Networking and the Internet-計算機概論筆記

一定愛配于天立教授開放課程食用:課程連結

Networking and the Internet

Network Classifications

• Scope
  • LAN: Local area network.
  • MAN: Metropolitan area network.
  • WAN: Wide area network.
• Ownership
  • Closed
  • Opened
• Topology (拓樸學)
  • Bus:
  • Ring:
  • Star:

Protocols

• Token Ring
  • Popular in ring topology.
  • Token and messages are passed in one direction.
  • Only the machine which gets the token can transmit its message.
• CSMA/CD (Carrier sense, mutiple access with collision detection)
  • Popular in bus topology.
  • Broadcasting.
  • When collision, both machines wait for a random time before trying again.
• CSMA/CA (Carrier sense, mutiple access with collision avoidence)
  • Popular in wireless Ethernet.
  • Broadcasting.
  • Detect if a channel is idle, if so, wait for a random time and then detect again. If the channel is still idle, then start sending.

Wireless and Access Point(AP)

• Wi-Fi(wireless fidelity)
• IEEE 802.11-Standard for wireless network(b, g, i, n, ac...)

Repeater，Bridge，Switch(Compatible Networks)

Reference: link

• The protocol between these devices have to be the same.
• Repeater(Amplifier)
  • Passing through messages.
  • Connecting two compatible networks
• Bridge
  • Only passing those messages addressed to the other side.
  • Connecting two compatible networks more efficiently.
• Switch(Multiple Bridge)
  • A bridge with multiple connections.
  • Connecting mutiple compatible networks efficiently.

Router(Incompatible Networks)

• Router
  • Building a network of networks.(The protocol can be different)
  • Most come with firewall management.

Interprocess Communication

• Server-Client
  • One server, several clients.
  • Clients initiate communications by sending requests.
• P2P(Peer-to-Peer)
  • Two processes communicating as equals.
  • The most popular distribution mode nowadays.

Distributed Systems

• Infrastructure can be provided by standardized toolkits.
  • Ex: Java Beans，.NET framework.

Internet Architecture

• Domain
  • A network or an internet controlled by one single authority.
• ICANN(Internmet corporation for assigned names and numbers)
  • Supervise the registration of doimains
• Gateway
  • A router that connects a domain to the rest of the Internet.

Internet Composition

• Internet Service Provider(ISP)
  • Allow customer to connect their domain to the ISP's equiment or join the domain already established by the ISP.

IP Addresses

• IP(internet protocol)address
  • IPv4 -> 32bits(all are allocated already)
  • IPv6 -> 128bits

Name Server vs Domain Server

• Name server:
  • Name servers organize and route traffic across the internet to get you to the right server.
• Domain Name Server(DNS)
  • A server that provide you with server information.

Internet Application

• VoIP(Voice over Internet protocol)
• email(electronic mail)
• FTP(file transfer protocol)
• telnet and ssh(secure shell)
• P2P

Browsers

• HTTP(Hyper text transfer protocol)
• URL(uniform resource locator)
• How a browser get access to a webpage(document):

Client-side and Server-side

• Client-side(The program is executed on one's pc)
  • Java applets
  • Javascript
  • Flash
• Server-side(The program is executed on the server)
  • CGI
  • Servlets
  • PHP
• Online game use both techniques.

Internet Protocol

Reference: link

• Layers

  • OSI Model

    Reference: link

  
  • TCP/IP Model
    • Application: constructs message into packets.
    • Transport: chops message into packages.
    • Network: handles routing through the Internet.
    • Link handles actual transmission of packets.
• Port
  • Incoming messages are delivered to different applications by unique port numbers.

TCP/IP

• TCP and UDP(Transport Layer)
  • TCP(transmission control protocol):handshake berfore sending packets. => slow but reliable.
  • UDP(user datagram protocol): directly sending packets. => fast but not reliable.
• IP(NEtwork Layer)
  • routing based on IP(IPv4, IPv6)
• TCP and IP are two protocols. TCP/IP is a collection of protocols more than just TCP and IP.

Security

• Attacks

  • Malware
  • Denial of Service(Dos)
  • Spam

• Protections

  • Firewall
  • Spam filter
  • Proxy
  • Antivirus, antispyware

• Public/Private Keys System

  Reference: link

  • SSL(Secure Scoket Layer)
    • Application: sftp, https, ssh
  • To prevent fishing, a certificate authority is needed, to ensure to correctivity of a key.

RSA Algorithm

Reference: link

• Generation
• Encryption
• Decryption