Data-link layer (DLL)

(1) Layer 2 of the OSI Reference Model. Provides reliable transit of data across a physical link. The datalink layer is concerned with physical addressing, network topology, line discipline, error notification, ordered delivery of frames, and flow control. The IEEE divided this layer into two sublayers: the MAC sublayer and the LLC sublayer. Sometimes simply called the link layer. Roughly corresponds to the datalink control layer of the SNA model. (2) A layer with the responsibility of transmitting data reliably across a physical link (cabling, for example) using a networking technology such as Ethernet. The DLL encapsulates data into frames (or cells) before it transmits it. It also enables multiple computer systems to share a single physical medium when used in conjunction with a media access control methodology such as CSMA/CD.


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Layer 2 in the SNA architectural model. Responsible for the transmission of data over a particular physical link. Corresponds roughly to the datalink layer of the OSI model.
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<strong>Maturity Level Details:</strong><p style="margin: 0.8em 0px 1em; padding: 0px; text-align: justify; color: rgb(0, 0, 0); font-family: Helvetica, Arial, sans-serif; font-size: 12px;">Maturity levels consist of a predefined set of process areas. The maturity levels are measured by the achievement of the&nbsp;specific&nbsp;and&nbsp;generic goals&nbsp;that apply to each predefined set of process areas. The following sections describe the characteristics of each maturity level in detail.</p><strong>Maturity Level 1 - Initial</strong><br>At maturity level 1, processes are usually ad hoc and chaotic. The organization usually does not provide a stable environment. Success in these organizations depends on the competence and heroics of the people in the organization and not on the use of proven processes.<p style="margin: 0.8em 0px 1em; padding: 0px; text-align: justify; color: rgb(0, 0, 0); font-family: Helvetica, Arial, sans-serif; font-size: 12px;">Maturity level 1 organizations often produce products and services that work; however, they frequently exceed the budget and schedule of their projects.</p><p style="margin: 0.8em 0px 1em; padding: 0px; text-align: justify; color: rgb(0, 0, 0); font-family: Helvetica, Arial, sans-serif; font-size: 12px;">Maturity level 1 organizations are characterized by a tendency to over commit, abandon processes in the time of crisis, and not be able to repeat their past successes.</p><strong>Maturity Level 2 - Managed</strong><br>At maturity level 2, an organization has achieved all the&nbsp;specific&nbsp;and&nbsp;generic goals&nbsp;of the maturity level 2 process areas. In other words, the projects of the organization have ensured that requirements are managed and that processes are planned, performed, measured, and controlled.<p style="margin: 0.8em 0px 1em; padding: 0px; text-align: justify; color: rgb(0, 0, 0); font-family: Helvetica, Arial, sans-serif; font-size: 12px;">The process discipline reflected by maturity level 2 helps to ensure that existing practices are retained during times of stress. When these practices are in place, projects are performed and managed according to their documented plans.</p><p style="margin: 0.8em 0px 1em; padding: 0px; text-align: justify; color: rgb(0, 0, 0); font-family: Helvetica, Arial, sans-serif; font-size: 12px;">At maturity level 2, requirements, processes, work products, and services are managed. The status of the work products and the delivery of services are visible to management at defined points.</p><p style="margin: 0.8em 0px 1em; padding: 0px; text-align: justify; color: rgb(0, 0, 0); font-family: Helvetica, Arial, sans-serif; font-size: 12px;">Commitments are established among relevant stakeholders and are revised as needed. Work products are reviewed with stakeholders and are controlled.</p><p style="margin: 0.8em 0px 1em; padding: 0px; text-align: justify; color: rgb(0, 0, 0); font-family: Helvetica, Arial, sans-serif; font-size: 12px;">The work products and services satisfy their specified requirements, standards, and objectives.</p><strong>Maturity Level 3 - Defined</strong><br>At maturity level 3, an organization has achieved all the&nbsp;specific&nbsp;and&nbsp;generic goals&nbsp;of the process areas assigned to maturity levels 2 and 3.<p style="margin: 0.8em 0px 1em; padding: 0px; text-align: justify; color: rgb(0, 0, 0); font-family: Helvetica, Arial, sans-serif; font-size: 12px;">At maturity level 3, processes are well characterized and understood, and are described in standards, procedures, tools, and methods.</p><p style="margin: 0.8em 0px 1em; padding: 0px; text-align: justify; color: rgb(0, 0, 0); font-family: Helvetica, Arial, sans-serif; font-size: 12px;">A critical distinction between maturity level 2 and maturity level 3 is the scope of standards, process descriptions, and procedures. At maturity level 2, the standards, process descriptions, and procedures may be quite different in each specific instance of the process (for example, on a particular project). At maturity level 3, the standards, process descriptions, and procedures for a project are tailored from the organization's set of standard processes to suit a particular project or organizational unit. The organization's set of standard processes includes the processes addressed at maturity level 2 and maturity level 3. As a result, the processes that are performed across the organization are consistent except for the differences allowed by the tailoring guidelines.</p><p style="margin: 0.8em 0px 1em; padding: 0px; text-align: justify; color: rgb(0, 0, 0); font-family: Helvetica, Arial, sans-serif; font-size: 12px;">Another critical distinction is that at maturity level 3, processes are typically described in more detail and more rigorously than at maturity level 2. At maturity level 3, processes are managed more proactively using an understanding of the interrelationships of the process activities and detailed measures of the process, its work products, and its services.</p><strong>Maturity Level 4 - Quantitatively Managed</strong><br>At maturity level 4, an organization has achieved all the&nbsp;specific goals&nbsp;of the process areas assigned to maturity levels 2, 3, and 4 and the&nbsp;generic goals&nbsp;assigned to maturity levels 2 and 3.