Version 6.2 493 February 2011
SIP User's Manual 8. IP Telephony Capabilities
Blocking Incoming Calls from Unregistered Users: You can block incoming calls
(INVITE requests) from unregistered users (pertaining to USER-type IP Groups). By
default, calls from unregistered users are not blocked. This is configured using the
parameter SRD. The flowchart below depicts the process for blocking unregistered
users. When the call is rejected, the device sends a SIP 500 "Server Internal Error"
response to the remote end.
Figure 8-53: Blocking Incoming Calls from Unregistered Users
8.4.5 SBC Media Handling
Media behavior includes anything related to the establishment, management and
termination of media sessions within the SIP protocol. Media sessions are created using
the SIP "offer"/"answer" mechanism. If successful, the result is a bi-directional media (RTP)
flow (e.g. audio, fax, modem, DTMF). Each offer/answer may create more than one media
session of different types (e.g. audio and fax). In a SIP dialog, multiple offer/answer
transactions may occur, each may change the media sessions characteristics (e.g. IP
address, port, coders, media types, and RTP mode). The media capabilities exchanged in
an offer/answer transactions include the following:
Media types (Audio, Secure Audio, Video, Fax, Text...)
IP addresses and ports of the media flow
Media flow mode (send receive, receive only, send only, inactive)
Media coders (coders and their characteristics used in each media flow)
Other (standard or proprietary) media and session characteristics
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