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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)