First exams 2027 · SL & HL 2027 年首次开考 · SL 与 HL

A2.2.3 · Network architecture

A2.2.3 · 网络架构

Networking Models

网络模型

Streaming a bank statement from a central server and sharing a large video file directly between two laptops rely on two completely opposite ideas about who's actually in charge of providing a network service.

从中央服务器流式获取银行对账单,与在两台笔记本电脑之间直接共享一个大型视频文件,依赖的是关于究竟由谁来主导提供网络服务这一问题的两种完全相反的理念。

Core for SL & HL SL 与 HL 核心内容 Typically 4–6 marks · AO2 通常 4–6 分 · AO2 Command term: compare and contrast 命令词:compare and contrast(比较并对比)

Explainer

讲解

1

In the client-server model, devices take on one of two fixed roles: a client that requests a service, or a server that provides it. Control is centralised at the server.

在客户端-服务器模型中,设备承担两种固定角色之一:请求服务的客户端,或提供服务的服务器。控制权集中在服务器一方。

2

In the peer-to-peer (P2P) model, there is no dedicated server at all. Every connected device (peer) takes on the client role and the server role simultaneously, and the job of providing the network's services is spread across all of them.

在对等(P2P)模型中,根本没有专门的服务器。每一台连接的设备(对等节点)同时承担客户端角色与服务器角色,提供网络服务的工作分散在所有节点之间。

Explainer

讲解

Benefits and drawbacks

优点与缺点

Neither model is simply "better." Each one trades control and predictability for resilience and cost in the opposite direction from the other.

两种模型并非简单地谁"更好"。二者在控制力、可预测性,与韧性、成本之间,各自朝相反的方向做出取舍。

Client-server 客户端-服务器

Real example: a bank's own servers handling every customer's transactions.

真实例子:银行自己的服务器处理每一位客户的交易。

Advantage 优点
  • Centralised control (security, updates and data consistency are all managed from one place, which is straightforward to administer and monitor)
  • 集中控制 (安全性、更新和数据一致性都在同一个地方统一管理,便于管理和监控)
Disadvantage 缺点
  • Single point of failure and risk (if the server goes down or is compromised, every client depending on it is affected at once, and scaling it up to handle more demand costs real money)
  • 单点故障与风险 (一旦服务器宕机或被攻破,依赖它的每一个客户端都会同时受到影响,而扩容以应对更多需求也需要真金白银)
Peer-to-peer 对等网络

Real example: a group of computers sharing a large file directly with each other.

真实例子:一组计算机之间直接互相共享一个大文件。

Advantage 优点
  • No single point of failure, cheap to scale (there's no central server to bring the whole system down, and each new peer that joins adds capacity rather than just demanding more of it)
  • 没有单点故障,扩展成本低 (没有中央服务器可能拖垮整个系统,而且每加入一个新的对等节点都会增加系统容量,而不只是索取更多容量)
Disadvantage 缺点
  • Hard to coordinate, unpredictable availability (with no central authority, keeping every peer's settings and security patches consistent is genuinely difficult, and a service depending on a specific peer can simply vanish the moment that peer disconnects)
  • 难以协调,可用性难以预测 (没有中央权威机构,要让每个对等节点的设置和安全补丁保持一致确实很困难,而依赖某个特定节点的服务,一旦该节点断线就可能直接消失)

Worked example

示例讲解

Six real applications

六个真实应用

The statement names six real-world applications, three built on each model. Click each one to see why it uses that particular model, and a genuine benefit and drawback specific to it.

该考纲陈述列出了六个真实世界的应用,每种模型各占三个。点击每一个即可查看它为何采用该特定模型,以及针对它的一项真实优点与缺点。

Check your understanding

检验你的理解

A new messaging startup wants its service to survive even if its own company servers are ever taken offline, and it has very limited budget for expensive central infrastructure. Which networking model best fits, and why?

一家新的消息应用创业公司希望即使自己公司的服务器被下线,服务也能继续运作,而且它用于昂贵中央基础设施的预算非常有限。哪种网络模型最合适,为什么?

Common mistake

常见错误

Markers reported this pattern directly for this statement 考官针对该考纲陈述直接报告了这一模式

RecurringA genuinely documented pattern: candidates oversimplify the distinction between the two models into "client-server has a server, peer-to-peer doesn't," without considering the scalability and maintenance consequences that difference actually causes.

反复出现这是一个真实记录在案的模式:考生把两种模型的区别过度简化为"客户端-服务器有服务器,对等网络没有",却没有考虑这一区别实际带来的可扩展性与维护方面的后果。

✕

Oversimplified: "Peer-to-peer is better because there's no server that can fail." Names one real advantage but ignores that removing the central server also removes centralised coordination, which is exactly what makes maintaining consistent settings and security across every peer so difficult.

过度简化: "对等网络更好,因为没有服务器可能出故障。" 说出了一项真实的优点,却忽略了取消中央服务器也就取消了集中协调,而这正是让每个节点保持一致的设置和安全性变得如此困难的原因。

✓

Weighs the actual trade-off: "Peer-to-peer removes the single point of failure a central server represents, but that same lack of central authority makes coordinating updates, security patches and consistent behaviour across every peer genuinely difficult, a cost client-server doesn't have to pay." States the real benefit AND the genuine cost that comes with it, rather than treating one model as simply superior.

权衡真实的取舍: "对等网络消除了中央服务器所代表的单点故障,但同样是这种缺乏中央权威机构的状态,使得在每个节点之间协调更新、安全补丁和一致行为确实很困难,这是客户端-服务器模式无需承担的代价。" 既说出了真实的优点,也说出了随之而来的真实代价,而不是简单地认为某一种模型更优越。

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。

Question 1 · 2 marks 第 1 题 · 2 分

[2]Define the terms client and server.

[2]定义术语客户端(client)和服务器(server)。

Question 2 · 4 marks 第 2 题 · 4 分

[4]Compare and contrast the client-server and peer-to-peer models in terms of reliability.

[4]就可靠性方面比较并对比客户端-服务器模型与对等模型。

Question 3 · 4 marks 第 3 题 · 4 分

[4]Explain why blockchain systems are built on a peer-to-peer model rather than a client-server one.

[4]解释为什么区块链系统建立在对等模型而非客户端-服务器模型之上。

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。

Prototype render · mistake pattern grounded in real IB CS 2027 marker-report findings · not yet wired to live routes