What is Ethernet: Key Terms & Concepts

By B. Cyburt, Senior Design Engineer, March 26, 2018

Ethernet: The IEEE 802.3 protocol standard. It defines a system of interconnecting multiple devices to form a Local Area Network (LAN) for communicating and sharing information/resources.

DHCP / Dynamic Host Configuration Protocol: One means of assigning IP addresses to network devices automatically. (As opposed to static IP address assignment inside the device itself).

Gateway: A device used to regulate traffic between two different networks. In contrast, a Router regulates traffic between similar networks. The two terms are often used interchangeably and message routing functions are frequently integrated into one device (i.e. Residential Gateway or Router/Gateway).

Host, Client, Computer, Node, Server, & LAN Device: These terms refer to any Ethernet device connected to a network, as well as any device that has its own IP address.

IANA / Internet Assigned Numbers Authority: A non-government, internet-specific organization that assigns and allocates IP addresses to keep the numbers unique across the globe.

IP / Internet Protocol: Mechanism used on an Ethernet network to transport messages between nodes. This includes how they are addressed.

IP Address: A unique 32-bit ID number temporarily assigned to each Ethernet device interconnected on an IP network. It is usually in dotted decimal format as four groups of 8-bit integers (octets) from 0 to 255; with a decimal placed between octets (for IPv4 addresses).

MAC Address: The 48-bit MAChine address uniquely hard-coded into every Ethernet device. Routers use the IP address to locate a device, but the MAC address specifically identifies the device.  Given these points, you could say that the IP address is used for messages sent between routers/gateways. But in truth, the IP and MAC addresses are used between routers/gateways and LAN clients. The network router associates the fixed device MAC address with a unique and temporary IP address that it controls. Subsequently using either static IP address assignment, or a named DHCP server that automatically associates it dynamically, as the device connects to the network.

Static IP Address: IP address assignment fixed inside the device and doesn’t change during operation.

Subnet Mask: A 32-bit number used to sub-divide the IP address into two or more network groups by a logical AND combination between each IP address and corresponding mask bit. The result discerns the network address/ID from its node address space. Leading bits of the network ID are all set to “1,” and trailing bits are all set to “0” for the host address space. The maximum value of the trailing bits, minus 2, determine the largest number of devices that may connect to the sub-network identified (first/zero and last/all 1’s node address numbers are always reserved).

TCP / Transmission Control Protocol: Transport layer of an Ethernet network that makes host-host communication possible. It does this by establishing host-client connections, for example: imposing flow-control; synchronizing sequence numbers; segmenting large amounts of data; providing error recovery and retry; and multiplexing IP addresses to specific sockets. (A socket refers to a port number combined with an IP address.) TCP ensures messages are delivered/processed in the same order in which they were sent. It uses SYNch requests & ACKnowledgement messages to establish a connection before sending data.

TCP/IP or UDP/IP Stack: Complete set of networking protocols required to manage communication on a network. Although two principal protocols are indicated in the acronym, the reference to stack refers to all protocols required to communicate on an Ethernet network. This stack of “software” uses the concept of groups of protocols at various layers; the layers operate on a message that passes up/down the stack through adjacent layers. Each layer consequently does its part for transmitting/receiving that message. On the whole, the OSI Model has a seven-layer stack; while the modern Internet reference model or TCP/IP stack has four layers.

UDP / User-Datagram Protocol: Another transport layer protocol that is connectionless and does not include the error recovery mechanism of TCP. It does not guarantee message delivery, however it is faster. Additionally, it has less overhead as there is little error checking and no retry mechanism.