Temporary OSi Model and Fundementals

Open Systems Interconnection (OSI) Model

Developed in 1977 by the International Organization for Standardization

Reference Model

Used to categorize the functions of a network in the OSI Model during troubleshooting efforts

Physical Layer

Where transmission of bits across the network occurs and includes physical and electrical network characteristics

Transition Modulation

If it changes during the clock cycle, then a 1 is represented (otherwise, a 0 is represented)

Asynchronous

Uses start and stop bits to indicate when transmissions occur from the sender to the receiver

Synchronous

Uses a reference clock to coordinate the transmissions by both sender and receiver

Broadband

Divides bandwidth into separate channels

Baseband

Uses all available frequencies on a medium (cable) to transmit data. (Uses a reference clock)

Time-Division Multiplexing (TDM)

Each session takes a turn, using time slots, to share the medium between all users

Statistical Time-Division Multiplexing (StatTDM)

Dynamically allocates the time slots on an as-needed basis

Frequency-Division Multiplexing (FDM)

Divides the medium into channels based on frequencies and each session is transmitted over a different channel

Layer 1

Repeaters, passing along whatever is received. Fiber optic cable, Ethernet cable, Coaxial cable, Bluetooth, Wi-FI, Near Field Communication (NFC), Hubs, Access points, Media Converters

Data Link Layer

Packages data into frames and transmits those frames on the network

Media Access Control (MAC)

Physical addressing system of a device which operates on a logical topology

Logical Link Control (LLC)

Provides connection services and allows acknowledgement of receipt of messages. (the most basic form of flow control)

Isochronous

Network devices use a common reference clock source and create time slots for transmission

Synchronous

Network devices agree on clocking method to indicate beginning and end of frames and can use control characters

Asynchronous

Network devices reference internal clocks and use start and stop bits for synchronization

Packet Switching

Data is divided into packets and then forwarded

Circuit Switching

Dedicated communication link is established between two devices

Message Switching

Data is divided into messages which may be stored and then forwarded

Route Discovery and Selection

Manually configured as a static route or dynamically through a routing protocol

Connection Services

Augment Layer 2 connection services to improve reliability

Internet Control Message Protocol

Sends error messages and operational information to an IP destination

Transport Layer

Dividing line between the upper layers and the lower layers of the OSI model

Transmission Control Protocol (TCP)

Connection-oriented protocol that is a reliable way to transport segments across the network

User Datagram Protocol (UDP)

Connectionless protocol that is an unreliable way to transport segments across the network

Windowing

Allows the clients to adjust the amount of data in each segment

Buffering

Occurs when devices allocate memory to store segments if bandwidth is not readily available

Session Layer

Keeps Conversations separate to prevent intermingling of data

Set Up Session

Checking of users credentials and assigning numbers to sessions to help identify them

Maintain Session

Where data transfers back and forth across the network

Tear Down Session

Ending of a session after the transfer is done or when the other party disconnects

H.323

Used to set up, maintain, and tear down voice and video connections (operates over Real-time Transport Protocol (RTP)

NetBios

Used to share files over a network

Layer 5 Examples

H.323, RTP, NetBios

Presentation Layer

Formats the data to be exchanged and secures that data with proper encryption

Data Formatting

Data is formatted by the computer to have compatibility between different devices

Encryption

Used to scramble the data in transit to keep it secure from prying eyes and provide data confidentiality

Application Layer

Provides application-level services where users communicate with the computer

Application Services

Unites communicating components from more than one network application

Service Adevertisement

Sending out of announcements to other devices on the network to state the services they offer

Encapsulation

The process of putting headers (and trailers) around some data

Decapsulation

The process of removing headers (and trailers) around some data

Protocol Data Unit (PDU) Flag

A single unit of information transmitted in a computer network

SYN (Synchronization) Flag

Used to synchronize connection during the three-way handshake

ACK (Acknowledgment) Flag

Used during the three-way handshake, but also used to acknowledge the successful receipt of packets

FIN (Finished) Flag

Used to tear down the virtual connections created using the three-way handshake and the SYN flag

RST (Reset) Flag

Used when a client or server receives a packet that it was not expecting during the current connection

PSH (Push) Flag

Used to ensure data is given priority and is processed at the sending or receiving ends

