This is a simple paper outlining how to use some Risk Analysis Techniques with Network Engineering to obtain quantitative results. An attempt to turn network engineering from an artful guessing game into a science.
Reviewing our minimal cutsets there are a total of 39 different combinations of events that will cause our entire system to fail. Of these, there are five first order cutsets where a single failure will cause the top event to occure. These are single points of failure in our system. There are 34 second order cutsets whereby two separate failures are needed in order to cause the to event.
.P | V |
P | W |
P | Y |
P | X |
P | U |
Q | V |
Q | W |
Q | Y |
Q | X |
Q | U |
H | |
T | V |
T | W |
T | Y |
T | X |
T | U |
R | V |
R | W |
R | Y |
R | V |
R | W |
R | U |
S | |
O | V |
O | W |
O | Y |
O | X |
O | U |
K | |
L | M |
M | N |
N | L |
F | G |
I | G |
J | |
A | |
B | D |
B | E |
C | D |
C | E |
Despite the efforts of the system designers there are five separate and distinct single points of failure: H, S, K, J and A.
Despite all of the levels of redundancy built into the system, there are still only a maximum of two events that will be needed to cause the router to be isolated. This points to a lot of dependencies within our overall system and not a lot of depth in the redundancies that have been built in.
Although this qualitative analysis points to a lot of first and second order failure modes, it's not time panic and installing a building UPS, replacing all of the humans with robot controllers and specing out routers with redundant backplanes. These are single points of failure, but it is necessary to look at the probability of these failure events happening and the cost associated with redesiging and changing the system to eliminate them. This is where the quantatiative analysis comes in, allowing one to assess the level of risk in the system, and then properly assess if it is worth it to fix or not.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Version 0 | C | Plenty | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Router ID - www.blackhole-networks.com | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Area ID - FTA with Network Engineering | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Checksum OK | Construction | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | +- -+ | PAGE STILL | +- UNDER -+ | CONSTRUCTION | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+