07/20/18

Today was the end of the second week, meaning that we are in the middle of COSMOS. We finished the second layer of the internet, and began talking about the third layer.

• Cellular Terminology
  • Mobile
  • Base station
  • Mobile switching center (MSC)
  • Handoff/handover
  • Cell
• CDMA
  • Sender encodes its data signals with a code (chipping code) orthogonal to all other senders using the same medium
  • The resulting signals can be combined and sent at the same time
  • Like talking at the same time and then splitting it
  • The receiver uses the original code to get the original data from the combined signal
• GSM started as a version of TDMA but now incorporates CDMA. It is an international standard = popular in other countries. AT&T and T-Mobile use GSM
• CDMA is used in 40 countries
• Higher frequencies carry more data
• If you have a 4G phone, first it tries for a 4G signal, then 3G, then 2G (If you have an iPhone, you see 3G when it gets a 3G signal, and edge when it get to 2G)
• Packets → Datagram
• IP is connectionless - don’t need to shake hands before talking
  • Like cell phone texting, doesn’t need permission from receiver
  • Opposite to calls, has to answer
• Datagrams may go missing, duplicated, corrupted, delayed
• IP has “best effort service delivery”
• IP is media independent
  • Doesn’t matter what layer 2 protocol
• IP address is described with dotted decimal
  • 32 bit binary number
  • 4 numbers with 3 dots, each 0-255
• Mask is all ones and then zeroes
  • E.g. 255.255.0.0
  • /number of 1’s
• CIDR- classless interdomain routing
  • E.g. 255.240.0.0 = 1111 1111. 1111 0000. 0000 0000. 0000 0000
• What can IP address tell us
  • All 0s is address of the network itself
  • Lowest is 69.168.0.32
  • All 1s is broadcast