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    Networks - Access Protocols/PKI

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    1. Provide the different access protocols, such as Carrier Sense Multiple Access (CSMA), Carrier Sense Multiple Access with Collision Detection (CSMA/CD) and Wavelength Division Multiplexing Access (WDMA). Where would these types of protocols would be used? Explain the situations with examples.

    2. Describe an example of the Public Key Infrastructure that would explain the differing usages of symmetric and asymmetric encryption and how these encryption methods might use either a substitution or a transposition cipher.

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    1. Different Access Protocols

    Carrier Sense Multiple Access
    Carrier Sense Multiple Access (CSMA) is a probabilistic Media Access Control (MAC) protocol in which a node verifies the absence of other traffic before transmitting on a shared physical medium, such as an electrical bus, or a band of electromagnetic spectrum.

    Carrier Sense" describes the fact that a transmitter listens for carrier wave before trying to send. That is, it tries to detect the presence of an encoded signal from another station before attempting to transmit. If a carrier is sensed, the node waits for the transmission in progress to finish before initiating its own transmission.

    "Multiple Access" describes the fact that multiple nodes send and receive on the medium. Transmissions by one node are generally received by all other nodes using the medium.

    Concurrent transmission by multiple nodes results in frame collisions. The multiple transmissions interfere with each other so that all are garbled and receivers are unable to distinguish the overlapping received signals from each other. It is impossible to entirely prevent collisions in CSMA networks.

    Carrier Sense Multiple Access With Collision Detection
    In Carrier Sense Multiple Access With Collision Detection (CSMA/CD), sending nodes are able to detect when a collision occurs and stop transmitting immediately, backing off for a random amount of time before trying again. This results in much more efficient use of the media since the bandwidth of transmitting the entire frame is not wasted. However, it is not possible with all media (e.g., radio), and requires extra electronics (not really an issue with today's technology).

    Wavelength Division Multiplexing Access
    In fibre-optic communications, wavelength-division multiplexing (WDM) is a technology which multiplexes multiple optical carrier signals on a single optical fibre by using different wavelengths (colours) of laser light to carry different signals. This allows for a multiplication in capacity, in addition to making it possible to perform bidirectional ...

    Solution Summary

    The solution describes examples of public key infrastructure that would explain the differing usages of symmetric and asymmetric encryption.