It has been my understanding that the PMBOs each have a set of frequencies, but no two on the same band, and the scanning is first on one band then on another, etc. I know that there are stations that can only work a given PMBO on a given band, so in order for them to use the PMBO, the band that is suitable for them at the time needs to be checked periodically by the PMBO. Is that not the logic behind "scanning"?
Regards, Chuck AA5J At 11:27 AM 4/18/2005, you wrote: >The Erlang numbers are commonly used when sizing telephone systems. Just >look at an normal family. If you have four people in the house with one >phone, then the odds are pretty high that you will get contention over >the use of the phone. If you have two phones, the odds drop >dramatically. Three is even better and four goes to zero. But buying >four phone lines is expensive, especially when the probability of all >four people needing the same phone line is essentially 0. Erlang's >numbers are based on the probability for different types of needs. > >If there is only one PMBO, it doesn't matter if they are scanning or >not. There's a maximum of one connection. If there are two PMBOs, then >if they are on the same channel, there is a higher probability that >someone will try yo use both at the same time and cause contention. But >if they are on two different channels, then the odds go down. (duh!) > >Now if we go to three PMBOs on three different channels, things are >good. But can we handle about as much traffic if we only use two >channels? If a PMBO could hear and talk to all other devices then you >could only have two channels running at any time, therefore no >advantage. But since everyone hears differently, there could be some >sharing that occurs, but then the hidden transmitter problem occurs. > >I believe that I am correct in assuming that the PMBO is the fixed >station portion of the network, and if not, ignore everything else I'm >about to say. > >Now, where Erlangs enter the equation is how many conversations can >occur per day for 1, 2, or 3 PMBOs on different channels. Sometime >unexpected is that 2 PMBOs can handle more than 2* a single PMBO and >that 3 can handle more than three individual channels. The situation is >that conversations are not generally randomly spread out through the >day. There are some times where many people try yo talk at once. It's >some rough math, but it goes back to the phones in a home as explained >above. > >Now, in my book, it makes absolutely no sense for the PMBOs to be >scanning, that's something that the user stations should be doing. After >all, when you have two phones in the house, just look to see which one >is not in use. That's called scanning. > >Now the third option of two transceivers is doable, but generally only >if the transceivers are at different sites, which is really option B. I >had one network using adjacent channels for transcontinental traffic and >we found out that we had some big problems because the two channels were >nominally in the same passband for the receiver. The receiver would >adjust the AGC and bury the weak one in the noise. > > > >-----Original Message----- >From: digitalradio@yahoogroups.com [mailto:[EMAIL PROTECTED] >On Behalf Of Skip Teller >Posted At: Thursday, April 14, 2005 8:46 PM >Posted To: FT-817 >Conversation: [digitalradio] Winlink Scanning >Subject: [digitalradio] Winlink Scanning > > > >Does anybody here understand the application of Erlang B? > >I have put forth a suggestion on QRZ.COM that the scanning Winlink >PMBO's do serves to prevent a user from discerning if a PMBO is busy or >not before taking up a frequency and calling repetitively to find out. > >Here is my last question to K4CJX, who has not yet answered. Any >comments? I don't know anything about traffic analysis! > >------------ >Quote (k4cjx @ April 14 2005,09:54) > >Regarding scanning, use Erlang B, and basic traffic enginering, and you >can see that it is a more optimal solution to scan. > >------------ > >OK Steve, > >Here is an Erlang B calculator. > >http://www.cas.mcmaster.ca/~qiao/publications/erlang/newerlang.html > >What values do you assume for the case of: > >A: A Winlink PMBO scanning two frequenices, accepting connections on >only one frequency at a time. > >B: A Winlink PMBO monitoring one frequency only. > >C: A Winlink PMBO using two transceivers, scanning two frequencies. > >It looks like to me that the traffic handling capacity does not change >unless there are two transceivers at the PMBO, capable of connecting on >two different frequencies at the same time, and both feeding the >Internet with traffic simultaneously. This would increase the number of >lines from one to two. As Mark observed, one transceiver scanning two >frequencies still equals one line, not two, so I agree with his >observation. > >Do you agree? If not, then how did you arrive at a PMBO scanning two >frequencies as a more optimal solution and is it optimal for the user >population or for spectrum usage? > >Intuitively, it still seems to me that there is a tremendous advantage >to both the user and the spectrum to eliminate scanning so the user can >tell if a PMBO is available, or busy on an alternate scan frequency. In >the case of no scanning, it is CERTAIN he is not busy on an alternate >frequency, and if he is busy with a station you cannot detect, then when >he transmits his bursts, if you cannot hear that either, then you are >out of range, so you do not need to use up a frequency trying to connect >when there is no hope of making a connection. This keeps the frequency >free for for others to use, doesn't it? > >----------------------------- > >Here is additional information from Steve: > >----------------------------------- >Quote (k4cjx @ April 14 2005,08:23) >Regarding scanning. Most Winlink 2000 stations scan only two frequencies >per band. About 40 percent use more than one radio, so that they scan >only on the given band. Each scan takes approximately 2.4 to 3.0 >seconds. > >The purpose for scanning is to provide the user with a clear frequency >where possible. >Airmail reads the frequencies scanned by each station and ONLY CALLS for >3 seconds per frequency. > >So, after calling for 3 seconds, and no connect what does Airmal do >then? >------------------------------------ > >I still don't understand why there cannot be one station on each >frequency listening on a single frequency and not scanning two or three. >Please explain... > >Thanks... > >Skip KH6TY > >---------------------------------- > >I'd like to clearly understand this issue, so if anyone can explain, >please do so! > >Additional information can be found at http://winlink.org/status/ under >CMBO traffic. > >73, Skip KH6TY > > > > >The K3UK DIGITAL MODES SPOTTING CLUSTER AT telnet://208.15.25.196/ > >Yahoo! Groups Links > > > > > > > > > >The K3UK DIGITAL MODES SPOTTING CLUSTER AT telnet://208.15.25.196/ > >Yahoo! Groups Links > > > > > > > > > > >-- >No virus found in this incoming message. >Checked by AVG Anti-Virus. >Version: 7.0.308 / Virus Database: 266.9.16 - Release Date: 4/18/2005 Regards, Chuck Mayfield -- No virus found in this outgoing message. Checked by AVG Anti-Virus. Version: 7.0.308 / Virus Database: 266.9.16 - Release Date: 4/18/2005 The K3UK DIGITAL MODES SPOTTING CLUSTER AT telnet://208.15.25.196/ Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/digitalradio/ <*> 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/
