14.6. 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 administrator 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 servers 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 compared to supporting an in-house fax server

• Most fire and burglary systems have a modem that requires a POTS or Centrex line. For this reason, you're pretty much stuck supporting a legacy trunk until more security systems support IP networking for central office monitoring

• IP-enabled video surveillance will eventually replace many analog camera systems. If you're thinking about moving to IP-based surveillance (or heavy use of videoconferencing), consider the impact of digital video on your converged network as you plan your transition to VoIP.

• Asterisk voice mail can perform email notification and forward sound attachments of the recorded messages to email recipients. Asterisk also supports web-based voice mail retrieval

• It's very easy to create custom IVR greetings for Asterisk call flows using a basic sound recorder and the Unix-standard SoX sound conversion application

• Alternatively, you could use the Asterisk Monitor() command to transform your phone into a voice recorder for IVR greetings

• soxmix is used to merge two sounds together, such as background music and a foreground voice greeting

• Emergency dispatch/911 services are not handled by VoIP protocols. You must build an adequate solution to handle emergency calls

• POTS lines and PRI channels have built-in automatic location ID (ALI) signals that can alert the public safety dispatcher to a caller's location, but VoIP trunks usually don't

• There are a number of open source administrative user-interface tools for Asterisk, including Asterisk Management Portal (AMP).