On 1/7/2008, Daniel Roman wrote:
India was one of the last few countries requiring loop current limiting. I know they were in the process of redoing all their standards, but in one of the newest standards I have from January 2007, IR-CTI-01-03 JAN 2007, loop current limiting is still listed as a requirement. Does anyone have any updated information on this requirement? Seems a shame to have to design this into the hardware only for one country, it takes up so much space! Hi Dan: I agree that it would be a shame to have to include current limiting for India, given that the EU, and even France, stopped requiring it several years ago. I think it is probably an artifact that it continues to appear in some standards for India. The requirement is traceable to certain older central office line cards (mostly Alcatel, I believe) that depended on current limiting in order to operate properly. The French national network was at one time configured this way, but it no longer is. Perhaps India has, or once had, some Alcatel CO equipment that used French-style line cards. I do not have a good answer for your question, but I do have the following comments: 1) India's standards-writing process tends to be product-specific rather than interface-specific. It appears to me that for each product standard that gets issued, a different group of engineers writes the standard using whatever requirements they choose. Sometimes they simply borrow requirements that appear in other country's specifications. There is very little consistency among products with similar analog PSTN interfaces, such as modems, fax machines, and telephones. 2) In the past, the only place I have seen the current limiting requirement for India was in specifications for telephones. The requirements for modems, fax machines, and PBXs did not require current limiting. This has always seemed odd to me, since the phone company's central office has no way of knowing what type of terminal equipment is connected to a given analog PSTN line. If the 60 mA current limiter is required to protect the central office line card, it should be required for all types of terminal equipment. 3) In the past, the telephone specifications that called out current limiting were always the generic requirement "GR" type for equipment to be purchased by network operators, while the more general "IR" specifications for simple approval-to-sell in India did not contain any requirement for current limiting. It is troubling if the current limiting requirement is now creeping into some IR requirements. I see on the TEC web site that the specification you reference is for "System Employing Computer Telephony Integration." Does this standard explicitly call for current limiting on an analog PSTN FXO interface, or does it do so indirectly by referencing another standard? In the past, India's default interface requirement for 2-wire analog PSTN terminals was S/INT-2W/02.MAY2001, which did not require current limiting. I do not see that listed now on the TEC web site, but I see a similar-sounding standard IR/PST-01/01.SEP2005, "Terminal for Connecting to PSTN." Unfortunately, I do not have a copy of that standard. If in fact it is a replacement for the earlier 2-wire standard, it would be very interesting to see whether current limiting is called out. I'm sorry that I can't provide a direct answer to your question, but it appears that India's specifications have evolved slightly since the last time I looked into this problem. My suggestion would be to push back a little bit on TEC before you agree to include current limiting, possibly by citing some of the inconsistencies I have noted above. You might also be able to re-characterize your product so that it does not fall under the scope of a standard that calls out current limiting. I remain interested in whatever you eventually find out about this anomaly. Joe Randolph Telecom Design Consultant Randolph Telecom, Inc. 781-721-2848 (USA) [email protected] http://www.randolph-telecom.com <http://www.randolph-telecom.com/> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] Mike Cantwell [email protected] For policy questions, send mail to: Jim Bacher: [email protected] David Heald: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
