Lec06_physical layer.pptx

LEC06: PHYSICAL LAYER Purpose of the Physical Layer: The Physical Connection The physical layer of the OSI model sits at the bottom of the stack. It is part of the network access layer of the TCP/IP model. Without the physical layer, you would not have a network. All data being transferred over a ne...

LEC06: PHYSICAL LAYER Purpose of the Physical Layer: The Physical Connection The physical layer of the OSI model sits at the bottom of the stack. It is part of the network access layer of the TCP/IP model. Without the physical layer, you would not have a network. All data being transferred over a network must be represented on a medium by the sending node and interpreted on a medium by the receiving node. The physical layer is responsible for these functions. Before any network communications can occur, a physical connection to a local network must be established. This connection could be wired (Data is transmitted through a physical cable)or wireless(data is transmitted using radio waves), depending on the setup of the network. Devices on a wireless network must be connected to a wireless access point (AP) or wireless router. A Network Interface Card (NIC) connects a device to the network. Some devices may have just one NIC, while others may have multiple NICs (Wired and/or Wireless, for example). Not all physical connections offer the same level of performance. Purpose of the Physical Layer: The Physical It provides the means to transport the bits that make up a data link layer frame across the network media Accepts a complete frame from the Data Link Layer and encodes it as a series of signals that are transmitted to the local media The encoded bits that comprise a frame are received by either an end device or an intermediate device. This is the last step in the encapsulation process. Then, the bits are sent over the physical medium The physical layer encodes the frames and creates the electrical, optical, or radio wave signals that represent the bits in each frame and sent it. The destination node physical layer retrieves these individual signals from the media, restores them to their bit representations, and passes the bits up to the data link layer as a complete frame. Layer Physical Layer Characteristics :Physical Layer Standards The protocols and operations of the upper OSI layers are performed using software designed by software engineers and computer scientists. The services and protocols in the TCP/IP suite are defined by the Internet Engineering Task Force (IETF). The physical layer consists of electronic circuitry, media, and connectors developed by engineers. Therefore, it is appropriate that the standards governing this hardware are defined by the relevant electrical and communications engineering organizations. Physical Layer Characteristics: Physical Components Physical Layer Standards address three functional areas: Physical Components Encoding Signaling The Physical Components are the hardware devices, media, and other connectors that transmit the signals that represent the bits. Hardware components like NICs, interfaces and connectors, cable materials, and cable designs are all specified in standards associated with the physical layer. Physical Layer Characteristics: Encoding Encoding converts the stream of bits into (a predefined code) a format recognizable by the next device in the network path. Codes are groupings of bits used to provide a predictable pattern that can be recognized by both a sender and a receiver or by the next device. encoding is a method or pattern used to represent digital information Examples of encoding methods include Manchester encoding(shown in the figure) which represents a high- to low-voltage transition as a 0 bit and a low- to high-voltage transition as a 1 bit. The transition occurs at the middle of each bit period. Manchester encoding is used in older Ethernet standards, such as 10BASE-T. Ethernet 100BASETX uses 4B/5B encoding, and 1000BASE-T uses 8B/10B encoding. Physical Layer Characteristics: Signaling The physical layer must generate the electrical, optical, or wireless signals that represent the 1s and 0s on the media. The signaling method is how the bit values, “1” and “0” are represented on the physical medium (or the way that bits are represented). The physical layer standards must define what type of signal represents a 1 and what type of signal represents a 0 The method of signaling will vary based on the type of medium being used. Light Pulses Over Fiber-Optic Cable Microwave Signals Over Wireless Electrical Signals Over Copper Cable Physical Layer Characteristics: Bandwidth Different physical media support the transfer of bits at different rates Bandwidth is the capacity at which a medium can carry data. Digital bandwidth measures the amount of data that can flow from one place to another in a given amount of time; how many bits can be transmitted in a second. Factors determines the practical bandwidth of a network: The properties of the physical media The technologies chosen for signaling and detecting network signals. Physical media properties, current technologies, and the laws of physics play a role in determining available bandwidth. Unit of Bandwidth Abbreviation Equivalence Bits per second bps 1 bps = fundamental unit of bandwidth Kilobits per second Kbps 1 Kbps = 1,000 bps = 10 3 bps Megabits per second Mbps 1 Mbps = 1,000,000 bps = 10 6 bps Gigabits per second Gbps 1 Gbps – 1,000,000,000 bps = 10 9 bps Terabits per second Tbps 1 Tbps = 1,000,000,000,000 bps = 10 12 bps Physical Layer Characteristics: Bandwidth Terminology Terms used to measure the quality of bandwidth include: Latency, throughput, and goodput. Latency Amount of time, including delays, for data to travel