CC2570 Datasheet, PDF (10/32 Pages) Texas Instruments – 1- and 8-Channel ANT™ RF Network Processors

CC2570
CC2571
SWRS095A – FEBRUARY 2011 – REVISED MARCH 2011
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ANT-FS
A powerful feature of ANT is the ability to do efficient, automated, and secure downloads of bulk data from one
device to another. This is enabled using an extension to the ANT protocol called ANT-FS (File Share). While the
ANT-FS protocol can be implemented at the application level, the TI CC257X family has been designed with
ANT-FS integrated on-chip, allowing designers access to this powerful utility with minimal development effort,
enabling quick time to market.
The ability to perform file transfers enables all sorts of interesting use cases. In the personal monitoring
environment, data from sensors may be stored locally on a battery-operated hub and then uploaded to a PC,
cellphone, or other collection device for display, further processing, or transferring of data across a network.
The ANT-FS protocol defines communication between two devices, a client and a host. The host is typically the
higher-power device and may also be a gateway or a hub device. It is implemented as an ANT slave channel,
and its job is to download and upload files from and to client devices. The client is typically the lower-power
device and is the mobile storage device that interfaces to sensors. It is implemented as an ANT master channel.
The distinction between the host and client may not always be easy. For example, an ANT-FS session may
occur between two identical peer devices. The important point to remember is that both the client and the host
may be implemented with minimal resources that can be powered by a coin-cell battery.
ANT-FS defines three layers of communication: the link, authentication, and transport layers. Both the client and
the host traverse through these layers before any data exchange can occur. The purpose of these layers is to
provide a seamless, yet secure interface for transferring files between devices.
In the link layer, the client device advertises its presence by sending out a periodic beacon. The beacon contain
information pertaining to the client’s state and capabilities, as well as manufacturer and device type. This
information is used by the host device in the link layer to determine whether or not it should connect to a
particular device. Once a host detects a client device in the link layer that it wishes to communicate with, it sends
a link command to that device.
On receiving a link command from the host, the client moves to the authentication state. In the authentication
state, the client authenticate the host in order to establish a secure link. The authentication method is flexible and
may depend on a particular application. Three methods are currently defined by the ANT-FS specification:
pass-through, passkey, and pairing.
Pass-through authentication is really no authentication at all. The host simply sends a request to pass through
authentication. If the client supports this method, it accepts this request; otherwise, it is rejected. Passkey
authentication requires that the host send a unique passkey to the client. If the passkey matches that of the
client, authentication passes; otherwise, it is rejected. This method requires that the passkey be attained by the
host at some earlier point. The pairing method of authentication requires that the host send a command to the
client to request pairing. The client either passes this request to the user of the device (requiring a UI) or uses
some other method to determine if the pairing should be accepted (for example, proximity of the host device). If
pairing is accepted, the client may then send a passkey to the client to be used for future authentication
attempts.
Once authentication is accepted by the client, the client and the host move to the transport layer. In the transport
layer, the host can request a directory of files (analogous to a DOS-style directory). It can then request to
download, upload, and erase files stored on the client.
The ability to do secure file downloads is very powerful. While other technologies can support this use case, only
ANT is able to provide a system that is low-power enough to support the seamless use cases provided by
ANT-FS. In addition to performing generic file transfer, ANT-FS is also the base technology used by file-based
device profiles defined within the ANT+ ecosystem.
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