Principles of Communications Week 4 to Oct 26th/L7

 This week, we'll finish up BGP, and cover multicast routing.

General lessons from BGP - information hiding can be harmful to decentralised algorithms. but information hiding may be a necessary dimension to some distributed systems due to business cases (commercial inconfidence/competitive data). 

Are there other ways to retain decentralised or federated operations but to retain also confidentiality? Perhaps using secure multiparty computations (not covered in this course!). There are a number of other federated services emerging in the world (applications like Mastodon and Matrix, and also, federated Machine Learning systems like flower) so this probably needs a good solution.

Multicast has a great future behind it - some neat thinking, but largely replaced by application layer content distribution networks (e.g. netflix, youtube, apple/microsoft software update distribution), and the move away from simultaneous mass consumption of video/audio. For more info on limitations of multicast, this paper is a good (quick) read.

Are application layer overlays a solution to other "in network" alleged enhancements? Possibly - for example, Cloudflare obviate the need tor always on IPv4 or IPv6 addresses - this also wasn't covered in this course, but might be of interest. Thir work is described here and other papers of theirs may be of current interest.

Tup A previously unavailable route is announced as avail- able. This represents a route repair.

Tdown A previously available route is withdrawn. This represents a route failure.

Tshort An active route with a long ASPath is implicitly re-

placed
with a new route p ossessing a shorter ASPath. This represents b oth a route repair and failover.

Tlong An active route with a short ASPath is implicitly replaced with a new route p ossessing a longer ASPath. This represents b oth a route failure and failover. 

Couple of questions on Graphs in last section on BGP 

1. A Few Bad Apples - graph doesn't asymptote, despite being cummulative as it prefixes can be announced more than once (i.e. > 100%!)

2 How long does BGP take to adapt to changes - the legend refers to

Tup A previously unavailable route is announced as available. This represents a route repair.

Tdown A previously available route is withdrawn. This represents a route failure.

Tshort An active route with a long ASPath is implicitly placed

with a new route p ossessing a shorter ASPath. This represents b oth a route repair and failover.

Tlong An active route with a short ASPath is implicitly replaced with a new route p ossessing a longer ASPath. This represents b oth a route failure and failover.

Tup A previously unavailable route is announced as avail- able. This represents a route repair.

Tdown A previously available route is withdrawn. This represents a route failure.

Tshort An active route with a long ASPath is implicitly re-

placed
with a new route p ossessing a shorter ASPath. This represents b oth a route repair and failover.

Tlong An active route with a short ASPath is implicitly replaced with a new route p ossessing a longer ASPath. This represents b oth a route failure and failover.