5.2-2 Bellman Ford Distance Vector Routing (updated)

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Video presentation: Computer Networks and the Internet.
5.2 Routing algorithms: distance vector routing. Bellman-Ford distance-vector routing algorithm. An elegant, distributed routing algorithm!
Computer networks class.
Jim Kurose
Textbook reading: Section 5.2, Computer Networking: a Top-Down Approach (8th edition), J.F. Kurose, K.W. Ross, Pearson, 2020.
See gaia.cs.umass.edu/kurose_ross for more open student resources.

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2 июн 2024

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Комментарии : 21

@bobjones1196 Год назад

When I was a wee lil boye back in tallahasee I really just wanted to learn what the internet was like a city boy. Jimbo my man you are making that come true. As my gran pappy used to say, you're one of them people who've went and gotten dem selves a heart the size o' Texas.

@nirmalkarthik5892 6 месяцев назад

This was amazing! I feel like my mind has been expanded.

@bumjuncho3246 Год назад

Dear professor, shouldn't it be {9, infinity, 2} @10:50, for calculating Db(d)? I am a bit confused by why it's {9, 2, infinity}. Thank you for your time and effort for all of these greate videos!

@emresafacelik5016 Год назад

You are right but it is probably a set so it does not have to be ordered, it is bad for explanation though

@ricp Год назад

yeah, i'm glad I'm not the only one that saw it... it was confusing me. It should really by (9, infinity, 2) like you suggested

@chienthan12345 6 месяцев назад

I noticed the same thing

@maejshbrail2233 7 месяцев назад

grats on 11k subs!

@MrBusinessinn 2 года назад

Dear professor, why are the components in Bellman's formula differently assigned? For example the first element in parentheses -> cost is signed with c and the other cost with D? Thank you

@Mimonsi Год назад

Becasue the cost using "c" is the local value (a variable), and the D is a function, because it is received from another desination, maybe a bit like a recursive call.

@goedeck1 5 месяцев назад

Why does z care about path to x via y when x direct is the min.

@ahmedsalahucf 2 года назад

magnifique!

@goedeck1 5 месяцев назад

9:32 To be in the right order shouldn't Db(d)=min{Cb,a +Da(d), Cb,c + Dc(d), Cb,e + De(d)} = min{9,2,~}=2 ? ~= inf. OOPS LOOKS LIKE SOMEBODY ALREADY NOTED THIS😮

@yoki004 6 месяцев назад

I think there might be an error at the slide on 17:50; seems like 50 should be 5 and the 60 should be 6 despite being spoken as 60?

@MiaoMiaoMiMiMi 6 месяцев назад

The slides also have small errors - bullet point 3 should be y computes new cost to x via "z" (instead of y)

@goedeck1 4 месяца назад

Yeah when did x,z go from 5 to 50. The book I have is the same way. Also, do packets get sent before and during all the routing cost settlement?

@cclemon2531 2 месяца назад

@@goedeck1 we should consider the path from z to y to x which is 1+4. As we not only focus on the direct path.

@torvasdh 12 дней назад

idk if this is too late, but each node only knows of it's neighbors. It can't see the full graph. So; Y has it's direct link to X set to 60. Y sees that and asks its neighbors what their link costs are. - Neighbor X says its cost is 60 - Neighbor Z says its cost is 5. That 5 comes from the path of (Z->Y->X). Remember, the neighbors don't say what the path is, just that it's cost is lowest. Y doesn't know that itself is in that shortest path from Z. Y now sees cost of 5 from Z, so it uses that and adds 1 to it for it's own cost. Y->X is now 6 and it alerts its neighbors. Z receives an alert from Y that is has a new lowest cost. That cost is 6. Z checks its neighbors link costs: - Neighbor X says its cost is 50. Z now sees cost of 6 from Y, so it uses that and adds 1 to it for it's own cost. X->Z is now 7 and it alerts its neighbors. Z then alerts Y and X of its new lowest cost and the cycle repeats. This process will rebound back and forth with Z and Y alerting each other back to back until the link cost hits 51, where the new path from node Z->X will choose the direct link to X instead of through Y (which is now 51)