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- TELECOM Digest Sun, 6 Feb 94 06:29:00 CST Volume 14 : Issue 63
-
- Inside This Issue: Editor: Patrick A. Townson
-
- Time Domain Reflectometers (Mark Earle)
- More California / Caller ID Questions (Ethan C. Tuttle)
- Can I Request LTN For ANI on All Trunks? (Barton F. Bruce)
- Information on Northridge, CA Switch After Earthquake? (Jodi Weber)
- Trick to Get Free NYNEX Screening (Barton F. Bruce)
- Telecommunications Over Cable Lines (Paul Jonathan E. Go)
- NTI Recommendations With Care! (Steve Bauer)
- A Cheap Long Distance Service (Allen Walker)
- "Miniplex" == Digital Local Loop? (Ray Berry)
- For Sale: PBX, Dual Channel Bank, DSX Panel (Paula Toledo)
- Request For Cellular Phone Standards (R. Chandrasekar)
- Data-Communication on Voice Lines in Bell Atlantic Territory (Ed Lally)
- More Information on the Economics of Dial-Back Services (Wolf Paul)
- CompuServe's New Rates Effective February 6, 1994 (Ray Normandeau)
- Extend-A-Phone (Ray Normandeau)
- Looking For Reviews of Routers (Rob Ryan)
- Help Wanted With NET2 Test Spec for X25 (Dave McConnell)
- Re: Clock Slip and { Once More (Lars Poulsen)
- Re: Clock Slip and { Once More (Bill Mayhew)
-
- TELECOM Digest is an electronic journal devoted mostly but not
- exclusively to telecommunications topics. It is circulated anywhere
- there is email, in addition to various telecom forums on a variety of
- public service systems and networks including Compuserve and GEnie.
- Subscriptions are available at no charge to qualified organizations
- and individual readers. Write and tell us how you qualify:
-
- * telecom-request@eecs.nwu.edu *
-
- The Digest is compilation-copyrighted by Patrick Townson Associates of
- Skokie, Illinois USA. We provide telecom consultation services and
- long distance resale services including calling cards and 800 numbers.
- To reach us: Post Office Box 1570, Chicago, IL 60690 or by phone
- at 708-329-0571 and fax at 708-329-0572. Email: ptownson@townson.com.
-
- ** Article submission address only: telecom@eecs.nwu.edu **
-
- Our archives are located at lcs.mit.edu and are available by using
- anonymous ftp. The archives can also be accessed using our email
- information service. For a copy of a helpful file explaining how to
- use the information service, just ask.
-
- TELECOM Digest is gatewayed to Usenet where it appears as the moderated
- newsgroup comp.dcom.telecom. It has no connection with the unmoderated
- Usenet newsgroup comp.dcom.telecom.tech whose mailing list "Telecom-Tech
- Digest" shares archives resources at lcs.mit.edu for the convenience
- of users. Please *DO NOT* cross post articles between the groups. All
- opinions expressed herein are deemed to be those of the author. Any
- organizations listed are for identification purposes only and messages
- should not be considered any official expression by the organization.
- ----------------------------------------------------------------------
-
- Date: Sat, 5 Feb 94 09:11:40 CST
- From: mearle@cbi.tamucc.edu (Mark Earle)
- Subject: Time Domain Reflectometers
-
-
- Last time I needed one of these, we called a company in Los Angeles,
- LeaseMetric. They supply specialized test gear short term; will ship
- second day or overnight, etc. Generally, you need a corporate P.O. or
- a credit card with a pretty high limit/available credit line.
-
- We used a TDR to verify cables pulled by subcontractors were run with
- no splices.
-
- The TDR we used had an o-scope, and a small calibrated dial, and some
- "range" buttons. You clip the tdr on the cable under test, and you get
- a flat line on the scope. Turn the range knob, until a "bump" appears.
- Read the digits on the range knob/range buttons; it is accurate to
- about three inches.
