Lecture #30
- Announce
- Finish Reading Chapter 12, Computer Communications
- Start Reading Chapter 11, Security
Computer Communications
- One of the Great Ideas
- Modes of Communications
- Computer and humans communicate
- Computers talk to each other
- Now Humans use computers to talk to each other
- Email, Chat, etc.
- News; started at Duke CS
- IRC: Many thousands of people, 1000 channels
- Voice
- Video
- Like Most of Computing: Layers upon Layers
- Basic Communications
- In binary
- Represented by something over some medium by something
- started with terminals connected to computers
- Communicated by voltages on wires
- Then modems allowed communication over phone lines
- Turn binary representing voltages into audio tones
- Dial up computer communications
- Time sharing systems
- Bulletin boards
- USENET (started at Duke, UNC, Bell Labs)
- Basic Communications
- Fixed/Dial Up
- Topography
- Star
- Point to Point
- Ring
- Bus
- Network
- Connection Mode
- Circuit Switched
- connection made
- e.g. Telephone System
- exclusive use of part of medium
- interactive use possible
- Message Switched
- store and forward
- batch
- shared facilities
- Packet Switched
- shared medium
- interactive use possible
TCP/IP
- Ethernet (Bus Example)
- Also called LAN
- Many nodes (hosts, stations, ...) on same bus
- Each has address (unique!)
- All messages "broadcast" with dest and src address
- Everyone listens for their address
- Potential security problem
- Collisions possible
- ethernet.gif,
ethernet.ps
- Internet -- a network of LANs that are interconnected
- Packets -- the currency of the Internet
- The Layers
- The Physical Layer
- Hardware (e.g. Ethernet)
- The Ethernet Packet
- The IP (Internet Protocol) Layer
- The IP Packet
- Hardware Independence
- The TCP (Task Control Protocol) Layer
- The Application Layer
- Packets Within Packets
- Reliability
- Addressing (Layers Again!)
- Hardware Address (Ethernet Address)
- unique 6 octet (8 bit -- byte) number
- usually 6 groups of two hex digits: b3 fe 13 21 a5 41
- centrally administered
- IP Address
- 4 octet number: e.g. 128.109.40.1
- usually 4 decimal number separated by periods
- network part ;host part
- Centrally Administered
- Domain Name
- hierarchical system
- root: edu, com, mil, net, country
- hostname; suborg; organization
- e.g. oberon.cs.duke.edu
- person on host is e.g. ramm@oberon.cs.duke.edu
- Applications
- email
- news
- talk
- ftp
- anonymous
- archives
- free software
- weather servers
- forecasts
- weather maps
- finger
- telephone
- telnet
- rlogin
- irc
- information services
- Client/Server
- Print Server
- File Server
- Name Server
- WWW
- Computer Security / Confidentiality
- Basic Ideas
- Passwords
- Encryption
- Whole New Chapter on these Topics
