Information Technology Reference
In-Depth Information
The ease of networking, even though it is a slow, peer-to-peer method, has both
helped and hurt Apple users. It has helped by making the network a quick and nat-
ural solution to data and print sharing that must have made IBM-style PC users envi-
ous (or at least confused). On the other hand, the relatively low speed and
proprietary nature of the native network, without expensive upgrade modules for
Ethernet or Token-Ring, initially put AppleTalk users at a comparative disadvantage.
The original LocalTalk connection used a cumbersome shielded cable, but then
Farallon Computing made a compatible adaptation called PhoneNet on twisted pair
wiring. This is the simple LocalTalk connection that most users are familiar with.
Many users employ standard telephone cord to connect devices. This telephone cord
is typically the flat silver-satin type 4-wire cable, although twisted-pair cable will
work even better. The network runs at only 230.4 kbps, so the normal crosstalk and
attenuation problems are not as severe. LocalTalk can operate well on TIA-568-C.
The same comments apply to potential wiring problems with LocalTalk that
were stated for any of the twisted-pair networks. Because LocalTalk can use ordi-
nary flat phone wire, many users will simply purchase preassembled cables, which
have few faults. However, this wiring method sometimes leads to long runs of wire
being routed around furniture and across traffic areas. Any abrasions or cuts in the
cable will have network consequences. Often a network must be split at some point
and terminated to diagnose such cable problems.
FDDI
Fiber Distributed Data Interface (FDDI) is a fiber-optic networking technology that
operates at 100 Mbps. It employs dual, counter-rotating, token-passing rings. The
network concept is actually fairly complex and is different from either Ethernet or
Token-Ring.
Network nodes that sit on the primary fiber ring are called
dual-attach nodes
and employ a sophisticated automatic wraparound of the FDDI signal in the event
of a cut in the ring. This is somewhat akin to the backup path in Token-Ring, but
the fiber in an FDDI ring is expected to take a diverse path to the next node in line.
In the event of a fiber cut or other failure, the dual-attach nodes at each end auto-
matically loop back and the network continues without the missing component.
Each dual-attach node has two dual fiber connectors for a total of four individual
fiber-optic connections. Each connector has a fiber input and output, but the FDDI signal
actually passes from one input, through the node processor, and out the opposite connec-
tor's output fiber onto the next node. This produces dual signals in opposite directions.
Another type of node, called a
single-attach node
, implements the basic FDDI
protocol, but attaches point-to-point in a star fashion to a concentrating node. This
