TCP Congestion Control with a Misbehaving Receiver

Reviewer: Mark Meras (mm446)

Main Contribution

This paper is by Savage et al. is an important contribution. It describes (a) how a misbehaving receiver can attempt to force the sender to send data faster and (b) how senders can prevent this behavior. The paper argues that TCP can be modified without introducing assumptions about receiver behavior.

Key Ideas

TCP has several vulnerabilities that a malicious receiver can exploit. These include ACK division, DupACK spoofing, and optimistic ACKing.
These can be solved in several ways. The solution to ACK division is to moidfy the congestion control mechanisms to operate at byte granularity or to guarantee segment-level granularity encapsulation.
The solution to DupACK spoofing involves modifying the TCP packet format to include from fields: Nonce and Nonce Reply, the first filled with random data. This is not great, because both the sender and the receiver need to be modified. Alternatively, the sender can keep track of outstanding segments sent above the missing segment.
Optimistic ACKing can be reduced by using a Nonce (see above), and also by randomly varying the size of outgoing segments by a small amount.

Critique of Contribution

This paper makes an important contribution by explaining malicious techniques for exploiting TCP and ways to prevent exploits. These solutions are very important for maintaining TCP fairness.

Open Question

Issues of trust in TCP need to be explored further, since TCP is no longer used in a collaborative manner.