What is a Network

A network refers to the connection that allows devices to exchange data and resources with each other. This connection can be a physical connection or wireless.

The uses of a network include

• Communication methods such as email, video conferencing and instant messaging.

• Allow devices to communicate with other devices such as printers.

• Allow to store and share files

• Provided access to read and write information

• Share software and programs

Networking Communication Layers

There are 2 established communication layer models which both model the network except for how they group their layers due to the view of data vs the system.

OSI is a conceptual framework that characterises and standardises how the network functions on a system level.

TCP/IP focuses on the protocol and how the data should be transmitted at each layer.

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OSI Model (Open Systems Interconnection Model)

The OSI is split into 7 layers from lowest to highest Physical, Data Link, Network, Transport, Session, Presentation and Application

Physical

The actual ones and zeros called bits (binary digits) are transferred through the infrastructure. The bit rate is controlled here.

Data Link

The format call frame in which the bits are arranged to form data on the network. Establishes the connection between 2 nodes through mac-addresses (Media Access Control) and uses network protocol, error checking and synchronizes frames. This layer also defines permissions to transmit and receive data

Network

The path that the data with travels over the network. The process requires the sender to separate the data into segments called network packets and the receiver reassembles the packets back into the data.

Transport

Transmits the data using transmission protocols such as TCP (Transmission Control Protocol) and UDP (User Datagram Protocol). It breaks the data from the session layer into segments which are sent separately and reassembled at the destination for the session layer. It decides the flow rate based on connection, checks for errors and re-requests for missing or incorrect segments.

Session

The session layer starts, maintains and ends the connection for communication through controlling ports and sessions. To allow for continuous transfer of data when needed.

Presentation

Ensure that the data is in the correct format and will encrypt the data if needed. Allows for the conversion from Application to Session and vice versa.

Application

The software and programs such as a website that a person uses to interact with the network. Protocols used are Hypertext Transfer Protocol (HTTP) for Webpages, File Transfer Protocol (FTP) for files transfer from server to client, Post Office Protocol (POP) for emails when between the receiver's email server and the receiver, Simple Mail Transfer Protocol (SMTP) for when emails are moving between 2 mail serves, and Domain Name System (DNS) for the distributed naming system for resources on the internet.

TCP/IP (Transmission Control Protocol/ Internet Protocol)

The TCP/IP is split into 4 layers from lowest to highest Network Interface, Network, Transport and Application layer. Each protocol stays within one layer, unlike the OSI model.

Network Interface

This layer encapsulates the physical and data link layer from the OSI model. This layer is also known as the data link layer, which consists of protocols that operate only on a link that interconnects nodes or hosts in the network.

Network

This layer is the same as the network layer from the OSI model. Also called the internet layer, this layer deals with packets and connects independent networks to transport the packets between network boundaries. The network layer protocols are IP and Internet Control Message Protocol, which is used for error reporting.

Transport

This layer encapsulates the transport layer from the OSI model. The layer is responsible for maintaining end-to-end communications across the network. TCP handles communications between hosts and provides flow control, multiplexing and reliability.

Application Layer

This layer encapsulates the session, presentation and application layers in the OSI model. Provide standardized data exchange called protocols. Examples include HTTP, FTP, POP, and SMPT. At this layer, the payload is the actual application data.

Network Topology

Network Topology refers to the structure and arrangement of the physical and logical nodes. A node refers to any electronic device that is attached to a network and is capable of creating, receiving, or transmitting information over a communication channel.

Physical topology refers to how devices are physically interconnected with wires, cables and Wi-Fi while a logical node refers to how the connections appear to the user and how data should transfer. The important Node in terms of networking are switches, hubs, routers and access points.

Switches

Switches allow devices on your network to communicate with each other in what is called a LAN (Local Access Network). Switches handle the local transmission and routing of data on the network (data link layer).

Hubs

Broadcasts data to every computer or Ethernet-based device connected to it. Compared to a switch operate on the physical layer and connects devices to a single node itself. The hub is a passive device that facilitates communication through it.

Routers

Routers connect networks to other networks. This includes the connection from the LAN to the internet. A router acts as a dispatcher. It analyzes data being sent across a network, chooses the best route for data to travel, and sends it on its way. Due to being the gateway between networks it often comes with security items such as Firewalls, VPNs and IPs. This limits and protects the data that leaves and enters the router.

Access Points

Access Points create a wireless local area network, or WLAN, usually in an office or large building. Access point typically connects to a switch, router

Types of Typologies

Star

There is a central node called a hub to which all other nodes a connected with no other nodes connecting. Most home and office networks have a physical star topology. If the hub goes down the network goes down

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Ring/Circular

The node is connected in a closed ring/loop with each node only connected to 2 other nodes (daisy-chained). Unidirectional rings only allow data to be transferred one way either clockwise or anti-clockwise. Bidirectional rings allow communication in both directions thus these networks are more resilient as information can move in either direction to reach a node compared to unidirectional rings.

Rings have been largely replaced by the star network. An example is Synchronous Optical Networking (SONET) which is used to transmit and multiplex multiple data streams across a fibre optic cable.

Point to Point

Two nodes are directly connected. This is similar to a traditional telephone line where only 2 phones can communicate with each other when a call was made. As with the traditional landline, the uses of circuit-switching or packet switching allow for the dynamic setup and removal of point-to-point configurations. Allows for the full use of connection for communication between 2 nodes.

Bus

There is a single cable like a bus route usually a network cable or coaxial cable and every node is connected in series along that cable. This is typically used in cable broadband distribution networks. Note that if the cable fails the whole network goes down.

