DA
Destination Address 
In an FDDI frame and token ring block, the station(s) for which the frame is intended. Addresses can be either 16 or 48 bits long. In an Ethernet packet, the field that consists of the first 6 bytes - 48 bits - of the packet following the preamble and start bit. 

DAC
Digital to Analog Converter

DAC
Dual-Attached Concentrator - FDDI 
A hub that is attached to both rings of an FDDI network or that offers a dual attachment to the FDDI network and is capable of accommodating a dual (primary and secondary counter-rotating) ring. 

DACL
Discretionary Access ControlList

DACS
Digital Access and Cross-connectSystem 
A digital switching device for routing and switching T1 lines among multiple T1 ports. It performs the functions of a normal "switch," except connections are typically set up in advance of the call, not with the call as in most low-bandwidth communications. 


DAEMON
Digital Access and Cross-connectSystem 
A digital switching device for routing and switching T1 lines among multiple T1 ports. It performs the functions of a normal "switch," except connections are typically set up in advance of the call, not with the call as in most low-bandwidth communications. 

DAP
Data Access Protocol

DAP
Directory Access Protocol - X.500

DARD
Dynamic Resource Allocation and Distribution

DARPA
Defense Advanced Research Projects Agency

DAS
Dual Attachment Station - An FDDI station that attaches to one or two higher-level concentrators in a dual homed configuration

DASD
Direct Access Storage Device

DCA
Data Communication Architecture

DCAP
Data Link Switching Client Access Protocol

DCC
Data Country Code - ATM

DCD
Data Carrier Detect. A hdw signal defined by RS-232-C that indicates that a modem is online and ready to transmit. 

D-Channel
Data Channel - ISDN 
The channel used for signaling data on an ISDN network.
Full-duplex, 16-Kbps - BRI - or 64-Kbps - PRI - ISDN channel.

DCE
A device that establishes and maintains a network interface session. DCE devices, such as modems, connect to data terminal equipment (DTE) devices, such as computers, using an RS-232 or CCITT V.24 standard interface

DCF
Data Composition Facilities

DDD
Direct Distance Dialing

DDI
Direct Dial In

DDR
Dial-on-Demand Routing - ISDN

DDRSDRAM

DDS
Dataphone Digital Service - AT&T ¨. A private line digital service with data rates to 56 Kb/s.

DE
Discard Eligibility 
- A bit indicating that a frame may be discarded in preference to other frames if congestion occurs to maintain the committed information rate. 
- The bit that is relevant in situations of high congestion, and indicates that the frame should be discarded in preference to other frames without the DE bit set. The DE may be set by the network or by the user; and once set can never be reset by the network. 

DECT
Digital Enhanced Cordless Telecommunications 
á DECT will evolve to 115 Kbps
á Then DECT will be merged with the GSM in the UMTS - Universal Mobile Telecommunication System. 
Norm : 802.11 Bandwidth: 1880 Mhz Voice is compressed at 32 Kbps 50 Meters inside building / up to 500 meters outside 

DFC
Data Flow Control

DFT
Distributed Functional Terminal - IBM¨. A 3270 hw/sw protocol used for communication between a terminal and a 3270 control unit that allows multiple concurrent logical terminal sessions.

DHCP
Dynamic Host Configuration Protocol - Ethernet protocol used in heterogeneous networks.

DID
Direct Inward Dial - Allows a user outside a company to dial an internal extension number without needing to pass through an operator or attendant. The dialed digits are passed to the PBX, which then completes the call.

DIN
Deutsche Industrie Norm connector

DISC
Disconnect

Distance Vector Protocol
A routing protocol that defines the best direct route between a source and its destination, in terms of the number of routing hops, regardless of speed. Routing Information Protocol - RIP - is an example of a distance vector protocol.

DIT
Directory Information Tree - X.500

DLC
Data Link Control. Based on the IEEE 802.2 standard. DLC is used for LAN PC-mainframe communications through a TIC. In SNA, the protocol stack layer that transmit messages across links and manages link-level flow and error recovery.

DLCI
Data Link Connection Identifier 
Frame Relay. Also used in a GSM network
A unique number assigned to a PVC end point in a frame relay network. 
Virtual Channel used in Frame Relay connection. 
A device designating a path between a source and its destination. Data link control interface. 

DLCMI
Data Link Control Management Interface

DLL
Data Link Layer 
Layer 2 of the OSI reference model, responsible for data transfer across a single physical connection or series of bridged connections between two network entities. Defines protocols governing the creation of data packets and transmission into and out of each node. Includes the logical link control - LLC - and media access control - MAC - sub-layers. 

DLSw
Data-Link Switching - RFC 1434 
SNA and NetBIOS traffic over TCP/IP networks using data-link layer switching and encapsulation.

