Users: Hybrid PBXs work

Cost savings, features outweigh wholesale TDM-to-IP upgrades.

While the industry pushes IP as the future of telephony services, network professionals who manage business phone networks say hybrid IP/legacy PBXs are helping introduce productivity gains and cost savings without forcing networks to undergo dreaded R&R - as in "rip and replace" - upgrades.

Most major PBX vendors have long offered IP options on their legacy gear. Early on, this let users tie together PBXs via IP over private WANs - converged voice/data T-1s and free inter-company long distance were among key drivers. This hybrid approach, mixing IP and legacy TDM technology, is now extending into the areas of employee productivity and new applications in some companies.

Hybrid IP/TDM voice switches are typically legacy PBXs with digital phones and ISDN interfaces that are IP-enabled - with cards that put the PBX on the LAN (similar to a server network interface card) or gateways that translate voice signals between IP and TDM.

To continue reading, register here and become an Insider. You'll get free access to premium content from CIO, Computerworld, CSO, InfoWorld, and Network World. See more Insider content or sign in.

While the industry pushes IP as the future of telephony services, network professionals who manage business phone networks say hybrid IP/legacy PBXs are helping introduce productivity gains and cost savings without forcing networks to undergo dreaded R&R - as in "rip and replace" - upgrades.

Most major PBX vendors have long offered IP options on their legacy gear. Early on, this let users tie together PBXs via IP over private WANs - converged voice/data T-1s and free inter-company long distance were among key drivers. This hybrid approach, mixing IP and legacy TDM technology, is now extending into the areas of employee productivity and new applications in some companies.

Hybrid IP/TDM voice switches are typically legacy PBXs with digital phones and ISDN interfaces that are IP-enabled - with cards that put the PBX on the LAN (similar to a server network interface card) or gateways that translate voice signals between IP and TDM.

The IP-enablement approach lets users keep TDM handsets on desktops, while giving them computer telephony features - such as click-to-dial from a PC and unified voice/e-mail. IP phones can connect to the PBX via gateways and installing software on the PBX that lets it recognize IP endpoints as digital extensions.

With true hybrid PBX gear, the phone switches can handle TDM-based or IP-based handsets, connecting to IP phones via a LAN interface and digital phones through a regular telecom rack. These devices see both kinds of handsets as equals on the network - limitations of each technology notwithstanding.

Third-quarter 2005 market estimates from Merrill Lynch show IP telephony systems growing at 31% from the same quarter a year ago, while TDM PBX sales dropped by 20%.

Avaya is one company following the hybrid telephony trend in the industry - moving towards IP while maintaining TDM presence. Merrill Lynch says Avaya's TDM PBX sales shrunk 3% from the second to the third quarter of 2005, and compared with the same quarter a year ago sales are down 20%. Meanwhile, its hybrid IP voice sales grew 14%.

But analysts say Avaya's TDM business brought in an average of $100 million to $150 million per quarter over the past two years. No vendor of telephony gear would sneeze at that revenue, however much its marketing material looks like an all-VoIP manifesto.

A hybrid Avaya PBX at Quaker Chemical, a chemical manufacturing company in Conshohocken, Pa., gives employees the ability to work from home and inexpensively have in-office extensions follow them home.

Some users install islands of pure-IP PBXs among a larger TDM infrastructure, usually in branch sites or small remote offices. Such proof-of-concept rollouts are common, but others find integrating IP into the larger PBX network is more effective.