Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!cs.utexas.edu!uunet!netsys!vector!telecom-gateway From: well!fgk@lll-crg.llnl.gov (Frank G Kienast) Newsgroups: comp.dcom.telecom Subject: Re: Quirks of ESS in my exchange Message-ID: Date: 2 Jul 89 16:07:01 GMT Sender: news@vector.Dallas.TX.US Reply-To: Frank G Kienast Organization: Whole Earth 'Lectronic Link, Sausalito, CA Lines: 60 Approved: telecom-request@vector.dallas.tx.us X-Submissions-To: telecom@eecs.nwu.edu X-Administrivia-To: telecom-request@vector.dallas.tx.us X-TELECOM-Digest: volume 9, issue 221, message 2 of 7 Thanks for all the responses to my questions about quirks in my ESS exchange. In addition to responses to this group, I have received nearly a dozen mail responses. The following is a summary of responses so far. Sometimes not receiving a dialtone is caused by the fact that the switch scans the subscriber loops. A bug in the software occasionally causes it to go off into oblivion until it times out and resets. (No explanation yet for the sequence of ascending tones that are sometimes heard just before receiving a dialtone.) Getting disconnected in the middle of a call (which I forgot to mention happens on local calls as well as long distance) could be caused by the failure of the (mechanical) relays which are driven by the ESS software (I had thought before that electronic switches were used). Inability on occasion to program in call forwarding is caused by a temporary lack of available memory, which is dynamically allocated when the request is made. Someone asked me if the 72# and 73# codes were a typo (they thought they were *72 and *73). I checked and 72# and 73# are indeed correct, but I tried *72 and *73 and these work also. Apparently they are interchangable. Sometimes receiving a recording after dialing three invalid digits, and on other occasions not receiving any response until seven digits are dialed may result from changes to the on-line database which are constantly being made due to trunk changes, the addition of new exchanges, etc. ESS screens each digit as it is dialed, so the capability of detecting an invalid sequence before seven digits are dialed is built in. The mixup between the "You must first dial a 1" and the "Your call cannot be completed as dialed" recordings is apparently a programming mistake. (The software comes with the switch, right? Wouldn't all switches of the same type and company have this problem then?) Getting different recordings after the first recording times out is also a programming problem (Hmm.. maybe they used GOTO's to branch to the routines that play the various recordings and forgot the jump out between them :-)) The tones heard when connecting to an AT&T operator are MF (Multi-Frequency) tones which are used by the network for routing calls. They are combinations of 700-900-1100-1300-1500-1700 Hz. Apparently intermediate routing is required because my area is served by a small telephone company that is not a former part of Bell. In response to questions I have received: I am in the 804-979 exchange. The local phone company is Centel. I believe they have a Northern Telecom switch. Finally, I'm wondering if someone could recommend a good book on ESS. I have only a very basic knowledge of telephone switching systems, but have a good understanding of programming (from high level languages down to assembly language) and electronics. I'm looking for such things as the history of ESS systems, problems that were encountered in their design and how they were overcome, information on the hardware and software typically used (type of processor and operating system, some sample flow charts or code, etc.), a listing of the various ESS versions (#1,1A, etc.) and their specifications, etc. Please let me know if you have any recommendations on what book(s) to read and where they can be obtained. In real life: Frank Kienast Well: well!fgk@ucbvax.Berkeley.EDU CIS: 73327,3073 V-mail: 804-980-3733