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10/15/2023 CMPS 3171: Network Design Chapter 08 – OSI Physical Layer (1) 1 Objectives  Explain the role of Physical layer pr...

10/15/2023 CMPS 3171: Network Design Chapter 08 – OSI Physical Layer (1) 1 Objectives  Explain the role of Physical layer protocols and services in supporting communication across data networks.  Describe the role of signals used to represent bits as a frame as the frame is transported across the local media  Describe the purpose of Physical layer signaling and encoding as they are used in networks  Identify the basic characteristics of copper, fiber and wireless network media  Describe common uses of copper, fiber and wireless network media 2 CMPS3171 - SC08-PhysicalLayer 1  10/15/2023 Physical Layer: Communication Signals Upper OSI layer protocols prepare data from the human network for transmission to its destination. The Physical layer controls how data is placed on the communication media by: – encoding the binary digits that represent Data Link layer frames into signals – transmitting and receiving these signals across the physical media - copper wires, optical fiber, and wireless - that connect network devices. 3 Physical Layer: Communication Signals Physical Layer Purpose This layer accepts a complete frame from the Data Link layer and encodes it as electrical, optical, or microwave 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. The delivery of frames across the local media requires the following Physical layer elements: –The physical media and associated connectors –A representation of bits on the media –Encoding of data and control information –Transmitter and receiver circuitry on the network devices This layer also retrieves signals from the media, restores them to their bit representations, and passes the bits up to the Data Link layer as a complete frame. 4 CMPS3171 - SC08-PhysicalLayer 2  10/15/2023 Physical Layer: Communication Signals Physical Layer Operation  The media does not carry the frame as a single entity.  The media carries signals, one at a time, to represent the bits that make up the frame.  There are three basic forms of network media on which data is represented: 1. Copper (electrical pulses) 2. Fiber (patterns of light) 3. Wireless (radio transmission) 5 Physical Layer: Communication Signals Physical Layer Standards  The Physical layer consists of hardware, developed by engineers, in the form of electronic circuitry, media, and connectors.  The standards governing this hardware are defined by the relevant electrical and communications engineering organizations.  By comparison, the protocols and operations of the upper OSI layers are performed by software and are designed by software engineers and computer scientists. E.g. TCP/IP suite are defined by the Internet Engineering Task Force (IETF) in RFCs. 6 CMPS3171 - SC08-PhysicalLayer 3  10/15/2023 Physical Layer: Communication Signals Physical Layer Standards There are four areas of the Signals Physical layer standards: 1. Physical and electrical properties of the media 2. Mechanical properties (materials, dimensions, pinouts) of the Connectors connectors 3. Bit representation by the signals (encoding) 4. Definition of control information signals Hardware components such as NICs, interfaces and connectors, Cables and NICs cable materials, and cable designs are all specified in standards associated with the Physical layer. 7 Physical Layer: Communication Signals Physical Layer Fundamental Principles The three fundamental functions of the Physical layer are: – Data encoding A method of converting a stream of data bits into a predefined "code. – Signaling Defines what type of signal represents a "1" and a "0". This can be as simple as a change in the level of an electrical signal or optical pulse or a more complex signaling method. – The physical components The electronic hardware devices, media and connectors that transmit and carry the signals to represent the bits 8 CMPS3171 - SC08-PhysicalLayer 4  10/15/2023 Physical Signaling and Encoding Signaling Bits for the Media The transmission of the frame across the media occurs as a stream of bits sent one at a time Each signal placed onto the media has a specific amount of time to occupy the media – i.e. its bit time. Signals representing the bits on the media will depend on the signaling method in use. Bits are represented on the medium by changing one or more of the following characteristics of a signal: –Amplitude –Frequency –Phase Successful delivery of the bits between transmitter and receiver is accomplished by the use of a clock. 9 Physical Signaling and Encoding Signaling Methods Signaling methods to represent bits on the media can be complex. Some methods may use one attribute of signal to represent a single 0 and use another attribute of signal to represent a single 1. Two of the simpler techniques to illustrate the concept are: –Non-Return to Zero (NRZ) A 0 may be represented by one voltage level on the media during the bit time and a 1 might be represented by a different voltage on the media during the bit time. –Manchester Encoding Indicates a 0 by a high to low voltage transition in the middle of the bit time. For a 1 there is a low to high voltage transition in the middle of the bit time. 10 CMPS3171 - SC08-PhysicalLayer 5  10/15/2023 Physical Signaling and Encoding Encoding – Grouping Bits  Encoding represent the symbolic grouping of bits prior to being presented to the media  By using an encoding step before the signals are placed on the media, we improve the efficiency at higher speed data transmission  Signal Patterns provide frame detection by beginning each frame with a pattern of signals representing the start of a frame and another pattern of bits signaling the end of the frame.  