On 10/20/2010, Charles Grasso wrote:
We are rsing the “NORMA Oficial Mexicana NOM-151-SCT1-1999” for use with
the Mexican phone system. I am looking for any other sources either with
COFETEL or other organizations/facilities that have any input/understanding of
the expectations/specifics of phone and modem interfacing with the Mexican
PSTN.
For instance, with the Modem Spec for the US, we tie as much of the
requirements to FCC Part 68/TIA 968 but rely on a long list of TIA specs for
anything not directly called out in TIA 968, for everything from Caller ID to
Stutter Dial Tone to Ringing methods. Does anyone know of any Mexican
standards that outline other modem functional specifications?
Hi Charles:
Mexico's NOM-151 is much more comprehensive than FCC Part 68, so there are
fewer parameters left unspecified than in FCC Part 68. As a colleague of mine
used to say, "A block of wood will pass FCC Part 68." This is actually true
because the requirements in Part 68 are harms-based. So, a product that meets
FCC Part 68 provides little confidence that the user will be satisfied with
the actual performance of the product.
NOM-151 goes much further than Part 68, and includes several performance
specifications. In addition to the Part-68-style specifications on impedance
and signal power, NOM-151 specifies the following types of parameters that are
not covered by Part 68:
* Speech levels for handset telephony
* DTMF dialing
* Ringer response and ringer loudness
* Radiated RF emissions
* Susceptibility to radiated and conducted RF
I think the only important function that is not covered by Nom-151 is caller
ID. I *think* that most of Mexico's central offices use the Telcordia caller
ID signalling method that is used in the USA, but I am not certain. I can
look into this if you like. Regarding the extra requirements called out in
NOM-151, most are fairly straightforward and can typically be passed with
minor tweaking of a typical USA design. The two tests that a typical USA
design will fail are:
1) Providing a very specific impedance to incoming ring signals
2) Passing the very rigorous tests for immunity to radiated and conducted RF
I would recommend that you perform the above tests at a local lab here in the
USA to confirm that you pass the NOM-151 tests before you submit for formal
testing in Mexico. That step can save you a lot of time, money, and
frustration.
Joe Randolph
Telecom Design Consultant
Randolph Telecom, Inc.
781-721-2848 (USA)
j...@randolph-telecom.com
http://www.randolph-telecom.com <http://www.randolph-telecom.com/>
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