Re: 2-1 splitter-like jack to be used with CAT5 cables?
From: Enrique Perez-Terron (enrio_at_online.no)
Date: 09/17/05
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Date: Sat, 17 Sep 2005 01:35:03 +0200
On Fri, 16 Sep 2005 21:16:10 +0200, Joe Pfeiffer <pfeiffer@cs.nmsu.edu>
wrote:
> Albretch Mueller <lbrtchx@hotmail.com> writes:
>
>> is there such a thing as a 2-1 splitter-like jack like the ones they
>> use for
>> telephones or broadband/DSL modems with more than one outgoing
>> connector?
>>
>> Or should people use a front telephone splitter and 2 DSL modems?
>
> Ummm, what is it you really want to do?
>
> Trying to answer your questions in reverse order, the second option
> you suggest simply won't work. The two modems will just be stepping
> on each other in trying to talk on the line.
>
> I've got a hunch what you're really asking for with the first option
> is whether there is a way to put two computers on the output from a
> single DSL modem. If I'm guessing right, the answer is "yes, but it
> doesn't look much like a phone Y-jack and internally doesn't work
> anything like the same way." What you're looking for here is a
> "router" with multiple ethernet jacks on the downstream side (assuming
> I'm guessing right on your actual goal).
Based on similar assumptions, my setup could be an example. I have an
ADSL modem and two computers. The ADSL modem speaks PPPoE,
"Point-to-Point Protocol (o)ver Ethernet". In the middle I have an
"ethernet" hub.
(I say "ethernet" in quotes, because the modern equipment running
IEEE 802-dot-something is a bit different from the original ethernet,
but we all keep saying "ethernet". The data contents of the packets
is identical, though.)
Because of the nature of the PPPoE protocol, only one of my PC's can
talk directly to the ADSL modem. But I don't have to flip switches or
disconnect or connect cables to change. I let the first PC establish
the conversation with the ADSL modem, but if that PC goes down or
anything, I just enable the second PC to do the same with a keystroke.
Whichever PC has the PPPoE conversation tells the other and serves as
gateway to the internet. The two PCs have identical firewall/nat
masquerading set up, but the non-gateway will never see its firewall
rules triggered.
When the two PCs talk to eachother, the communication goes through
the same hub. Yet, the communication between the PCs is IP datagrams
while the communication between the gateway and the ADSL modem is not.
But they are all "ethernet" datagrams. The hub only sees the data as
ethernet packets with some (varying) kind of payload. The hub does
not care what the payload is.
Even if the packets go throught the same wires and the same hub, all
the IP datagrams are "inside" the firewall. The PPPoE datagrams
carry the "outside" traffic like in a tunnel.
Compared to Joe's proposed router, my hub is more like a dead wire,
but the PC that is serving as the gateway is the router.
-Enrique
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