AASTRA 6700i series, 9143, 9480i, 9480i CT SIP Administrator Guide EN - Manual (Page 486)

41-001343-01 Rev 03, Release 3.2.2 5-209
P-Preferred Identity Header for BLA Accounts
The IP Phones support the BLA specification, draft-anil-sipping-bla-02, which states that the
P-Preferrred-Identity header (RFC3325) gets added to the INVITE message to indicate the
Caller-ID that is used for the call.
BLA Support for Message Waiting Indicator (MWI)
The IP Phones have an option for a Busy Line Appearance (BLA) configured line to send a
SUBSCRIBE SIP message for a Message Waiting Indicator (MWI).
You can configure this feature using the configuration files or the Aastra Web UI.
Limitations
The following are limitations of the BLA Support for MWI feature:
• The phone shows MWI for the first matching identity if more than one line with different user
names has the same BLA account.
• If a normal line has the same user name as the BLA user of another line, the phone shows
MWI only for the normal line.
Use the following procedure to configure BLA support for MWI.
Note: The P-Preferred-Identity for BLA accounts is also sent for hold/
unhold messages.
Notes:
1. If you change the setting on this parameter, you must reboot the
phone for it to take affect.
2. Both the “sip explicit mwi subscription” and “sip mwi for bla
account ” parameters must be enabled in order for the MWI subscription
for BLA to occur.
3. The MWI re-subscription for the BLA account uses the value set for
the "sip explicit mwi subscription period" parameter to re-subscribe.
4. Whether or not the "sip mwi for bla account" parameter is enabled,
the priority for displaying MWI does not change.