OSI Model: Physical Layer & Network Admin

• The unit of work is unit 8
• The subject matter is the physical layer of the OSI model
• The topic is planning and administrating networks

Introduction to the Physical Layer

• The physical layer transports bits across network media.
• It accepts data link layer frames and delivers them as bits into the physical medium.
• Bits are encoded as signals to be transmitted over local media.
• The CPU creates protocol data units (PDUs) from layers 6 to 3, and delivers the packets to the Network Interface Card (NIC).
• The NIC handles encapsulation/decapsulation, managing layers 1 and 2 without CPU intervention.
• The physical layer is the final step in encapsulation
• Receiving devices decapsulate the frame and determine the next action.

Physical Layer Characteristics

• The physical layer defines mechanical, electrical, and functional characteristics to activate, maintain, and deactivate physical transmission connections.
• Physical characteristics definition of interfaces with the transmission medium.
• Transmission medium characteristics definition.
• Digital data encoding.
• Line configuration.
• Physical topology.
• Transmission mode
• Transmission speed.

Level 1 Functions

• Specifications for electrical, mechanical, and functional aspects of connectors.
• Guided media characteristics definition.
• Digital data is encoded to represent 0s and 1s as electrical signals for transmission.
• Line Configuration: the manner in which devices connect to the medium in point-to-point or multipoint setups.
• Physical Topology: the arrangement of network device connections.
• Transmission Modes: Simplex, half-duplex, full-duplex are the three types
• Transmission Speed: communication bit rate.

Communication Signals

• The transmitter encodes frames in bits as electrical signals.
• The sender does not take into consideration how the frames are transmitted till arrival
• Each device retransmits messages, encoding them based on the connected medium such as fiber optic, UTP/STP, or wireless.
• The physical layer provides transport media for data link layer frame bits.
• Components: physical media and related connectors.
• Bit representation in media.
• Data and control information coding.
• Receiver and transmitter circuit systems in network devices.

Signal Types

• Signal type depends on the medium involved
• Pulse patterns are used for electrical signals
• Patterns of light are used for optical signals
• Radio transmission patterns are used for wireless signals
• The physical layer helps recognize the beginning and end of a frame

Standards

• Alike other layers the physical layer relies on established standards for hardware characteristics
• There standards define: physical and electrical properties for the media, mechanical properties (materials, dimensions, pin diagrams) for connectors
• The standards also define the representation of bits using signals (encoding) and the definition of control information signals.
• Standards are TCP/IP established and maintained by IETF
• There are also established standards by ISO, ANSI, IEEE, ITU, EIA/TIA and FCC

Encoding

• Encoding is a method to convert data bit streams into a code
• Encoding also provides control codes to identify a frames start and and end boundaries

Signaling

• Signaling represents bits
• It uses 1s and 0s in the different mediums

Bit Signaling for Media

• Synchronization is needed between sender and receiver clocks
• Frame start delimiter is usually used
• There are different signaling methods for representing 0s and 1s

Bit Coding for Media

• Signaling is bit representation in physical media
• Coding is when bits are grouped symbolically before presented to the mediums
• coding detects errors more efficiently

Frame Signal Recognition

• The physical layer decodes signals of framed mediums then passes it as binary code.

Code Groups

• Code groups are consecutive code bit sequences translated as data bit patterns

Code Group Benefits and Drawbacks

• Overhead in additional bits to transmit
• Error reduction
• Aid in distinguishing data bits from control bits

4B/5B Coding Example

• 4 data bits translate to 5 bits for transmission
• Bytes split into two sets of four bits, each converted into a 5-bit code
• Using this coding yields an actual data throughput of 125 Mbps

1000Base-T IEEE 802.3ab

• Each 8-bit group is divided into four groups of 2 bits
• The coding results in a real data flow of 1000 Mbps

Data Transport Capacity

• Data transfer measurements include:
• Bandwidth
• Throughput
• Usable transfer capacity

Bandwidth

• Bandwidth indicates the information quantity capable of flowing one place to another

Bandwidth Units

• Bits per second (bps) is the essential bandwidth measurement unit equal to 1 bps
• Kilobits per second (kbps) are equal to 1,000 bps, expressed as 10^3 bps.
• Megabits per second (Mbps) is equal to 1,000,000 bps, or 10^6 bps.
• Gigabits per second (Gbps) are equal to 1,000,000,000 bps, or 10^9 bps.
• Terabits per second (Tbps) is equal to 1,000,000,000,000 bps, or 10^12 bps.

Bandwidth Analogy

• Bandwidth is analogous to water flow in a pipe and traffic flow on a highway
• Low flow correlates with few liters of water flow where as Large flow correlates with more litres of water
• More bandwidth cables enable faster file transfers.
• More bandwidth would allow for a greater number of vehicles to circulate during the same time in a freeway
• Bandwidth is traffic lanes, vehicles are transmittable information .

Internet Connections Bandwidth

• ISP-contracted bandwidth determines file download and internet browsing speed.
• Each internet connection has two bandwidth values

Bandwidth Types

• Download: from Internet to computer/network
• Uploading: from computer/network to Internet
• Fiber optic has high bandwidth, transmitting more data than twisted pair or coaxial cables.

Throughput

• Throughput measures bit transfer across media in a period, signifying transmission speed.
• Throughput differs from bandwidth influenced by: quantity and traffic types; and quantity of networked devices

Usable Transfer Capacity

• Usable data transfer during a specified period is considered as usable transfer capacity

Usable Transfer Capacity Example

• File transfers between two hosts on a LAN
  • 100 Mbps Bandwidth
  • 60 Mbps Throughput (shared usage)
  • 40 Mbps Usable Transfer Capacity (header consideration)
• Data throughput reflects the network actual performance
• Usable transfer rate measures transferable data after removing protocol header traffic.

