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switch and half-duplex lines ?

 
 
jh3ang
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      05-20-2006
Hello !

I don't understand that in the following situation how come each host
can have 10 Mbps ?
I mean the router that serves internet connection has just only one
wire to Switch, how can each host can have 10Mbps internet connection ?

*******
Switch is connected with Router, and this Switch has 10 hosts connected
to it with half-duplex.
Switch serves 10Mbps. Router serves internet connection.
*******

 
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Christoph Gartmann
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      05-20-2006
In article <(E-Mail Removed). com>, "jh3ang" <(E-Mail Removed)> writes:
>I don't understand that in the following situation how come each host
>can have 10 Mbps ?
>I mean the router that serves internet connection has just only one
>wire to Switch, how can each host can have 10Mbps internet connection ?
>
>*******
>Switch is connected with Router, and this Switch has 10 hosts connected
>to it with half-duplex.
>Switch serves 10Mbps. Router serves internet connection.
>*******


A 10Mbps connection means the standard definition on how the two devices
exchange information. This doesn't necessarily mean that the actual data
rate is rellay this high. It is similar to electricity: one circuit has a
fuse with 10A, the other may have 16A. This doesn't mean that the actual
flow is that high, it is usually a lot smaller.

Regards,
Christoph Gartmann

--
Max-Planck-Institut fuer Phone : +49-761-5108-464 Fax: -452
Immunbiologie
Postfach 1169 Internet: gartmann@immunbio dot mpg dot de
D-79011 Freiburg, Germany
http://www.immunbio.mpg.de/home/menue.html
 
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BernieM
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      05-21-2006

"jh3ang" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) ups.com...
> Hello !
>
> I don't understand that in the following situation how come each host
> can have 10 Mbps ?
> I mean the router that serves internet connection has just only one
> wire to Switch, how can each host can have 10Mbps internet connection ?
>
> *******
> Switch is connected with Router, and this Switch has 10 hosts connected
> to it with half-duplex.
> Switch serves 10Mbps. Router serves internet connection.
> *******
>


They don't. They have a 10 Mbps link to the switch. The router I assume
also has a 10 Mbps link to the switch that traffic from all 10 hosts gets
funnelled through. Its Internet connection then become a bigger bottleneck
limiting traffic flow from all 10 hosts. TCP then reduces throughput to
some degree based on end-to-end latency etc.

As a side note ... if using a switch configuring links as half duplex is a
bit of a waste.

BernieM


 
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Peter
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      05-21-2006
Greetings,

> *******
> Switch is connected with Router, and this Switch has 10 hosts connected
> to it with half-duplex.
> Switch serves 10Mbps. Router serves internet connection.
> *******


Each of the 10 hosts has a road capable of passing 10 cars at a Time,
however all those roads meet at an intersection to travel down a MAIN
road that can only pass 10 cars at a time. All 100 cars cannot access
the MAIN road at the same time, so they have to QUEUE up to pass
though the intersection to access the MAIN road. This is exactly what
a Switch does, it sequences access for 10 dedicated ports to 1 SHARED
port by Queuing traffic. If all 10 Hosts wanted access at EXACTLY the
same time, then they would only be able to get the equivalent of 1Mb
of bandwidth each.

The PHYSICAL path is 10Mb, but it is extremely rare that you would
find 10 x 10Mb ports all wanting 10Mb at EXACTLY the same time. In
real terms the road is almost NEVER full of traffic, so the 10Mb
Shared port is shared out by Multiplexing the traffic from the other
ports. This multiplexing is handled by a "store and forward" approach.

BTW, if your Switch truly is an Etherswitch and not a Hub, then to get
the best possible performance you should be using a FULL Duplex
setting for all hosts that can support that. A Hub can only do
Half-Duplex.

Cheers.............pk.

--
Peter from Auckland.
 
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jh3ang
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      05-21-2006
Great Answer !

 
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MC
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      05-24-2006
jh3ang wrote:
> Great Answer !
>

All hosts most likely are not streaming a full 10mb worth of data out
either. most are small amoutns of data at anyone time. Most PC's will
not push near that amount of data out with normal web browsing.

We have a few 1000 hosts on our netowrks all going out a 20mb
connection, not using 25 percent of that bandwidth at any peak time.



 
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