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Unit 5 - Notes

CAP321 10 min read

Unit 5: Network devices and troubleshooting

1. Introduction to Wired and Wireless Media

Transmission media refers to the communication channels that carry data from a sender to a receiver. They form the Layer 1 (Physical Layer) of the OSI model. Media is broadly categorized into two types: Guided (Wired) and Unguided (Wireless).

Wired (Guided) Media

Wired media utilizes a physical, tangible path to transmit signals. Data is constrained within the boundaries of the cable.

  • Characteristics: High security, high bandwidth, less susceptible to environmental interference (depending on the shielding), physically bounded.
  • Common Types: Co-axial, Twisted Pair (UTP/STP), Fiber-Optic.

Wireless (Unguided) Media

Wireless media transmits data through electromagnetic waves without utilizing a physical conductor. The air (or a vacuum) serves as the transmission medium.

  • Characteristics: Highly flexible, allows for mobility, easier deployment in difficult terrains, but generally less secure and more susceptible to interference (EMI/RFI).
  • Common Types:
    • Radio Waves: Used for multicasting and long-distance communication (e.g., AM/FM radio, Wi-Fi).
    • Microwaves: Used for unicast communication; requires line-of-sight (e.g., satellite links, cellular networks).
    • Infrared: Used for short-range communication; cannot penetrate solid objects (e.g., TV remote controls, short-range device pairing).

2. Physical Components

Network physical components are the tangible hardware devices required to construct a network.

  • Network Interface Card (NIC): A hardware component that allows a computer to connect to a network. Every NIC has a unique, hardcoded 48-bit MAC (Media Access Control) address.
  • Repeater: A Layer 1 device used to regenerate or amplify a signal to extend the distance it can travel, preventing signal degradation (attenuation).
  • Hub: A legacy Layer 1 multiport repeater. When a hub receives a data frame on one port, it broadcasts it to all other ports, leading to high collision rates.
  • Switch: A Layer 2 (Data Link Layer) multiport device. Unlike a hub, a switch learns MAC addresses and forwards data frames only to the intended destination port, significantly reducing collisions and improving bandwidth utilization.
  • Router: A Layer 3 (Network Layer) device that connects different networks together. It uses IP addresses to determine the best path to forward data packets.
  • Modem (Modulator-Demodulator): Converts digital signals from a computer into analog signals for transmission over telephone lines or cable systems, and vice versa.
  • Wireless Access Point (WAP/AP): A device that allows wireless networking devices to connect to a wired network using Wi-Fi.

3. Familiarization with Cables

3.1 Co-axial Cable

Co-axial cable conducts electrical signals using an inner conductor surrounded by a concentric conducting shield, separated by an insulating material.

  • Structure:
    1. Inner Conductor: Solid copper wire (carries the data signal).
    2. Dielectric Insulator: Plastic layer surrounding the core.
    3. Metallic Shield: Braided copper or aluminum mesh (protects against EMI).
    4. Outer Jacket: PVC or Teflon casing.
  • Types:
    • Thinnet (10Base2): Highly flexible, maximum range of 185 meters.
    • Thicknet (10Base5): Thicker core, maximum range of 500 meters.
  • Connectors: BNC (Bayonet Neill-Concelman) connectors, F-type connectors (common in cable TV).

3.2 UTP (Unshielded Twisted Pair) Cable

UTP is the most common cable used in modern LANs. It consists of color-coded copper wires twisted together.

  • Structure: Typically four pairs of twisted copper wires encased in a plastic jacket. The twisting is crucial as it cancels out Electromagnetic Interference (EMI) from external sources and crosstalk from adjacent pairs.
  • Categories:
    • Cat 5e: Speeds up to 1 Gbps at 100 MHz.
    • Cat 6: Speeds up to 10 Gbps (for short distances, up to 55m) at 250 MHz. Contains a plastic spline to separate pairs.
    • Cat 6a: Speeds up to 10 Gbps (up to 100m) at 500 MHz.
  • Connectors: RJ45 (Registered Jack 45).

3.3 Fiber-Optic Cable

Fiber-optic cables transmit data as pulses of light rather than electrical signals, making them completely immune to EMI and capable of massive bandwidth over long distances.

