Received: by bu-cs.BU.EDU (5.58/4.7) id AA27571; Fri, 13 Jan 89 00:07:08 EST Message-Id: <8901130507.AA27571@bu-cs.BU.EDU> Date: Fri, 13 Jan 89 00:00:51 EST From: The Moderator Reply-To: TELECOM@bu-cs.BU.EDU Subject: TELECOM Digest V9 #13 To: TELECOM@bu-cs.bu.edu TELECOM Digest Fri, 13 Jan 89 00:00:51 EST Volume 9 : Issue 13 Today's Topics: Dialing For Dollars Re: New way to donate money Race conditions in a PBX Glare (was Race Conditions in a PBX) Cellular Info Re: Finding Your Ringback Number Many thanks! [Moderator's Note: Address changes recommended by relay.cs.net were implemented today, as per message in yesterday's Digest. If you see anything flaky, please advise. P. Townson] ---------------------------------------------------------------------- From: Kenneth_R_Jongsma@cup.portal.com To: telecom-request@xx.lcs.mit.edu Subject: Dialing For Dollars Date: Thu, 12-Jan-89 08:54:15 PST Regarding the message about the local telco in Washington collecting $5 or $10 depending on what number you dialed... AT&T (and probably the others) has been getting geared up to offer a similar service nationwide. That is, certain 900 numbers will be billed at whatever rate the info provider wishes. You may get connected to a recording similar to current 900 service or you may get put through to a live person or computer system similar to current 800 service. Think of Compuserve with your telco doing the billing instead of Compuserve billing your credit card. ------------------------------ Date: Tue, 10 Jan 89 9:19:09 CST From: Will Martin -- AMXAL-RI To: telecom@bu-cs.bu.edu Subject: Re: New way to donate money Re the "moderator's note" on the subject of donating by making a phone call: This looks to have enormous potential for abuse. Someone who gets access to a company office's telephones or those of a university, say, could make hundreds of phone calls, donating thousands of dollars to their favorite cause, with no way to trace the false donations back to the real caller. Traditionally, the potential for abuse of illicit access to someone else's telephone was limited by the fact that they usually could only call other people and run up a long-distance bill, but, after the abuse was detected, such calls could be eventually charged to the called party, or the actual caller could be identified by looking at the pattern of calls or talking with some of the called parties (and threatening them with being charged for those calls, sometimes! :-). Now, with 976 numbers and other such automatically-charged services, the abuse potential went up, but was still limited by time and (probably) boredom -- after an abuser gets into an office and makes ten 976 calls, he's probably bored by it and will stop. He has no incentive to continue, unless all he wants is to attack the company, and even then it gets tiring. Now, with this new option, though, there is an incentive. He can both hurt the company and direct thousands of dollars to some cause he supports, be it "save the baby seals" or "right to life" or "planned parenthood" or The Committee To Re-Elect The President or whatever... Even though some mechanism will probably be implemented to allow "backing out" of such donations, especially if such a pattern of abuse is detected, it will still be a hassle, be after-the-fact, and not all illicit "donations" will be detected or reversed. This gives the person with a grudge an incentive to make many many many calls; he doesn't even have to wait to listen to any spiel, but can just repeatedly make calls. With an autodialer device, a determined hacker could tap into a line and run up a multi-thousand-dollar string of "donation" calls in just a few minutes, if we want to get technological about it... Maybe it still is a good idea -- as long as the only people who get donations are causes I approve of, that is... :-) Will Martin [Moderators Note: I think the answer to this is that most telcos allow blocking of 900/976 numbers, to prevent abuse of any kind, which would presumably include the abuse described by Mr. Martin. I suspect also that there would be some cancellation clause in the telco's contract with the charity, which gives the telco total recourse for uncollectibles. P. Townson] ------------------------------ Date: Wed, 11 Jan 89 13:44:31 EST From: map@gaak.LCS.MIT.EDU (Michael A. Patton) To: telecom@bu-cs.bu.edu Subject: Race conditions in a PBX From: hiraki@ecf.toronto.edu (Lester Hiraki) Date: Mon, 9 Jan 89 14:16:47 EST Does anyone know how to solve the following problem? Consider a simple PBX which works as follows: [... Describes race condition on bidirectional loop-start lines ...] Assuming loop-start lines, can this race condition be avoided? Note, not all business have ground-start lines. I understand ground-start lines eleminate this very problem? Can someone explain how ground- start lines work? I used to work for a company that made equipment for telephone connection. The answer to your question is that Loop-Start lines are not supposed to be used bi-directionally, except for cases where this does not matter (i.e. where the person answering the call and the person wanting to dial would often be the same person anyway). Full PBX equipment should not use Loop-Start bi-directionally. Frequently the people involved