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NEWS: Modem Trunking Issues Solved!!!Recent investigations revealed that SWBT was not delivering service to 46 modems in our dial-up pool. SWBT reports, and we have verified, that the problem is fixed.All dial-up users were affected. While users may still receive a busy message, it should be because all 207 modems are actually busy instead of only 161.November 10, 1998We have verified that the trunking issues are finally solved. We thank everyone who assisted in discovering and correcting these issues. Usage statistics crashed last night, but accounting reports indicated that we used all 207 modems between 9:00 p.m. and 10:00 p.m. last night. Networking will continue to pursue adding more capacity.
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 | We had an error in reporting modem usage (up to 24 more than were actually in use). |
| This has been corrected and verified through other methods. |
| SWBT had their switch programmed incorrectly making 46 modems unavailable. |
| This should be fixed, but is awaiting verification by actual users. |
| If you connect to Mark from off campus, please let us know if it's before November 11th. |
After extensive work, redesign, and reprogramming by Southwestern Bell, the busy modem problem should be fixed. If you receive a busy or the infamous "We're sorry, all circuits are busy now. Please try your call again later" message, PLEASE fill out the busy report form if less than about 200 modems are in use. We made improvements for the weekend, but SWBT admitted today that they still had a programming oversight that should have been corrected at about 3:30 p.m. today.
For those of you wandering what happened, two problems were discovered. The first was a usage reporting problem on our end and the second was a trunk overflow problem on SWBT's end.
When the Off Campus Modems In Use page was added, a minor programming error caused it to also report the number on on-campus modems in the figure. This caused us to think that we had up to 24 more modems in use than actually were. The program has been updated and cross-checked with other methods to verify the accuracy. We have nine total spans delivering 23 modems per span for a total of 207 possible connections to Missouri State University. We thought that only the last span was not being used since we topped out at 184 users, but found that we were actually topping out at 161 users. Please note that this was a reporting error only and did not affect the operation of the modem pool.
The biggest problem was that someone at SWBT did not understand the limits of their equipment. We had asked for the nine trunks to rotate round-robin, but were told that we had to fill one trunk (or span) before it would overflow to the next. (Please note that a span is a single PRI consisting of 23 user channels and a trunk can be comprised of one or more spans.) We accepted this and SWBT programmed their telephone switch accordingly. We since found out that the last two spans were not being used. The reasons were because their switch has a limit of no more than five overflows. Once the fifth overflow occurred, a sixth was impossible which left two spans unused.
The astute reader will catch a discrepancy here: five overflows should be six trunks for a total of 138 users, not the 161 as stated above. This is because, unknown to us, SWBT had organized the first two spans into a single trunk. Therefore, the overflow went 46 + 23 + 23 + 23 + 23 + 23 for 161 total calls. After discussing options, Missouri State University chose to have SWBT regroup the nine spans in five trunks of two spans each except for the last which would remain unchanged. This sets up the overflow to 46 + 46 + 46 + 46 + 23 and are organized to connect to Sara, Marie, Clark, Jim and Mark respectively. If you ever call in from off campus and connect to Mark (only before Nov 11th), please let us know!!!! This will prove that the spans, trunks, and overflows are working properly.
Busy signals or messages could still occur if latent demand drive utilization higher, but we hopefully now have 46 more lines in service to better serve our users. Unfortunately, we discovered that SWBT cannot deliver a busy signal (to most locations) when all of our trunks are busy. The message, by the way, does not include any code at the end as SWBT had indicated.
Check out All Circuits
Busy not from Missouri State University news item for the rest of the story.
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