Switching to VoIP

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Legacy Trunks

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Legacy Trunks

Legacy trunks are links that connect private voice switches using a traditional tech-

nology like FXO/FXS or T1. There may be many reasons why you use legacy trunks,

even if your heart’s desire is to move totally to VoIP:

• Legacy trunks are the only way to integrate legacy PBXs with VoIP systems.

• Existing legacy trunks, especially point-to-point T1s, may be subject to service

contracts that require you to maintain them for a while—sometimes as long as

seven years from the date of inception.

• Legacy trunks are known for quality. Since they derive from the circuit-switched

PSTN, legacy trunks have intrinsic bandwidth guarantees. If you can’t justify (or

convince other decision-makers on) the merits of packet-switched QoS across

your private network, then legacy trunks provide a solid connection between

voice switches.

Private Analog Lines

If two PBXs are in the same building or on the same campus, they can be connected

by analog copper and FXO/FXS interfacing. This technique is effectively the same as

that in Project 12.2 that linked two softPBXs using a POTS line. The difference in

this case is that you aren’t using the PSTN; you’re just using a standard telephone

cable with RJ11 connectors on both ends. One end connects to an FXO/FXS port on

each PBX. ...