User guide

SIP Telephony122
Voice over IP (VoIP)
without the hash key and code number procedures with a con-
cluding hash key can be used. An overview of code number proce-
dures that can be used is located in the Configurator on the Sys-
tem Info: Codes page. Activate “SIP phones”. Please also note
the corresponding information in the “Forum 500 / Forum 5000 –
Standard Terminals” user guide.
Alongside code number procedures, SIP subscribers can also use
a series of functional features realized via the SIP protocol. The
Forum 523/524 is the ending for all SIP connections as opposed to
what is usually the case on the Internet. This enables SIP sub-
scribers to use Forum 523/524 features. Direct data exchange is
thus not possible between two SIP subscribers. The following table
shows the possible features.
Features Notes
Incoming and outgoing
calls with call number
display (CLIP)
A SIP telephone requires a call
number display for CLIP.
Parallel connection of
multiple SIP subscribers
SIP subscribers must be logged on
under the same user identification.
Enquiry, toggling, call
waiting, three-way
conference, reject
Operation or feature must be
available on the SIP telephone or in
the SIP software.
Call transfer before and during a call; operation
must be available.
Blind Transfer SIP only: forwarding an incoming call
without accepting the call; feature
must be supported by SIP telephone
or by the SIP software.
Keypad as “INFO”
message
DTMF tones cannot be securely
transferred “in band” via compression
codecs. Digital “out band” transferral
as “INFO” SIP message or via
RFC 2833/4733 is supported. This
feature must be available and
activated on a SIP telephone or in the
SIP software.