Chapter 2: Conceptual Models/Networking Devices

Conceptual model

a representation of a system or a process.

used in networking to help understand end-to- end network communication.

Open Systems Interconnection (OSI) model

a seven-layer network conceptual model created by the International Organization for Standardization (IOS)

characterizes and standardizes the communication functions of a computing system. (difference)

-hardware dependent

-abstraction layers classify network devices

-it’s read vertically with each system functioning at only 1 layer. Ex: a networking device operates at layer 2.

Department of Defense (DoD) model

a four-layer network conceptual

model implemented as the Internet protocols suite. The DoD model is

commonly known as the TCP/IP model.

prepares and forwards data packets over a network. (difference)

-protocol dependent

-abstraction layers describe network protocols

-called by name, not number

-top down(upper layer 7 & lower layer 1)

-it’s read horizontally, despite its vertical presentation. Ex: A network protocol operates at multiple layers.

abstraction layer

a generalization of a system, process, or device.

Encapsulation

the process of adding a header or trailer so data is transmittable. (before transmission)

header

an information field added before a piece of data before transmission.

trailer

an information field added to the end of data before transmission.

protocol data unit(PDU)

data encapsulated with an abstraction layer's header or trailer.

payload

•data encapsulated with every abstraction layer's header or trailer. The recipient of a payload must remove any headers or trailers to properly process the original data.

Decapsulation

the process of removing a header or trailer so data is receivable. (after transmission)

(OSI) Layer 7

application layer, where a network protocol interacts with a network-aware application. (Ex: SMTP interacts with a email application.)

(OSI) Layer 6

presentation layer, where data is prepared for transmission between the application layer and the session layer. (Ex: an encrypted email)

(OSI) Layer 5

session layer, where a data transmission channel known as a session is established between communicating devices. (Ex: a session between a client’s web browser and a web server.)

(OSI) Layer 4

model transport layer, where data from the upper-level layers is divided into smaller- sized blocks of data for faster transmission.

• references the network protocols TCP & UDP

The PDU created depends on whether TCP or UDP is used for data transport.

Two PDUs are created:

• A segment is the PDU created by TCP, and includes a TCP header consisting of connection state information known as a TCP flag.

• A datagram is the PDU created by UDP, and includes a UDP header.

lower level layer

Transmission control protocol (TCP)

a network protocol used to establish a guaranteed, connection-oriented communication channel between communicating devices.

User datagram protocol (UDP)

a network protocol used to provide non-guaranteed, connectionless data transport for communicating devices.

a communications protocol for time-sensitive applications like gaming, playing videos, or Domain Name System (DNS) lookups.

-has speedier communication because it does not spend time forming a firm connection with the destination before transferring the data.

(OSI) Layer 3

network layer, where data receives logical address information needed to reach the recipient's network.

A packet is the PDU created by IP, and includes an IP header consisting of logical address information.

• A packet needs to know the route, or path, to reach the final destination because not every network is directly connected.

• A packet can take one of many routes to a different network.

• A packet should take the most efficient route among the different networks between a packet's source and destination.

•A router is a layer 3 networking device connecting at least two networks.

•A routing protocol is a network protocol used by a router to determine the most efficient route to a destination network.

Internet Protocol(IP)

used to address data sent over the internet or another network.

(OSI) Layer 2

data link layer, where data is transmitted to the recipient node.

A frame is the PDU created by layer 2 containing data transmission parameters and physical address.

Two sublayers are used to construct a frame:

• Logical link control (LLC) is a layer 2 sublayer providing data flow control, error detection, and error correction.

• Media access control (MAC) is a layer 2 sublayer providing physical address and frame synchronization.

•A frame needs to know how to reach the recipient node because not every node is directly connected.

•Many networks are a hybrid topology with at least one central node connecting several nodes together.

•A switch is a layer 2 networking device serving as a central node for at least two other nodes.

(OSI) Layer 1

physical layer, where a payload is transmitted across a network medium.

A bounded media network uses a physical cable type at layer 1. The physical cabling transmits a payload as a series of electrical or light pulses.

