Communication network systems refer to the collection of various transmission networks, data terminal equipment (DTE), communication networks and tributary stations, etc. which are able to hold interoperation and interconnection to work as a single entity. Communication security enables these networks to work without hindrance and security failures. This book provides comprehensive insights into this field. The various studies that are constantly contributing towards advancing technologies and evolution of this field are examined in detail in this text. It is appropriate for students seeking in-depth knowledge about this subject, as well as for experts. This book will serve as a valuable guide for all associated with this field