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Hub vs Switch: Which is better

Posted on 2001-07-23
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Last Modified: 2008-03-04
Hi,
Which is better to use on a 10/100 Ethernet (RJ45)network, a switch or a hub? The switch seems to (generaly) cost more than the hub. And usually more $ means better...but why? Could someone offer an explanation of the benifits and drawbacks of each, please?
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Question by:Jammin
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by:alexcwp
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The Switch is better than the Hub because it is more intelligent. For example, Port A needs to send data to Port B, the hub will simply flood all available ports, while swicth will forward the data to appropriate port. So, u practically have more bandwidth to be used when using switch.

Other than these, switch provides other benefits like VLAN, layer-3 switching, etc.
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by:Jammin
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alexcwp,
Thanks for the explanation but it is the etc's that I am particularly interested in! Could you be more specific and fill in (all) the details. Eg. What is VLAN? Layer-3 switching? etc.
Thanks, Rich
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by:Beluga
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Switches have a number of features that make them more "intelligent" than hubs. Not all of them are truly charecteristics of switches, but you'll find most/all switches have them.

Bridging (the intelligence mentioned by alexcwp) means that the switch keeps track of which MAC addresses are connected to each of it's ports. It then directs traffic only to the relevant destination.

Store & forward: if the switch tries to transmit data to a busy port, but can't because of collisions, it will "back off" and retry a short time later. But it will *still* accept packets for that port and store them in its buffer - it won't drop them. This is more intelligent than the collision-sensing on most hubs and network cards.

Cut through: if the switch still can't get data through, it will "jabber" the port (send it garbage data) until all the other devices on that port detect the busy network and back off. The switch then sends the data in the brief space of time before the other devices retry.

Needless to say, if you've got a busy network that uses all switches (no hubs), then cut-through could be a hinderence rather than a help - each switch fighting with the other for bandwidth. A common way to install networks is to connect the servers to a fast central switch, then connect this to hubs in each department/floor. The switches are then working in the busiest part of the network, which is usually where they are most effective. Although depending on the size of the network, you may need additional switches, eg. one per floor then hubs in each department.

So the answer is - one is not necessarily better than the other, it depends on the application. If switches were always better, no-one would be selling hubs anymore!
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by:Nenadic
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I, personally, disagree with Beluge. I believe that switches ARE always better because, as mentioned above, they offer true bandwidth to each segment (connection between computer and switch), unlike a hub which shares a total bandwidth accross the all computers.

Layer-3 Switching, since you asked, is in effect - routing. Switch understands the IP addressing information, on top of MAC (physical) addressing. This allows a switch to separate your network into broadcast domains and not just collision domains.

VLAN stands for Virtual LAN and means that you can have logically separate networks on the same physical segment. In other words, you can have multiple subnets, using same cable runs. The advantage of this is security mostly, as traffic is not really reduced in this way. But, although the traffic is on same cables, the computers on different VLANs cannot 'see' each other as they have different network addresses.

Also, some switches help reduce overall network traffic in situations where multicasting is used. They can intelligently decide whether to forward multicasts or not, by communicating with neighboring switches.

A lot of advanced switches offer redundancy and failover. And, they can offer Gigabit, fiber optic, as well as 100/10 connectivity, whereas hubs are limited to 100/10.

I think that the only advantage hubs have over switches is the cost. So, if you have a very small network (10 or so computers) a switch may be replaced by a hub. But, there are switches now that are very cheap and even in the above situation, I would be hard-pressed to choose a hub.
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by:Beluga
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Well, I'll agree that it's a contentious issue! :o)

My view is that switches make management and troubleshooting more difficult over a network, eg. packet sniffing. But (on Nenadic's side) more switches means more segments and less traffic per segment overall.

One other view from the web:

"Networks that are not congested can actually be negatively impacted by adding switches. Packet processing delays, switch buffer limitations, and the retransmissions that can result sometimes slows performance compared with the hub based alternative." (See http://www.lantronix.com/training/tutorials/switching.html )

I don't wholly agree with this, but provide it as an example of yet another view. Like I say, it's a contentious issue & I know different people who support different sides of the argument. I stand by my comment "it depends on the application".

I'll also just mention that while many switches support features like VLAN and Layer 3, not all do. You won't find them on cheaper switches, although they are becoming more commonplace.


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by:Nenadic
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Yes, that is an important thing, actually. Switches can start at a hundred dollars and go into tens of thousands. So, naturally, the cheap ones will not be nearly as capable as the most expensive one.

Jammin, my comment above had to do with switches in general, not any one or all of them. So, maybe the best thing would be for you to give us an idea of the structure or intended structure of your network, so that answers can become more specific.
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melchioe earned 300 total points
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I'm gonna quibble about the definition of cut-through switching, since it strongly impacts the whole discussion of the benefits of shared vs. switched.  Cut-through switching improves throughput performance by forwarding frames before the entire frame has been received. Since the port does not wait to receive the CRC at the end if the frame, it cannot determine the integrity of the data received. Switches operating in cut-through mode can propagate invalid frames through a network.

Cut-through in *no way* intentionally jabbers a port.  BTW, the definition of jabber is wrong too - a jabber is defined in the 802.3 standard as a frame longer than the maximum legal size (1518 bytes).  It's not necessarily garbage.

Garbage certainly can result in the case of bad frames, since the switch forwards the frame before the it realizes the frame has an error.  (note that switches (layer 2, not layer 3) do *frames*, not *packets*.  In my experience, sources of bad frames *tend* to be fairly localized (bad NIC, misbehaving driver or software on a PC), and many switches that use cut-through also temporarily change from cut-through to store-and-forward if the error level on a port goes too high.  There are also several different kinds of cut-through: adaptive, FastForward, and FragmentFree (FragmentFree is the default switching mode on the Catalyst 1900 series switch).