-
- Newer versions of the TDR of course do this automatically, and can
- even use a laptop as a terminal, storing stuff in a flat file, and
- allowing automated test routines to be written using the terminal
- program macro language (I've seen this done with Procomm Plus in
- particular).
-
- For more general information on TDR's, you might contact Techtronix,
- Hitachi, or other "major" vendors of test gear.
-
- Other uses of TDR's: On radio towers, to verify location of splices in
- transmission line; to find bullet holes in feedlines. In underground
- wires or cables, to find where they "turn" without digging up the
- whole landscape, etc. Quite a handy device.
-
-
- mwearle@mcimail.com
-
- ------------------------------
-
- From: ethan@medisg.Stanford.EDU (Ethan C. Tuttle)
- Subject: More California / Caller ID Questions
- Date: Sat, 05 Feb 1994 10:19:06 -0800
- Organization: Stanford University
-
-
- I have a technical/political question about CallerID in California:
-
- Say someone calls me long distance from an LEC that supports Caller
- ID. My understanding is that the long distance carrier would pass the
- Caller ID info to my LEC, which would then forward those digits to my
- CallerID equipment. EXCEPT, perhaps, in California. Does the Caller
- ID legislation in CA protect the privacy of those outside of the
- state? As a Californian, do I get that Caller ID info from
- out-of-state callers?
-
- More important, does (or will) PacBell actually forward the Caller
- ID info? I don't yet have a Caller ID box to test. I tried to ask
- PacBell, but all they seem to know about Caller ID is 'uh, no.'
-
- I am primarily interested in Caller ID as a cheap transport mechanism
- for ANI.
-
-
- Ethan Tuttle
-
- ------------------------------
-
- From: Barton.Bruce@camb.com (Barton F. Bruce)
- Subject: Can I Request LTN For ANI on All Trunks?
- Date: 5 Feb 94 17:04:18 -0500
- Organization: Cambridge Computer Associates, Inc.
-
-
- The ANI number that the LEC presents to the FG-B trunk when you make a
- call need not be the actual physical line you are on (WTN), but may
- often be the Listed (LTN) number or possibly the Billing (BTN) number
- if they happen to differ for historical reasons.
-
- This seems to happen randomly, but sure would be nice to be able to
- ORDER in some standardised way.
-
- Now that many 800 mail order companies make effective use of
- recognising your number, it would be nice if all company two way G/S
- trunks into the PBX had *JUST* the LTN of xxx.x000 or whatever glamor
- number you have.
-
- We have MANY totally scattered numbers in DIFFERENT exchanges in the
- same hunt group. Folks at the far end may even have a "REDIAL-THE-LAST-
- CALLER" button on their 800 based support phones.
-
- I am having a devil of a time trying to convince telco to give me the
- ANI I want (LTN) on trunks I am adding. OTOH, I **KNOW** some folks
- out there have gotten telco to do this.
-
- Is there any magic incantation or better USOC code for ordering this?
-
- ------------------------------
-
- Date: Sat, 5 Feb 94 16:00:11 EST
- From: jodiweber@attmail.att.com
- Subject: Info on Northridge, CA Switch after Earthquake?
- Organization: AT&T
-
-
- I hope I haven't missed this already during the past few weeks, but
- I'm interested in any information regarding how badly the Northridge,
- CA switch was damaged during the earthquake a few weeks ago, where
- service was out, why and for how long.
-
- Apparently, after the quake there was no dial tone for a period of
- time, then users had to wait but were able to get dial tone. I'd
- appreciate any details on the situation.
-
- By the way, an addendum on the dial tone availability after the quake:
- While land lines were dead for some period of time, cellular service
- was uninterrupted (at least for one user in Northridge at the time).
-
-
- Jodi Weber
- jodiweber@attmail.com or jweber@cbnewsg.cb.att.com
-
- ------------------------------
-
- From: Barton.Bruce@camb.com (Barton F. Bruce)
- Subject: Trick to Get Free NYNEX Screening
- Date: 5 Feb 94 17:39:54 -0500
- Organization: Cambridge Computer Associates, Inc.