Signal patterns can indicate: start of frame, end of frame, and frame contents. 11 Physical Signaling and Encoding Encoding – Grouping Bits Encoding techniques use bit patterns called symbols The Physical layer may use a set of encoded symbols called code groups to represent encoded data or control information. E.g. code bits 10101 could represent the data bits 0011. Although using code groups introduces overhead in the form of extra bits to transmit, they improve the robustness of a communications link. This is particularly true for higher speed data transmission. Advantages using code groups include: –Reducing bit level error –Limiting the effective energy transmitted into the media –Helping to distinguish data bits from control bits –Better media error detection These are important considerations in supporting high speed transmission over the media. 4 bits of data are turned into 5-bit code symbols for transmission over the media system. 16 of 32 code groups allocated for data bits, the rest used for control symbols and invalid symbols 12 CMPS3171 - SC08-PhysicalLayer 6  10/15/2023 Physical Signaling and Encoding Data Carrying Capacity  Different physical media support the transfer of bits at different speeds  Data transfer can be measured in three ways: –Bandwidth The capacity of a medium to carry data is described as the raw data bandwidth of the media –Throughput Throughput is the measure of the transfer of bits across the media over a given period of time –Goodput The measure of usable data transferred over a given period of time, and is therefore the measure that is of most interest to network users  As an example, consider two hosts on a LAN transferring a file: –The bandwidth of the LAN is 100 Mbps –Due to the sharing/media overhead the throughput between the computers is only 60 Mbps –With the overhead of the TCP/IP encapsulation process, the actual rate of the data received by the destination computer, goodput, is only 40Mbps. 13 Physical Media Types of Physical Media Various standards organizations have contributed to the definition of the physical, electrical, and mechanical properties of the media available for different data communications These specifications guarantee that cables and connectors will function as anticipated with different Data Link layer implementations. As an example, standards for copper media are defined for the: – Type of copper cabling used – Bandwidth of the communication – Type of connectors used – Pin-out and color codes of connections to the media – Maximum distance of the media 14 CMPS3171 - SC08-PhysicalLayer 7  10/15/2023 Physical Media Copper Media  The most commonly used media for data communications is cabling that uses copper wires to signal data and control bits between network devices.  Types of media: include: Unshielded Twisted Pair (UTP), Coaxial and Shielded Twisted Pair (STP)  A single type of physical connector may be used for multiple types of connections. E.g. RJ-45 connectors are used in LANs and WANs with different media types.  Data is transmitted on copper cables as electrical pulses and the timing and voltage values of these signals are susceptible to interference or "noise" from outside the communications system.  These unwanted signals can distort and corrupt the data signals being carried by copper media.  Radio waves and electromagnetic devices such as fluorescent lights, electric motors, and other devices are potential sources of noise. 15 Physical Media Unshielded Twisted Pair (UTP)  Four pairs of color-coded wires that have been twisted together and then encased in a flexible plastic sheath.  The twisting has the effect of canceling unwanted signals and helps avoid interference from internal sources called crosstalk.  TIA/EIA-568A stipulates the commercial cabling standards for LAN installations that includes elements such as: –Cable types –Cable lengths –Connectors –Cable termination –Methods of testing cable  Cables are placed into categories according to their ability to carry higher bandwidth rates. E.g. Cat 5, 5e, 6, 7, 8  Different situations may require UTP cables to be wired according to different wiring conventions i.e. Straight-through, crossover and rollover cables 16 CMPS3171 - SC08-PhysicalLayer 8  10/15/2023 Physical Media Other Copper Cable Two other types of copper cable are used: –Coaxial All the elements of the coaxial cable encircle the center conductor. Because they all share the same axis, this construction is called coaxial, or coax for short. Replaced by lower cost and higher bandwidth UTP for Ethernet installations. Use: Wireless & Cable access, Hybrid Fiber Coax (HFC) –Shielded Twisted-Pair (STP) STP cable shields the entire bundle of wires within the cable as well as the individual wire pairs. STP provides better noise protection than UTP cabling, however at a significantly higher price. Use: Token-ring, 10GB Ethernet 17 Physical Media Copper Media Safety Electrical Hazards –Defective network devices could conduct currents to the chassis of other network devices –Undesirable voltage levels can result from devices with different ground potentials –May conduct voltages caused by lightning to network devices Fire Hazards –Sheaths may be flammable –May produce toxic fumes when heated or burned 18 CMPS3171 - SC08-PhysicalLayer 9  10/15/2023 Physical Media Fiber Media  Glass or plastic fibers to guide light impulses (bits) from source to destination.  