  Wireless sensor networks (WSNs) have many potential applications [1, 5] and
unique challenges. They usually consist of hundreds or thousands small sensor
nodes such as MICA2, which operate autonomously; conditions such as cost,
invisible deployment and many application domains, lead to small size and
limited resources sensors [2]. WSNs are susceptible to many types of link layer
attacks [1] and most of traditional networks security techniques are unusable
on WSNs [2]; due to wireless and shared nature of communication channel,
untrusted transmissions, deployment in open environments, unattended nature and
limited resources [1]. So, security is a vital requirement for these networks;
but we have to design a proper security mechanism that attends to WSN's
constraints and requirements. In this paper, we focus on security of WSNs,
divide it (the WSNs security) into four categories and will consider them,
include: an overview of WSNs, security in WSNs, the threat model on WSNs, a
wide variety of WSNs' link layer attacks and a comparison of them. This work
enables us to identify the purpose and capabilities of the attackers; also, the
goal and effects of the link layer attacks on WSNs are introduced. Also, this
paper discusses known approaches of security detection and defensive mechanisms
against the link layer attacks; this would enable it security managers to
manage the link layer attacks of WSNs more effectively.