An unbounded media network uses a wireless signal at layer 1. The wireless signal transmits a payload using a series of radio waves. A radio wave is artificially generated energy that radiates electrical current into open space.

A PDU is not created at layer 1. Layer 1 is where a payload is transmitted as a series of binary numbers on the network medium.

• A binary number is a number expressed in a base-2 numeral system, also called the binary numeral system. A bit, or binary digit, is a single digit in a binary number. A binary number's digit is represented as a zero or one. Ex: 10101110 is an 8-bit binary number.

(DoD) Application layer

where a network-aware application interacts with transmitted data.

prepares data for transmission to the transport layer.

also establishes a session between communicating devices.

does not create a PDU because a receiving user's application presents data in a desired format. Examples of application-layer functions include:

• Remote access between nodes for troubleshooting.

• Email services between an email client and email server.

• File transfers between a file transfer client and a file transfer server.

highest layer of DoD Model

(DoD) Transport Layer

where end-to-end payload delivery from source to destination occurs. The PDU created by the transport layer is a TCP segment or a UDP datagram. End-to-end payload delivery is made possible by the information contained within a TCP or UDP header.

A port address, or port, is a 16-bit unsigned number that uniquely identifies a network application or service on a host. Port addresses are included in a TCP or UDP header to associate a payload with a specific process or service.

Using a distinct port for each process or service allows a single device to simultaneously recognize multiple traffic types. Ex: A device can simultaneously receive website traffic and email traffic because each service is associated with a unique port.

A TCP header is a 10-field, 20-byte header containing connection and payload delivery details for a segment. A TCP header is used to establish a three-way handshake for payload delivery.

A UDP header is a 4-field, 8-byte header containing connection and payload delivery details for a datagram. A UDP header is used to provide best-effort payload delivery.

(DoD) Internet Layer

where hop-to-hop data delivery from source to destination occurs. The PDU created by the internet layer is a packet. End-to-end payload delivery is made possible by the information contained within an IP header.

An IP header is a header containing connection and payload delivery details for a packet. An IP header uses one of two formats because two versions of IP exist:

• IP version 4 (IPv4) is the fourth version of IP, which provides internetworking capabilities on the internet and packet-switched networks.

• IP version 6 (IPv6) is the sixth version of IP, which provides internetworking capabilities on the internet and packet-switched networks.

(DoD) Network Access Layer

where data transfer between two devices on the same network occurs.

•The PDU created by the network access layer is a frame. A completed frame is transmitted as a series of binary numbers on the network medium.

•An Ethernet frame is a 6-field, 64-byte header and trailer containing data transmission parameters and MAC addresses.

• A media access control (MAC) address is a unique 48-bit identifier burned into a network interface controller.

• A network interface controller (NIC), or network interface card (NIC), is hardware connecting a networked device to bounded media.

Layer 1 devices

a device used to interact with network media in some way.

not involved in the encapsulation or decapsulation of data. Common layer 1 devices include hubs, repeaters, media converters, and modems:

• A hub is a legacy networking device used as a central node to provide connectivity for multiple networked devices.

• A repeater is a legacy networking device used to regenerate, or repeat, a signal transmitted on network media.

• A media converter is a networking device used as an adapter to connect different network mediums.

• A modulator/demodulator (modem) is a networking device used to convert a digital data signal to or from an analog carrier signal.

The OSI model abstraction layers are used to classify a device based on function. The OSI model focuses on networking devices rather than networked devices.

• A networking device is a device used to establish network connectivity. Ex: A switch is a networking device.

• A networked device is a device connected to a network. Ex: A personal computer connected to a LAN is a networked device.

Layer 2 devices

typically serves as a central node providing connectivity to multiple networked devices. Common layer 2 devices include bridges, switches, and wireless access points.

• A bridge is a legacy networking device used as a central node providing connectivity to two network segments. A bridge uses the destination MAC address contained in a frame to determine where to transmit a payload. A bridge is considered a legacy device because a bridge has only two physical connection points, or ports. Bridges are the predecessor to switches.

