Sip Gateway; Outbound Proxy - Snom ONE IP Technical Manual

Deploying the snom ONE IP Telephone System
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A SIP registration trunk can also be used to connect two or more snom ONE systems
together, as in a branch/head office configuration (see "Connecting Branch Offices
Together" on page 142).

SIP Gateway

The gateway trunk is typically used to talk to a PSTN or cellular gateway, which could
authenticate the call leg on the IP address in the system. However, some ITSPs that
do not have a session boarder controller and require a public IP address use gateway
trunks. A gateway is defined as a device that converts media from one network or pro-
tocol to another. This type of trunk is used for a media gateway.
SIP gateways are used to transport public switched telephone network (PSTN) termi-
nated signaling across an Internet protocol (IP) network. The gateway sits between the
PSTN and the IP network (Figure 4-4). Unlike the SIP registrations trunk, the gate-
way model does not register—It just sends the traffic to the destination. In this model,
the system uses the caller-ID of the system to indicate the extension that initiated the
outgoing call (if that extension did not block the caller-ID). This model is typically used
with PSTN gateway hardware located on customer premises, but it can also be used to
link two snom ONE systems together as long as they are routable to each other, i.e.,
both are on public IP addresses or on the same private network.
SIP Gateway Trunk
Media
PSTN
Gateway
Figure 4-4. Example of SIP Gateway Trunk

Outbound Proxy

The outbound proxy trunk can be used to communicate with any other type of SIP
proxy or IP telephone system or to join two IP telephone system deployments together.
The outbound proxy trunk is a direct connection to the network and is similar to the
gateway model. The difference is in the way anonymous calls are made and in how the