**3.2.3 Communications Access for Land Mobiles**

The Communications Access for Land Mobiles (CALM) framework is an ISO TC204 initiative that specifies a common architecture, network protocols and communication interface definitions for wired and wireless communications using various access technologies including cellular 2nd generation, cellular 3rd generation, satellite, infra-red, 5 GHz micro-wave, 60 GHz millimetre-wave, and mobile wireless broadband (CALM, 2007). These and other access technologies that can be incorporated are designed to provide broadcast, unicast and multicast communications between mobile stations, between mobile and fixed stations and between fixed stations in the ITS sector.

The CALM concept is therefore developed to provide a layered solution that enables continuous or quasi continuous communications between vehicles and the infrastructure, or between vehicles, using such (multiple) wireless telecommunications media that are available in any particular location, and have the ability to migrate to a different available media where required. Media selection is at the discretion of user determined parameters.

The motivations behind this standardization effort are the following:


The following communication types are supported by CALM:


At a high level, on the one side there are multiple services possibly operating simultaneously all requesting communications services, whereas on the other side there is a possibility of multiple communications media opportunities in the vehicle to handle the transaction. In the middle CALM is located managing quasi continuous communications using the available media, to satisfy the needs of one or multiple applications. It is important to understand that the vehicle may be maintaining multiple simultaneous sessions.

Finally, it is important to highlight that the specifications and standards of CALM are not a physical piece of equipment. While CALM may indeed operate through a "box" designed to achieve its tasks, it is actually a set of protocols, procedures and management actions. The implementation is actually a commercial decision.
