Key Concepts in Networking and OSI Model

Network

Two or more connected computers that can share resources such as data and office machines.

Workstations

Common network component.

Servers

Common network component.

Hosts

Common network component.

Hubs

Connectivity device that connects other devices together into a network.

Switches

Connectivity device that connects other devices together into a network.

Routers

Connectivity device that connects networks together.

Physical Topology

A type of map that defines the specific characteristics of a network, such as where all the workstations and other devices and servers connect to and what gives the network its structure.

Logical Topology

What the network equipment 'sees,' in contrast to the physical layout.

Mesh Topology

A network topology covered in this chapter.

Hybrid Topology

A network topology covered in this chapter.

Star/hub and spoke Topology

A network topology covered in this chapter. Also referred to as a hub-and-spoke topology.

Spine and leaf Topology

A network topology covered in this chapter. This architecture is found in data centers to provide low-latency connectivity to servers.

Point to point Topology

A network topology covered in this chapter.

Point to multipoint Topology

A network topology illustrated in this chapter.

Three-tier hierarchical model

A network architecture model covered in this chapter. Includes Core, Distribution, and Access layers.

Core Layer

Provides services in the three-tier model.

Distribution Layer

Provides services in the three-tier model.

Access Layer

Provides services in the three-tier model.

Collapsed core model

Used to reduce costs by collapsing the core and distribution tiers into one tier.

Network Segmentation

Any small section of the network that may be connected to, but isn't actually a piece of, the backbone.

Backbone

The common connecting point for all segments. Needs fast, robust technology.

Service Entry Point

Clearly defined boundary where one entity hands off a connection to another.

Demarcation point (demarc)

The common term used for the service entry point, defining the point of responsibility.

Smart jack

A piece of equipment a carrier will usually terminate with, allowing them to run diagnostics up to the physical point where the customer's network connects.

North-south traffic

Typically leaves the network through a routed connection.

East-west traffic

Typically resides in the immediate network. Examples include database replication, file transfers, and interprocess communication between server farms and data centers.

LAN (Local Area Network)

A network typically found in your home or workplace. Used to connect a group of hosts, typically restricted to a particular geographic location.

WAN (Wide Area Network)

Used to connect various LANs together. A connection that connects your home or workplace to the Internet. Typically used for Internet connectivity.

Peer-to-peer

A network connection method. A network architecture mentioned in the assessment test and review questions.

Client-server

A network connection method. A network architecture mentioned in the assessment test and review questions.

vNIC (virtual network interface card)

A virtualized piece of hardware that connects the virtual machine operating system to the network. Used to connect a virtual machine to a virtual switch (vSwitch).

MPLS (Multiprotocol Label Switching)

Technology that uses labels to switch traffic. An alternative to dynamic multipoint VPN.

Fibre Channel

Typically found inside a Storage Area Network (SAN). Also referred to as FC.

SAN (Storage Area Network)

Where Fibre Channel is typically found inside.

MAN (Metropolitan Area Network)

A network type used in a metropolitan area to connect an organization together.

CAN (Campus Area Network)

A connectivity method that connects several LANs together in a small geographic area.

PAN (Personal Area Network)

A network that connects personal devices in close proximity.

Internetwork

A network connecting multiple LANs, often with routers.

Workgroup

A logical grouping of computers on a local area network (LAN) based upon a department's function.

Open Systems Interconnection (OSI) Reference Model

A seven-layer hierarchical model that was developed to enable different networks to communicate reliably between disparate systems.

Layer 1 - Physical

One of the seven layers of the OSI model.

Layer 2 - Data link

One of the seven layers of the OSI model. This layer deals with frames. Layer 2 switches and bridges operate at this layer.

Layer 3 - Network

One of the seven layers of the OSI model. This layer deals with IP addresses. Routers operate at this layer.

Layer 4 - Transport

One of the seven layers of the OSI model, also known as the Host-to-Host layer, where connection-oriented (TCP) and connectionless (UDP) protocols operate, using segments.

Layer 5 - Session

One of the seven layers of the OSI model.

Layer 6 - Presentation

One of the seven layers of the OSI model.

Layer 7 - Application

One of the seven layers of the OSI model that deals with the upper-layer user data.

Internetworking Models

Models developed because, in early networks, computers could only communicate with others made by the same manufacturer.

Encapsulation

The process of encoding data as it goes down the OSI model layers, where data is wrapped with protocol information at each layer.

Modulation Techniques

Techniques discussed in Chapter 2, including Frequency-division multiplexing (FDM) and Time-division multiplexing (TDM).

Connection-oriented session

Sessions that involve a three-way handshake to establish connection parameters and form a bidirectional connection before data transfer begins, exemplified by TCP.

TCP three-way handshake

The process used by connection-oriented protocols like TCP to establish a connection, involving the exchange of SYN, SYN/ACK, and ACK segments.

Connectionless protocol

Protocols that do not establish a virtual circuit before sending data, exemplified by UDP.

Virtual circuit

Connections opened between applications by connection-oriented protocols that the operating system currently has open.

Protocol data units (PDUs)

Units used by each layer of the OSI model to communicate and exchange information, holding control information attached to the header or trailer of the data.

SYN, SYN/ACK, ACK

The names for the segments exchanged during the TCP three-way handshake process.

Frequency-division multiplexing (FDM)

A modulation technique used in analog and digital modulation where several low-pass information signals are transferred simultaneously over the same shared physical network using separate passband channels.

Time-division multiplexing (TDM)

A method of transmitting and receiving many independent signals over a common signal path using synchronized network devices, where each signal appears on the line only a fraction of the time.

Baseband

Refers to a signal being modulated using the complete available bandwidth.

Digital baseband modulation methods

Methods, also known as line coding, used to transfer a digital bit stream over a baseband channel in Ethernet networks.

Bandwidth

How a signal is measured.

Frequency

How the capacity to carry the signal in a cable is measured.