Old Protocol Could Save Massive Bandwidth

GFD writes: "The EETimes has a story about a relavtively old protocol for structured information call ASN.1 could be used to compress a 200 byte XML document to 2 bytes and few bits. I wonder if the same could be done with XHTML or even regular HTML."

Comments

ASN.1 not suitable

[cartman]

ASN.1 is the basis of a great many protocols, LDAP among them. What is not mentioned in the article is that ASN.1 is a binary protocol and is therefore not human-readable. It may save space for bandwidth-constrained applications. However, bandwidth has a tendency to increase over time. When all wireless handhelds have a megabit of bandwidth, we would sorely regret being tied to ASN.1, as LDAP regrets it now.

Not to mention, ASN.1 does not generally reduce the document size by more than 40% compared to XML. Think about it: how much space is really taken by tags?

It's also worth noting that there is lots of documentation surrounding XML. With ASN.1 you have to download the spec from ITU which is an INCREDIBLY annoying organization and their specs are barely readable and they charge money to look at them, despite the fact that they are supposedly an open organization. The IETF and the W3C are actually open organizations; ITU just pretends to be. ITU does whatever it can to restrict the distribution of their specifications.

Re:ASN.1 not suitable

[pegacat]

This is pretty much right. I do a lot of work on X500 / ldap / security, and ASN1 is used throughout all this. It does a pretty good job, but as the poster points out, the ITU is a completely brain damaged relic of the sort of big company old boys club that used to make standards. It's very difficult to get info out of them. (Once you get it though, it's usually pretty thorough!)

As for the 'compression', well, yes, it sorta would be shorter under many circumstances. ASN1 uses pre-defined 'global' schema that everyone is presumed to have. Once (!) you've got that schema, subsequent messages can be very terse. (Without the schema you can still figure out the structure of the data, but you don't know what its for). For example, I've seen people try to encode X509 certificates (which are ASN.1) in XML, and they blow out to many times the size. Since each 'tag equivalent' in ASN.1 is a numeric OID (object identifier), the tags are usually far shorter than their XML equivalents. And ASN.1 is binary, whereas XML has to escape binary sequences (base64?).

But yeah, ASN.1 is a pain to read. XML is nice for humans, ASN1 is nice for computers. Both require a XML parser/ ASN.1 compiler though. ASN.1 can be very neat from an OO point of view, 'cause your ASN.1 compiler can create objects from the raw ASN.1 (a bit like a java serialised object). But I can't see ASN.1 being much chop to compress text documents, there are much better ways of doing that around already (and I thought a lot of that stuff was automatically handled by the transport layer these days?)

And just for the record... the XML people grabbed a bunch of good ideas from ASN.1, which is good, and LDAPs problems are more that they screwed up trying to do a cut down version of X500, than that they use ASN.1 :-)!