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Introduction to Networks

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  1. Introduction to Networks

  2. Use networked computers to: • Create or download catalog records for our holdings • Create and distribute electronic bibliographies • Computer networks allow us to: • Order books online • Receive access to online databases • Receive software updates The library A system view Environment U s e r s Inputs Outputs Transformational process energy money materials personnel information products services Many of our products and services are delivered via computer network (e.g., virtual reference)

  3. Connectivity of Public Libraries Information Use Management & Policy Institute http://www.ii.fsu.edu/plinternet_findings.cfm

  4. Computers in libraries Stand-alone pc or Mac Mainframe & "dumb" terminals Networked computers and peripherals

  5. Local Area Network (LAN) A communication network used by a single organization over a limited distance which permits users to share information and resources.* *Schatt, Stan. 1992. Understanding local area networks. 3rd ed. Carmel, Indiana: SAMS.

  6. Local Area Network elements Transmission medium - type of wires or other media Network topology - architecture Transmission protocol - rules followed when sending signals Software

  7. Transmission media (1) Unshielded twisted pair (UTP) • Least expensive (CAT 5e 1,000 feet for $260 in Spring 2011) • Four pairs grouped in plastic sheath • Each pair consists of two insulated wires twisted together • Limited range - max 100 meters (328 feet)

  8. Twisted pair (cont.) Category 5 – up to 100 Mbps Category 6 – up to 1000 Mbps

  9. Transmission media (2) • Coaxial cable • Copper conductor surrounded by insulation • Span distance of 185 meters (607 feet) for thin Ethernet 10BASE-2) Copper conductor Plastic insulation layer Braided metal shield Cable jacket

  10. Transmission media (3) Fiber-optic cable • Expensive • Immune to electromagnetic or radio-frequency interference • Capable of sending signals several miles • Fast Coating Glass Core Cladding Strengthening fibers Cable jacket

  11. Fiber optic transmission Glass Core Cladding Cladding (light-refracting) Light source Cut-away view Glass fiber (light-transmitting)

  12. ν * λ = c Transmission media (4) 109 Hz Wireless • Radio waves • Can travel long distances  interference • Can penetrate buildings • Omnidirectional • Low bandwidth • Microwaves • Travel in straight line • Good signal to noise ratio • Do not penetrate buildings well • Light waves • Unidirectional - require laser and photodetector on both ends for two-way transmissions • Line of sight--requires precise alignment of sender and receiver • High bandwidth 1011 Hz 1015 Hz

  13. Network architecture - star topology OPAC printer OPAC Circulation OPAC

  14. Network architecture - ring topology

  15. Ring topology

  16. FDDI (Fiber Distributed Data Interface) Bidirectional token ring network

  17. Network architecture - bus topology Circulation & Server OPAC Bus OPAC OPAC printer

  18. Network architecture - bus topology using switch or hub Hub

  19. Network protocol - token ring Token passes from node to node Token Msg. Token IEEE Std. 802.5 ISO/IEC 8802-5 Msg. Rec.

  20. Network protocol - Carrier-Sense Multiple Access with Collision Detection (CSMA/CD) • User's workstation generates a signal to send • Listens to detect a carrier signal from any other user • If no other signal is detected, first user's message is sent • User listens for message collision. If detects collision, waits random period of time, then restarts process IEEE Std. 802.3 ISO/IEC 8802-3

  21. EtherNet frame (packet) format FRAME CHECK SEQUENCE DESTINATION ADDESS SOURCE ADDRESS PREAMBLE TYPE DATA

  22. Mix and match wiring and control topologies Star wiring with token passing

  23. Network of networks Bridge

  24. Adding wireless Access point for wireless IEEE Std. 802.11 ISO/IEC 8802-11

  25. Wide Area Networks (WANs) • Component entities can be miles apart • Often consist of multiple local area networks linked together • Largest WAN is the Internet

  26. Internet – Two tales converge • Late 1950s - Department of Defense communications went through public telephone network, considered vulnerable • DOD wanted command-and-control network that could survive nuclear war

  27. A robust proposition Switching office Telephone system Toll office Toll office Baran’s proposed distributed switching system

  28. Internet beginning • ARPANET (Advanced Research Projects Agency Network - U.S. Dept. of Defense Program) First connections: 1. UCLA (hooked up 9/2/69) 2. Stanford Research Institute (10/1/69) 3. UCSB (11/1/69) 4. Univ.of Utah (12/69)

  29. Internet characteristics Highly redundant network (many ways to get from point A to point B) (Baran’s idea) Uses packet switching (Clark’s idea)

  30. Switched telephone network A B Switchboard

  31. Long distance telephone switching B A Trunk line

  32. If roads were like telephones…

  33. Traffic flow Beretania

  34. Packet switching Each message divided into packets • Source • Destination • Packet number of how many packets • Data Packet switches (nodes on Internet) use distributed adaptive routing

  35. Packet-switched network switch switch switch switch switch switch

  36. Network redundancy switch switch switch X switch switch switch

  37. Required in order to be on the Internet • Physical connection to someone who is already part of the Internet • Utilize Internet Protocol • Suite of software: telnet, ftp, etc. • IP address hypatia.slis.hawaii.edu 128.171.58.11

  38. Surfing the 'Net Server Request messages Text, graphics, error messages Client Webserver application responds to requests from client Browser application sends requests to server

  39. Getting a Web page • Get numerical IP address • Establish connection with machine running server • Send request for file to server • Server sends file • Release connection • Display text • Repeat above steps to request images

  40. Universal Resource Locator (URL) http://www.cool.com/mystuff/myfile.html machine directory file name protocol

  41. Getting the IP address What is numerical address of www.cool.com? Domain Name Server Browser 123.157.78.99

  42. nslookup command on UNIX Tashi delek%nslookup www.ala.org Server: dns1.hawaii.edu Address: 128.171.3.13 Non-authoritative answer: Name: www.ala.org Address: 66.158.92.67

  43. The IP address 128.171.58.11 Network class No. of Network Bytes Example A 1 8.0.0.0 B 2 128.171.0.0 C 3 199.1.1.0 University of Hawai`i is a Class B network

  44. The IP address 128.171.94.192 UH Network Subnet Machine

  45. Establish a connection Client sends “connection request” to server Server sends “connection accepted” response to client

  46. Requesting & receiving file Client sends "GET /mystuff/myfile.html" command to server Server looks in mystuff directory Server sends myfile.html to client

  47. Release connection Client sends disconnect request to server Server closes connection

  48. Display text and images Browser displays text and images in accordance with directions in HTML tags

  49. Sending data Client sends "GET /mystuff/myfile.html" command to server msg msg msg 1 2 3

  50. Sending data Client sends "GET /mystuff/myfile.html" command to server msg 1 To: 123.157.78.99