Chapter 3
1. B. OSI Layer 1, the physical layer, defines how to physically transmit bits using some kind of physical medium, like a cable or radio waves. OSI Layer 2, the data link layer, defines protocols that control and manage the transmission, including the definition of data link frames, which include addresses, and fields to help perform error detection.
2. B. The four-wire circuit cable supplied by the telco connects to the device acting as the CSU/DSU. That can be an external CSU/DSU or a CSU/DSU integrated into a router serial interface card. LAN switches do not have serial interfaces, and router serial interfaces do not have transceivers.
3. C. Leased lines can run at various preset speeds. These include multiples of 64 kbps, up through ...
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