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Definition
FireWire, originally developed by Apple Computer, Inc is a cross platform
implementation of the high speed serial data bus -define by the IEEE 1394-1995
[FireWire 400],IEEE 1394a-2000 [FireWire 800] and IEEE 1394b standards-that move
large amounts of data between computers and peripheral devices. Its features simplified
cabling, hot swapping and transfer speeds of up to 800 megabits per second. FireWire
is a high-speed serial input/output (I/O) technology for connecting peripheral
devices to a computer or to each other. It is one of the fastest peripheral standards
ever developed and now, at 800 megabits per second (Mbps), its even faster . Based
on Apple-developed technology, FireWire was adopted in 1995 as an official industry
standard (IEEE 1394) for cross-platform peripheral connectivity. By providing
a high-bandwidth, easy-to-use I/O technology, FireWire inspired a new generation
of consumer electronics devices from many companies, including Canon, Epson, HP,
Iomega, JVC, LaCie, Maxtor, Mitsubishi, Matsushita (Panasonic), Pioneer, Samsung,
Sony and FireWire has also been a boon to professional users because of the high-speed
connectivity it has brought to audio and video production systems. In
2001, the Academy of Television Arts & Sciences presented Apple with an Emmy
award in recognition of the contributions made by FireWire to the television industry.
Now FireWire 800, the next generation of FireWire technology, promises to spur
the development of more innovative high-performance devices and applications.
This technology brief describes the advantages of FireWire 800 and some of the
applications for which it is ideally suited.
TOPOLOGY
The 1394 protocol is a peer-to-peer network with a point-to-point signaling environment.
Nodes on the bus may have several ports on them. Each of these ports acts as a
repeater, retransmitting any packets received by other ports within the node.
Figure 1 shows what a typical consumer may have attached to their 1394 bus. Because
1394 is a peer-to-peer protocol, a specific host isn't required, such as the PC
in USB. In Figure 1, the digital camera could easily stream data to both the digital
VCR and the DVD-RAM without any assistance from other devices on the bus
FireWire
uses 64-bit fixed addressing, based on the IEEE 1212 standard. There are three
parts to each packet of information sent by a device over FireWire:
"
A 10-bit bus ID that is used to determine which FireWire bus the data came from
" A 6-bit physical ID that identifies which device on the bus sent the
data
" A 48-bit storage area that is capable of addressing 256 terabytes
of information for each node!
The
bus ID and physical ID together comprise the 16-bit node ID, which allows for
64,000 nodes on a system. Individual FireWire cables can run as long as 4.5 meters.
Data can be sent through up to 16 hops for a total maximum distance of 72 meters.
Hops occur when devices are daisy-chained together. Look at the example below.
The camcorder is connected to the external hard drive connected to Computer A.
Computer A is connected to Computer B, which in turn is connected to Computer
C. It takes four hops for Computer C to access camera.
The 1394 protocol supports
both asynchronous and isochronous data transfers.
Isochronous
transfers:
Isochronous transfers are always broadcast in a one-to-one or one-to-many fashion.
No error correction or retransmission is available for isochronous transfers.
Up to 80% of the available bus bandwidth can be used for isochronous transfers.
Asynchronous transfers: Asynchronous transfers are targeted to a specific
node with an explicit address. They are not guaranteed a specific amount of bandwidth
on the bus, but they are guaranteed a fair shot at gaining access to the bus when
asynchronous transfers are permitted. This allows error-checking and retransmission
mechanisms to take place. <<back |