The first layer and also the lowest layer for the OSI layer is called Physical Layer. The physical layer consists of all basic hardware transmission technologies and electrical specifications for devices used to connect to the network, including the shape and layout of pins in connectors, voltages, cable specifications and broadcast frequencies.
The function of the OSI Physical Layer is to do the transmission of the data across the network media the bits that make up a Data Link layer frame. This layer accepts a complete frame from the Data Link layer and encodes it as a series of signals that are transmitted onto the local media. The encoded bits that comprise a frame are received by either an end device or an intermediate device.
Physical Layer Ethernet standard can found in this layer. Ethernet will work within the Physical Layer and the Data Link Layer. The same apply to other local area networks, such as token ring and IEEE 802.11, as well as personal area networks such as Bluetooth.
The purpose of the Physical layer is to sending and receiving of data. It also handled the exchanging between the demonstrations of digital data and signals broadcasting over a transportation channel.
There are three types of medium for different type of signal, such as copper cable which is support electrical signal, optical-fiber cable which is support light pulse signal and the last is wireless media which is support microwave signal
Layer 2 : Data Link Layer
The second layer of the OSI model is called Data Link Layer. In this data link layer will provide consistent transit of data across a physical link. The data link layer is concerned with physical addressing, network topology, physical link management, error notification, ordered delivery of frames, and flow control.
When Data Link Layer gets the data from the Physical Layer, it will check for the physical transmission errors and packages bits into frames.
OSI Data Link Layer has two other sub layers, such as Media Access Control (MAC) layer and Logical Link Control (LLC) layer. Media Access Control is use to manage how and where computers on the network get access to the information and consent to broadcast it. While for the Logical Link Control layer which is use for frame management, error checking, and flow control of data. The HDLC, LSL, and ATM are the implemented protocols on his layer.
Layer 3 : Network Layer
Layer 4 : Transport Layer
Layer 5 : Session Layer
Layer 6 : Presentation Layer
Layer 7 : Application Layer
Dev by International Organization for Standardization to improved set of protocols for less confusion and easier standardization of networking products among multiple vendors.
Bus Network Topology
Figure 2.1 Bus Network Topology
(Source: Maksim, 2006, Network Topologies, viewed on 16th March 2011 http://en.wikipedia.org/wiki/File:NetworkTopologies.png)
The Figure 2.1 shows a bus network with six computer or other devices which is called nodes. Each node is shown as a sphere, the main cable which is called bus shown as a horizontal line, and connections to the bus appear as vertical lines.
The physical topology for the bus network topology is connecting all the computers with a single and long cable. The design for the bus network topology is the simplest design to connect multiple clients if compare to other network topology design.
The bus network topology is simple and reliable, even if one of the nodes is broken or corrupted will not affected the network, other computer can still connect to each other. But if once the main cable broken can disable the whole network.
By using this network topology can easy to implement and extend, node can be added anywhere as long as connected to the main cable but there is a limit number of stations. Besides that, bus network topology is the cheapest network topology. The disadvantages for bus network topology is low security because of the data transmissions are visible for all the computers and if there is a virus in the network will affect the all the computer that connecting a same network.
(Source: Anonymous, Network Topology, 2011)