LE does not have a Remote Name Request like BR/EDR has. It does have
the ability to fairly efficiently request the remote device name,
however, which we should implement. Currently the only support we offer
for obtaining the remote device name is to pluck it out of the
Advertising packets (Formatted identically to EIR) which works for most
devices, but as with BR/EDR, there is no requirement that devices
include their name in their advertising data.
The Device Name characteristic is Mandatory, and may only exist once for
a device. If it is less than 20 bytes may therefore be read with a
single ReadByType GATT command (uuid16: 0x2a00) over the full 1-0xFFFF
range. It must also be readable without security, so can be done without
first going through SMP.
We may not want to featurize this particular functionality at all, since
all of the components to obtain this info is already available: We just
need to set up an ATT socket in BlueZ, and make the request. However,
when we talk about Scanning for devices, and automatically forwarding
the Remote Name via a MGMT evevnt, the precedence is there to supply it
from the kernel. And if we were to go down that path, we would also
want to simultaneously offer access to the equally Mandatory and
Unsecured "Appearance" Characteristic (uuid16: 0x2a01) which is LE's
sort-of equivilent to the BR/EDR Class-Of-Device.
So: What are the feelings about doing Remote Name (And Appearance)
discovery in the kernel, probably as part of the LE Discovery mechanism?
I favor putting it in the kernel, due to the equivalent functionality
available to BR/EDR there.
Also, there is no coincidence that I offer this RFC at the same time as
I bring up the Write Signed Command functionality from earlier today.
Both concern usages of GATT (or at least ATT) in a way not currently
supported. It is also a case where ideally, we would use a low-latency
connect-read-disconnect methodology.
--
Brian Gix
[email protected]
Employee of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum
Hi Chen,
On 11/18/2011 9:28 PM, Chen Ganir wrote:
> On Sat, Nov 19, 2011 at 01:39, Brian Gix<[email protected]> wrote:
>> Those are otherwise good points (not all devices will automatically start
>> advertising again) however ServiceChanged should never be attempted to be
>> read. We should only obtain this via an Indication from the remote device,
>> and at any rate it is only shared with Trusted devices, so we would have to
>> be Bonded.
>>
>> However, I would definitely NOT try to re-read Name/Appearance at every
>> connection. Those should definitely be cached, and not re-read unless we
>> get the ServiceChanged Indication.
>>
> ServiceChanged is irrelevant here. ServiceChanged will only notify you
> if the handles changed, not if the value changed. Name and appearance
> can and should be read, since we may get only the short name in the
> advertising data, and we wil need the full name. In addition, a device
> may change its name, and we will not be notified of this (GAP name
> characteristic does not notify/indicate). Name may change just like it
> does in BR/EDR.
I don't think we should do anything automatically on start-up.
If we know that we do not have the full name (if the Adv data has it
flagged as "Partial") then we should of course fetch the full name from
the characteristic. However, if we get in the habit of re-reading data
just because it *may* have changed, then we lose track of what LE is all
about, which is minimization of over-the-air traffic.
If a particular high level app wants refresh the Name and/or Appearance,
then of course which should provide that ability, but I might consider
that App to be poorly written barring a compelling need, like perhaps an
indication that it needs to be re-paired. Single mode LE devices will
generally be single mode because they want to limit these unneeded
transactions. LE Profiles are designed to not require Polling type
activities, which a Name or Appearance refresh would be.
--
Brian Gix
[email protected]
Employee of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum
On Sat, Nov 19, 2011 at 01:39, Brian Gix <[email protected]> wrote:
> Hi Chen, Claudio,
>
> On 11/18/2011 2:30 PM, Claudio Takahasi wrote:
>>
>> Hi Brian/Vinicius,
>>
>> On Fri, Nov 18, 2011 at 7:08 PM, Vinicius Costa Gomes
>> <[email protected]> ?wrote:
>>>
>>> Hi Brian,
>>>
>>> On 11:39 Fri 18 Nov, Brian Gix wrote:
>>>>
>>>> LE does not have a Remote Name Request like BR/EDR has. ?It does
>>>> have the ability to fairly efficiently request the remote device
>>>> name, however, which we should implement. ?Currently the only
>>>> support we offer for obtaining the remote device name is to pluck it
>>>> out of the Advertising packets (Formatted identically to EIR) which
>>>> works for most devices, but as with BR/EDR, there is no requirement
>>>> that devices include their name in their advertising data.
