On Wed, 2014-05-07 at 15:30 +0530, Suresh Kumar N. wrote: > On Tue, May 6, 2014 at 9:42 PM, Dan Williams <dcbw@xxxxxxxxxx> wrote: > > On Tue, 2014-05-06 at 14:27 +0530, Suresh Kumar N. wrote: > >> On Mon, May 5, 2014 at 8:38 PM, Dan Williams <dcbw@xxxxxxxxxx> wrote: > >> > On Mon, 2014-05-05 at 11:07 +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) > >> > > >> > Or both at the same time. > >> > > >> >> Is there a Standard defining the way a Data Card should be enumerated? > >> > > >> > There is no single standard. There is a few "standards" and multiple > >> > proprietary mechanisms, and sometimes these are combined in the same > >> > device. > >> > > >> > The device simply enumerates as a normal USB device, providing to the > >> > host computer one or more USB interfaces. > >> > > >> > Each USB interface can be any one of: > >> > > >> > 1) serial interface (AT, QCDM, WMC, WDM, CDC-ACM, etc) > >> > 2) pseudo-ethernet NIC (proprietary, CDC-ETHER, CDC-NCM, etc) > >> > >> In such case (pseudo-ethernet NIC) do we assume that the firmware on > >> the USB Dongle is responsible to establish IP address? > >> In other words how does IP address allocation occur in this case? > > > > Thank you very much for such a clear and exhaustive explanation. > > > The firmware is always involved, because the IP address comes from the > > cellular network, and the firmware is what receives it. The firmware > > must then provide that address to the host, so that the host can > > communicate with the network. This happens in a few ways: > > > > 1) firmware implements a DHCP server, IPv6 Router, etc; host uses DHCP > > client or IPv6 Router Discovery to obtain IP address and DNS details > > > > 2) firmware provides static IP address and DNS details over AT commands > > > > 3) firmware provides static IP address and DNS details via proprietary > > protocols (QMI, MBIM, etc) > > > > 4) firmware implements PPP over serial port and provides IP address and > > DNS details via IPCP/IPV6CP > > Based on 1) and 2), Firmware refers to be driver code implemented on > USB device-side, but 3) and 4) refer to Firmware implemented on > Host-side. > Does Firmware here refer to Host-side or USB device-side? "Firmware" here always refers to USB device side. So all 4 of these refer to things that the USB device can do, based on what the USB device has implemented in its firmware. It's up to the host to determine which protocols the USB device firmware implements, and then to speak to the USB device with those protocols to determine the IP address the host must use to communicate with the USB device firmware. > > > > Most modems still support #4 over at least one AT-capable serial port. > > Many modems implement multiple methods (eg, Qualcomm firmware often does > > #1, #3, and #4). > > > > Note that in all cases, connection setup (with the APN and other > > details) must occur via control channels (with AT, QMI, MBIM, etc) > > before you can use any of these methods to obtain an IP address from the > > firmware. > > > > There is actually another class of "plug and play" 3G dongle that > > provides a NAT-ed IP network (192.168.0.x or 10.x) to the host over what > > looks like a USB ethernet NIC. These appear exactly like a normal USB > > ethernet dongle or a home router to the host, and to configure the > > device, you use a web browser on the host like you would with a home > > router. None of the 3G stuff is exposed to the host. One example is > > Huawei HiLink devices like the E3256, though not all HiLink-branded > > devices operate this way. > > In all of the above, how do we visualize the Connect/Disconnect option > provided by the Host side application? The steps you must take are *always* dependent on the specific modem that you are communicating with. Depending on which protocols the modem implements your host application must do many different things. > 1. Is it defined to just Enable/Disable a network interface (USB > ethernet NIC) on Host side, but in that case would the Active context > get Deactivated? Your host application must perform setup and context activation using the control channel protocols (AT commands, proprietary protocols, etc) before it can start real IP networking. Perhaps a concrete example will help. This is the procedure for connecting an Ericsson "MBM" (F3507, F3607, F5521, etc) modem. This modem provides 2 CDC-ACM ports which are used for AT command communication, and a CDC-ETHER port which emulates an ethernet interface. Both of these ports use standard protocols and are handled automatically by the Linux kernel drivers. 1) first, check and ensure that the modem is registered on the network with AT+CGREG. Once the modem has registered, you can proceed. 2) check for an existing PDP context that matches the APN you want to use. If there is one, save that PDP context ID for the next step. If not, create on with AT+CGDCONT and your APN 3) Set authentication for the given PDP context ID with AT*EIAAUW 4) Request data session activation with AT*ENAP 5) Poll AT*ENAP until it reports that you are connected 6) Finally you can run DHCP on the network port to get your IP address and DNS servers For many devices from Option NV, you follow much the same procedure except that the authentication command is AT$QCPDPP for Qualcomm-based chipsets, and AT_OPDPP for non-Qualcomm based chipsets (step 3 above). Then you use the AT_OWANCALL command to request the data session (step 4). Then to retrieve the IP configuration (step 6), you use AT_OWANDATA which returns the IP address, which you then apply to the network port. DHCP is not used with these devices. Huawei devices often have different AT commands (AT^NDISDUP and AT^DHCP) for data session activation. Many Qualcomm devices support QMI, which is used instead of AT commands for data session setup. So you see, what procedure you use to start the data session depends on exactly what specific USB device you are using. Dan > OR > 2. Is it defined to Activate/Deactivate context? > > > > > Dan > > > >> > 3) proprietary control protocols (CnS, QMI, etc) > >> > 4) standard non-serial control protocols (MBIM) > >> > > >> > A modem can provide any of these in combination. Which port speaks what > >> > protocol is detected by one or more of the following methods: > >> > > >> > a) USB VID/PID and interface number hardcoded in the drivers or in > >> > userland udev rules > >> > b) USB interface type (eg, serial port or NIC port, done in userland) > >> > c) probing with known request/response to determine different > >> > communication protocols used if the port type is indeterminate > >> > >> Thanks for the information. > >> > >> > > >> > Dan > >> > > >> >> Please correct if my understanding is not correct or incomplete. > >> >> > >> >> Thanks in advance for your clarifications. > >> >> > >> >> Warm Regards, > >> >> Suresh > >> >> -- > >> >> To unsubscribe from this list: send the line "unsubscribe linux-usb" in > >> >> the body of a message to majordomo@xxxxxxxxxxxxxxx > >> >> More majordomo info at http://vger.kernel.org/majordomo-info.html > >> > > >> > > >> -- > >> To unsubscribe from this list: send the line "unsubscribe linux-usb" in > >> the body of a message to majordomo@xxxxxxxxxxxxxxx > >> More majordomo info at http://vger.kernel.org/majordomo-info.html > > > > -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
