[Elecraft] Ethernet serial servers... Re: USB to serial angst

[Matt Zilmer]

Most networking involves some degree of character-level latency.  In
general, data are arranged in packets (or frames), each of which
contains some number of characters or bytes, as payload.

If data to/from is buffered, it takes time to accumulate enough data
(or to pass enough time) to make it worth the cost to move the packet.
This comes down to buffering, first hop transmission, routing/transit
time, and receiving the packet, then passing back up the stack to the
waiting application or device.  There is more to it, but that's the
basic idea.  Most serial <=> Ethernet connections work like this.

Serial has transit time, plus send/receive processing time, but there
is less buffering since each character is handled independently of
those that follow.  This is true for point to point links like RS232.

USB is similar to networking, but without the routing.  And transit
times are usually quite a bit shorter.  It depends on the USB topology
and a few other things.  But a single hop USB-style could be
significantly shorter than TCP/IP over Ethernet, even 100BaseT.  The
differences are overheads associated with each type of medium and
network configuration / topology.  If a packet enters the "cloud"
(Internet) there is no simple way to predict how soon it will squirt
out at at the destination.

There are more issues than the above, but didn't want to put everyone
to sleep.  And I'm no authority - I'm sure others will add to the mix.
But please don't flame me on this.  I didn't invent TCP/IP or the
Ethernet medium....  :)  Or OC-48, Frame Relay, ATM, Sonet, etc.

73,
matt W6NIA
K3 #24



On Tue, 16 Mar 2010 19:02:41 +0000, you wrote:

>I imagine latency to be small, possibly negligible if one uses a microwave 
>link line of sight.  It's a dream I have to put my K3 in a remote spot with 
>line-of-site control via radio (amateur radio or possibly 2.4GHz 
>licence-free).  Unfortunately I think there are licensing issues over here 
>which might prevent it.  Anyone done it with the K3?
>
>David
>G3UNA
>>
>
>>
>> Agree completely on latency.  Getting low latency on a remote station
>> might be too much until we can set the service quality on the entire path.
>>
>> 73, Tom n4zpt
>> 
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