>>>>
>>>> The Device Name characteristic is Mandatory, and may only exist once
>>>> for a device. ?If it is less than 20 bytes may therefore be read
>>>> with a single ReadByType GATT command (uuid16: 0x2a00) over the full
>>>> 1-0xFFFF range. It must also be readable without security, so can be
>>>> done without first going through SMP.
>>>>
>>>> We may not want to featurize this particular functionality at all,
>>>> since all of the components to obtain this info is already
>>>> available: We just need to set up an ATT socket in BlueZ, and make
>>>> the request. ?However, when we talk about Scanning for devices, and
>>>> automatically forwarding the Remote Name via a MGMT evevnt, the
>>>> precedence is there to supply it from the kernel. ?And if we were to
>>>> go down that path, we would also want to simultaneously offer access
>>>> to the equally Mandatory and Unsecured "Appearance" Characteristic
>>>> (uuid16: 0x2a01) which is LE's sort-of equivilent to the BR/EDR
>>>> Class-Of-Device.
>>>>
>>>> So: What are the feelings about doing Remote Name (And Appearance)
>>>> discovery in the kernel, probably as part of the LE Discovery
>>>> mechanism? ?I favor putting it in the kernel, due to the equivalent
>>>> functionality available to BR/EDR there.
>>>
>>> I am in favor of this, more because of the Appearance than the Name
>>> discovery. The Name most well behaved devices will provide through
>>> the Advertising Data, Appearance we can only discover via GATT and
>>> it is very useful for the user.
>>
>> IMO, the first attempt needs to be in the userspace. Name, Appearance
>> and *ServiceChanged* can be read on every reconnection. Appearance
>> will be exposed though adv data also, it is being discussed by the BT SIG.
>>
>> If we implement the characteristic storage properly, I don't think we need
>> to read the Name and Appearance always since it will not change.
>>
>> Another aspect against do it in the kernel as part of the discovery
>> procedure is "connectable and bondable mode", probably we will have
>> problems to re-connect. Peripherals may leave the bondable mode or
>> doesn't send advertises automatically after disconnection.
>
> Those are otherwise good points (not all devices will automatically start
> advertising again) however ServiceChanged should never be attempted to be
> read. ?We should only obtain this via an Indication from the remote device,
> and at any rate it is only shared with Trusted devices, so we would have to
> be Bonded.
>
> However, I would definitely NOT try to re-read Name/Appearance at every
> connection. ?Those should definitely be cached, and not re-read unless we
> get the ServiceChanged Indication.
>
ServiceChanged is irrelevant here. ServiceChanged will only notify you
if the handles changed, not if the value changed. Name and appearance
can and should be read, since we may get only the short name in the
advertising data, and we wil need the full name. In addition, a device
may change its name, and we will not be notified of this (GAP name
characteristic does not notify/indicate). Name may change just like it
does in BR/EDR.
> Does anyone object to permanently deciding to NOT do Remote Name/Appearance
> request at device discovery time? Or in the kernel at all? ?Particularly if
> the SIG is heading towards exposing the Appearance in Advertising data, this
> whole thing becomes nearly moot. ?I agree with Chen and Claudio that
> attempting this at Discovery will likely cause the rare IOP problem, and the
> only drawback to Not doing it would be the rare BD Addr and no Appearance
> shown during scanning.
>
> --
> Brian Gix
> [email protected]
> Employee of Qualcomm Innovation Center, Inc.
