ADTRAN 4200659L1 - Manual (Page 29)

Chapter 1. Introduction
61200659L1-1 MX2800 STS-1 User Manual 1-7
TL1
Transaction Language 1 (TL1) is an ASCII based language that
supports both command-response and autonomous (NE) message
generation. Commonly, TL1 is used over a X.25 packet network
but is completely independent of any physical layer protocols. For
the MX2800 STS-1, TL1 is implemented as a Telnet session
running over either Ethernet or PPP. Only one TL1 Telnet
connection can be active at a time.