DAD

Disciplined agile delivery (DAD) is a process decision framework that enables simplified process decisions around incremental and iterative solution delivery. DAD builds on the many practices espoused by advocates of agile software development, including Scrum, agile modeling, lean software development, and others.
 
The primary reference for disciplined agile delivery is the book of same name, written by Scott Ambler and Mark Lines.
 
In particular, DAD has been identified as a means of moving beyond Scrum. According to Cutter Senior Consultant Bhuvan Unhelkar, "The DAD framework provides a carefully constructed mechanism that not only streamlines IT work, but more importantly, enables scaling." Paul Gorans and Philippe Kruchten call for more discipline in implementation of agile approaches and indicate that DAD, as an example framework, is "a hybrid agile approach to enterprise IT solution delivery that provides a solid foundation from which to scale.

Daily Meeting

The daily meeting is one of the most commonly practiced Agile techniques and presents opportunity for a team to get together on a regular basis to coordinate their activities.

Daily Scrum

Stand-up team meeting. A plan, do, review daily session.

Dark Fibre

A dark fibre or unlit fibre is an unused optical fibre, available for use in fibre-optic communication.
 
The term dark fibre was originally used when referring to the potential network capacity of telecommunication infrastructure, but now also refers to the increasingly common practice of leasing fibre optic cables from a network service provider, or, generally, to the fibre installations not owned or controlled by traditional carriers. In common vernacular, dark fibre may sometimes still be called "dark" if it has been lit by a fibre lessee and not the cable's owner.
 
A dark fibre network or simply dark network is a privately operated optical fiber network that is run directly by its operator over dark fibre leased or purchased from another supplier. This is in contrast to purchasing bandwidth or leased line capacity on an existing network. Dark fibre networks may be used for private networking, or as Internet access or infrastructure.

DASS1

Digital Access Signalling System 1 (DASS1) is a proprietary protocol defined by British Telecom to provide ISDN services in the United Kingdom. It is now obsolete, having been replaced by DASS2. This too will become obsolete over the coming years as Q.931, a European standard, becomes widely adopted in the EU.

DASS2

Digital Access Signalling System 2 (DASS2) is an obsolescent protocol defined by British Telecom for digital links to PSTN based on ISDN. Although still available on request, it has been superseded by ETS 300 102 ("EuroISDN").
 
DASS2 is an improved version over DASS1, based on experiences with DPNSS.
 
In the UK, the ISDN concept was first introduced to customers by BT with their DASS2 connections. DASS2 (Digital Access Signalling System) is a BT-designed signalling standard, and was introduced before the Q.931 standard was finalised by the international community. British Telecom used the term ISDN when describing their DASS2 lines.
 
DASS2 lines are provided to customers on a 2Mbit/s link and can handle 30 simultaneous calls (64kbit/s each). DASS2 is still offered by BT and other UK carriers. Q.931 is the name of the CCITT document that describes the agreed signalling format for International ISDN. CCITT had previously been known as International Telegraph and Telephone Consultative Committee. The organisation set out the internationally agreed standards for telecommunications, and subsequently evolved into the ITU. In the United Kingdom, the Q.931-based protocol is ETS 300 102 (also known as EuroISDN). This is a very close implementation of the original CCITT specification. It is a 2Mbit/s service as with DASS2, but the feature capability is far greater and has negated the problems associated with DASS2, including echo problems and circuit spikes. In the UK, both DASS 2 and EuroISDN (ETS 300 102) lines are available to customers with EuroISDN as the preferred signalling type. Customers normally choose the desired signalling system, as this will be dictated by their CPE (Customer Premises Equipment), usually a PABX.
 
Most modern PABXs can handle many different types of signalling system, however the trend seems to be away from the DASS2 (which is no longer being developed by BT and has been known to deny problems with their DASS2 circuits), and towards the internationally recognised Q.931 standard, which is utilised by many country's telephony service providers.
 
The CCITT specify the standards for the layers 1, 2 and 3 signalling messages. The layer 3 messages are the messages which actually control the call setup, teardown, and routing.
 
