What is Working Group 16

CALM Concept

ISO TC204 WG16 is developing a family of International Standards based on the CALM (Communications access for land mobiles) concept. This family of standards 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. 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 "Intelligent Transport Systems" (ITS) sector.

ISO 21217 describes the common architectural framework around which CALM-compliant communication entities called ITS stations are instantiated, and provides the architectural reference for use by the CALM family of International Standards including the lower layer service access point specifications described in, network protocol specifications described in (IPv6 networking) and (non-IP networking), and the ITS station management specifications described in.

The relationship between the members of the CALM family of standards is shown in Figure 1.. The numbers in the boxes are references to the ISO standard in which the indicated functionality is specified.

The functional requirements for information transmission in the ITS sector over large distances using wireless access technologies may be very different from the requirements for e.g. European "Dedicated Short Range Communication" (DSRC). In ITS, large volumes of data are required for purposes such as safety, traffic information and management, video downloads to mobile stations for tourist information and entertainment and navigation-system-updates. In order to support such services, mobile stations need to be able to communicate over longer ranges with fixed stations, and the system must be able to hand over sessions from one fixed station to another. Thus the CALM family of International Standards is explicitly designed to enable quasi-continuous communications, communications of protracted duration, and short messages and sessions of high priority with stringent time constraints.

CALM-complaint systems provide the ability to support handover of different types. One of the essential features of the CALM concept is the ability to support media independent handover (MIH), also referred to as heterogeneous handover, between the various access technologies supported by CALM, e.g., cellular, satellite, microwave, mobile wireless broadband, infra-red, DSRC. With this flexibility, CALM-complaint systems provide the ability to use the most appropriate access technology for message delivery. Selection rules are supported that include user preferences and access technology capabilities in making decisions as to which access technology to use for a particular session, and when to handover between access technologies or between service providers on the same access technology. It is also important to note that communication between ITS stations is peer-to-peer regardless of the networks providing the connectivity. This provides flexibility in designing applications for the ITS sector.

A fundamental advantage of the CALM concept over traditional systems is that applications are abstracted from the access technologies that provide the wireless connectivity and the networks that transport the information from the source to the destination(s). With reference to figure 1, this means that ITS stations are not limited to a single access technology and networking protocol and can implement any of those supported, and the ITS station management can make optimal use of all these resources. To exploit this flexibility, CALM-complaint systems provide the ability to support handover of different types including those involving a change of communication interface (which may or may not involve a change of access technology since ITS stations may have multiple communication interfaces using the same access technology), those involving reconfiguration or change of the network employed to provide connectivity, and those involving both a change in communication interface and network reconfiguration.

One of the essential features of the CALM concept is the ability to support heterogeneous handover, also referred to as media independent handover (MIH) between various access technologies supported by ITS stations. With this flexibility, CALM-complaint systems provide the ability to use the most appropriate access technology for information exchange. Selection rules are supported that include user preferences and access technology capabilities in making decisions as to which access technology to use for a particular session, and when to handover between access technologies or between service providers on the same access technology. Note that while this flexibility is very important in providing quasi-continuous connectivity, applications may be restricted to specific access technologies and operational frequency bands if required.

The CALM architecture makes provision for rapid session initialization, where this is required, e.g. for road safety applications.

The CALM architecture supports a variety of different ITS station implementations, ranging from "simple single-box implementations" up to "complex distributed implementations" where the complete ITS station functionality is distributed in several physical boxes interconnected with wired or wireless local networks. The instantiation of access technologies used for these local station-internal networks follows the same principles as the instantiation of access technologies used to connect to external networks.

Text and figures are taken from the CALM Architecture document. Please note that this content is subject to change as the CALM developments and standardization evolve.