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Re: [hylafax-users] problems with Multitech Modem MT 2834ZDXb



On 2003.10.07 12:54 Steve Tuckner wrote:

People might want to chime in on whether they have had better
experiences receiving (as that seems to be the major issue) with the
ConexantFirmware versus AgereFirmware modems in class 1. The
controller
code and DSP code for these are obviously different. But in class 1
the
only significant difference is the DSP code. I don't have clear data
on
which is "better". It probably will depend upon the line conditions
that
the particular modem is used on, as different DSP implementations
handle
different line impairments better or worse.

Generally speaking I've seen less problems in HylaFAX with Rockwell/Conexant-based modems in Class 1 than with Lucent/Agere-based modems in Class 1. For example, I see +FCERROR which later becomes fatal on Lucent/Agere-based modems much more than I do on Rockwell/Conexant-based modems. It is a rather small difference, however, and of course none of these problems are easily reproducible.


However, I suspect that HylaFAX could do a much better job of handling the Lucent/Agere behavior, since HylaFAX Class 1 support seems to have been developed with the Rockwell/Conexant chipsets. For example, according to T.31, following the AT+FTM=x from the DTE the DCE must respond CONNECT immediately, and then the DCE proceeds in bringing up the high-speed carrier. (Frankly, I think its a stupid specification, but that's just how it is.) The Agere chipsets follow the spec here whereas the Conexant chipsets don't. (The Conexants respond CONNECT several hundred milliseconds later, seemingly after the carrier is raised.) Thus we have the Class1TMConnectDelay (currently in HylaFAX CVS) config option which is designed to help HylaFAX "cope" with the spec-following Agere. So Agere may not so much be to blame as the fact that HylaFAX Class 1 was coded with Rockwell behavior in mind.

Lee.

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