Topic 3: Physical Layer

• A physical connection to a local network has to be established before any network communication can occur.
• A Network Interface Card (NIC) connects a device to the network.
• Some devices may have just one NIC while others may have multiple NICs
• The physical layer

  • Transports bits 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.
  • This is the last step of the encapsulation process
  • The next device in the path to the destination receives the bits and re-encapsulates the frame, then decides what to do with it.

  
• poop

  A) Transmission Control Protocol/Internet Protocol(TCP/IP)

  B) Internet Engineering Task Force (IETF)

  C) hardware

  D) International Organization for Standardization (ISO)

  E) Electronic Industries Alliance (EIa)

  F) Telecommunications Industry Association (TIa)

  G) International Telecommunication Union Telecommunication

  H) Standardization Sector (ITU-T)

  I) American National Standards Institute (ANSI)

  J) Institute of Electrical and Electronics Engineers(IEEE)

  
• The Physical Layer Standards addresses the functional areas of Physical Components, Encoding and Signaling
• The Physical Components are the hardware devices, media, and other connectors that transmit the signals that represent the bits.
• Encoding converts the stream of bits into a format recognizable by the next device in the network path.
• Examples of encoding methods include Manchester, 4B/5B, and 8B/10B.
• The signaling method is how the bit values, “1” and “0” are represented on the physical medium which varies based on the type of medium being used.
• 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, or how many bits can be transmitted in a second.
• Physical media properties, current technologies, and the laws of physics play a role in determining available bandwidth.
• The fundamental unit of bandwidth is the bits per second (bps). Other units used also include:

  • Kilobits per second (Kbps)
  • Megabits per second (Mbps)
  • Gigabits per second (Gbps)
  • Terabits per second (Tbps)
• Latency is the amount of time, including delays, for data to travel from one given point to another
• Throughput is the measure of the transfer of bits across the media over a given period of time
• Goodput is the measure of usable data transferred over a given period of time and can be calculated by Goodput = Throughput - traffic overhead
• 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.
• Limitations of copper cabling:

  • 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).

  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.
• There are 3 types of copper cabling:

  A) Unshielded Twisted-Pair (UTP) Cable

  B) Shielded Twisted-pair (STP) Cable

  C) Coaxial Cable

  
• UTP copper wires is the most common networking media and are terminated using RJ-45 connectors. These wires interconnects hosts with intermediary network devices.
• Key characteristics of UTP:

  1. The outer jacket protects the copper wires from physical damage
  2. Twisted pairs protect the signals from interference.
  3. Color-coded plastic insulation electrically isolated the wires form each other and identified each pair.

  
• Differences between STP and UTP:

  • STP has better noise protection than UTP
  • STP is more expensive than UTP
  • STP is harder to install than UTP

  Similarities between STP and UTP:

  • Both are terminated with RJ-45 connectors
  • Interconnects hosts with intermediary network devices
• Key Characteristics of STP

  1. The outer jacket protects the copper wires from physical damage
  2. Braided or foil shield provides EMI/RFI protection
  3. Foil shield for each pair of wires provides EMI/RFI protection
  4. Color-coded plastic insulation electrically isolates the wires from each other and identifies each pair

  
• Straight-through and Crossover UTP Cables have difference use cases.

  • Ethernet straight-through cables connect hosts to network devices
  • Ethernet Crossover (Legacy) provides host-to-host, switch-to-switch and router-to-router connections.
  • Rollover is Cisco's proprietary cable and connects host serial port to Router or Switch Console Port, using an adapter
• Properties of Fiber-Optic Cabling

  • Not as common as UTP 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 wave guide to transmit light between the two ends with minimal signal loss
• There are 2 types of fiber optic media:

  • Single mode fiber is used for long-distance applications has a very small core and uses expensive lasers
  • Multimode fiber has a larger core but uses less expensive LEDs to transport up to 10Gbps over 550m
• Fiber-optic cabling is now being used in four types of industry:

  • Enterprise Networks -Used for backbone cabling applications and interconnecting infrastructure devices
  • Fiber-to-the-Home (FTTH) -Used to provide always-on broadband services to homes and small businesses
  • Long-Haul Networks -Used by service providers to connect countries and cities
  • Submarine Cable Networks -Used to provide reliable high-speed, high-capacity solutions capable of surviving in harsh undersea environments at up to transoceanic distances.
• There are 4 types of fiber-optic connectors

  A) Straight-Tip (ST) connectors

  B) Lucent Connector (LC) Simplex connectors

  C) Subscriber Connector (SC) Connectors

  D) Duplex Multimode LC connectors

  
• Optical fiber is 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.
• Wireless media 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
• 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
  • Wireless NIC Adapters - Provide wireless communications capability to network hosts