With which of the following forms of acknowledgment can the sender be informed by the data
receiver about all segments that have arrived successfully?

A.
Block Acknowledgment

B.
Negative Acknowledgment

C.
Cumulative Acknowledgment

D.
Selective Acknowledgment

Explanation:

Selective Acknowledgment (SACK) is one of the forms of acknowledgment. With selective
acknowledgments, the sender can be informed by a data receiver about all segments that have

arrived successfully, so the sender retransmits only those segments that have actually been lost.
The selective acknowledgment extension uses two TCP options: The first is an enabling option,
“SACK-permitted”, which may be sent in a SYN segment to indicate that the SACK option can be
used
once the connection is established. The other is the SACK option itself, which can be sent over an
established connection once permission has been given by “SACK-permitted”.
Answer option A is incorrect. Block Acknowledgment (BA) was initially defined in IEEE 802.11e as
an optional scheme to improve the MAC efficiency. IEEE 802.11n capable devices are also
referred to as High Throughput (HT) devices.Instead of transmitting an individual ACK for every
MPDU, multiple MPDUs can be acknowledged together using a single BA frame. Block Ack (BA)
contains bitmap size of 64*16 bits. Each bit of this bitmap represents the status (success/failure) of
an MPDU.
Answer option B is incorrect. With Negative Acknowledgment, the receiver explicitly notifies the
sender which packets, messages, or segments were received incorrectly that may need to be
retransmitted.
Answer option C is incorrect. With Cumulative Acknowledgment, the receiver acknowledges that it
has correctly received a packet, message, or segment in a stream which implicitly informs the
sender that the previous packets were received correctly. TCP uses cumulative acknowledgment
with its TCP sliding window.