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Ethical hacking simplified! (System fundamentals ) OSI reference Model explained continuation.

continuaton

Network addressing

A router must keep record of all its routing protocols differently in its routing table. Every routing protocol keep track of a network with different addressing scheme(IP,IPX and IPv6). For example when sending letter to humans of different languages, the letter has to read the language of the destined person, so that the message would serve its purpose.

Interface: This is the exit interface of the network on the router, to reach to the destined network. It can again be referred to the interface on the router, which packet took to reach to its destination.

Metric: This refers to the distance between to transmission network and the destined network. This distance is measured using hop(number of routers packet passed before reaching to the destined network) count.

Router is the device that works in this layer. An article will be published about the networking devices. Stay turned!

Data Link Layer

This layer is in-charge of delivering data to destined host on the network. When data reached the router on the network. Router doesn't care about the host, all it care about is the destined network. If it send forward the packet the exit interface, the router is through with its work. Upon arriving into the destined network, something must carry on from where the routing stopped. That device is known as switch. As I already mentioned that router deals with IP address (which is a 32bits logical address), the switch deals with MAC also known as hardware address. This is a 48bits address. MAC address is a static address, which is assigned by the manufacturer of the NIC(network interface card). NIC is the card (hardware) on any device that give it the privilege to join the network. Without NIC there is noway one can join football match without legs! Legs are the interface in which humans used to physically control the ball. That's the same with NIC on the network, although NIC doesn't control the network, but without NIC no device can be present on the network. When data is sent over a network, it is encapsulated. So when the router receive the packet, it strip it and check for the destination IP address. When its not in its own network, it re-encapsulate it and forward it to the next hop (router that is more closer to the destined network). One thing you have to know is the main data will never be accessed until it reached is destination.

IEEE (institute of electric and electronic engineers) data link layer has two sub-layers.

MAC(media access control) 802.3: This deals with how packets are been placed on the media. Accessing the media in this sub-layer is based on first come, first serve. The packets here share the same bandwidth. The name physical addressing is defined here, as well as logical topologies.

LLC(logical control unit) 802.2: This is responsible for identifying network layer protocols and then encapsulate them back. This sub-layer tell the data link layer what to do with a packet once the frame is received. When the host receive the frame, it looks into the LLC header to get where the packet is destined, through the IP addressing. This sub-layer again provides flow control and sequencing of control bits.
The devices here are switches and bridges. An article will be published about the networking devices. Stay turned!


Physical layer

Physical layer primary assignment is to send and receive bits. Bits(binary digits) is a base two numeric numbers which only contains 1 and 0. 1 and 0 is the only thing the computer or any other smart devices understand.
The physical layer communicate directly with the communication media (fiber optic, cables and wireless signals). Fiber optic uses light impulses, cable uses electric signals and wireless signals uses the audio or radio frequencies to send and receive data. Different technologies are used to encode and decode different communication medium.
This layer specifies the electrical, mechanical, procedural and functional requirements for enabling, maintaining and disabling communication between end devices. DTE(data terminal equipment) and DCE (data communication equipment) identification is done within the physical layer. The DCE is located at the service provider while the DTE is located at the end-user or the attached device. Again DCE can be describe as the serving device while the DTE is at the client end. DTE converts user data into signals, light impulses or frequency so as to be transmitted. DCE converts data signals, frequency and light impulses at the ISP (internet service provider) end.

The devices here are the Hub and the repeater. An article will be published about the networking devices. Stay turned!

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