1s軌域之逆旋水子 撰寫於文章 <3XeQ7i$GTJ@bbs.ee.ntu.edu.tw>...
>※ 引述《"網中人" <netman2000@crosswinds.net>》之銘言:
>: 在工作站對網路廣播之前﹐都會先傾聽一下有沒其它人在使用網路﹐如果聽起來很

>: 靜﹐則它會發送廣播。但要是網路上仍然嘈嘈的呢﹖(這個情形就是bus形態最擔心
>: 的)﹐這時候工作站就需等待了。
>: 假如節點A和節點B相隔得太遠的話﹐當他們傾聽的時候可能都還沒聽得到對方有話

>: 說﹐就都同時把封包出去﹐這就是所謂的碰撞(collision)了。如果當一個碰撞發生
>: 了﹐整條網線都會充滿了噪音回響﹐如果第一個節點監測到有這樣的頻率回響﹐它
就會
>: 發出一個更高頻的信號去告訴別的節點碰撞已經發生﹐這樣全部節點都不會再發送
封包
>
>這段對 collision 的描述真是生動啊,不過用「噪音回響」這種說法,我實在
>是無法接受。還有發生碰撞後,會再發出更高頻的信號這種講法,我認為也有必
>要再查證一下。
>
嗯﹐我也不知道如何翻譯好﹐我將英文版(Networking the small office, by Patrick
T. Campbell, SYBEX)的抄出來吧﹕

If a collision occurs it will cause a frequency "ripple" on the cable. The
first node to detect this increased frequency "ripple" will send out a high
frequency signal that will cancel out all other signals. This signal tells
all nodes that a collision has occurred and that all nodes on the network
should stop sending packets. At this point, each node waits a random amount
of time, then tries broadcasting again. They can do this up to 16 times
before giving up.

CSMA/CD provides a means for reducing packet collision. Before transmitting,
it broadcasts a signal known as the carrier-sensing signal to see if any
other workstation are broadcasting. If not, it gives the workstation the
"all-clear" and the workstation transmits its packet. If, however, the
carrier-sensing signal detects another workstation's transmittal, CSMA/CD
tells the workstation to wait before broadcasting.

This process works fine so long as network traffic isn't heavy and the LAN's
cables aren't any longer than they're rated to be. If either of those
conditions exist, then collisions are likely to happen regardless of
CSMA/CD. CSMA/CD isn't in charge of making sure that only one workstation
transmits at a time: it's in charge of making sure that all workstations are
quiet before one transmits. If two workstations  happen to begin
transmitting at the same time, there's nothing that CSMCA/CD can do to avoid
the collision.