Build Information:
Version 1.10.7 (v1.10.7-0-g6b931a1 from master-1.10)
Copyright 1998-2014 Gerald Combs <gerald@wireshark.org> and contributors.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
Compiled (64-bit) with GTK+ 2.24.14, with Cairo 1.10.2, with Pango 1.30.1, with
GLib 2.34.1, with WinPcap (4_1_3), with libz 1.2.5, without POSIX capabilities,
without libnl, with SMI 0.4.8, with c-ares 1.9.1, with Lua 5.1, without Python,
with GnuTLS 2.12.18, with Gcrypt 1.4.6, without Kerberos, with GeoIP, with
PortAudio V19-devel (built Apr 22 2014), with AirPcap.
Running on 64-bit Windows 7 Service Pack 1, build 7601, with WinPcap version
4.1.3 (packet.dll version 4.1.0.2980), based on libpcap version 1.0 branch
1_0_rel0b (20091008), GnuTLS 2.12.18, Gcrypt 1.4.6, without AirPcap.
Intel(R) Core(TM) i5-3340M CPU @ 2.70GHz, with 8071MB of physical
memory.
Built using Microsoft Visual C++ 10.0 build 40219
Wireshark is Open Source Software released under the GNU General Public
License.
Check the man page and http://www.wireshark.org for more information.
--
>From the dissection code in file packet-gsm_a_dtap.c the comment says that it
conforms to 3GPP TS 23.040 version 6.6.0 Release 6.
/*
* [3] 10.5.3.9 Time Zone and Time
*/
static guint16
de_time_zone_time(tvbuff_t *tvb, proto_tree *tree, packet_info *pinfo _U_,
guint32 offset, guint len _U_, gchar *add_string _U_, int string_len _U_)
{
guint8 oct;
guint32 curr_offset;
char sign;
nstime_t tv;
struct tm tm;
curr_offset = offset;
/* "unused" part of structure */
tm.tm_wday = 0;
tm.tm_yday = 0;
tm.tm_isdst = -1;
oct = tvb_get_guint8(tvb, curr_offset);
tm.tm_year = (oct & 0x0f)*10 + ((oct & 0xf0) >> 4) + 100;
oct = tvb_get_guint8(tvb, curr_offset+1);
tm.tm_mon = (oct & 0x0f)*10 + ((oct & 0xf0) >> 4) - 1;
oct = tvb_get_guint8(tvb, curr_offset+2);
tm.tm_mday = (oct & 0x0f)*10 + ((oct & 0xf0) >> 4);
oct = tvb_get_guint8(tvb, curr_offset+3);
tm.tm_hour = (oct & 0x0f)*10 + ((oct & 0xf0) >> 4);
oct = tvb_get_guint8(tvb, curr_offset+4);
tm.tm_min = (oct & 0x0f)*10 + ((oct & 0xf0) >> 4);
oct = tvb_get_guint8(tvb, curr_offset+5);
tm.tm_sec = (oct & 0x0f)*10 + ((oct & 0xf0) >> 4);
tv.secs = mktime(&tm);
tv.nsecs = 0;
proto_tree_add_time_format_value(tree, hf_gsm_a_dtap_time_zone_time, tvb,
curr_offset, 6,
&tv, "%s", abs_time_to_ep_str(&tv,
ABSOLUTE_TIME_LOCAL, FALSE));
curr_offset += 6;
/* 3GPP TS 23.040 version 6.6.0 Release 6
* 9.2.3.11 TP-Service-Centre-Time-Stamp (TP-SCTS)
* :
* The Time Zone indicates the difference, expressed in quarters of an
hour,
* between the local time and GMT. In the first of the two semi-octets,
* the first bit (bit 3 of the seventh octet of the
TP-Service-Centre-Time-Stamp field)
* represents the algebraic sign of this difference (0: positive, 1:
negative).
*/
oct = tvb_get_guint8(tvb, curr_offset);
sign = (oct & 0x08)?'-':'+';
oct = (oct >> 4) + (oct & 0x07) * 10;
proto_tree_add_text(tree,
tvb, curr_offset, 1,
"Timezone: GMT %c %d hours %d minutes",
sign, oct / 4, oct % 4 * 15);
curr_offset++;
/* no length check possible */
return(curr_offset - offset);
}
>From the 3GPP 23.040 document itself the Timezone is said to:
... "take into account daylight saving time, such that when the sending entity
changes from regular (winter) time to daylight saving (summer) time, there is a
change to the value in the Time Zone field, for example in the UK the winter
setting is 00000000 and the summer setting is 01000000"...
The way I understand this, is that apart from the most significant bit, that is
used as a sign, the 2nd most significant bit is used to denote the daylight
saving time. If my interpretation is correct then the dissector would translate
the DST bit as a number and would affect the calculated timezone value much
more than a simple +1 hour during summer.
