congestion control (tcp)

Question 1

what is congestion control

Answer 1

• ensure the routers and links dont get overwhelmed with too much data
• provide fair amount of resources to each user

Question 2

2 types of congestion control

Answer 2

1) reservation based:
- end host asks network for capacity
- routers along flow path get allocated resources
- resource is not availible ->flow is rejected

2) feedback based:
- end host does not ask for capacity and just starts sending
- gets feedback from network and adjusts send rate

Question 3

what is congestion window

Answer 3

• to avoid congestion
• increases slowly
• decreases fast

Question 4

how to calc the effective window

Answer 4

eff win = (max win - (last byte sent - last byte acked))

basicly the max window minus the amount of data in flight

Question 5

AMID

Answer 5

• algo to inc dec the congestion window
• inc win by 1 for each RTT
• divide win by 2 when timeout occures or packet is lost

Question 6

how to tell if a packet is lost

Answer 6

supose packet is lost, and receiver gets the next packet. it still expects the lost one so it sends another ACK for it. once the sender gets 3 dup acks it re transmits the packet

or if the sender waits too long for an ack it will resend the packet.