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum
> --
> To unsubscribe from this list: send the line "unsubscribe linux-bluetooth"
> in
> the body of a message to [email protected]
> More majordomo info at ?http://vger.kernel.org/majordomo-info.html
>
Chen Ganir
[email protected]
Hi Chen, Claudio,
On 11/18/2011 2:30 PM, Claudio Takahasi wrote:
> Hi Brian/Vinicius,
>
> On Fri, Nov 18, 2011 at 7:08 PM, Vinicius Costa Gomes
> <[email protected]> wrote:
>> Hi Brian,
>>
>> On 11:39 Fri 18 Nov, Brian Gix wrote:
>>>
>>> LE does not have a Remote Name Request like BR/EDR has. It does
>>> have the ability to fairly efficiently request the remote device
>>> name, however, which we should implement. Currently the only
>>> support we offer for obtaining the remote device name is to pluck it
>>> out of the Advertising packets (Formatted identically to EIR) which
>>> works for most devices, but as with BR/EDR, there is no requirement
>>> that devices include their name in their advertising data.
>>>
>>> The Device Name characteristic is Mandatory, and may only exist once
>>> for a device. If it is less than 20 bytes may therefore be read
>>> with a single ReadByType GATT command (uuid16: 0x2a00) over the full
>>> 1-0xFFFF range. It must also be readable without security, so can be
>>> done without first going through SMP.
>>>
>>> We may not want to featurize this particular functionality at all,
>>> since all of the components to obtain this info is already
>>> available: We just need to set up an ATT socket in BlueZ, and make
>>> the request. However, when we talk about Scanning for devices, and
>>> automatically forwarding the Remote Name via a MGMT evevnt, the
>>> precedence is there to supply it from the kernel. And if we were to
>>> go down that path, we would also want to simultaneously offer access
>>> to the equally Mandatory and Unsecured "Appearance" Characteristic
>>> (uuid16: 0x2a01) which is LE's sort-of equivilent to the BR/EDR
>>> Class-Of-Device.
>>>
>>> So: What are the feelings about doing Remote Name (And Appearance)
>>> discovery in the kernel, probably as part of the LE Discovery
>>> mechanism? I favor putting it in the kernel, due to the equivalent
>>> functionality available to BR/EDR there.
>>
>> I am in favor of this, more because of the Appearance than the Name
>> discovery. The Name most well behaved devices will provide through
>> the Advertising Data, Appearance we can only discover via GATT and
>> it is very useful for the user.
>
> IMO, the first attempt needs to be in the userspace. Name, Appearance
> and *ServiceChanged* can be read on every reconnection. Appearance
> will be exposed though adv data also, it is being discussed by the BT SIG.
>
> If we implement the characteristic storage properly, I don't think we need
> to read the Name and Appearance always since it will not change.
>
> Another aspect against do it in the kernel as part of the discovery
> procedure is "connectable and bondable mode", probably we will have
> problems to re-connect. Peripherals may leave the bondable mode or
> doesn't send advertises automatically after disconnection.
Those are otherwise good points (not all devices will automatically
start advertising again) however ServiceChanged should never be
attempted to be read. We should only obtain this via an Indication from
the remote device, and at any rate it is only shared with Trusted
devices, so we would have to be Bonded.
However, I would definitely NOT try to re-read Name/Appearance at every
connection. Those should definitely be cached, and not re-read unless
we get the ServiceChanged Indication.
Does anyone object to permanently deciding to NOT do Remote
Name/Appearance request at device discovery time? Or in the kernel at
all? Particularly if the SIG is heading towards exposing the Appearance
in Advertising data, this whole thing becomes nearly moot. I agree with
Chen and Claudio that attempting this at Discovery will likely cause the
rare IOP problem, and the only drawback to Not doing it would be the
rare BD Addr and no Appearance shown during scanning.
--
Brian Gix
[email protected]
Employee of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum
Hi Brian/Vinicius,
On Fri, Nov 18, 2011 at 7:08 PM, Vinicius Costa Gomes
<[email protected]> wrote:
> Hi Brian,
>
> On 11:39 Fri 18 Nov, Brian Gix wrote:
>>
>> LE does not have a Remote Name Request like BR/EDR has. It does
>> have the ability to fairly efficiently request the remote device
>> name, however, which we should implement. Currently the only
>> support we offer for obtaining the remote device name is to pluck it
>> out of the Advertising packets (Formatted identically to EIR) which
>> works for most devices, but as with BR/EDR, there is no requirement
>> that devices include their name in their advertising data.
