[컴퓨터네트워크] 1. Introduction (1)

Overview/roadmap

1. What is the Internet?
2. What is a protocol?
3. Network edge: hosts, access network
4. Network core: packet/circuit switching, internet structure
5. Performance: Loss, Delay, Throughput
6. Protocol layers, service models
7. Basic network security
8. Internet history

 

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1. What is the Internet?

1) What's the Internet: "nuts and bolts" view

▶ Billions of connected computing devices

• hosts = end systems
• running network apps at Internet's edge

▶ Communication links

• fiber, copper, radio, satellite
• transmission rate: bandwidth

▶ Packet switches: forward packets

• routers and switches
  - router: 작은 영역
  - switch: 큰 영역

▶ Networks: collection of devices, routers, links managed by an organization.

 

▶ Internet: "network of networks"

• Interconnected ISPs(Internet Service Protocols)

▶ Protocols: control sending, receiving of messages

• Ex) HTTP(Web), TCP/IP, WiFi, 4G, Ethernet, streaming video, Skype...

▶ Internet standards

• RFC(Request For Comments)
• IETF(Internet Engineering Task Force)

 

2) The Internet: a service view

• Infrastructure: provides services to applications.
• Provides programming interface for apps.

 

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2. What's a protocol?

▶ Protocols define:

• Format
• Order of messages sent and received among network entities
• Actions taken on message transmission
• Receipt

 

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3. Network edge: hosts, access network

1) A closer look at Internet structure

▶ Network edge

• Hosts
  - Client: request 요청
  - Server: request 받음
• Servers

Network edge

 

▶ Access networks

: The network that physically connects end system(host) to the first router(edge router).

• Wired/Wireless communication links

Access network

 

▶ Network core

: Interconnected routers

Network core

 

2) Access networks

▶ How to connect end systems to edge router?

▶ What to look for:

• transmission rate (bit per second) of access network?
• shared/dedicated access among users?

 

3) Access network: DSL(digital subscriber line)

DSL(digital subscriber line)

: Use existing telephone line to central office DSLAM.

• Data over DSL phone line --> Internet
• Voice over DSL phone line --> Telephone network

1. DSL modem: 컴퓨터의 digital signal --> 전화선의 analog signal
2. 전화선: voice and data is transmitted simultaneously at different frequencires over dedicated line to central office.
3. CO(Central Office) - DSLAM(DSL Access Multiplexer): analog signal --> digital signal
   --> Telephone network: PSTN
   --> Internet

• upstream과 downstream의 속도가 다르다. 일반적으로 downstream의 속도가 더 빠르다.

 

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1. What is the Internet?

• "nuts and bolts" view
  - Hosts = End systems
  - Communication links --> bandwidth: transmission rate
  - Routers, Switches
  - Protocols
• A service view
  - Provides programming interface for apps.

 

2. What is a protocol?

: Protocols define formats, order of messages sent and received among network entities, and actions taken on message transmission, receipt.

 

3. Network edge: hosts, access network

• A closer look at Internet structure
  - Hosts(Client, Server) <-> Servers
  - Access networks: Connects end system(host) to the edge router
  - Network core: Interconnected routers
• Access networks: Connects end system(host) to the edge router
• Access network: DSL(digital subscriber line)
  - DSL modem: digital signal --> analog signal
  - Dedicated line to CO(central office).
  - CO(central office) -- DSLAM(DSL access multiplexer): PSTN(telephone network), Internet