WANs vs LANs: Leased Lines

Wide Area Networks (WANs) vs. Local Area Networks (LANs)

• WANs and LANs are distinct network types but related.
• Geographical scope distinguishes LANs from WANs.
• LANs are restricted to small areas, like a single floor, office, or building.
• Campus LANs link buildings in areas like industrial parks or college campuses.
• WANs link geographically distant LANs such as different cities or countries.
• A WAN example is connecting LANs 3,000 miles apart, such as New York and San Francisco.
• WANs enable geographically distant parts of an organization to function as if they were local.

WAN Connections

• WAN connections use circuits or links leased from service providers or telecom companies, not enterprise-owned ones.
• Leased lines are provisioned by and leased to the enterprise.

Types of Leased Lines

• Synchronous serial, circuit-switched, and packet-switched lines (e.g., Frame Relay) are common leased lines.
• Point-to-point circuits are widely implemented in modern networks.

Point-to-Point Circuits

• Point-to-point circuits connect two specific points (A and B) exclusively.
• Point-to-point circuits, also known as private lines or circuits, are dedicated to the user.
• Point-to-point circuits are typically full duplex, sending and receiving data simultaneously.

Components of WAN Connectivity

• Customer Premise Equipment (CPE), leased lines, WAN switches/routers, central offices (COs), and demarcation points (Demarcs) are key components.
• Customer premise equipment (CPE) resides at an enterprise's network.
• CPE includes a router and a Channel Service Unit/Data Service Unit (CSU/DSU).
• CSU/DSU provides timing and synchronization with the service provider's network.
• CSU/DSU can be a separate device or integrated into a serial card on the router.
• The local loop or last mile is the leased line from the CPE to the service provider's network.
• On the service provider's side, the leased line connects to a WAN switch or router.
• Central offices (CO) are service provider locations equipped to provision circuits to customers geographically.
• The demarcation point (Demarc) marks where the service provider's responsibility ends and the customer's begins.
• The service provider's network connects to a Demarc, where customers connect their equipment as a "line in the sand" that clarifies responsibility.

Review of WANs and LANs

• Geography differentiates LANs and WANs.
• WANs involve considerable distances between LANs within an organization.
• Connectivity between LANs to form a WAN is achieved through leased lines, with point-to-point lease lines being a common option.
• Understanding the components of a lease line (CPE, Demarc, local loop, central office) is crucial for troubleshooting, ordering circuits, and understanding provisioning.