Interface to set LE connection parameters

Hi,

LE profiles have different requirements for connection parameters. Mainly trying to balance between power consumption and latencies. Probably more will factors will be in future.

Currently I have plan to introduce new l2cap socket option which can be used before connection creation to set inital settings and also change settings while having a connection.

Since there is no equivalents in EDR/BR connection I'm planning to make then apply only LE connection.

Other question which parameters should be exposed to user space? Connection creation and connection update have these common parameters. Connection creation has in addition some other parameters also but they should be handled in some other way.

	__le16   conn_interval_min;
	__le16   conn_interval_max;
	__le16   conn_latency;
	__le16   supervision_timeout;
	__le16   min_ce_len;
	__le16   max_ce_len;

So far I have had two ideas. The first is to simply expose all these fields with sock_opt. In that way profiles would be able to define their requirements also in future without any sock opt changes.

Second is to define BT_LE_LOW_LAT for low latency connection requirements and BT_LE_LOW_POWER connection where the latency is not an issue. It would make usage of this sock opt interface simplier. OTOH the only user should be bluetoothd so it doesn't need to be as simple as possible.

Comments please.

Ville

Hi Ville,

As you note the different profiles would likely have different connection parameters. The different profiles may be running on the same LE link (indeed the same L2CAP [fixed] channel).

Do you have a view on how the different profiles - on the same link - would have different requests arbitrated, and where that arbitration would be done? I'd imagine that the API towards the profiles should be of the abstract form - such as you mention (eg BT_LE_LOW_LAT). This would make it easier to arbitrate the different requests, as compared to if the profiles see an API of the "numerical" form (eg interval = N ms). I guess the arbitration could happen in user or kernel space; as long as there is something with singleton-like semantics to do it.

Also - a quick observation: yes, the connection parameters are only for LE links; however they have some semantic similarity with sniff mode in BR. Especially in the abstract form ("Low Latency" verus "Low Power"). Does BlueZ present an API like this already for BR (I'm new to BlueZ...I was more of a Symbian guy ;)? If not it might be worth having one API for both BR/Sniff and LE/Connection Parameters - and do the appropriate mapping "under the hood".

Cheers,

Tim

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Ville Tervo
Sent: 15 November 2010 12:07
To: [email protected]
Subject: [RFC] Interface to set LE connection parameters

Hi,

LE profiles have different requirements for connection parameters. Mainly trying to balance between power consumption and latencies. Probably more will factors will be in future.

Currently I have plan to introduce new l2cap socket option which can be used before connection creation to set inital settings and also change settings while having a connection.

Since there is no equivalents in EDR/BR connection I'm planning to make then apply only LE connection.

Other question which parameters should be exposed to user space? Connection creation and connection update have these common parameters. Connection creation has in addition some other parameters also but they should be handled in some other way.

	__le16   conn_interval_min;
	__le16   conn_interval_max;
	__le16   conn_latency;
	__le16   supervision_timeout;
	__le16   min_ce_len;
	__le16   max_ce_len;

So far I have had two ideas. The first is to simply expose all these fields with sock_opt. In that way profiles would be able to define their requirements also in future without any sock opt changes.

Second is to define BT_LE_LOW_LAT for low latency connection requirements and BT_LE_LOW_POWER connection where the latency is not an issue. It would make usage of this sock opt interface simplier. OTOH the only user should be bluetoothd so it doesn't need to be as simple as possible.

Comments please.

Ville
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Hi Tim,

Please stop top posting on this ml.

I guess the latency should override power requirements. Low power profile can operate on low latency link but low latency profile fails on high latency. Of course this gets much more complicated if there are more requirements.

Are these (latency and power) the only characteristics we need to deal with. There might be some also. I'm not too familiar with profile drafts.

I think I need to get more details from profile specs and try to find out the requirements from them.

Right now I'm trying to find out what would be the right interface from kernel to user space.

Actually this has been discussed earlier and we need also some api to change sniff behaviour. Reason for this is broken devices which does not turn on normal mode when low latency is needed. I guess Jaikumar had some patches regarding this?

Ville

Ville,

Agreed.

I think these are the main issues; however I wonder whether link supervision timeout may conflict for different use cases. Even if it is not the link supervision the lifetime of the physical link may differ between profiles (some may want the link up for a long time but send no data). Slightly off-topic; but still it raises issues around the type of API and the arbitration of different profile requirements on the same link.

As an aside, it's not just the application profiles. If you have a link to a device with high latency and need to do more service search using GATT then you might want to lower the latency temporarily. This may impact the type of API control you give GATT applications versus any in-built GATT service discovery.

I think it's a bit deeper than broken devices: the specifications offer no real way for devices to agree why a particular mode (eg active or sniff) is needed at a particular time. This then gives interoperability problems because one side may decide it wants sniff mode; but the other does not know why.

Tim

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Hi,

Well maybe we could have some sort of QoS API for l2cap sockets, for instance using link supervision timeout would be very nice to detect link loss on audio profiles where 20 sec. is way too big, and the timeout to enter sniff mode could be dynamically adjusted. Normally we don't export those for userspace but I guess for LE this has to be done anyway and iirc l2cap sockets require privileges so basically only root will be able to play with this so e.g. would be able bluetoothd to adjust the parameter depending on the profile.

Luiz Augusto von Dentz
Computer Engineer

Hi Ville,

If you go with the abstraction in userspace (inside bluetoothd) will be easy to create usage profiles on top of it or even do a fine tune of the parameters for a specific usage. New profiles should be created in the future and we can't foresee its requirements. And I'm seeing that we will have many many different use cases for LE in the future. It can be hard to extend the API if we do the abstraction in the kernel because we can't break the API that we are going to create.

We also have to check if we really need all the parameters you are proposing, maybe we can simplify that API. What about you send a e-mail explaining why we should add each parameter to the API?

Gustavo F. Padovan
http://profusion.mobi

Hi Ville,

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Ville Tervo
Sent: Monday, November 15, 2010 4:07 AM
To: [email protected]
Subject: [RFC] Interface to set LE connection parameters

Hi,

LE profiles have different requirements for connection parameters. Mainly trying to balance between power consumption and latencies. Probably more will factors will be in future.

Currently I have plan to introduce new l2cap socket option which can be used before connection creation to set inital settings and also change settings while having a connection.

Since there is no equivalents in EDR/BR connection I'm planning to make then apply only LE connection.

Other question which parameters should be exposed to user space? Connection creation and connection update have these common parameters. Connection creation has in addition some other parameters also but they should be handled in some other way.

	__le16   conn_interval_min;
	__le16   conn_interval_max;
	__le16   conn_latency;
	__le16   supervision_timeout;
	__le16   min_ce_len;
	__le16   max_ce_len;

So far I have had two ideas. The first is to simply expose all these fields with sock_opt. In that way profiles would be able to define their requirements also in future without any sock opt changes.

Second is to define BT_LE_LOW_LAT for low latency connection requirements and BT_LE_LOW_POWER connection where the latency is not an issue. It would make usage of this sock opt interface simplier. OTOH the only user should be bluetoothd so it doesn't need to be as simple as possible.

Comments please.

[MTsai] - how about following parameters,

Scan internal,
Scan window,
Peer address type,

Thanks,

Mike

Ville
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Hi Mike,

These are connection creation parameters. Maybe BT_LE_LOW_LAT/BT_LE_LOW_POWER could be used also for these values. But I think they should defined in some other way.

Ville