Design of a Next-Generation Packet NetworkBdale Garbee, N3EUA

Current amateur packet radio experience centers around 1200 baud half-duplex AFSKoperation for both local and long-haul use. Technologies are discussed that have thepotential to effect a fundamentally different environment for the next generation ofpacket networking. A preliminary proposal is made for an example network configura-tion in the Rocky Mountain Region. Applications, ramifications, and problems facingthe new network are discussed.

Background

While the existence of 1200 baud half-duplex as adefacto modem standard for packet radio hasundoubtedly proven extremely beneficial to the rapidgrowth of this operating mode, the fact that ourstandard has been 1200-baud has probably causedmany would-be packeteers from the communicationsand software industries to go look for somethingmore exciting to play with. This has probablydelayed the development of higher-performancepacket links, since the existing packet user base hasfor the most part appeared content with the statusquo.

There is a substantial difference in performancebetween existing wired networks, and thetechnology that we are using on our RF links. Sosubstantial, in fact, as to make the applicationspossible with contemporary packet radio qualitativelydifferent from those possible on commercial andacademic networks. In particular, we have for themost part limited ourselves to remote login, filetransfer, and electronic mail capabilities.

As a group, we have become so accustomed to 1200-baud operation, that there now exists a substantialmental hurdle to be overcome before any realadvancement can be made in packet radio’s future.We need to open our minds to the possibilities thatexist with technology that is available today. Wealso need to break the traditional “I’ll do it my way”reputation that surrounds amateur radio, and learnhow to work together if we intend to plan and buildsubstantially faster networking resources for amateuruse worldwide.

Goals

If we are to discuss methods for dramaticallyincreasing the throughput of packet radio networks,it is important for us to have a consistent vision ofwhat our goals are. When we are evaluating the

potential impact of any specific change orimprovement in our network, we must do so withclear knowledge of what we are trying to achieve.

The most significant reason for wanting to increasethe speed of our networks is the potential forexperiencing qualitatively different, really excitingapplications. One of the problems with our current1200-baud technology is that interactive applicationsare slow. This leads us to speak of howinappropriate packet radio is for keyboard tokeyboard QSO’s, and to talk about how wonderfulbackground tasks like electronic mail are. In reality,we are first and foremost amateur radio operators,and that tends to imply that we like to becommunicators. For many hams, communicationequates with “live and direct”, real-time radiocommunications.

Many of the modes we already enjoy in amateurradio have digitally oriented counterparts that we canand should explore. Amateur TV, or fast-scan,enthusiasts might enjoy a network of live HDTVtransmissions, all running on suitably fast shareddigital backbones. Repeater cross links mightbecome much more common with higher fidelitythrough application of digital voice transmission overthe same shared digital network.

But even if all we can envision is the same set oftasks that we perform with packet radio today,wouldn’t it be neat to have them run 50, 100, or even1000 times faster?

Technology

If we are going to make any qualitative difference inpacket radio operation, we will need to migrate tohigher speed modem and radio technology. A lot ofwork has been underway in this area in the last yearthat is worth reviewing.

Perhaps the most widely publicized project for higher-

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speed packet links has been the TAPR developmentproject aimed at producing a 9600-baud direct FSKpacket modem and radio combination. First unveiledat the Dayton Hamvention, the initial units promiseblack box operation, with HDLC data in and out onone side (or RS-232 with an optional built-in TNCboard), and an antenna connector on the other sidefor 2 meter operation. Compatible with the KSNGdesign TAPR has offered in kit form, and which hasformed the basis of at least one commercial offering,the TAPR unit is destined to set a new standard for“low-end” packet radio operation. If operated inconjunction with a full-duplex digital repeater, 9600baud can form the basis of a metropolitan packetchannel that will provide substantially improvedperformance with existing 1200-baud applications.

The WAIQDSY 56 kilobit modem design has seengradually increasing acceptance in the last year. Partof the reason this modem has not seen wider use(also true of the KSNG 9600 baud design, and afundamental driving force in the TAPR 9600 baudproject) is that it is not a complete, turnkey solution.In order to put a 56kb station on the air, one neededto be willing to modify TNC-2 hardware or experimentwith PC plug-in cards to get a digital data stream, andthen had to locate and purchase an externaltransvetter to move the modem’s output from the28Mhz region to some frequency of local use, suchas 220Mhz or 430Mhz. While none of these problemsare insurmountable (witness the number of stationson the air in Georgia and elsewhere!), they haveundoubtedly hindered widespread use of thismodem design. The prospects for this unit willimprove with the availability of other hardware thatwill be described shortly.

