Assorted notes from COEN 233 that I found interesting.

The OSI Reference Model is simply that; a reference model, it does not reflect real architecture. The TCP/IP Reference Model more closely mirrors reality.

Computers on the same hub can view all traffic for that hub. Hubs utilize ethernet. Switches and bridges (which are synonymous in this case) use MAC addresses to ensure that the data is routed correctly.

Wireless access points (wifi), switches, hubs, exist in the Data Link layer.

When 'connection' / 'connectionless' is used in networking they generally mean 'logical connection'. For example, UDP is connectionless; a datagram is a discrete message and there is no 'connection' set up between the sender and receiver (even though a physical connection needs to be present for the receiver to somehow receive the message).

Virtual LAN occurs on the Data Link Layer, via switches which send ethernet data over the network.

There are multiple ways that mobile phones / wifi can 'multiplex' (ie share) a carrier's resources. Time-division multiplexing refers to assigning each device a time slot. The device will transmit during a time slot and receive data during a time slot. Each device can also be assigned a frequency to use, which is called frequency division multiplexing. CDMA comes from CDM (code division multiplexing) which means that the time slots have variable length and their length is specified in a header.

Simplex means sender only sends, receiver only receives. Half duplex means both parties can send and receive, however only one party may send at a time. Full duplex means both parties can send and receive at the same time.

Last-mile ISPs pay tier 1 ISPs to use the internet backbone. So, Comcast pays L3 for use of the internet backbone.