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【互联网科普系列】线缆与WiFi – 译学馆
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The Internet: Wires, Cables, & Wifi

The Internet | Wires, Cables, and Wi-Fi
我是泰丝·温洛克 谷歌的一名软件工程师
My name is Tess Winlock, I’m a software engineer
我的问题是:图片 短信 或者电子邮件 是怎样从一个设备
at Google. Here’s a question: How does a picture, text message, or email get sent from one device
发送到另一台设备的?它不是魔法 而是互联网一个有形的 客观存在的被用来传递信息的系统
to another? It isn’t magic, it’s the Internet. A tangible, physical system made to move information.
互联网有点像邮政服务 但是邮递的具体东西有点不同
The Internet is a lot like the postal service, but the physical stuff that gets sent is a
little bit different. Instead of boxes and envelopes, the Internet ships binary information.
Information is made of bits. A bit can be described as any pair of opposites: on or
开或关 是或否 一般我们以1来代表开 0来代表关
off, yes or no. We typically use a 1 meaning on, or a 0 meaning off. Because a bit has two
因为比特有两种可能的状态 我们称之为二进制代码8比特构成了1字节

possible states we call it binary code. 8 bits strung together makes 1 byte. 1000 bytes
1000字节构成了一个千字节 1000个千字节构成了一个兆字节 通常一首歌占有大约3-4兆字节
all together is a kilobyte. 1000 kilobytes is a megabyte. A song is typically encoded
无论是一张图片 一个视频 或一首歌
using about 3-4MB. It doesn’t matter if it’s a picture, a video, or a song, everything
on the Internet is represented and sent around as bits. These are the atoms of information.
但它不是物理的将0和1从一个地方运送到另一个地方 或从一个人传递给另一个人
But it’s not like we’re physically sending 1s and 0s from one place to another or one
那么 线缆上运输的具体物体到底是什么?
person to another. So what is the physical stuff that actually gets sent over the wires
恩 让我们来看一个小例子吧
and the airways? Well, let’s look at a small example here of how humans can physically
communicate to send a single bit of information from one place to another. Let’s say that
假设我们以打开一盏灯来代表1 关闭灯代表0或使用哔哔声类似摩尔斯密码这样的信号
we can turn on a light for a 1 or off for 0. Or use beeps or similar sorts of things
这些方法虽有效 但相当的慢 且容易出错 依赖操作的人
to Morse code. These methods work but they’re really slow, error prone, and totally dependent
我们真正需要的是能完成这一工作的机器回顾历史 我们已经建造了许多系统
upon humans. What we really need is a machine. Throughout history, we’ve built many systems
that can actually send this binary information through different types of physical mediums.
今天 我们在物理上运用电、光、电磁波来发送二进制数字 为了用电来发送1比特
Today, we physically send bits by electricity, light, and radio waves. To send a bit via electricity,
imagine that you have two lightbulbs connected by a copper wire. If one device operator turns
如果设备操作员打开电源 灯亮 关闭电源 灯灭
on the electricity then the lightbulb lights up. No electricity, then no light. If the
operators on both ends agree that light on means 1 and light off means 0, then we have
a system for sending bits of information from one person to another using electricity. But
但是我们有个小问题 如果你想要一次发送五次个0
we have kinda a small problem, if you need to send a 0 five times in a row, well how
can you do that in such a way that either person can actually count the number of 0s?
解决办法就是引入计时器 操作员达成约定
Well the solution is to introduce a clock or a timer. The operators can agree that the
1秒发送1比特 接收者将坐下来记录每秒
sender will send 1 bit per second and the receiver will sit down and record every single
观察线上发送的是什么 要想一次发送五次个0 你只需要关掉灯
second and see what’s on the line. To send five 0s in a row, you just turn off the light,
等五秒 另一端的人就会记下完整的5秒数据
wait 5 seconds, the person at the other end of the line will write down all 5 seconds.
至于一次五个1 打开灯 等五秒 记录每秒
For five 1s in a row, switch it on, wait 5 seconds, write down every second. Obviously we’d like
很明显 我们想要以比每秒1比特快的速度发送信息 就需要增加带宽
to send things a little bit faster than one bit per second, so we need to increase our
bandwidth – the maximum transmission capacity of a device. Bandwidth is measured by bitrate,
它是我们在一段时间内实际能发送的二进制数字的数量 通常以秒为单位
which is the number of bits that we can actually send over a given period of time usually measured
另一个测量速度的方式是延时 也就是
in seconds. A different measure of speed is the latency, or the amount of time it takes
一比特从一个地方到另一个地方 从发射源到请求设备所用的时间
for one bit to travel from one place to another, from the source to the requesting device.