in an actual installation don't know this and so you get the problem you describe. We occasionally ran into the opposite problem where the phone company wanted to install Ground-Start lines because they assumed our equipment was a PBX when in fact it was terminate-only. In later models we provide small amounts of originate-like service and had to provide a Ground-Start interface to avoid exactly this problem. It is my impression that the conversion from Loop-Start to Ground-Start is fairly simple on most CO equipment (they managed to do about 10 lines in half an hour when we put in a PBX), but there are some low-end PBX vendors that can't provide Ground-Start trunking. ------------------------------ Date: Wed, 11 Jan 89 08:26:01 PST From: HECTOR MYERSTON Subject: Glare (was Race Conditions in a PBX) To: telecom@bu-cs.bu.edu Ref Hiraki@ecf-toronto's query. The condition you describe is known as glare and is as old as the hills. The way to avoid it is not to use ground-start for two-way trunks. The way to >minimize< is to have one end select trnks from the "top" of the trunk group, the other from the "bottom". You will still occasionally get glare but less often. Ground Start is the common signaling method for this type of trunk. Trunk seizure is initiated from either end by grounding one of the wires. Normally (a dangerous word to use here) the PBX grounds the Ring and the CO grounds the Tip to initiate calls. ------------------------------ To: mcsd!killer!comp-dcom-telecom From: tim@Athena.UUCP (Tim Dawson) Subject: Cellular Info Date: 11 Jan 89 21:53:43 GMT In article ghg@en.ecn.purdue.edu (George Goble) writes: > >I just got off the phone with John Covert. He had information which >said that ATT (when they went to #4 ESS toll switches) was the cause >of the roamer ports going off hook. The #4 ESS only allows a one-way >connection until the remote end goes off hook. To provide some added information, this is referred to as answer supervision in the telephone industry, and must be known and programmed in both the Cellular switch and the serving CO. The "off-hook" on the roamer port is actually generated in the Cellular switch, not by Bell. The reason for this is that due to the connection only being one way initally, if the Cellular switch does not return Early Answer Supervision (I.E. when the switch Connects as opposed to a mobile phone answering), the audio path from Bell to the Cellular system is never established and the dialed digits never make it to the Cellular system which then times out and fails the call. Answer supervision is NOT the same thing as an off-hook condition. Answer supervision typically consists of a wink being returned to th C.O (E&M signalling at least) by the Cellular system and is totally irrelevant as to whether the Cellular switch is actually connected to and "listening to" the trunk circuit. The primary reason that Bell uses this is probably just as likely to be to increase billable revenue as it is to prevent toll fraud. Bell feels that they have every right to bill for a call (local or long distance) which terminates to a Cellular system roamer port since they ARE passing audio and the call is utilizing their facilities for a period of time (while you dial the mobile number after receiving the second dial tone). Hopefully someday the Bell companies will agree to exchange billing information with the Cellular carriers and then what is known as Calling Party Billing (where the person who called eats the entire bill INCLUDING the cellular air time, instead of just a local call or whatever, just like a normal long distance land-land call) will be possible. Then whenever that jerk salesman trying to sell you widget X of a wrong number comes in, you could rest comfortably knowing that you won't have to pay for it! tad (First posting, so no signature yet!) ------------------------------ Date: Thu, 12 Jan 89 00:40:38 EST From: Miguel_Cruz@ub.cc.umich.edu To: telecom%bu-cs.BU.EDU@um.cc.umich.edu Subject: Re: Find Your Ringback Number Re: moderator's response to my system to find one's ringback number Point well taken. I would never recommend or advocate running something like that after nightfall, and even in the daytime, attempt it on your own conscience. A better solution might be to secure a list of all exchanges in your area code; about 10 valid exchange prefixes are always left out of an area code's numbering plan for plant test functions such as ringback. A trip to the public library's phone book section would give one the information necessary for cross-referencing prefixes. Miguel Cruz ------------------------------ Date: 9 Jan 89 11:23:34 EST (Mon) From: gmeeca!sb@tis.llnl.gov Subject: Many thanks! To: telecom@bu-cs.bu.edu My sincerest thanks to everybody who was kind enough to post their responses to the Tiny Tim request. I have forwarded all the information to the appropriate source (father's friend), who was truly overwhelmed. -- Bradley W. Smith (gmeeca!sb@tis.llnl.gov) 2813 Dayton Drive Ann Arbor, MI 48108 (313) 677-2424 [Moderators Note: And thank you for sharing with us. Remember, we will be expecting a follow-up message as the project continues, and at its conclusion as well. PT] ------------------------------ End of TELECOM Digest *********************