Network

There are two ways building a network, wired or wireless.

Today most routers allow for a mixed environment.

Devices needing a reliable high speed connection like a NAS are connected by wire, mobile devices like laptops by WiFi.

Wired

This is called ethernet (IEEE 802.3).

Wiring is UTP (Unshielded Twisted Pair),
CAT 5e is the most common as it can be used used for both 100 Mbit/s and Gigabit Ethernet networks.

As more and more PCs have a 1000Mbs ethernet connection, 5e is the way to go.

Cat 6 and 6a allow for even higher speeds.

Straight or crossover cable.

If you connect 2 PCs with a straight cable you connect the plus to the plus and the min to the min. This won't work, you need a crossover cable.
If you connect a PC to a switch the crossing is all ready done inside the switch so you need a straight cable.
Luckily more and more devices are auto sensing. You can connect them with a straight or a patch cable, they simply smell it.

Bits not Bytes
Network speed is expressed in Bits per second.
A 100 Mb network is 100 Mega Bits per second.
Dividing it by eight gives you the bytes per second
This is the throughput including all the overhead as generated by the protocol.

Wireless

This is called WiFi.

The standard is 802.11 followed by a character.
G is very common, it has a maximum data rate of 54 Mbit/s
N is coming up, it has a maximum data rate of 108 Mbit/s

Wired or wireless

Price: Cat 5 cables are very cheap.
Stability: Wireless is less stable, it might drop the connection now and then
Privacy: wireless can be received by everybody in the neighborhood. A good encryption (WPA) is required.
Health, there is no scientific evidence that exposure to high frequency radio is harmful. On the other hand, the use of WiFi is to short to say anything about long term health risk.
Some wireless routers has the option to throttle the power.
Efficiency: wired is faster. A 100 Mbits wired connection is not 2 but 4 times as fast as a 54 Mbit/s wireless connection. To maintain the wireless connection and to encrypt it generates a lot of overhead.
Freedom: that’s where wireless excels, you can sit anywhere, no cables laying on the floor.

Ethernet over Power

Exactly what it is, using the electricity network in your home to do the networking.
If WiFi fails you and you don't want the ethernet cables in your room, this is the way to go.

Power over Ethernet

The reverse, as most devices uses low voltage DC, you might send the power over a Ethernet cable. Twisted pair cables offers 4 twisted pairs. In most cases only 2 are used.
This is great if you have troubles getting the AC to the device. You might also use it if you want to get rid of a wall wart.

Audio and networking

A typical audiophile worry is whether audio over the network will ever sound right.
Small wonder, if you pay Stealth Audio Cables $6,500.00 for a 1 m RCA interconnect to connect your CD player to your amp, you can't believe that sending audio over a CAT5 ( $50,00 for 100 meter) or over WiFi can sound right.
The answer is simple, you don't send audio over the network, you transfer data from one device to another. Networks are build to do bit perfect data transmission.

Although above is true, you never know for sure....

Don't worry, high end is discovering computer audio so there is high end cat 5 cable

Audioquest RJ45-G CAT5e/Ethernet Cable

Long grain copper conductors: Fewer Impurities, Less Distortion
Solid High Density PE: Ensures stable geometry and minimum interaction with signal flow
Critical Twist Geometry: Each pair has a different twist rate to prevent inter-channel interference
Gold-Plated Contacts

Starting a $ 25 a meter