KEY TERMS
application layer - Layer 7 of the OSI reference model. This layer provides services to application processes (such as email, file transfer, and terminal emulation) that are outside the OSI reference model.
bandwidth - The amount of information that can flow through a network connection in a given period of time.
bridge - A Layer 2 device designed to create two or more LAN segments, each of which is a separate collision domain.
broadcast - A data packets that is sent to all nodes on a network. Broadcasts are identified by a broadcast address.
broadcast domain - The set of all devices that receive broadcast frames originating from any device in the set.
bus topology - Commonly called a linear bus, this topology connects all the devices with a single cable. This cable
proceeds from one computer to the next like a bus line going through a city.
Collision - In Ethernet, the result of two nodes transmitting simultaneously. The frames from each device impact and
are damaged when they meet on the physical medium.
collision domain - In Ethernet, the network area within which frames that have collided are propagated. Repeaters and
hubs propagate collisions; LAN switches, bridges, and routers do not.
data center - A globally coordinated network of devices designed to accelerate the delivery of information over the
Internet infrastructure.
data link layer - Layer 2 of the OSI reference model. Provides transit of data across a physical link. The data link layer is
concerned with physical addressing, network topology, line discipline, error notification, ordered delivery of frames, and
flow control.
de-encapsulation - Unwrapping data in a particular protocol header.
encapsulation - Wrapping data in a particular protocol header.
extended-star topology - A network in which a star network is expanded to include an additional networking device
that is connected to the main networking device.
extranet - Intranet-based applications and services that employ extended, secure access to external users or
enterprises.
firewall - A router or access server designated as a buffer between any connected public networks and a private
network.
flooding - A traffic-passing technique used by switches and bridges in which traffic received on an interface is sent out
all that device’s interfaces except the interface on which the information was received originally.
frame - A logical grouping of information sent as a data link layer unit over a transmission medium.
full-mesh topology - Connects all devices (nodes) to each other for redundancy and fault tolerance.
hierarchical topology - Created similar to an extended-star topology. The primary difference is that it does not use a
central node. Instead, it uses a trunk node from which it branches to other nodes.
hub - A common connection point for devices in a network. Hubs commonly connect segments of a LAN. A hub contains
multiple ports. When a packet arrives at one port, it is copied to the other ports so that all the segments of the LAN can
see all the packets.
Intranet - A common LAN configuration. Intranets are designed to be accessed by users who have access privileges to
an organization’s internal LAN.
local-area network (LAN) - A high-speed, low-error data network covering a relatively small geographic area (up to a few
thousand meters). LANs connect workstations, peripherals, terminals, and other devices in a single building or another
geographically limited area.
Media Access Control (MAC) - A hardware address that uniquely identifies each node of a network. This address
controls data communication for the host on the network.
metropolitan-area network (MAN) - A network that spans a metropolitan area. Generally, a MAN spans a larger
geographic area than a LAN but a smaller geographic area than a WAN.
microsegmentation - Allows the creation of private or dedicated segments—one host per segment. Each host receives
instant access to the full bandwidth and does not have to compete for available bandwidth with other hosts.
network interface card (NIC) - A printed circuit board that fits into the expansion slot of a bus on a computer
motherboard. Also can be a peripheral device.
network layer - Layer 3 of the OSI reference model. This layer provides connectivity and path selection between two
end systems. The network layer is the layer at which routing occurs.
Open System Interconnection (OSI) reference model - A network architectural model developed by the ISO. This model
consists of seven layers, each of which specifies particular network functions, such as addressing, flow control, error
control, encapsulation, and reliable message transfer. The OSI reference model is used universally as a method for
teaching and understanding network functionality.
Packet - A logical grouping of information that includes a header containing control information and (usually) user data.
Packets most often refer to network-layer units of data.
partial-mesh topology At least one device maintains multiple connections to others without being fully meshed. A
partial-mesh topology still provides redundancy by having several alternative routes.
peer-to-peer communication - A form of communication in which each layer of the OSI model at the source must
communicate with its peer layer at the destination.
physical layer - Layer 1 of the OSI reference model. The physical layer defines the electrical, mechanical, procedural,
and functional specifications for activating, maintaining, and deactivating the physical link between end systems.
presentation layer - Layer 6 of the OSI reference model. This layer ensures that information sent by the application
layer of one system can be read by the application layer of another.
protocol - A formal description of a set of rules and conventions that govern how devices on a network exchange
information.
protocol suite - A set of related communications protocols that operate together and, as a group, address
communication at some or all of the seven layers of the OSI reference model. Not every protocol stack covers each layer
of the model, and often a single protocol in the suite addresses a number of layers at once. TCP/IP is a typical protocol
suite.
repeater - A networking device that exists at Layer 1, the physical layer, of the OSI reference model. The purpose of a
repeater is to regenerate and retime network signals at the bit level, allowing them to travel a longer distance on the
medium.
ring topology - A topology in which hosts are connected in the form of a ring or circle. Unlike the physical bus topology,
the ring topology has no beginning or end that needs to be terminated.
router - A type of internetworking device that passes data packets between networks based on Layer 3 addresses. A
router can make decisions regarding the best path for delivery of data on the network.
segment - In the TCP specification, a logical information group at transport layers of the OSI reference model.
session layer - Layer 5 of the OSI reference model. This layer establishes, manages, and terminates sessions between
applications and manages data exchange between presentation layer entities.
star topology - The most commonly used physical topology in Ethernet LANs. The star topology is made up of a central
connection point that is a device such as a hub, switch, or router, where all the cabling segments meet.
storage-area network (SAN) - A dedicated, high-performance network that moves data between servers and storage
resources.
switch - A device that connects LAN segments, uses a table of MAC addresses to determine the segment on which a
frame needs to be transmitted, and reduces traffic. Switches operate at much higher speeds than bridges.
throughput - The rate of information arriving at or passing through a particular point in a network system.
transport layer - Layer 4 of the OSI reference model. This layer is responsible for reliable network communication
between end nodes. The transport layer provides mechanisms to establish, maintain, and terminate virtual circuits,
transport fault detection and recovery, and information flow control.
virtual private network (VPN) - A private network constructed within a public network infrastructure such as the global
Internet.
wide-area network (WAN)- A data communications network that serves users across a broad geographic area and
often uses transmission devices provided by common carriers.