A major issue with cut-through is that it doesn't work when going from 10Mbps to 100Mbps - e.g. a 24-port 10mbps switch with a 100 mbps uplink.  For this and other reasons, cut-through is much more common on the edge rather than anywhere near the core.

All that said, switching is ALWAYS better than a shared medium.  The reason you sometimes see a mixed network is purely cost.  The reason you see people still selling hubs is the same - hubs are cheaper, since there is less processing and no memory involved.

if you are planning a relatively simple network (say, less than 100 users, and few segments), with fairly reliable hardware and software, cut-through can be used as long as it's cost effective.  Once you start getting larger, straight store-and-forward is much better, once you factor in troubleshooting issues.  Even if you get better deals with cut-through, I'd stay away from them since it's very hard to troubleshoot the bad frames that sneak through.  Also, if you need to reconfigure your network later and use the swtich to go from 10Mbps to 100Mbps, you won't have to figure out which ones are cut-through if you don't buy any in the first place.

Once final note:  I feel that switches make management and troubleshooting MUCH more straightforward than a shared network.  They also tend to contain problems much better.  Yes, they make sniffing a bit more difficult.  But they also make people stealing information much more difficult (network managers are not the only ones sniffing! :))  If I need to sniff an entire network, I just configure a port as a mirror of the uplink, and then I can sniff to my heart's content.  I'd much rather do that than compromise either efficiency or security of my network.

Did the original question sound like homework to anyone else?
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by:melchioe
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Another thing - that Lantronix statement has a few logical holes in it in my opinion.  When they talk about switch buffer limitation, I can't imagine that any current switch will have buffer problems on a non-congested network (the ONLY situation where Lantronix recommends hubs).  Further, retransmissions are eliminated in a switiching enrivonment unless there is a buffer overflow - and then, it only affects the one node that is ooverflowing its buffer, not anyone else.

Finally, a normally operating Ethernet will lose less than 1% of bandwith to collisions, preferably less than 0.5%.  Once collisions reach 5% of total traffic, you have a clear indication of some problem - either physical layer problems or too many nodes in the collision domain.  
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by:Basseke_NL
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For a clear explanation go to this url:
http://www.wown.com/j_helmig/switch.htm

The difference between them is explained quite clearly. Most of the site is quite okay, if you want to know about windows networking.

Regards,
Bas
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by:GuitarWizard
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Not sure if it was mentioned above as I skimmed through everything, but switches also offer the full amount of bandwidth across all ports...i.e, if you have a 100Mbps 4-port hub, you get 25Mbps per port.  If you have a 100Mbps 4 port switch, you get the full 100Mbps bandwidth at each port.  Throw in full duplexing, and that jumps to 200Mbps.  The more ports you're using, the more of a difference you'll notice between a hub and a switch.  I personally do not use hubs any more, but that's me.

As I'm sure was explained above, with hubs, you get a #$%@load of broadcast traffic on large networks (and even smaller ones if the network use is heavy).  Switches "learn" where the nodes are on the network (store and forward...which I did see mentioned above), therefore all but eliminating broadcast traffic.  This results in a "quiet" network, resulting in generally far less collisions, and a highly efficient network.  

Does price dictate whether or not a product is better?  Not always.  Yeah, switches comparatively cost more than hubs...for the reasons stated above and by everyone else.  But, is a $5,000 Cisco switch better than a $3,000 HP switch?  Depends upon your needs...don't just buy something because it costs more therefore is "supposed to be better".

Go with a switch...
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by:melchioe
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I just remembered another drawback of cut-through switching: in an Ethernet network, if a switch is running in cut-through mode, it counts as a repeater with regards to the 5-4-3 rule.  If it is running in store-and-forward, it acts as a switch and starts the segment count again.  So running store-and-forward will let you increase the depth of layering in a network.  Although it's not generally necessary to go that deep.
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by:wwhitehouse
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Switches are generally much better than hubs.  

Hubs typically have no intellegence associated with them.  The receive a packet on one tap, the repeat it out all the other taps.  This causes all the network traffic to be everywhere.

Switches have several layers of intelligence.  The can be setup to learn what tap has what IP downstream (Tree Spanning)and will only send through that tap.  If the packet fails, it starts again by transmitting it out all the taps until it can identify which part of the tree the destination resides and then only transmit to that IP via that branch.

Other good things about switches is that they do a much cleaner conversion between 10BT and 100BT than any hub I've run across.  So if you have older NIC's or older CAT3 cable in your facility,  The switch can be used to keep the data flowing at the proper rate.

Switches are costing closer & closer to hubs.  If they are in the same cost range, go with the switch.
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by:melchioe
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Welcome to EE, wwhitehouse!  The convention here is that unless you are 300% sure that your answer is correct (and you are the first person posting it), submit your suggestions as a comment rather than an answer.  If you submit as proposed answer, it locks the question, the question disappears from the "waiting for answer" section, and there will be virtually no activity on it after that.

It's a convention that is a tad different than other forums, but it's the way things are usually done here.

Everything you said is generally correct, but your bottom line suggestion was certainly not unique or the first...

Again, welcome to EE!
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by:Jammin
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Thanks ALL!
I'd Like to Accept melchioe's "comment" 7/24/01 @6:22AM
I learned A lot. I'll go with a switch. Thanks to all again.
Rich

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by:Jammin
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Thanks All, I learned Alot.

Rich
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