Networks and Stuff

1
Networks and Stuff

• Networks and wiring em

2
Networks

• Connecting things together
• Can be
• Computers
• Embedded devices
• Telephones
• Radios
• TVs
• 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 were 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 its 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!
• 64 616 4 100. (52 510 2)
• 00, 11, . 10 A, 11B,.15F ( 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 (110105107)
• 1011 in binary (18041211) 11 in decimal.

14
A little more

• 1101 0011 11 followed by 3
• So, 1101 0011 B3 (B11)
• B3 1116 31 179 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 doesnt 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.