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

• 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.

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.

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.)

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.

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.

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.

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.

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.

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.

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.

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

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.

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)

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!)

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!)

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.)

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’.

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.

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!)

The Solution…

• Move local areas onto isolated frequencies and use network gateways to link these together.

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)

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.

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 (kf8kk@iook.org) 1/2006