>>
>> The Device Name characteristic is Mandatory, and may only exist once
>> for a device. If it is less than 20 bytes may therefore be read
>> with a single ReadByType GATT command (uuid16: 0x2a00) over the full
>> 1-0xFFFF range. It must also be readable without security, so can be
>> done without first going through SMP.
>>
>> We may not want to featurize this particular functionality at all,
>> since all of the components to obtain this info is already
>> available: We just need to set up an ATT socket in BlueZ, and make
>> the request. However, when we talk about Scanning for devices, and
>> automatically forwarding the Remote Name via a MGMT evevnt, the
>> precedence is there to supply it from the kernel. And if we were to
>> go down that path, we would also want to simultaneously offer access
>> to the equally Mandatory and Unsecured "Appearance" Characteristic
>> (uuid16: 0x2a01) which is LE's sort-of equivilent to the BR/EDR
>> Class-Of-Device.
>>
>> So: What are the feelings about doing Remote Name (And Appearance)
>> discovery in the kernel, probably as part of the LE Discovery
>> mechanism? I favor putting it in the kernel, due to the equivalent
>> functionality available to BR/EDR there.
>
> I am in favor of this, more because of the Appearance than the Name
> discovery. The Name most well behaved devices will provide through
> the Advertising Data, Appearance we can only discover via GATT and
> it is very useful for the user.
IMO, the first attempt needs to be in the userspace. Name, Appearance
and *ServiceChanged* can be read on every reconnection. Appearance
will be exposed though adv data also, it is being discussed by the BT SIG.
If we implement the characteristic storage properly, I don't think we need
to read the Name and Appearance always since it will not change.
Another aspect against do it in the kernel as part of the discovery
procedure is "connectable and bondable mode", probably we will have
problems to re-connect. Peripherals may leave the bondable mode or
doesn't send advertises automatically after disconnection.
BR,
Claudio
>
>>
>> Also, there is no coincidence that I offer this RFC at the same time
>> as I bring up the Write Signed Command functionality from earlier
>> today. Both concern usages of GATT (or at least ATT) in a way not
>> currently supported. It is also a case where ideally, we would use a
>> low-latency connect-read-disconnect methodology.
>>
>> --
>> Brian Gix
>> [email protected]
>> Employee of Qualcomm Innovation Center, Inc.
>> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-bluetooth" in
>> the body of a message to [email protected]
>> More majordomo info at http://vger.kernel.org/majordomo-info.html
>
>
> Cheers,
> --
> Vinicius
Brian, Vinicius,
On Sat, Nov 19, 2011 at 00:08, Vinicius Costa Gomes
<[email protected]> wrote:
> Hi Brian,
>
> On 11:39 Fri 18 Nov, Brian Gix wrote:
>>
>> LE does not have a Remote Name Request like BR/EDR has. ?It does
>> have the ability to fairly efficiently request the remote device
>> name, however, which we should implement. ?Currently the only
>> support we offer for obtaining the remote device name is to pluck it
>> out of the Advertising packets (Formatted identically to EIR) which
>> works for most devices, but as with BR/EDR, there is no requirement
>> that devices include their name in their advertising data.
>>
>> The Device Name characteristic is Mandatory, and may only exist once
>> for a device. ?If it is less than 20 bytes may therefore be read
>> with a single ReadByType GATT command (uuid16: 0x2a00) over the full
>> 1-0xFFFF range. It must also be readable without security, so can be
>> done without first going through SMP.
>>
>> We may not want to featurize this particular functionality at all,
>> since all of the components to obtain this info is already
>> available: We just need to set up an ATT socket in BlueZ, and make
>> the request. ?However, when we talk about Scanning for devices, and
>> automatically forwarding the Remote Name via a MGMT evevnt, the
>> precedence is there to supply it from the kernel. ?And if we were to
>> go down that path, we would also want to simultaneously offer access
>> to the equally Mandatory and Unsecured "Appearance" Characteristic
>> (uuid16: 0x2a01) which is LE's sort-of equivilent to the BR/EDR
>> Class-Of-Device.
