145.09 is fine… why move frequency?
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145.09 is fine… Why Move Frequency?. How your packet operating will improve after changing frequency. (Or… Why I don’t want to wait for some guy halfway across the state to stop transmitting before I can get a reasonably good packet connection!). The Present Situation. - PowerPoint PPT PresentationTRANSCRIPT
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145.09 is fine…
Why Move Frequency?
How your packet operating will improve after changing frequency.
(Or… Why I don’t want to wait for some guy halfway across the state to stop transmitting before I can get a
reasonably good packet connection!)
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The Present Situation
• Nearly everyone is on 145.09 throughout the state
• Works fine sometimes but boggs down now and then.
• Cannot get reliable connections to distant nodes.
• Sometimes even my local node doesn’t hear me well.
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When it works… 1 user
• Craig N8KMY connects to the KAL node 15 miles away.
• He hears KAL and KAL hears N8KMY.
• It’s a beautiful thing, no retries, good and fast responses and data throughput.
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Add 1 distant user…
• Lyle AB8CB gets on from the Soo and connects to the WA8OOH-10 Telpac node.
• Neither N8KMY nor KAL can hear AB8CB directly, but KAL can hear WA8OOH-10 marginally.
• The converse is true as WA8OOH can hear KAL, but not N8KMY.
(NOTE: Coverage regions shown may be exaggerated mildly to account for variations in station performance.)
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Some facts to remember…
• A packet station will not transmit if it hears another station currently transmitting on the frequency, even if it’s too weak to copy.
• Any data errors received will cause the incoming packet to be ignored.
• When two stations ‘double’ the resulting audio often has audio products called a ‘heterodyne’ that are of varying levels depending on the comparative signal strengths of the stations doubling.
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Life in Slow Motion..
• N8KMY is connected to KAL and sends the command to read a message.
• AB8CB is connected to WA8OOH-10 and sends the command to read a message
• KAL receives N8KMY’s command just fine, as does WA8OOH-10 receives AB8CB’s command.
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The Slow Response…
• KAL starts transmitting the packet with the message information to N8KMY
• WA8OOH-10 has to wait until KAL is finished sending the packet before it sends it’s information to AB8CB
• AB8CB thinks WA8OOH-10 is a bit slow today, but doesn’t realize WA8OOH-10 is waiting for the large packet from KAL to finish being transmitted.
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Dropped Packet #1…• KAL finishes transmitting and
now WA8OOH-10 is sending it’s long packet to AB8CB.
• N8KMY, hearing the KAL packet, sends the ACK acknowledgement packet to KAL. N8KMY cannot hear WA8OOH-10 and thinks it’s transmitting ‘in the clear’.
• KAL does not decode the ACK from N8KMY because N8KMY ‘doubled’ with WA8OOH-10 and there was enough heterodyne noise in the decoded audio for even a single bit of error in the data.
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Repeated Packet #1…
• Since KAL did not get the ACK acknowledgement packet from N8KMY it resends the long information packet again.
• WA8OOH-10 has to wait again while KAL transmits the retry packet.
• Possibly, while KAL is transmitting the ‘retry packet’, AB8CB is having no luck getting through to WA8OOH-10 because he is now ‘doubling’ with the KAL signal as heard by WA8OOH-10.
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N8KMY is lucky…
• Lucky for N8KMY that WA8OOH-10 was not transmitting when his station sent the ACK acknowledgement to KAL on receipt of the first part of the message information.
• KAL now sends the second information packet of the message N8KMY is reading.
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AB8CB Reads His Mail…
• AB8CB commands WA8OOH-10 to send him his first mail message and lucky for him, KAL was not transmitting at the time.
• WA8OOH-10 has the information packet ready to send but waits for KAL to finish transmitting it’s packet to N8KMY.
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KB8TAS Joins in…
• Jerry, KB8TAS makes a connection to the W8COL COLBBS Tnc-bbs to check for mail.
• COLBBS hears KB8TAS, WA8OOH-10, KAL and N8KMY
• KB8TAS hears KAL and COLBBS but not N8KMY, AB8CB, nor WA8OOH-10
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COLBBS Lists the mail…
• When WA8OOH-10 finishes sending it’s info to AB8CB, COLBBS jumps on and quickly sends it’s information to KB8TAS while KAL waits to send the next packet to N8KMY.
• AB8CB sends an ACK acknowledgement to WA8OOH-10 to acknowledge the last packet heard, but doubles with COLBBS and the ACK packet is lost, WA8OOH-10 will have to resend/retry the previous packet.
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N8KMY wonders what happened…
• N8KMY hasn’t gotten any more text of his message in a while, it is as if KAL doesn’t hear him well any more.
• Lots of packets are flying, but they are all retries with the same data.
(on the right, a young KF8KK holds a bit of data)
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KB8TAS wonders what gives…
• KB8TAS manages to get the mail listing from COLBBS but wonders why it was so slow in coming.
(on the right, WA5ZAI has had enough with retries!)
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Is the Internet down…
• AB8CB thinks that perhaps there’s a problem with the internet gateway at WA8OOH-10 as the mail took ‘forever’ to come in.
(on the right is where dropped packets go– into a place one best not venture!)
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Want to add one more…
• WZ8N from Manistee attempts to connect to DX cluster K8MV-2 via digipeater GRTR00 and get a DX listing
• Use your imagination as to what happens next…
(well– not quite as bad as hurricane katrina.)
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What Was Happening
• Packet works using ‘Carrier Sense Multiple Access’ (CSMA) and expects only one transmitter to be active at any given moment.
• CSMA works great when everyone can hear everyone else– even faintly.
• CSMA fails when there are stations not heard by everyone else--- these are called ‘hidden transmitters’.
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The Hidden Transmitter Dilemma
• When you have ‘hidden transmitters’ there is ‘doubling’ on the packet network which often results in dropped packets and retries.
• Doubling on packet is worse than on FM voice as all you need is one erroneous data bit for the entire packet to get dropped.
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Dismal Future Outlook?
If everyone stayed on the same 145.09 channel…
For every new station that activates the entire system slows down a bit more.
(just like $6 gas would slow the economy!)
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The Solution…
• Move local areas onto isolated frequencies and use network gateways to link these together.
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The Benefits…
• Reliable performance
• Faster response
• Greater functionality (N8KMY would now be able to reliably converse keyboard-to-keyboard with AB8CB, or even WB8TKL waaay downstate.)
(some of the best networks look like a haywired mess at times… well, sort-of)
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How Can I Help?
• Smile when you change the frequency of your packet transceiver.
• Rejoice at the smaller number of retries.
• Encourage more hams to explore the packet mode.
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Final Thoughts
• Packet networks are much like living entities that evolve and change.
• As usage increases there may be another frequency move recommended.
• We’re all in this together, with a common goal, smile and be happy!
73 de KF8KK ([email protected]) 1/2006