<p style="margin: 0.8em 0px 1em; padding: 0px; text-align: justify; color: rgb(0, 0, 0); font-family: Helvetica, Arial, sans-serif; font-size: 12px;">At maturity level 4 Subprocesses are selected that significantly contribute to overall process performance. These selected subprocesses are controlled using statistical and other quantitative techniques.</p><p style="margin: 0.8em 0px 1em; padding: 0px; text-align: justify; color: rgb(0, 0, 0); font-family: Helvetica, Arial, sans-serif; font-size: 12px;">Quantitative objectives for quality and process performance are established and used as criteria in managing processes. Quantitative objectives are based on the needs of the customer, end users, organization, and process implementers. Quality and process performance are understood in statistical terms and are managed throughout the life of the processes.</p><p style="margin: 0.8em 0px 1em; padding: 0px; text-align: justify; color: rgb(0, 0, 0); font-family: Helvetica, Arial, sans-serif; font-size: 12px;">For these processes, detailed measures of process performance are collected and statistically analyzed. Special causes of process variation are identified and, where appropriate, the sources of special causes are corrected to prevent future occurrences.</p><p style="margin: 0.8em 0px 1em; padding: 0px; text-align: justify; color: rgb(0, 0, 0); font-family: Helvetica, Arial, sans-serif; font-size: 12px;">Quality and process performance measures are incorporated into the organization.s measurement repository to support fact-based decision making in the future.</p><p style="margin: 0.8em 0px 1em; padding: 0px; text-align: justify; color: rgb(0, 0, 0); font-family: Helvetica, Arial, sans-serif; font-size: 12px;">A critical distinction between maturity level 3 and maturity level 4 is the predictability of process performance. At maturity level 4, the performance of processes is controlled using statistical and other quantitative techniques, and is quantitatively predictable. At maturity level 3, processes are only qualitatively predictable.</p><strong>Maturity Level 5 - Optimizing</strong><br>At maturity level 5, an organization has achieved all the&nbsp;specific goals&nbsp;of the process areas assigned to maturity levels 2, 3, 4, and 5 and the&nbsp;generic goals&nbsp;assigned to maturity levels 2 and 3.<p style="margin: 0.8em 0px 1em; padding: 0px; text-align: justify; color: rgb(0, 0, 0); font-family: Helvetica, Arial, sans-serif; font-size: 12px;">Processes are continually improved based on a quantitative understanding of the common causes of variation inherent in processes.</p><p style="margin: 0.8em 0px 1em; padding: 0px; text-align: justify; color: rgb(0, 0, 0); font-family: Helvetica, Arial, sans-serif; font-size: 12px;">Maturity level 5 focuses on continually improving process performance through both incremental and innovative technological improvements.</p><p style="margin: 0.8em 0px 1em; padding: 0px; text-align: justify; color: rgb(0, 0, 0); font-family: Helvetica, Arial, sans-serif; font-size: 12px;">Quantitative process-improvement objectives for the organization are established, continually revised to reflect changing business objectives, and used as criteria in managing process improvement.</p><p style="margin: 0.8em 0px 1em; padding: 0px; text-align: justify; color: rgb(0, 0, 0); font-family: Helvetica, Arial, sans-serif; font-size: 12px;">The effects of deployed process improvements are measured and evaluated against the quantitative process-improvement objectives. Both the defined processes and the organization's set of standard processes are targets of measurable improvement activities.</p><p style="margin: 0.8em 0px 1em; padding: 0px; text-align: justify; color: rgb(0, 0, 0); font-family: Helvetica, Arial, sans-serif; font-size: 12px;">Optimizing processes that are agile and innovative depends on the participation of an empowered workforce aligned with the business values and objectives of the organization. The organization's ability to rapidly respond to changes and opportunities is enhanced by finding ways to accelerate and share learning. Improvement of the processes is inherently part of everybody's role, resulting in a cycle of continual improvement.</p><p style="margin: 0.8em 0px 1em; padding: 0px; text-align: justify; color: rgb(0, 0, 0); font-family: Helvetica, Arial, sans-serif; font-size: 12px;">A critical distinction between maturity level 4 and maturity level 5 is the type of process variation addressed. At maturity level 4, processes are concerned with addressing special causes of process variation and providing statistical predictability of the results. Though processes may produce predictable results, the results may be insufficient to achieve the established objectives. At maturity level 5, processes are concerned with addressing common causes of process variation and changing the process (that is, shifting the mean of the process performance) to improve process performance (while maintaining statistical predictability) to achieve the established quantitative process-improvement objectives.</p>
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Layer 6 of the OSI model. The layer of the ISO Reference Model responsible for formatting and converting data to meet the requirements of the particular system being utilized. The OSI layer that determines how application information is represented (i. e. , encoded) while in transit between two end systems.
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Standardized datalink layer address ingrained into a NIC that is required for every port or device that connects to a LAN. Other devices in the network use these addresses to locate specific ports in the network and to create and update routing tables and data structures. MAC addresses are 6 bytes long and are controlled by the IEEE. Also known as
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Layer 1 of the OSI model. The OSI layer that provides the means to activate and use physical connections for bit transmission. In plain terms, the physical layer provides the procedures for transferring a single bit across a physical medium, such as cables.
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