A key challenge of B-MAC is implementing check intervals that are very short, which ensures a reasonable length for the preamble.
The Low Power Listening (LPL) approach used by B-MAC which employs a long preamble is suboptimal in terms of energy consumption, is subject to overhearing, as well as it introduces excess latency at each hop .
B-MAC is a CSMA-based protocol that utilizes low power listening and an extended preamble to achieve low energy consumption.
On the other hand, X-MAC which is based on B-MAC uses the preamble sampling mechanism to achieve low power communication without synchronization.
Asynchronous duty-cycling MAC protocols such as Aloha with preamble sampling  and B-MAC
 do not require any time synchronization and reduce idle listening by Low Power Listening (LPL).
B-MAC (Berkeley MAC) is a contention-based asynchronous MAC protocol for WSNs .
This MAC shares many features with B-MAC and belongs to asynchronous MAC protocols.
In B-MAC , each node wakes up periodically at each polling interval.
X-MAC  has been proposed to overcome the drawbacks of B-MAC.
Preamble Length 271bytes B-MAC
Wake-up Interval 100msec B-MAC
Sampling Time 2.
B-MAC utilizes a long preamble to achieve low power communication.
WiseMAC uses a similar method to B-MAC, but the sender learns the schedules of the receiver wake-up periods by using time division multiple access (TDMA) as the control channel, and schedules its transmissions to reduce the length of the extended preamble.