  • Structure:
    1. Core: Ultra-thin strand of glass or plastic (carries the light).
    2. Cladding: Material surrounding the core that reflects light back into the core (Total Internal Reflection).
    3. Buffer: Protects the fiber from physical damage.
    4. Jacket: Outer protective layer.
  • Types:
    • Single-Mode Fiber (SMF): Small core, uses lasers, supports massive distances (tens of kilometers), higher cost.
    • Multi-Mode Fiber (MMF): Larger core, uses LEDs, supports shorter distances (up to 550m), lower cost.
  • Connectors: SC (Subscriber Connector), LC (Lucent Connector), ST (Straight Tip).

4. Installation of Cables

Installation Best Practices

  • Avoid EMI Sources: Never route UTP or Co-axial cables near fluorescent lights, electric motors, or power lines.
  • Bend Radius: Do not bend cables beyond their maximum bend radius (usually 4 times the cable diameter for UTP) to avoid damaging the internal structure.
  • Cable Ties: Do not overtighten zip ties, which can crush the pairs in UTP cables and cause crosstalk. Velcro is preferred.

Installing Specific Cables

  • Co-axial: Requires termination with BNC or F-connectors using a specialized coaxial crimping tool. Ensure the central copper core is not bent and the braided shield does not touch the core (which causes a short).
  • UTP: Pulled through conduits or drop ceilings. Terminated at wall jacks (keystone jacks) using a punch-down tool, and at the device end using RJ45 connectors. Maximum run length is strictly 100 meters.
  • Fiber-Optic: Requires extreme care. Bending too sharply will break the glass core. Splicing (joining two fibers) requires highly specialized equipment (fusion splicers) and precise polishing. Ends must be kept immaculately clean.

5. RJ45 Connector Punching (Crimping)

To terminate a UTP cable with an RJ45 connector, a process called "crimping" is performed.

Tools Required

  • RJ45 Connectors
  • UTP Cable (Cat5e/Cat6)
  • Cable Stripper
  • Crimping Tool
  • Cable Tester

Step-by-Step Procedure

  1. Strip the Jacket: Use the cable stripper to remove about 1.5 to 2 inches of the outer PVC jacket. Be careful not to nick the inner wire insulation.
  2. Untwist and Separate: Untwist the exposed wire pairs down to the jacket base. Straighten them out completely.
  3. Arrange Color Code: Arrange the wires side-by-side according to the desired standard (T568A or T568B).
  4. Trim: Group the wires tightly and trim them perfectly straight across, leaving about 0.5 inches (1.25 cm) of exposed wire.
  5. Insert: Holding the RJ45 connector with the clip facing down and the gold pins facing up, slide the wires into the connector. Ensure each wire goes into its respective groove and pushes all the way to the end of the plug. Ensure the outer cable jacket goes up into the connector (to be grabbed by the strain relief).
  6. Crimp: Insert the RJ45 connector into the crimping tool and squeeze the handles firmly. This pushes the gold contacts into the wires and locks the strain relief onto the jacket.
  7. Test: Use a LAN cable tester to verify continuity and ensure no wires are crossed or disconnected.

6. Straight and Cross Cable Configuring Concepts

Ethernet networking relies on two primary pinout standards for RJ45 termination: TIA/EIA-568A and TIA/EIA-568B.

  • T568A Color Code (Pin 1 to 8): White/Green, Green, White/Orange, Blue, White/Blue, Orange, White/Brown, Brown.
  • T568B Color Code (Pin 1 to 8): White/Orange, Orange, White/Green, Blue, White/Blue, Green, White/Brown, Brown.

Straight-Through Cable

  • Configuration: Both ends of the cable are terminated using the same standard (either T568A on both ends or T568B on both ends). T568B is the most common industry standard.
  • Use Case: Connects unlike devices (devices that transmit and receive on different pins).
    • PC to Switch
    • Router to Switch
    • PC to Hub

Crossover Cable

  • Configuration: One end of the cable is terminated using the T568A standard, and the other end is terminated using the T568B standard. This physically crosses the transmission (Tx) and receiving (Rx) pins.
  • Use Case: Connects like devices (devices that transmit and receive on the same pins).
    • PC to PC directly
    • Switch to Switch
    • Router to Router
  • Note: Modern devices support Auto-MDIX, a feature that automatically detects the required cable connection type and configures the connection appropriately, making crossover cables largely obsolete in modern environments.

