Switching to VoIP

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Chapter 14: Traditional Apps on the Converged Network

Key Issues: Traditional Apps

on the Converged Network

• VoIP protocols and standards don’t always make turnkey provisions for “old

reliable” telephony applications like fax, modems, E911, voice mail, and admin-

istrator interface software.

• T.30 faxes and modems don’t work over non-real-time voice pathways such as

VoIP networks, unless a lossless codec is used and no jitter occurs.

• Lower modem baud rates are more likely to be successful if you inexplicably

decide to run modems over VoIP anyway.

• Two ITU standards define your options for implementing Fax over IP, or FoIP.

They are T.37 and T.38.

• T.37 is the store-and-forward, email-based Fax-over-IP solution.

• T.38 is the real-time, transport-inclusive FoIP solution.

• The SpanDSP module package for Asterisk gives you the ability to build fax serv-

ers that use Digium’s Zaptel TDM hardware.

• Hylafax is a freely available (and more cost-effective than Asterisk with

SpanDSP) package for building Linux-based fax servers. It uses cheap, abundant

fax/modem cards instead of Digium cards.

• For small to medium businesses, hosted fax services can be a money saver com-

pared to supporting an in-house fax server.

• Most fire and burglary systems have a modem that requires a POTS or