User's Guide for ZyXEL Omni 56K USB Modem
Cdecisive for the quality and the speed of a modem's transfer capabilities.
DCD Data Carrier Detected – a control signal line of the RS-232C interface.
DCE Data Communications Equipment is typically a modem or other type of communication
device. The DCE sits between the DTE (data terminal equipment) and a transmission
circuit such as a phone line.
Decryption The act of restoring an encrypted file to its original state.
Demodulation Transferring analog signals into digital data bits.
Denial of Service Act of preventing customers, users, clients or other machines from accessing data on a
computer. This is usually accomplished by interrupting or overwhelming the computer with
bad or excessive information requests.
Digital The use of a binary code to represent information, such as 0/1, or on/off.
Digital Loopback
Test A modem test procedure that transfers the received digital data back to the modulator and
transmits them out.
Digital Signature Digital code that authenticates whomever signed the document or software. Software,
messages, Email, and other electronic documents can be signed electronically so that they
cannot be altered by anyone else. If someone alters a signed document, the signature is no
longer valid. Digital signatures are created when someone generates a hash from a message,
then encrypts and sends both the hash and the message to the intended recipient. The
recipient decrypts the hash and original message, makes a new hash on the message itself,
and compares the new hash with the old one. If the hashes are the same, the recipient
knows that the message has not been changed. Also see Public-key encryption.
DIP Switch Dual inline package switch. DIP switches are abundant in the world of electronic
equipment. They are used to set certain parameters on a printer, modem or other peripheral
devices. No DIP switches can be found in ZyXEL modems. ZyXEL modems let you
perform all settings from the front panel or through command sequences.
DLE The ASCII code that is used in voice data mode to separate data segments from command
segments.
DRAM Dynamic RAM that stores information in capacitors that must be refreshed periodically.
DSL Digital Subscriber Line technologies enhances the data capacity of the existing twisted-pair
wire that runs between the local telephone company switching offices and most homes and
offices. There are actually seven types of DSL service, ranging in speeds from 16 Kbits/sec
to 52 Mbits/sec. The services are either symmetrical (traffic flows at the same speed in both
directions), or asymmetrical (the downstream capacity is higher than the upstream
capacity). DSL connections are point-to-point dedicated circuits, meaning that they are
always connected. There is no dial-up. There is also no switching, which means that the
line is a direct connection into the carrier’s frame relay, ATM (Asynchronous Transfer
Mode), or Internet-connect system.
DSP Digital signal processor. ZyXEL modems are equipped with this/these device(s). DSPs
generate, process and analyze all signals.
DSLAM A Digital Subscriber Line Access Multiplexer (DSLAM) is a network device, usually at a
telephone company central office, that receives signals from multiple customer Digital
Subscriber Line connections and puts the signals on a high-speed backbone line using
multiplexing techniques. Depending on the product, DSLAM multiplexers connect DSL