1      Chapter 1: introduction

1.1    What is the Internet? What is a protocol?

1.1.1   The Internet: a “nuts and bolts” view

Billions of connected computing devices:

• hosts (主机) = end systems (端系统)
• running network apps (应用) at Internet’s “edge” (边缘)

Packet switches (分组交换机) : forward packets (分组) (chunks of data)

• routers (路由器) , switches (交换机)

Communication links (通信链路)

• fiber (光纤) , copper (铜) , radio (无线电) , satellite (卫星)
• transmission rate (传输速率): bandwidth (带宽)

Networks

• collection of devices, routers, links: managed by an organization

Internet: “network of networks”

• Interconnected ISPs (Internet Service Providers, 因特网服务提供商)

protocols are everywhere

• control sending, receiving of messages (报文)
• e.g., HTTP (Web), streaming video, Skype, TCP, IP, WiFi, 4G, Ethernet

Internet standards

• RFC: Request for Comments (请求评论)
• IETF: Internet Engineering Task Force (因特网工程任务组)

1.1.2  The Internet: a “services” view

Infrastructure that provides services to applications:

• Web, streaming video, multimedia teleconferencing, email, games, e-commerce, social media, inter-connected appliances, …

provides programming interface to distributed applications (分布式应用程序):

• “hooks” allowing sending/receiving apps to “connect” to, use Internet transport service
• provides service options, analogous to postal service

1.1.3  What’s a protocol?

Network protocols:

• computers (devices) rather than humans
• all communication activity in Internet governed by protocols

Protocols (协议) define the format, order of messages sent and received among network entities, and actions taken on message transmission, receipt

1.2    Network edge: hosts, access network, physical media

1.2.1  A closer look at Internet structure

Network edge (网络边缘) :

• hosts (主机): clients and servers
• servers often in data centers (数据中心)

Access networks (接入网), physical media (物理媒体):

• wired, wireless communication links

Network core (网络核心) :

• interconnected routers
• network of networks

1.2.2  Access networks and physical media

Q: How to connect end systems to edge router?

l  residential access nets

l  institutional access networks (school, company)

l  mobile access networks (WiFi, 4G/5G)

1.2.2.1  Access networks: cable-based access

frequency division multiplexing (FDM, 频分复用): different channels transmitted in different frequency bands

HFC: hybrid fiber coax (混合光纤同轴)

• asymmetric: up to 40 Mbps – 1.2 Gbps downstream transmission rate, 30-100 Mbps upstream transmission rate

network of cable, fiber attaches homes to ISP router

• homes share access network to cable headend

1.2.2.2  Access networks: digital subscriber line (DSL, 数字用户线)

use existing telephone line to central office DSLAM

• data over DSL phone line goes to Internet
• voice over DSL phone line goes to telephone net

24-52 Mbps dedicated downstream transmission rate

3.5-16 Mbps dedicated upstream transmission rate

1.2.2.3  Access networks: home networks

 

1.2.2.4  Wireless access networks

Shared wireless access network connects end system to router

l  via base station aka “access point”

Wireless local area networks (WLANs)

• typically within or around building (~100 ft)
• 802.11b/g/n (WiFi): 11, 54, 450 Mbps transmission rate

Wide-area cellular access networks

• provided by mobile, cellular network operator (10’s km)
• 10’s Mbps
• 4G cellular networks (5G coming)

1.2.2.5  Access networks: enterprise networks

companies, universities, etc.

mix of wired, wireless link technologies, connecting a mix of switches and routers (we’ll cover differences shortly)

Ethernet: wired access at 100Mbps, 1Gbps, 10Gbps

WiFi: wireless access points at 11, 54, 450 Mbps

1.2.2.6  Access networks: data center networks

high-bandwidth links (10s to 100s Gbps) connect hundreds to thousands of servers together, and to Internet

 

1.3    Network core: packet/circuit switching, internet structure

1.4    Performance: loss, delay, throughput

1.5    Protocol layers, service models

1.6    Security

1.7    History