Networking and Security - Application, Internet, and Physical Layer

This article discusses the application, internet, and physical layer of networking and security. It covers topics such as client-server architecture, peer-to-peer network model, cloud computing, ARP, IP addressing, subnet mask, and physical layer.

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Networking and Security
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Topic 3: Application Layer of the Internet
The application layer of the internet/network model gives network users the ability to
interact with devices and services such as Facebook, google web server and maps among many
other applications available services in the network. These networks allow sharing of resources
depending on the architecture used, with some machines serving as dedicated servers and clients
or client/server simultaneously. As such, application have different architectures ranging from
client-server, peer-to-peer, host-based and cloud based architecture.
At the local levels of the network, the application (services) allows network users an
access to shared network resources such as printers, network faxes and distributed mails, and
shared and attached memory.
The client-server architecture takes the model of ‘services provider and a consumer’ with
user applications such as email, FTP clients and web browsers being the clients-consumers and a
dedicated server- the service provider- that meets the requests made by the applications. The
clients’ application request for such services as file server and information stored in the database
servers.
In the peer-to-peer network model, each of the connected devices can act as a server and
a client simultaneously, requesting for services from other devices in the same network and
servicing requests made by them too. With these networks, server roles are distributed among
connected devices hence no need for dedicated server. Host based network exist where a
machine.
Other modes of interaction in the network are through the cloud computing- cloud
architecture in which the cloud is looked to as either infrastructure as a services or software as a

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service and platform as a services. In such a scenario, the cloud is used to host a wide range of
services and applications, including software, applications and associated data.
Communication in a network is managed by a protocol stack- which determines how
messages are to be sent, structured and displayed. Each protocol adds a protocol header to the
message being sent as a way of supplying information to the associated layer of the destination
machine.
Topic 5: The Internet (Network) Layer
This protocol serves to manage and deliver traffic from host to host over long distances.
These host are identified through network addressing, and these addresses must be made
visible/public so that packets are no sent to the wrong recipients. Addressing is made using the
Address Resolution Protocol, Dynamic Host Configuration Protocol or could be done manually.
The ARP determines MAC addresses of all machines on a local network with a specific IP by
sending broadcast messages asking which host machine has particular IP address.
The internet protocol (IP) addressing mechanism is used to uniquely identify host machines in a
network. The IPv4 addressing uses 32 bits long numbers that are always expressed as decimal
numbers for ease of understanding. An IP address can be configured manually or automatically.
When configuring the address manually, one types in the IP value in to their OS while with
automatic addressing, the DHCP responds to a machines request for IP settings with an IP
address, subnet mask and other relate setting. An IP address is made up of two parts- a high
order (network bits) that is common to all host ion an IP network and a low order- (node bits)
that is used to specify a particular host.

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Other addressing mechanisms provided for in the IP network model include the subnet
mask, and the dynamic name system which is used to convert IP addresses to names. The sub net
mask address is applicable to all machines and is expressed in bits of 1 indicating the network
position followed by bits of 0 that indicates the node portion of the host machine. The sub net
mask address, therefore, are used to show the number of bits in an IP network dedicated to the
network and the node portions.
Addressing helps in determining type of communication- either local or remote, in
routing of packets and messages sent over different networks.
Topic 7: physical Layer
In an IP network, the layer that is used to connect computers and other network devices is
called the physical link. Being the first layer in the OSI model, the layer deals with transmissions
of bit-level information and data between the connected devices, and largely support
mechanical/electrical interfaces for synchronization purposes.
Since data exist I two format- analog and digital signals, with the digital data representing
data digitally in bits of 1s and 0s, and the analog data taking any length of bit, all analogue data
has to be digitized before transmission. Modulator Demodulator (MODEM) is an example of
device that is used to convert (and reconvert to original format) an analog signal to a digital one.
The layer offers communication, data flow, multiplexing, and encoding services in the
network. It is in the same layer that physical transmission cables and media are interfaced. Data
flow could either be simplex- a one direction flow, half duplex- a two direction data flow, but in
one at any given time and full duplex flow- two direction flow of data in concurrency or
simultaneous manner.

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Multiplexing is used to divide communication channel and sharing bandwidth among the
connected devices for thus supporting multiple conversations at a time. Multiplexing is either
achieved through time division multiplexing, frequency division and wavelength division
multiplexing.