>>
>> So: What are the feelings about doing Remote Name (And Appearance)
>> discovery in the kernel, probably as part of the LE Discovery
>> mechanism? ?I favor putting it in the kernel, due to the equivalent
>> functionality available to BR/EDR there.
>
> I am in favor of this, more because of the Appearance than the Name
> discovery. The Name most well behaved devices will provide through
> the Advertising Data, Appearance we can only discover via GATT and
> it is very useful for the user.
>
>>
>> Also, there is no coincidence that I offer this RFC at the same time
>> as I bring up the Write Signed Command functionality from earlier
>> today. Both concern usages of GATT (or at least ATT) in a way not
>> currently supported. It is also a case where ideally, we would use a
>> low-latency connect-read-disconnect methodology.
>>
>> --
>> Brian Gix
>> [email protected]
>> Employee of Qualcomm Innovation Center, Inc.
>> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-bluetooth" in
>> the body of a message to [email protected]
>> More majordomo info at ?http://vger.kernel.org/majordomo-info.html
>
>
> Cheers,
> --
> Vinicius
> --
> To unsubscribe from this list: send the line "unsubscribe linux-bluetooth" in
> the body of a message to [email protected]
> More majordomo info at ?http://vger.kernel.org/majordomo-info.html
>
I really do not think this is a good idea. Forcing a connection while
scanning for devices is not a good idea for LE devices, which may
require a push button or some other user intervention to get
discoverable/connectable. Trying to connect to it while scanning may
cause it to stop being discoverable/connectable (if the device does
not become discoverable after disconnection), which will result in the
device either becoming non connectable, or require the user to press
the button again, which is making things more difficult and
complicated. I would suggest relying on the advertising data, and get
the remote name, or every other GAP related GATT characteristics once
a connection is established for the purpose it was supposed to be.
Best regards,
Chen Ganir
Hi Brian,
On 11:39 Fri 18 Nov, Brian Gix wrote:
>
> LE does not have a Remote Name Request like BR/EDR has. It does
> have the ability to fairly efficiently request the remote device
> name, however, which we should implement. Currently the only
> support we offer for obtaining the remote device name is to pluck it
> out of the Advertising packets (Formatted identically to EIR) which
> works for most devices, but as with BR/EDR, there is no requirement
> that devices include their name in their advertising data.
>
> The Device Name characteristic is Mandatory, and may only exist once
> for a device. If it is less than 20 bytes may therefore be read
> with a single ReadByType GATT command (uuid16: 0x2a00) over the full
> 1-0xFFFF range. It must also be readable without security, so can be
> done without first going through SMP.
>
> We may not want to featurize this particular functionality at all,
> since all of the components to obtain this info is already
> available: We just need to set up an ATT socket in BlueZ, and make
> the request. However, when we talk about Scanning for devices, and
> automatically forwarding the Remote Name via a MGMT evevnt, the
> precedence is there to supply it from the kernel. And if we were to
> go down that path, we would also want to simultaneously offer access
> to the equally Mandatory and Unsecured "Appearance" Characteristic
> (uuid16: 0x2a01) which is LE's sort-of equivilent to the BR/EDR
> Class-Of-Device.
>
> So: What are the feelings about doing Remote Name (And Appearance)
> discovery in the kernel, probably as part of the LE Discovery
> mechanism? I favor putting it in the kernel, due to the equivalent
> functionality available to BR/EDR there.
I am in favor of this, more because of the Appearance than the Name
discovery. The Name most well behaved devices will provide through
the Advertising Data, Appearance we can only discover via GATT and
it is very useful for the user.
>
> Also, there is no coincidence that I offer this RFC at the same time
> as I bring up the Write Signed Command functionality from earlier
> today. Both concern usages of GATT (or at least ATT) in a way not
> currently supported. It is also a case where ideally, we would use a
> low-latency connect-read-disconnect methodology.
>
> --
> Brian Gix
> [email protected]
> Employee of Qualcomm Innovation Center, Inc.
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum
> --
> To unsubscribe from this list: send the line "unsubscribe linux-bluetooth" in
> the body of a message to [email protected]
> More majordomo info at http://vger.kernel.org/majordomo-info.html
Cheers,
--
Vinicius