ORP and Flow Control in Packet Networks

Question 1

What is the objective of flow control?

Answer 1

compromise between:
- throttling connections
- keeping delay and buffer overflow at reasonable level

Question 2

What is end to end window flow control?

Answer 2

window size tradeoff
- small: avoid delay and congesiton
- large: allow full spees transmission

Question 3

What is the downside to windows?

Answer 3

don’t regulate end to end delay
don’t guarantee minimum data rate

Question 4

What is node by node window flow control?

Answer 4

separate window for every VC and pair of adjacent nodes

Question 5

What are the disadvantages of end to end and node by node window flow control?

Answer 5

E to E: high propagation delay relative to packet size

N by N: small window size

Question 6

What is the idea of a rate control scheme?

Answer 6

give each session a guarantee data rate according to needs

generate desired rate for various connections

Question 7

What is the leaky bucket scheme?

Answer 7

• to join transmission queue
• packet has to get permit from permit queue
• new permit generated every 1/r seconds
• r is desired output rate
• as long as number of permits doesn’t exceed threshold

Question 8

What is a combined ORP and flow control?

Answer 8

balance between high throughput and mean network delay at reasonable level

Question 9

What is the optimal solution to the combined ORP and flow control equation?

Answer 9

x_p = 0
r_w = 0

Question 10

How does a penalty function for throttling work?

Answer 10

bigger penalty the less you carry

Question 11

What is the optimality condition?

Answer 11

C/[(C-r)^2] = a/[(r_bar - y_^2]