-
-
- A most interesting bill stuffer from NYNEX just now details a back
- door way to get FREE screening to eliminate collect and third party
- billing abuse to your number rather than paying their usual 97 cents
- per month.
-
- Seems you can now LEGALLY request that they NOT give your name and
- address to other carriers if you so request.
-
- Of course they say that if you have their LEC calling card and place
- that restriction they will have to CANCEL your card. Seems they can't
- just restrict your use to IXCs that just bill via the LEC's billing
- service, and so might have to divulge the billing information were you
- to use the card with the 'wrong' carrier.
-
- So *IF* I request them to NOT divulge my name , I get my card
- cancelled, **AND** I get F R E E collect and third party screening
- tossed on the line(s) FREE!
-
- So if you want that service, or are paying for it now, and don't have
- KIDS that ever might need to call collect in some emergency, you can
- now arrange for free screening by requesting the right set of options.
-
- In my case my kids have their ROA cards that have no CC charges and
- are preferred, but they ALSO know the PIN on the all too obvious LEC
- card. If there were some accident or whatever, I really WANT them to
- be able to use the easy LEC card number or be able to call collect.
-
- But I am sure some other folks would like this new free NYNEX service :-)
-
-
- [TELECOM Digest Editor's Note: Actually no, telco cannot refuse to
- give your name and address to other carriers *for billing purposes
- only*, even if you have a non-published number. So go ahead and cancel
- your calling card if that is what you wish, but bear in mind that if
- someone calls you via a phone subscribed to a carrier who *does not*
- check the database used jointly by AT&T/MCI/Sprint and the local Bell
- companies, and you accept collect charges, then you *will* get billed
- for the call anyway, and the AOS/COCOT firm which originated the call
- will get your name, address and phone number. 'Billed Number
- Screening' as it is called (where collect and third-party calls are
- blocked right on the spot at the time/place of origin) ONLY works when
- the database is consulted. Some of the larger carriers (other than the
- Big Three who all cooperate on this) maintain their own database also.
- For example, Integratel does their own thing and does not consult the
- database used by AT&T.
-
- So regardless of what you advise your local telco (acting as billing
- and collection agent for the Big Three), unless you call Integratel
- and tell them the same thing (and Oncor to name another example) then
- the payphones of those companies will still be passing along collect
- calls (at outrageous rates I might add!) unchallenged, and your local
- telco will bill for them because under the law they have to. Integratel
- will add you to their database on behalf of their clients at your request
- with no qualms. Its no skin off their nose since all they do is bill
- for a bunch of small outfits. PAT]
-
- ------------------------------
-
- From: pj@cco.caltech.edu (Paul Jonathan E. Go)
- Subject: Telecommunications Over Cable Lines
- Date: Sat, 5 Feb 1994 17:29:45 PST
-
-
- In the Philippines, we have a severe shortage of telephone lines. If
- one does not bribe someone at the phone company, the wait for a new
- phone line is measured in years or decades. However, the cable systems
- do not seem to have a backlog.
-
- (1) How are cable networks usually set up?
-
- (a) Are they in a "bus" or "star" topology?
-
- (b) How are signals transmitted? Are they FDMA?
-
- (2) What kind of equipment is needed to turn the cable network into
- a telecommunications network?
-
- Could you point out a reference that might answer these questions?
-
- Thanks in advance.
-
-
- Paul Jonathan E. Go Caltech MSC 1028 Pasadena CA 91126
-
- ------------------------------
-
- From: STEVE BAUER <fnbw1100@ink.org>
- Subject: NTI Recommendations With Care!
- Date: Sat, 5 Feb 94 19:53:35 CST
-
-
- Jeff,
-
- I am running the NOrthern Telecom Meridian Mail (GP) Voice Mail
- system. I have been pleased with the equipment, but can't say that
- NTI is an easy company to work with. Forget technical support unless
- you have an emergency. It's just not available.
-
- I could write an entire TELECOM Digest on the troubles I have had
- trying to get someone to even bid on a maintenance contract and on
- parts to upgrade the system.
