The following criteria were applied in defining the architecture for the Universal Serial Bus.

1.Ease of use for PC peripheral expansion

2. Low-cost solution that supports transfer rates up to 12 Mbs.

3. Full support for the reat-time data for voice, audio, and compressed video.

4.Protocol flexibility for mixed-mode isochronous data transfers and asynchronous messaging.

5. Integration in commodity device technology.

6.Comprehend various PC configurations and form factors.

7.Provide a standard interface capable of quick diffusion into product

8.Enable new classes of devices that augment the PC’s capability.

1394-1995 is an IEEE designation for a high performance serial bus. This serial bus defines both a backplane physical layer and a point-to-point cable –connected virtual bus. The backplane version operates at 12.5, 25 or 50 Mbits/sec, whereas the cable version supports data rates of 100, 200 and 400 Mbits sec across the cable medium support in the current standard.

The primary application of the cable version is the integration of I/O connectivity at the back panel of personal computers using a low-cost, scalable , high-speed serial interface. The 1394 standard also provides new services such as realtime I/O and live connect/disconnect capability for external devices including disk drivers, printer, and hand-held peripheral such as scanner and cameras.

The need for 1394 and other next-generation network topologies and protocols is driven by the rapidly growing need for mass information transfer. Typicalk LANs and WANs simply cannot provide cost-effective connection capabilities nor do they easilysupport guaranteed bandwidth for “mission critical”applications. Additionally, parallel high-speed communications such as SCSI are not suited to long distances and do not support live connect/disconnect, making reconfiguration time-consuming. Other factors driving next generation protocols such as 1394 include the need for reliability, durability and universal interconnection.

IEEE 1394 is a video-speed serial interconnect that is now an IEEE standard. Like USB, 1394 enable plug-and-play peripheral connectivity, provides power to peripherals helping to eliminate each one having its own power supply, and supports isochronous data transfer. 1394, however, takes these capabilities to video speeds. USB and 1394 serve different needs which will coexist for the foreseeable further. Peripherals that do not require the high data transfer rates possible with 1394 will remain with USB. Eventually, PCs will need only USB and 1394 serial ports to handle all external I/O, dramatically simplifying life for PC users.

The topology of 1394 is shown in figure below. Any device can be connected to any other device, so long as there are no loops. A 1394 network can support up to 63 devices, The devices can be hot swapped. If a device is added or removed, the bus will reset, reconfigure, and resume operation as two independent busses. 1394 also offers peer-to-peer connectivity, so peripherals can talk to one another without intervention from the PC.

USB has what is known as a star-tiered topology shown in below.The PC acts as the host. Each device is connected to a hub, which provides sockets and power and acts as a reperter. Hubscan be either self-powered or bus powered. They can also be cascaded. The USB topology supports up to 127 devices.

USB offers speeds ranging from 1 Mbits per secondto 12 Mbits per second.1394-1995 offers speeds starting at 100 Mbits per second and defining going up to 400 Mbits per second. P1394b will start at 800 Mbits per second and is defining speeds of up to 3200 Mbits per second.

As mentioned previously, 1394 and USB are complimentary technologies. USB is a medium bandwidth connection for telephony products, digital still cameras, monitors, keyboards, mice, and other similar I/O devices. 1394 is a high-speed bus designed for digital video cameras, DVD players, mass storage devices, and other peripherals that require greater bandwidth.

USB is a very low-cost interconnect technology. Low-speed USB implementations for devices such as mice and keyboard typically cost less than $1 in OEM quantities, and even the medium-speed implementations for devices like scanners and modems are in the $1-2 range in OEM quantities. Due to relatively lower volumes and higher complexity, 1394 implementations are currently in the $15 range. This cost is expected to decrease as volume builds over the next few years.

Tomorrow’s PC will have need for low-cost, low-bandwidth devices like mice, keyboards, and modems. USB provides a good fit for these devices. Tomorrow’s PC will also need a high-speed interface for connecting to high-speed printer, hard drivers, and camcorders. 1394 is the technology that will allow these devices to interoperate with the PC. Both USB and 1394 will coexist on further PC platform to meet a wide range of growing peripheral interconnectivity needs.