CompTIA Network+ Preparation · lesson 25 of 30 · 25 min
WAN Concepts
A WAN (Wide Area Network) connects geographically separated networks. Unlike LANs, WANs typically use service provider infrastructure. Key WAN concepts:
CPE (Customer Premises Equipment) — equipment at the customer site (router, modem). The demarcation point (demarc) is where the provider’s responsibility ends and the customer’s begins.
Local loop — the connection from the customer to the provider’s nearest facility (CO — Central Office). Also called the “last mile.”
CSU/DSU (Channel Service Unit/Data Service Unit) — converts between LAN signals and WAN signals. Used with T1/T3 lines. Often integrated into modern routers.
WAN Connection Types
Leased line — dedicated point-to-point connection. Always available, consistent bandwidth. Expensive. T1 (1.544 Mbps), T3 (44.7 Mbps), E1 (2.048 Mbps).
MPLS (Multiprotocol Label Switching) — provider-managed WAN. Uses labels instead of IP routing for fast forwarding. Supports QoS. Common enterprise WAN technology. Not internet-based — private provider network.
Metro Ethernet — Ethernet extended over a metropolitan area. Provider delivers Ethernet handoff to customer. Scalable bandwidth. Replacing legacy WAN technologies.
DSL (Digital Subscriber Line) — broadband over telephone lines. ADSL: asymmetric (faster download than upload). VDSL: faster, shorter distance. Distance-limited.
Cable broadband — internet over cable TV infrastructure (DOCSIS standard). Shared medium — bandwidth shared with neighbors.
Fiber (FTTH/FTTP) — fiber optic to the home/premises. Highest speeds, lowest latency. Symmetrical upload/download possible.
Satellite — internet via satellite. Available anywhere with line of sight to sky. High latency (600ms+ for geostationary). LEO satellites (Starlink) reduce latency significantly.
SD-WAN (Software-Defined WAN) — uses software to manage and optimize WAN connections. Can combine MPLS, broadband, and LTE. Centrally managed. Cost-effective alternative to pure MPLS.
Exam Tip
MPLS uses labels, not IP routing — supports QoS and is provider-managed. SD-WAN combines multiple WAN links with software control. Satellite has high latency. T1 = 1.544 Mbps, T3 = 44.7 Mbps.
Key Terms
Key Terms
Knowledge Check — 10 Questions
Network+ — WAN Technologies
MPLS forwards traffic based on:
- IP destination addresses
- Labels assigned by the provider
- MAC addresses
- Port numbers
- Answer: Labels assigned by the provider
MPLS uses short labels instead of IP routing lookups — faster forwarding. Labels are assigned at the network edge. The demarcation point is:
- The customer’s router
- Where provider responsibility ends and customer responsibility begins
- The ISP’s core router
- The firewall
- Answer: Where provider responsibility ends and customer responsibility begins
The demarc is the handoff point — everything on the provider side is their responsibility; everything past it is the customer’s. T1 provides a bandwidth of:
- 512 Kbps
- 1.544 Mbps
- 44.7 Mbps
- 100 Mbps
- Answer: 1.544 Mbps
T1 = 1.544 Mbps (24 DS0 channels × 64 Kbps each). T3 = 44.7 Mbps (28 T1s).
Which WAN technology has the highest latency?
- Fiber
- Cable
- MPLS
- Geostationary satellite
Answer: Geostationary satellite
Geostationary satellites orbit at ~35,786 km — signal round-trip takes 600ms+. LEO satellites (Starlink) reduce this to ~20-40ms.
SD-WAN allows organizations to:
- Replace all WAN with satellite
- Combine multiple WAN links (MPLS, broadband, LTE) managed by software
- Use only fiber connections
- Eliminate the need for routers
- Answer: Combine multiple WAN links (MPLS, broadband, LTE) managed by software
SD-WAN uses software to intelligently route traffic across multiple WAN links — can reduce costs by replacing expensive MPLS with broadband. DSL is limited by:
- Number of users
- Distance from the central office
- Time of day
- IP address availability
- Answer: Distance from the central office
DSL signal degrades over distance — the farther from the CO, the slower the connection. VDSL is faster but has even shorter range.
Cable broadband uses which standard?
- DSL
- DOCSIS
- SONET
- T-carrier
Answer: DOCSIS
DOCSIS (Data Over Cable Service Interface Specification) is the standard for internet over cable TV infrastructure.
A CSU/DSU is used with:
- Fiber optic connections
- T1/T3 leased lines
- Cable broadband
- Wireless WAN
- Answer: T1/T3 leased lines
CSU/DSU converts between the LAN signal and the WAN signal on T1/T3 lines. Often integrated into modern WAN routers. Metro Ethernet provides:
- Wireless metropolitan coverage
- Ethernet handoff from the provider over a metropolitan area
- DSL over Ethernet
- Satellite Ethernet
- Answer: Ethernet handoff from the provider over a metropolitan area
Metro Ethernet extends Ethernet connectivity across a city — provider delivers an Ethernet port to the customer, scalable bandwidth.
The local loop connects the customer to the provider’s _____ Office.
Answer: Central
The local loop (last mile) runs from the customer premises to the provider’s Central Office (CO) where it connects to the provider’s network.
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