Finally, the fourth protocol (GeNIMA) uses all previous features as well as network interface support for mutual exclusion, eliminating all interrupts or asynchronous protocol processing.
Overall, we see from Figure 8 that GeNIMA, which leverages all our general-purpose NI extensions to eliminate interrupts and asynchronous protocol processing, improves application performance by on average 38% for applications that end up performing quite well and up to 120% for applications that still do not perform very well under SVM.
Second, while is possible to design asynchronous protocols
with safety properties similar to those of the synchronous protocols, the timeliness properties satisfied by asynchronous protocols
are much weaker; the delays with which processes learn of new updates, joins, and failures are bounded only when certain stability conditions hold.
In this section, we will review the operations of two asynchronous protocols
, X-MAC and RIX-MAC, that use short preambles and receiver-initiated transmission.
A good number of asynchronous protocols are proposed as MAC layer solutions for WSNs.
Hybrid MAC protocols aim to leverage advantages and mitigate the disadvantages of the synchronous and asynchronous protocols two.
One of the biggest changes to affect data communications was the FCC's decision early last March to give the Bell operating companies (BOCs) waiver of Computer II structural separation requirements so they can perform conversion from asynchronous protocols
to X.25 packet-switched network protocols in facilities located in their central offices.
There are several important duty cycling MAC protocols which have been proposed, such as synchronous protocols [1-3] and asynchronous protocols
Most of the existing asynchronous protocols
 exploit a random back-off scheme to deal with collisions while X-MAC  can partially avoid collisions by exchanging preamble and ACK packets.