对人类来说每秒一比特是相当快的 很难保持这样的速度
In our human analogy, one bit per second was pretty fast but kinda hard for a human to
keep up with. Let’s say that you actually want to download a 3MB song in 3 seconds,
每1兆有八百万比特 即大约每秒八百万比特的比特率
at 8 million bits per megabyte that means a bit rate of about 8 million bits per second.
很明显 人类无法做到发送或接收每秒八百万比特 但机器就没问题
Obviously, humans can’t send or receive 8 million bits per second but a machine could
do that just fine. But now there’s also the question of what sort of cable to send these
messages over and how far the signals can go. With an ethernet wire, the kind that you
那种你能在你家 办公室 或学校找到的东西几百英尺就会出现可测量到的信号损失或干扰
find in your home, office, or school you see measurable signal loss or interference over
just a few hundred feet. For the Internet to work all around the world, we need to have
我们必须有一种可替换的方法来长距离发送比特数据 甚至要能穿过大海
an alternative method to send bits really long distances. We’re talking like across
那么 我们还能用什么?我们知道什么能通过电线比电移动的还要快呢?
oceans. So what else can we use? What do we know that moves a lot faster than just electricity
是光 我们能够用光缆将比特像光束一样从一个地方发送到另一个地方
through a wire? Light. We can actually send bits as light beams from one place to another
光缆是一束使用玻璃制成的线缆 可以反射光线
using a fiber optic cable. A fiber optic cable is a thread of glass engineered to reflect
当你使用光缆来发送光束 光会一直上下碰撞前行
light. When you send a beam of light down the cable, light bounces up and down the length
直到它被另一端接收 反射角不同
of the cable until it is received on the other end. Depending on the bounce angle, we can
我们能够同时发送大量的比特 它们全部以光速移动
actually send multiple bits simultaneously, all of them traveling at the speed of light.
因此光缆是非常快的但更重要的是 长距离传输信号并不损耗
So fiber is really really fast. But more importantly the signal doesn’t really degrade over long
distances. This is how you can go hundreds of miles without signal loss. This is why
we use fiber optic cables across the ocean floors to connect one continent to another.
2008年 亚历山大港附近有一段电缆被剪断
In 2008 there was a cable that was actually cut near Alexandria, Egypt which really interrupted
the Internet for most of the Middle East and India. So we take this Internet thing for
granted but it’s really a pretty fragile, physical system. And fiber is awesome but
但是它也相当昂贵 且难以处理 大多数情况下
it’s also really expensive and hard to work with. For most purposes, you’re going to find
我们使用铜芯电缆来替代那么 我们怎样不使用线缆来发送信息?怎样无线传输?
copper cable. But how do we move things without wires? How do we send things wirelessly? Radio.
Wireless bit sending machines typically use a radio signal to send bits from one place
to another. The machines have to actually translate the 1s and 0s into radio waves of
接收机器倒转这个过程 在你的电脑上将它转换为二进制
different frequencies. The receiving machines reverse the process and convert it back into
binary on your computer. So wireless has made our Internet mobile. But a radio signal doesn’t
但是无线电传输距离有限 否则会变得杂乱因此 你无法在芝加哥收到洛杉矶的电台
travel all that far before it gets completely garbled. This way you can’t really pick up
尽管无线电非常伟大 今天 它依然要依赖于有线网络
a Los Angeles radio station in Chicago. As great as wireless is, today it still relies
如果你在一个咖啡馆使用WIFI 这些二进制数字由无线路由器发送传输
on the wired Internet. If you’re in a coffee shop using wifi, then the bits get sent to
其实 它仍然需要通过有线电缆来长距离传输数据
this wireless router and then are transferred through the physical wire to travel the really
long distances of the Internet. The physical method for sending bits may change in the
也许会变成卫星间的激光传输 或是气球上的无线电波 还是无人机传输
future, whether its lasers sent between satellites, or radio waves from balloons, or drones, but
the underlying binary representation of information and the protocols for sending that information
几乎不会改变 互联网上的每件事
and receiving that information have pretty much stayed the same. Everything on the Internet,
不论它是文字 电子邮件 图片 猫狗视频 都可归结为1和0
whether it’s words, emails, images, cat videos, puppy videos, all come down to these 1s and
它们被电子脉冲 光束 无线电波伴随着人类的爱传播到世界每个角落
0s being delivered by electronic pulses, light beams, radio waves, and lots and lots of love.