ERCB: ASN.1 Commmunication Between Heterogenous Systems

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Vital Statistics

Title	ASN.1 Commmunication Between Heterogenous Systems
Author	Olivier Dubuisson (tr. Phillipe Fouquart)
Publisher	Morgan Kaufman http://www.mkp.com/
Copyright	2001
ISBN	0-12-63361-0
Pages	562
Price	$49.95

ASN in Depth

ASN.1 Commmunication Between Heterogenous Systems, by Olivier Dubuisson (and translated by Phillipe Fouquart), covers the ASN.1 specification for data interchange protocol notation. An ASN.1 spec can be used to generate the source code for a support library for a arbitrarily complex data stream. ASN.1 concerns itself with expressively describing the payload of a protocol. Details of the encoding are configurable, but the bindings are generated at compile time and packet formatting handled at run time transparently to application programmers.

ASN.1 is thus sort of like a data-only CORBA. It can be appreciated only by those who have ever had to implement "by hand" a complex interchange protocol from the API level down to the bit- and byte-order on the wire.

Dubuisson, a research engineer at France Telecom, is that society's voice on ISO ASN.1. Readers may remember my review of John Larmouth's 1999 work ASN.1 Complete (http://www.ercb.com/brief/brief.0156.html). Larmouth is also associated with ISO ASN.1.

Dubuisson's book, like Larmouth's, is a complete introduction authored by an accomplished domain expert. But where Larmouth's earlier book was a computer science work for those requiring a detailed technical overview, ASN.1 Commmunication Between Heterogenous Systems is a detailed technical user's reference to a middleware metaphor whose user group and store of practical experience have broadened considerably in the short interval between the two books.

ASN.1 Commmunication Between Heterogenous Systems is usage oriented. It is divided into four parts:

History of ASN.1
User's Guide and Reference Manual
Encoding Rules and Transfer Syntaxes
ASN.1 Applications

In effect, there is some overlap between the two works. Larmouth's long-term contribution to ASN.1 dating back to the 1980s is acknowledged by Dubuisson in a technical context. Larmouth's book is an examplararily clear exposition of the theory, purpose, basic structure and early evolution of ASN.1. The present book is intimately engaged in the practice of ASN.1.

Dubuisson makes daring descents into technical detail that tickle me the way Dostoevsky tickles me literarily. It's a sound and astute volume for the budding expert, and not for the dilettante. Not only must you delight in mulling over bit encodings and drillings in grammar, you have to be a bit of a lawyer:

If a type is tagged, directly or indirectly, in the IMPLICIT mode (i.e., the tag is marked IMPLICIT, or it is not marked but the module contains the clause IMPLICIT TAGS in its header), only the tags preceding the keyword IMPLICIT are transmitted in BER (in particular, the DEFAULT tag, of class UNIVERSAL, is not encoded except if a tag marked, directly or indirectly, EXPLICIT is found after the tag marked IMPLICIT).

Having read both books, I find this perfectly clear technically and satisfactory aesthetically. De gustibus, it's not the sort of writing everyone will enjoy. Be warned also that the single sentence above is not the longest in the book -- it's merely the longest one I felt like typing into this review.

If you needed the earlier Larmouth work, you probably need Dubuisson's ASN.1 Commmunication Between Heterogenous Systems. Enjoy it. I did.

-- Jack J. Woehr (jwoehr@attglobal.net)

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