V.34 FAX MODEM (VoIP)

14.12
V.34 gained popularity because it allowed dial-up modems to get higher speed Internet connectivity. The popular mode of operation is at 28,800 bps with the option of supporting up to 33,600 bps. This rate is three times faster than V.29 and twice as fast as the previous V.17 modems. V.34 [ITU-T-V.34 (1998)] supports 14 rates starting from 2400 to 33,600 bps in steps of 2400 bps [URL (Canata)]. Fax machines used to use the popular speeds of 9600 and 14,400 bps. Recently, fax machines were upgraded to 33,600 bps, which has increased fax transmission by two times compared with previous 14,400-bps machines. Up to 14,400 bps, the machines are called group-3 supported machines. V.34-supported machines are SG3. V.34 also makes use of TCM and QAM. In
general, V.34 is a more involved processing and memory-taking module compared with V.17. To upgrade an existing solution, it is required to account for this difference. For new design, catering to V.34 may be the requirement.
Some counterarguments on the use of V.34 fax over IP exist. In many countries of Asia (Japan and Korea) and Europe, broadband data connections are provided to the users through asymmetric digital subscriber line (ADSL2), very high-speed DSL (VDSL), VDSL2, and fiber. This broadband with proper implementation of quality of service (QoS) are making end- t o- end packets delivery with end – t o – end delays comparable with 50 ms and absolutely no packet drops. Thus, a justification can be made for using the fax pass-through mode. The front-ends and pass-through modes are made perfect. Hence, future higher speed fax may be just fax pass-through.
Some benefits of higher speed fax are given in [ITU-T-V.34 (1998)]. In VoIP, cost and duration of call may not be an issue. With the current improvements in various technologies, a user will be more comfortable in sending a fax quickly, which creates a better perception (time response) to the user with V.34 support. V.34-based fax solutions have created few additional requirements in the detection process.
• ANSam, /ANSam answering tones are generated in SG3 fax calls.
• Additional signaling messages are conveyed in V.21 as per V.8. Incorporation of V.8 became a requirement in SG3.
• On the module level, the G3 mode was using an echo canceller with the option of disabling it. In SG3, it has to be disabled.
• The pass-through mode has to disable echo cancellers for V.34.
• G3 modules of V.17/V.29 are not compatible with scaled rates of V34. To interoperate between G3 and SG3 fax machines, the SG3 machine cannot use V.34 in fax over IP. It may use V.17 or V.29 modes in fallback modes.