Many times I have been asked to explain “ briefl y ” how SDH, SONET, and the
OTN “ exactly ” work. The questions came mainly from new colleagues, stu-
dents, and users of these technologies, personally or via the usenet newsgroup
comp.dcom.sdh - sonet. I could have referred them to the standards documents,
but to provide a more consistent and clear answer I decided to write this
pocket guide. The objective of this book is that it can be used both as an
introduction as well as a reference guide to these technologies and their spe-
cifi c standards documents.
