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Week 9: The Internet & Assessment 2 第 9 周：互联网与阶段评估 2

Core Concepts 核心概念

1. Internet Structure and Domains (6.1 - 6.2)

The Internet is a global network of interconnected networks. The Domain Name System (DNS) acts as the phonebook of the Internet, translating human-readable hostnames (e.g. www.google.com) into IP addresses. The DNS structure is hierarchical, starting with the root servers, top-level domains (TLDs like .com, .org), and authoritative name servers.

2. Dynamic Host Configuration Protocol (DHCP) (6.3)

DHCP dynamically assigns IP addresses, subnet masks, default gateways, and DNS server addresses to client devices as they join a network. The assignment process follows the four-step DORA Handshake:

  • Discover: Client broadcasts a request looking for a DHCP server.
  • Offer: Server broadcasts or unicasts an available IP configuration offer.
  • Request: Client requests the offered IP address.
  • Acknowledge: Server confirms the lease assignment to the client.

1. 互联网结构与域名 (6.1 - 6.2)

互联网是相互连接的网络的全球网络。域名系统 (DNS) 充当互联网的电话簿，将人类可读的主机名（如 www.google.com）解析为 IP 地址。DNS 结构是分层的，从根服务器开始，到顶级域名（TLD 如 .com, .org）以及权威名称服务器。

2. 动态主机配置协议 (DHCP) (6.3)

DHCP 在客户端设备加入网络时，动态分配 IP 地址、子网掩码、默认网关和 DNS 服务器地址。分配过程遵循四个步骤的 DORA 握手：

  • 发现 (Discover)： 客户端广播寻找 DHCP 服务器。
  • 提供 (Offer)： 服务器广播或单播提供可用的 IP 配置。
  • 请求 (Request)： 客户端请求所提供的 IP 地址。
  • 确认 (Acknowledge)： 服务器向客户端确认租约分配。

Concept Visualization: DHCP DORA Process 概念可视化：DHCP DORA 流程

This diagram represents the step-by-step DORA packet exchange between a client PC and a DHCP Server to obtain an IP configuration.

此图表示客户端 PC 与 DHCP 服务器之间为获取 IP配置而进行的逐步 DORA 数据包交换。

Client PC DHCP Server 1. DISCOVER (Broadcast) 2. OFFER (Unicast) 3. REQUEST (Broadcast) 4. ACKNOWLEDGE (Unicast)

Tips 提示

  • DHCP Exclusion: You should exclude static IP addresses assigned to network devices (printers, switches, routers, servers) from the DHCP lease pool to prevent IP address conflicts.
  • DORA Broadcast: The Discover and Request messages are broadcast because the client does not have an IP address yet and does not know the specific IP of the DHCP server.
  • DHCP 排除： 应在 DHCP 租约池中排除分配给网络设备（打印机、交换机、路由器、服务器）的静态 IP 地址，以防止 IP 地址冲突。
  • DORA 广播： 发现和请求消息是广播的，因为客户端当时尚未被分配 IP 地址，也不知道 DHCP 服务器的具体 IP。

Practical Exercises & Step-by-Step Guide 实践练习与分步指南

Exercise 1: Router DHCP Server Configuration 练习 1：路由器 DHCP 服务器配置

Steps to configure:

  1. In Cisco Packet Tracer, select a 2911 Router and connect it to a 2960 Switch. Connect PC0 and PC1 to the Switch.
  2. Click Router -> go to CLI tab. Configure GigabitEthernet 0/0 interface: 
    Router(config)# interface gigabitEthernet 0/0
Router(config-if)# ip address 192.168.1.1 255.255.255.0
Router(config-if)# no shutdown
  3. Configure IP exclusion range (addresses reserved for switches, servers, printers): 
    Router(config)# ip dhcp excluded-address 192.168.1.1 192.168.1.10
  4. Define DHCP Address Pool: 
    Router(config)# ip dhcp pool LAN-POOL
Router(config-dhcp)# network 192.168.1.0 255.255.255.0
Router(config-dhcp)# default-router 192.168.1.1
Router(config-dhcp)# dns-server 8.8.8.8
  5. Verify: Click PC0 -> Desktop -> IP Configuration -> Select **DHCP**. It should automatically acquire IP `192.168.1.11`.

