Why was the hub faster than the switch?

Why was the hub faster than the switch?
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Subject Author Date
Why was the hub faster than the switch? RobW 12-04-2005
Posted by Warren on December 5, 2005, 8:45 pm
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James Knott wrote:
> Even cut through switches have to store data, while waiting for previous
> data to pass. So the first packet will start as cut through, but more and
> more of it will be stored. Any additional packets behind it, will be
> stored until the wire is free. However, TCP has mechanisms to detect such
> congestion and back off the transmission rate, to reduce that congestion.
> Also, some switches can cause a source to slow down.

On the other hand, with a hub there is a potential for more collisions which
will result in delays and re-transmissions. So while there may be an initial
(very minute) hit to through-put when replacing a hub with a switch, as more
devices are added, the switch becomes more and more efficient.

But if we're talking about an internet connection using a cablemodem (as
would be on-topic for this group), this is largely insignificant. It's like
comparing a 0.1% upgrade on a highway vs. a stop sign further up the road.
Hardly worth the time it takes to consider.

--
Warren H.

==========
Disclaimer: My views reflect those of myself, and not my
employer, my friends, nor (as she often tells me) my wife.
Any resemblance to the views of anybody living or dead is
coincidental. No animals were hurt in the writing of this
response -- unless you count my dog who desperately wants
to go outside now.

This fall, vacuum up your leaves instead of raking:
http://www.holzemville.com/mall/blackanddecker/blowers.html




Pure Networks
Posted by Reed on December 5, 2005, 10:17 pm
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Tom Stiller wrote:
>
>
>>f/fgeorge wrote:
>>
>>>wrote:
>>>
>>>
>>>
>>>>Could someone give me a technical reason why, when I connected a cable
>>>>modem
>>>>and three computers to a hub, it was faster than connecting a cable modem
>>>>and three computers with a switch?
>>>>
>>>>I know that routers are the solution, but I am in a debate and am drawing
>>>>on
>>>>my past experience. For example, when using a packet sniffer, you want to
>>>>be a part of the same collision an broadcast domain. You can do that with
>>>>a
>>>>hub, but you can't with a switch.
>>>>
>>>>It must be the same principle when you only have 2 or 3 computers on the
>>>>same network and collisions are not a problem. Am I right and if I am,
>>>>could someone explain why?
>>>>
>>>>TIA
>>>>
>>>
>>>The switch should be faster. The switch directs the data to a specific
>>>port while a hub makes all the lights blink when a data transfer is
>>>underway because it is broadcasting to all of the ports. This slows
>>>down data transfers.
>>>go here for more info: http://www.darron.net/network/secondpage.html
>>>
>>
>>What f/fgeorge says is true but not the whole story. All switches
>>introduce some amount of throughput delay into the data transfer from
>>input port to output port. The delay can be more or less depending on
>>which class of switch; "store and forward", or "cut-through" is used.
>>
>>SF is worst because the complete incoming frame has to be received and
>>"stored" in the switch before it is allowed to start being sent out the
>>output port. This is primarily for error checking purposes.
>>
>>CT is faster because data starts being output as soon as switch has
>>enough data to know which output port to send it to.
>
>
> Does that mean that switches which support speed switching (e.g. 10/100
> Mbps) will always store and forward when moving data between a 10 Mbps
> port and a 100 Mbps port?
>
>
IIRC, all 10/100 switches are store and forward, since cut-through would
fail when the 10M port is the input and 100M is the output (causing an
under-run condition).

Also, it appears some posters still miss the point about sw vs hub being
application dependent. Switches were developed to help those local
networks that had a need for any to any connectivity. When 10 (or any
number more than 1) users on PCs are trying to access the same
cablemodem, a switch is no help, and may actually hurt, as the OP may
have learned the hard way.

--reed


Posted by David H. Lipman on December 6, 2005, 11:03 am
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| IIRC, all 10/100 switches are store and forward, since cut-through would
| fail when the 10M port is the input and 100M is the output (causing an
| under-run condition).
|
| Also, it appears some posters still miss the point about sw vs hub being
| application dependent. Switches were developed to help those local
| networks that had a need for any to any connectivity. When 10 (or any
| number more than 1) users on PCs are trying to access the same
| cablemodem, a switch is no help, and may actually hurt, as the OP may
| have learned the hard way.
|
| --reed

It depends on the POV. The E-switch on a Cable/DSL Router is also being used to
share local
area networking such as IPX/SPX, SMB or NetBIOS over IP. There can be 253 nodes
on such a
SOHO LAN. The collision domain isolation of an E-switch will help on the LAN
side very
well. Additionally, since an E-Switch can send and receive at the same time and
so can DSL
or Cable Internet connections, there is that benefit as well.

The problem is that cheap SHO Router or cheap SOHO standalone E-switches use
cheap chip-sets
with higher latency than their enterprise.corporate counterparts. The trade-off
is lower
price for higher latency.

--
Dave
http://www.claymania.com/removal-trojan-adware.html
http://www.ik-cs.com/got-a-virus.htm



Posted by on December 6, 2005, 7:10 pm
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wrote:

>Could someone give me a technical reason why, when I connected a cable modem
>and three computers to a hub, it was faster than connecting a cable modem
>and three computers with a switch?
>
>I know that routers are the solution, but I am in a debate and am drawing on
>my past experience. For example, when using a packet sniffer, you want to
>be a part of the same collision an broadcast domain. You can do that with a
>hub, but you can't with a switch.
>
>It must be the same principle when you only have 2 or 3 computers on the
>same network and collisions are not a problem. Am I right and if I am,
>could someone explain why?
>
>TIA
>
I bet you had a duplex mis-match on the switch. This would cause
terribly slow speeds compared to a connection on the Hub that was
autonegotiating fine.

I run into this all the time. The first thing I do with any ethernet
connection of any kind is to force the devices to full duplex/100
Mbps. This will eliminate any device from guessing incorrectly during
the N-way negotiation.

With the speeds involved with Home Broadband the various types of
switching methods will have little to do with latency, assuming the
switch didn't come out of a cracker jack box...

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