and capacity issues are determined by a multitude of factors. Some are
within your control, some are not. As with so many other performance issues,
avoidance of bottlenecks is an important objective. Network transmission
is governed by the slowest link. Factors affecting network delivery include:
Carrying capacity (bandwidth) of the local area network
Bandwidth of the institution's Internet connection
Speed and capacity of the network server
Read speed and data transfer rate of storage devices
Image file size
User demand at any particular time
Amount of competing network traffic (at all network levels)
Speed of any "on-the-fly" processing steps
Time required for authentication and other security checks
Capabilities of the end user's computer, including:
Video subsystem performance
Speed of Internet connection
are a variety of network technologies that might be encountered between
an image server and the ultimate recipient. The following table presents
some of the more important ones, in declining order by speed, in MB/second.
Network Data Transfer Rates
fastest of these networks are used only for major Internet backbones.
The next tier are local area networks, while the slowest are consumer
services. The speeds given are theoretical maximums, which are rarely,
if ever, encountered in real installations. Note that the fastest network
is more than 175,000 times faster than the slowest.
one knows the transmission speed of a network it is possible to compute
the approximate time it will take a file of any particular size to make
its way across. Use this formula:
on Transmission Speed t
(time in seconds) = number of megabytes in file ÷ (transmission
speed (in MB/sec) x .8)
A 1 MB file can theoretically make it across a 10BaseT Ethernet network
in 1 / (1.25 x .8) = 1 second. The .8 takes into account that 80%
of rated speed is about the best one can expect to realistically encounter.
Since most networks share bandwidth amongst users, the more traffic
they handle, the lower the overall transmission speed. When saturated,
performance can fall dramatically.