Mobile networks 101: a buyer’s course

Start here if you buy connectivity but did not train as a network engineer. Each module is one sitting, one diagram and three questions; the last one turns it into a provider checklist.

10 lessons

The network in one page
basics explainer 4 min read Lesson 1 / 10

A mobile session is three networks plus a database lookup. Here is which layer owns the problem, and why the SIM is not the phone.
Radio, spectrum and dBm
basics explainer 4 min read Lesson 2 / 10

Why a negative number is a measurement, and why low band and high band buy different things.
Cells, coverage and capacity
basics explainer 4 min read Lesson 3 / 10

Why full bars can still be unusable: capacity is shared, and interference is a quality problem, not a coverage problem.
Generations, refarming and sunsets
basics explainer 4 min read Lesson 4 / 10

5G is not one thing, and a sunset is a device clock. Decide whether a device survives the next network change.
Roaming: home routing vs local breakout
basics explainer 4 min read Lesson 5 / 10

Two roaming architectures: send traffic home or exit near the device. What each changes in path, control, measurement and the rules that apply.
Identity: four numbers and an eUICC ID
basics explainer 3 min read Lesson 6 / 10

Subscription, card, device, number and chip: which identifier answers which question, and what a SIM swap actually changes.
APN and private access
basics explainer 3 min read Lesson 7 / 10

An access point name chooses the data exit. Here is what a public APN, a private APN and an IPsec tunnel over a public APN each change.
MNO, MVNO and who owns what
basics explainer 3 min read Lesson 8 / 10

The operator owns spectrum and the radio; the virtual operator buys access and can own the customer. Here is how to read each role before a launch.
Bandwidth is not speed
basics explainer 3 min read Lesson 9 / 10

Bandwidth is the pipe. Latency, jitter and loss decide how an application feels. Measure the one that matches the job.
Buying connectivity: what to ask
basics explainer 3 min read Lesson 10 / 10

A provider conversation that produces evidence: route, profile, measurement, responsibility and exit. Ask for the answer that can be checked.