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Physical Planning Considerations
5
Data Transmission
McDATA Products in a SAN Environment - Planning Manual
5-4
Consider the following when determining the number and type of
transceivers to use:
•
Distance between a director or fabric switch and the attached
Fibre Channel device or between fabric elements communicating
through an ISL.
•
Cost effectiveness.
•
Device restrictions or requirements with respect to existing
fiber-optic (multimode or singlemode) or copper cable.
Data transmission distance is a factor governing the choice of
Distance
transceiver type, fiber-optic cable type, and transmission rate. When
using multimode cable, if the core diameter or data transmission rate
increases, the data transmission distance decreases.
Link budget is another governing factor. A link budget is the
attenuation (in dB) a connection between devices can sustain before
significant link errors or loss of signal occur. When using multimode
cable, if the core diameter or data transmission rate increases, the link
budget decreases.
Cable-conversion, repeater, patch-panel, or other connections within
a link also decrease the link budget. Each connection introduces a
nominal signal loss of at least one dB through the link. Patch panel
connections (with one connection at each side of the panel) typically
introduce a two dB signal loss through a link.
Other variables such as the grade of fiber-optic cable, device
restrictions, application restrictions, buffer-to-buffer credit limits, and
performance requirements can also affect data transmission distance
and link budget.
Table 5-1
lists unrepeated data transmission distance and link budget
as a function of fiber-optic cable type and data transmission rate.
When using multimode cable, note the decrease in performance as
the cable core diameter or data transmission rate increases. When
using singlemode cable, performance is a function of transceiver
type. Data transmission distance and link budget are not affected by
data transmission rate.
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