URG (Urgent) Flag

Similar to PSH and identifies incoming data as urgent

MAC Address

Physical address that is used to identify a network card on a local area network

Ether Type

Used to indicate which protocol is encapsulated in the payload of a frame. IPV4 or IPV6 would be indicated here

Wireshark

Packet analyzer that can pull apart some network traffic and show different layers of the OSI model

Networks

Encompass a diverse range of connections extending to both wireless networks and wired networks

Clients

Devices that users access the network with

Servers

Provide resources to the network

Hubs

Older network devices that connect other devices like clients and servers over a local area network

Switches

“Smarter hubs” that provide more security and more efficient bandwidth utilization

Wireless Access Points (WAPs/APs)

Allow wireless devices to connect to a wired network

Routers

Used to connect different networks together

Firewalls

Security barriers between internal networks and the external world (usually the Internet)

Load Balancers

Devices or software that distribute network or application traffic across multiple servers

Proxy

Acts as an intermediary between a user’s device and the Internet

Intrusion Detection Systems (IDS)

Detect unauthorized access or anomalies and alert administrators

Intrusion Prevention System (IPS)

Not only detect threats, but also take action to prevent intrusion

Controllers

In Software-Defines Networking (SDN) context, these are central units used to manager flow control to networking devices.

Network-attached Storage (NAS) Device

Dedicated file storage system that provides data access to a heterogeneous group of clients

Storage Area Network (SAN)

High-speed network that provides access to consolidated block-level data storage

Media

In networking, it refers to the physical materials used to transmit data

Wide Area Network (WAN) Link

Used to connect networks over large geographical areas

Client/Server Model

Utilizes a dedicated server to provide access to network resources (files, scanners, printers, etc.)

Peer-to-Peer Model

Peers or other machines (e.g., laptops, desktops) can share resources together directly

Personal Area Network (PAN)

Smallest type of wired or wireless network which usually covers a distance about 10 feet or less

Local Area Network (LAN)

Connects components in a limited distance, generally up to about 100 meters or 300 feet

Campus Area Network (CAN)

A building-centric LAN that is spread across numerous buildings in a certain area

Metropolitan Area Network (MAN)

Connects locations that are scattered across the entire city

Wide Area Network (WAN)

Connects geographically disparate internal networks

Network Topology

Refers to the arrangement of different elements like links, nodes, clients, and servers that make up a computer network

Physical Topology

Used to show how the network devices and components are physically cabled and connected together

Logical Topology

Talks about how the traffic is actually going to flow in the network

Point-to-point Topology

Simplest form of network topology that involves a direct connection between two devices

Ring Topology

A network configuration where each device is connected to two other devices, forming a circular data path

Fiber Distributed Data Interface (FDDI)

Used to conduct data transmissions on fiber optic line sin a local area network. Runs on Dual ring structure

Bus Topology

All of the network devices are connected to a single central cable, called the bus or backbone

Star Topology

One of the most common network layouts that is in use today

Hub-and-spoke Topology

A variation of the star topology where the central node (hub) is connected to multiple nodes (spokes)

Mesh Topology

Features a point-to-point connection between every single device on the network to create a robust and redundant network. There is Full-mesh Topology & Partial-mesh Topology

Full-mesh Topology

Every node is connected to every other node in the network

Partial-mesh Topology

Some nodes are organized in a full mesh scheme, while others are only connected to one or two devices in the network

Infrastructure Mode

The most common type of wireless network that uses a wireless access point as a centralized point

Ad Hoc Mode

Decentralized wireless network which creates Peer-to-Peer connections and does not require a router or access point

Wireless Mesh Topology

An interconnection of different types of nodes, devices, and radios

Datacenter

Any facility that businesses and other organizations use to organize, process, store, and disseminate large amounts of data

Utah Data Center

Intelligence Community Comprehensive National Cybersecurity Initiative Data Center

Three-tiered hierachi

Core, Distribution/Aggregation, Access/ Edge

Collapsed Core

Network architecture where the core and the distribution layers are being merged into a single layer

Spine and Leaf Architecture

An alternative type of network architecture that focuses on the communication within the data center itself

Spine

Connects switches in a full mesh topology

Leaf

Consist of all the access switches