📘 12-01: WAN Fundamentals¶

🌍 LAN vs. WAN¶

	LAN	WAN
Scope	Building/campus	Large geographic area
Ownership	Private	Provider/telco (NSP)
Differ at	—	Layers 1 & 2 (access, media, topology)
Share	—	Layer 3+ protocols (IP, TCP/UDP)
Examples	Office switch network	The Internet, multi-site company

LANs and WANs differ at Layers 1–2 but use the same Layer 3+ protocols. WANs are typically owned by providers like AT&T, Verizon, Comcast.

🌍 WAN Selection Factors¶

Choosing a WAN technology depends on:

Traffic load / required bandwidth
Budget
Geographic breadth
Commercially available technology at the site
Latency and reliability needs (SLA)

📌 Key Boundary Terms¶

Term	Meaning
Demarc	Boundary between provider and customer responsibility
Last mile	Link from provider to the customer premises
CSU/DSU	Terminates a digital leased line (T1/T3) to the router
CPE	Customer Premises Equipment

📌 The Router's Role¶

Routers manage internetwork communication — forwarding packets between separate networks using IP, choosing paths, and tying LANs into the WAN/Internet.

Tip

Key idea — A WAN spans wide distances, is provider-owned, and differs from a LAN at Layers 1–2. Selection balances bandwidth, budget, geography, availability, latency, and SLA.