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Building a Network with OSI

Building a Network with OSI. Chapter 3. Contents. Explain the major functions of network hardware Describe the functions of network software Define each of these functions as part of the OSI seven-layer model. Overview. The Big Job.

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Building a Network with OSI

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  1. Building a Network with OSI Chapter 3

  2. Contents • Explain the major functions of network hardware • Describe the functions of network software • Define each of these functions as part of the OSI seven-layer model

  3. Overview

  4. The Big Job • Whenever you have a big job to do, it helps to break it down into discrete chunks or functions • For example, moving your family from one city to another could be broken down into: • What to move • How to pack • How to load the van • How to unload the van • The job of moving data from one place to another is also a big job

  5. OSI Seven-Layer Model • The big job of moving data from one place to another is broken down into functions defined by the OSI Seven-Layer Model

  6. Case Study Example • Let’s look at the process of networking from a conceptual viewpoint • Assume we are just trying to move a file from one PC to another in a small office • One of the workers has just completed a new employee handbook • She needs to transfer the Word document to the other worker for review

  7. Case Study Example • The file could be copied to a diskette and handed over to the other worker – called Sneakernet – but that’s not necessary today • The document may be transferred using the network • The next section examines the various hardware required

  8. Let’s Get Physical

  9. Cables • Most networks use a cable like that shown as a physical channel to move the bits of data Unshielded Twisted Pair (UTP) cable Uses 4 wires: 2 for sending and 2 for receiving data

  10. Hubs • Each computer system has a cable leading to a device called a hub • Usually located in a closet • The hub sends the data received from one system to all the other systems attached to it

  11. Network Interface Card • Network Interface Cards (NICs – pronounced “Nicks”) are installed in PCs • Network cables are attached to the NICs

  12. NIC to Hub Connections • Cables run from the NIC in the PC to a jack on the wall • Cables run through the walls to the closet where they connect to a hub

  13. Network Cabling System

  14. Network Interface Cards • Since all the networked systems are connected to the same hub, each system must have a unique identifier • Media Access Control (MAC) address • A unique address burned into a ROM chip on the network card • Each MAC address is 12 hex characters or 48 bits in length MAC address printed on surface of chip – it’s burned inside the chip.

  15. MAC Addresses • MAC addresses are 48 bits long • Usually represented using hexadecimal characters (12 hex digits = 48 bits) • Here’s a typical MAC address: 004005-607D49 Identifies the manufacturer Unique serial number determined by the manufacturer No two MAC addresses are ever the same!

  16. WINIPCFG • Used on Windows 98/Me systems to view network configuration MAC address

  17. ipconfig /all • Used on Windows NT/2000/XP systems to view network configuration MAC address

  18. Bits • A MAC address is a series of ones and zeros called bits • Data is sent using pulses of electricity, light, or radio waves

  19. Frames • Data is sent across the network in frames • Frames are discrete chunks of data

  20. Fields • Frames are made up of fields that contain information • Frames typically contain the recipient’s MAC address, the sender’s MAC address, the data itself, and a cyclic redundancy check (CRC) for error checking

  21. Data • What is inside the data part of the frame? • It could be part of a file, a print job, a web page, anything • NICs do not care what the data, or payload, is

  22. Frame Size • Different networks use different sizes of frames • Many frames hold about 1500 bytes of data • The sending software breaks up large amounts of data into smaller chunks • The receiving station must then put the chunks back together in the proper order

  23. Processing Framesq • All devices on the network see the frame, but only the device that it is addressed to will process it • Every frame is received by every NIC • The MAC address is used to decide if the frame belongs to a given device

  24. Getting Data on the Cable • Only one system may speak at a time since the cable is shared • Processes are used to keep two NICs from talking at the same time

  25. Getting To Know You • How does the sending NIC know the MAC address of the NIC to which it is sending data? • Most of the time the two devices have talked before, so the destination MAC address is already known • If the MAC address is not known, then a broadcast message is sent over the network • The destination device will respond by sending its MAC address • A broadcast MAC address is FF-FF-FF-FF-FF-FF

