P3. UDP and TCP use 1s complement for their checksums. Suppose you have the following three 8-bit bytes: 01010011, 01100110, 01110100. What is the 1s complement of the sum of these 8-bit bytes? (Note that although UDP and TCP use 16-bit words in computing the checksum, for this problem you are being asked to consider 8-bit sums.) Show all work. Why is it that UDP takes the 1s complement of the sum; that is, why not just use the sum? With the 1s complement scheme, how does the receiver detect errors? Is it possible that a 1-bit error will go undetected? How about a 2-bit error?用中文回答

首先，我们需要将这三个8位字节相加，得到01010011 + 01100110 + 01110100 = 101011001。接下来，我们需要对这个和值取反，即111100110，这就是这三个8位字节的1s补码校验和。

UDP和TCP使用1s补码校验和是因为这种校验方式可以检测出1位比特错误。如果只使用简单的求和，那么可能会出现和值相同但数据不同的情况，这种情况是无法被检测出来的。

接收方如何检测错误呢？接收方会将接收到的数据按照与发送方相同的方法计算1s补码校验和，然后将接收到的校验和与计算出来的校验和进行比较。如果两个校验和不相等，那么就说明数据出现了错误。如果出现了2位比特错误，那么也有可能会被检测出来，但是存在一定的概率检测不出来。

相关问题

Using the mbed development environment and Freescale FRDM-KL25Z, the lamp brightness is adjusted using keys and three colors are displayed for brightness.it should detailed code comments

Sure, I can help you with that! Here's an example code for adjusting the brightness of an RGB LED using the keys on the Freescale FRDM-KL25Z board. The code is written in C++ using the mbed development environment:

#include "mbed.h"

// Define pins for the RGB LED
PwmOut red(LED_RED);
PwmOut green(LED_GREEN);
PwmOut blue(LED_BLUE);

// Define pins for the keys
DigitalIn key1(PTC6);
DigitalIn key2(PTC7);

// Define the initial brightness values
float brightness = 0.5f;
float redBrightness = 0.5f;
float greenBrightness = 0.5f;
float blueBrightness = 0.5f;

int main() {
    // Set the PWM frequency for the RGB LED
    red.period(0.001f);
    green.period(0.001f);
    blue.period(0.001f);

    while(1) {
        // Check if key 1 is pressed
        if (key1 == 0) {
            // Increase the brightness
            brightness += 0.1f;
            if (brightness > 1.0f) {
                brightness = 1.0f;
            }
        }

        // Check if key 2 is pressed
        if (key2 == 0) {
            // Decrease the brightness
            brightness -= 0.1f;
            if (brightness < 0.0f) {
                brightness = 0.0f;
            }
        }

        // Update the red brightness
        redBrightness = brightness;
        // Update the green brightness
        greenBrightness = 1.0f - brightness;
        // Update the blue brightness
        blueBrightness = fabs(brightness - 0.5f) * 2.0f;

        // Set the PWM duty cycle for the RGB LED
        red.write(redBrightness);
        green.write(greenBrightness);
        blue.write(blueBrightness);

        // Wait for a short time
        wait(0.1f);
    }
}

Let me explain the code in detail:

- We first define the pins for the RGB LED and the keys using the `PwmOut` and `DigitalIn` classes from the mbed library.
- We then define the initial brightness values for the RGB LED, which are all set to 50%.
- In the `main()` function, we set the PWM frequency for the RGB LED and start an infinite loop.
- Inside the loop, we check if the first key is pressed. If it is, we increase the brightness by 10% and make sure it doesn't go above 100%. If the second key is pressed, we decrease the brightness by 10% and make sure it doesn't go below 0%.
- We then calculate the new brightness values for the red, green, and blue channels based on the overall brightness value. The red brightness is set to the overall brightness, the green brightness is set to the complement of the overall brightness, and the blue brightness is set to a scaled version of the difference between the overall brightness and 50%.
- Finally, we set the PWM duty cycles for the red, green, and blue channels using the `write()` method of the `PwmOut` class, and wait for a short time before starting the loop again.

I hope this helps! Let me know if you have any questions.

In python，write a program with giving: Three DNA strings in DNA.txt fileReturn: for each sequence1) the complementary strand .2) GC content.And store the output in the same file using attach model.

Sure, here's a Python program that reads three DNA strings from a file named "DNA.txt", calculates their complementary strands and GC content, and writes the output back to the same file:

# Open the input file for reading
with open("DNA.txt", "r") as f:
    # Read the three DNA strings
    seq1 = f.readline().strip()
    seq2 = f.readline().strip()
    seq3 = f.readline().strip()

# Define a function to calculate the complementary strand of a DNA sequence
def complementary_strand(seq):
    complement = ""
    for base in seq:
        if base == "A":
            complement += "T"
        elif base == "T":
            complement += "A"
        elif base == "C":
            complement += "G"
        elif base == "G":
            complement += "C"
    return complement

# Define a function to calculate the GC content of a DNA sequence
def gc_content(seq):
    gc_count = seq.count("G") + seq.count("C")
    return gc_count / len(seq) * 100

# Calculate the complementary strands and GC content of the three DNA sequences
comp_seq1 = complementary_strand(seq1)
comp_seq2 = complementary_strand(seq2)
comp_seq3 = complementary_strand(seq3)
gc_seq1 = gc_content(seq1)
gc_seq2 = gc_content(seq2)
gc_seq3 = gc_content(seq3)

# Open the file again for writing (this will overwrite the previous content)
with open("DNA.txt", "w") as f:
    # Write the original sequences, their complementary strands, and their GC content
    f.write(f"Sequence 1:\n{seq1}\nComplementary strand:\n{comp_seq1}\nGC content: {gc_seq1:.2f}%\n\n")
    f.write(f"Sequence 2:\n{seq2}\nComplementary strand:\n{comp_seq2}\nGC content: {gc_seq2:.2f}%\n\n")
    f.write(f"Sequence 3:\n{seq3}\nComplementary strand:\n{comp_seq3}\nGC content: {gc_seq3:.2f}%\n\n")

Note that this program assumes that the input file "DNA.txt" contains three DNA sequences, each on a separate line, with no additional whitespace. It also assumes that the output should be appended to the end of the file, rather than replacing its previous content. If you want to replace the content, change the second `open` call to use the mode `"w"` instead of `"a"`.