-
- In a nutshell, the equipment is nice, but the NTI is just too big and
- one division does not talk to another.
-
- I will be happy to discuss things in more detail by phone if you would
- like.
-
-
- Steve Telecommunication manager
- INTRUST Financial Corporation (316) 383-1144
-
- ------------------------------
-
- From: Allen Walker <allen0@delphi.com>
- Subject: A Cheap Long Distance Service
- Date: Sat, 5 Feb 94 23:13:54 -0500
- Organization: Delphi (info@delphi.com email, 800-695-4005 voice)
-
-
- If anyone is interested, I have found a telco long distance service
- that only charges $2.60/hr. Those calls can be placed at any time of
- day to anywhere (even your own state) at that rate. There are some
- other restrictions. If anyone wants info, send email to Allen0@delphi.com.
-
-
- [TELECOM Digest Editor's Note: There are so many of these things (notes
- about 'cheap long distance') showing up here in the mail each day. It
- has gotten almost as bad as 'Make Money Fast'. That one is showing up
- fresh on various Usenet newsgroups at the rate of about once every two
- weeks now (as the net increases in size so will the number of Make Money
- Fast postings; in snail mail I get two or three such chain letters *each
- week* in my PO Box), and the 'cheap long distance' resellers are also
- all over the place now, and bound to increase in numbers. So, Allen0,
- tell us about 'the one you found which charges $2.60 per hour'. How they
- manage to do that -- long distance calls day or night, inter/intrastate
- at 4.33 cents per minute -- without some deceptive nonsense having to do
- with multi-level-marketing or some other gimmick we've read about here
- several times in the past -- should make great reading. Tell us about it
- here so that you are not bothered with a lot of email, that is unless
- you are selling 'what you found' and want the email. PAT]
-
- ------------------------------
-
- From: ray@hebron.connected.com (Ray Berry)
- Subject: "Miniplex" == digital local loop?
- Date: Sat, 5 Feb 1994 13:31:36 -0800
- Organization: Ascendant Systems
-
-
- US West recently installed two numbers in my residence on a single
- copper pair. They did this by installing a Raychem "Miniplex 4-in-3
- RT", which supposedly muxes two lines onto a single pair by converting
- both to a digital data stream, which is deciphered at the CO by a
- mating card.
-
- When the installer explained this to me, I became a bit wary about
- fax and data signals making it through, but both seem to work fine (at
- least for 1 data + 1 simultaneous voice call; I haven't tested it with
- two simultaneous data transmissions).
-
- Being a techie type I'd like to know more about this device but
- don't know where to ask. Can someone here expound further?
-
-
- ray berry kb7ht rjberry@eskimo.com ray@connected.com 73407.3152@compuserve.com
-
- ------------------------------
-
- From: toledo@unixg.ubc.ca (Paula Toledo)
- Subject: For Sale: PBX, Dual Channel Bank, DSX Panel
- Date: 6 Feb 94 00:17:54 GMT
- Organization: The University of British Columbia
-
-
- 3 MSU Redcom
- Configured with 28 extensions
- 8 Ground start circuits
- 20 DID circuits
-
- Westcom dual channel bank
- 20 DID cards
- 8 Ground start cards
-
- 25 circuit DSX panel
-
- For more information e-mail Paula at Toledo@unixg.ubc.ca
-
- ------------------------------
-
- From: News account <news@shakti.ncst.ernet.in>
- Subject: Request for Cellular Phone Standards
- Organization: National Centre for Software Technology, Bombay, India.
- Date: Sun, 6 Feb 1994 07:25:38 GMT
-
-
- Greetings!
-
- A colleague wants to know where standards for Cellular Phones may be
- obtained from. He is interested in some standard called US94 or US95,
- in particular. Are these available online? If so, where? If not, whom
- should one contact to get these standards?
-
- Any info on this would be much appreciated.
