Part 1: Data Rate Calculations In the last module you learned a formula for calculating bit rate, R = b/t, that is the number of bits divided by the...

In the last module you learned a formula for calculating bit rate, R = b/t, that is the number of bits divided by the time. This formula expresses the number of bits that are transmitted over a circuit in a given period of time. In practice, however, we are not only concerned with the number bits transmitted, but also with the number of data bits transmitted over a circuit. The data bits are those that the sender decides to send to the receiver, and do not include the overhead bits used by the networking protocols involved. Recall that the protocols that send messages on a circuit use some of the available bits to store metadata (overhead) for protocol communication. From a data perspective, the bit rate on a circuit can be termed the maximum data rate because it calculates the theoretical maximum number of data bits that can be sent over a network circuit if the protocols were to use no overhead bits. Effective data rate is a rate that takes into account the overhead of the protocols involved.

In this part, you will perform effective data rate calculations with two scenarios. Each scenario gives you the maximum data rate of the circuit, along with details of the protocol(s) involved, and asks you to calculate the transmission efficiency and effective data rate. For full credit, the calculations you use to derive the answers must be shown.

Scenario 1: 22,000 ASCII characters are being transmitted over a 2 Mbps circuit. The protocol uses 8-bits for each ASCII character, as well as 2 parity bits (used for error detection and correction) for each ASCII character.

a. Calculate the transmission efficiency of sending these characters using this protocol.

b. Determine the effective data rate of sending these characters using this protocol.

Scenario 2: A web browser sends an HTTP packet using TCP over IP over Ethernet. The web browser request consists of 125 bytes. The HTTP protocol adds an additional 25 bytes of overhead to the request as part of the HTTP packet. The transmission occurs over a 1 Gbps circuit.

a. Calculate the transmission efficiency of sending this packet using the specified protocol. All protocols involved add some overhead bytes to the request. Unless the scenario otherwise specifies a specific number of bytes, use the nominal header sizes for the protocols.

b. Determine the effective data rate of sending this packet over this circuit.

Part 2: Error Correction

In this module, you learned that some communication protocols implement error correction, which is a mechanism that both detects and corrects errors that occur between the sender and receiver of a message. You also learned that one common method of error correction is automatic repeat request (ARQ), in which the sender and receiver detects potential errors in each protocol data unit (PDU) sent, and retransmits them when appropriate.

In this part, you are given different scenarios for which the sender initially transmits some PDUs, and different situations occur after initial transmission. For each scenario, indicate complete & numbered series of steps which describe exactly how the receiver ultimately successfully receives all transmitted PDUs, assuming continuous ARQ is being used with a sliding window of 2. Recall that continuous ARQ is capable of retransmitting PDUs when necessary. In your steps, the sender should successfully receive acknowledgment (ACK) from the receiver for all transmitted PDUs. The final step for each scenario will thus be receipt of the last ACK.

Scenario 1: The sender transmits two PDUs without error.

Scenario 2: The sender transmits two PDUS, and only the second PDU has an error.

Scenario 3: The sender transmits two PDUs without error, but both PDUs are lost before they arrive at the receiver.

Scenario 4: Three PDUs are transmitted by the sender without error. However, the acknowledgment (ACK) of the second PDU sent by the receiver is lost before it arrives at the sender.

Part 3: Transport Protocols

An organization has written an application that allows all of their employees to send messages instantly or to an inbox to other employees. The application was written to use the UDP transport protocol, and works well most of the time. However, some employees complain about several issues. Sometimes messages do not make it to the recipient and no one is notified. Some messages arrive with some of the original text missing, or with some text corrupted with garbage characters. In rare cases, long messages arrive with out-of-order text where what was typed at the end actually appears at the beginning of the message, or vice-versa.

The project manager is considering what could be done to remedy these issues. He suspects switching to TCP could help, but is not entirely sure. Answer the following questions to help the project manager decide.

a. Why might the application exhibit the issues the employees complain about?

b. What could be done by the application to correct these issues without switching to TCP?

c. How might switching to the TCP protocol solve these issues without requiring the changes in part b?

d. Other than items mentioned in item c, what would be the advantages of switching to the TCP protocol?

e. What would be the disadvantages of switching to the TCP protocol?