Page 520 - From GMS to LTE

506 From GSM to LTE-Advanced Pro and 5G

accomplished is the BLE/HTTP gateways that receive HTTP GET requests containing
proprietary or standardized requests to read data from a sensor. The gateway then que-
ries the corresponding attributes in the device and returns the result it receives via an
HTTP answer to the requesting entity. The advantage of this approach is that the
requesting device, which communicates over IP, is decoupled from the Bluetooth Low
Energy communication. Furthermore the gateway can communicate with the Bluetooth
device in the most energy‐efficient way possible. To set attributes in a BLE device,
HTTP PUT requests are sent to the gateway, which then translates the request into
Bluetooth commands to change the values of attributes on a BLE device. The downside
of this approach is that an intelligent gateway is required to translate between the
Bluetooth and the IP‐based world.
Another approach to connecting BLE devices to the Internet is to implement an IP pro-
tocol stack directly on the BLE device and use an IP‐protocol‐layer gateway to connect the
BLE device to fixed and wireless IP‐based networks. An example of such a gateway could
be a Wi‐Fi access point connected to the Internet that also includes a BLE interface and
implements IETF RFC 7668 for IPv6 communication over Bluetooth Low Energy [30].
Figure 7.34 shows the protocol stack used for transporting IPv6 packets over the BLE
air interface. To advertise that a device is BLE IPv6‐capable, the IP Protocol Support
Profile (IPSP), which includes the IP Protocol Support Service (IPSS), has been added
to the list of official BLE profiles. A major difference from the previously discussed BLE
profiles is that the Attribute Protocol (ATT) is not used for the exchange of user data,
i.e. the IPv6 packets. Instead, an adaptation layer specification referred to as ‘6LoWPAN’
(IPv6 over Low power Wireless Personal Area Network) is used to define how IPv6
packets are transported over BLE link layer packets. Up to Bluetooth 4.1, each link layer
packet could only transport 27 user data bytes. As IPv6 packets are typically much
larger they have to be split into several smaller chunks and reassembled at the other
end. Bluetooth 4.2 introduced an increased payload size of 257 user data bytes per link
layer packet, thus significantly reducing protocol overhead and increasing transmission
speeds when large amounts of data are transferred over the BLE link.
IETF RFCs referenced in RFC 7668 further describe how BLE devices should configure
their IPv6 protocol stack at power up and how IPv6 headers are to be compressed,
which would otherwise be a significant overhead.

UDP / TCP / other IP Protocol Support Service

IPv6 Generic Attribute Prole (GATT)
6LoWPAN for BLE Attribute Prole (ATT)

L2CAP

Host Controller Interface
Link Layer

BLE Physical Layer

Figure 7.34 IPv6 over Bluetooth Low Energy.