STUN and ICE
The device supports standard STUN based on RFC3489 and RFC5389 for passing inbound RTP
packets to the device sitting behind NATs.
The parameters that control the STUN feature are found in the ITSP Profile X - General:: section:
● STUNEnable - Enables this feature (default is NO or FALSE).
● STUNServer - The IP address or domain name of the external STUN server to use. STUN feature
is disabled if this value is blank, which is the default.
● X_STUNServerPort - The STUN Server's listening UDP port. Default value is 3478 (standard
STUN port).
The STUN feature used in this context is only for RTP packets, not SIP signaling packets, which
typically do not require STUN. The device sends a STUN binding request right before making or
answering a call on SP1/2. If the request is successful, the device decodes the mapped external
address and port from the binding response and uses them in the m= and c= lines of its SDP offer or
answer sent to the peer device. If the request fails, such as STUN server not found or not responding,
the call goes on without using external address in the SDP.
Standard RTP requires the use of an even-numbered port in the m= line. If the external port is not an
even number, the device changes the local RTP port and redoes STUN, and continues to do this as
many as four times or until an even external port number is found. If the fourth trial still results in an
odd external port number, the call goes on without using an external address in the SDP.
The device supports standard ICE based on RFC5245. ICE is done on a per-call basis for
automatically discovering which peer address is the best route for sending RTP packets. To enable
ICE on the device, set the
ITSP Profile X - General
::X_ICEEnable parameter to YES (or TRUE). The
default is NO (or FALSE).
ICE is effective if STUN is also enabled. However, STUN not a requirement for using ICE on
the device. If STUN is enabled and an external RTP address different from its local address is
discovered, the device offers two ICE candidates in its SDP:
● The local (host) address (highest priority)
● The external (srflx or server reflexive) address
Otherwise, only the local host candidate is shown in the device's SDP. Note that the device uses the
srflx address in the m= and c= lines of the SDP if STUN is enabled and successful.
If ICE is enabled and the peer's SDP has more than one candidate, the device sends STUN requests
to each peer candidate from its local RTP port. As soon as it receives a response from the highest
priority candidate, the device concludes ICE and uses this candidate to communicate with the peer
subsequently. Otherwise, the device allows as long as 5 seconds to wait for the response from all
the candidates, and selects the highest priority candidate that has a response. Once ICE completes
successfully, the device further applies symmetric RTP concept to determine the peer's RTP address
(that is, sends them to the address from which the the peer's RTP packets are coming).
SIP Service Provider Features
Learn about some of the SIP Trunk service features that are supported on your Poly ATA device.
You can configure as many as four SIP accounts or SIP Trunks on the device. For the purposes
of this document and elsewhere on the device system information page, documentation, and the
76
Chapter 12Service Providers
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