zellich@stl-07sima.army.mil (Rich Zellich) (07/27/90)
Speaking of phones used as an intercom ... does anyone have any
recommendations (or pointers of *any* kind) for these things?
My condominium building has a Trigon phone in the courtyard; this
phone allows a two-digit code to pulse-dial residents' regular
seven-digit numbers through a dedicated residential line to the CO (we
had to get the line connected from one of the residences to get a
residential rate). It also looks for a "5" DTMF tone and, on seeing
one, sends an electrical signal to two solenoid-operated locks in
upper-level entry doors.
The Trigon has died - two batteries hard-soldered to a circuit board are
now trash, and the service company says they have to send the board
back to the manufacturer to replace the batteries, expected to take three
weeks or so and cost at least $300! They will also sell us a
replacement - "better", what- ever that means - system for about
$1000. I have talked to one local business phone supplier so far, and
he has spent almost two weeks researching possible replacements, with no
luck as far as I can tell (no call-back, anyway, after one followup to
make sure he hadn't forgotten about me).
Considering I can buy a whole Panasonic PBX cheaper than the $1000
they want for what amounts to one memory-phone with one added feature
(looking for a tone, and activating an electrical signal for 10
seconds), both the $300 repair and $1000 replacement costs seem just a
tad steep.
One catch is that the phone is out in the weather, on our mailbox wall
under an overhanging entry deck, so it has to be waterproof and also
able to take extremes of heat and cold (the Trigon doesn't like
anything below about twenty degrees F, and is apparently only
moderately moisture proof).
At this point, we're considering just buying a memory phone, if we can
find a weatherproof one, and ignoring the requirement to remotely open
solenoid-operated locks (that circuit has been mostly out of order
for over 18 months, anyway). We *must* have at least an 18-number
capacity, and 36 is desirable (the downstairs units have open access
to their doors, so don't really need the phone access).
Any help would be much appreciated.
Rich <zellich@stl-07sima.army.mil>
<zellich@st-louis-emh2.army.mil>TELECOM Moderator <telecom@eecs.nwu.edu> (07/27/90)
I've seen some units which are nothing more than autodialers programmed to ring the seven-digit number of the tenant desired, who in turn must press a button to unlatch the lock on the front door. There are various problems with this arrangement. 1) The tenant must have phone service, else no front door intercom. 2) Not only must the tenant have phone service, the line has to be equipped with call-waiting. Otherwise, a guest at the front door gets a busy signal and may have to wait several minutes to be admitted to the building ... not a nice thing on a cold or rainy day. 3) If the tenant changes phone numbers and forgets to notify the management of the building, front door calls will go to an intercept, or to perhaps the new owner of the number. 4) The tenant must *not* have call-forwarding, otherwise in his absence, his front door calls will be forwarded also, causing confusion for the person at the front door and perhaps the recipient of the call. Generally, an autodialer arrangement at the front door is not a very good setup ... particularly in a large, multi-unit apartment complex. A far better alternative is to use a type of hybrid centrex offered by some telcos, or premises equipment available from many telecom vendors specially designed for the purpose of front door intercom service. The best service of its kind is, thanks to the MF Judgment, no longer available except to grandfathered customers of Illinois Bell. Called "Enterphone Front Door Service", it was contained entirely in the central office. The next best system I've seen comes from GTE/Canada, and is called "Interphone Service". Please note the only difference in the name is the /I/ and the /E/ of the first word. The big difference is that the GTE/Canada version is Customer Premises Equipment which functions precisely like the central office version banned by the judge. In both versions, here is how it works: A weather-proof, very sturdy phone is mounted at the front door or gate of the apartment complex. Two pairs serve it; one for the phone and the other to operate the latch on the door. The phone itself is a speakerphone, with nothing for the public to touch or get their hands on except the touchtone buttons. No switchhook, no exposed wires. A metal grill over the speaker. "Dial Code Numbers" are two, three or four digits, depending on the size of the apartment complex. Dialing zero defaults to the management office or caretaker. Pressing the first button of the code number activates the phone, and opens the line to receive the remaining one, two or three digits, which are the actual code numbers. Typically, the first