ASN.1 the Abstract Syntax Notation One is a description language designed for communication protocols. While many people will never have heard of it, ASN.1 is used widely in the telecoms environment and has been used in defining some of the Internet protocols we all use daily, for example the Simple Network Management Protocol (SNMP) used to control routers and switches that make up the fabric of the Internet. The advantage of using ASN.1 to describe a protocol is that a number of standard tools exist to parse ('compile') ASN.1 descriptions to prove validity of the protocol, or to encode and decode messages.
ASN.1 is undoubtedly a heavyweight subject, but this book tries to break it into more manageable chunks by dividing the topic into four sections. Section I covers the commonly used features of ASN.1, with less used features only appearing in the more comprehensive section II. Section III covers the fundamental principals of ASN.1 encoding and as the author states '...this text is only for the curious! There is no need for standards writers or coders to know about these encodings'. Finally, Section IV gives a brief history of the development of ASN.1 and an outline of some of the applications using it.
ASN.1 Complete is exactly what it says on the cover, complete. The problem is that I suspect very few people will have a need for such a complete coverage and in being complete, it is sometimes hard to find the information required quickly, especially as the index is shorter than the table of contents and neither is really sufficient. If you work with ASN.1 regularly, you will probably know most of the relevant information already. If you are just starting to use ASN.1, this book (especially section I) will be helpful, however the poor index may limit the use you make of the book as your experience grows.