The layer 3 messages or call control messages are the minimum messages that must be understood by the interfacing equipment. Individual service providers may publish their own documentation which details further messages that will be transported in addition to Q.931 messages. There are a number of additional European documents that cover supplementary services. These cover features that may be instigated by exchanges via the ISDN and require a higher degree of layer 3 implementation.

data modeling

the analysis of data objects that are used in a business or other context and the identification of the relationships among these data objects.

Data Plane

See User Plane

Database Lead

Projects with large and/or critical database components may assign a database lead responsible for design and construction issues relating to the database portions of the system.

Date Warehouse

In computing, a data warehouse (DW or DWH), also known as an enterprise data warehouse (EDW), is a system used for reporting and data analysis, and is considered a core component of business intelligence. DWs are central repositories of integrated data from one or more disparate sources. They store current and historical data in one single place7that are used for creating analytical reports for workers throughout the enterprise.
 
The data stored in the warehouse is uploaded from the operational systems (such as marketing or sales). The data may pass through an operational data store and may require data cleansing for additional operations to ensure data quality before it is used in the DW for reporting.
 


 
 

DCE

Data Circuit-terminating Equipment

data circuit-terminating equipment(DCE) is a device that sits between the data terminal equipment (DTE) and a data transmission circuit. It is also called data communication(s) equipment and data carrier equipment. Usually, the DTE device is the terminal (or computer), and the DCE is a modem.

 

DDK

driver development kit

a set of programs and related files that are used to develop a new software or hardware driver or to update an existing legacy application driver for an operating system.

DDOS

Distributed Denial of Service

In computing, a denial-of-service attack (DoS attack) is a cyber-attack in which the perpetrator seeks to make a machine or network resource unavailable to its intended users by temporarily or indefinitely disrupting services of a host connected to the Internet. Denial of service is typically accomplished by flooding the targeted machine or resource with superfluous requests in an attempt to overload systems and prevent some or all legitimate requests from being fulfilled.[1]
 
In a distributed denial-of-service attack (DDoS attack), the incoming traffic flooding the victim originates from many different sources. This effectively makes it impossible to stop the attack simply by blocking a single source.
 
A DoS or DDoS attack is analogous to a group of people crowding the entry door of a shop, making it hard for legitimate customers to enter, disrupting trade.
 

 

Decomposition Estimation

See bottom-up estimation. Refers specifically to creating estimates for the decomposed parts of a system.

Defect

A failure of a system or process to perform as specified, or expected.
A behavior or representation that does not conform to project plans or goals. Deviation from the expected or defined representation of information in an artifact. Nonconformance of a system, process, or artifact to a standard. Defects are a type of corrective activity management item.

Defect Management

The representation of identified defects and the planning, tracking, and control related to ensuring all identified defects are managed. Part of both quality and corrective activity management.

Defect Report

A request to modify an artifact due to lack of conformance to a standard, requirement, project need, or a failure/error.

Definition of Done

The definition of done is an agreed upon list of the activities deemed necessary to get a product increment, usually represented by a user story, to a done state by the end of a sprint.

Definition of Ready

involves creating clear criteria that a user story must meet before being accepted into an upcoming iteration. This is typically based on the INVEST matrix.

Deliverable

Any artifact or set of artifacts that are delivered as output from a project or other well defined set of work.

Deplhi

Object Pascal refers to a branch of object-oriented derivatives of Pascal, mostly known as the primary programming language of Delphi.

Deployment

The process and/or act of installing and readying a software system for use, including integration and customization that is specific to a particular site.

Deployment Lead

Projects with complex deployment needs may assign an individual to plan and oversee execution of deployment and possibly operational and maintenance related issues.

Deployment Plan

A plan specifying the method of releasing a system. Includes items like target platforms, configuration to release, etc.

DER

Distinguished Encoding Rules

ER (Distinguished Encoding Rules) is a restricted variant of BER for producing unequivocal transfer syntax for data structures described by ASN.1. Like CER, DER encodings are valid BER encodings. DER is the same thing as BER with all but one sender's options removed.
 
