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Progress Report 13

April 2d, 1997


The cut-over of Mitchell High School's computer labs from a shared wired T-1 from it to the District servers, to a wireless feed to Coronado High School and thence to the district via Coronado's wired T-1 was trickier than anyone expected.

School District 11 has a network in which all 55 schools are directly connected to the District's computer/gateway via either full T-1 for data (high schools), shared T-1s with voice and data (middle schools), and 56Kbps twisted-pairs to all the elmentary schools. A *very* flat network architecture, with DHCP (dynamic assignment of all work station IP addresses) operating from the center. BUT, 'bridging' rather than 'routing' to all the points in the network. And the use of Class A IP address licence, exclusive to the district, (not announced to the Internet), all behind the firewall to the outside (no system can be pinged from outside the district.) With each of 5 clusters of schools (centered on a high school) using a network of the style 10.6 (Coronado) or 10.7 (Mitchell).

When Dave Walsh of LANTech, the regional/integrator for the Solectek radios, set up the Solectek 200E systems (radio + diagnostic, configuration + router) with a monitor and keyboard, he made the radios into routers, with static addresses, (which had to be identified as such in the DHCP data base). A 10.7 net number at Mitchell and a 10.6 number at Coronado.

The directional (dish) antennas are mounted on the roofs, on the towers, of the respective schools, to reach the 9 miles between the schools. The RF cable runs down into the building through conduits, into rooms close by a patch panel in the case of Mitchell, and next to an Ethernet wall panel that runs further downstairs to the patch panel, at Coronado. In order to prevent undue line loss over long runs of the RF cable between the antennas and the radios, Solectek has an FCC wavier, permitting it to put a line-booster on the RF cable (hardware-security key protected from use on any other installation.) This lets Solectek drop RF cable up to 200 feet from the antenna, without loss of signal. So the radio and router itself can be placed conveniently, either in central patch-panel utility rooms, or in offices where they are connected into the network with short pieces of 10baseT wiring at walls.

At Coronado this meant putting the radio on a file cabinet in a school office, and connecting it directly into a numbered Wall Ethernet outlet, and doing a corresponding plug change at the patch panel that controls all interconnections, in the patch panel and outside T-1 terminus room.

At Mitchell the radio sits right next to the central patch panel, in a utility room, and the Ethernet is directly plugged into the patch panel.

Dave Walsh quickly configured the two routers attached to the radios (all in one box) to route packets between the radios and then onto any machine inside each high school. Tests of the radios confirmed they would talk to each other, and their IP addresses were reachable from each other. And *within* each school, the radio and its router could be reached (pinged) by any machine in the school. BUT no workstation in one school, or at the District Headquarters could reach (ping) the network in the other high school, over the radio link!

This problem took a few days to sort out, compounded by the fact that a US West T-1 line went out from the District to Coronado, all during Spring Break, when staffing was low. The problem, as it turned out, was that the radios had to be 'bridged' not 'routed' - like the rest of the network, AND the entire Mitchell High School had to become just an extension (like a LAN network) of Coronado's IP network 10.6. So all workstations at Mitchell had to be assigned, dynamically by the DHCP server/data base, a 10.6 number, as if all the workstations at both schools were in the same place on the same ethernet LAN network.

Because of the DHCP IP assignment system, this only required shutting down all Mitchell workstations, so when they came back up, they would automatically get 10.6 rather than the 10.7 assigned net numbers. No big deal. EXCEPT that meant that the radio/routers no longer could be reached from the District my SNMP software permitting remote diagnosis. (It would require physical trips to the radio locations, and putting a monitor and keyboard on them to get traffic data or troubleshoot.) This MAY be correctable, later.

By the end of the Spring Break week the network was operating correctly, so the plug was pulled at Mitchell that fed all the educational workstations (such as the 45 Power-PCs in its computer lab) into the shared T-1 back to the District (shared with the 'Administrative' traffic at Mitchell), and it was plugged directly into the radio ethernet port.

So as of the school week of April 1st, 1997, the entire educational computer Internet network at Mitchell High School goes over the 2Mbps (rated) 2.4Ghz spread spectrum wireless link, 9 miles to Coronado, where it traverses the Coronado wired T-1 to the District Headquarters. And preliminary 'ping' analysis shows the Mitchell network is operating as well, if not better, than it did when it was connected to the District by hard wire.

This setup will remain in place until the end of the School Year (end of May) so we can test the performance of the radios under normal student load, through spring (it is snowing as I write) weather, and get some comparative idea of its price/performance.


One major finding in THIS specific installation became clear through all the work, and cost of getting a setup finally to work involving a large urban high school, from our original goal of connecting that high school to the District Headquarters, only 4 miles away, but a known-to-be awkward physical problem in that there was no obvious way to link the two over masking hills in the city. That finding was that in THIS specific 55 school urban school district case, where the Headquarters (where the Internet POP was as well as the terminating point for all data and phone networks) is down in a terrain 'hole' surrounded by large (100+ foot) trees, that it would NOT be a good idea to try and make the 'backbone' network between the District location and the 5 major high schools, wireless. The added costs (relays, towers needed) to the basic radio costs would not be justified over US West T-1 lines to those same 5 schools, with educational-discount prices. Not at least or until the radios of the Solectek class dropped to the $1,000 each (instead of $6,000) range.

HOWEVER, it became clear that, since the District operates, and has even configured its network, on the 'school cluster' basis, where the middle and elementary schools associated with a High School are (1) physically close to their parent high school and (2) currently the District is paying for at least 55 direct US West data and voice links between the schools and the district, that the BEST use of wireless to cut recurring monthly costs from the phone company, would be to operate radios BETWEEN the 5 high schools to each of their cluster middle and elementary schools, leaving the link between the high schools and the district, telco wired. This could result in large monthly-cost savings, and could even bring higher data speeds to the elementary schools, without monthy costs, than it is getting now with US West 56kbs copper links.

I had a brief discussion with School Superintendent Burnley about that possibility, while this work described above was going on. Since the District is embarking on a broad plan of telecommunications (voice and data) upgrading, paid for by the Bond Issue that finally passed the district last year, there is reason to believe that the Solectek wireless installation-test, for all its delays and costs, taught everybody valuable lessons that they can now apply within the large urban district. And the new network engineer hired by the DIstrict - from government and corporate experiential data network, but no wireless, base - is now interested in how wireless can help cut the large monthly costs the District has to pay for its past, totally telco wired, solutions.


Dave Hughes