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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