Lecture A4 Network / Internet. Computing and Art : Nature, Power, and Limits CC 3.12: Fall 2007

Transcription

1 Lecture A4 Network / Internet Computing and Art : Nature, Power, and Limits CC 3.12: Fall 2007

2 Instructor Functionalia Chipp Jansen, Course Web Page Today: Network Concepts Internet Specifics Clients and Servers IP Address and Domain Name Servers

3 What is a network? when computers talk to each other, this is called a network purpose: to share resources, physical (hardware), digital (software and data) open system = a system whose architecture is not a secret Internet is a distributed network - robust to failure, or attack

4 ARPAnet

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9 Components of a Network the network can have different kinds of computers and peripherals attached to it router camera printer toaster

10 Toaster? British Design - queried the local weather via the network, burned an appropriate symbol on your toast.

11 WAN vs. LAN What is a LAN? What is a WAN? What kind of network is the internet?

12 WAN vs. LAN What is a LAN? networks in which computers are physically connected to each other in the close geographical proximity are called local area networks (LANs) What is a WAN? other networks are called wide area networks (WANs) What kind of network is the internet? the internet is a wide area network

13 Network Topologies Hub - Star the way in which the computers are connected to each other is called the network s topology

14 Kinds of Network Topologies bus (linear model; inexpensive to run cables, but not robust to node failure) (back-bones of the internet)

15 Kinds of Network Topologies ring (example: IBM token ring)

16 Kinds of Network Topologies star (can be expensive to run cables, but robust to node failure)

17 Kinds of Network Topologies hub (efficient; internet model) (scalable, centralized point of failure) file-server workstation workstation hub workstation printer

18 Network Architecture Open System Interconnection (OSI) reference model or 7-layer model 1. application layer 2. presentation layer 3. session layer 4. transport layer 5. network layer 6. data link layer 7. physical layer All People Seem To Need Data Processing.

19 What is a layer? layers allow us to break-down a large task (i.e. communicating over a network) into smaller tasks provides abstraction a collection of related functions that provides services to the layer above it and receives service from the layer below it application provides service presentation session receives service

20 OSI / 7-layer model 1. application layer displays data, communicates with lower layers via presentation layer programmers writing applications (i.e. web-browser) use this layer s functionality end-user s use the application itself 2. presentation layer 3. session layer 4. transport layer 5. network layer 6. data link layer 7. physical layer

21 OSI / 7-layer model 1. application layer 2. presentation layer converts application layer data to forms understandable by other layers, and back; translates the meaning of the bits special-packaging encryption 3. session layer 4. transport layer 5. network layer 6. data link layer 7. physical layer

22 OSI / 7-layer model 1. application layer 2. presentation layer 3. session layer exchange of data between applications dialog and synchronization between applications manages and terminates the connections between the local and remote application 4. transport layer 5. network layer 6. data link layer 7. physical layer

23 OSI / 7-layer model 1. application layer 2. presentation layer 3. session layer 4. transport layer transfer of data through network; effects flow control; provides some error recovery TCP (transmission control protocol) and UDP (universal datagram protocol) operate at this layer post-office - handles / classifies the parcels 5. network layer 6. data link layer 7. physical layer

24 OSI / 7-layer model 1. application layer 2. presentation layer 3. session layer 4. transport layer 5. network layer physical routing of data from one computer to another; facilitates sender finding receiver IP, Internet Protocol - addressing Routers operate at the network level fragmentation - can break a package up into smaller packages (packets), handles resending (packet switched) shipping network - sacks of mail, trucks, airplanes 6. data link layer 7. physical layer

25 Packet-switching Sending units in smaller chunks: 1. More efficient: line of people at a busy pay-phone 2. React to failure and congestion: avoiding traffic jams 3. Improves reliability: part of message will arrive, and can resend

26 OSI / 7-layer model 1. application layer 2. presentation layer 3. session layer 4. transport layer 5. network layer 6. data link layer manages transmissions of low-level data; detects and corrects transmission errors point-to-point links 7. physical layer

