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Computer Networking

Computer Networking. Bits and Bytes. Putting information into a form that a computer can deal with… “A” = 01000001 “B” = 01000010. Information “Encoding”. … 065 01000001 A 066 01000010 B 067 01000011 C 068 01000100 D 069 01000101 E 070 01000110 F 071 01000111 G ….

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Computer Networking

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  1. Computer Networking

  2. Bits and Bytes • Putting information into a form that a computer can deal with… • “A” = 01000001 • “B” = 01000010

  3. Information “Encoding” • … • 065 01000001 A • 066 01000010 B • 067 01000011 C • 068 01000100 D • 069 01000101 E • 070 01000110 F • 071 01000111 G • …

  4. Review (maybe) • Have a bit… • 0 or 1 • Take a whole byte… • Eight bits • R represents a letter or numeral or punctuation mark

  5. Transmission of Information • Bandwidth • Bits per second • Kilo • Mega • Giga

  6. A Computer Network • What is a computer network? A network is a collection of computers or computer-like devices that can communicate across a common transmission medium.

  7. A Computer Network • In a network, requests and data from one computer pass across the transmission medium (which might be a network cable or a phone line) to another computer. • Example: four node network

  8. A Computer Network • A computer interacts with the world through one or more applications (software) that perform specific tasks and manage input and output. • If that computer is part of a network, then some of those applications must be capable of communicating with applications on other network computers.

  9. A Computer Network • A network protocol is a system of common rules that helps to define the complex process of transferring data. The data travels from an application on one computer, through the computer’s network hardware, across the transmission medium to the correct destination, and up through the destination computer’s network hardware to a receiving application.

  10. Application Software Application Software Network software within the operating system Network software within the operating system Network Interface Card (NIC) Network Interface Card (NIC) Computer Network Transmission medium

  11. A Computer Network • A network is usually described as being a local area network (LAN) or a wide area network (WAN)

  12. Local Area Network (LAN) • Many types of LAN technologies have existed over the years • One predominant LAN technology exists today - Ethernet

  13. Ethernet • Contention media access method • Allows many computers on the same network to share the same bandwidth (basically share a common medium or connection) • Easily scalable – easy to improve and incorporate new technology as it becomes available

  14. Ethernet • Uses Carrier Sense Multiple Access with Collision Detect (CSMA/CD) • CSMA/CD is a protocol designed to allow multiple computers to share the network medium successfully • Designed to manage collisions

  15. Ethernet • What is a collision? • (example of four node 10Base-2 network) • All computers share the connection • Only one can transmit at a time • Suppose computer C is transmitting information to computer D • C “takes over” the wire – sends electrical signals onto the wire

  16. Ethernet • All computers on the network detect the transmission • Only D will process the transmitted data because C has addressed the information to D • A collision will occur if two computers attempt to transmit at the same time (like a group of people talking at a party) B

  17. Ethernet • CSMA/CD – if a transmitting computer detects another computer attempting to transmit, it sends out a long “jam” signal that causes all computers on the network to be silent • A “back off” scheme is used to figure out who gets to transmit first

  18. Ethernet • On a busy Ethernet network collisions can be a big problem • SLOW!

  19. Types of Ethernet • Ethernet was initially developed by Digital Equipment Corporation, Intel, and Xerox • The IEEE took their design and created the official network standard • The IEEE called this standard 802.3 • 802.3 is the family name for all wired Ethernet types

  20. Types of Ethernet – 10Base2 • 10Mbps • Baseband technology • 185 meters (length) – almost 200 meters • 30 devices per segment • Uses coaxial cable (coax), BNC and T-connectors to connect to a network • Referred to as thinnet

  21. Types of Ethernet – 10Base5 • 10Mbps • 500 meters (length) • Up to 2500 meters with repeaters • Up to 1024 devices for all segments • Uses a large (thick) coaxial cable • Referred to as thicknet

  22. Types of Ethernet – 10BaseT • 10Mbps • Uses Category 3 UTP wiring (phone wire) • Each device connects to a hub or switch • Only one device per segment (or wire) • Uses RJ-45 connectors • Supports a star topology

  23. Types of Ethernet – 100BaseT(X) • 100Mbps • Uses Category 5,6, or 7 UTP wiring • Up to 100 meters (length) • Only one device per segment (or wire) • Uses RJ-45 connectors • Supports a star topology

  24. Types of Ethernet – 100BaseFX • 100Mbps • Uses fiber optic cabling • Up to 412 meters (length) • Used for point-to-point connections • Uses ST or SC connectors

  25. Types of Ethernet – 1000BaseT • 1000Mbps • Up to 100 meters (length) • Category 5, 6, or 7 UTP wiring • Only one device per segment (or wire) • Uses RJ-45 connectors • Supports a star topology

