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Cayman modem/router in a DSL network question

TXShaman asked
Hey, everyone.  Just wanted to get some quick responses from anyone who can help.  I'm trying to put together a brochure for our clients who want to switch to DSL (from ISDN or dialup).  These are small businesses that may not be able to afford much in the way of equipment... so...

SWBell provides customers in TX with Cayman modems.  I believe these also have a built-in router and DHCP functions.  On the front are 4 10Base-T Ethernet ports.

Okay, let's say that the office has 10 to 20 PCs connected to 2 3Com switches.  A group of servers is also connected to a small hub that is, in turn, plugged into the switches.

So, in my best textual representation:

PC    PC     PC    PC...      Server     Server...
|     |      |     |               |     |
|     |      |     |               |     |
|     |      |     |               _______
|     |      |     |               HUB
|     |      |     |                |
|     |      |     |               |
|     |      |     |              |
      S W I T C H

(Sorry for the lo-tech graphic, but my brain works this way.)

Okay, the DSL modem plugs into the Switch and everyone's happy, right?  Now, my network knowledge isn't very advanced, but my first question is:  I need to connect the switch(es) to the DSL modem using a crossover cable, right?  If not, why?

2nd question:  If the DSL modem/router supports DHCP, then will the PCs on the switches be able to receive IP addresses from the DSL modem?

And finally, if anyone can point me to some really good DSL knowledge bases I would appreciate it.  The ones I've found so far are mediocre, and they include EverythingDSL.com (good, but not as deep as I want to go), and SWBell.net is about useless for info.  Cayman router website is also limited.  Thanks, all.

100 points to the best FIRST discussion that helps me to get a grip on this... 50 points I'll award in a second posting to the runner-up.  Thanks.


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An additional question:  If you connect 4 PCs to a small hub, and then connect that hub into a switch, why will or will not it work?

I guess what my questioning all comes down to is that I haven't figured out what the rules are for connecting dis-similar devices (hubs, switches, routers, etc).  Frequently I see wiring closets with a mixture of devices and want to better understand what the rules are for mixing the devices.  


As long as you have the Uplink/crossover cable correct, it'll work.

The difference between a hub and a switch is:

Hub - sends all packets to all connections and the PC that the packet is intended for uses it and all others ignore it.

Switch - Knows what connection each IP is at and only sends packets for IPs to the correct connector.

So, Hubs use up bandwitch on all connections for every packet and switches don't waste that bandwith.



So a switch can handle a hub that is supporting 4 or more devices?  A switch port doesn't limit itself to only 1 device?  What's to keep a person from buying a 4 port switch and 8 4-port hubs... each hub plugs into a switch so you can support 32 devices on 1 4-port switch?  Would this work?  If it does, what does it do to bandwidth?


Yes, it'll work.

Assuming 100mbit cards/switches/hubs on full duplex.

The 4 port switch would manage all the IPs on each port.  So each port effectively has 200mb of bandwidth.  100mb each way sending and receiving at the same time and only sending to the ports that should have the data.

Each hub would then split the bandwidth between it's ports because it sends all data to all ports.

Now, if you have switches instead of hubs, they should be able to route all traffic on the ports they should go to and in theory give full bandwidth across the whole network.

This is my understanding (from reading the Linksys switch/hub boxes - it is advertising, so, it may be misleading) and I really hope that if I am wrong, someone will read this and let us know.


In an effort to help clean up the open questions, I am going thru old questions that I have participated in.

This question needs closed either by deleting it or PAQing it.

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3. Otherwise, just delete it.

Les MooreSr. Systems Engineer
Top Expert 2008

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I recommend: points to dilligaffuq

if there is any objection or other expert commentary to this recommendation then please post in here within 7 days.


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Finalized as proposed


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