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VK2TV > NETWRK 31.07.08 06:13l 52 Lines 1865 Bytes #999 (0) @ WW
BID : 45026_VK2TV
Read: GUEST
Subj: Re: TXDs and DCD
Path: IZ3LSV<IK2XDE<DB0RES<ON0AR<N9ZZK<VK7HDM<VK2TV
Sent: 080731/0357Z @:VK2TV.#MNC.NSW.AUS.OC #:42251 [Kempsey, QF68JX] $:45026_VK
From: VK2TV@VK2TV.#MNC.NSW.AUS.OC
To : NETWRK@WW
# Generated by: TstHWin v2.21b - Registered to VK2TV
# On : 7/31/2008 13:57:12
# UTC: 7/31/2008 3:57:12 A
>From: ZL1ANM@ZL1AB.#06.NZL.OC
>To : NETWRK@WW
>
>
>>From: KV7J@KV7J.#WNV.NV.USA.NA
>>To : NETWRK@USA
>>
>> NET-2.TXT
>> TXDs AND DCD
>> ------------
>>
>>Affecting all network configurations is TXD. This is the period following
>>transmitter key-up and beginning of the packet. Its purpose is to allow
>>time for the transmitter to become fully turned on before the packet
>>commences.
>
>Yes, but that's not its entire purpose. A receiving TNC requires quite a few
>bytes of flag signal to synchronize its clocking mechanism with the incoming
>data, and to determine that this data is in fact flags of the expected baud
>rate. The presence of flags indicates that a packet frame will soon follow.
>
>If TXD is reduced to too small a value, the receiving TNC can miss packets,
>which will have to be resent.
>
>In general, where there is any doubt, an extra 50 milliseconds of TXD flags
>will guarantee good reception while hogging only 50mS of extra channel time
>on each transmission. If those extra 50mS of flags are removed so that TXD
>is at a bare minimum, the time penalty when a frame is missed is not less
>than the time consumed by a repeat request + retransmission of (M x PACLEN),
>where M = Maxframe.
>
>You can see that the benefits of reducing TXD towards absolute minimum become
>scarcely worthwhile, while greatly increasing the danger of missed frames and
>channel overloading due to repeats.
>
>73 de Neil ZL1ANM
>
We need to also consider that not everyone runs unmuted audio to their
TNC/modem. The TXD value needs to take into consideration rx response time.
Cheers ... Ray vk2tv
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