Paper review: TCP Congestion Control with a Misbehaving Receiver

Reviewer: Kevin Hofstra

1. How can an end to end session be modified to create no incentive for a malicious node to attempt to decrease their reaction to congestion control? Should this take place on the sender or receiver side? What functions of the current TCP are susceptible to modification and what are the ways of changing them?
2. A comparative analysis of several distinct modifications to TCP and an evaluation of how they can be made less attractive or ineffective. A study of different changes that can be made to TCP that create little additional overhead, yet are able to prevent evading of congestion control.
3. A. The different types of vulnerabilities in TCP (Method):

i. ACK Division

(the receiver divides the acknowledgements into m pieces, each of which causes congestion window to grow m times as fast)

ii. DupACK spoofing

(the receiver sends back multiple acknowledgements for each received packet, causing the rate of transmission to be increased)

iii. Optimistic ACKing

(the receiver acknowledges a packet before it has been received so that the next packet can be sent even before the other has arrived. A shorter RTT will increase the throughput)

2. Solutions to their respective problems

i. ACK Division- only increment cwnd when a valid ack arrives covering the entire window

ii. DupACK spoofing- Create a Nonce field and only increase cwnd when recieveing an ACK with a nonce reply value that was sent and not yet received.

iii. Optimistic ACKing- A cumulative nonce value that ensures that the receiver has received all segments up to that point. They must add nonces of each of those packets received in order to acknowledge them.

3. These mechanisms must be done at the sender end because it is the receiver that will gain from the added throughput. In the internet it is the receiver (end user web browser) would like the packets faster, and it is in the interest of the sender that congestion would be avoided since he does not gain from sending out more throughput than congestion would allow.

4. Critique the main contribution
• Significance- 4 This is a problem that could see a lot growth with open source, and it must be implemented on the sending end since the receiving end has incentive to avoid TCP congestion control.
• Convincing- 3 The ideas for prevention are not very concrete, and though they sound good in theory, look much harder to implement in practice. The paper was more able to suggest ideas for prevention then actually implementing them.
5. System researchers and builders should recognize that prevention of modification of TCP congestion control can only be prevented by reducing the incentive. The sender must foresee the receiver wishing to increase the throughput past its congestion control, and not allow it to falsely indicate what it is actually receiving.