Sip Trunking - NEC UNIVERGE SV9100 Manual

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2.6.3

SIP Trunking

SIP Trunking
SIP (Session Initiation Protocol) is a protocol used for Voice over IP. It is defined by the IETF (Internet
Engineering Task Force) in RFC3261. The SV9100 can use SIP to connect to another SV9100 system, an
Aspire, an XN120 or a third party SIP enabled product.
SIP can also be used to provide external trunks to the SV9100 from ITSP's (Internet Telephony Service
Providers).
The SV9100 must be 'certified' to connect to a particular ITSP or PBX, there is a list of certified carriers
available, please refer to your support partner for more information.
From the SV9100's point of view there are two types of SIP Trunks, 'Networking Mode' and 'Carrier Mode'.
Each system in the network must have:
GCD-CP10
GPZ-IPLE
IP Trunk License(s)
Networking Mode
This mode is usually used to connect to other NEC systems (SV9100, SV8100, Aspire, XN120) using SIP
although some SIP Carriers use this mode to provide external SIP Trunks. The systems connect to each
other using an internal routing table. The call is always attempted even if the remote end point is down.
Each system does not know the state of the other because there is no registration procedure.
If this method is used to connect to an ITSP, the customer's public IP address will be used as a security
measure.
Carrier Mode
This mode is usually used to connect the SV9100 to an ITSP to provide external SIP Trunks. The SV9100
uses the customer's internet connection to register to the ITSP's SIP server (although some ITSP's provide
a dedicated circuit just for voice).
The SV9100 registers to the ITSP using a User ID and Password for security, this registration is constantly
maintained. If the registration is lost the trunk ports will return busy tone allowing an overflow trunk group to
be utilised.
Network Address Translation (NAT)
NAT will cause a problem for SIP Trunks if the SV9100 has been assigned private IP addresses. The
problem is that the SV9100's IP address is embedded in the SIP signalling messages which cannot be
manipulated by the NAT router. The NAT router can only change the IP header information.
When an outgoing packet arrives at a SIP server, the SIP server reads the SV9100 IP address from the SIP
information which will be an internal private IP address. This address is not routable on the Internet
resulting in communication problems.
This problem is resolved by entering the public IP address in the SIP signalling messages instead of the
private IP address. This is done by enabling the NAPT Router option and entering the Public IP address of