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1
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- 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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2
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- 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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3
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- 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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4
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- 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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5
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- 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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6
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- 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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7
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- 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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8
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- 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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9
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- 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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10
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- 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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11
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- 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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12
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- 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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13
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- 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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14
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- 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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15
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- 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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16
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- 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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17
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- 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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18
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- 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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19
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- 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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20
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- 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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21
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- Move local areas onto isolated frequencies and use network gateways to
link these together.
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22
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- 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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23
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- 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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24
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- 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 (kf8kk@iook.org) 1/2006
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Notes