from one given point to another Throughput The measure of the transfer of bits across the media over a given period of time Many factors that influence throughput: amount of traffic , type of traffic, and latency created by the number of network devices encountered between source and destination. Goodput The measure of usable data transferred over a given period of time Goodput = Throughput - traffic overhead (for establishing acknowledgments, encapsulation, and retransmitted bits). sessions, Goodput is always lower than throughput, which is generally lower than the bandwidth. Copper Cabling : Characteristics of Copper Cabling Copper cabling is the most common type of cabling used in networks today. It is inexpensive, easy to install, and has low resistance to electrical current flow. However, copper cabling is limited by distance and signal interference Limitations: Attenuation – the longer the electrical signals have to travel, the weaker they get. The electrical signal is susceptible to interference from two sources, which can distort and corrupt the data signals (Electromagnetic Interference (EMI) and Radio Frequency Interference (RFI) and Crosstalk). crosstalk is a disturbance caused by the electric or magnetic fields of a signal on one wire to the signal in an adjacent wire. Mitigation: Strict adherence to cable length limits will mitigate attenuation. Some kinds of copper cable mitigate EMI and RFI by using metallic shielding and grounding. Some kinds of copper cable mitigate crosstalk by twisting opposing circuit pair wires together. Copper Cabling: Types of Copper Cabling Fiber-Optic Cabling: Properties of Fiber-Optic Cabling Not as common because of the expense involved Ideal for some networking scenarios Transmits data over longer distances at higher bandwidth than any other networking media Less susceptible to attenuation, and completely immune to EMI/RFI Made of flexible, extremely thin strands of very pure glass Uses a laser or LED to encode bits as pulses of light The fiber-optic cable acts as a waveguide or light pipe to transmit light between the two ends with minimal signal loss Fiber-Optic Cabling: Types of Fiber Media Single-Mode Fiber Very small core Uses expensive lasers Long-distance applications (spanning hundreds of kilometers) Multimode Fiber Larger core Uses less expensive LEDs LEDs transmit at different angles bandwidth Up to 10 Gbps over 550 meters Dispersion refers to the spreading out of a light pulse over time. Increased dispersion means increased loss of signal strength. MMF has greater dispersion than SMF, with a the maximum cable distance for MMF is 550 meters. Fiber-Optic Cabling: Fiber versus Copper Optical fiber is primarily used as backbone cabling for high-traffic, point-topoint connections between data distribution facilities and for the interconnection of buildings in multi-building campuses. Because fiberoptic cables do not conduct electricity and have low signal loss, they are well suited for these uses. Implementation Issues UTP Cabling Fiber-Optic Cabling Bandwidth supported 10 Mb/s - 10 Gb/s 10 Mb/s - 100 Gb/s Distance Relatively short (1 - 100 meters) Relatively long ( 1 - 100,000 meters) Immunity to EMI and RFI Low High (Completely immune) Immunity to electrical hazards Low High (Completely immune) Media and connector costs Lowest Highest Installation skills required Lowest Highest Safety precautions Lowest Highest Wireless Media: Properties of Wireless Media It carries electromagnetic signals representing binary digits using radio or microwave frequencies. This provides the greatest mobility option. Some of the limitations of wireless: Coverage area - Effective coverage can be significantly impacted by the physical characteristics of the deployment location. Interference - Wireless is susceptible to interference and can be disrupted by many common devices. Security - Wireless communication coverage requires no access to a physical strand of media, so anyone can gain access to the transmission. Shared medium - WLANs operate in half-duplex, which means only one device can send or receive at a time. Many users accessing the WLAN simultaneously results in reduced bandwidth for each user. Wireless Media : Types of Wireless Media The IEEE and telecommunications industry standards for wireless data communications cover both the data link and physical layers. Wireless Standards: Wi-Fi (IEEE 802.11) - Wireless LAN (WLAN) technology- uses a contention-based protocol known as Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA). The wireless NIC must first listen before transmitting to determine if the radio channel is clear. If another wireless device is transmitting, then the NIC must wait until the channel is clear. Bluetooth (IEEE 802.15) - Wireless Personal Area network (WPAN) standard that uses a device pairing process to communicate over distances from 1 to 100 meters. WiMAX (IEEE 802.16) –(Worldwide Interoperability for Microware Access) Uses a point-tomultipoint topology to provide broadband wireless access. Zigbee (IEEE 802.15.4) - Low data-rate, low power-consumption communications, primarily for Internet of Things (IoT) applications Wireless Media: Wireless LAN In general, a Wireless LAN (WLAN) requires the following devices: Wireless Access Point (AP) - Concentrate wireless signals from users and connect to the existing copper-based network infrastructure. Home and small business wireless routers integrate the functions of a router, switch, and access point into one device. Wireless NIC Adapters capability to network hosts - Provide wireless communications Network Administrators must develop and apply stringent security policies and processes to protect WLANs from unauthorized access and damage. THANKS! Best Regards!