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International Baccalaureate · IB Diploma · Computer Science · HL Tópico 2 3:34 Narração em inglês · Legendas em inglês + 中文 gravadas
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Transcrição
A small message can arrive late on a high-bandwidth link.
即使在高带宽链路上，小消息也可能延迟到达。
Capacity and delay measure different properties.
容量和时延衡量的是不同的属性。
Packets carry addressed data through a network.
数据包在网络中传输带地址的数据。
A layered model separates responsibilities such as application meaning, transport delivery and network routing.
分层模型将职责分离，例如应用层语义、传输层交付和网络路由。
Bandwidth describes capacity; throughput is the achieved data rate; latency is delay.
带宽描述容量；吞吐量是实际达到的数据传输速率；延迟是指延时。
Throughput is the achieved rate of useful data transfer.
吞吐量是有用数据传输的实际速率。
Latency is the delay experienced in communication.
延迟是通信过程中经历的延时。
Transmission time depends on data size and rate.
传输时间取决于数据大小和速率。
Total delay may also include propagation, processing, and queueing.
总延迟还可能包括传播、处理和排队时间。
Encryption protects content under its assumptions but does not remove congestion or every metadata exposure.
加密在假设条件下保护内容，但不会消除拥塞或所有元数据暴露。
In the lab: Trace a message route using a documented local model.
在实验室中，使用已记录的本地模型追踪消息路由。
Record payload size, units and measured time.
记录有效载荷大小、单位和测量时间。
Use school-approved networks and synthetic messages; do not scan or intercept another user traffic.
仅使用学校批准的网络和合成消息。 不得扫描或拦截其他用户的流量。
Known: an eight megabit file crosses a two megabit per second link.
已知：一个八兆比特的文件穿过一条二兆比特每秒的链路。
Ideal transmission time equals size divided by rate, which is eight divided by two, equaling four seconds.
理想传输时间等于大小除以速率，即八除以二，等于四秒。
Protocol overhead, other users, and latency can make observed completion slower.
协议开销、其他用户和延迟可能导致实际完成速度变慢。
Your turn: A 12 megabit file crosses a 3 megabit/s link.
轮到你了。 一个12兆比特的文件通过一条3兆比特每秒的链路传输。
Calculate ideal transmission time.
计算理想传输时间。
A megabyte is eight megabits before considering overhead.
在考虑开销之前，一个兆字节等于八兆比特。
A faster rated link does not guarantee low latency or secure endpoints.
更快的标称链路并不能保证低延迟或安全的端点。
Not true: A high-bandwidth connection guarantees zero latency.
不正确。 高带宽连接并不能保证零延迟。
Bandwidth is capacity - how much can flow per second.
带宽是容量，即每秒能传输多少数据。
Latency is delay - how long one signal takes.
延迟是时间差，即一个信号传输所需的时间。
A high-capacity link can still have high latency, for example a satellite connection.
高容量链路仍可能具有高延迟。 例如卫星连接。
Packets carry addressed data through a network.
数据包在网络中传输带地址的数据。
Transmission time depends on data size and rate.
传输时间取决于数据大小和速率。
Watch for: A megabyte is eight megabits before considering overhead.
请注意：在考虑开销之前，一兆字节等于八兆比特。
Convert the data size to bits first.
先把数据量换算成比特。
Dividing by the link rate gives the ideal transmission time, for example 12 megabits at 3 megabits per second is 4 seconds.
除以链路速率得到理想传输时间，例如12兆比特以每秒3兆比特传输需要4秒。
Propagation and other delays come on top.
传播延迟等其他延迟要另外加上。
A 12 Mb file crosses a 3 Mb/s link with 0.10 s propagation delay.
一个12兆字节的文件通过一条3兆比特每秒的链路传输，传播延迟为0.10秒。
Give ideal time until the last bit arrives.
请给出最后一位比特到达的理想时间。
Can doubling bandwidth remove all delay?
将带宽翻倍能否消除所有延迟？
The time is 12 divided by 3, plus 0.10, which is 4.10 seconds, omitting other delays.
时间等于 12 除以 3，加上 0.10，即 4.10 秒，忽略其他延迟。
Doubling the bandwidth gives 2.10 seconds; propagation remains.
带宽翻倍后为 2.10 秒；传播时延保持不变。
Protocol and queueing may add delay.
协议和排队可能会增加延迟。
Measure from transmission start to last-bit arrival.
测量从发送开始到最后一位到达的时间。
Serial transmission time and propagation delay add under this ideal model.
在此理想模型下，串行传输时间与传播延迟相加。
Increasing bandwidth changes only the first term; store-and-forward hops and queueing would add further terms.
增加带宽仅改变第一项。 存储转发跳数和排队会进一步增加其他项。
Retrieve the technical meanings, then vary one input in the original transfer and justify the model condition.
回顾相关技术术语，然后在原始迁移中改变一个输入变量，并论证模型条件的合理性。