配置步骤：

  1. 在 Cisco Packet Tracer 中，选择一个 2911 路由器并将其连接到 2960 交换机。将 PC0 和 PC1 连接到交换机。
  2. 点击路由器 -> 进入 CLI 选项卡。配置 GigabitEthernet 0/0 接口： 
    Router(config)# interface gigabitEthernet 0/0
Router(config-if)# ip address 192.168.1.1 255.255.255.0
Router(config-if)# no shutdown
  3. 配置 IP 排除范围（为交换机、服务器、打印机保留的 IP 地址）： 
    Router(config)# ip dhcp excluded-address 192.168.1.1 192.168.1.10
  4. 定义 DHCP 地址池： 
    Router(config)# ip dhcp pool LAN-POOL
Router(config-dhcp)# network 192.168.1.0 255.255.255.0
Router(config-dhcp)# default-router 192.168.1.1
Router(config-dhcp)# dns-server 8.8.8.8
  5. 验证：点击 PC0 -> 桌面 -> IP 配置 -> 选择 **DHCP**。它应自动获取 IP `192.168.1.11`。

Vocabulary Matching Game 词汇配对游戏

Match the DHCP/Internet term on the left with its definition on the right. (Click a term, then click its matching definition). 将左侧的 DHCP/互联网术语与右侧的定义进行配对。（点击术语，然后点击匹配的定义）。

DNS Hierarchy
DHCP Discover
DHCP Offer
DHCP Exclude
DORA Handshake
IP pool configuration proposed by DHCP server to client DHCP 服务器向客户端建议的可用 IP 地址配置
Four-step protocol exchange to lease dynamic IP addresses 用于租用动态 IP 地址的四个步骤协议交换
Distributed naming system translating human hostnames to IP addresses 将人类可读主机名转换为 IP 地址的分布式命名系统
Preventing static addresses from being assigned to clients dynamically 防止已分配的静态地址被动态分配给普通客户端
Initial broadcast packet from a client searching for DHCP servers 客户端发送的寻找可用 DHCP 服务器的初始广播包

Continuous Assessment 2 (20% Weight) 阶段评估 2 (权重 20%)

Course: Business Data Communication (DBDC2623)  |  Duration: 2 Hours  |  Total Marks: 50 Marks

SECTION A: MULTIPLE CHOICE (20 MARKS) 选择题部分（共 20 分）

Answer ALL questions. 1 mark per question.

1. Which mode allows data to flow in one direction only?

2. The OSI model consists of how many layers?

3. Which layer is responsible for logical addressing?

4. Attenuation refers to the:

5. Which topology features a central controller?

6. In a digital signal, bit rate is measured in:

7. Which media uses light for data transmission?

8. What does PCM stand for?

9. Which is an unguided transmission medium?

10. FDM requires signals to be:

11. Data flow between two devices is:

12. Which layer manages dialogue control?

13. The physical layer concerns:

14. ASK stands for:

15. Noise is defined as:

16. Which coding scheme is unipolar?

17. A periodic signal completes a pattern in a:

18. Circuit switching creates a:

19. Which is a connecting device?

20. The TCP/IP application layer is equivalent to:

SECTION B: STRUCTURED QUESTIONS (20 MARKS) 问答题部分（共 20 分）

QUESTION 1  (4 Marks)
Explain the functions of the following layers in the OSI model:
a) Physical Layer (2 marks)
b) Data Link Layer (2 marks)

QUESTION 2  (6 Marks)
Distinguish between 'Analog Signals' and 'Digital Signals'. Provide ONE (1) example of where each is used.

QUESTION 3  (6 Marks)
Describe THREE (3) types of transmission impairments that can affect a signal during transmission.

QUESTION 4  (4 Marks)
Compare 'Parallel Transmission' and 'Serial Transmission' based on speed, cost, and typical usage.

SECTION C: ESSAY QUESTIONS (10 MARKS) 应用论述题部分（共 10 分）

QUESTION 1
Network models are the foundation of data communication.
a) Illustrate the seven layers of the OSI Model in correct order. (7 Marks)
b) Discuss the concept of 'Encapsulation' and 'Decapsulation' as data moves through the layers of the TCP/IP suite. (3 Marks)