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Re: BLE central device as GATT server
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Re: BLE central device as GATT server

  • Subject: Re: BLE central device as GATT server
  • From: András Kövi <email@hidden>
  • Date: Mon, 11 Nov 2013 16:00:26 +0100
Even thought the specification may allow you to create a GATT server on the central side (as I understood it from the specifiaction), the iOS Core Bluetooth does not provide this functionality. The DB is tied to the CBPeripheraManager which is the peripheral role. At the same time "The nRF8001 is a pure BLE Peripheral device, and it can not be used as a Central." (https://devzone.nordicsemi.com/index.php/can-the-nrf8001-be-used-as-a-central) So I suppose the nRF8001 cannot scan for devices or start a connection. As a consequence, it is not able to connect to the GATT server implemented by the CBPeripheralManager.

So what you can do:
- the mRF8001 must advertise
- the iOS device must scan for the nRF8001
- the iOS device must connect the nRF8001 and discover its services.

At this point it's up to you how you implement the communication. It is possible to have a single service with a single characteristic on the nRF8001 side and implement a higher level protocol that implements a database in a GATT serverish way. This is not preferred for several reasons (this is not the usual way of doing things and you lose most of the optimizations provided by the underlying stacks) but it's your choice.

Regards,
Andras


2013/11/11 Walter Stephan <email@hidden>
Ok, so maybe we're not talking about the same thing.

I'm designing an accessory using a NRF8001 chip by Nordic Semiconductor, which (according to the datasheet) can only act as a *Peripheral*.

In their forums, Nordic wrote the following:

[start quote]

First, there is the concept of Central/Peripheral, which has to do with establishing a link. This is also known as the GAP role. A Peripheral can advertise, to let other devices know that it's there, but it is only a Central that can actually send a connection request to establish a connection. When a link has been established, the Central is sometimes called a Master, while the Peripheral could be called a Slave.

[...]

Then, you have the roles of a GATT Server and a GATT Client. Normally, the Server is the device that contains data, that the Client can read.

However, there is no connection between these roles. Even though it is most common for a Peripheral to be a Server and a Central to be a Client, it is perfectly possible to have a Peripheral that is only a Client, or a Central that is both a Server and a Client.

[end quote]

So I assumed that an app on an iOS device would always act as a *Central*, but could be a GATT client (the most common use case), a GATT server (as with ANCS or Time Service), or both at the same time. (Am I wrong here?)

From documentation, code examples and mailing list discussions I have only found examples of implementing a GATT client. I would like to know if it's possible in iOS to implement a GATT server when acting as a central.

I am not an iOS developer, but as an embedded engineer I'm trying to define a proprietary BLE profile which should work with iOS. I could of course define services on the peripheral, but having the GATT service on the central seems more natural for my use case.

I have developed a prototype using a BLE dongle on a PC, so I know it is possible to have a Central acting as a GATT server in general, but I wonder if iOS supports that.


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  • Follow-Ups:
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References: 
 >BLE central device as GATT server (From: Walter Stephan <email@hidden>)
 >Re: BLE central device as GATT server (From: András Kövi <email@hidden>)
 >AW: BLE central device as GATT server (From: Walter Stephan <email@hidden>)
 >Re: BLE central device as GATT server (From: John Earl <email@hidden>)
 >AW: BLE central device as GATT server (From: Walter Stephan <email@hidden>)
 >Re: BLE central device as GATT server (From: András Kövi <email@hidden>)
 >AW: BLE central device as GATT server (From: Walter Stephan <email@hidden>)

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