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Networks and Stuff

Networks and Stuff. Networks and wiring ‘em. Networks. Connecting things together Can be: Computers Embedded devices Telephones Radios TV’s Anything!. Lots of different types. One directional or two directional Addressed or non-addressed broadcast/hubbed or switched or even ringed!

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Networks and Stuff

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  1. Networks and Stuff Networks and wiring ‘em

  2. Networks • Connecting things together • Can be: • Computers • Embedded devices • Telephones • Radios • TV’s • Anything!

  3. Lots of different types • One directional or two directional • Addressed or non-addressed • broadcast/hubbed or switched or even ringed! • Internetworked or not • None of ‘em or all of ‘em!

  4. Hubs or Switches • Linear: everything wired together in a straight line. • Hub: A box repeats the signal from one computer or thingy to all the others ones. “Star topology”. Cable TV. • Switch: A box sends information from one thingy to only the thingy that needs to hear. “Switched star topology”. Telephones.

  5. Layers (Simplified!) • Physical Layer: thing over which communication takes places. Wires, radio, and so on. • Transport Layer: way in which information is transmitted • Application Layer: thing we do with network. Software we run, and so on. • Pieces of net are called nodes.

  6. Physical Layer • Lots of different ways to move signals around • Wires: few wires, lots of wires • Fibre Optics • Wireless: radio, space, lots of transmission methods. Bluetooth, spread spectrum, OFDM, and more! • Same physical layer can be used for different types of networks

  7. Transport Layer • Really a group of different layers • Contains the main protocols: TCP/IP (internet), ATM, WAP • Where the information that we’re moving around is described • Can operate over many different physical layers

  8. Application Layer • Higher protocols that are specific to the applications • HTTP for web • SMTP for mail • Telnet for logins • Software that communicates over the network • Can work over different transport layers and physical layers.

  9. Addressing • Can say where the information comes from, or, usually, where it’s going, or both. • Can have lots of wires that send the address, and more wires that send the data -- computer bus. SCSI bus, GPIB bus (science data), printers. FAST! • Can have address and data sent in sequence -- telephones, the internet, USB. Slower, but wiring simpler. LOTS of addresses!

  10. Packets, Frames, Cells, and all that stuff • Often data is sent in pieces of information, one “byte” after another. • The pieces can contain addresses, followed by information describing what kind of communication is being used, and then the data. • Packets, Frames, and Cells are just different ways of doing this. • Ethernet and Internet based on packets.

  11. Ethernet (IEEE 802.3) • Transport (actually, link) layer: very simple packets with addresses based on 6 bytes of data (note: Internet v4 has only 4!) • In raw form, based on “carrier-sense multiple access with collision detection”, CSMA/CD: every computer hears every other one, and waits for a quiet spot to send information. • Basis for all modern networks.

  12. Ethernet addresses • Byte has 8 “bits”, like digits. Number 0-255. 100 = 0110 0100 = #64 (Hexadecimal!). 4 bits = nybble! • #64 = 6*16 + 4 = 100. (52 = 5*10 + 2) • 0=#0, 1=#1, …. 10 =#A, 11=#B,….15=#F (= 1111 binary). #FF = 255 = 1111 1111 • All ethernet cards have a unique ethernet address. 48 bits = 6 bytes.

  13. A little more on Binary • Digits are 0 or 1 • Just like decimal has each digit worth 10 times the one to the right, binary has each digit worth twice the value to the right. • So, 157 in decimal = (1*10*10+5*10+7) • 1011 in binary =(1*8+0*4+1*2+1*1) = 11 in decimal.

  14. A little more • 1101 0011 = “11” followed by “3” • So, 1101 0011 = #B3 (#B=11) • #B3 = 11*16 + 3*1 = 179 decimal • In other words, each “hex” digit is 16 times the one to the left.

  15. Physical Layer • Serial link: 100 = #64 = 0110 0100 = OFF ON ON OFF OFF ON OFF OFF • Only for Local Area Network • Different forms • 10B5 or “Thick Ethernet” - 100 nodes per segment, 10Mbps • 10B2 or “Thin Ethernet” - 30 nodes per segment, 10Mbps • 10/100/1000 BT, twisted pair, 2 nodes, 10Mbps to 1Gbps • 10/100/1000 BF, fibre optic

  16. Ethernet Packets • Six bytes destination • Six bytes source • 2 bytes type or length (for IEEE) • 46-1500 bytes data (“payload”) • 4 bytes checksum • If checksum is wrong, throw away packet

  17. Not everything is IP • Windows networking • Novell • Apple networking • A lot of the basic controlling protocols (ARP, and more)

  18. Not everything is ethernet • GPIB: science and medical • SCSI: large disk storage • Firewire and USB: simple networking, nanosatellites! • MIL-STD-1553B: jet fighters, the space station!

  19. Physics!!! • All wiring has noise • Communication systems need a range of electrical or radio frequencies to transmit on: “bandwidth” (Hz, or cycles per second) • The bigger a bandwidth you need to listen to, to communicate, the more noise you pick up • further you go, more noise you pick up

  20. More physics • Eventually noise swamps signal • Maximum length (10BaseT = 100m) • Maximum data rate • Lower data rates go further • 1000BaseT doesn’t go very far! T1 (1.5Mbps does)! • Fibre Optic, very low noise, goes far! 2km or more. Also high bandwidth, so high data rate.

  21. Project Groups • Groups sizes • 1: 1: (IP number, security, interop) • 2: 1 group: (WML) • 3: 2 group: (Bluetooth), (WAP) • 4: 1 (3/2): 3G network (compat/social?) • 5: 1: environment and networks, space, and all that stuff.

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