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Networking 1

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Transcript

  • 1. Networking
  • 2. Analogy
  • 3. Networking
    • A network is two or more computers connected together so that they can exchange information
    • Networks extend the bus, they convey 0’s and 1’s among computers
  • 4. Networking
    • Networks began with the military
    • Army, Navy, and Air force all had computers, and wanted to communicate with each other
    • Networks and Protocols were created
  • 5. The URI Network Envision Lab INTERNET URI Network Gateway Gateway
  • 6. What do you need to communicate?
    • Physical way to send message
      • Smoke signals
      • drum
  • 7. What do you need to communicate?
    • What does the message mean?
    • When will the message start?
    • When will it end?
    • Who is it meant for?
    • What kind of message is it?
    • Does it require a reply?
    • What code do you use?
  • 8. Basic Components of a Data Communication System
    • Sending Device
    • Communications Link
    • Receiving Device
  • 9. Sending Device - Modem
    • Modem = modulate/demodulate
    • Converts digital signal to analog and vice versa
    •   User who connects to the computer via telephone services
    • speeds 56k (56,000 bps)
    • directly connected to the internet (unlike LAN)
  • 10. Sending Device - Modem
    • US Robotics Internal PCI Faxmodem
    • $34.99
  • 11. Sending Device – Cable Modem
    • Sold by the cable company
    • Requires Ethernet
    • Puts home computer on LAN
    • Speeds > 1 Mbps (1 million bytes per second)
  • 12. Sending Device – Cable Modem
    • Linksys Cable Modem
    • $99.99
    • Up to 42 Mbps download speeds, 10 Mbps upload
    • “ Always on” connection
  • 13. Sending Device – Cable Modem
    • D-Link Fast Ethernet PCI Network Adapter
    • $19.99
    • 10/100 Mbps Ethernet or Fast Ethernet compatible
  • 14. Sending Device - DSL
    • Alternative to cable for faster internet access then dial-up
    • Offered by phone company (via phone line)
    • Data transfer of 128,000 – 256,000 bps
    • (128k – 256k)
  • 15. Sending Device - DSL
    • Zoom ADSL Bridge Modem 5515 - DSL modem
    • ~ $60.00
  • 16. Protocols
    • To send a message, you need an agreed upon way to pulse the bits (0s and 1s) of the message
    • Protocol - A set of rules for the exchange of data
    • Protocols make sure that everything is in order before it is sent
  • 17. Protocols
    • How fast to pulse the bits?
    • How to mark the start and end of a message?
    • What computer the message is for?
    • What kind of message is it?
    • Does the message require a reply?
    • Is the whole message coming or just part of it?
    • What part of the message is this?
  • 18. Terminology
    • LAN – Local Area Network
      • A network of computers directly connected together by the same network management
      • URI Dorms, CS Dept, network within a business
  • 19. Terminology
    • WAN – Wide Area Network
      • A network of computers, usually physically separated from each other by great distances
      • Sometimes under the same management, sometimes under different management
  • 20. ISO’s 7 Layer Model
  • 21. Physical Layer
    • The Physical Layer describes the physical properties of the various communications media, as well as the electrical properties and interpretation of the exchanged signals. Ex: this layer defines the size of Ethernet coaxial cable, the type of BNC connector used, and the termination method.
    • How media gets from one place to another
  • 22. Speed
    • 10baseT LAN = 10Mbits/sec
    • 100baseT LAN = 100Mbits/sec
    • ISDN = 64Kbit/sec
    • Modem = 56Kbits/sec
    • Cable Modem/DSL = 1.2 Mbits/sec and up
    • T1 = direct connection at 1.5 Mbits/sec
    • T3 = 24 parallel T1 lines
    • Wireless – 11 Mbs
  • 23. Connection Medium – Wire Pairs
    • Twisted pair copper (phone lines)
    • Inexpensive, already installed
    • Susceptible to noise
  • 24. Connection Medium – coaxial copper
    • Faster, less prone to noise
    • Conductive wires in an enclosure
    • Laid underground
    • Carry cable TV
  • 25. Connection Medium - Fiber
    • Glass fibers over which light is pulsed
    • No metal
    • Faster then coaxial
    • Materials less expensive and lighter
  • 26. Connection Medium - Microwave
    • Fast, cost effective
    • Line of sight transmission
  • 27. Connection Medium - Radiowave
    • Used for long range transmissions
    • a station on earth sends signal to a satellite orbiting the earth, which has a transponder that receives the signal, amplifies the signal, changes the frequency and sends it back down to another earth station
  • 28. Hardware – NIC or Modem
    • NIC – network interface card
    • Collection of hardware and software resources that allow a computer to communicate to networks
  • 29. Hardware - NIC
    • Microsoft Networking 10/100 Ethernet PCI Adapter
    • $6.99
  • 30. Hardware - Gateways
    • Gateways connect two dissimilar networks or two computers with different interface cards
    • Transfers data from one network to another
  • 31. Hardware - Bridge
    • Connects similar networks
  • 32. Hardware - Router
    • Hardware that looks at IP addresses and sends data to another router
    • Finds a path from one computer to another
  • 33. Hardware - Router
    • Much of the work to get a message from one computer to another is done by a router
      • Ensures info doesn’t go where it’s not needed
      • Makes sure info reaches its destination
  • 34. Hardware - Router
    • Linksys Wireless Router
    • $ 99.99
  • 35. Hardware - Router
    • Netgear 4-Port Cable/DSL Router
    • $59.99
  • 36. Data Link Layer
    • The Data Link Layer describes the logical organization of data bits transmitted on a particular medium.
