CH1-LECTURE_1.pdf
- 1. Lecture 1 Basics of Data communication and Computer Networks Tameru H. AASTU, Depart of Software Engineering 1 Chapter 1
- 2. Network “ ... communication system for connecting end-systems” End-systems a.k.a. “hosts” PCs, workstations dedicated computers network components Chapter 1 2
- 4. Fundamental Characteristics • The effectiveness of a data communication system depend on four fundamental characteristics: • Delivery • Accuracy • Timelines • Jitter Chapter 1 4
- 5. Five Components of Data Communication Chapter 1 5 1. Message 2. Sender 3. Receiver 4. Medium 5. Protocol
- 6. Direction of data flow Chapter 1 6 Simplex Half Duplex Full Duplex
- 7. Multiaccess vs. Point-to-point • Multiaccess means shared medium. • many end-systems share the same physical communication resources (wire, frequency, ...) • There must be some arbitration mechanism. • Point-to-point • only 2 systems involved • no doubt about where data came from ! Chapter 1 7
- 8. LAN - Local Area Network • Connects computers that are physically close together ( < 1 mile). • high speed • multi-access • Technologies: • Ethernet 10 Mbps, 100Mbps • Token Ring 16 Mbps • FDDI 100 Mbps Chapter 1 8
- 9. WAN - Wide Area Network • Connects computers that are physically far apart. “long-haul network”. • typically slower than a LAN. • typically less reliable than a LAN. • point-to-point • Technologies: • telephone lines • Satellite communications Chapter 1 9
- 10. MAN - Metropolitan Area Network • Larger than a LAN and smaller than a WAN - example: campus-wide network - multi-access network • Technologies: • coaxial cable • microwave Chapter 1 10
- 11. Internetwork • Connection of 2 or more distinct (possibly dissimilar) networks. • Requires some kind of network device to facilitate the connection. Net A Net B Chapter 1 11
- 12. The Internet • millions of connected computing devices: hosts = end systems • running network apps • communication links • fiber, copper, radio, satellite • routers: forward packets (chunks of data) Chapter 1 12 Home network Institutional network Mobile network Global ISP Regional ISP router PC server wireless laptop cellular handheld wired links access points
- 13. The Internet Chapter 1 13 Internet Mapping Project, Bill Cheswick
- 14. A Network of Networks • roughly hierarchical • Tier-1 ISPs provide national, international coverage • Tier-2 ISPs provide regional coverage • Tier-3 and lower levels provide local coverage • any tier may sell to business and residential customers • any ISP may have a link to any other ISP (not strictly hierarchical) Chapter 1 14
- 15. Many Different Internet Service Providers • Each network is independent • Interoperability requires using Internet standards: IP, TCP • the Internet is global and must run these standards • your private intranet can do whatever you want it to do Chapter 1 15
- 16. Internet Design Principles • minimal assumptions about services network should support • ability to send packets • no reliability or security • end-to-end principle • keep the core of the network as simple as possible, • put complex functionality at the edges • exception: significant performance improvement Chapter 1 16
- 17. What’s a protocol? human protocols: • “what’s the time?” • “I have a question” • introductions … specific msgs sent … specific actions taken when msgs received, or other events network protocols: • machines rather than humans • all communication activity in Internet governed by protocols Chapter 1 17
- 18. What’s a protocol? a human protocol and a computer network protocol: Chapter 1 18 Q: Other human protocols? Hi Hi Got the time? 2:00 TCP connection request TCP connection response Get http://www.awl.com/kurose-ross <file> time
- 19. Protocol • An agreed upon convention for communication. • both endpoints need to understand the protocol. • Protocols must be formally defined and unambiguous! • Protocols define • format, • order of msgs sent and received among network entities, • actions taken on msg transmission, receipt • We will study lots of existing protocols and perhaps develop a few of our own. Chapter 1 19
- 20. Programs & Processes • A program is an executable file. • A process or task is an instance of a program that is being executed. • A single program can generate multiple processes. Chapter 1 20
- 21. Client - Server • A server is a process - not a machine ! • A server waits for a request from a client. • A client is a process that sends a request to an existing server and (usually) waits for a reply. Chapter 1 21
- 22. Client - Server Examples • Server returns the time-of-day. • Server returns a document. • Server prints a file for client. • Server does a disk read or write. • Server records a transaction. Chapter 1 22
- 23. Servers • Servers are generally more complex (more interesting). • Basic types of servers: ¨ Iterative - server handles one client at a time. ¨ Concurrent - server handles many clients at a time. • We will study the differences later. Chapter 1 23