1. What is the maximum throughput of ARQ (Automatic Repeat Request) for sending 10,000-bit messages on a 1 Mbps satellite link with 100 ms (one-way) delay (denoted by D)?
Resolution:
Send 10000 messages on a 1Mbps satellite link with a transmission time of 10000/1000000 = 10ms,
It takes 10+ (100) * 2 = 210ms to receive the postback confirmation, so the maximum throughput is: 10/210 * 1000kbps = 47.62kbps
2. Using sliding windows, 10 packets per window, RTT is 100 ms, assuming there are 1250 bytes packets, what is the maximum throughput? (Note that the 1250 byte data packet is 10000 bits. To find the maximum throughput, assume that the network capacity is not a limiting factor and ignore the packet loss)
Resolution:
The amount of data transmitted by an RTT is 10 × 1250Bytes × 8bits / Byte = 100000bits
maximum throughput = the amount of data transmitted per unit time = 100000bits / 100ms = 1 000 000bits / s = 1Mbps.
3. In the selective retransmission protocol, when the frame number is 4 bits and the size of the transmission window and the reception window are the same, what is the maximum size of the transmission window?
Resolution:
In the selective retransmission protocol, the size of the sending window cannot exceed the size of the receiving window, and the size of the receiving window ranges from 0 to (maximum frame number + 1) / 2. The frame number is 4 bits, then the maximum frame number = 1111 (2) = 15, the maximum size of the receiving window = (15 + 1) / 2 = 8.
4. Suppose an Internet checksum (4-bit word) is used to send a message 1001110010100011. What is the value of the checksum?
Resolution:
1011
5. In the fallback n-frame protocol, when the frame number is 5 bits, what is the maximum size of the transmission window?
Resolution:
31
6. Error correction codes, such as Ethernet, are often used in LAN transmission coding with a relatively low error rate.
Resolution:
Incorrect
7. The data link layer uses the selective retransmission protocol (SR) to transmit data. The sender has sent data frames 0 ~ 3, and has now received the confirmation of frame 1, and the frames 0 and 2 time out in sequence What is the number of frames that need to be retransmitted?
Resolution:
2.
Frames 0 and 2.
