A2.3.2 · Data transmissions
A2.3.2 · 数据传输
Comparing Data Transmission Media
比较数据传输介质
A tutoring centre wiring a small back office and a warehouse cabling a fleet of handheld scanners would make very different choices about how to move their data, and both could be entirely right for their own situation.
一家小型补习中心为其后台办公室布线,和一座仓库为其手持扫描仪机队布线,两者在数据传输方式上的选择会截然不同,而这两种选择对各自的情况而言都可能完全正确。
Explainer
讲解
Every network connection has to physically carry its data somehow, and there are only three real options: two kinds of cable, and no cable at all. None of the three is simply "the best," each one trades away something to gain something else.
每一条网络连接都必须以某种物理方式传输数据,而实际上只有三种选择:两种电缆,以及完全不用电缆。这三者中没有哪一个单纯是"最好的",每一种都需要以某方面的牺牲换取另一方面的优势。
Fibre-optic cable carries data as pulses of light through a thin strand of glass or plastic.
光纤电缆以光脉冲的形式,通过一根细小的玻璃或塑料纤维传输数据。
Twisted-pair cable carries data as electrical signals through pairs of copper wires twisted together (the twisting itself helps cancel out some interference).
双绞线电缆以电信号的形式,通过成对绞合在一起的铜线传输数据(绞合本身有助于抵消部分干扰)。
Wireless transmission carries data as electromagnetic waves, radio frequencies most commonly, with no physical cable connecting the two ends at all.
无线传输以电磁波(最常见的是无线电波)的形式传输数据,两端之间完全没有物理电缆连接。
Explainer
讲解
Comparing all eight factors
比较全部八个因素
The statement names eight specific factors a comparison must cover. A "compare" answer that only mentions speed is incomplete, a genuinely strong answer draws on several of these eight, matched to whatever the scenario actually needs.
该考纲陈述列出了比较时必须涵盖的八个具体因素。一份只提到速度的"compare(比较)"答案是不完整的,真正有力的答案会根据情境的实际需求,从这八个因素中选取多个加以论述。
| Factor因素 | Fibre-optic光纤 | Twisted-pair双绞线 | Wireless无线 |
|---|---|---|---|
| Bandwidth带宽 | Highest of the three, into the tens of gigabits per second三者中最高,可达每秒数十吉比特 | Good for most office and home use, an order of magnitude below fibre-optic适合大多数办公和家庭使用,比光纤低一个数量级 | Lowest, and shared between every device connected to the same access point三者中最低,且由连接到同一接入点的所有设备共享 |
| Installation complexity安装复杂度 | Highest, needs specialised splicing tools and trained installers最高,需要专用的熔接工具和经过培训的安装人员 | Low, a common do-it-yourself job for a small office低,小型办公室常见的自行安装工作 | Lowest, no cable run at all, mainly configuring an access point最低,完全无需布线,主要工作是配置接入点 |
| Cost成本 | Highest, both the cable and the specialised labour最高,电缆本身与专业人工都昂贵 | Low, a long-established, widely available technology低,是一项历史悠久、普及广泛的技术 | Low up front, though extending coverage with extra access points adds cost前期成本低,但通过增设接入点扩大覆盖范围会增加成本 |
| Range传输距离 | Longest, tens of kilometres between repeaters最长,中继器之间可达数十公里 | Short, roughly 100 metres for a modern Ethernet cable短,现代以太网电缆约为 100 米 | Shortest, roughly 90 metres in clear conditions, and shrinking fast through walls最短,在无遮挡条件下约为 90 米,穿过墙壁后迅速缩短 |
| Interference susceptibility抗干扰能力 | Immune, it's light, not electricity完全免疫,因为传输的是光而非电 | Susceptible to nearby electrical equipment unless shielded除非加以屏蔽,否则容易受到附近电气设备的干扰 | Highly susceptible, to other wireless devices, physical obstructions and even a microwave oven极易受到干扰,来自其他无线设备、物理障碍物,甚至微波炉 |