DER is a subset of BER providing for exactly one way to encode an ASN.1 value. DER is intended for situations when a unique encoding is needed, such as in cryptography, and ensures that a data structure that needs to be digitally signed produces a unique serialized representation. DER can be considered a canonical form of BER. For example, in BER a Boolean value of true can be encoded as any of 255 non-zero byte values, while in DER there is one way to encode a Boolean value of true.
 
The most significant DER encoding constraints are:
 

1. Length encoding must use the definite form
   
   1. Additionally, the shortest possible length encoding must be used
      
2. Bitstring, octetstring, and restricted character strings must use the primitive encoding
   
3. Elements of a Set are encoded in sorted order, based on their tag value
   DER is widely used for digital certificates such as X.509.

DES

Data Encryption Standard

The Data Encryption Standard is a symmetric-key algorithm for the encryption of electronic data. Although insecure, it was highly influential in the advancement of modern cryptography.
 
Developed in the early 1970s at IBM and based on an earlier design by Horst Feistel, the algorithm was submitted to the National Bureau of Standards (NBS) following the agency's invitation to propose a candidate for the protection of sensitive, unclassified electronic government data. In 1976, after consultation with the National Security Agency (NSA), the NBS eventually selected a slightly modified version (strengthened against differential cryptanalysis, but weakened against brute-force attacks), which was published as an official Federal Information Processing Standard (FIPS) for the United States in 1977.
 
The publication of an NSA-approved encryption standard simultaneously resulted in its quick international adoption and widespread academic scrutiny. Controversies arose out of classified design elements, a relatively short key length of the symmetric-key block cipher design, and the involvement of the NSA, nourishing suspicions about a backdoor. Today it is known that the S-boxes that had raised those suspicions were in fact designed by the NSA to actually remove a backdoor they secretly knew (differential cryptanalysis). However, the NSA also ensured that the key size was drastically reduced such that they could break it by brute force attack. The intense academic scrutiny the algorithm received over time led to the modern understanding of block ciphers and their cryptanalysis.
 
DES is insecure. This is mainly due to the 56-bit key size being too small. In January 1999, distributed.net and the Electronic Frontier Foundation collaborated to publicly break a DES key in 22 hours and 15 minutes (see chronology). There are also some analytical results which demonstrate theoretical weaknesses in the cipher, although they are infeasible to mount in practice. The algorithm is believed to be practically secure in the form of Triple DES, although there are theoretical attacks. This cipher has been superseded by the Advanced Encryption Standard (AES). Furthermore, DES has been withdrawn as a standard by the National Institute of Standards and Technology.

 

Design

Software design. The creation of abstracted models and plans for implementing requirements in software. Also denotes the design CKA. See CxStand_Design for more information.

Design Lead

Responsible for the system architecture and overseeing design activities.

Design Pattern

In software engineering, a software design pattern is a general, reusable solution to a commonly occurring problem within a given context in software design. It is not a finished design that can be transformed directly into source or machine code. It is a description or template for how to solve a problem that can be used in many different situations. Design patterns are formalized best practices that the programmer can use to solve common problems when designing an application or system.
 
Object-oriented design patterns typically show relationships and interactions between classes or objects, without specifying the final application classes or objects that are involved. Patterns that imply mutable state may be unsuited for functional programming languages, some patterns can be rendered unnecessary in languages that have built-in support for solving the problem they are trying to solve, and object-oriented patterns are not necessarily suitable for non-object-oriented languages.
 
Design patterns may be viewed as a structured approach to computer programming intermediate between the levels of a programming paradigm and a concrete algorithm.

Design to Tools

The content of a system is determined by what is directly supported by existing software tools

Desk Check

An informal review in which the author asks one or more people to read an artifact with the intent of finding defects.

Detailed Design

Commonly used term that captures parts of high level design and low level design. See CxStand_Design for more information.

Detailed Schedule

Fine grain project schedule that includes tasks, estimated effort, assigned resources, dependencies, etc. Usually created in a bottom-up fashion from a work plan. Normally implemented as a sliding window that covers a project's headlights. Compare to business schedule.

Developer

Synonym for software engineer, usually used when referring to design and construction activities.