The development effort that is likely to have the mostsignificant impact on packet radio in the near term isthe N6GN project to design RF modems (or true“packet radios”) for the 9OOMhz and 1.2Ghz band,that provide 250 kilobits per second using direct FSK.With an estimated parts cost of under $200 per unit,these may well be a good choice for our next long-haul backbone step. And eventually, they showgreat promise as the technology of choice for end-user connection to the network. By the time thispaper is published, prototype units should be in thedemonstration and testing phase.

When we are investigating backbone links, anotherproject worth knowing about is another that N6GNhas been working on. With nudging from N3EUA,N6RCE, and others, the design of a IOGhzmicrowave digital link, using cheap surplus

gunnplexer modules, and providing data rates from 1to 10 megabits per second, is now in the PC Boardlayout phase. Prototypes were shown at the DaytonHamvention in April 1989, operating at 1 Mbps, andwork is progressing on development of kits forproliferation of this technology. Microwave links areparticularly attractive for backbones, because of therelatively low power levels required, the availability ofvery large amounts of system gain with moderatelysized antennas (dishes), the fundamentally point-to-point nature of the technology, and the resultingpossibility of frequency reuse. Whenever thegeography and environment allow, use of microwadebands for amateur packet radio backbone linksshould be strongly encouraged.

Now that we’ve talked about all this wonderful RFgear that’s just around the corner, and which canprovide substantially faster raw data link speeds, howdo we generate and accept bits that fast? It’s acombination of hardware evolution, and softwareinnovation. In the digital hardware arena, there aretwo projects underway that are worthy of note.

Two years ago, the PS186 packet switch board wasunveiled. For a variety of unfortunate reasons, theunits have never been produced. That is about tochange. AEA is expected to be shipping units in thevery near future, and a port of the KASQ software isunderway by N3EUA. Bluntly, the PSI86 is the mostlikely packet switch candidate for the next round ofpacket network improvements. Based around an80186, the unit provides 4 high speed HDLC channelswith full DMA, capable of over 1 Mbps per channel,full duplex. In addition, the unit draws very littlepower, and includes features like a “firecode” resetcircuit for “pushing the big red button” remotely, andit’s single-board configuration makes it ideally suitedfor mountaintop packet switch operation.

Simultaneously, Mike Chepponis K3MC hascompleted the design of a plug-n card for the IBM PCand compatibles that will provide two or morechannels of fast HDLC, capable at-least of handlingthe N6GN 250kbps radios. Sporting an onboard V40microprocessor, the design allows migration of partof the networking code onto the card and away fromthe main computer, making for faster and moreefficient network operation. In addition, it appearsthat it will be possible for this unit to run in astandalone configuration, providing some subset ofthe PS-186 functionality when less capability isrequired for packet switch sites.

With these two pieces of digital hardware, arriving atalmost exactly the same time as the N6GN faster RF

solutions, we are suddenly faced with a completehardware solution for faster packet operation at boththe end user and network backbone levels! Andmost excitingly, the cost of a PS-186 based packetswitch site with a 900Mhz/l2Ghz or 1 OGhz RF setupfor the backbone link(s), and one or more channelsof contemporary or new-technology RF for localaccess, has the potential to cost about the samenumber of dollars as a site with an equivalent numberof ports of 1200-baud TNC, firmware, and commercialFM radios!

It is probably not surprising that most of the high-performance digital development is happening hand-in-hand with creation of device drivers and improvednetworking capabilities in the KA9Q TCP/IP softwareimplementation. To date, the KASQ package is theonly software that has been available to test packethardware at speeds faster than the 9600 baud range.This is in part due to the ready availability of fullsource code. But even more importantly, the TCP/IPprotocol suite is a mature set of protocols, that haveevolved in an environment of heterogeneouscomputer systems connected by a wide assortmentof networking technologies at various speeds. Sincethis is a pretty accurate description of the emergingamateur packet network, we should not be surprisedthat the TCP/IP protocols also work well in ourenvironment! Particularly since the KA9Q packageprovides all of the common AX.25 functionality,compatibility with existing NET/ROM networks, and afairly reasonable programmer’s interface fordevelopment of new applications. At least initially,the KA9Q package will be the software of choice foroperating on our next generation network.

