Connection HandoverΒΆ

To transfer larger amounts of data between two NFC devices an alternative carrier connection such as Bluetooth or WiFi can be identified and initiated with NFC.

The NFC Forum Connection Handover specification defines the framework that allows to negotiate an alternative carrier for further data transfer. The device that intends to share data sends a Handover Request message to the service urn:nfc:sn:handover of the peer device. The request informs about the alternative carrier(s) that the requester has available. The peer device determines if any of the alternative carriers matches a local carrier and returns a Handover Select message with one or multiple matching alternative carriers. That information allows the requester to determine its final candidate, if any, and use that carrier for the actual data transfer.

Connection Handover can also be performed if one of the devices does not have a P2P cabable NFC implementation but uses an NFC Tag. In this case the requester acquires connection handover select information by reading the tag without prior sending information about its local alternative carrier technologies. The main difference is thus that the selector can not adapt its response to the capabilites of the requester and, if the tag is not internally connected to the host processor, it can also not adapt to dynamic properties of the selectable carriers.

The default data format for an NFC Tag for connection handover is an NDEF message that is a Handover Select Message which allows multiple carriers or configurations to be included. A Simplified Tag Format can be used if only one carrier is available and additional features of the Handover Tag Format are less important than tag size.

Version 1.3 of the NFC Forum Connection Handover specification introduced a three party model where a third device mediates connection handover between two other devices. This allows to establish an alternative carrier connection between two devices that can not, or not easily, be brought into near field communication distance. The mediation process is basically to acquire alternative carrier information from one device in a first conversation and then negotiate a suitable technology with the other device in a second conversation.

Connection handover using NFC has become an important enabler of easy-to-use spontaneous data sharing between many types of consumer electronics devices. It is thus an important goal that any NFC-enabled device with alternative carrier technologies implements and utilizes connection handover in an interoperable way.

Interoperability Test Requirement

The interoperability test scenarios require that an NFC Device with alternative carrier technologies such as Bluetooth or Wi-Fi implements the NFC Forum Connection Handover specification.

Terminology:

Negotiated Handover
When two devices run in NFC P2P mode, negotiated handover is used by the device that intends to transfer content to propose alternative carriers and learn which ones match the capabilities of the other device.
Handover Tag Format
A device using the handover tag format presents alternative carrier information in the form of a Handover Select Message. This is especially useful if the device has multiple carriers or carrier configurations available. Additionally, if the tag is internally connected to the host processor it may present carrier power states matching reality.
Simplified Tag Format
A device using the simplified tag format presents a single alternative carrier in one NDEF record that marks both start and end of the NDEF message.
Handover Requester
The device that intends to send data over an alternative carrier and thus transmits a Handover Request Message to an NFC Peer Device or reads alternative carrier information from an NFC Tag.
Handover Selector
The device that replies a Handover Select Message to an NFC Peer Device or supplies alternative carrier information on an NFC Tag.

Handover Mediator

A device tthat acquires alternative carrier information from two other devices to select a suitable alternative and request that a connection be established.