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Lecture 1 Internet

This lecture introduces key concepts of internet communication systems, focusing on end-systems as hosts, LANs, WANs, and MANs. It explains the differences between multi-access and point-to-point networks, the roles of various technologies like Ethernet and FDDI, and the hierarchical structure of ISPs. Key design goals of the Internet, including interoperability and fault tolerance, are discussed alongside important design principles. Additionally, the lecture explores protocols that govern communication in networks, highlighting the importance of formal definitions in ensuring reliable data exchange.

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Lecture 1 Internet

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  1. Lecture 1Internet CPE 401 / 601Computer Network Systems slides are modified from Dave Hollinger and Daniel Zappala

  2. Network “ ... communication system for connecting end-systems” End-systems a.k.a. “hosts” PCs, workstations dedicated computers network components Internet

  3. 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 ! Internet

  4. 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 Internet

  5. 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 Internet

  6. MAN - Metropolitan Area Network • Larger than a LAN and smaller than a WAN - example: campus-wide network • multi-access network • Technologies: • coaxial cable • microwave Internet

  7. Internetwork • Connection of 2 or more distinct (possibly dissimilar) networks. • Requires some kind of network device to facilitate the connection. Net A Net B Internet

  8. PC Mobile network server Global ISP wireless laptop cellular handheld Home network Regional ISP access points wired links Institutional network router 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) Internet

  9. The Internet Internet Mapping Project, Bill Cheswick Internet

  10. 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) Internet

  11. Internet

  12. 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 Internet

  13. Internet Design Goals • primary goal: interoperability among existing networks • a network of networks • obey administrative boundaries • secondary goals • fault tolerance • multiple transport protocols • support a variety of networks • distributed management • cost effective, low effort for host attachment, accountability • first three were more important, so remaining four did not receive as much attention • no mention of security Internet

  14. 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 Internet

  15. Network Models • Using a formal model allows us to deal with various aspects of Networks abstractly. • We will look at a popular model (OSI reference model). • The OSI reference model is a layered model. Internet

  16. Layering • Divide a task into pieces and then solve each piece independently (or nearly so). • Establishing a well defined interface between layers makes porting easier. • Major Advantages: • Code Reuse • Extensibility Internet

  17. The Internet Hourglass Internet

  18. The Internet at each Hop Internet

  19. Process Process Interface Protocols Transport Transport Peer-to-peer Protocols Network Network Data Link Data Link Interface and Peer-to-peer Protocols • Interface protocols describe communication between layers on the same endpoint. • Peer-to-peer protocols describe communication between peers at the same layer. Internet

  20. 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 Internet

  21. TCP connection response Get http://www.awl.com/kurose-ross Got the time? 2:00 <file> time What’s a protocol? a human protocol and a computer network protocol: Hi TCP connection request Hi Q: Other human protocols? Internet

  22. 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. Internet

  23. 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. Internet

  24. 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. Internet

  25. 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. Internet

  26. 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. Internet

  27. Thought Exercise • Come up with an example of a layered system. • Describe the interface and peer-to-peer protocols for your example. Internet

  28. Layering Example: Federal Express Addressed Envelope Letter • Letter in envelope, address on outside • FedX guy adds addressing information, barcode. • Local office drives to airport and delivers to hub. • Sent via airplane to nearest city. • Delivered to right office • Delivered to right person Addressed Envelope Letter Internet

  29. Layered Software Systems • Network software • Operating systems • Windowing systems Internet

  30. Unix is a Layered System Applications Libraries System Calls Kernel Internet

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