Improve your paging network with satellite-linked terminals: Still using telephone lines? Connect all the termimals in a paging network via a two-way satellite link to improve network reliability, reduce service outages and increase transmission speed. Us
The adoption of TNPP (Telocator Network Paging Protocol) was a big step forward for the radio paging industry. Using TNPP, independent paging providers can link up with other providers using telephone lines to create networks that greatly extend their coverage, while keeping costs to a minimum. Page One and SoutherNet are two paging networks taking advantage of this protocol. In 1996, SoutherNet began implementing a two-way satellite paging system using TNPP that promises to improve network reliability dramatically and to reduce operating costs. It also provides the potential of virtually unlimited coverage.
Paging networks Typically, networks involve multiple paging terminals connected via telephone wirelines in a chain, ring or star configuration. A page can originate at any terminal in the network. As a TNPP packet passes from terminal to terminal along telephone lines, each terminal determines from the packet’s header whether the packet is addressed to it. If so, it sends the appropriate pages to its transmitter(s). If not, it passes the packet on to the next terminal.
Of course, using this protocol requires a system equipped with TNPP-capable paging terminals. Chuck Moffatt of B&M Communications, Tupelo, MS, (a member company of SoutherNet) said, “I would imagine that, between four of us SoutherNet members, there’s over a hundred of those terminals in use, all of which are TNPP-capable.”
When the chain breaks There are, however, problems with the chain type of TNPP network, Moffatt said. “We have telephone company wirelines connecting terminal-to-terminal throughout the SoutherNet, but if the phone lines have a breakdown, the affected part of the network is put out of service. For example, if we had a phone line break in Chattanooga, TN, SoutherNet would be divided into two halves, and neither half could communicate with the other. Or, if someone lost a terminal, again, the network would be divided in two.”
Two-way satellite paging SoutherNet’s solution to this problem is a form of radio paging in which all the terminals in a network are connected via a two-way satellite link, rather than through telephone wirelines. Moffatt said that this new way of networking has never been tried before. “Most people take wirelines, like Network USA, which carry pages to Pensacola (FL) where they uplink it to a satellite and receive the page at all their multiple locations. We’ve done away with the wirelines and gone all two-way. To my knowledge, no one else had tried it until we did.”
Before two-way satellite paging could be implemented, a number of technical hurdles had to be overcome. In the end, the solution was arrived at through the collaborative efforts of a number of parties, including SoutherNet member companies; Zetron, Redmond, WA; G.E. SpaceNet, Chicago; and NSN, Avon, CO.
TDMA VSAT networks “NSN is a satellite services integrator and a broker of space time,” said Todd Theel, director of data sales at NSN. “We have a TDMA VSAT network (time-division, multiple-access; very small aperture terminal), which is typically used for credit card verification and point-of-sale, batch-type traffic. What NSN has done is to take that technology and apply it to the paging world to supply TNPP traffic connectivity. We call it “TNPPath,” and we’re using the system for terminal-to-terminal communications. What SoutherNet asked us to do was modify the system to do multi-TNPP inputs aggregated into a broadcast TNPP network.”
TNPP for satellites TNPP uses packets of information that are distributed among paging terminals in a network. A packet can contain the address of the destination paging terminal(s), information about the page itself, error-checking information and other elements necessary for communication. A paging terminal that receives a packet can tell which pages to transmit, which ones to pass along to other terminals in the network and what information (if any) has become corrupted.
Because it involves terminal-to-terminal communication through a satellite, rather than directly over wirelines, some unique problems had to be solved before TNPP would work in such a system.
“Each TNPP packet has a number,” Moffatt said. “Each port on a TNPP card remembers the last 64 TNPP serial numbers. If it sees that serial number, it disregards it as being an illegal serial number (as if it bounced back from another terminal). In a network using telephone wirelines, the packets are given a new serial number as they are passed along, so there’s no chance of that happening. On a satellite, however, there’s no terminal to reserialize them.”
After consulting with Zetron’s technical support staff (Zetron played a major role in the TNPP development process), the SpaceNet designers’ solution was to write a program that would take the packet, strip off the packet number and send it down in increments so that each packet could be given a new packet number.
NSN’s Theel explained how the satellite system handles a page. “All the pages come into the terminals at the various SoutherNet sites. Then there’s a link that takes it back_via satellite_to the hub in Chicago [which is owned by G.E. SpaceNet]. The hub in Chicago takes the TNPP information from the 15 to 20 outlying sites, puts it all together and then puts it back out on the satellite so that it is broadcast, in effect, back out to all the sites.
“All the local information goes into the system, and what comes back is the combined network traffic. The system works very quickly. I think the average response time is two to three seconds,” Theel said.
The satellite advantage Moffatt said this new two-way satellite system has many advantages over wirelines. “With the satellite, if a terminal goes out, only that area is out of service. Plus, the satellite is faster. We have gobs of traffic on this thing, and we don’t have collisions. We’re carrying network traffic. We’re carrying neighbor-to-neighbor traffic. We’re carrying zone traffic. All this traffic is there, but if it doesn’t pertain to us, the TNPP mapping in the Zetron model 2200 paging terminal throws it away.”
Moffatt said that, in addition to avoiding network-crippling outages due to wireline breaks, the new two-way satellite system saves money. “For a four-way data circuit that crosses the Mississippi River, the phone company charges about $2,500 a month. The satellite only costs about $250 a month_quite a difference. There’s a couple of places where a data circuit crossing the Smoky Mountains costs $4,800 a month; so you can see, there’s some tremendous savings to be gained.”
Hardware For a paging provider to participate in two-way satellite paging, the first requirement is a network running TNPP-capable paging terminals and an understanding of how TNPP works. The next requirement is the special hardware needed to link the paging terminal to the satellite, which is being provided to SoutherNet by NSN.
“We supply a VSAT, which typically consists of a 1.2-meter transmit antenna, a 200mW transceiver and an IDU (indoor unit),” said NSN’s Theel. “The indoor unit is a small computer with a satellite transceiver working in Ku band and running on GSTAR 4. It’s got complete coverage of the United States, so anybody could become a nationwide system overnight if they wanted to, and if they got the affiliates together.”
SoutherNet goes satellite SoutherNet began implementing the two-way satellite system in early 1996.
“NSN wanted us to put in 20 satellite links within the first year,” Moffatt said. “We’ve already got 15 installed or on order. When we get five more installed, our monthly rate will drop with each new site installed. As we add more links, our rate will come down even further, which is nice.”
SoutherNet is committed to this new system, so it is requiring all potential new members to purchase their own satellite receiver. “If you want to join SoutherNet,” Moffatt said, “you will have to have four transmitters up-and-running, a TNPP-capable terminal and a satellite receiver. That’s a sizable investment, but if someone is going to join us, they will have access to the whole system, so we want something in return.”
