Alcatel 060170-10, User Manual, Page: 18 / 430

VoIP Telephone Calls
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VoIP Telephone Calls
H.323 VoIP telephone calls, which can carry either voice, facsimile, or modem transmissions
over IP networks, are switched to the packet-based network and connected to the calling
destination (an IP device) via a unique IP address and local/remote dialing plan (actually two
Alcatel VoIP Network Dialing Schemes rolled into one). The numerical IP address, also serv-
ing to identify calls intended for VoIP networks, is determined and translated from a destina-
tion telephone number in a phone directory database while it is being entered, and the call is
in progress. (It should be noted here that callers do not need to remember the IP addresses,
only the called party or destination phone number). See Chapter 3, “Network Dialing
Schemes,” for more information on the AVNDS.
H.323 VoIP telephone calls are transparent so callers don’t have to worry about any special
procedures, except being aware of a dialing plan that may require them to dial a prefix, such
as 7, before a call can be placed across the VoIP network. This would be similar to current
dialing plans requiring callers to dial 9 before an office call can be placed (9 is the prefix
most often used by PBXs to access the PSTN).
VoIP calls initiated from standard telephone handsets after a preset number of digits are
dialed, for example, can be immediately transmitted using IP data networks whereby digital
or analog signals, meant to set up connections for carrying information, are intercepted by
Alcatel’s H.323 VoIP gateways in the network. These gateways translate the phone numbers
into IP addresses, convert the information to digital packet form, and then deliver the calls
over the network and the PSTN as shown below.
A VoIP Call Scenario
Once a VoIP network is set up a typical VoIP call scenario might go something like this.
VoIP Call Scenario — Step 1: Call Setup
Step
1
PBX #2
VoIP H.323 Gateway
VoIP H.323 Gateway
VPN
PBX #1
Destination
IP Address
Source
IP Address
Local Telephone Number
Remote Telephone Number
Call setup begins
Dial Tone
Dial
Destination
Number