Proposal

In order to illustrate how we might combine theemerging hardware and software technologies to theproblem of building our next generation “dreamnetwork”, let’s take a look at a real situation. Withoutbeing overly specific and detailed, here is a proposalthat will be made for the Rocky Mountain Region,centered around Colorado.

The existing packet backbone is composed almostentirely of NET/ROM compatible nodes operatingeither single-ported on 145.01 Mhz, or in some casesdual-ported to 446.8 Mhz as a backbone frequency.There is a dense population concentration along theColorado front range of the Rocky Mountains,including relatively isolated RF communities inDenver, Colorado Springs, Northern Colorado aroundFort Collins, and so forth. The average distancebetween these clusters of humanity is between 40

and 50 miles. To the west, there are scatteredclusters of activity in and around the high-altitude skicountry, and at Grand Junction on the western edgeof the state. Paths between switch sites on theEast/West backbones are frequently far enoughapart to preclude easy application of microwavetechnology such as the NGGN IOGhz design. To theSouth, a couple of long hops connect New Mexicoand Texas, and to the North, very reasonable pathsconnect into Wyoming.

Two problems then exist. One is fitting technologiesto needs, and sequencing changes to achievemaximum benefit early in the process. The second isgaining sufficient support (monetary, political, andvolunteer labor) to make the plan succeed. This is atough battle, particularly when the technical solutionproposed is esoteric enough (at least compared tocontemporary amateur packet technology) to seem“scary”.

First, existing relay sites should have their digitalhardware replaced with PS-186 boards. Equippedwith a standalone version of the KA9Q NOSsoftware, these boards will interoperate with theexist ing NET/ROM backbone, and provide afoundation for building better links.

Second, links along the Front Range that are ofmoderate distance should be upgraded to 1 Mbpslinks on lOGhz, if possible in parallel with the existing1200 baud technologv unt i l the new l inks arestabilized and proven. ’ Because there is a potentialfor tremendous data transfer needs among the highpopulation densities in this area, the technologyproviding maximum data rate over point-to-point linksis the obvious choice.

Third, the sites along the East/West paths and to theSouth, where distances are perhaps too great forreliable 1OGhz operation, should be equipped with1.2Ghz NGGN units at 250kbps. We choose 1.2Ghzover 900Mhz primarily because part of Colorado isincluded in the area closed to amateur use of the9OOMhz band. These radios, combined with gainantennas (perhaps using power splitters or duplicatedTX gain blocks for multiple point to point links), havethe potential of operating reliably over the path

lengths involved (on the order of a hundred miles,between 14,000 foot peaks...). T h e 1QGhztechnology is favored because of cost (less thm$100 parts cost per end including a 2-foot dish!), datarate, and fundamental point to point operation... butthere are undoubtedly locations where dishes arother microwave bi ts and pieces wil! not beappropriate.

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Simultaneously with installation of these fasterbackbone links, we should investigate better localaccess ports. The advantages of full duplexrepeaters for true CSMA/CD operation have beenwidely discussed. In Colorado, a mixture of 1200baud and 9600 baud full duplex ports is probably agood initial step, with 56kb cross-band full duplexworthy of consideration.

Making It Happen

Before we go out and start building things, we oughtto be prepared to spend some time assessing thecurrent usage patterns on our existing packetnetwork links. As appealing as it might seem at times,removing an existing facility to make room for ‘biggerand better” is rarely a wise move. We need to makesure that any new facility we install, and any facilitythat we upgrade, provides a growth path for existingusers.

If we are going to successfully upgrade our majorpacket facilities to a substantially higher level ofperformance, we’re going to need to enlist all the helpwe can get. In particular, some energy should beexpended investigating applications that are outsideof the traditional uses of packet radio. Armed withideas, we can then approach groups that are notknown for being strong packet supporters, withsome hope of gaining cooperation and support.

The N6GN 1OGhz microwave links have as an optionan audio sub-channel, that might be used to providephone patch capabilities to a remote repeater site thatwe want to equip with fast links. The expansion busof the PS-186 might be utilized to support customhardware providing remote control and telemetry forexisting RF gear at a switch site. I’m sure you canthink of other such possibilities.

It is a fact of life that many of the best RF sites forhigh speed packet backbone hardware are currentlycontrolled by FM repeater or fast-scan video usergroups. The key to gaining access to these sites isfinding ways to add value to their operation whenthey allow us rack and tower space. In Colorado, theemerging relationship between the Rocky MountainPacket Radio Association (RMPRA), and the Pike’sPeak FM Association (PPFMA) is an example of howthis can really work.