-
- May I request you to send your responses by email to:
-
- mickey@saathi.ncst.ernet.in
-
-
- Thank you,
-
- R Chandrasekar Email: mickey@ncst.ernet.in
- National Centre for Software Technology Fax : +91 (22) 621 0139
- Gulmohar Cross Road No. 9 Phone: +91 (22) 620 1606
- Juhu, Bombay 400 049, INDIA Telex: +81 (11) 78260 NCST IN
-
- ------------------------------
-
- Subject: Data-Communication on Voice Lines in Bell Atlantic Territory
- From: el3@cellar.org
- Date: Sun, 06 Feb 94 01:28:46 EST
- Organization: The Cellar electronic community and public access system
-
-
- DAVIDSON <DAVIDSON@am.medcolpa.edu> writes:
-
- > I don't question the data provided here, but I suggest the "plug" for
- > a conditioned line may be overstated. I have found now at two
- > locations that a trouble call to 611 has resulted in a visit from a
- > repairman who in both instances swapped pairs until he found me a
- > quieter one. In one case, this was an internal job at my business
- > location and required tracing lines through 4-5 junction boxes in a
- > 70+ year old three story building. The repairman came back twice. In
- > the other case, it was at my temporary residence, the repairman took
- > 10-15 minutes to find a quieter pair and even set-up a new demarc for
- > it. I paid nothing in either case to assure reliable 14.4Kbps connections.
-
- I don't know how reliable this is, but both our office phone person
- and my modem manufacturer (home use) claim that there's no physical
- difference between POTS and data service pairs. They claim that the
- only difference is in price (with many local carriers charging a
- premium for the data service).
-
-
- Ed Lally el3@cellar.org
-
- ------------------------------
-
- From: cc_paul@aaf.alcatel.at (Wolf Paul)
- Subject: More Information on the Economics of Dial-Back Services
- Reply-To: Wolf.Paul@aaf.alcatel.at
- Organization: Alcatel Austria Research Center, Vienna, Austria
- Date: Sun, 6 Feb 1994 04:00:16 GMT
-
-
- After the recent repost here in the Digest of information on
- Communications Systems International's Dial-Back service I wrote to
- Mr. Beatty and eventually received a DOS program from him which
- permits one to select any country of origin and any target country,
- and find the rate charged by CSI for a call during any one of three
- time periods (11p-8a, 8a-5p, 5p-11p US time, probably Mountain, since
- CSI is located in Colorado).
-
- Of course, the most interesting relation to me was Austria-US, and the
- prices quoted for that are:
-
- First Minute 1.50 / 1.99 / 1.59
- Add'l Minute 1.14 / 1.57 / 1.21
-
- Then I looked into the current phone book to find out what our local
- phone company (the Austrian PTT) charges for a call to the U.S.:
-
- AS 18 / minute == $ 1.50
-
- Thus for much of the time, the regular long distance charge is as
- cheap or even cheaper than CSI's rate, especially during those hours
- when I am likely to reach anyone in the U.S.
-
- Add to that (a) the monthly minimum charge and (b) the inconvenience
- of only being able to call from the number where the dial-back box is
- going to call you back at, and I begin to wonder if this is such a
- good deal at all.
-
- Of course you can forget about using the service to call European,
- Middle Eastern or North African countries as well; there are slightly
- more substantial savings to be realized when calling countries in
- Latin America or the Far East.
-
- But since my need to call these places is rather limited, I guess I
- will currently pass on Mr. Beatty's service.
-
-
- Wolf N. Paul, Computer Center wnp@aaf.alcatel.at
- Alcatel Austria Research Center +43-1-391621-122 (w)
- Ruthnergasse 1-7 +43-1-391452 (fax)
- A-1210 Vienna-Austria/Europe +43-1-2206481 (h)
-
- ------------------------------
-
- Subject: CompuServe's New Rates Effective February 6, 1994
- From: ray.normandeau@factory.com (Ray Normandeau)
- Date: 6 Feb 94 00:09:00 GMT
- Organization: Invention Factory's BBS - New York City, NY - 212-274-8298v.32bis
- Reply-To: ray.normandeau@factory.com (Ray Normandeau)
-
-
- I was wondering if you would save by switching to CompuServe's
- $8.95/month membership rather than the $2.50/month membership?
