Networking Terms & Concepts - Functionkey Inc.


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Functionkey Inc.

Functionkey Inc. is a 501(c)3 non-profit organization.

Networking Terms & Concepts


What You Need to Know - These basic networking concepts will be foundation from which we will build on:


OSI model

The Open Systems Interconnection (OSI) model defines seven different functional layers:

  1. physical
  2. data link
  3. network
  4. transport
  5. session
  6. presentation
  7. application

This model allows network engineers and network vendors to easily discuss and apply technology to a specific OSI level.

This separation lets network engineers divide the overall task of getting one application to talk to another into distinct more manageable sections. Each level has certain attributes that describe it and each level interacts with its adjacent levels in a clear defined manner. Knowledge of the layers above layer 7 is not mandatory, but understanding that interoperability is not always about electrons and photons will help.


These devices operate at layer 2 of the OSI model and use logical local addressing to move frames across a network. Devices in this category include Ethernet in all its variations, VLANs, aggregates, and redundancies.


These devices operate at layer 3 of the OSI model and connect IP subnets to each other. Routers move packets across a network in a hop-by-hop fashion.


These broadcast domains connect multiple hosts together on a common infrastructure. Hosts communicate with each other using layer 2 media access control (MAC) addresses.

IP addressing and subnetting

Hosts using IP to communicate with each other use 32-bit addresses. Humans often use a dotted decimal format to represent this address. This address notation includes a network portion and a host portion, which is normally displayed as


These layer 4 protocols define methods for communicating between hosts. The Transmission Control Protocol (TCP) provides for connection-oriented communications, whereas the User Datagram Protocol (UDP) uses a connectionless paradigm. Other benefits of using TCP include flow control, windowing/buffering, and explicit acknowledgments.


Network engineers use this protocol to troubleshoot and operate a network, as it is the core protocol used (on some platforms) by the ping and traceroute programs. In addition, the Internet Control Message Protocol (ICMP) is used to signal error and other messages between hosts in an IP-based network.

Data center

A facility used to house computer systems and associated components, such as telecommunications and storage systems. It generally includes redundant or backup power supplies, redundant data communications connections, environmental controls (e.g., air conditioning and fire suppression), and security devices. Large data centers are industrial-scale operations that use as much electricity as a small town.


Multiprotocol Label Switching (MPLS) is a mechanism in high-performance networks that directs data from one network node to the next based on short path labels rather than long network addresses, avoiding complex lookups in a routing table. The labels identify virtual links (paths) between distant nodes rather than endpoints. MPLS can encapsulate packets of various network protocols. MPLS supports a range of access technologies.

Northbound interface

An interface that conceptualizes the lower-level details (e.g., data or functions) used by, or in, the component. It is used to interface with higher-level layers using the southbound interface of the higher-level component(s). In architectural overview, the northbound interface is normally drawn at the top of the component it is defined in, hence the name northbound interface. Examples of a northbound interface are JSON or Thrift.

Southbound interface

An interface that conceptualizes the opposite of a northbound interface. The southbound interface is normally drawn at the bottom of an architectural diagram. Examples of southbound interfaces include I2RS, NETCONF, or a command-line interface.

Network topology

The arrangement of the various elements (links, nodes, interfaces, hosts, etc.) of a computer network. Essentially, it is the topological structure of a network and may be depicted physically or logically. Physical topology refers to the placement of the network’s various components, including device location and cable installation, while logical topology shows how data flows within a network, regardless of its physical design. Distances between nodes, physical interconnections, transmission rates, and/or signal types may differ between two networks, yet their topologies may be identical.

Application programming interfaces

A specification of how some software components should interact with each other. In practice, an API is usually a library that includes specification for variables, routines, object classes, and data structures. An API specification can take many forms, including an international standard, vendor documentation, or the libraries of a programming language.

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