27 OSI / 7-layer model 1. application layer 2. presentation layer 3. session layer 4. transport layer 5. network layer 6. data link layer 7. physical layer sends electronic signals, or bits 0 s and 1 s) (usually linked to above layer) wired ethernet network vs. wireless network

28 network information units and formats information units are passed from one layer to another headers are added as information passes from upper to lower layer terminology is defined below (it is often not used clearly or precisely): frame - information unit whose source and destination are the data link layer packet - information unit whose source and destination are the network layer segment - information unit whose source and destination are the transport layer message - information unit whose source and destination are the application, presentation or session layers datagram - information unit in a connectionless network

29 network/internet protocols protocol = set of rules for how computers communicate with each other IP: internet protocol, i.e., moving data via TCP or UDP TCP: transmission control protocol (computer computer); can retransmit if errors UDP: user datagram protocol; no error checking, fast messaging HTTP: hypertext transfer protocol (computer browser) FTP: file transfer protocol SMTP: simple mail transfer protocol

30 internet addresses IP address = Internet Protocol address every computer on the internet has a unique address dotted quad notation = four numbers separated by dots (.); e.g., (which is the address of the CIS dept web server...) - every number in the address is between 0 and 255 (*do you know why?) address can be stored in 32 bits; there are four formats, depending on the size of the network (i.e., the size of each of the numbers in the dotted quad notation is defined by the format...)

31 internet address subnetting is a standard (defined in 1985) to divide a large network into a number of smaller networks (this is what a router does) network subnet host prefix number number IP address a computer is assigned one IP address - assigned statically (manual) - assigned dynamically (DHCP)

32 Randall Munroe.

33 Domain Names provides a more convenient way to address a computer on the internet than the numeric IP address (we like naming things) structured hierarchically example: (which is more general?) no correspondence between parts of a domain name and numbers in IP common domain names : com, edu, gov, uk and other country-based domains (TLDs - top-level domains), (what about.tv? or.fm?) name server maintains correspondence between numeric IP address and domain names; DNS = internet domain name system = group of domain name servers

34 URLs URL - uniform resource locator - what web-browsers use (not exclusive!) 3 Parts 1. Protocol (i.e. telephone vs. fax) 2. DNS name 3. path to a file on the server

35 clients and servers server computer on a network which carries out some service for another computer client the other computer for whom the server is carrying out the service

36 types of servers file servers (provides files for clients) database servers (specialized file server: provides databases structured files for clients) what is a database? key concepts: SQL (structured query language), hierarchy, records, fields web servers (specialized file server: provides files that make up the components of a web site, e.g., html documents, video clips, etc) groupware manages scheduling for individuals and groups of co-workers collaborators provides reports (e.g., billing) for collaborators supports mailing lists for collaborators

37 mail servers (provides mail sending, receiving, storage) object servers (provides access to distributed objects ) print servers (manages a print queue) adds requests to the queue schedules requests instructs printer regarding requests provides status on requests to clients application servers (provides access to particular applications, e.g., game servers)

38 Client-Server Architecture presentation and logic layer web browser == client internet presentation and logic layer web browser == client processing layer application server, web server internet internet or LAN data layer web server data layer file server, database server, web server two-tier architecture client-server advantages: three-tier architecture isolates data storage technology places more burden on server (instead of client) and distributes tasks amongst server(s) follows object-oriented and modular paradigms

39 Telegarden ( ) Ken Goldberg - UC Berkley Prof.

40 Tillie, the telerobotic doll ( ) Lynn Hershman ( )

41 About now in Chicago; about here, now Video, wind sensors, fans Chicago - West Virginia connection. Michael Rodemer, 1996

42 TO DO Homework A (part 1 and 2) DUE Sunday, September 16, 11:59 pm via as a TEXT FILE attachment. READ: Reed, Chapter 1 Reed, Chapter 3 Reed, Chapter 6