    • Determines speed at which data is pulsed over the medium and adds special bits to indicate the start and stop of transmission
  • 37. PPP
    • Point to Point protocol
    • Used by modems
    • No collisions
    • Windows has PPP built into dial-up adapter software
  • 38. Ethernet
    • Protocol used on LANs and by cable modems
    • Collisions
      • all computers use the same cable
      • The node “listens” to see if the cable is in use
      • CSMVCD – carrier sense multiple access w/ collision detection
  • 39. Internet or Network Layer
    • The Network Layer describes how a series of exchanges over various data links can deliver data between any two nodes in a network.
    • Allows computers on different networks to talk to each other
    • Adds bits of data to determine where data is headed
  • 40. IP Address
    • Each computer is assigned a unique IP address
    • ISP gives you a dynamic IP address
    • LAN gives you a fixed IP
    • We are currently using IPv4 which was developed 20 years ago
  • 41. IPv4
    • IIPv4, IP addresses have 4 bits fields
    • Each bit field is represented using a binary number and is referred to as an octet
    • They each have eight positions when viewed in binary form
    • If you add all the positions together, you get 32, which is why IP addresses are considered 32-bit numbers
  • 42. IPv4
    • Since each of the eight positions can have two different states (1 or 0) the total number of possible combinations per octet is 2 8 or 256
    • So each octet can contain any value between 0 and 255, Eg. homepage.cs.uri.edu is 131.128.81.37
  • 43. Classes
    • The four octets are used to create classes of IP addresses
    • Classes can be assigned to a particular business, government or other entity based on size and need
  • 44. Classes
    • There are 5 classes in IPv4 plus some special addresses
    • The five IP classes are: A,B,C,D, and E
  • 45. Net and Host
    • The five octets are split into two sections: Net and Host
    • Net always contains the first octet
      • Used to identify the network that a computer belongs to
    • Host always contains the last octet
      • Used to identify the actual computer on the network
  • 46. Default Network
    • 0.0.0.0
  • 47. Class A
    • Used for very large networks
    • IP addresses with a first octet from 1 to 126
    • The other three octets are used to identify each host
    • There are 126 class A networks with 16,777,214 possible hosts
    • 2,147,483,648 unique IP addresses
    • 115. 24.53.107
  • 48. Loopback
    • 127.0.0.1
    • Used as a loopback address
    • Used by the host computer to send messages back to itself
    • Commonly used for troubleshooting and network testing
  • 49. Class B
    • Used for medium sized networks
    • IP addresses with an octet from 128 to 191
    • The second octet is also part of the Net Identifier
    • The other two octets are used to identify each host
    • 16,384 class B networks with 65,534 possible hosts
    • 1,073,741,824 unique IP addresses
    • 145.24 .53.107
  • 50. Class C
    • Used for small to mid-sized businesses
    • IP addresses with a first octet from 192 to 223
    • Second and Third octets are also used as part of the Net identifier
    • Last octet is used to identify the host
    • 2,097,152 class C networks each with 254 possible hosts
    • 536,870,912 unique IP addresses
    • 195.24.53 .107
  • 51. Class D
    • Used for multicasts
    • The first four bits are 1110
    • The other 28 bits are used to identify a group of computers the multicast message is intended for
    • 268,435,456 addresses
    • 224. 24.53.107
  • 52. Class E
    • Used for experimental purposes
    • They have never been documented or utilized in a standard way
    • First four bits are 1111
    • 240. 24.53.107
  • 53. Broadcasts
    • Messages that are intended for all computers on a network are sent as broadcasts
    • These messages always use the IP address 255.255.255.255
  • 54. IPv4
    • Combine the four octets and you get 2 32 or a possible 4,294,967,296 unique values
    • We are running out of IP addresses!
    • In the next 5 – 15 years we will be switching to IPv6, which uses 128 bit IP addresses
    • Until then we use NAT
  • 55. NAT
    • Network Address Translation
    • Allows your home network to share a single internet connection over a single IP address
    • Also, NAT keeps your home network fairly secure
  • 56. DNS
    • Domain Name Server
    • Translates names like homepage.cs.uri.edu to IP addresses
    • You can use a name or an IP address in a web browser
      • http://homepage.cs.uri.edu/courses/fall2004/csc101s1
      • http://131.128.81.37/courses/fall2004/csc101s1
  • 57. Transport Layer
    • The Transport Layer describes the quality and nature of the data delivery.
