Lecture 25 Zoom Q&A


Q: assignment 7 is the last assingment?

A1: live answered

A2: yes


Q: is the presentation for the personal project slideshow based?

A1: It’s totally up to you how you decide to di the presentation – we’ll post some more guidelines/tips on good teaching presentations later this week likely

A2: It can be if you like. You could also do as whiteboard session, live-coding, whatever allows you to best convey the content


Q: how does pacific gigacorp make money though? do they get kickbacks from your ISP?

A1: live answered


Q: do they actually sit on the bottom? or are they suspended somewhere?

A1: live answered


Q: are these fiber optic, or copper?

A1: newer ones are fiber optic


Q: Who owns these cables?

A1: live answered

A2: live answered

A3: both companies and countries


Q: Why can’t this done via satellites?

A1: live answered

A2: Latency to satellites is much slower than going directly over a cable!


Q: Is that what Starlink is addressing?

A1: Yes, they use low-earth satellites


Q: Elon Musk sateline company


Q: What is the 60 byte packet specification?

A1: 60 bytes is maximum size of IpV4 header


Q: Are there concerns about people/countries sabotaging the cables since they are exposed?

A1: https://blogs.oracle.com/internetintelligence/the-threat-of-telecom-sabotage-v3


Q: Do you just call traceroute on terminal on a mac to check this?

A1: Yep!

A2: Yeah you should be able to call that comand in your terminal to look at the route to any server


Q: in traceroute, it seems to show the route to a website, but is information sent back to your computer along the same route?

A1: Not necessarily, each packet routes independent of previous

A2: Links go down, aren’t bi-directional, etc


Q: can a graph node link to itself?

A1: Yes, that is possible


Q: How do internet networks avoid cycles?

A1: live answered


Q: would the traveling salesman problem be implemented on a weighted graph?

A1: yes, exactly!


Q: Can a lot of graph problems be solved with bactracking and/or dynamic programming?

A1: Yep!


Q: prerequisite graphs are when edges are directed from a node to its prerequisite nodes, not the other way around?

A1: It would be up to define which way you wanted to model the structure


Q: do graphs have a type? like int or string?

A1: There is a more complex version that has template form


Q: can basicgraph do weighted graphs?

A1: live answered


Q: where is the node from b to c?

A1: live answered


Q: Can graphs connect the different types

A1: live answered


Q: Is a, b, a considered a cycle if a and b are adjacent nodes?

A1: Yes

A2: If the edge between then is undirected/bidirectional then yes


Q: does basicgraph also give the most optimal route (in the weighted graph case)?

A1: BasicGraph does not have path finding algorithms

A2: The basicgraph class is a means for representing graphs - if you want to run algorithms that find optimal paths, you need to do that in top of the representation (Which we’ll talk about on Wednesday)


Q: Does Stanford’s BasicGraph use adjacency lists?

A1: Yes


Q: Could we potentially also represent a graph as a struct, containing a data value and a set of pointers to neighbors?

A1: Yes!


Q: What is Facebook main production language?

A1: live answered


Q: Which courses cover graphs?

A1: CS103, CS161, CS166, CS168,…