Developer Integration Test

DIT

Integration test performed by a developer in the system test environment after a project build as part of releasing functionality.

development environment

the set of processes and programming tools used to create the program or software product.

Development Environment

DE

The hardware and software environment that construction work occurs in.

development process

a set of tasks performed for a given purpose in a software development project.

DevOps

development/operations

bridges the gap between agile teams and operational delivery to production.

DHCP

Dynamic Host Configuration Protocol

The Dynamic Host Configuration Protocol (DHCP) is a network management protocol used on UDP/IP networks whereby a DHCP server dynamically assigns an IP address and other network configuration parameters to each device on a network so they can communicate with other IP networks. A DHCP server enables computers to request IP addresses and networking parameters automatically from the Internet service provider (ISP), reducing the need for a network administrator or a user to manually assign IP addresses to all network devices.

Diagram

A graphical representation of a system, process, or other information.

DLE

Digital Local Exchange

DLP

Data Link Protocol

Protocols that can be utilized at the Data Link layer of the OSI model. These protocols include token ring, FDDI, and Ethernet. Ethernet Data Link protocols are broken out into addressing and framing standards

DMZ

Demilitarized Zone

In computer security, a DMZ or demilitarized zone (sometimes referred to as a perimeter network) is a physical or logical subnetwork that contains and exposes an organization's external-facing services to an untrusted network, usually a larger network such as the Internet. The purpose of a DMZ is to add an additional layer of security to an organization's local area network (LAN): an external network node can access only what is exposed in the DMZ, while the rest of the organization's network is firewalled. The DMZ functions as a small, isolated network positioned between the Internet and the private network and, if its design is effective, allows the organization extra time to detect and address breaches before they would further penetrate into the internal networks.

 

DN

Directory Number

A telephone number is a sequence of digits assigned to a fixed-line telephone subscriber station connected to a telephone line or to a wireless electronic telephony device, such as a radio telephone or a mobile telephone, or to other devices for data transmission via the public switched telephone network (PSTN) or other private networks.
 
A telephone number serves as an address for switching telephone calls using a system of destination code routing. Telephone numbers are entered or dialed by a calling party on the originating telephone set, which transmits the sequence of digits in the process of signaling to a telephone exchange. The exchange completes the call either to another locally connected subscriber or via the PSTN to the called party. Telephone numbers are assigned within the framework of a national or regional telephone numbering plan to subscribers by telephone service operators, which may be commercial entities, state-controlled administrations, or other telecommunication industry associations.

DNB

Dun and Bradstreet Business File

DNS

Domain Name System

The Domain Name System (DNS) is a hierarchical decentralized naming system for computers, services, or other resources connected to the Internet or a private network. It associates various information with domain names assigned to each of the participating entities. Most prominently, it translates more readily memorized domain names to the numerical IP addresses needed for locating and identifying computer services and devices with the underlying network protocols. By providing a worldwide, distributed directory service, the Domain Name System is an essential component of the functionality on the Internet, that has been in use since 1985.

DNS - A

IpV4 A Record

An A record maps a domain name to the IP address (IPv4) of the computer hosting the domain. Simply put, an A record is used to find the IP address of a computer connected to the internet from a name.
 
The A in A record stands for Address. Whenever you visit a web site, send an email, connect to Twitter or Facebook or do almost anything on the Internet, the address you enter is a series of words connected with dots.

DNS - AAAA

IPv6 DNS record

Returns a 128-bit IPv6 address, most commonly used to map hostnames to an IP address of the host

DNS - CNAME

Canonical name record

Alias of one name to another: the DNS lookup will continue by retrying the lookup with the new name.

DNS - DNAME

Alias for a name and all its subnames, unlike CNAME, which is an alias for only the exact name. Like a CNAME record, the DNS lookup will continue by retrying the lookup with the new name.

DNS - SRV

Service locator

Generalized service location record, used for newer protocols instead of creating protocol-specific records such as MX.

DNS - TXT

Txt Record

Originally for arbitrary human-readable text in a DNS record. Since the early 1990s, however, this record more often carries machine-readable data, such as specified by RFC 1464, opportunistic encryption, Sender Policy Framework, DKIM, DMARC, DNS-SD, etc.

