🚀 go-pugleaf

GSM Recommendation 03.40, clause 9.3.2.11, defines the Time Zone
field used in SMS messages, as being "the difference", in units
of quarter hours, "between the local time and GMT".  Clause 8.15
of GSM 07.07 suggests a range of valid values from -47 to +48
(ie -11 3/4 hours to +12 hours).

This wording is ambiguous about which side of the Greenwich
meridian is positive and which is negative.  Of the 2 carriers
I'm familiar with in eastern Australia, Telstra stamps messages
as -36 and Optus stamps them as +40.  In hours, that's -9 and
+10, being a 19 hour difference.

Telstra cannot be correct, as eastern Australia's offset from GMT
is either 10 or 11 hours, depending on local daylight savings
(it's currently 10 hours).  We are currently 9 hours ahead of the
local time in Greenwich, which itself is an hour ahead of GMT
because of northern hemisphere daylight savings.

But who is correct about the plus or minus?  In the light of
the -47 to +48 range, I'd assume the answer is given by the
convention about whether the time at the International Date Line
is before or after GMT.  Encarta says it's 12 hours ahead, making
Optus correct and Telstra wrong (on 2 counts).

I have an uneasy feeling that this figure is vitally important
for the "message life" / "validity period" of messages passed
between network carriers, because the date-time stamp itself is
always given in local time.  The zone provides the correct
alignment for interworking.  Do messages passed to Telstra with a
life of 24 hours get only 5?

Falsely positive values would work the other way.  Messages going
FROM such a carrier would be deleted too early.

And if I'm right, are other carriers creating this unseen black
hole for messages to disappear into?

John Henderson