This question's explanation and your answers so far.
図のように，ADSLモデムを介してPCからインターネット上のWebサーバを利用するため，機器の接続作業を行っている。 ＬＡＮ（破線で囲まれた範囲）内では，ＰＣ１―ハブ―ＡＤＳＬモデムが横一列に接続され，ハブの下にＰＣ２が接続されている。ＡＤＳＬモデムはＬＡＮの外のインターネットに接続し，インターネットの先にＷｅｂサーバがある。 ＰＣ１に接続されたＬＡＮケーブルをハブの空きポートに接続したところ，そのポートのリンクランプが点灯した。このことだけで判断できることとして，適切なものはどれか。
To be able to “access” PC2 or the ADSL modem within the same LAN, upper-layer (Layer 3 and above) settings such as IP address assignment must all be correctly in place, in addition to the physical connection. The lit link lamp only indicates the physical link between PC1 and the hub, and cannot tell whether the device is in a state where it can communicate with other devices.
Encrypted communication (such as SSL/TLS) is established by exchanging procedures with the other party at an upper layer close to the application, and is on a completely different level from the establishment of a physical-layer link. There is not even any guarantee that a path is connected all the way to the Web server on the Internet, so this can by no means be determined from the link lamp lighting up.
Completing a connection to the Internet requires many conditions to be met, such as line connection and authentication at the ADSL modem and obtaining an IP address. What the link lamp indicates is only the physical connection between PC1 and the hub; whether the modem beyond it or the Internet side is usable cannot be known from this single fact.
正解 The link lamp on a hub port lighting up is a signal indicating that a physical-layer link (Layer 1 of the OSI reference model) has been established electrically between that port and the device at the other end of the cable plugged into it (here, PC1). In other words, the only thing that can be read with certainty from this single fact is the “completion of the physical wiring” — namely that the cable is properly inserted and signals can be exchanged with no break or poor contact. In the figure as well, PC1 and the hub are wired next to each other, and what the link lamp indicates is limited to this physical connection between PC1 and the hub. Therefore, choice “エ”, which states that “the physical wiring from PC1 to the hub has been completed,” is appropriate.