• A switch is a layer 2 networking device serving as a central node for at least two other nodes. A switch improved on a bridge's capabilities by providing more ports to connect more devices. A switch receives a payload on one port, uses the destination MAC address in the frame to locate the recipient's port, and switches the payload out of the recipient's port.

• A MAC address table, or MAC table, is a table that maps each network device's MAC address to a switch's physical port.

• A wireless access point (WAP) is a layer 2 networking device serving as a central node for at least two other wireless nodes. A WAP can operate as a standalone device or act as a bridge between a LAN and a WLAN. A WAP provides switch-like capabilities to wireless networked devices.

Layer 3 devices

typically serves as a node used to connect an internal network to an external network. Some vendors refer to a layer 3 device as a boundary, gateway, or edge device. Common layer 3 devices include routers, layer 3 capable switches, and wireless LAN controllers.

• A router is a layer 3 networking device connecting at least two networks. A large network is typically divided into multiple subnetworks, or subnets, to improve network performance. A switch is unable to communicate across subnets without a router. A router is also used to connect an internal network to an external network like the Internet. A routing table, or route table, is a rule table determining how a router routes a payload based on the destination's IP address.

• A layer 3 switch, or layer 3 capable switch, is a switch providing both layer 2 and layer 3 functions. A layer 3 switch is considered a multifunction device. A multifunction device (MFD) is a single device capable of providing multiple functions.

• Most WLANs require multiple WAPs to provide sufficient coverage. Centrally managing multiple WAPs improves WLAN performance and streamlines WAP configuration. A wireless LAN controller (WLC) is a centralized device used to control and configure multiple managed WAPs.

Layer 4 devices

used to make forwarding decisions during payload transport. Many layer 4 devices function both at layer 4 and the upper level layers for payload transport.

• Load balancing is the act of distributing network traffic among multiple devices to improve performance and prevent overload. A load balancer is either a hardware device or software service used to enforce load-balancing configurations.

• Voice over IP (VoIP) is a protocol group used to enable analog telephone conversations, or telephony, to occur over the internet. A voice gateway is either a hardware device or software service used to convert telephony into digital packets for transmission via VoIP.

• An intrusion detection system (IDS) is a device or a software application that detects a malicious activity or a security policy violation in a system. An intrusion prevention system (IPS) is an IDS that blocks a threat to a network.

• A firewall is a network device or a software program that controls inbound and outbound traffic based on a set of rules.

• A proxy server is a network device or a software program intended to protect internal nodes by acting as an intermediary device for external network resources.

Networked Devices

a device connected to a network.

is intended for one user or service, whereas a networking device is intended for multiple users or multiple services.

can be categorized as a client, server, or peer:

• A client accesses a network resource from a server, but does not share network resources with other clients.

• A server shares a network resource with a client.

• A peer shares and accesses a network resource.

PCs, laptops, smartphones, tablets, printers, and VoIP phones:

• A personal computer (PC) is a stationary single user computer usually connected to a network as a wired networked device.

• A laptop is a portable single user computer usually connected to a network as a wireless networked device.

• A smartphone is a portable single user computer and cellular phone connected to a cellular network.

• A tablet is a portable single user computer with a touchscreen as the primary input device.

• A printer is a hardware device used to produce a printed copy of computer data.

• A VoIP phone is a networked device used to provide client connectivity to a VoIP service.

Smart devices

a traditionally non-computing electronic device with computing and networking capabilities.

can connect to a network and the internet. 

Internet of Things (IoT)

the networking of traditionally non-computing physical objects such as sensors and health-monitoring wristbands.

• Smart device and IoT examples include:

• Smart refrigerator

• Smart speaker

• Smart thermostat

• Heating ventilation and air conditioning (HVAC) sensor

• Smart doorbell

 industrial control system (ICS)

an industry-specific collection of smart devices, computing devices, and networking equipment used for industrial process automation.

Supervisory control and data acquisition (SCADA)

an ICS used to supervise machinery and industrial processes. SCADA is used by businesses in many different industries such as utilities, food, and oil refining.