DNS Spoofing

DNS spoofing, also referred to as DNS cache poisoning, is a form of computer security hacking in which corrupt Domain Name System data is introduced into the DNS resolver's cache, causing the name server to return an incorrect result record, e.g. an IP address. This results in traffic being diverted to the attacker's computer (or any other computer).

Docker

Docker is a collection of interoperating software-as-a-service and platform-as-a-service offerings that employ operating-system-level virtualization to cultivate development and delivery of software inside standardized software packages called containers.[The software that hosts the containers is called Docker Engine

Document Collaboration

Document and file collaboration are the tools or systems set up to help multiple people work together on a single document or file to achieve a single final version. Normally, this is software that allows teams to work on a single document, such as a Word document, at the same time from different computer terminals or mobile devices. Hence, document or file collaboration today is a system allowing people to collaborate across different locations using an Internet, or "cloud", enabled approach such as for Wikis such as Wikipedia
 
Tools such as Confluence & SharePoint can be used for Document Collaboration

Domain Name

A domain name is an identification string that defines a realm of administrative autonomy, authority or control within the Internet. Domain names are formed by the rules and procedures of the Domain Name System (DNS). Any name registered in the DNS is a domain name. Domain names are used in various networking contexts and for application-specific naming and addressing purposes. In general, a domain name represents an Internet Protocol (IP) resource, such as a personal computer used to access the Internet, a server computer hosting a web site, or the web site itself or any other service communicated via the Internet. In 2017, 330.6 million domain names had been registered.
 
Domain names are organized in subordinate levels (subdomains) of the DNS root domain, which is nameless. The first-level set of domain names are the top-level domains (TLDs), including the generic top-level domains (gTLDs), such as the prominent domains com, info, net, edu, and org, and the country code top-level domains (ccTLDs). Below these top-level domains in the DNS hierarchy are the second-level and third-level domain names that are typically open for reservation by end-users who wish to connect local area networks to the Internet, create other publicly accessible Internet resources or run web sites.
 
The registration of these domain names is usually administered by domain name registrars who sell their services to the public.
 
A fully qualified domain name (FQDN) is a domain name that is completely specified with all labels in the hierarchy of the DNS, having no parts omitted. Labels in the Domain Name System are case-insensitive, and may therefore be written in any desired capitalization method, but most commonly domain names are written in lowercase in technical contexts.

 
Domain name space
Today, the Internet Corporation for Assigned Names and Numbers (ICANN) manages the top-level development and architecture of the Internet domain name space. It authorizes domain name registrars, through which domain names may be registered and reassigned.
 
 
The hierarchical domain name system, organized into zones, each served by domain name servers.
The domain name space consists of a tree of domain names. Each node in the tree holds information associated with the domain name. The tree sub-divides into zones beginning at the DNS root zone.

 
 

Dot1Q

IEEE 802.1Q, often referred to as Dot1q

IEEE 802.1Q, often referred to as Dot1q, is the networking standard that supports virtual LANs (VLANs) on an IEEE 802.3 Ethernet network. The standard defines a system of VLAN tagging for Ethernet frames and the accompanying procedures to be used by bridges and switches in handling such frames. The standard also contains provisions for a quality-of-service prioritization scheme commonly known as IEEE 802.1p and defines the Generic Attribute Registration Protocol.
 
Portions of the network which are VLAN-aware (i.e., IEEE 802.1Q conformant) can include VLAN tags. When a frame enters the VLAN-aware portion of the network, a tag is added to represent the VLAN membership.[a] Each frame must be distinguishable as being within exactly one VLAN. A frame in the VLAN-aware portion of the network that does not contain a VLAN tag is assumed to be flowing on the native VLAN.

Dot1Q trunking

A simple view for dot1q (802.1q) trunking:
For ease of understanding the Dot1q (802.1q) trunking between switches can be seen as pipes (VLANs) inside a main pipe (Trunk) to connect VLANs that are being distributed on different switches.