  26. Types of Ethernet – 1000BaseSX • 1000Mbps • Uses fiber optic cabling • Up to 550 meters (length) depending upon the size of the cable • Uses a 850 nanometer laser • Uses ST or SC connectors

  27. Types of Ethernet – 1000BaseLX • 1000Mbps • Uses fiber optic cabling (multi-mode or single-mode) • Up to 10 kilometers depending on type of cable used • Uses a 1300 nanometer laser

  28. Ethernet Addressing • Media Access Control (MAC) address is stored on every Ethernet network interface card • 48 bits long (6 bytes) • Unique for each network interface card made (hopefully)

  29. Ethernet Addressing • This computer: MAC = 00-02-2D-6D-CD-9B (base 16) • In binary: 00000000-00000010-00101101-01101101-11001101-10011011

  30. Ethernet Frames • Ethernet divides data to be transmitted into frames • Ethernet frame has six parts: • Preamble (8 bytes) • Destination MAC address (6 bytes) • Source MAC address (6 bytes) • Type or length (2 bytes) • Data (64 – 1500 bytes) (usually) • FCS (4 bytes)

  31. 10Base2, 10Base5 • Good news - no devices needed to control traffic on the network • Bad news – no devices available to control traffic on the network

  32. Ethernet (Star Topology) • 10BaseT, 100BaseT(X), 1000BaseT, 1000BaseSX, 1000BaseLX… • Require a device at center of star • Ethernet hub –or– Ethernet switch

  33. Ethernet Hubs and Switches • Hub – any frames transmitted by a connected computer are sent out all ports (to all connected computers) • Switch – “learns” which computers are connected, what port they are connected to, and only transmits frames out the port that the specific receiving computer is connected to

  34. Hubs, Switches, Collisions • Consider a 4-node 10Base2 network, a 4-node 10BaseT network with a hub, and a 4-node 10BaseT network with a switch: • Which network will have the most collisions? the least?

  35. Hubs, Switches, Collisions • A network with a hub is a single collision domain (bad!) • A network with a switch has a separate collision domain for each port (good!)

  36. Ethernet Hubs and Switches • Hubs – single collision domain, single broadcast domain • Switches – multiple collision domains, single broadcast domain • Hubs and switches can be used together in a network

  37. Ethernet Broadcasts • A broadcast frame has destination address of FF-FF-FF-FF-FF-FF (binary all 1’s) • A switch will send broadcast frames out every port (except the one on which the frame was received)

  38. Ethernet Broadcasts • Broadcasts are sometimes necessary • Broadcasts are sometimes evil

  39. Broadcast Domains • Example: Consider an Ethernet network with an 8-port switch fully connected: How many broadcasts domains are in this network? How many collision domains are in this network?

  40. How Does A Switch Work? • It records the source MAC address in every frame it receives and stores it in the filter table with the associated port from which it came • If a switch receives a frame destined for a MAC address that is not in the filter table, the switch will send it out every port

  41. Real World Show and Tell • HP Procurve 2848 switch • Can mix Ethernet standards on one device • 1000Base-LX or 1000Base-SX • 1000Base-T/100Base-T/10Base-T autosensing

  42. That’s a Wrap on Ethernet(for now) • Other LAN technologies: • FDDI (Fiber Distributed Data Interface) • Token Ring • LocalTalk (Apple)

  43. Application Software Application Software Network software within the operating system Network software within the operating system Network Interface Card (NIC) Network Interface Card (NIC) Remember This?(Let’s refine it…) Transmission medium

  44. Application Software Network software within the operating system Network Interface Card (NIC) Network Layers – OSI Model(Open Systems Interconnection) Application Layer Presentation Layer Session Layer Transport Layer Network Layer Data Link Layer Physical Layer

  45. Why All the Layers? • Provides a model for how communication should take place • Real world example – organization chart in a business (president, VP, mid-managers, low-managers, entry-level staff…)

  46. Why All the Layers? • Software developers only have to be concerned with a particular layer’s functions • Allows many companies (vendors) to develop software that will work together • Allows various types of network hardware and software to communicate • Changes in one layer don’t cause problems in other layers

  47. Role of Each Layer in OSI Model • Application Layer – provides an interface between the application software (e.g. Internet Explorer, AIM…) and the lower network layers • Presentation Layer – translates data to standard format; provides encryption and data compression

  48. Role of Each Layer in OSI Model • Session Layer – “directs traffic” (will not be emphasized – just know that it exists and where)

  49. Role of Each Layer in OSI Model • Transport Layer • takes streams of data from application software and upper layers • converts data stream into segments • opens communication with receiving computer • Provides either “reliable” or “unreliable” communication to receiving computer

  50. Role of Each Layer in OSI Model • Network Layer • Manages network addresses • Responsible for transporting data to other computers which may not be attached to the local area network • Takes segments from transport layer • Sends datagrams (or packets) to data link layer

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