UFC 4-021-02NF
27 September 2006
change 1, 23 October 2006
6-7.1.2.1 Single-Mode. Light travels through the inner core of the fiber only. Single-
mode allows long distance information transfer up to 100 miles. Single-mode requires
use of laser transmitter source that adds to the cost. Refer to Figure 6-4.
6-7.1.2.2 Multi-Mode. In multi-mode configuration, light travels through the inner and
outer core paths. Multi-mode is recommended for most applications less than three to
four miles. Refer to Figure 6-5.
Figure 6-4. Single-Mode Fiber Optic
Figure 6-5. Multi-Mode Fiber Optic
6-7.2
Direct Subscriber Lines (T-1 Lines). Direct subscriber lines, also called T-1
lines, are commonly used in data transmission media systems for connecting remote
sites. T-1/DS1 lines are permanent point-to-point links through public networks. The
bandwidth capacity of a T-1 line is 1.544 Mbps. The cost of the leased line is dependent
on distance and existing capacity or infrastructure. T-1 lines are uniquely assigned to a
customer, such that only the DoD information would be transmitted over the assigned
conductors (typically fiber optic).
6-7.3
Wireless. For security reasons, only use wireless if other media cannot be
used. Wireless broadband networks make use of radio frequency transmission between
towers. Wireless systems have high data transmission rates and do not require
installation of cable, nor rely on existing copper infrastructure. Wireless communications
are affected by line-of-sight topography and extreme weather conditions (such as rain,
snow, or fog). Security can be achieved by vendor encryption and decryption at each
node. The design and cost estimate must consider equipment and software for
equipment and software for authentication servers and encryption systems. Some radio
modem units can provide data transmission rates of several megabits per second - at
ranges up to ten or more miles between modems. One disadvantage of wireless
systems is the systems are susceptible to jamming.
6-7.3.1 Frequency Allocation. Frequency allocation or radio frequency spectrum
planning is a critical issue and in some areas of the world a show-stopper. Because a
frequency is allocated on a near-by base does not mean it will be authorized for the
facility in question. Frequency allocation is a long lead-time item. Employment of radio
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