Clarification regarding USB Data Card (Dongle) enumeration in Linux udev

Clarification regarding USB Data Card (Dongle) enumeration in Linux udev

[Suresh Kumar N.]

Hi,

I am new to udev and device enumeration.

I am interested to know how USB Data Card would get enumerated.

Based on my understanding Data Card can get enumerated below 2 possible ways -
  1. As a modem
  2. As a Network Interface Card (NIC)

Is there a Standard defining the way a Data Card should be enumerated?

Please correct if my understanding is not correct or incomplete.

Thanks in advance for your clarifications.

Warm Regards,
Suresh

Re: Clarification regarding USB Data Card (Dongle) enumeration in Linux udev

[Greg KH]

On Sun, May 04, 2014 at 02:52:23PM +0530, Suresh Kumar N. wrote:
> Hi,
> 
> I am new to udev and device enumeration.
> 
> I am interested to know how USB Data Card would get enumerated.
> 
> Based on my understanding Data Card can get enumerated below 2 possible ways -
>   1. As a modem
>   2. As a Network Interface Card (NIC)
> 
> Is there a Standard defining the way a Data Card should be enumerated?

What do you mean by "data card"?

As for how the device is enumerated, that depends on the device itself,
and how it tells the operating system it should be talked to through its
configuration descriptors.  See the USB spec for more details about
this.

greg k-h

Re: Clarification regarding USB Data Card (Dongle) enumeration in Linux udev

[Suresh Kumar N.]

Dear Greg,

Data Card here refers to 3G Dongle.

Yes, it is right; device enumeration depends on the device itself.
But, there must be some guideline defined regarding the same.

As per the link (http://www.linux-usb.org/usb.devices.txt) USB device
cannot be enumerated as Network controllers, please correct me if
something has been overlooked.

Would all 3G Dongle devices be enumerated as "ACM USB modems"?

Warm Regards,
Suresh

On Sun, May 4, 2014 at 9:46 PM, Greg KH <greg@kroah.com> wrote:
> On Sun, May 04, 2014 at 02:52:23PM +0530, Suresh Kumar N. wrote:
>> Hi,
>>
>> I am new to udev and device enumeration.
>>
>> I am interested to know how USB Data Card would get enumerated.
>>
>> Based on my understanding Data Card can get enumerated below 2 possible ways -
>>   1. As a modem
>>   2. As a Network Interface Card (NIC)
>>
>> Is there a Standard defining the way a Data Card should be enumerated?
>
> What do you mean by "data card"?
>
> As for how the device is enumerated, that depends on the device itself,
> and how it tells the operating system it should be talked to through its
> configuration descriptors.  See the USB spec for more details about
> this.
>
> greg k-h

Re: Clarification regarding USB Data Card (Dongle) enumeration in Linux udev

[Greg KH]

On Mon, May 05, 2014 at 09:13:08AM +0530, Suresh Kumar N. wrote:
> Dear Greg,
> 
> Data Card here refers to 3G Dongle.

There is not any "standard" for these.

> Yes, it is right; device enumeration depends on the device itself.
> But, there must be some guideline defined regarding the same.
> 
> As per the link (http://www.linux-usb.org/usb.devices.txt) USB device
> cannot be enumerated as Network controllers, please correct me if
> something has been overlooked.

Not true, I have a usb network device right here.

> Would all 3G Dongle devices be enumerated as "ACM USB modems"?

Not at all, some show up as a custom USB to serial device, some as a
network device, and others as a ACM modem.

Again, look at the USB descriptors in the device, that will tell you how
the device is to be communicated with.

greg k-h

Re: Clarification regarding USB Data Card (Dongle) enumeration in Linux udev

[Suresh Kumar N.]

On Mon, May 5, 2014 at 10:39 PM, Greg KH <greg@kroah.com> wrote:
> On Mon, May 05, 2014 at 09:13:08AM +0530, Suresh Kumar N. wrote:
>> Dear Greg,
>>
>> Data Card here refers to 3G Dongle.
>
> There is not any "standard" for these.
>
>> Yes, it is right; device enumeration depends on the device itself.
>> But, there must be some guideline defined regarding the same.
>>
>> As per the link (http://www.linux-usb.org/usb.devices.txt) USB device
>> cannot be enumerated as Network controllers, please correct me if
>> something has been overlooked.
>
> Not true, I have a usb network device right here.

In such a case, who configures or should configure IP address to this
network device?.

>
>> Would all 3G Dongle devices be enumerated as "ACM USB modems"?
>
> Not at all, some show up as a custom USB to serial device, some as a
> network device, and others as a ACM modem.

So it all depends on the Vendor (providing the 3G Dongle) about how
the device gets enumerated (again based on the USB descriptors in the
device).

>
> Again, look at the USB descriptors in the device, that will tell you how
> the device is to be communicated with.

Thanks for the information Greg.

>
> greg k-h