IM would be a better analogy than a party line. John - K8OCL
>From: KV9U <[EMAIL PROTECTED]> >Reply-To: [email protected] >To: [email protected] >Subject: Re: [digitalradio] 3kHz or 500Hz Re: Updates on effect of FCC R&O >Date: Mon, 23 Oct 2006 09:42:55 -0500 > >Jim, > >Your analogy of the party line phone is quite correct. Packet suffers >from not only time sharing, but also has a really bad modulation scheme >for HF and should never have been used for this purpose. > >While some of this technology can be used on VHF and above frequencies, >it just does not seem appropriate for HF use due to the difficulty we >have with throughput versus the need for bandwidth limitations due to >the much narrower BW available and the long distance propagation which >greatly increases the number of users of a given frequency. And not >necessarily the users of that server either, but for other reasons, >since no one owns an HF frequency. We are completely unlike a commercial >or government channel. That is why BBS systems, ALE, or other > >Higher speeds require better conditions or wider bandwidths. I can see >this useful for connecting to those limited resources, i.e., e-mail or >BBS server, since there may be only one of those you can connect to at >a given time from your QTH. Faster speeds means that operators can clear >their traffic and let the next station connect. The other reason for >higher speeds on HF would be for emergency use, but whatever design you >have for emergencies, must be regularly exercised during normal times to >insure it will be there when the emergency arrives. > >73, > >Rick, KV9U > > >jgorman01 wrote: > > >It is my understanding that all users CAN NOT share the frequency "at > >the same time". Most high-speed connections are dedicated, I know > >pactor is. I am not sure about ALE, but from a cursory view, I > >believe it is also. Packet is the only protocol I know that is > >designed to share a frequency, but it is also a lot slower because of > >this. This is what I meant by a party line analogy. You have > >sequential use, not concurrent use of a given frequency. > > > >This makes the analogy more like 10, 20, or 30 people sharing a PC or > >phone. Using the example of 60 minutes versus 10 minutes, each person > >has to wait 10 minutes multiplied by the number of people ahead of > >them. Plus you need a way to assign people in the sequence. Are you > >going to be willing to wait 10 minutes for your IM to be sent, even >iffile:///C:/Documents%20and%20Settings/Owner/Application%20Data/Microsoft/Internet%20Explorer/Quick%20Launch/Mozilla%20Firefox.lnk > ><cid:[email protected]> > >it is sent quickly when you gain access? > > > >The original argument was that higher speeds allow faster sending > >thereby clearing the frequency quicker. However, this only works if > >people are willing to wait until their turn comes around. If they > >need or just simply want immediate access, as IM implies, they will > >use another frequency. This immediately reduces the spectrum > >efficiency of the wider modes. In many cases and even perhaps most, > >more narrow modes would work better to give instant access to more > >people in the same bandwidth as a wider mode. In other words, they > >can SHARE the same BANDWIDTH. > > > >My main point is that sharing spectrum is a complicated equation with > >many variables. A simple argument doesn't always take into account > >all the variables necessary to make an informed decision or it > >contains several assumptions that may or may not be valid. One of > >these assumptions implicit in the original argument is that people are > >willing to wait until the frequency clears to use it. That wait time > >may be seconds or even minutes (10 minutes in the example). It also > >implies that there is a method of queuing requests for the frequency > >or of collision avoidance. Neither of these assumptions were discussed > >or proven. > > > >Jim > >WA0LYK > > > > > > > Need a Digital mode QSO? Connect to Telnet://cluster.dynalias.org Other areas of interest: The MixW Reflector : http://groups.yahoo.com/group/themixwgroup/ DigiPol: http://groups.yahoo.com/group/Digipol (band plan policy discussion) Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/digitalradio/ <*> Your email settings: Individual Email | Traditional <*> To change settings online go to: http://groups.yahoo.com/group/digitalradio/join (Yahoo! ID required) <*> To change settings via email: mailto:[EMAIL PROTECTED] mailto:[EMAIL PROTECTED] <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