-
- If you use 2400 bps the break-even point is at 50 minutes as can be seen from
- the spread sheet results below.
-
- Hourly Meter Monthly
- Minutes Hours Rate Total Rate Total
-
- 50 .83 $12.50 10.42 2.50 $12.92
- 50 .83 $4.80 4.00 8.95 $12.95
-
-
- Ray Normandeau
- Normandeau Newswire (J 5) at the Invention Factory BBS, 212-274-8110.
-
-
- [TELECOM Digest Editor's Note: Could you give us more details about
- how the new rate structure works? What are the prices now? PAT]
-
- ------------------------------
-
- Subject: Extend-A-Phone
- From: ray.normandeau@factory.com (Ray Normandeau)
- Date: 6 Feb 94 01:49:00 GMT
- Organization: Invention Factory's BBS - New York City, NY - 212-274-8298v.32bis
- Reply-To: ray.normandeau@factory.com (Ray Normandeau)
-
-
- I have an Extend-A-Phone manufactured in 1981. It is a Model R900
- Handheld = c. 49.89 Mhz Base = c. 1.7 Mhz No dial pad.
-
- I was always happy with this phone. I only used it when visiting other
- people's apartments. Never needed to dial. The fact that the base at
- 1.7 Mhz is unlikely to be monitored by anyone is fine with me.
-
- Anyone else have one?
-
- Within the last year or so it stopped functioning.
-
- When I checked battery with a multi-meter voltage seemed to be OK.
-
- Anyone else encounter such a problem and corrected it?
-
- If so, how?
-
-
- Thanks,
-
- Ray Normandeau
- Normandeau Newswire (J 5) at the Invention Factory BBS, 212-274-8110
-
- ------------------------------
-
- From: rryan@panix.com (Rob Ryan)
- Subject: Looking For Reviews of Routers (Harvard Labs Review)
- Date: 5 Feb 1994 17:51:55 -0500
- Organization: System Constructs, Inc
-
-
- I'm looking for the text of a review of routers by Harvard Labs. Does
- anyone out there know anything about it? Can anyone point me in the
- right direction? If not, then any similar unbiased review of routers.
-
-
- Thanks.
-
- ------------------------------
-
- From: Dave@daisy.ee.und.ac.za,
- Subject: Help With NET2 Test Spec For X25
- Date: 6 Feb 1994 08:27:02 GMT
- Organization: Consultancy in Advanced Technology
-
-
- Hi,
-
- I need to do some qualification testing of an X25 implementation. Our
- local telecom company informs me that the NET2 test suite is what is
- required to be met but cannot supply me with a test specification
- (believe it or not!). They apparently have a machine programmed with
- the test suite but don't have the spec itself. Does anybody know where
- I could get the Net2 test specification for X25? An ftp sight would be
- the best but any info will help.
-
-
- Thanks,
-
- Dave McConnell (cat@daisy.ee.und.ac.za)
-
-
- [TELECOM Digest Editor's Note: We have some readers of this Digest at
- the telkom.za site. Perhaps someone will respond and help you. PAT]
-
- ------------------------------
-
- From: lars@Eskimo.CPH.CMC.COM (Lars Poulsen)
- Subject: Re: Clock Slip and { Once More
- Organization: CMC Network Products, Copenhagen DENMARK
- Date: Sun, 6 Feb 94 00:00:30 GMT
-
-
- In article <telecom14.61.1@eecs.nwu.edu> mikelong@netcom.com (Mike
- Long) writes:
-
- > About two years ago I first ran into the clock slip problem and seeing
- > {{{{ on my screen. The problem finally cleared up after ...
- > Now I see ^?{ combination rather than {{{{ plus a few interspersed
- > random characters.
-
- > Now my question is this: what is it about clock slip that causes a {
- > character or 01111011 to appear on my screen? Now it is possible that
- > I saw ^?{ before but I only remember the {{{.
