(Ethernet issues) RE: [Asterisk-Users] Survey: Grandstream improvements.........

[Robert Hajime Lanning]

<quote who="Michael T Farnworth">
> On Tue, 21 Oct 2003, rnc Info Lists wrote:
>
>> Michael,
>> How would you be able to connect all phones in a room to one socket?
>> The
>> Ethernet specificiation has a limit to the number of hubs/switches that
>> can be inline.  (or at least it used to).  The only way I can see to
>> connect all phones to one socket would be to daisy chain them.  This
>> would
>> not be a good solution since:
>> - all phones would use the same 10mbps segment, chances for collisions
>>   would be high
>> - rules of Ethernet would be violated so even if it did work it may stop
>>   at any point with some other normally minor change.
>
> I defer to your knowledge in this area, but I would be interested to know
> what the limit is in terms of the number of devices that can be put
> inline.
>
> On the subject of collisions it seems to me that individual phone
> bandwidth use is relatively limited when compared to the 10Mbit/s
> available, so would the problem really be that substantial?
>
> Personally I currently have:
>
> Hub <-> Phone <-> Phone <-> Laptop
>
> No visible problems here, so certainly 3 phones in a line would seem to
> work.  I suppose it all comes down to how many phones you put in a line.
>
> Michael

Too many switches/hubs will cause late collisions.  Late collisions are
ethernet collisions that happen after the transmitting station has finished
transmitting.

If it is a store and forward switch, then the switch can retransmit on
collision, otherwise the packet is completely lost.

This is the same reason why an ethernet cable cannot be over 300 feet.
The first bit of the ethernet frame must get to the farthest node in
an ethernet segment before the last bit is transmitted by the originating
station.  This length is based on speed one bit takes to span the distance
and the minimum ethernet frame size (64 bytes).

Currently the limit is 5 non-"store and forward" switches/hubs.

-- 
END OF LINE