So if that makes sense then a better representation is that packets are tagged as they go into the trunk link, like below.
The packets are tagged with the VLAN ID, that the port they are received on is configured with. When they are received on the other end they are then sent to the appropriate VLAN ports.

So how does the switch know which ports to send the packet to, the switches are assigned with the VLAN number.

 

Downstream

In a telecommunications network or computer network, downstream refers to data sent from a network service provider to a customer.
 
Although the best dial-up modems are called 56 kbit/s modems, downstream speeds can be limited to a few tens of kilobits per second with even lower upstream speeds. Asymmetric digital subscriber line (ADSL) and cable modems, two popular Internet access technologies, greatly improved downstream speeds reaching several Mbit/s. Mobile broadband and satellite Internet access providers also often have lower upstream speeds than downstream.
 
One process sending data primarily in the downstream direction is downloading. However, the overall download speed depends on the downstream speed of the user, the upstream speed of the server, and the network between them.
 
In the client–server model, downstream can refer to the direction from the server to the client.

Downstream

Used to refer to project activities and artifacts that occur later in a project lifecycle, often after significant construction has begun. Includes coding, low level design, testing, deployment, and system use. See upstream.

DP

Distribution Point

In LLU - The green termination box which is situated between the exchange and the customer premise, utilized as a junction point.
In FTTC - A piece of equipment that separates out a fibre into smaller pieces
 
 
 

 

DPI

Deep Packet Inspection

Deep packet inspection (DPI) is a type of data processing that inspects in detail the data being sent over a computer network, and usually takes action by blocking, re-routing, or logging it accordingly. Deep packet inspection is often used to ensure that data is in the correct format, to check for malicious code, eavesdropping and internet censorship[1] among other purposes. There are multiple headers for IP packets; network equipment only needs to use the first of these (the IP header) for normal operation, but use of the second header (such as TCP or UDP) is normally considered to be shallow packet inspection (usually called stateful packet inspection) despite this definition.[2]
 
There are multiple ways to acquire packets for deep packet inspection. Using port mirroring (sometimes called Span Port) is a very common way, as well as an optical splitter.
 
Deep Packet Inspection (and filtering) enables advanced network management, user service, and security functions as well as internet data mining, eavesdropping, and internet censorship. Although DPI has been used for Internet management for many years, some advocates of net neutrality fear that the technique may be used anticompetitively or to reduce the openness of the Internet.[3]
 
DPI is used in a wide range of applications, at the so-called "enterprise" level (corporations and larger institutions), in telecommunications service providers, and in governments.

DPNSS

Digital Private Network Signalling System

The Digital Private Network Signalling System (DPNSS) is a network protocol used on digital trunk lines for connecting to PABX. It supports a defined set of inter-networking facilities.
 
DPNSS was originally defined by British Telecom. The specification for the protocol is defined in BTNR188. The specification currently comes under the Network Interoperability Consultative Committee.

DQ

Data Quality

Draft

An artifact under revision control but not yet under change control.

driver

a program that interacts with a particular device or special kind of software. The driver contains special knowledge of the device or special software interface that programs using the driver do not.

DSCP

Diff-Serve Code Point

Differentiated services or DiffServ is a computer networking architecture that specifies a simple and scalable mechanism for classifying and managing network traffic and providing quality of service (QoS) on modern IP networks. DiffServ can, for example, be used to provide low-latency to critical network traffic such as voice or streaming media while providing simple best-effort service to non-critical services such as web traffic or file transfers.
 
DiffServ uses a 6-bit differentiated services code point (DSCP) in the 8-bit differentiated services field (DS field) in the IP header for packet classification purposes. The DS field replaces the outdated IPv4 TOS field.

DSDM

dynamic systems development method

agile development methodology, now changed to the 'DSDM project management framework'.

DSL

Digital Subscriber Line

Digital subscriber line (DSL; originally digital subscriber loop) is a family of technologies that are used to transmit digital data over telephone lines. In telecommunications marketing, the term DSL is widely understood to mean asymmetric digital subscriber line (ADSL), the most commonly installed DSL technology, for Internet access.

