1. Radio fundamentals
| Term | Meaning |
|---|---|
| Spectrum | Radio frequencies licensed by regulators (e.g. HAKOM in Croatia, ECC/CEPT in Europe, FCC in US, ITU globally). Auctioned to operators |
| Hz / kHz / MHz / GHz | Frequency. Low bands (700–900 MHz) travel far and go through walls; high bands (3.5 GHz, 26 GHz) are fast but short-range |
| Band | A defined slice of spectrum, numbered by 3GPP (B3, B20, n78…) |
| Bandwidth | Width of a channel in MHz; more = more speed |
| Licensed / unlicensed | Operators pay for licensed; Wi-Fi uses unlicensed (2.4, 5, 6 GHz) |
| Path loss / fading | Signal weakens with distance and obstacles; multipath makes it fluctuate |
| dB / dBm | Logarithmic units. dBm is absolute power (0 dBm = 1 mW). +3 dB = double power |
| Link budget | Total gain and loss between transmitter and receiver, decides cell range |
| Antenna gain, tilt (electrical / mechanical) | Focus and aim of the antenna |
| Sector | One antenna covers a 120° slice; a site usually has 3 |
| Cell / site / tower / RRH | Coverage area / location / mast / Remote Radio Head (radio mounted on the mast) |
| Macro / micro / pico / femto cell | Coverage from km down to a room |
| DAS | Distributed Antenna System — indoor coverage in stadiums, malls |
| Repeater | Amplifies a signal (simple coverage extender) |
| Interference | Unwanted signals from neighbours; fought with frequency reuse, power control, ICIC |
| Frequency reuse | Same frequency reused in distant cells |
| Handover / handoff | Passing a connection from cell to cell |
| Cell reselection | Idle phone choosing a better cell |
| Drive test / OSS counters (KPIs) | Measuring coverage and quality: drop rate, setup success, throughput |
| SNR / SINR / BER / BLER | Signal-to-Noise Ratio / +Interference / Bit Error Rate / Block Error Rate |
| HARQ | Hybrid Automatic Repeat Request — fast retransmission with soft combining |
| Latency / jitter / packet loss | Delay / delay variation / lost packets — the three enemies of voice and video |
Multiple access: how users share the air
| Method | Used in | Idea |
|---|---|---|
| FDMA | 1G, GSM | Each user has own frequency |
| TDMA | GSM | Own time slot |
| CDMA | IS-95, 3G | Own code, all at once |
| OFDMA | LTE downlink, 5G NR, Wi-Fi 6 | Many narrow subcarriers shared |
| SC-FDMA | LTE uplink | OFDMA-like but power-efficient |
| SDMA / MU-MIMO | LTE-A, 5G | Different users separated by antenna beams |
| NOMA | research (6G) | Non-orthogonal sharing |
Modulation (more bits per symbol = faster, but needs a clean signal)
BPSK (1 bit) → QPSK (2) → 16QAM (4) → 64QAM (6) → 256QAM (8) → 1024QAM (10). GSM uses GMSK; EDGE uses 8-PSK.
