Networks and Stuff Networks and wiring ‘em

Networks n Connecting things together n Can be: –Computers –Embedded devices –Telephones –Radios –TV’s –Anything!

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

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

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

Physical Layer n 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! n Same physical layer can be used for different types of networks

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

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

Addressing n Can say where the information comes from, or, usually, where it’s going, or both. n 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! n Can have address and data sent in sequence -- telephones, the internet, USB. Slower, but wiring simpler. LOTS of addresses!

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

Ethernet (IEEE 802.3) n Transport (actually, link) layer: very simple packets with addresses based on 6 bytes of data (note: Internet v4 has only 4!) n 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. n Basis for all modern networks.

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

A little more on Binary n Digits are 0 or 1 n 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. n So, 157 in decimal = (1*10*10+5*10+7) n 1011 in binary =(1*8+0*4+1*2+1*1) = 11 in decimal.

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

Physical Layer n Serial link: 100 = #64 = = OFF ON ON OFF OFF ON OFF OFF n Only for Local Area Network n Different forms –10B5 or “Thick Ethernet” 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

Ethernet Packets n Six bytes destination n Six bytes source n 2 bytes type or length (for IEEE) n bytes data (“payload”) n 4 bytes checksum n If checksum is wrong, throw away packet

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

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

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

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

Project Groups n 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.