Information Technology Reference
In-Depth Information
9.3.1 Topology
There are two bus categories:
•
Cable
. This is a bus which connects external devices via a cable, The cable environment
is a non-cyclic network with finite branches consisting of bus bridges and nodes (cable
devices). Non-cyclic networks contain no loops and results in a tree topology, with de-
vices daisy-chained and branched (where more than one device branch is connected to a
device). Figure 9.1 shows an example of an IEEE-1394 Splitter which has three branches
and the telephone is daisy-chained from the digital camera.
The finite branches restriction imposes a limit of 16 cable hops between nodes. There-
fore branching should be used to take advantage of the maximum number of nodes on a
bus. 6-bit node addressing allows up to 63 nodes on each bus, while 10-bit bus address-
ing allows up to 1023 buses, interconnected using IEEE-1394 bridges. Devices on the
bus are identified by node IDs. Configuration of the node IDs is performed by the self ID
and tree ID processes after every bus reset. This happens every time a device is added to
or removed from the bus, and is invisible to the user.
A final restriction is that, using standard cables, the length between nodes is limited to
4.5 m. This can be increased by adding repeaters between nodes, but lengths are expected
to improve as work on the standard ensues. Although a PC is shown in Figure 9.1, a
principal advantage of IEEE-1394 is that, unlike USB, no PC is actually required to form
a bus, and devices can talk to each other without intervention from a computer.
•
Backplane
. This type is an internal bus. An internal IEEE-1394 device can be used
alone, or incorporated into another backplane bus. For example, two pins are reserved
for a serial bus by various ANSI and IEEE bus standards. Implementation of the back-
plane specification lags the development of the cable environment, but one could image
internal IEEE-1394 hard disks in one computer being directly accessed by another
IEEE-1394 connected computer.
Printer
Printer
IEEE-1394
splitter
IEEE-1394
Splitter
TV/Stereo
TV/Stereo
PC
Digital
Camera
PC
Digital
Camera
DVD
Telephone
DVD
Telephone
Figure 9.1
IEEE-1394 topology example
