Sun Microsystems 1.0 - Manual (Page 50)

24 SunFDDI/P 1.0 Adapter User’s Guide—May 1997
4
High Performance FDDI Networks
FDDI networks increase the potential to carry more information, rather than
create faster connections. If the applications running over the network do not
use the available bandwidth efficiently, you will not see much improvement in
the performance of your network by using FDDI.
You can obtain optimum performance by balancing the complementary
objectives of maximum throughput and minimum access delay:
•
Throughput is a measure of the ring use. Network efficiency is defined as
the ratio of actual throughput to theoretical maximum bandwidth (100
Mbps).
•
Access Delay is the time a station waits before it can transmit on the
network. This is largely dependent on how fast the permission token rotates
around the ring.
For some applications (for example, bulk data transfers), throughput is critical;
other applications (for example, voice or video applications) are more sensitive
to access delay.
Ring Latency Improvement
The ring latency is the physical delay inherent in the FDDI network. It is
dependent on the number of stations in the ring and the overall length of the
ring. The speed of the microprocessor in the FDDI station also has a significant
effect on ring latency.
The FDDI specifications define a network that supports up to one thousand
physical connections with a total ring length of 200 km (100 km per ring in a
dual-ring topology). There are two physical connections for each dual-attached
station; therefore, in theory, up to five hundred dual-attached stations could be
connected in a single ring. In reality, optimum performance is obtained by
limiting the number of connections to less than one hundred stations in an
unsegmented ring.
Performance improvements are possible by changing the topology of the
network, trading off the total number of stations in comparison to the overall
length of the ring, and selecting faster machines to act as FDDI stations.
However, these modifications are rarely practical in an established network.