2. The network behind the antenna
RRU/RU ── fronthaul ── DU ── midhaul ── CU ── backhaul ── core ── internet / interconnect
| Segment | Role | Technology |
|---|---|---|
| Fronthaul | Radio head ⇄ baseband unit | Dark fibre, CPRI, eCPRI, WDM |
| Midhaul | DU ⇄ CU | Ethernet / fibre |
| Backhaul | Cell site ⇄ core | Fibre, microwave (E-band 70/80 GHz), satellite, leased lines |
| Aggregation / metro | Collects sites | Ethernet rings, MPLS |
| Core / transport | Data-centre and national links | DWDM optical + IP/MPLS |
| Edge / MEC site | Local compute | Small data centre |
| BBU / baseband | Digital radio processing | In a cabinet (D-RAN) or pooled hub (C-RAN) |
Transport technologies
| Term | Meaning |
|---|---|
| TDM / E1 / T1 | Time-division multiplexing; E1 = 2.048 Mbit/s with 32 × 64 kbit/s channels (30 voice + 2 signalling); T1 = 1.544 Mbit/s |
| SDH / SONET | Synchronous Digital Hierarchy (STM-1 155 Mbit/s, STM-4, STM-16, STM-64) |
| PDH | Plesiochronous Digital Hierarchy — older multiplexing |
| ATM | Asynchronous Transfer Mode — 53-byte cells, used in 3G transport |
| Ethernet / Carrier Ethernet / Metro-E | Now dominant; MEF defines services (E-Line, E-LAN) |
| MPLS / LDP / RSVP-TE / Segment Routing | Label-based forwarding with traffic engineering |
| L2VPN / L3VPN / VPLS / EVPN | Virtual private networks over MPLS/IP |
| VLAN / QinQ | Logical separation on Ethernet |
| IP / IPv4 / IPv6 | The addressing and routing layer |
| BGP / OSPF / IS-IS | Routing protocols (BGP between operators, OSPF/IS-IS inside) |
| DWDM / CWDM / ROADM | Many wavelengths on one fibre |
| PON / GPON / XGS-PON | Fibre to the home (also used for backhaul) |
| FTTH / FTTx / xDSL / DOCSIS | Fixed access: fibre / copper / cable |
| Timing: GPS, PTP (IEEE 1588), SyncE | Radio cells need precise time and phase (TDD especially) |
| QoS: DiffServ / DSCP / CoS / EF / AF | Packet priority markings so voice beats downloads |
| OAM / BFD / Y.1731 | Monitoring and fast failure detection |
Internet-side services of a mobile core
| Term | Meaning |
|---|---|
| DNS | Name → IP. Operators run their own resolvers; DNS is also used inside the core to find nodes (e.g. SGW/PGW selection via NAPTR) |
| DHCP / SLAAC | How a device gets an address |
| NAT / CGNAT / NAT64 | Sharing a few IPv4 addresses among many users; 464XLAT for IPv6-only mobile |
| Firewall / DPI / TDF | Packet filtering / Deep Packet Inspection / Traffic Detection Function — classify and shape traffic |
| Content filtering, zero-rating, parental control | Operator services using DPI |
| CDN / caching | Content near the user |
| Transparent proxy / TCP optimisation / WAN opt. | Speed-ups for mobile links |
| AAA / RADIUS / Diameter | Authentication, Authorisation, Accounting |
| LI / LEA | Lawful Interception for Law Enforcement Agencies — mandated in every network |
| Data retention | Legal storage of call/connection records |
| Roaming hubs / IPX / GRX | Where operators interconnect; GRX = GPRS Roaming eXchange (older name of IPX data roaming) |
| S8HR / LBO / HR | Roaming architectures: Home-Routed (data returns to home PGW), Local Break-Out (local), S8 Home Routed for VoLTE roaming |
3. Operations, monitoring, business
| Term | Meaning |
|---|---|
| OSS | Operations Support Systems — fault, performance, configuration (inventory, ticketing, planning) |
| BSS | Business Support Systems — customers, orders, billing, CRM |
| NMS / EMS / SON | Network/Element Management System / Self-Organising Networks (auto-optimisation) |
| FCAPS | Fault, Configuration, Accounting, Performance, Security — the five management functions |
| KPI / KQI / SLA / MOS | Key Performance/Quality Indicator / Service Level Agreement / Mean Opinion Score (voice quality 1–5) |
| NOC / SOC | Network / Security Operations Centre |
| MVNO / MVNE / MNO | Mobile Virtual Network Operator (no own radio network; resells) / Enabler / Mobile Network Operator |
| Tower company (TowerCo) | Owns masts and leases to operators |
| RAN sharing (MORAN / MOCN) | Multiple operators sharing a radio network (own spectrum / shared spectrum) |
| Roaming (IR / IOT) | International Roaming / Inter-Operator Tariff; BEREC / EU "Roam like home" regulates EU prices |
| ARPU / churn / CAPEX / OPEX | Average revenue per user / customers leaving / investment / running cost |
| Regulator | Grants licences, enforces rules, handles numbering and portability |
| GSMA, 3GPP, ETSI, ITU, IETF, GSMA IR.xx | Standards/industry bodies and documents |
Remember this: a call or SMS only works because of three layers: the radio (spectrum, modulation, cells), the transport (fibre, microwave, MPLS, IP) and the core (signalling + policy + charging). Problems can sit in any layer — always ask "which layer?" first.