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D

Data Encryption Standard (DES)

Encryption is the process of encoding an information bit stream to secure the data content. The DES algorithm is a common, simple and well-established encryption routine. An encryption key of 56 bits is used to encrypt the packet. The receiver must use the exact same key to decrypt the packet. Otherwise, garbled data will be produced.

Data Mode

In modems and many wireless radios, Data mode is a mode of operation through which connected modems exchange the content of their message. This is the primary mode of operation. When the string "O" is passed to the radio, it enters Data mode. Command mode is initiated when the string "AT+++" is sent to the wireless radio, from which point instructions are issued in the form of AT commands.

Command mode is used to initiate connections and alter the settings for those connections, while Data mode is dedicated to the information that two connected radios are exchanging. Command mode is roughly analogous to dialing a phone number, while Data mode is roughly analogous to a conversation between two people once one successfully calls the other.

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Data Rate

Data rate indicates the speed at which information is sent, expressed in bits per second (bps). Data rate applies to everything that is sent, both overhead (headers) and payload (data).

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DCE

Data Communication Equipment. Hardware devices that set up and manage data exchange, connecting the circuit between data source and destination. A modem is a kind of DCE.

Declaration of Conformity

In order for a product to be exported to Europe, the product needs a Declaration of Conformity (DoC). The EC DoC should contain all relevant information to identify the following:

  • The name and address of the manufacturer or authorized representative that is issuing the DoC.
  • The product name, type or model number, and any relevant supplementary information.
  • All relevant provisions with which the product complies.
  • The reference standards or other normative documents.
  • All supplementary information, as needed.
  • Date of issue of the declaration.
  • Signature and title (or an equivalent marking) of an authorized person.
  • The statement that the declaration is issued under the sole responsibility of the manufacturer and, if applicable, the authorized representative.

Delayed Data Response

As a PS-poll procedure, the station must transition to the active state until receiving a downlink frame from the access point. See Power Save Polling for more information.

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Device Name

See Client Name.

DFS

DFS (Dynamic Frequency Selection) refers to a section of the 802.11h specification that allows unlicensed Wi-Fi devices to operate in 5 GHz frequency bands shared with with existing weather and military radar systems. Although wireless infrastructure can detect the presence of radar, wireless clients cannot. Because of this, wireless clients must first passively scan DFS channels to detect whether or not beacons are heard on that particular channel. Once beacons are detected, the client is allowed to actively scan on that channel. If the access point detects radar, the client must move to an alternate channel designated by the access point.

For more information on DFS, refer to the Optimizing Operation at 5 GHz white paper which can be found here.

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DFS Channels (SCU Global Setting)

DFS Channels is an SCU Global setting that indicates support (or lack of support) for 5 GHz (802.11a) channels where dynamic frequency selection (DFS) is required. This setting is supported in v2.0 and later. DFS Channels options include:

  • On - Turns on support for 5 GHz channels where DFS is required.
  • Off - Turns off support for 5 GHz channels where DFS is required.
  • Optimized - When set to Optimized and scanning for the first time, the radio scans all active channels and all available DFS channels. From this scan, the radio creates and maintains a list of up to three DFS channels where beacons were detected. During subsequent scans, the radio still scans all active channels but only scans the DFS channels listed from the first scan (where beacons were detected).

When the radio loses or resets the connection, the radio returns to scanning all available DFS channels as it did when scanning for the first time after being set to Optimized. From this scan, the radio again creates a list of DFS channels where beacons were detected.

Note: The Optimized setting is not supported in the MSD30AG and SSD30AG radios. If DFS Channels is set to Optimized directly in the registry, the setting will function as On (versus Optimized).

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DFS Scan Time (SCU Global Setting)

Because passive scanning consumes a longer period of time, DFS Scan Time (an SCU Global setting) enables you to determine the dwell (listen) time (in milliseconds or ms) when passively scanning on a DFS channel.

Note: When decreasing the scan time (to a value lower than the default) for DFS channels, corresponding changes in the infrastructure's beacon period are recommended. For optimal performance and reliability, Laird recommends a dwell time that is 1.5 times that of the beacon period. For example, if the DFS scan time is set to 30 ms, the beacon period should be adjusted to 20 ms.

Note: If you adjust this parameter directly in the registry, and configure it to a number outside of the 20-500 ms range, the setting value will return to the default (120 ms).

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DHCP

DHCP (Domain Host Configuration Protocol) is a protocol for dynamically assigning IP addresses to network computers. With DHCP, a computer can automatically be given a unique IP address (selected from a master list by the DHCP server) each time the computer connects to the network.

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Diagnostics (SCU Diags window)

From the SCU Diags window, Diagnostics allows you to attempt to (re)connect to an access point and provide a more thorough dump of data than is obtained with (Re)connect. The dump includes radio state, profile settings, global settings, and an SSID list of access points in the area.

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Diagnostics Window - SCU

The Diagnostics window of the SCU provides status information about the Wi-Fi and Bluetooth radio, as well as testing and debug options. The Diagnostics window is a feature of SCU versions 4.0 and later.

The following features are accessible from the Diagnostics Window:

  • Status Icons
  • About SCU
  • Advanced
    • Status
    • Ping Tools
    • Debug

Diags Window - SCU

The Diags windows enables you to troubleshoot connection issues with SCU. The following properties and options are available from the Diags window:

Dipole

An antenna consisting of two metal conductors (such as a rod or wire) positioned side by side. Voltage is applied between the two conductors at the center.

Directional Antenna

An antenna which uses a narrow field of transmission in order to radiate more effectively in one direction, boosting transmission and reception.

Driver

Software that controls the operation of hardware in a host machine. Drivers communicate software instructions over the interface to the hardware, translating and regulating the device’s behaviour.

Driver (SCU Main window)

Driver is an SCU Main window parameter that indicates the current version of the device driver.

DSSS

Direct-sequence spread spectrum (DSSS) is a modulation technique that disperses the data frame signal over a relatively wide portion of the frequency band. This technique creates greater immunity to RF interference. This method is used by the IEEE 802.11b specification.

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DTE

Data Terminal Equipment. Device which controls communication channels and is the destination and source of data. A computer is a DTE.

DTIM

A DTIM (delivery traffic indication map) is a signal sent (as part of a beacon) by an access point to a station device in sleep mode. This signal alerts the device to a packet that is awaiting delivery.

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DTIM Interval

The DTIM interval is the interval at which the DTIM appears in beacons.For example, if the DTIM interval is set to 2, every second beacon will have the map. If the beacon period is 100 ms (with the DTIM interval set at 2), the DTIM will transmit every second beacon or five times per second.

The DTIM interval feature allows a power-saving station to only wake up at the appropriate time for data. The higher the DTIM interval, the longer the station can sleep.

Note: The ideal DTIM interval setting is a balance between throughput and power savings. A lower DTIM interval in higher throughput but shorter batter life.

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DUT

Device Under Test; refers to a manufactured product undergoing testing.