대한임베디드공학회논문지 제 15권 제 5호 2020년 10월 251 ⓒ IEMEK J. Embed. Sys. Appl. 2020 Oct. 15(5) 251-259 ISSN : 1975-5066 http://dx.doi.org/10.14372/IEMEK.2020.15.5.251 Dynamic Adjustment of Hello and Hold Timer in AODV Routing Protocol Daniel Godfrey, Ki-Il Kim * Abstract : Ad hoc On-demand Distance Vector (AODV) protocol and its variants employ two important timers, hello and hold timer to keep track of topology changes. Moreover, hold timer is computed by multiplying constant value to hello timer. But, this configuration leads to inaccurate settings of hold timer. To solve this problem, in this paper, we propose a new dynamic adjustment of hello and hold timer scheme by removing dependency between them. A new metric to measure mobility is applied into hello timer, while expected link lifetime does holder timer. Simulation results show a significant reduction in the number of messages, a fact suggesting that it is possible to maintain and in some cases improve the performance of AODV with a minimum amount of messages released into the network. Keywords : AODV, Link duration, Link change rate, Hello timer, Hold timer *Corresponding Author (kikim@cnu.ac.kr) Received: Jul. 9, 2020, Revised: Aug. 25, 2020, Accepted: Sep. 1, 2020. D. Godfrey: Chungnam National University (Ph.D. Student) K. Kim: Chungnam National University (Prof.) ※ This research was supported by Basic Science Research Program through the National Research Foundation of Korea funded by the Ministry of Education (2018R1D1A1B07043731). Ⅰ. ꝏꝏ Mobile Ad-hoc Networks (MANETs) are wireless networks consisting of self-configured mobile nodes communicating with each other over a wireless channel without the need for a fixed infrastructure. Regardless of their outstanding practical advantages in the deployment of mobile networks, routing data in MANETs is still a challenging task due to technical challenges brought by dynamic network topology and limited resources such as power and bandwidth [1]. In traditional MANETs, nodes use periodic refresh messages to constantly track local link changes and update accordingly. Despite their importance, Traditional MANETs nodes tend to send refresh messages at fixed rates, of which were preconfigured based on a trial-and-error approach. To track topology changes caused by the random movement of mobile nodes, MANET uses different techniques such as link-layer sensing and refresh messages, commonly referred to as Hello messages [2]. Hello messages provide a mechanism for neighborhood discovery and update process. The validity of topology information exchanged between nodes highly depends on two important timers; namely the Hello interval and the neighbor timeout timer. The latter determines the time during which detected neighbor information is considered to be valid [3]. Depending on the type of MANET protocol being implemented, nodes may require to regularly update and preconfigure routes to every other node in the network (proactive routing) or may do so only if required (reactive routing) [4], hence the importance of Hello message mechanism varies depending on