Very large raw data bandwidth rates.  Immune to electromagnetic interference and will not conduct unwanted electrical currents due to grounding issues or lightning  Can be operated at much greater lengths than copper media, without the need for signal regeneration  Optical fiber media implementation issues include: –More expensive (usually) than copper media over the same distance (but for a higher capacity) –Different skills and equipment required to terminate and splice the cable infrastructure –More careful handling than copper media  Because light can only travel in one direction over optical fiber, two fibers are required to support full duplex operation. 19 Physical Media Fiber Media (continued)  Primarily used as backbone cabling for high-traffic point-to-point connections between data distribution facilities and for the interconnection of buildings in multi-building campuses.  Either lasers or light emitting diodes (LEDs) generate the light pulses that are used to represent the transmitted data as bits on the media.  Electronic semi-conductor devices called photodiodes detect the light pulses and convert them to voltages that can then be reconstructed into data frames. 20 CMPS3171 - SC08-PhysicalLayer 10  10/15/2023 Physical Media Wireless Media  Electromagnetic signals at radio and microwave frequencies that represent the binary digits of data communications.  Not restricted to conductors or pathways, as are copper and fiber media.  Works well in open environments but certain construction materials used in buildings and structures, and the local terrain, will limit the effective coverage.  Is susceptible to interference and can be disrupted by such common devices as household cordless phones, some types of fluorescent lights, microwave ovens, and other wireless communications.  Because it requires no access to a physical strand of media, devices and users who are not authorized for access to the network can gain access to the transmission.  Therefore, network security is a major component of wireless network administration. 21 Physical Media Types of Wireless Networks Four common data communications standards that apply to wireless media are: Standard IEEE 802.11 –Commonly referred to as Wi-Fi –Wireless LAN (WLAN) technology that uses a contention or non-deterministic system with a Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) media access process. Standard IEEE 802.15 –Commonly known as "Bluetooth“ –Wireless Personal Area Network (WPAN) standard that uses a device pairing process to communicate over distances from 1 to 100 meters. Standard IEEE 802.16 – –Commonly known as WiMAX (Worldwide Interoperability for Microwave Access) –Uses a point-to-multipoint topology to provide wireless broadband access. Global System for Mobile Communications (GSM) –Includes Physical layer specifications that enable the implementation of the Layer 2 General Packet Radio Service (GPRS) protocol to provide data transfer over mobile cellular telephony networks. Other wireless technologies such as satellite communications provide data network connectivity for locations without another means of connection. 22 CMPS3171 - SC08-PhysicalLayer 11  10/15/2023 Physical Media Wireless LAN Wireless LANs require the following network devices: –Wireless Access Point (AP) - Concentrates the wireless signals from users and connects to the existing copper- based network infrastructure such as Ethernet. –Wireless NIC adapters - Provides wireless communication capability to each network host. Standards include: IEEE 802.11a - 5 GHz/ speeds of up to 54 Mbps. Because it operates at higher frequencies, it has a smaller coverage area and is less effective at penetrating building structures. Not interoperable with the 802.11b and 802.11g standards IEEE 802.11b - 2.4 GHz/ speeds of up to 11 Mbps. Devices implementing this standard have a longer range and are better able to penetrate building structures than 802.11a. IEEE 802.11g - 2.4 GHz/ speeds of up to 54 Mbps. Devices implementing this standard therefore operate at the same radio frequency and range as 802.11b but with the bandwidth of 802.11a. IEEE 802.11n - 2.4 GHz or 5 GHz frequency, data rates of 100 Mbps to 210 Mbps with a distance range of up to 70 meters. While benefits of savings on costly premises wiring and the convenience of host mobility, network administrators need to develop and apply stringent security policies and processes to protect wireless LANs from unauthorized access and damage. 23 Physical Media Media Connectors 24 CMPS3171 - SC08-PhysicalLayer 12  10/15/2023 Layer 1 Summary The following was covered:  The role of Physical layer protocols and services in supporting communication across data networks.  The purpose of Physical layer signaling and encoding as they are used in networks.  The role of signals used to represent bits as a frame is transported across the local media.  The basic characteristics of copper, fiber, and wireless network media.  Common uses of copper, fiber, and wireless network media. 25 CMPS3171 - SC08-PhysicalLayer 13