Wide Area Network (WAN)
1. Definition
A Wide Area Network (WAN) is a network that spans a very large geographical area — a state, country, continent or the entire globe — connecting multiple LANs and MANs through public or leased telecommunication links. It is generally not owned by a single organisation: an enterprise owns the routers and end devices, but the transmission lines are leased from telecom carriers and ISPs. The Internet is the largest WAN, itself a network of networks.
2. Characteristics
| Feature | Typical value |
|---|---|
| Coverage | City-to-city, country, global (hundreds to thousands of km) |
| Speed | 2 Mbps to 10 Gbps per link (lower than LAN per link) |
| Ownership | Multiple parties — customer + telecom carrier/ISP |
| Latency | Tens to hundreds of milliseconds |
| Error rate | Higher than LAN (long distance, mixed media, weather for wireless) |
| Media | Leased fibre, MPLS, DSL, cable, microwave, satellite, 4G/5G |
| Devices | Routers, modems/CSU-DSU, WAN switches, firewalls |
| Cost | High recurring cost — bandwidth is rented monthly |
| Administration | Shared responsibility; troubleshooting crosses organisations |
3. WAN Technologies
| Technology | Nature | Typical use |
|---|---|---|
| Leased line (T1/E1, T3/E3, STM) | Dedicated point-to-point circuit, always on, fixed capacity | Connecting branches with predictable traffic |
| MPLS | Carrier packet-switched backbone with labels and QoS guarantees | Enterprise multi-site WANs, bank branch networks |
| DSL (ADSL/VDSL) | Broadband over existing telephone copper | Homes and small offices |
| Cable broadband (DOCSIS) | Broadband over cable TV coaxial plant | Homes |
| Metro Ethernet | Carrier Ethernet across a city | Campus-to-campus, ISP last mile |
| VPN over the Internet | Encrypted tunnel over public internet (IPsec, OpenVPN, WireGuard) | Secure remote access / site-to-site at low cost |
| SD-WAN | Software-defined selection of links (MPLS + broadband + LTE) | Modern branch networking with policy routing |
| Frame Relay / ATM / ISDN | Legacy packet/circuit technologies | Historical (mostly retired) |
| Satellite (VSAT, LEO) | Wireless through a satellite | Remote/rural areas, ships, disaster recovery, Starlink backhaul |
| Cellular 4G/5G | Wireless carrier data | Mobile branches, backup links, IoT |
4. How a WAN is Built
LAN-A (Delhi office) LAN-B (Mumbai office)
┌────────────────────┐ ┌────────────────────┐
│ PCs ─ Switch │ │ PCs ─ Switch │
│ │ │ │ │ │
│ Router ───────┼── leased line / MPLS cloud ──┼────── Router │
└────────────────────┘ (ISP / telecom carrier) └────────────────────┘
│
┌────────┴────────┐
│ Carrier WAN │ routers + fibre/microwave/satellite links
│ (Internet) │ packet switching, BGP routing, TTL
└─────────────────┘
- Router at each site connects the LAN to the carrier link and performs routing between the site and the outside world.
- CSU/DSU or modem terminates the carrier circuit (converts between the LAN's digital format and the carrier's signalling).
- The carrier cloud provides the transmission path — packet-switched, so the path may vary per packet (datagram) or follow a virtual circuit (MPLS).
- Backup links (4G/5G or a second ISP) keep the WAN alive when the primary fails.
5. LAN vs MAN vs WAN
| Basis | LAN | MAN | WAN |
|---|---|---|---|
| Full form | Local Area Network | Metropolitan Area Network | Wide Area Network |
| Coverage | Room to campus, ≤ 1 km | A city, 5-50 km | Country to global, hundreds-thousands of km |
| Speed | 100 Mbps-100 Gbps | 10 Mbps-10 Gbps | 2 Mbps-10 Gbps per link |
| Ownership | Private, one organisation | Private or public (cable/ISP), city scale | Multiple carriers and organisations |
| Latency | Microseconds-ms | Low ms | Tens-hundreds of ms |
| Error rate | Lowest | Low | Highest of the three |
| Media | UTP, fibre, Wi-Fi | Fibre (metro Ethernet), coax, microwave | Leased fibre, MPLS, DSL, satellite, 5G |
| Devices | Switch, hub, AP | Switch/router, DWDM gear | Router, modem, WAN switch |
| Setup cost | Low, no recurring | Moderate, some recurring | High, heavily recurring |
| Example | College lab, office LAN | City cable TV network, city-wide Wi-Fi, metro Ethernet | Internet, bank branch network, airline reservation system |
6. Advantages and Limitations
| Advantages | Limitations |
|---|---|
| Connects offices, branches and users across the globe | High recurring cost — bandwidth and equipment |
| Centralised data, applications and management across sites | Complex to design, configure and troubleshoot |
| Enables cloud services, ERP, e-mail and remote work | Higher latency and error rate than LAN |
| Backup links and redundant paths give resilience | Security exposure — traffic crosses third-party networks, so encryption is needed |
| Scalable — bandwidth can be upgraded as needed | Dependence on carrier SLAs; an ISP outage halts business |
| Enables e-commerce, telemedicine, e-governance | Requires skilled network engineers; change management is slow |
7. Exam Points
- Define a WAN and list its characteristics — 5 marks, frequent.
- Differentiate LAN, MAN and WAN (tabular) — 5 marks, almost certain.
- Name any five WAN technologies and state one use of each — 5 marks.
- Explain the role of routers, modems and leased lines in a WAN — 5 marks.
- What is MPLS/SD-WAN and why do enterprises use it? — 3 marks.
- Advantages and disadvantages of a WAN — 5 marks.
- Draw a labelled diagram of two LANs connected through a WAN — 5 marks.