Which one of the following statements is not true concerning DTIMs?

A Delivery Traffic Indication Message (DTIM) is a specific type of Traffic Indication Map (TIM) used to manage buffered broadcast and multicast traffic for stations in Power Save mode. The TIM information element, present in all beacons from an Access Point, contains a DTIM Count field. This field counts down from the DTIM Period value to zero. Only when the DTIM Count field is zero is the beacon frame considered a DTIM. Since the DTIM Period is typically a value greater than one, most beacons are not DTIMs; they are regular TIMs that simply decrement the counter. Therefore, the statement that every beacon frame must contain a DTIM is false.

A. This statement is true. The primary purpose of a DTIM is to signal to sleeping stations that the AP is about to transmit buffered broadcast and/or multicast traffic.

B. This statement is true. Stations in Power Save mode must awaken to listen for every DTIM beacon to receive group-addressed traffic, so the DTIM interval dictates this part of their wake-up cycle.

C. This statement is considered true in this context. While the IEEE standard formally defines DTIM as a "Message," it is a component of the Traffic Indication Map (TIM) element, and "Map" is often used interchangeably.

1. IEEE Std 802.11™-2020. IEEE Standard for Information Technology—Telecommunications and Information Exchange between Systems Local and Metropolitan Area Networks—Specific Requirements - Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications.

Section 9.4.2.6, "TIM element": This section defines the DTIM Count and DTIM Period fields. It states, "The DTIM Count field indicates how many beacon frames (including the current beacon frame) will appear before the next DTIM. A DTIM Count of 0 indicates that the current TIM is a DTIM." This directly proves that not all beacons are DTIMs.

Section 11.2.1.6, "PS-Poll, DTIM, and TIM": This section explains that after a DTIM beacon is transmitted, the AP sends any buffered broadcast or multicast frames. This validates option A.

2. CWNP, LLC. (2021). CWAP-404 Certified Wireless Analysis Professional Official Study Guide.

Chapter 5, "MAC Frame Analysis": The guide explains that the DTIM Period value, configured on the AP, determines how often a DTIM beacon occurs (e.g., a period of 3 means every third beacon is a DTIM). This confirms that not every beacon is a DTIM. It also details that STAs must wake for DTIMs, supporting option B.