GSM (originally Groupe Speciale Mobile, later Global System for Mobile Communication) was first standardized in 1991 as the dominant 2nd generation (2G) fully digital mobile network.

Key properties:

• First fully digital mobile network standard — this was the major leap from 1G (analog)
• Primarily designed for voice, but from mid-1995 added data services: SMS, fax, and even notebook connectivity
• GPRS extension (around 2000) enabled mobile internet, though at very low data rates

GSM frequency bands:

GSM-900 system specifics:

• 124 frequency pairs (channels), each 200 kHz wide
• Uses TDMA (Time Division Multiple Access) with 8 time slots per channel
• This means one GSM-900 carrier can handle 8 simultaneous calls

Tip: The switch from analog (1G) to digital (2G/GSM) was like the switch from vinyl records to CDs — digital enables error correction, encryption, and multiplexing that are simply impossible with analog signals.

Go deeper:

• GSM (Wikipedia) — history, architecture, and why 2G became the global standard.
• GSM frequency bands (Wikipedia) — the full band plan behind the P-GSM-900 / DCS-1800 / PCS-1900 table.

Digital transmission enabled encryption, error correction, efficient multiplexing, and data services — none of which were possible with analog 1G networks.

Advantages of digital over analog:

• Encryption — analog calls could be eavesdropped with a simple radio scanner; GSM encrypts the air interface
• Error correction — digital signals can include redundancy bits to detect and correct transmission errors
• Efficient spectrum use — TDMA allows multiple users to share one frequency channel by taking turns in time slots
• Data services — SMS, and later GPRS for packet data, are fundamentally digital concepts
• Compression — voice can be digitally compressed to use less bandwidth
• Consistent quality — digital is either decodable or not; no gradual quality degradation like analog static

Disadvantages to consider:

• Cliff effect — when the signal drops below a threshold, it doesn't gracefully degrade (like analog getting staticky); it just cuts out completely
• Latency — digital encoding/decoding adds processing delay
• Complexity — significantly more complex hardware and software required

Go deeper:

• NATEL — Oral-History video on Switzerland's mobile network (PTT-Archiv, Wikimedia) — the Swiss side of the 1G→2G story: how the analog NATEL networks gave way to digital GSM, told by the people who built them.