Understanding Network Flows

Network Applications are classified as end host applications being used to perform a task like a Web page request from a Web Server.
What types of applications are running over the top of network. Some common applications are:
1.       Web Browsing
2.       IP Telephony
3.       Videos
4.       Email
5.       Database Applications
To run these applications, we have some sort of requirements to run these applications. These requirements  are like bandwidth, delay, security and reliability.

Bandwidth: How much data we can data we can send over the link in a given time. Bandwidth is a key attribute to run these applications. We need to first examine the bandwidth to travel the data for supporting particular examinations.
Bandwidth is the capacity of a link means how fast data can be pass over it. Like a highway is considered to be a bandwidth, and the number of car running over it in a point of time is the called as throughput.
Similarly, the filtering action of a funnel is considered as the bandwidth of the funnel.
Delay: The time during which a packet moves from one end of host to another end. It is also called as latency of the link. If we ping a particular host to 25 times,  the number of replies we get is calculated as delay.
For example, if we dial a phone call the duration over which call has been answered is called as Delay.
For a network operation, Bandwidth of a link should be high and delay is less.
Another, important requirements are Reliability and Security.
Reliability is considered as the data to be sent to another host is the as per the requirements or relevant to the application.
Reliability can be understand as if we request for a web page from a server, the server has sent the html coded page, not other applications like .jpeg image or a ASCII code, anything.Link reliability is also very important.

Security is the data authenticity, to increase the security of data various password authentications has been provided along with Frame Relay, VPN installations, layer 2 Ethernet security, or layer3 IP Security.
It is very important to understand the traffic flows in a network, because we always take care that traffic should reach with reliability and should have minimum delay.
For example, a client downloading a page from a web server, a voice calls between two people.
Network devices processes flow on the basis of OSI layer it operates.
Like layer 2 switches categorizes flow based on MAC addresses.
Layer 3 categorizes the flow based on IP addresses.

Layer 4 categorizes flow based on the TCP and UDP headers.

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