Client-Server Approach

• Single computer that serves as the server

Peer to Peer

• Each peer can connect to other peer, cab be more reliable

Primary-secondary computing

• "inverse" of the client-server

New issues for networked apps

• Perfermance

  • Throughput: operations per second (server-side on client-server)
    • Typical way to improve is to add more nodes, or parallelism
  • Latency: Measures the time difference between the request and response
    • Typical way to improve is to cache data on the client

  Often those 2 factors are competing objective

• Correctness

  • Out-of-order execution
    • "serialization"
    • We can explain system behaviors as if all actions took place in some order
  • Out-of-date caches
    • Some caches must be up-tp-date
    • Other caches? Ok to be a bit out of date
    • To solve it, we need to do cache validation

• Security

  • Skipped for now...

Technologies that are used to solve the issues

Circuit switching - traditional telephony

Packet switching (Assumes we have computers)

Break the message you want to send into reasonably smaller packages

Dump all the small packages to the nearest network

• each packet is independent
• each packet's route is independent
• it's the recipient's job to deal with the resulting mess
• Flakier
  • Packets get lost
  • Packets received out-of-order
  • Packets duplicated

Internet Protocol Suite

The "peace treaty" that computers can talk to each other and no one company's computer can control the whole web

Documented Specified in in Internet RFCs (Request For Comments)

• Basic ides: layers (1-lowest, 4-highest)

1. Link layer
   1. hardware-oriented, point to point, only cares about the connection btwn 2 nodes
2. Internet layer
   1. Packets. The protocol talks about how packets will get form a to b
3. Transport Layer
   1. Data channels
4. Application layer
   1. We take the lower layers(Channels, packet) and tailor it for a particular application.

Protocols: networks :: APIs : programs

IPv4 and IPv6

IPv4 - 32bits addresses

specify what a packet look like

an IPv4 packet has:

header includes:

senders' IP,

recipient's IP,

protocol number,

TTL (hop count → count how many nodes that you have been in ) avoids infinite loops

Checksum(16 bits) can catch transmission errors (OR all the 16 bit content)

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