I want to know what is mlln modem and how we instaal and troubleshoot it

MLLN means "Managed Leased Line Network". It's a network -- usually between two locations, I believe -- that is available and on 24/7.


INTRODUCTION TO MANAGED LEASED LINE NETWORKS (MLLN) (http://www.tnd.bsnl.co.in/eis/eis0304/EI%20MLLN%20SYSTEM.pdf)

Although I've heard of it, I can't answer your question. Maybe someone else can.