LANCOM 1722 VoIP – LANCOM 1723 VoIP – LANCOM 1724 VoIP – LANCOM 1823 VoIP
Chapter 1: Introduction
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VoIP for companies through SIP trunking
One of the biggest hurdles for companies that fully migrate to VoIP is to main-
tain 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 subscrib-
ers 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
LANCOM VoIP Routers over a single connection to a SIP provider, assuming
that the provider also supports Direct Dialing In (DDI) and can provide multi-
ple connections simultaneously. Generally speaking, SIP providers that offer
SIP trunking can acquire the existing telephone numbers from the former tel-
ecomms provider.
Connecting local exchange lines with a remote SIP gateway
Companies with nation-wide and internationally distributed sites are often
interconnected with VPN already. A LANCOM VoIP Router can be used not
only to connect the SIP, ISDN or analog telephones at a branch office to the
SIP-PBX at headquarters; it can also integrate the branch office's local tele-
phone 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 LANCOM
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 LANCOM 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 automat-
ically selects the appropriate connection to be used for forwarding the
call.
