Subject:            Four year old GSM SMS bug!
Date:               Sun, 21 Sep 1997 12:20:20 GMT
From:               ken@birchanger.demon.co.uk (Ken Wheatley)
Organization:       Birchanger Anonymous
Newsgroups:         alt.cellular.motorola


I've recently discovered a bug in Motorola handsets that results in
them rejecting good SMS messages in some circumstances. It concerns
the time zone part of the service center time stamp field (TP-SCTS).
This indicates the timezone of the message originator represented as
the number of quarter hours difference from UCT (GMT). The sign bit
(according to the GSM phase 1 specs) is in bit 3 of the seventh octet,
with 1 as negative. However, if you set this bit the 'phone rejects
the message.

However, if you set bit 7 of the same octet instead it works. Now, the
GSM spec was amended in October 1993 - the older version says use bit
7. So this bug has been there for four years!

It's more serious than it sounds, as any service centre attempting to
set the time zone will not have messages accepted by Motorolas if the
offset happens to cause bit 3 to be set; e.g. if the offset is (say)
three hours.

Cheers,

Ken