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Network Solutions OverviewExisting USB Networking standards were drawn up with what we can call infrastructure devices in mind. In other words, the device is an access method to another network. These solutions don’t quite meet the requirements for handhelds, but they are a good place to start. 1.1 Examples of infrastructure devices1.1.1 Ethernet Dongle In the simplest case, a USB Network adapter is simply an access point to an existing Ethernet segment. It is comparable to a PCI Ethernet card except that there is no need to open the case. The market for these devices is limited because most computers now come with pre-installed Ethernet interfaces, either by a PCI add-in card or on the main board. 1.1.2 Residential broadband device Some ADSL and Cable modems offer a USB access method, meaning that it is possible to use USB instead of Ethernet. This access method best typifies what USB is all about - the ability to add Ethernet capability to a PC without opening the case and installing an additional peripheral card. In the case of cable/DSL modems, the Ethernet segment is completely virtual, never actually materializing as either UTP or Coax. In effect, the USB is treated as a 802.3 physical layer. To the host computer, it looks like an Ethernet dongle and is treated as if the modem was connected via real Ethernet.In most cases the modem acts in exactly the fashion it would if connected via "real" Ethernet except that it must supply its own MAC address and will typically extend that to the remote (ISP) host as the whole circuit's physical MAC. Network Functions For Traditional Infrastructure USB Devices
Note that Belcarra can implement the above two drivers as a single device with a dual configuration allowing it to be supported by RNDIS Class drivers under Windows and CDC Class drivers on other OS’s. While it is possible to directly utilize these protocols to implement a USB network, they were originally designed to implement infrastructure devices (see 1.1.1 and 1.1.2 above) See BLAN below for an alternative. Network Functions For Handheld USB Devices
The growth of smart handheld devices with USB device ports has presented a set of unique problems to the OEM and user - that of easily allowing more than one such device to be connected to the host system at any given time (for example, many products have hard-coded IP addresses in their application software) In addition, there are cases where allowing peripherals to "see" each other and possibly the external WAN (Web) make sense and will give rise to a whole new class of applications. Since USB is by nature an asymmetric (1 host, many peripherals) and host-controlled facility, it was necessary to bring such connections to the higher level of bridged TCP/IP. The Belcarra BLAN protocol and USBLAN™ application suite do exactly this, providing a facility that allows smart peripherals to participate in a peer-to-peer fashion using standard Internet facilities such as Web, FTP, SMB (Windows file/peripheral sharing), NFS (Network File System), etc. Other Functions For Handheld USB Devices
Older USB "smart" devices have used this function to emulate the originally hard-wired serial devices from previous versions of the hardware. In this way the OEM may re-use the original host application software with no modification. The limitation is that serial host communications are limited in speed to that of the typical hard-wired serial port - a fraction of the actual speed of the USB port. In addition, the proprietary nature of the serial host application software has limited the interoperability of new smart devices.
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