Data link layer,physical layer.

Hello guys, how are you? I am fine and as you already understood, there is new part of my project. In this post, I am going to write about last week’s learning process. If you are interested, you can read and get short view about topic and our lessons.
. This week’s topics were Data Link and Physical Layers, which are called TCP/IP network access layers. As I mentioned before, when sending some data, firstly it is encapsulated to segment/datagram in Layer 4(Transport Layer), then to packet in Layer 3 (Network Layer). After it is encapsulated to frame in Layer 2 (Data-Link Layer), and then to Bitstream/Bitcode in Layer 1 (Physical Layer). Let me explain about Layer 2 shortly. Addressing type used in frame, which is encapsulated by Data-Link Layer, is called MAC address or physical address. Main functions of Data-Link Layers are to allow upper layers to access the media using framing and to control how the data is taken from media by using media access control and error detection. In addition, it consists of two sublayers, called Logical Link Control (LLC) and Media Access Control (MAC) where one is responsible for implementation on software, while other is implemented on physical part (hardware). All data-link protocols help to encapsulate frame from Layer 3 PDU. There are different frame fields in Layer 2 such as Preamble, Source and Destination MAC-addresses, etc.
. The lowest layer of OSI model is physical layer, where frame from data-link layer is encoded into bitsream or bitcode and signals are generated. First function of this layer is data encoding, which differentiates data bits from control bits, enhances error detection and converts stream into defined code. Defined code is grouping of bits for providing predictable pattern that can be recognized by both sender and receiver. Second function of Layer1 is signaling. There are three types of signaling: electric signals (used in copper media), light signals (used in fiber optic) and microwave or electromagnetical signals (used in wireless connection). Shortly, signaling method is method of representing the bits by “0”,”1”.There are three methods of signaling, which are amplitude, frequency and phase. Also, there are physical components in Layer1, which are electronic hardware devices, media and connectors that can transmit signals to represent bits. Using proper hardware and media is important in network connection, therefor physical layer is important. On lesson, we did laboratory work using physical hardware. We built Ethernet Crossover Cable and tested it. We used equipment such as cable, 2RJ-45 connectors, RJ-45 crimping tool, wire cutter, wire stripper and Ethernet cable tester. Crossover cables are normally used to connect hubs to hubs or switches to switches, but they can also be used to directly connect two hosts to create a simple network. We cut two ends of cable with wire stripper and removed cable jacket with wire cutter. Then we inserted four cable pairs in order T-568A/B standard into RJ-45 connector at the end of cable. After checking is everything correct, we put RJ connector with cable into the crimper and crimped it down to fix connector on the end of cable. Then our instructor checked our work using Ethernet cable tester and everything was working. Finally, we are going deeper to networks and now we know about all layers of networking. We have general imagination on how connection is set and what is happening in process. Material and labs are getting hard, so I hope I can understand and successfully finish this course