Wireshark · Wireshark-users: [Wireshark-users] 答复: Is that a bug in packet-gsm_sms.c ?

["damker" <damker@xxxxxxxx>]

Oh , in 3GPP TS 23.040 the PI is a Mandatory parameter .



On Apr 3, 2011, at 5:52 AM, damker wrote:

> means that it can be a FCS with PI?

No.  It means that a message can have an FCS and a PI, but they're separate
octets.

According to 3GPP TS 23.040, an SMS-DELIVER-REPORT message has a
TP-Failure-Cause (TP-FCS) if it's reporting an error, and always has a
TP-Parameter-Indicator (TP-PI).

The check in question is trying to determine whether the octet in question
is the TP-FCS from a delivery report from an RP-ERROR or the TP-PI from a
delivery report from an RP-ACK.  If it's the former, it adds it as a TP-FCS
and advances the offset to the next octet, which is the TP-PI, otherwise it
doesn't report it at all and leaves the offset alone.  The code after that
fetches the octet at the offset in question - which is the offset after the
TP-FCS if it's determine to be a TP-FCS, and the offset of the field
determined *not* to be a TP-FCS otherwise - and adds it as a TP-PI.

So, not a bug.

(Amusingly, a text message was being received, and responded to, in our
household at the same time I was looking this up - and, yes, it was over a
UMTS network.)
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