A short haul modem is a device that provides local communication between the datalogger and a computer with an RS-232 serial port. It transmits data up to 6.5 miles over a four-wire unconditioned line (two twisted pairs).
Answer option B is incorrect. An optical modem is a device that is used for converting a computer's electronic signals into optical signals for transmission over optical fiber. It also converts optical signals from an optical fiber cable back into electronic signals. It provides higher data transmission rates because it uses extremely high capacity of the optical fiber cable for transmitting data.
Answer option C is incorrect. An acoustic modem provides wireless communication under water. The optimum performance of a wireless acoustic modem system depends upon the speed of sound, water depth, existence of thermocline zones, ambient noise, and seasonal change.
Answer option A is incorrect. A controllerless modem is a hardware-based modem that does not have the physical communications port controller circuitry. It is also known as WinModem or software modem. A controllerless modem is very inexpensive and can easily be upgraded with new software.

A global area network (GAN) is a network that is used for supporting mobile communications across an
arbitrary number of wireless LANs, satellite coverage areas, etc. The key challenge in mobile communications
is handing off the user communications from one local coverage area to the next.
Answer option B is incorrect. A wide area network (WAN) is a geographically dispersed telecommunications
network. The term distinguishes a broader telecommunication structure from a local area network (LAN). A
wide area network may be privately owned or rented, but the term usually connotes the inclusion of public
(shared user) networks. An intermediate form of network in terms of geography is a metropolitan area network
(MAN). A wide area network is also defined as a network of networks, as it interconnects LANs over a wide
geographical area.
Answer option D is incorrect. A home area network (HAN) is a residential LAN that is used for communication
between digital devices typically deployed in the home, usually a small number of personal computers and
accessories, such as printers and mobile computing devices.
Answer option A is incorrect. The Local Area Network (LAN) is a group of computers connected within a
restricted geographic area, such as residence, educational institute, research lab, and various other
organizations. It allows the users to share files and services, and is commonly used for intra-office
communication. The LAN has connections with other LANs via leased lines, leased services, or by tunneling
across the Internet using the virtual private network technologies.