DLSw +
Data-Link Switching Plus - Cisco ¨

DLU
Dependent Logical Unit - SNA / SSCP

DMI
Digital Multiplexed Interface - AT&T ¨

DMP
Data Movement Processor - Cisco ¨

DMT
Discrete Multi-Tone 

DMTF
Distributed Management Task Force. An industry consortium developing, supporting and maintaining industry standards for PC management.

DN
Distinguished Name - X.500. A collection of attributes, referring to an LDAP directory entry.

DNIC
Data Network Identification Code - CCITT

DNIS
Dial Number Id Service. A call association/processing application that informs the service operator of the telephone number the caller dialed. 

DNS
Domain Name Server. Addressing system that incorporates the domain name into the IP address.

DoD - ARPA
Department of Defense's Advanced Research Project Agency 

DOD
Direct Outward Dial - IP Telephony

DOM
Document Access Model - API which allows the manipulation of documents - XML

DOR
Dial Optimized Routing

DoS
Denial of Services

DOS
Disk Operating System

DPCM
Differential Pulse-Code Modulation

DPLL
Digital Phase-Locked Loop

DPNSS
Digital Private Network Signaling System

DPS
D Channel Packet-Switched

DPSK
Differential Phase Shift Keying

DQDB
Distributed Queue Dual Bus - IEEE 802.6 - MAN

DR
Disconnect Request

DS
Direct Spreads - also called WCDMA

DS-0
Digital service, level 0. Common carrier digital transmission service at 64 Kb/s. 

DS-1
Digital service, level 1. Multiplexed Telephone Signal - 1.544 Mbit/s also known as T1.

DS-3
Digital service, level b. Multiplexed Telephone Signal - 44.736 Mbit/s also known as T3.

DSAP
Destination Service Access Point - IEEE 802 
An internal address of a specific software entity to which data must be delivered when it arrives at its destination, according to the IEEE 802.3 LLC - Logical Link Control - standard. This information may be included in the data field of an 802.3 transmission frame

DSE
Data Switch Equipment

DSL
Digital Subscriber Line. Modems on either end of a single twisted pair wire that delivers ISDN Basic Rate Access. 

DSLAM
Digital Subscriber Line Access Multiple

DSLIC
Digital Subscriber Line Interface Circuit 

DSN
Delivery Status Notification. 

DSP
Digital Signal Processor

DSPU
Down Stream Physical Unit - The DSPU uses an intermediary SNAª device to communicate with the host.

DSR
Data Set Ready - Modem

DSRS
Data Signal Rate Selector

DSSS
Direct Sequence Spread Sequence
Wireless network. Data transfer secured. Better than FHSS.

DSU
Digital Service Unit 
Device between a DTE and a numeric device. usually via a CSU.
Converts an RS-232 interface.
A device connecting data terminal equipment (DTE) to digital communication lines that ensures that data to be transmitted across the network is formatted correctly. 

DSX
Digital System Cross-Connect switch. T1

DTE
Data Terminal Equipment. Equipment that is a source or destination of transmitted data.

DTM
Dynamic Synchronous Transfer Mode - Net Insight ¨ 

DTMF
Dual Tone Multi Frequency
Norm Q23 
Each number is generating two frequencies. A low then a high frequency.

DTR
Data Terminal Ready - Modem

DVM
Data/Voice Multiplexer

DVMRP
Distance Vector Multicast Routing Protocol 
A protocol in the IP suite that allows a router to advertise shortest-path routes to multicasting source networks - networks containing hosts with the capability of issuing multicast datagrams-. Each multicasting router periodically issues routing information on each DVMRP circuit, which represents the sum of the hop metrics along the shortest path from the router to the given source network. 

DWDM
Dense Wavelength Division Multiplexing 
DWDM multiplexes the length of the waves on a same optical fiber. It uses the technology EDBFA : Erbium Doped Fiber Amplifiers.

There are several standards : 
OC-48 - 2.4 Gbps
40 channels = 100 GBps
96 channels = 240 GBps

OC-192 - 10 GBps
16 channels = 160 GBps
40 channels = 400 GBps
80 channels = 800 GBps 
128 channels = 1280 GBps 

OC-768 - 40 GBps 
16 channels = 640 GBps 
40 channels = 1600 GBps 

The bandwidth forecasted in 2001 99.8 terabits/second You can use wavelength router for that technology. Cisco has a protocol called Wavelength Forwarding Optical Transport Domain. The capacity increases by adding a wavelength.

DWORD
A data type composed of hexadecimal data with a max. allotted space of 4 bytes.

DXI
Data Exchange Interface - ATM - RFC 1483