OSI Layers 1 and 2 PDF

OSI: Layers 1 and 2 Yaovi SOGLO [email protected] Objective ▪ Understand the role of the Physical and Data Link layers in the OSI model. ▪ Identify the different transmission media and their importance. ▪ Understand the concept of MAC addressing and its role in switching....

OSI: Layers 1 and 2 Yaovi SOGLO [email protected] Objective ▪ Understand the role of the Physical and Data Link layers in the OSI model. ▪ Identify the different transmission media and their importance. ▪ Understand the concept of MAC addressing and its role in switching. 2 Physical layer 3 The physical layer: definition and role ▪ The physical layer is responsible for transmitting data over the physical network. ▪ It defines the physical specifications of the cabling, connectors and electrical signals used to transmit data. ▪ Manages electrical, optical or radio signal characteristics. 4  Transmission media ▪ Transmission media are all the means by which a signal can be carried from its place of production to its destination with the least possible attenuation, dispersion or distortion. ▪ There are two categories of transmission media: Wired transmission media: coaxial cables, twisted pair cables and optical fibers; Wireless transmission media: radio waves (electromagnetic), infrared beams and laser beams. 5  Cable media: Coaxial cable ▪ Historically, they have been used for local networks and telecommunications. ▪ Coaxial cables are made up of a conductive wire, surrounded by an insulator, itself surrounded by a layer of conductors (the shield), the whole wrapped in an insulating protection. ▪ These network cables are quite powerful, with speeds ranging from 56 Kilobits to several Gigabits. ▪ These cables transmit both analog and digital signals. ▪ Example: 10B5 (10Mbps, Baseband, 500m), 10B2 (10Mbps, Baseband, 200m). 6 Wired media : Twisted pair cables ▪ Twisted pair cable is made up of eight wires, twisted in pairs to avoid the impact of interference. ▪ These are the cables most commonly used in LAN connections today. ▪ They are fitted with an RJ45 connector, hence the name RJ45 cable. Twisted pair cables: Category and shielding Category Maximum speed Bandwidt Application h Local area networks (LANs), home and Cat 5e Up to 1 Gbps 100 MHz office Internet connections ▪ There are several categories of network cable, classified mainly Up to 10 250 MHz Enterprise networks, according to their ability to Cat 6 Gbps (55 m) medium-sized cabling transmit high-speed data. systems Cat 6a Up to 10 500 MHz High-speed business ▪ Each category corresponds to a Gbps (100 m) connections set of performance standards defined by ISO/IEC. Cat 7 Up to 10 600 MHz Interference-sensitive Gbps environments Cat8 Up to 40 2000 MHz Data centers, very Gbps high-speed connections 8  ▪ Network cables are often shielded to protect them Twisted pair cables: from electromagnetic interference (EMI) and external disturbances. Category and ▪ Here are the most common types of shielding: shielding Cable Description Benefits Disadvantages type Unshielded twisted- Flexible, economical Sensitive to UTP pair cable electromagnetic interference A metal foil surrounds Good interference Less individual shielding FTP all twisted pairs protection, flexible per pair Each pair of wires is Good protection More rigid, more STP individually shielded against EMI and RFI expensive Individual pair Maximum protection Costly and inflexible S/FTP shielding and global against interference shielding 9  Twisted pair cables: Crimping ▪ The art of joining the connector to the end of the cable is called "crimping". ▪ When crimping a network cable, there are certain standards to be respected, depending on the type of cable required. ▪ Today, only straight cables are used, as network cards can easily differentiate between transmission and reception. ▪ Connecting the wires inside a cable isn't just done any old way: you have to follow a color code. ▪ Specific wires are used for transmission and reception: ▪ 1 and 2 in Transmission ▪ 3 and 6 in Reception. 10  Cable media: fiber optics ▪ Optical fibers transmit signals by means of light pulses. ▪ These light pulses are emitted at one end of the optical fiber, propagate through the fiber to the other end, where they are picked up by a light receiver. ▪ Today, there are basically two types of fiber: single-mode fiber ; multimode fiber. 11 Cable media: fiber optics Multimode fiber: works with white light, and therefore all wavelengths. Multimode fiber is less efficient and can only cover a distance of around 2 km. It is most often used for urban interconnections. Single-mode fiber: it transmits a single wavelength of light, i.e. a single color. It therefore works with lasers, which can be green, blue, red, etc. It can cover a distance of around 60 km, with a record of around 8,000 km. This is how we linked the United States and Europe, using single-mode fiber in the Atlantic, and repeating the light signal every 60 km. 12 Wireless media ▪ Wireless technologies use electromagnetic waves as their medium. ▪ Bits are transmitted using electromagnetic waves as a medium, via modulation techniques. ▪ These waves are transmitted and received by the antennas built into every wireless card. ▪ These techniques are obviously weaker than cable transport, whether optical or copper. ▪ Already, waves attenuate with the distance they travel: beyond a certain distance, the transmitted signal is too weak to be picked up. ▪ The range of wireless is therefore limited, whereas cables are capable of a much longer reach. 13 Wireless media ▪ In addition, walls and other objects tend to attenuate the electromagnetic waves passing through them, reducing signal amplitude. ▪ The wavelengths used are often radio waves. ▪ Infrared waves are rarely used in computer networks. ▪ Similarly, microwaves are not used in wireless networks. ▪ All current wireless networks use radio waves, i.e. waves with frequencies between 9 kHz and 300 GHz. 14 The Data Link Layer 15 Definition and role Ensures communication between two adjacent nodes. Manages data encapsulation in frames, error control and media access. Underlay : ❖ LLC (Logical Link Control): Manages flow control and error correction. ❖ MAC (Media Access Control): Manages access to the transmission medium and MAC addressing. Equipment: Network card, Switch 16  MAC address Key concept: every device on a network has a MAC (Media Access Control) address, which is a unique identifier assigned to each device's network card. MAC address structure: The MAC address is a 48-bit string, generally represented in hexadecimal form. o The first three bytes (OUI identifier) identify the network card manufacturer. o The last three bytes form a unique identifier assigned by the manufacturer (NIC). 17  A switch is a network device that connects several node devices within Role of a single local area network (LAN). Switches are used to transfer Ethernet frames according to the destination MAC address. switches To do this, they can use unicast, multicast or broadcast. Unicast: Communication from one node to another. Multicast: Communication from a node to a specific group. Broadcast: Communication to all nodes on the network. 18  MAC addressing and switching ▪ Network switching is a crucial element of modern network infrastructure. ▪ This is a process that enables the transfer of data packets from one device to another within the same network. ▪ Network switching is essential for improving network connectivity and performance. ▪ When a switch receives a frame, it consults its MAC table to decide where to send the frame, based on the recipient's MAC address. ▪ If the address is not present in the table, the switch sends the frame on all ports (except the one on which it arrived), a process known as flooding. 19 Conclusion 20  Conclusion Summary of key points: Physical layer: Transmission of bits over physical media (wired and wireless). Data Link Layer: Encapsulation of frames and management of media access using MAC addressing. Switching: Switches play an essential role in frame transmission based on MAC address. 21 Thank you for your attention!