  26. Moving Frames – Step 1 • The sending system’s network software hands some data to the NIC • The NIC begins building a frame

  27. Moving Frames – Step 2 • After the NIC creates the frame, it adds the CRC and data to it • It also puts its MAC address and the destination’s MAC address in the frame

  28. Moving Frames – Step 3 • When no other NIC is using the cable, it sends the frame through the cable

  29. Moving Frames – Step 4 • The frame propagates down the wire to the hub • The hub creates a copy of the frame to send to every other system • The receiving device processes the frame

  30. Moving Frames – Step 5 • The receiving station checks the CRC value in the frame • If the value matches what it should, then the NIC sends the data portion to the network operating system for processing • If the value does not match, the frame has errors and must be resent

  31. Beyond the Single Wire – Network Software

  32. Beyond the Single Wire • What if one system is using a modem to dial into the network? • What if one of the systems is a Macintosh?

  33. Routers • A single network with single hub can only support up to 1,024 computers before the network becomes too slow • Routers are used to chop large networks up into smaller ones

  34. Network Protocols • Network protocols define rules for how systems are addressed, how to chop data up into chunks, how to deal with routers, and so on • As a network grows a more universal addressing method than MAC addresses is needed • TCP/IP are the most popular universal addressing protocols

  35. Transmission Control Protocol (TCP) Internet Protocol (IP) Gives each device on the network a unique numeric identifier IP addresses consist of four 8-bit numbers Each 8-bit number ranges from 0 to 255 192.168.4.232 No two systems on the same network share the same IP address TCP/IP

  36. DHCP • IP addresses must be manually configured on each device • Or they may be automatically configured using Dynamic Host Configuration Protocol (DHCP) • Each system in a network has two addresses • MAC address burned into a chip on the NIC • IP address configured through software

  37. Sample Network with Addresses

  38. Packets • The network software creates a packet that contains the sending and receiving IP addresses along with the data • The packet is enclosed within a frame that contains the sending and receiving MAC addresses IP packet in a frame IP packet IP packet with frame added

  39. Connecting to the Internet • To connect the local network to the Internet a router is needed • The local hub is connected to the router • The router is connected to the Internet through a phone line • The phone line uses a different kind of frame, so the router strips the frame and creates a new one

  40. Connecting to the Internet Router removing network frame and adding one for telephone line Adding a router to the network

  41. Moving through the Internet • The router strips off the MAC addresses and uses the type of addressing the phone company uses instead • The frame uses the IP address to guide it to the receiving system • The receiving router strips off the telephone frame and adds the MAC address for the receiving system • The NIC strips off the MAC header and hands the frame off to the NOS

  42. Assembly and Disassembly • Most data is much larger than a single frame • Network protocols chop up the data into smaller packets and gives each one a sequence number • The sequence numbers are used by the receiving system to put the packets back in order and to assemble them • Transmission Control Protocol (TCP) is one such protocol

  43. Sessions • If the receiving system also has a printer to share on the network, then it may receive packets for print jobs as well as packets for files • The sending system must also contact the receiving system to make sure it is ready to handle a print job as well • The software that handles these processes is called session software

  44. Multiple Sessions Single session Multiple sessions

  45. Standardized Formats • Macintoshes and PCs use very different formats • Standardized formats have been created that allow very different operating systems to exchange data

  46. VPNs • Virtual Private Networks (VPNs) enable a user away from the office to connect to the corporate network via the Internet

  47. Encryption • Many networks encrypt data to prevent unauthorized access • Both the sending and receiving system must know the encryption method used

  48. Network Applications • Users use network applications to exchange data on a network • My Network Places in Windows for files • Internet Explorer or Netscape Navigator for web pages • Outlook Express for e-mail

  49. Copy a File Across a Network • The next few slides illustrate a typical process that takes place to copy a file from one machine to another over the network

  50. My Network Places • The receiving station finds the remote file using My Network Places

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