7. Topologies and Architecture

Network Topologies

Topology refers to the physical or logical layout of a network.

  • Bus Topology: All devices share a single communication cable (the backbone). Terminators at both ends prevent signal bounce.
    • Pros: Cheap, easy to install for small networks.
    • Cons: If the main cable fails, the entire network fails. High collisions.
  • Ring Topology: Each device connects exactly to two other devices, forming a circle. Data travels in one direction.
    • Pros: Orderly network operation, performs better than bus under heavy load.
    • Cons: A single cable break breaks the entire ring (unless dual-ring architecture is used, like FDDI).
  • Star Topology: All devices connect to a central hub or switch. Most common topology today.
    • Pros: Easy to troubleshoot; failure of one cable only affects one node. Easy to add/remove devices.
    • Cons: Requires more cable. The central device represents a single point of failure (SPOF).
  • Mesh Topology: Devices are connected to multiple other devices. In a Full Mesh, every node connects to every other node.
    • Pros: Supreme redundancy and fault tolerance.
    • Cons: Extremely expensive and difficult to scale due to the sheer number of cables required.
  • Tree Topology: A hierarchical combination of Star and Bus topologies. Root nodes connect to lower-level nodes.
  • Hybrid Topology: A combination of two or more different topologies (e.g., Star-Bus).

Network Architecture

Defines how resources are managed and distributed.

  • Client-Server: A centralized model where dedicated Servers manage resources, security, and administration. Clients (PCs, laptops) request resources from the Server. Highly secure and scalable, but expensive to implement.
  • Peer-to-Peer (P2P): A decentralized model where every computer (peer) acts as both client and server. No central authority. Cheap and easy to setup, but lacks central security and scales poorly beyond 10-15 computers.

8. Troubleshoot Network

Network troubleshooting is the process of identifying, diagnosing, and resolving network problems. It generally follows a structured methodology, often utilizing the OSI model (starting from Layer 1 and working upwards).

Systematic Troubleshooting Methodology

  1. Identify the problem (Gather information, symptoms).
  2. Establish a theory of probable cause (Question the obvious).
  3. Test the theory to determine cause.
  4. Establish a plan of action to resolve the problem.
  5. Implement the solution or escalate.
  6. Verify full system functionality.
  7. Document findings, actions, and outcomes.

Hardware / Physical Troubleshooting (Layer 1 & 2)

  • Check Link Lights: Look at the NIC and switch ports. A solid green light usually indicates a physical connection; a blinking light indicates activity. No light means no physical link.
  • Check Connections: Ensure the RJ45 cable is securely snapped into the port.
  • Cable Testing: Use a LAN tester to check for broken wires, shorts, or incorrectly mapped pins in the cable.
  • Swap Components: Swap the patch cable with a known-good cable. Move the connection to a known-good switch port to isolate the hardware failure.

Software / Command-Line Troubleshooting (Layer 3 & Above)

Operating systems include built-in command-line tools for network diagnostics:

  • ipconfig (Windows) / ifconfig or ip a (Linux/Mac):
    Displays the current IP configuration. Used to verify if the machine has received a valid IP address from the DHCP server (or if it defaulted to a 169.254.x.x APIPA address, indicating network isolation).

    CMD
        ipconfig /all

  • ping:
    Uses ICMP (Internet Control Message Protocol) echo requests to test connectivity to another host. Used to check if a remote device is reachable and to measure latency.

    CMD
        ping 8.8.8.8

    Troubleshooting flow: Ping loopback (127.0.0.1) -> Ping local IP -> Ping Default Gateway -> Ping external IP (e.g., Google DNS).

  • tracert (Windows) / traceroute (Linux/Mac):
    Maps the journey a packet takes to reach its destination, displaying every router (hop) along the path. Excellent for pinpointing exactly where a connection drops.

    CMD
        tracert www.google.com

  • nslookup:
    Queries the DNS (Domain Name System) server to resolve a domain name to an IP address, or vice versa. Used to troubleshoot DNS resolution failures.

    CMD
        nslookup www.google.com

  • netstat:
    Displays active network connections, routing tables, and a number of network interface statistics. Useful to see which ports are open and listening on the machine.

    CMD
        netstat -an

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