hop 30 of 32 · 5 min
Networking without a cable
Radio is a shared medium with no wire to isolate it, which makes almost everything harder.
What changes
The medium is shared and open. Anyone in range receives every frame, so encryption is not optional the way it can be on a switched wire.
Signal degrades with distance and obstacles, so the data rate varies continuously as you move.
Collisions cannot be detected, which is why CSMA/CA and per frame acknowledgements exist.
Loss is frequent and is not congestion, which TCP misreads.
WiFi generations
| Standard | Name | Band | Practical rate |
|---|---|---|---|
| 802.11n | WiFi 4 | 2.4 and 5 GHz | up to 300 Mbps |
| 802.11ac | WiFi 5 | 5 GHz | up to 1 Gbps |
| 802.11ax | WiFi 6 | 2.4, 5, and 6 GHz | higher, and better under load |
The band trade is worth knowing: 2.4 GHz travels further and through walls better, and is crowded, shared with microwaves and older devices. 5 GHz is faster and shorter range. A device choosing the wrong one is a common cause of a slow connection in a house with a strong signal.
WiFi 6's real improvement is not peak speed but behaviour with many devices at once, which is what an office or a lecture hall actually needs.
Security
| Status | |
|---|---|
| WEP | broken, crackable in minutes |
| WPA2 | still common, vulnerable to offline guessing of weak passwords |
| WPA3 | current, resists offline guessing, individual encryption on open networks |
The practical point about open networks: on unencrypted WiFi every frame is readable by anyone in range. TLS protects the content, so a modern web session is reasonably safe, but the destinations remain visible.
Mobile networks
A cellular network divides an area into cells with a base station each, and handover moves a device between them mid conversation.
| Typical latency | Typical rate | |
|---|---|---|
| 3G | 100 to 500 ms | a few Mbps |
| 4G LTE | 30 to 50 ms | tens of Mbps |
| 5G | 1 to 10 ms | hundreds of Mbps |
5G's latency reduction is the more interesting half. Rates were already adequate for most uses, while single digit latency opens applications that could not tolerate a round trip before.
Designing for it
Assume variable bandwidth, high and changing latency, sudden loss of connectivity, and metered data. That means retry with backoff, cache aggressively, send less, and never assume a request that was sent was received, because a connection can vanish between the two.