 

DSLAM

Digital Subscriber Line Access Multiplexor

Allows telephone lines to make faster connections to the Internet. It is a network device, located near the customer's premises and connects multiple customers Digital Subscriber Lines (DSL) to a high-speed Internet backbone line using multiplexing techniques.

 

DTE

Data Terminal Equipment

Data terminal equipment (DTE) is an end instrument that converts user information into signals or reconverts received signals. These can also be called tail circuits. A DTE device communicates with the data circuit-terminating equipment (DCE). The DTE/DCE classification was introduced by IBM.

 

DTMF

Dual Tone Multi Frequency

Dual-tone multi-frequency signalling (DTMF) is an in-band telecommunication signalling system using the voice-frequency band over telephone lines between telephone equipment and other communications devices and switching centres. DTMF was first developed in the Bell System in the United States, and became known under the trademark Touch-Tone for use in push-button telephones supplied to telephone customers, starting in 1963.[1] DTMF is standardized as ITU-T Recommendation Q.23.[2] It is also known in the UK as MF4.
 
The Touch-Tone system using a telephone keypad gradually replaced the use of rotary dial and has become the industry standard for landline and mobile service. Other multi-frequency systems are used for internal signalling within the telephone network.

 

DTT

Digital Terrestrial TV

Digital terrestrial television (DTTV or DTT) is a technology for broadcast television in which land-based (terrestrial) television stations broadcast television content by radio waves to televisions in consumers' residences in a digital format. DTTV is a major technological advance over the previous analog television, and has largely replaced analog which had been in common use since the middle of the last century. Test broadcasts began in 1998 with the changeover to DTTV (aka Analog Switchoff (ASO) or Digital Switchover (DSO)) beginning in 2006 and is now complete in many countries. The advantages of digital terrestrial television are similar to those obtained by digitising platforms such as cable TV, satellite, and telecommunications: more efficient use of limited radio spectrum bandwidth, provision of more television channels than analog, better quality images, and potentially lower operating costs for broadcasters (after the initial upgrade costs).

DTV

Digital TV

Digital television (DTV) is the transmission of television signals, including the sound channel, using digital encoding, in contrast to the earlier television technology, analog television, in which the video and audio are carried by analog signals. It is an innovative advance that represents the first significant evolution in television technology since color television in the 1950s. Digital TV makes more economical use of scarce radio spectrum space; it can transmit multiple channels in the same bandwidth occupied by a single channel of analog television, and provides many new features that analog television cannot. A switchover from analog to digital broadcasting began around 2006 in some countries, and many industrial countries have now completed the changeover, while other countries are in various stages of adaptation. Different digital television broadcasting standards have been adopted in different parts of the world

Duplex

A duplex communication system is a point-to-point system composed of two or more connected parties or devices that can communicate with one another in both directions. Duplex systems are employed in many communications networks, either to allow for a communication "two-way street" between two connected parties or to provide a "reverse path" for the monitoring and remote adjustment of equipment in the field. There are two types of duplex communication systems: full-duplex (FDX) and half-duplex (HDX).
 

 

 
 
Full Duplex

 
Half Duplex

 

DVSR

Dynamically Verified Static Routing

Dynamically Verified Static Routing (DVSR) is a proprietary routing protocol of the former Redback (now Ericsson) available on SmartEdge and Smart Services Router products.
 
DVSR can be defined as a semi-dynamic and semi-static routing protocol.
 
A DVSR route is based on static routing principle, but the router regularly checks for the next hop availability before the prefix can be injected into the local routing table and redistributed towards other routing tables. The DVSR route configuration allows the setup of success and failure counters used to declare the route as active or not. It could be described as a number of DVSR router attempts to ping the next hop; in case of a given number of successful replies the route is added to the local routing table or, after a set number of consecutive failures, the route is withdrawn.
 
SmartEdge routers support DVSR as a unique edge routing feature in addition to static routing and regular IGPs, such as IS-IS, OSPF, and RIP. DVSR is similar to normal static routing. The main difference is that the DVSR's next hop, or some other relevant host IP address, is dynamically verified by this protocol before the prefix can be injected into the local routing table. In many ISP networks, using static routing without proper next-hop checks results in black holing of network traffic.