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Legacy devices and analog telephone lines still useful, despite VoIP

Supporting legacy devices and analog telephone lines will be part of your due diligence well into the foreseeable future despite the high rate of VoIP and IP telephony deployments. Find out which legacy interfaces you can expect to use in the future and the best practices for dealing with them.

You would think that legacy devices and interfaces would quickly fade away to judge by all the vendor and service provider hype around VoIP and IP telephony. Not so. The analog line and legacy endpoint are still alive and have reasons to continue existing.

Non-telephone legacy interfaces and analog telephone lines are always an issue because some of these lines are more permanent than the lines to telephones and rarely need to be moved or reassigned. These are the forgotten lines. People and their telephones move around, but the non-phone devices usually have a long and static connection.

When a VoIP/IPT RFI or RFP is written, most enterprises do not fully specify the legacy interfaces that require support. The connection to legacy interfaces is usually underestimated by the telecom staff and, through ignorance, is unknown to the IT staff.

Before you can eliminate the analog telephone lines and VoIP gateways, you must consider the many cases where analog lines will need to continue operating for many years.
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In many cases, the enterprise does not have a current inventory or description of the legacy interfaces. It's only after the VoIP/IPT implementation begins that the enterprise discovers all the legacy interfaces. IT and communications managers cannot force the retirement of all the analog lines and devices, and this also creates problems.

Before you can eliminate the analog telephone lines and VoIP gateways, you must consider the many cases where analog lines will need to continue operating for many years. Supporting the legacy interfaces is a VoIP gateway problem. You need to ensure that the gateway you are considering can support the legacy interfaces. Many gateways pose problems, and some will not support the less common interfaces.

The proponents of VoIP/IPT promote cost savings. If you cannot eliminate all the legacy devices and analog lines, then the anticipated cost reduction will be less. If the gateway does not support all the interfaces, the enterprise has to continue to use analog lines to the PSTN. This will reduce the ROI and increase the TCO.

The enterprise staff needs to inventory the legacy and analog interfaces. Here is a list of common interfaces that you can expect to continue using for the foreseeable future:

  • Analog fax machines that operate the T.30 standard
  • Dial-up PC modems, point-of-sale devices and credit-card readers

Some VoIP gateways limit the modem speed.

  • Alarm system connections
  • Telemetry systems

They usually have timeout and signaling problems through VoIP gateways.

  • TDD support for hearing impaired
  • Elevator and emergency phones
  • Secret lines for special conditions such as a whistle-blower connection that is not traceable to the source
  • Analog phones in otherwise unoccupied buildings.

I found a university that had 200 buildings with analog phones, but only 100 buildings were continuously occupied.

  • The janitor's closet
  • Phones in common areas that have little or no physical security
  • That guard shack that is thousands of feet from any building and can be economically accessed only by an old analog line
  • The phone line outside a building that is used to call the guards for off-hours access should be an analog line to ensure security.

Would you put an Ethernet/IP port there?

  • Emergency phones as a lifeline (to support communications when all else fails) to the PSTN use analog connections
  • Warehouse phones where it is expensive to install Ethernet lines just for a phone
  • Supervisory control and data acquisition connections that are designed for analog lines
  • Intercom lines
  • Announcement lines
  • Turret systems for traders
  • Access to mobile channels
  • Mobile channel interconnection
  • Server connections for healthcare, such as dictation, patient/bed/transport tracking and nurse call stations
  • Legacy key systems like the 1A2

The legacy interface and analog telephone lines in the enterprise, government or educational institution are more common than even the average telecom person realizes. Potential VoIP/IPT customers invariably keep finding more analog lines/interfaces in use that must stay as analog connections for the foreseeable future.

The best practices for dealing with legacy interfaces are:

  • An exhaustive inventory should be made of all devices connected to the PBX and carriers before issuing an RFP or entering into a contract for the PBX replacement and service provider connections.
  • Do not assume any of the analog devices/lines will automatically disappear when an IP PBX is implemented.
  • Interviewing the security department to see which devices are currently connected or intended to be connected to the PBX. In some jurisdictions, only analog/TDM lines are allowed for connection to emergency services like police and fire departments and ambulance corps.
  • The engineering, manufacturing and health groups should be polled to see what they assume will be connectable to the IP PBX that may still operate on analog lines.

An additional reason to continue using the analog lines is to avoid installing LAN cabling. One company, Phybridge, has the ability to extend Ethernet devices over analog lines with its special LAN switch. This allows the organization to recycle an existing asset (analog lines) and reduce the cabling cost. Consider using DSL modems in house to connect to lower-speed Ethernet devices such as IP hard phones over thousands of feet of analog cable.

When IT staff members are in charge of the VoIP/IPT migration, they rarely have any idea of the connections to non-phone devices. Many organizations have had to order analog lines to the PSTN to support some non-phone devices because the VoIP gateway does not support them. This means these legacy device connections are separate from the rest of the organization's control and management systems. These connections may also create security problems and limit emergency response scenarios.


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