Many municipalites have developed their GIS on a single workstation, and have since found that other departments have a need for the spatial data the system contains. While a multiple user ArcInfo license or ArcView2 can provide access within the building, providing access for X-Window sessions or NFS connectivity to other buildings across town can be difficult. This paper describes the City of Fitchburg's experiences in using the cable television system to allow telnet and NFS access from the Police, Fire, Water and School Departments at a low initial charge and no monthly charge. Moreover it explains how this option is potentially available to every municipality, given a simple clause in the Cable Franchise License between the municipality and the local Cable provider. The paper goes on to describe the difficulty the City has experienced in using this system.
In August of 1993 the City of Fitchburg, Massachusetts, obtained the necessary channel space and purchased and installed RF Modems to create an I-Net, or Institutional Network, to allow data transmission over the city cable television system. The system was used to connect the Police and Fire Departments to the Fitchburg Geographical Information System (GIS) in City Hall. The system was expanded soon thereafter to service the Water Department and School Department.
The City had been developing a UNIX-based ArcInfo geographical information system since early 1990. A wide variety of very useful information had been entered into the city's GIS over the previous several years, such as engineering maps, parcel attributes and ownership, municipal census data, building footprints, hydrant location and information, zoning and ward lines, watershed and wetland boundaries, floodplain areas, and other geographic information.
While this information was available to other departments in City Hall, such as the Mayor, Assessors, and Engineering, the city didn't have and could not afford high speed phone lines or a wide area network to service remote buildings such as Police, Fire, Water/Public Works, and School Buildings.
Fortunately, a member of the city's Cable Oversight Committee discovered a clause in the municipal cable license that provided for the implementation of an I-NET, or Institutional Network, capable of video or data transmission to connect city buildings. While I-Nets are typically used to connect buildings for video transmission, it was a golden opportunity to distribute GIS data to other city departments at an affordable cost.
The city contracted with Clear Concept Consultants of Needham to install Zenith LAN 4000 and ChannelMiser broadband modems from the Zenith Electronics Corporation of Glenview Illinois to connect the Police and Fire Departments to the GIS. The Lan4000 product plugs into an ISA bus on an PC, and essentially provides a terminal node on the cable network. The ChannelMiser has an AUI port to plug into an existing ethernet network to act as a protocal converter or repeater.
SunSoft PC-NFS and Esri ArcView for Windows was installed on the remote PCs, and Police and Fire personnel underwent a three hour training session to utilize the system. This setup enabled NFS mounts from the PCs to the Sun workstation at City Hall, and provided the ability to view the city's GIS data in "real time". This avoided the problem of maintaining separate data attributes for various city departments.
The cable network is maintained by the city's Cable TV provider, Cablevision Inc. of Hudson, Massachusetts, at no cost to the city. Two channels of space (12mhz) are provided in the contract, but one of the forward channels (from the modem to the head end) was "lent" to the local community acccess channel for video programming. Cablevision provided $25,000 in start-up funds to assist with the development and implementation of the I-Net in addition to the necessary channel space.
Four months after the initial installation between Police and Fire, the Water Department and the School Department Administration Building came on-line, as these sites are referenced in the city's contract with the cable company. A personal computer in the GIS room at City Hall was connected with a broadband modem, as we wanted a way to check the operation of the network conveniently.
There were a number of problems from the beginning unrelated to the operation of the network. From the outset, the conventional RAM requirements of PC-NFS has been a problem. The PC in the Police Department was also used with a DOS database used to keep track of restraining orders. The overhead requirements of the PC-NFS software prevented that database from operating properly, so a batch file had to be devised to "swap out" the autoexec.bat and the config.sys files to load and unload the PC-NFS program.
Another problem centered on the performance of ArcView on a 386 PC drawing 11,000 polygons of parcel information. Of interest to virtually everyone is the parcel ownership information. The City's 11,000 parcel coverage has a robust attribute set. This information was breathtakingly slow in drawing, on the order of ten minutes for screen refreshes. To users unfamiliar with a mouse and windows in general, and ArcView's glacial pace in responding to mouse clicks, it proved to be a difficult adjustment.
Not to say the network wasn't a problem. The remote PCs would "hang" at start-up intermittently and not recognize the server, which drove the Water Department nuts, because they were using the I-Net to transfer meter readings to the Treasurer's computer at City Hall. This work was done at 5:00 AM, and was necessary to get the crews on the streets. Therefore it was very frustrating when the system didn't work. Of course, the consultant for the RF-Modem would blame the cable company, and the cable company would blame the Zenith equipment. After over a year of at least intermittent (and generally acceptable) performance, the Water Department modem just quit working altogether.
Of more pressing importance, at least to the GIS staff, was the poor performance of the networked PC in the GIS room. The Water Department was doing file transfers, so intermittent performance wasn't a problem. As long as the file was sent, it didn't matter if the transfer took a few extra seconds. Telnet or X-Window sessions were another matter. Even under the best of circumstances, X-Window sessions were characterized by halting, intermittent performance just bad enough to drive the user crazy. It worked, but in a "start and stop" sort of way. You had to either type blindly, or wait for your text to catch up every few minutes.
I had about concluded that that was as good as this stuff gets, when the consultant temporarily replaced the Lan4000 Bus card with an ethernet card and ChannelMiser. The performance then was excellent, virtually indistinguishable from being on the local network. For one week this setup worked, and it became obvious the problem was with the Lan4000 cards.
One week later the new Zenith cards, MCN-AT, were installed to replace the Lan 4000. Performance then degraded to about the level that existed before. Testing is still ongoing, but it appears that the ChannelMiser is the preferred solution to networking over the cable system. The ChannelMiser is more expensive (US$2,000 instead of $1,000 for the AT bus product), but apparently delivers superior performance and will service an existing ethernet network.
Another issue in the mix is the knowledge and the willingness of the local cable provider to work with digital information. For an I-Net to work properly, the amplifiers in the cable system need to be set up for two-way performance, and properly balanced. Cablevision, our local provider, was initially unfamiliar with what was required to make the system work properly. While their knowledge base has improved, there are still problems with system performance that must be attributed to the condition of the cable plant, and which still need to be resolved.