| Attenuation信号衰减 | Very low, signal strength barely drops over long runs非常低,信号强度在长距离传输中几乎不下降 | Noticeable over distance, boosters are needed past a certain length随距离增加而明显,超过一定长度需要增设中继放大器 | Highest, signal strength fades quickly with distance and walls最高,信号强度随距离和墙壁迅速衰减 |
| Reliability可靠性 | Very high, unaffected by weather and largely by interference非常高,不受天气影响,也基本不受干扰影响 | Good within its shorter range, but exposed to nearby electrical noise在其较短的传输距离内表现良好,但容易受到附近电气噪声的影响 | Variable, affected by interference, distance and how many devices are competing for airtime不稳定,受干扰、距离以及争用信道的设备数量影响 |
| Security安全性 | Hardest to tap without physically cutting into the cable若不物理剪断电缆则极难窃听 | Easier to tap than fibre-optic, but still needs physical access to the cable比光纤更容易被窃听,但仍需接触到电缆本身 | Weakest by default, an attacker never needs physical access at all, just to be in range默认情况下最弱,攻击者完全不需要接触设备,只需处于信号范围内 |
Notice the pattern: fibre-optic wins on almost every technical factor, and loses only on cost and installation complexity, which is exactly why it dominates long-distance backbones but rarely reaches an individual home office.
注意这一规律:光纤几乎在每一项技术因素上都占优,只在成本和安装复杂度上处于劣势,这正是它主导长途骨干网络、却很少铺设到个人家庭办公室的原因。
Worked example
示例讲解
Choosing a medium for three real jobs
为三个实际场景选择传输介质
The command term is "compare," and a comparison only becomes useful once it's actually applied to a decision. Three genuinely different jobs, three genuinely different right answers.
命令词是"compare(比较)",而比较只有在真正应用于一项决策时才有意义。三个截然不同的场景,三个截然不同的正确答案。
Job 1: a tutoring centre's back office. Six desktop computers in one small room, on a tight budget, set up by the owner over a weekend.
场景一:补习中心的后台办公室。一间小房间里的六台台式电脑,预算紧张,由店主利用一个周末自行搭建。
Job 2: linking a university's two buildings. A new library, 2 kilometres from the main data centre, needs a fast, highly reliable connection carrying sensitive research data.
场景二:连接大学的两栋建筑。一座新图书馆距离主数据中心 2 公里,需要一条快速、高度可靠的连接来传输敏感的研究数据。
Job 3: a warehouse's handheld barcode scanners. Staff constantly walk the floor scanning stock, and the layout changes every few months as shelving gets rearranged.
场景三:仓库的手持条码扫描仪。员工不断在仓库地面走动扫描库存,而货架布局每隔几个月就会重新调整。
The actual skill being tested: not memorising which medium "wins" in general, since none of them does, but identifying which one or two factors matter most for a GIVEN scenario, and reasoning from there. Job 3's answer would be wrong for Job 2, and vice versa.
这里真正考察的技能:并非死记哪种介质"总体上最好"(因为没有哪种介质总是最好),而是识别在特定情境下哪一两个因素最为关键,并据此进行推理。场景三的答案放到场景二上就是错的,反之亦然。
Check your understanding
检验你的理解
A hospital wants to connect its MRI scanner (in a room lined with electromagnetic shielding, generating a strong magnetic field) to its imaging server one floor below, and the images must arrive completely intact for a diagnosis to be trusted. Which medium best fits, and why?
一家医院想要将其 MRI(核磁共振)扫描仪(位于一间衬有电磁屏蔽层、会产生强磁场的房间内)连接到楼下一层的影像服务器,而且图像必须完整无误地送达,诊断结果才能被信任。哪种介质最合适?为什么?
Common mistake
常见错误
RecurringA genuinely documented pattern: candidates correctly name a suitable medium for the given scenario, but never state WHY it suits that scenario specifically, and lose the mark reserved for the justification.
