WAN - Wide Area Network
Are used when communication needs to travel over a larger geographical area.
Dedicated links:
Also called leased line or point-to-point link.
T-carriers:
Dedicated lines that can carry voice and data information over trunk lines.
S/WAN - Secure WAN:
Based on VPNs that are created with IPSec.

WAN Technologies
CSU/DSU - Channel Service Unit / Data Service Unit:
Is required when digital equipment will be used to connect a LAN network to a WAN network.
DSU converts digital signals to be transmitted over the telephone company's digital lines.
CSU is the unit that connects the network directly to the telephone company's line.
Provides a digital interface for DTE - Data Terminal Equipment.
Provides an interface to the DCE - Data Circuit-Terminating Equipment device.
Switching:
Circuit switching - Sets up a virtual connection that acts like a dedicated link between two systems.
Packet switching - Packets can travel along many different routes to arrive to the same destination.
Frame relay:
Is a WAN protocol that operates at the data link layer.
Uses packet-switching technology.
CIR /committed information rate - Companies that pay more to ensure that a higher level of bandwidth will always be available to them.
Two main types of equipment used:
- DET / Data Terminal Equipment - Customer owned.
- DCE / Data Cricuit-Terminating Equipment - Service provider's
     or phone company's
Virtual Circuits:
PVC / Permanent virtual circuit - Works like a private line for a customer with an agreed-upon bandwidth availability.
SVC / switched virtual circuits - Require steps similar to a dial-up and connection procedure.
X.25:
Is an older WAN protocol that defines how devices and networks establish and maintain connections.
Is a switching technology.
Data is divided into 128 bytes and encapsulated in High-level Data Link Control (HDLC) frames. The frames are then addressed, and forwarded across the carrier switches.
ATM - Asynchronous Transfer Mode:
Is a switching technology.
Uses a cell-switching technology. This means that data is segmented into fixed size cells, 53 bytes, instead of variable-size packets.
Is a high-speed networking technology used for LAN, WAN and service provider connections
Sets up virtual circuits, which act like dedicated paths between the source and destination. These virtual circuits can guarantee bandwidth and QoS.