Re: Serial (rs232 etc.) to IP

On 26 Oct 2005 10:57:55 -0700, cs_posting@xxxxxxxxxxx wrote:

>> ..and by doing this also ruin the serial line throughput when a half
>> duplex protocol is used with short message frames. Some converters
>> wait 10-100 ms after the last serial character received, before the
>> (TCP or UDP) IP-frame is sent. For instance at 115200 bit/s, this
>> corresponds to 100-1000 character times.
>
>This is a valid concern, however there's a bit of a problem with single
>character packets when many common embedded TCP devices try to talk to
>common desktop operating systems.
>
>TCP requires that you hang onto all outgoing data until it has been
>acknowledged, because if it's not acknowledged you will have to resend
>it. Most embedded implementations handle this by sending a packet, and
>then being unable to send another until the first has been
>acknowledged. The Windows TCP stack often takes as much as 200 ms to
>acknowledge a packet when only one is outstanding, so single character
>packets can be slowed down to the rate of only five per second!

If you are using a protocol that was initially written for serial line
communication with normal CRC checks and timeout controls, why bother
with TCP, just use simple UDP. If the UDP frame is lost, let the
original serial line protocol timeout mechanism handle any missing
data.

Paul

.

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