反复出现这是一个真实记录在案的模式:考生正确说出了适合该情境的介质,却从未说明为什么该介质具体适合这个情境,因而失去了论证部分应得的分数。
Names it, doesn't justify it: "Use fibre-optic cable for the connection." Correctly identifies a workable medium, but a scenario question always awards a separate mark for tying that choice back to the scenario's own specific requirement.
只说名称,未加论证: "使用光纤电缆进行连接。" 正确识别出了一种可行的介质,但情境题总会为将该选择与情境本身的具体需求相联系而单独设置分数。
Names it AND justifies it: "Use fibre-optic cable, because it supports the high bandwidth this scenario needs over long distances without the signal loss twisted-pair or wireless would suffer." Ties the recommendation directly to a factor the scenario actually raises, which is what earns both marks.
既说名称又加论证: "使用光纤电缆,因为它能够在长距离上支持本情境所需的高带宽,而不会像双绞线或无线那样出现信号损耗。" 将建议直接与情境实际提出的因素相联系,这正是同时拿到两分的关键。
Revision questions
复习题
Past-paper style. Write an answer, then reveal the marking points and mark yourself.
采用历年真题风格。写下答案,然后展开评分要点给自己打分。
[2]Identify two factors relevant to selecting a data transmission medium for a network.
[2]列出两项在为网络选择数据传输介质时相关的因素。
Marking points
评分要点
- Any two of: bandwidth needed, cost, distance or range, installation complexity, interference in the environment, attenuation over distance, reliability, security, and whether the devices need to move.
- 以下任选两项:所需带宽、成本、距离或传输范围、安装复杂度、环境中的干扰、随距离的衰减、可靠性、安全,以及设备是否需要移动。
[3]Explain why fibre-optic cable is preferred over twisted-pair cable for long-distance connections between buildings.
[3]解释为什么在建筑物之间的长距离连接中,光纤电缆比双绞线电缆更受青睐。
Marking points
评分要点
- Fibre-optic carries data as light, so it is immune to electrical interference and has very low attenuation, keeping the signal strong over long runs.
- It also has the highest bandwidth and the longest range (tens of kilometres between repeaters).
- Twisted-pair only reaches about 100 metres, loses signal over distance and is susceptible to interference from nearby electrical equipment, so it is unsuitable for a long link between buildings.
- 光纤以光传输数据,所以免疫电气干扰,衰减非常低,在长距离上信号保持强劲。
- 它还有最高的带宽和最长的传输距离(中继器之间数十公里)。
- 双绞线只能到约 100 米,随距离丢失信号,而且易受附近电气设备的干扰,所以不适合楼与楼之间的长链路。
[4]A logistics company needs to connect delivery-tracking handheld devices that move continuously around a large depot. Suggest a suitable transmission medium and justify your choice.
[4]一家物流公司需要连接在大型仓库中持续移动的送货追踪手持设备。请建议一种合适的传输介质,并论证你的选择。
Marking points
评分要点
- Suggest wireless transmission.
- The handheld devices move continuously around the depot, so a cable is not possible; wireless needs no physical connection and supports mobility.
- The lower bandwidth and shorter range of wireless are acceptable here because the devices only send small scans, and access points can be placed to cover the depot.
- Interference and security would need managing (encryption, well-placed access points).
- 建议无线传输。
- 手持设备在仓库里持续移动,所以电缆不可行;无线不需要物理连接,支持移动。
- 无线较低的带宽和较短的距离在这里可以接受,因为设备只发送小的扫描数据,而且可以布置接入点覆盖仓库。
- 干扰和安全需要管理(加密、位置合理的接入点)。
Flashcards
记忆卡片
Active recall for this statement’s key terms.
针对本条考纲陈述关键术语的主动回忆练习。
Keep this statement’s practice with you
把这条考纲陈述的练习保存下来
Free account: unlock every revision question and flashcard for A2.3.2, and every other IB CS 2027 statement.
免费账户:解锁 A2.3.2 以及所有其他 IB CS 2027 考纲陈述的全部复习题和记忆卡片。