DistOS 2023W 2023-01-16

Video from the second half of class is available in Brightspace in the Zoom portal.

Notes

Lecture 3
---------

Group reports
 - can be bullet points, but paragraphs are better
 - should be self-contained, should be readable by someone who hasn't done the readings
    - but you don't have to summarize the entire paper, just make the points you discussed clear
    
Monday group reports are due Friday
Wednesday group reports are due Monday
(and responses are due Sunday night)

Multics
 - idea of "utility computing"
    - that's why they cared about security
 - Multics was supposed to be distrubuted, in a sense
    - terminals everywhere connected by data links (phone lines)

Multics is before computer networking was a thing
 - distributed system was one mainframe with lots of terminals in remote places


Resource-Sharing Computer Communications Networks
 - so, why this paper?
 - because their discussion is "distributed operating systems"

What is this paper arguing for?  What is the technical innovation?
 - what is the innovation relative to?

Circuit-switched networks - old
Packet-switched networks - new

What were circuit-switched networks designed for?
What are their key advantages?

with circuit switched, as long as someone was on a phone call,
there was a "wire" dedicated to to that call
  - and for long distance, that was a significant amount of resources,
    hence the cost

Originally this was all analog, but then it became digital
 - but idea was still to have a dedicated connection between callers
 - how do you make a "virtual" wire?
    - can use packets to send data
    - but have explicit bandwidth reservations and latency requirements
      - resources are still reserved for each call to ensure quality
 - this is circuit-switched networks

Packet-switched networks are different
 - each packet is considered independently
 - normally, delivery is "best effort" - no resource reservation
   - so packets can get dropped at any time
   - endpoints have to handle retransmission, network won't do it for you

Packet-switched networks are fundamentally more efficient
 - no wasted resources on reservations
 - and is okay because we're transmitting data, delays are fine
   (voice data is much more latency sensitive)

What did they want this network for?
 - file transfers
 - email (which is a kind of file transfer)
 - remote access to computers (remote terminals)

What was an IMP equivalent to?
 - mostly like an ethernet interface
 - but also aspects of a router

Why was it called the ARPANet?
 - (D)ARPA - one of the research arms of the US military

They are talking about the Internet and IP packets, that's what they built

How to read a research paper?
 - read the intro and discussion/conclusion first
    - see what the authors were trying to say
 - look at the figures, see what they say
 - look at background/related work, what other systems is this connected to
 - look at results - why do they think their system is any good?
 - then read the paper from the beginning
 - a pure linear read is almost never the best idea