Course Name: Computer Networking – Class of 2006
Professor: Dr. Gertrude Levine
Name: Chaudhry Siddharth
Email: siddchaudhry@fdu.edu
Sub: Regarding the Byzantine General Problem
---------------------------------------------------------------------------------
Reliable computer system must be able to deal with failure of one or
more of its components. Whenever a failed component exhibits a
type of behavior it is generally referred as Byzantine General
Problem. This type of behavior is often overlooked and involves
mainly sending conflicting information to different parts of system.
This research was supported in part by NASA and the Army
Research office and Ballistic Missile Defense.
Basic Goals of BGP
1) All loyal generals decide on same plan of action
2) A small number of traitors cannot cause a bad plan to be
adopted.
To satisfy condition first all general use the same method of combing
information to come up with a plan.
Consider the formal definition with an army example
Assume that we have one commanding general and his subordinate
generals
Conditions to be assumed
All loyal subordinate generals obey the same order.
If the commanding general is loyal then every subordinate general
follows the order.

Problem
1) Oral message can be easily changed.
2) No Solution works unless more than 2/3rd of general are loyal
3) Even with 3 generals one traitor makes the protocol fail.
Understanding the Problem through Figures.

Solution for Oral Messages

We have assume the following conditions for Oral Messaging:
1) Every message which is sent is delivered correctly.
We assume that traitor is not capable to interfere communication
between two generals
2) Receiver has knowledge of who have sent the message.
Traitors are not capable to confuse the message by sending extra
message
3) Absence can be detected
Default message is “Retreat”
The ALGORITHM for Oral message is as follows:

What if we are not fully connected?
What are Practical Implications of this algorithm?

The Conclusion is as Follows
Reference:
“http://homes.cerias.purdue.edu/~crisn/courses/cs590T/cs590T_lect4
_byzantine_generals.pdf”