    • Ensures that messages are received error free and in the right order
  • 58. Packets
    • Data is broken up into fixed sized packets
    • Each packet is marked with a sequence number
  • 59. TCP
    • Transmission Control Protocol
    • TCP enables two hosts to establish a connection and exchange streams of data
    • TCP guarantees delivery of data and also guarantees that packets will be delivered in the same order in which they were sent
  • 60. UDP
    • Uniform Data Protocol
    • UDP provides very few error recovery services, offering instead a direct way to send and receive data over an IP network
    • It's used primarily for broadcasting messages over a network
  • 61. Session Layer
    • The Session Layer describes the organization of data sequences larger than the packets handled by lower layers. Ex: this layer describes how request and reply packets are paired in a remote procedure call.
  • 62. Presentation Layer
    • The Presentation Layer describes the syntax of data being transferred. Ex: this layer describes how floating point numbers can be exchanged between hosts with different math formats.
  • 63. Application Layer
    • The Application Layer describes how real work actually gets done. Ex: this layer would implement file system operations.
  • 64. HTTP
    • H yper T ext T ransfer P rotocol
    • HTTP defines how messages are formatted and transmitted, and what actions Web servers and browsers should take in response to various commands
    • For example, when you enter a URL in your browser, this actually sends an HTTP command to the Web server directing it to fetch and transmit the requested Web page
  • 65. SMTP
    • S imple M ail T ransfer P rotocol
    • a protocol for sending e-mail messages between servers
    • Adds the date, and header (to from) to message
  • 66. POP and IMAP
    • POP
      • Post office protocol
      • Download messages to local server
      • Stores e-mail messages in a text file
    • IMAP
      • I nternet M essage A ccess P rotocol
      • Your e-mail stays on the server
  • 67. FTP
    • F ile T ransfer P rotocol
    • The protocol for exchanging files over the Internet
    • FTP is most commonly used to download a file from a server using the Internet or to upload a file to a server
  • 68. Telnet
    • Terminal Emulation program
    • For logging into remote servers
    • To start a Telnet session, you must log in to a server by entering a valid username and password
    • Your computer acts as a terminal by remotely logging into another computer
  • 69. Telnet
    • Telnet is not very secure, it sends your password unencrypted
    • Many system administrators block the use of Telnet
  • 70. SSH
    • Developed by SSH Communications Security Ltd., Secure Shell is a program to log into another computer over a network, to execute commands in a remote machine, and to move files from one machine to another
    • It provides strong authentication and secure communications over insecure channels.
  • 71. SSL
    • S ecure S ockets L ayer
    • Encrypts the data before it goes to TCP/IP and decrypts upon receiving
    • Allows secure transmission of data, used when you buy stuff online, and when you transmit passwords
  • 72. OSCAR
    • Used for AOL instant messanger
  • 73.
    • A business manager writes a long report and wants to send it by US Mail.
    • Data being e-mailed from one computer to another.
  • 74.
    • The manager hands the report to a secretary who generates mailing labels using standard addressing conventions of to address and from address.
    • The computer adds bits to the e-mail message which represent the “from”, “for”, and “subject” fields. The structure and placement of this data is determined by SMTP.
  • 75.
    • The secretary hands the labels and the reports to a mail clerk.
    • The e-mail application sends the data to the TCP/IP stack in the computer’s operating system.
  • 76.
    • The clerk adds the zip code to the mailing labels.
    • The operating system adds does a DNS lookup of the e-mail’s host name address to get the IP address. It adds bits representing the IP address to the data.
  • 77.
    • The clerk knows the weight limit of the US postal service, so he breaks the report into several envelopes and puts an address label on each one. He also puts a sequence number (1,2,3…) on each letter.
    • The operating system breaks the e-mail message into TCP packets.
  • 78.
    • The clerk puts the envelopes in the outbox of the company.
    • The computer sends the data to the network card or modem.
  • 79.
    • The US postal service comes by and picks up the envelopes at certain times.
    • The network card broadcasts the data over the data link layer. The data link layer dictates when the packets can be broadcast.
  • 80.
    • The US postal service uses hand carriers, trucks, and airplanes to get the envelopes to their destination.
    • The data travels over many types of network media, such as wire pairs, microwave, and satelite.
  • 81.
    • The envelopes go to the local post office, then the regional post office, then the central post office, then the local post office of the receiver. Each post office has a set of rules as to where to send certain zip codes.
    • The data goes through various gateways and routers. Each router has rules as to where to send certain IP addresses.
  • 82.
    • A clerk on the receiving end watched the mail truck go by and continually asks, “Anything for out company?”
    • The network card in the receiving computer constantly watched traffic on the network looking for packets with their IP address.
  • 83.
    • The receiving clerk collects envelopes off the local mail trucks until he has all the envelopes that make up the report. If any envelopes are missing, he calls the sending clerk and asks him to resend that envelope.
    • The receiving computer’s TCP stack collects all packets and puts them into order. If any are missing, it signals the sending computer to re-send the missing packet.
  • 84.
    • When all the envelopes have arrived, the clerk gives them to the secretary. The secretary takes out the pieces, puts a nice “to” “from” cover letter on the report, and hands it to the manager.
    • The receiving computer uses an e-mail program that understands SMTP to display the e-mail header and the text on the e-mail.

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