Exploring the OSI Physical Layer

 

     The overall task of the Physical layer is that the Physical Layer creates a connection between a device and the transmission medium. The Physical Layer deals with the physical attributes of the connection that’s used to transmit data across a single link. The physical layer also encodes the data for transmission and determines the shape of the connectors and the types of mediums used for transport. The modulation of the bit encoding is one of the best ways to determine how fast data can be transmitted across the link, whether that link is wireless, copper, or fiber optic.

So, what are some of the things the Physical Layer does?

    1. Converts signal from one form to another so it can be transmitted
    2. Bit-by-bit delivery
    3. Bit synchronization for synchronized serial communication
    4. Start signals and stop signals for asynchronous serial communication
    5. Carrier sensing and collision detection to deal with undeliverable packets

 What are some protocols associate with the Physical Layer?

    1. Digital Subscriber Line. (DSL)
    2. Integrated Services Digital Network (ISDN)
    3. Infrared Data Association (IrDA): Infrared Physical Layer Specification (IrPHY)
    4. Universal Serial Bus (USB)
    5. Bluetooth (WPAN)
    6. Controller Area Network (CAN bus)
    7. Recommended Standard 232 (RS232)
    8. Wifi (IEEE 802.11)
    9. Ethernet (IEEE 802.3)
    10. Token Ring (IEEE 802.5)

    It's important to know how to troubleshoot the Physical Layer. Some symptoms of physical layer problems include loss of connectivity, network bottlenecks or congestion, high CPU utilization rates, and console error messages. These can indicate common physical layer issues, like power related issues, hardware faults, cabling faults, attenuation problems, noise, interface configuration errors, exceeding the design limits, and CPU overload.

To troubleshoot these problems, I’d use the troubleshooting method: 

    1. Identify the problem
    2. Theorize a solution
    3. Test your solution
    4. Plan and implement the solution
    5. Verify it worked
    6. Document the incident

    I would compare the TCP/IP model to the task of Fedex delivering packages. The Physical Layer is the function of the roadways that the Fedex Trucks drive on, like the cables, NIC cards and signals.

    The Data Layer with the Ethernet header and trailer around the Frame is like the Fedex trucks, encapsulating everything and verifying that the packages are good. The Network Layer with the IP header on the Packet is like the label on the shipping boxes, informing the sorters where to send it. The Transport Layer with the TCP header on the Segment is like the manufacturer packaging, labeling the package and telling the recipient how to use it.  The Application Layer data is the actual product, the thing at the center of it all, the content that you're actually asking for.

    The reason that I think that the Physical Layer 1 is like roadways is because the function is really similar to cables, in that it connects things together in a fundamental way and allows more complicated concepts to operate on top of it.