Land Mobile Radio (LMR) systems are deployed by organizations requiring instant communication between geographically dispersed and mobile personnel. Typical users of LMR systems include police departments, fire departments, medical personnel, EMS, and the military.
Current LMR systems can be configured to provide for radio communications between a site and subscriber units in the field. A subscriber unit may be a mobile unit or a portable unit. LMR systems can be as simple as two subscriber units communicating between themselves and a site over preset channels, or they can be complex consisting of tens of thousands of subscriber units and multiple sites.
LMR systems may be configured to cover a large geographical area by providing hundreds of sites. For security purpose, when a previously unknown site intends to communicate with other sites in an LMR system, the previously unknown site needs to be authenticated. Current methods for authentication of a previously unknown site generally require manual configuration of all sites in an LMR system. Also, in order to provide secure communication among the sites, messages among the sites need to be encrypted. At present, encrypted messages are generally unicast, requiring high bandwidth. Multicast messaging is the most bandwidth efficient form of one-to-many IP communications. However, the standard method of multicast encryption, IPSec, is a point-to-point tunneling protocol; multicast over IPSec is converted to unicast. While messages encrypted with a public key may be multicast, however it is generally more computationally expensive to use public key encryption for voice packet transmission.