Despite the growing literature on many aspects of communications technology, relatively little has been published on the functioning and planning of complete networks. The long-awaited 2nd edition of this seminal and bestselling telecommunications book is intended to fill that gap, discussing the structure and performance of networks in the context of the services they provide. It is written with the young engineer in mind, but will give professional specialists a deeper understanding of their work too. Much of the material has been developed from teaching within successive IEE Vacation Schools.