Channel Verification

• All communication channels face disturbances
• Disturbances are a group of internal actions which modify a signal so the sent and received signal are dissimilar

Attenuation

• Signal power loss over distance requires restoration via concentrators and repeaters

Delay Distortion

• As wave propagation speed varies with frequency, different signal components travel at varying speeds which results in overlapping causing data loss.
• It is offset by equalization techniques

Noise

• Noise is any disruptive element added to a transmission signal
• It is important to maximize the signal/noise ratio
• There are different types of noise

Electromagnetic Interference (EMI) & Radio Frequency Interference (RFI)

• External signal origin.
• Radio and TV Systems often act as copper cable antennas.

Crosstalk

• Also known as diafonia
• Close proximity causes one cable's signal to be absorbed by another.
• Common in untwisted media.

Thermal Noise

• Unique to Electrical Signals
• It comes from the electron movement across the conductor
• This is comparatively less than other noises

Physical Media: Communication Connection

• See video for more info: https://www.youtube.com/watch?v=EOH0UblAuoE

Media Properties

• Standards set by organizations that define properties of media used in data communications.
• The standards define different physical and electrical media properties

Physical Media Standards Examples

• Copper cable types
• Communication bandwidth
• Connector styles
• Pin and color codes for connectors
• Maximum media distances.

Communication Channels

• Two types of channels

Communication Channels

• Physical Cable (Wired Networks)
• Electromagnetic Radiation (Wireless Networks)

Physical Cable Types

• Metallic Cables are metal- typically copper-based, transmitting data via electrical impulses.
• Fiber Optic Cables are wires made of glass or plastic and which uses pulsed light for information transmission

Ethernet Wired Connections

• Twisted Pair Cable is a red cable that is more commonly used to connect network devices in a LAN setup

Fiber Optic Cables

• Fiber cables made from glass or plastic with:
• Large channel capacity used for massive information transfer
• Used in backbone networks (large business and data centers)
• Fiber cables are largely utilizes in telephone companies.

Twisted Pair Cables

• Commonly used in modern LANs.
• These contain twisted pairs, each strand is about ½ millimeter in diameter.
• LANs use four-pair cables.

Twisting Methodology

• Each transmission line consists of two copper wires that are insulated by plastic.
• Pairs are twisted into a double helix which is known as "Twisted pair cable".
• Cancels electrical fields and reduces electromagnetic interference.

Twisted Pair Cable Connector

• Twisted pair cable uses RJ45 and RJ49 connecter

Jack Component

• Jack components are found in network equipment, wall sockets and connection panels

Cable Properties and Use cases

• Operates on short distances
• Over long distances it can suffer interferences and attenuation.
• Also cannot support a high speed.
• This cable makes use of 2 pairs in both sending and receiving modes
• The hilos varían al igual que el número de vueltas o trenzados por pulgada

Twisted Pair Cable Types

• Metallic coating determines sensitivity to recubrimiento as well as categorization

Cable types

• UTP (Unshielded Twisted Pair)
• STP (Shielded Twisted Pair)
• S/STP (Screened Shielded Twisted Pair)
• FTP (Foil Shielded Twisted Pair)

UTP (Unshielded Twisted Pair) Cable

• Uncoated pairs
• Absent global protection
• Susceptible to Interferences
• Flexible

STP (Shielded Twisted Pair) Cable

• Each pair features conductive mesh of aluminum.
• Provides great noise resilience
• Each cable can be either all or partially protected

S/STP (Screened Shielded Twisted Pair) Cable

• Individually foil-shielded twisted pair encased in mesh.
• STP Cable is the cable which adds a global screen
• Woven material screen
• Displays large noise cancelling

FTP (Foil Shielded Twisted Pair) Cable

• Completely shield each twisted pair
• Posses global Conductor screen built of aluminum.
• Provides enhanced protection over UTP and are more competitive in price with STP cables.

Identifying Screen Type

• The code preceding "/" signifies the cable protective shield, while the code trailing "/" signifies paired shield

Shield Types

• U = (unshielded): no protective shield
• F = (foil shielding): aliminium shield
• S = (braided shielding): braided outer protective layer; external protection

Cable Types

• TP = (twisted pair): twisted pair cable

Cable type attributes

• Cable categorization determined by:
• Pair quantity.
• Twists/meter
• Materials of build.
• Structured wiring guidelines.
• ....

Category 6 Cables

• Achieves 1 Gbps; reaching 10 Gbps in optimum conditions at less than 55m

Other Cable types

• Category 6A, reaching 10Gbps at 100m
• Category 7, using SSTP cables
• Category 7A, reaching 10 Gpbs at 100m

Cable Speeds

• Ethernet commonly uses a BASE-T cable
  • Ethernet delivers 10 Mbps
  • Fast Ethernet delivers 100 Mbps
  • Gig Ethernet delivers 1 Gbps
  • 10 Gig Ethernet delivers 10 Gbps
• All Cable types uses a copper medium

Twisted Pair Cabling Schemes

• TIA/EIA defines 2 cabling schemes, T568A and T568B.
• Cabling diagram defines wiring order at the end, for selection during installation
• There's 2 cables based on application, Direct cables/Crossed cables

Direct Cable

• It's the most popular
• Assigns the same wiring standard on both ends.
• Used to Connect separate devices.
• Switch to router or PC hub are prime examples

Crossover Cable

• Different wire connection patterns at each end of the cable
• Connects similar network devices

Verifying the connection Speed

• To know what speed your computer is capable of, view the Connection Speed
• To do so find the Configuration Tab, visit Internet to find Hw properties to see linkage and speed