There are several methods used to transport digital files from
one site to another using one or more of the delivery systems described above.
The transfer methods include:
Modems: The function of a modem
is to convert the digital data produced on a computer into an analog signal
that can be transmitted over standard communication systems such as telephone
or cable. The data is received by a remote computer where a modem converts
the analog signal back into digital data that can be interpreted by the computer.
The name modem is short for MOdulator/DEModulator.
Telephone Modems: are one of the most popular means
of transferring data. Transmitting speeds are usually 28.8 kbps or 56.6
kbps.
Cable Modem: Also called broadband, cable modem
connection is always on or active, unlike a dial-up line to an ISP which
is connected only when the telephone modem is activated. It is capable of
transmitting digital files at speeds of 60 Mbps.
ADSL (Asymmetrical Digital Subscriber Line): Developed
by the communications industry, ADSL allows for the transfer of files up
to 6 Mbps in one direction while data can pass in the other direction at
a speed of 64Kbps.
ISDN (Integrated Services Digital Network):
There are two ISDN bandwidths, which use telephony as the method to deliver
the electronic files:
BRI (Basic Rate Interface): BRI is capable of handling
128 kbps.
PRI (Primary Rate Interface): PRI can handle up
to 1.544 Mbps.
T Lines: T lines offer a much more efficient method
of transporting files because of their high transmission speeds. They are
best suited for communications between two sites (LANs, WANs, Internet) that
are always transmitting large files back and forth.
T-1 Line: A T-1 line is a leased line which is capable
of transmitting 1,544,000 bits per second. At maximum capacity, a T-1 line
can transmit 1 Mb of information in just over five seconds.
T-3 Line: Like the T-1 line, the T-3 line is another
leased line connection, but it has a much higher transmission rate. It is
capable of moving data at a rate of 44,736,000 bits per second which is
the equivalent of 1 Mb of information in less than 1/5th of a second.
Ethernet: Used with LANs and WANs, an Ethernet is
a networking cabling system that transmits data at high speeds. LANs can be
interconnected using routers and bridges, but these can become bottlenecks
for the system as usage increases. The result is that the high transfer speeds
of the Ethernet can be compromised by the interconnecting points. LAN switches
can be used in place of the conventional interconnections to assist in relieving
the bottlenecks and increase the bandwidth.
Standard Ethernet: Transmits at 10 Mbps.
Fast Ethernet: Transmits at 100 Mbps.
Gigabit Ethernet: Transmits at 1 Gb (1,000 Mbps).
Fiber Optics: Systems using fiber optic cables are
replacing copper wire systems as a means of delivering communication signals
and transferring electronic files. Fiber optic systems use light pulses sent
through fiber lines rather than electronic pulses transmitted through standard
copper lines. Information from copper wires is brought into a transmitter
which converts the electronic pulses into the light pulses. A LED (Light Emitting
Diode) or ILD (Injection-Laser Diode) are used to generate the light pulses.
The translating or conversion points are the weak point in the system because
much of the speed gained with fiber optic cables can be lost when the light
pulses are converted to or from electronic pulses. LANs (Local Area Networks)
such as those found in large industrial facilities or local school systems
are excellent applications for fiber optic systems.
Store and Retrieve Systems: The sender transmits files
to an intermediate server site where it can be stored until the recipient
is ready to download the files on their computer. Storing the files at an
intermediate server site offers convenience for both the sender and the recipient
and allows a file to be downloaded by multiple recipients. The intermediate
site may have limits on the amount of time that a file can be stored before
the system is purged of older files.
Frame Relay Systems: A frame relay system is a closed
data network. Digital data is transferred between sites with dedicated lines.
The system offers high transmission speeds and a high degree of security which
are features that are important when files are frequently transferred between
specific sites.
Sneakernet: Sneakernet is a popular name for moving
data from one computer to another with the use of removable media such as
disks. Disks can be sent through the mail or shipped with an overnight service
to their destination if the transfer of the information is not immediately
required. There are several options for transferring files using removable
media:
Standard Floppy Disk: A standard floppy disk has
a capacity of only 1.44 Mb and may be useful for the smallest files, but
it is not very practical for larger that files that contain multiple images.
SyQuest® Cartridges: SyQuest® cartridges,
which were the standard in the 90's are now being replaced with alternative
methods with increased capacities. They have capacities of 40 Mb and 80
Mb.
Iomega® Zip® Disk: The Zip disks have become
very popular with their smaller physical size and larger capacity. Zip disks
are available in 100 MB and 250 Mb capacities.
Iomega® Jaz® Disks: Jaz® disks have
a capacity of 1 Gb or 2 Gb.
Imation SuperDisks™: The SuperDisk™ has
a capacity of 120 Mb.
You may need to change the method or methods of transfer periodically
due to changing technology and to accommodate customer needs.
More than one transfer method may be required for transmitting
a file. For example, a file may be sent on a T-1 line for rapid transfer to
a Local Area Network where it is shared and used by multiple computers within
the network.