digit pressed is '1' or '0'. Pressing '0' both opens the phone line and dials zero. Calls are timed out after 45 seconds or one minute, at the option of the owner of the system. The rationale is that the phone is intended only for identifying and authorizing a visitor, or to conduct a limited amount of business on the way in or out of the property. The central office version requires dedicated pairs to the apartment complex. A tenant may change phone numbers, but the pair serving the apartment must never be changed. In the central office, jumpers from the Enterphone equipment to the pairs serving the tenant need to be correctly attached. If an installer working on the street or at the tenant's apartment building has some reason to swap out pairs, then a corresponding change has to be made in the CO. The CPE (Customer Premises Equipment) version merely requires that *house pairs* never be swapped out without reprogramming the unit. The GTE/Canada device (the CPE version) merely calls for all incoming CO pairs to the apartment building to go in one side of the unit, and all the house pairs to come out the other side. In both versions, a call is handled like this: The front door phone cannot be called. It will only handle *outgoing* calls, of a minute's or less duration. Visitor looks up the name of the person they are visiting, and dials the associated code number. No where in the entrance directory is reference made to apartment number or actual phone number. The unit receives this information, and translates it into a *wire pair* associated with the apartment (or, as the case may be, with the management office, the janitor's quarters, etc). It tests the line for busy. If the line is not busy, it breaks the connection to the CO, seizes the pair, and sends ringing voltage to the telephone in the apartment. The ringing cadence (usually, two short, clipped rings, a pause, and two more short rings) identifies the source of the call to the resident. The resident answers the phone in the usual way, and is connected to the front door speaker phone. The door can be opened by dialing '4', or admission can be denied by simply hanging up. Either dialing '4' breaks the phone connection (while holding the electric latch open a pre-detirmined number of seconds -- usually five or six seconds), or simply hanging up breaks the connection without unlatching the door. In any event, the connection will be broken after 45 seconds or one minute. If an outside call should arrive on the line while the pair is hooked to the door circuit, then the unit detects this. The caller continues to hear ringing, and the tenant gets a 'call-waiting' signal. The tenant can open the door by dialing '4', at which point the connection will immediatly break and the central office call will be put through immediatly, or the tenant can dial '8' to deny admission at the door, disconnect and pull the central office call. If the tenant simply hangs up the phone, the door is disconnected, admission denied, and the central office call commences ringing on the tenant's phone. If the unit receives a front door call and in picking the associated house pair find it to test busy, then the same thing more or less happens in reverse: the tenant receives a 'unique-sounding' call-waiting tone (different than telco's call-waiting tone), and can either ignore it or flash to answer it. By flashing, the tenant cause the door system to split the connection; put the central office on hold and bring in the front door call. The tenant then does the same as stated above, by dialing '4' to open the door and return to the central office call in progress; dialing '8' to deny the door and return to the central office call in progress, or replace the receiver to deny admission and disconnect both parties. (In some exchanges, merely hanging up causes the central office to send a ring back, as a reminder that you 'left someone on hold'). Both versions, CO or CPE, allow the use of rotary or touchtone phones by the tenant. Neither version is influenced by call-forwarding, since they seize the actual pair to the apartment without going through the central office switch. Both versions supply sufficient ringing voltage to trigger an answering machine; thus your answering machine could answer the front door for you and request that the visitor leave a message. Neither version relies on the tenant having actual phone service. If the tenant's phone service is disconnected, or not yet turned on, then the phone instrument will be dead except for those times when there is a front door call. Unfortunatly, both versions cause an adverse reaction to modems on the line, just like 'regular' call-waiting will do, and there is no way to suspend front door calls, as can be done using *70 on central office calls. The CO version runs a pair from the central office to a relay at the customer's premises which in turn triggers the door latch. The CPE version has the circuitry