Universal Serial Bus
The Universal Serial Bus (USB) is a serial 4-wire bus (GND, Power and a differential Data Signal transferred over 2 wires). A quite clever designed protocol for communication between the PC Host and peripheral devices like e.g. DVB Receivers. Since devices are defined as dumb clients that get polled by the USB Host Controller, USB device chipsets can be very cheap compared to IEEE1394 chips that provide essentially the same functionality.
Governed by the USB Consortium, USB specifications are openly available to the public on http:://www.usb.org.
Many USB DVB devices are available from an wide assortment of different vendors.
USB 1.1
This older Universal Serial Bus variant specifies data transfer rates of 1.5 Mbps (Low-Speed devices) and 12 Mbps (Full-Speed devices).
USB DVB devices adhering to the USB 1.1 standard will operate at the Full-Speed specification. However, because Full-Speed devices are limited to a overall datarate (incl. Protocol overhead) of about 12 Mbps, this essentially prevents these devices from receiving HDTV steams and makes it impossible to receive some high-datarate services. Only High-Speed USB 2.0 DVB devices are able to transfer the full MPEG2 Transport Stream or high-datarate Transponders.
USB 2.0
In terms of reception of digital TV (DTV) services, the 480 Mbps transfer rate of USB 2.0 overcomes several of the limitations of earlier USB 1.1 devices.