Compressed SMS (and other text messages)

Ian Stirling openmoko at
Wed Mar 21 01:31:25 CET 2007

Mikko Rauhala wrote:
> 'lo
> Didn't appear in the wiki, so I figured I'd throw it out there first:
> compressed SMS for when a persistent TLS-encrypted and -compressed
> Jabber connection just isn't there (eg. if it would be too expensive in
> a particular locale), but you need to send "long" text messages. With
> SMS, every 140 bytes costs loads of money. (Yes, it's 140 bytes, people;
> 160 characters in 7-bit charsets.)
> So. We can't very well send a compression dictionary along with each
> SMS. Instead, we'll start producing one upon sending the first SMS to
> another Moko user (might be necessary to mark Moko peers manually, or is
> there a way to identify them?). The recipient produces the same.
> The next message between the two will be compressed with the compression
> dictionary previously generated. The new data will deterministically
> modify the compression dictionary on both ends. These are cyclically
> numbered and several previous versions will be stored in case the
> parties get out of sync.
> Optional: Allow compression dictionary to be generated from a set of
> messages, and be transferred to another phone as a baseline (presumably
> when better connectivity is available). Or even as a final frozen
> dictionary, which would avoid possible races and other sync problems.

Several stock dictionaries, with the user - or phone saying which one it 
prefers at the start.
Users able to upload their dictionaries to a central repository if they 
If you've got a connection, you can determine the users preferred 
dictionary first?

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