Line/Daisy Chain

The line is similar to a bus, ring and point-to-point in that instead of a cable, nodes are daisy-chained directly like in a ring but the end nodes don't loop or connect so its shape is a line. If a node fails the network breaks in 2 at the failed node.

Tree

The tree consists of multiple separate star typographies with the hub and only the hub for each star-connected in series to a central cable similar to bus topography. This typology is typically used in a data centre.

Mesh

The mesh links nodes with connections so that there are multiple paths between any 2 points of the network available. If all nodes are directly connected to all other nodes then it is fully meshed, else it is called partially meshed. Meshing multiple paths increases resiliency but also increases cost. Military organisations often use mesh topologies to avoid breakdowns in communication.

Hybrid

When two or more topologies are merged in such a way that the resulting network does not exhibit one of the standard topologies. A hybrid topology is always produced when two different basic network topologies are connected.

Types of networks

Personal Area Network (PAN)

PANs typically serve one person and range from a few centimetres to a few meters. It allows for connecting devices in an individual workspace such as computers, tablets, peripherals, headphones, phones, personal digital assistants etc to communicate and transmit data.

Home Area Network (HAN)

HAN allows a user to interconnect multiple computers and other digital devices within the home. Encourages sharing of resources, files, and programs within the network. It supports both wired and wireless communication.

Local Area Network (LAN)

LAN is a network that interconnects devices/computers within a limited area such as a home, school, office etc through a router or server. This is done through a physical connection such as ethernet cables (LAN) or wireless via Wi-fi (WLAN).

LANs can serve between two or three users or thousand in an office/school. If too many devices connect can lead to congestion and bottlenecks in the network as all devices on a LAN can hear all communication passing through the LAN.

VLANs (Virtual LANs) use software to separate LANs into separate VLANs where only devices on the same VLAN can hear the communication helping reduce the load on the network. However, for devices on separate VLANs to communicate with each other inter-VLAN routing is required.

LANs allow multiple devices on a LAN to share a single internet connection, be a centralised location for communication and allow resource sharing such as printers.

Wide Area Network (WAN)

Often connects computers over large geographical distances and thus comprises multiple locations. WANs can also be a group of LANs that can be communicated with each other. A common example of a WAN is the internet.

Wireless Local Area Network (WLAN)

WLANs are the same as a LAN however instead of a traditional wire physical connection it uses wireless technology such as Wi-Fi, BlueTooth etc to communicate wirelessly. An example is a coffee shop wifi.

Campus Area Network (CAN)

CAN is bigger than a LAN but smaller than a MAN. Usually used in locations such as schools or universities. This network covers a limited geographical area including several buildings within that area.

Metropolitan Area Network (MAN)

MAN is bigger than a CAN but smaller than a WAN. Serves a singular geographical area such as a city or town etc.

Storage Area Network (SAN)

SAN is a type of computer network that is high-speed connections and connects groups of storage devices to several servers or computers. This network does not depend on LAN or WAN. Instead, a SAN moves the storage resources from the network to its high-powered network. A SAN provides access to block-level data storage. This allows for the storage to act like a local disk directly connected to the servers/computers.

Typically a network of hard drive disks is accessed by a network of servers.

System-Area Network (SAN)

A SAN is a type of computer network that connects a cluster of high-performance computers. It is a connection-oriented and high-bandwidth network. A SAN is a type of LAN that handles high amounts of information in large requests. This network is useful for processing applications that require high network performance.

Microsoft SQL Server 2005 uses SAN through a virtual interface adapter.

Passive Optical Local Area Network (POLAN)

A passive optical network (PON) is a fibre-optic telecommunications technology for delivering broadband network access to end customers. Using a point-to-multipoint topology and optical splitters to deliver data from a single transmission point to multiple user endpoints. POLAN refers to the usage of PON in a typical LAN setup.

Enterprise Private Network (EPN)

EPN is a type of computer network mostly used by a business that wants a secure connection over various office locations to share company computer resources.

Virtual Private Network (VPN)

A VPN is a type of computer network that extends a private network across the internet and lets the user send and receive data as if they were connected to a private network even though they are not. This can be done by either hardware or software. Through a virtual point-to-point connection users can access a private network remotely. VPN protects you from malicious sources by operating as a protected network connection that directly connects 2 devices.

Layers of a Network

A network can be generally separated into layers outer layers encapsulating inner layers. There are 3 layers in a network from inner to outer the intranet layer is contained in the extranet which in turn is contained in the internet.

Intranet

The intranet is the private and innermost layer of a network. It securely facilitates the share internal information and resources in an organisation such as a school or business. It allows for the internal members/employees to freely communicate with each other without transferring outside of this layer.

Examples include a social media site that only members of the organization can access to read and post information, a location to store internal files and documents and a place to communicate internal organisational updates and news.

Extranet

The extranet is the private and next outer layer of a network. It facilitates the sharing of information and resources between an organisation and trusted third parties such as business partners, suppliers and vendors, specific customers and other organisations typically through the Internet.

It allows for the communication of an allowed subset of information when compared to the intranet that authorised access the third parties need without exposing the intranet. It can also be the layer that protects and encapsulates the intranet from the internet and acts as a demilitarized zone that contains and exposes the external facing services to the internet.

Examples include systems that allow third parties to communicate and collaborate, integrated supply chains and communicated news that third parties have access to but not the general internet.

Internet

The Internet provides access to information and resource available to the general public. Unlike the other layers, there is only one in existence. The main use of the internet is to use the web and how emails and files are transferred.