When to Use the VoIP Feature

Use the VoIP feature whenever a call cannot be routed over the frame relay network using the Passport Access Network Link (PANL). You can use VoIP on existing IP routed networks.

The Passport 4400 VoIP feature is designed for operation in the following two ways:

• As a gateway behind a router.
• Connecting a frame relay network and an IP network together.

Here is a simple example of using VoIP to route voice calls across an existing IP network:

Where an IP network already exists to provide data communications and traffic, you can route voice calls to the various offices over the same network.

The next example shows a Passport network running over frame relay, with the addition of a Passport unit operating over an internal LAN:

A call can be placed using VoIP to any of the telephones. However, VoFR is the preferred mode for a call taking place between the two Passport units on the frame relay network. Also, if a call is selected for VoIP and traverses the frame relay network, the call still uses VoIP. The call is not converted to VoFR (PANL operation).

The next example shows the same network, but with the Passport unit on the far left side configured to accept and place calls only as VoFR (VoIP operation has not been configured in that unit):

The Passport unit on the far left cannot place calls to telephones on the far right Passport unit (which must use VoIP, because it is on an Ethernet LAN segment). Neither can the Passport unit on the far right place calls to telephones on the unit to the far left (that is configured to accept only VoFR calls).

Generally, the calling side decides whether to use VoIP or VoFR. The decision is based on the preferences in the calling Passport unit and on any constraints that are indicated by the called side. There are two types of constraints:

• The called side has no VoIP (VoIP operation has not been configured in that Passport unit). The Network Address Server (NAS) will have the VoIP address set to 0.0.0.0, to indicate that VoIP is not available. VoFR operation must be used to place a call to any of the voice channels of this Passport unit.
• The called side has no VoFR (the Passport unit is on an Ethernet segment and is not connected to a frame relay network). VoIP operation must be used. This is indicated in the NAS by having a false DNA configured. A false DNA is one where the first six digits are zeros (for example, 000000138674). VoIP operation must be used to place a call to any of the voice channels of this Passport unit.

The following example shows VoIP routing calls over the Internet. This is an application where VoFR (PANL) cannot be used.

VoIP supports all Passport 4400 voice services. This includes analog voice, T1, E1, ISDN BRI, fax, modem, AutoRingDown, Hoot-n-Holler, and Premium Voice.

If Voice over Frame Relay (VoFR) is available (PANL), this method of voice transmission is preferred. This is especially true for low speed network connections.