-
- > I know what to do about it, I'd just like to understand what is going
- > on. I was told before that the clock at the central office could be
- > slipping or was left in the wrong mode after a maintenance call.
- > Given that, how does the { get to my screen and why { and not some
- > other character?
-
- When the asynchronous link is idle, it is sending "mark" bits,
- 11111111111111111111111111111 .... which the modem encodes into some
- other pattern, which gets turned into tones, which get digitized at
- the CO and sent over a trunk ....
-
- The clock slip inserts (or drops) a bit in this other, digitized,
- bit stream. This causes a temporary difference in the pattern, which
- causes a couple of bit errors on the receiving end.
- Exactly what comes out depends on:
-
- - which modulation is used (2400, 9600, 14400 ...);
- - whether it's a bit insert or a bit delete, and whether the
- channel bank dropped a whole frame;
- But for a given trunk, these factors tends to be the same.
-
- It is common to see these with 2400 bps. For the last year, I have
- been using only V.32bis, and the error correction takes care of the
- junk.
-
-
- Lars Poulsen Internet E-mail: lars@CMC.COM
- CMC Network Products Phone: (011-) +45-31 49 81 08
- Hvidovre Strandvej 72 B Telefax: +45-31 49 83 08
- DK-2650 Hvidovre, DENMARK Internets: designed and built while you wait
-
- ------------------------------
-
- From: wtm@uhura.neoucom.EDU (Bill Mayhew)
- Subject: Re: Clock Slip and { Once More
- Organization: Northeastern Ohio Universities College of Medicine
- Date: Sat, 05 Feb 1994 16:48:59 GMT
-
-
- Modems use a scrambler polynomial which has a 16 bit cylce. This
- cyclic stream of 1s and 0s has an even division between the two
- values. When a call is placed, the modems sychronize the scrambler
- value at both ends, The scrambler data is eclusive-or'ed with the data
- at both ends so that under ideal conditions, the input and output data
- are identical. The purpose of using the scrambler data is to ensure
- an equal distribution between 1 and 0 while the cirucit is in an idle
- marking condition while no data are transmitted. This allows the
- demodulator at the receiver to stay in track with the other end.
-
- The design of the scrambler circuit ensures that a single bit error in
- the transmission will hit two adjacent characters in the output stream
- due the way the shift-register is tapped and the fact it is a 16 bit
- cycle. The design is no accident, as this assists in spotting
- transmission errors -- though I sure wouldn't count on this as
- insurance of being able to sptot errors.
-
- For an idle line, the most common error in the direction of the
- originate modem is ~r at 1200 bps. At 2400 bps, the most common error
- you'll see is _w. If you are using different byte lengths other than
- (8N1), you may see something else.
-
- Sure is irriating to have a T1 span dropping frames between you and
- the place you want to go. I went around on such a problem with then
- Ohio Bell for several years. I'd imagine the upper eschelon of
- craftpeople could have been aware of the problem because all the T1
- common equpment racks I've seen (which is hardly exhaustive of all
- available) have some sort of error lamp or LED that lights up and
- stays on when a framing error is received. Ohio Bell eventually fixed
- the problem, but didn't respond quickly because the POTS lines I was
- using met applicable specifications of the regualting tariff. If I
- were buying a conditioned line, things would have been different.
- Since we need to support itineratnt users from variable locations,
- dedicated lines were not a parctical or inexpensive consideration.
- Until the problem was solved, we bought Telebit modems that did not
- find the noise bothersome to their PEP protocol.
-
- I have a feeling that all that was necessary was to flip a switch on a
- T1 rack somewhere from FREE RUN to LOOP TIMING, but getting somebody
- to understand what I wanted and also willing to take action proved
- difficult.
-
-
- Bill Mayhew NEOUCOM Computer Services Department
- Rootstown, OH 44272-9995 USA phone: 216-325-2511
- wtm@uhura.neoucom.edu amateur radio 146.58: N8WED
-
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- End of TELECOM Digest V14 #63
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