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1-8 Voice over IP
1.4.1.3 VoIP for companies through SIP trunking
One of the biggest hurdles for companies that fully migrate to VoIP is
to maintain the existing telephone numbers. Normal provider SIP
accounts come with a telephone number for the transition to the
landline telephone network, but generally these numbers are selected
from a pool of numbers available to the provider. However, for
companies with a large number of telephone subscribers and
numbers, it is of decisive importance that existing telephone and
extension numbers are maintained after migrating to VoIP.
With the SIP trunking function, entire ranges of telephone numbers
made up of external numbers and their associated extensions can be
mapped by Swyx VoIP Routers over a single connection to a SIP
provider, assuming that the provider also supports Direct Dialing In
(DDI) and can provide multiple connections simultaneously.
Generally speaking, SIP providers that offer SIP trunking can acquire
the existing telephone numbers from the former telecomms provider.
1.4.1.4 Connecting local exchange lines with a remote SIP gateway
Companies with nation-wide and internationally distributed sites are
often interconnected with VPN already. A Swyx VoIP Router can be
used not only to connect the SIP, ISDN and analog telephones at a
branch office to the SIP-PBX at headquarters; it can also integrate the
branch office's local telephone lines into corporate communications
with help of the "SIP Remote Gateway" function.
The SIP remote gateway is active for outgoing and incoming calls.
• A company headquarters in New York can, for example, use a
Swyx VoIP Router with SIP gateway located at the Los Angeles
branch office to telephone with customers and suppliers located
in Los Angeles at local rates ("local break-out").
• For improved availability to customers located abroad, the New
York headquarters can, for example, use a Swyx VoIP Router
with SIP remote gateway located at their sales office in Italy.
Customers can then reach support or service numbers via a
standard national telephone number. Calls over the local
exchange line are received and directed within the company
network to the responsible employee. Call routing can be used
which identifies the customer's calling number and
automatically selects the appropriate connection to be used for
forwarding the call.