This article covers everything one like to know about networking basics including circuit switching vs packet switching, TCP/IP protocol fields, ARP/RARP protocol fields, what is IP address ,what is MAC address, networking devices which include hub, switch, bridge, router, gateway and firewall. In this section we will see OSI and TCP IP stack and describe functions of physical layer,data link,networking layer-IP,transport-TCP,application layers.

This article outlines OSI layers and TCPIP basics required for RF and Wireless Engineers. The OSI(Open system Interconnection) is developed for defining seven layers which makes two different vendors systems communicate. TCPIP is used for internet applications mainly. The figure describes how TCPIP layers map to OSI layers.

In OSI layer model, control is passed from one layer to the next, starting at the Layer 7, application layer in one station, proceeding to the succeeding bottom layer and so on till information reaches Layer 1.Then the information transmitted over the channel to the next station's Layer 1 and transmitted to succeeding layers till information delivered to Layer 7. Each Layer in the OSI model does the job for the previous layer and also adds prefixes information termed as "header". The data link layer adds suffixes called cyclic redundancy check as "trailer" which is used for error detection. The brief functionality of each OSI layer is mentioned below.

Application:

All the applications for user reside at this layer. It includes FTP, Telnet, e-mail etc.

Presentation:

It formats and encrypts data to be sent across a network. Its basic task is to make application layer and network layer talk to each other by processing the data. It provides independence to the application processes from differences in data representation by way of syntax conversion.

Session:

It Provides control mechanism to connect two applications running on different machines. It covers basic function to establish, to maintain and to release connections.

Transport:

It assures reliable data communication between two hosts. It is responsible for error recovery and flow control between two hosts. It also does multiplexing and de multiplexing functionalities for transmitting and receiving host respectively.

Network:

The main function is switching and routing of the packet. It adds logical addressing to do this. It also takes care of error handling, congestion control and packet sequencing.

Data Link:

It takes care of errors in the physical layer. It provides flow control and also does frame synchronization. ARQ is implemented to take care of retransmission in case of erroneous packets. In latest today's technologies it provides Medium Access Control functionality, hence known as MAC. MAC takes care of resource assignment to the end devices wanted to seek connection to the network for various applications (voice, data, etc.)

Physical:

It mainly takes care of bit stream transmission over physical medium (cable, air etc.). It provides the hardware means of sending and receiving data through cable or wireless medium. Some wireless standards viz. wlan, wimax, zigbee, LTE defines physical layer specifications which takes care of forward error correction and modulation-demodulation functionalities as well as making the information suitable to be transmitted. Following figure mentions logical structure of the layered protocols inside a computer on an internet. This figure is taken from RFC 1180 to describe the concept.

RFC1180 describes logical structure of protocols inside a typical internet enabled device as mentioned below.

Ethernet Cable--ENET Card--ARP/IP--TCP/UDP--Network Applications

As mentioned etnernet cable is connected directly with Ethernet card which has upper layer ARP or IP. This has upper layer TCP or UDP and above all applications are running.