| 1. | How many wire pairs does 100BASE-T use of a UTP copper cable? How many does 1000BASE-T use? |
| Answer: | The 100BASE-T standard uses two pairs (four wires in total), one pair for transmitting and another for receiving. The 1000BASE-T standard uses all four pairs (eight wires in total) of the UTP cable. Using echo cancellation, each pair is capable of transmitting and receiving simultaneously. |
| 2. | What are the physical differences between step and graded index multimode fiber? |
| Answer: | Step index multimode fiber has the same physical fiber properties throughout the core, which results in a sudden reflective "step" into the fiber cladding. In contrast, variations are imposed in the composition of graded index glass in the core, which results in a gradual increase in refraction toward the center of the core. |
| 3. | For 100BASE-FX, why is NRZ-I signaling used with 4B/5B encoding and not just straight NRZ? |
| Answer: | In Table 2-3, quite a few of the 5-bit codes have more ones than zeros. The reason that 100BASE-FX uses NRZ-I with 4B/5B is that more transitions are performed during long strings of ones using NRZ-I than with straight NRZ. |
| 4. | What error checking is performed with IP, UDP, and TCP? |
| Answer: | IP checks for errors in the IP packet only. UDP and TCP check for errors in the UDP header and segment payload, but only TCP retransmits erroneous segments. |
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| 5. | What is the purpose of the TCP three-way handshake? |
| Answer: | The TCP three-way handshake is used to synchronize TCP sequence numbers and exchange TCP options between TCP devices. |
| 6. | How is packet loss detected by TCP senders? |
| Answer: | Outstanding segments are detected by the sender with either a timeout or by receiving duplicate ACKs from the receiver. |
| 7. | Why is TCP bandwidth limited over satellite links? How can TCP bandwidth over satellite be accelerated? |
| Answer: | The TCP window size limits bandwidth over satellite connections due to high latency. Use of multiple TCP connections or the window scaling option (WSopt) or both are ways to accelerate the TCP bandwidth over satellite links. |
| 8. | What is the lowest level of content awareness in TCP/IP? |
| Answer: | The TCP urgent pointer is the lowest level of content awareness of the TCP/IP protocol suite. |