built into it, and a pair runs from the unit direct to the front door latch to open it on command. The length of time the door stays unlocked is adjustable; typically five seconds is adequate, but ten seconds may be preferred. Although the dial code number is usually assigned permanently to the wire pair serving the apartment, the code can be changed in the event of abusive behavior by someone at the door. Sometimes tenants will request that their dial code *not* be listed in the lobby directory, preferring only to give it to persons of their choice. The building manager can recieve calls on his regular phone in the same way with the appropriate dial code; in addition, dialing zero from the front door phone defaults to the manager's wire pair. In addition, the manager may choose to have an 'extension' of the actual front door phone in the office: this permits a limited amount of inter-building calls to tenants from the office, etc. With a special relay attached, it also permits audible supervision of visitors entering the building to see tenants. The manager can have a secret four digit code which functions like a loop-around, which when dialed simply 'rings back' and unlatches the door. This allows the manager, other employees, or trusted tenants to enter without a key if necessary. Another four digit code functions as a fire department bypass, unlatching the door and holding it unlatched until the system is reset. Still another four digit code functions as an emergency all-call, ringing all phones on the system at the same time to permit the manager to make an emergency announcement to tenants in the event of a fire, power outage, etc. The Interphone system from GTE/Canada can serve from as few as two to as many as 200 apartments. You purchase cards for the unit, with each card capable of handling a certain number of lines. The number of cards you must purchase to equip each apartment detirmines the overall cost of the unit. When Illinois Bell had their system on the market (prior to divestiture) they charged as follows: $5.50 per month for the lobby speakerphone and pair to the CO. $5.50 per month for the pair back to open the door. $50.00 per month for the common equipment in the CO. $1.10 per month for each apartment on the system. Useage was unlimited. Calls were not counted. Illinois Bell's contract gave a four hour turnaround on repair service at any time, where the common equipment or the door opening circuit and lobby phone were concerned. For the phones in the apartment, Bell's regular repair policies and charges applied. They usually gave four or five spare phones -- rotary dial, black, POTS instruments -- to the building manager as spares for placement in vacant apartments or in cases where a tenant did not otherwise have phone service for whatever reason. Patrick Townson
toddi@yang.cpac.washington.edu (Todd Inch) (08/01/90)
In article <10169@accuvax.nwu.edu> telecom@eecs.nwu.edu (TELECOM Moderator) writes: >The resident answers the phone in the usual way, and is connected to >the front door speaker phone. The door can be opened by dialing '4', >or admission can be denied by simply hanging up. Thanks for the interesting article. Do you know if the exterior keypad is disabled, or better yet, if the frequencies for a DTMF '4' are blocked to prevent the visitor from phreaking the thing open with a tone dialer? The one time I visited an apartment with a similar (but non-phone) system, the buttons were labelled with only apartment numbers. I couldn't remember my friend's apt # and had to find a pay phone to ask him. Disclaimer: Even though I said "tone dialer", I'm not a drug dealer. Todd Inch, System Manager, Global Technology, Mukilteo WA (206) 742-9111 UUCP: {smart-host}!gtisqr!toddi ARPA: gtisqr!toddi@beaver.cs.washington.edu [Moderator's Note: I believe -- am not certain -- that the tone pad goes dead once the required number of digits are entered by the guest seeking admission. A tone dialer might defeat the system. The building directory shows tenant name and code number -- not apartment number. The tenant must tell the guest what apartment number is involved. There are some definite tricks played with this service where the CO version is concerned: IBT says if a tenant has an off-premise extension on his line (a bridge to an answering service, for example), the OPX will *not* get the doorbell signal, nor if they were to pick up the phone during a front door intercom call would they be able to dial 4 and open the door. Yet the former caretaker of one such building here (with front door service via the CO rather than CPE) had his own apartment a half-block away. The phone in the office of the apartment building was OPX'ed to his apartment. He *was* able to receive front door calls at that location. Why? Because the OPX in his apartment was actually nothing more than multipled from the cable run to the apartment building and not a separate cable from the CO. PT]