Keeping It Happening

Even if we do our homework, plan our links carefully,and get as many groups as possible involved inimplementing our network, there are still several

problems that can crop up that deserve discussion.

An initial burst of enthusiasm followed by a loss ofinterest before any milestones are reached can be areal problem. The best way to counter thisphenomena is to sequence the installation of switchand local access improvements such that highvisibility sites are upgraded first. This way, themaximum number of folks will have a chance toexperience the improvements, and get excited aboutthe possibilities. And if you can grow the excitementby pulling in more and more new folks to help withthe effort, so much the better!

Despite our tradition in the amateur hobby ofworking with gentleman’s agreements, we need toconsider putting some of the decisions made,particularly between groups that don’t have a historyof beneficial cooperation, into writing. This will helpto make sure that the loss of a key member of theeffort won’t leave the two groups wondering what“the other guys” were supposed to do, or even worseleave two groups that won’t speak to each other!The things that most need to be documented arewho is going to pay for and implement each piece ofthe network, and what their expected schedule is.

And finally, as WOYNE has been heard to questionon innumerable occasions: “Who’s going to takecare of all this stuff?“ It’s easy to find people to drivehalf a day, climb a mountain, and install a new pieceof gear. It’s not too hard getting those folks or folkslike them out the first or second time somethingbreaks or gets hit by lightning. But what happens ayear or two down the road when the initial supportgroups have all burned out and gone back tochasing 40m DX, or rag-chewing on 80m?Considering carefully how to handle long-termupkeep of our networking facilities is a need thatcannot be overstated. If we’re going to go to thetrouble of building a real network, we need to be ableto maintain it!

Conclusion

Sitting back and thinking about all of the issues thatsurround the design, acquisition, installation, andmaintenance of a next-generation amateur packetradio network may make the problems seem to beinsurmountable. There are, in fact, some reallydifficult questions that need to be answered. But Ihope the message conveyed by this paper is thatnone of the problems are impossible to solve! Wecan, and should, strive for a major upgrade in qualityand performance of our packet network.

I’ve talked briefly about some of the technologiesthat might play a part in building our “dreamnetwork”. It seems particularly exciting that the PS-186, the K3MC fast I/O card, and really fast RFhardware by N6GN are all coming together at aboutthe same time. We’ve asked many times “where is myhigh-speed packet?” The answer is that it’s here, it’snow, and we no longer have any excuses for notimproving our networks!

It is hoped that by the time this paper is published,further details will have been worked out regardingthe development of a faster packet network inColorado. The author would be pleased to hear fromindividuals involved in similar efforts elsewhere.Electronic mail is preferred, bdale@col.hp.com on theInternet, 76430,3323 on Compuserve, or N3EUA @KAOWIE via packet BBS.

References:

Brock, M., Antonio, F., and Lafluer, T., A H i g hPetiormance Packet Switch ‘Proceedings of theSixth ARRL Computer Networking Conference.

Chepponis, M. and Karn, P., The KISS TNC: ASimple Host-to-TNC Communications Protocol,Proceedings of the Sixth ARRL Computer NetworkingConference.

Finch, R. and Avent, S., A Duplex Packet RadioRepeater Approach to Laye r OneEfficiency,Proceedings of the Sixth ARRL Computer NetworkingConference.

Avent, S. and Finch, R., A Duplex Packet RadioRepeater Approach to Layer OneEfficiency - PartTwo, Proceedings of the Seventh ARRL ComputerNetworking Conference.

Heatherington, D., A 56 Kilobaud RF Modem,Proceedings of the Sixth ARRL Computer NetworkingConference.

Kantor, B., Software Design Issues for the PS-186Advanced Packet NetworkController, Proceedingsof the Sixth ARRL Computer Networking Conference.

Chepponis, M. and Mans, B., A Totaiy AwesomeHigh-Speed l/O Interface for the IBM PCXT/AT/386 and Macintosh II Computers,Proceedings of the SeventhARRL ComputerNetworking Conference.

Garbee, B., More and Faster Bits: A Look at PacketRadio’s Future, Proceedings of the Seventh ARRLComputer Networking Conference.

Garbee, B., Djgitai Dreams, 7 3 Amateur Radio,October 1989.

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