比如在局端设备中通常关键接口是有备份接口的,而备份接口通常是发送关闭而接收打开(因为主备接口的配置除了物理MAC不一样,其他都是一样的,都打开的话对接设备必然就疯了),这时候如果对端设备打开了MDIX功能,就会因为备板这边发送关闭,对端无法检测到正确的电气连接而不断切换接收发送线序,这样也导致了备板接口状态变为时断时续,而一旦此时主板异常,备板在检测是否可以升主的过程中发现接口状态为断,导致逻辑异常。所以在类似的网络应用中,我们一般严格要求关闭MDIX,同时也关闭自适应。

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33
xinzha| | 2010-1-9 17:26 | 只看该作者
"在四对线中切换,直到找到能够正确建立电气连接的一种组合。"

这个叫   Auto-MDIX  或者是 Auto Cross

http://en.wikipedia.org/wiki/Auto-MDIX
sinanjj 发表于 2010-1-9 17:17

哦,谢了,我把auto给忘了

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34
sinanjj| | 2010-1-9 17:51 | 只看该作者
LZ,这个也是要有选择的,不见得PHY芯片带MDIX功能就是好。
比如在局端设备中通常关键接口是有备份接口的,而备份接口通常是发送关闭而接收打开(因为主备接口的配置除了物理MAC不一样,其他都是一样的,都打开的话 ...
xinzha 发表于 2010-1-9 17:20


同意, 就该规规矩矩的使, 不要用太复杂的东西. 容易出错.

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