Definitions...

• T1 & T3 – Transmission System 1 or T Carrier System
• E1 & E3 – European Carrier System or E Carrier System
• ATM – Asyncronous Trasfer Mode
• SONET – Syncronous Optical Network
• OC-1, > OC-192 – Optical Carrier

• These Technologies are used to describe a branch(s) within a WAN structure (Like the Internet)