More than 2 ad-hoc nodes?

I have a question about 802.11g ad-hoc mode. Everything I read refers to
ad-hoc mode as point-to-point, implying that only 2 computers can be so
networked. But I've also seen diagrams implying that an ad-hoc network can
be expanded beyond 2 nodes (no AP), using more than 2 ad-hoc nodes.

So what happens if there are 3 computers with a 802.11g ad-hoc, all
configured with the same SSID? Will all 3 be able to see and talk to each
other without having to disconnect from one and connect with the other? A
with B with C?

Or is 3 computers (one adhoc device per computer) with the same ad-hoc SSID
(within range of each other and on the same channel) illegal?

Thanks,
Bruce.

Hi

There is some Wireless Client Hardware that can do more than two.

However the resultant Network is Quirky.

Given that Wireless Cable DSL Router is close to the price of Client card,
it make much more sense to connect one computer to a Router via cable the
rest can be Wireless.



Jack (MVP-Networking).





"Bruce Chastain" <(E-Mail Removed)> wrote in message
news:uHTGc.5018$(E-Mail Removed) ink.net...
> I have a question about 802.11g ad-hoc mode. Everything I read refers to
> ad-hoc mode as point-to-point, implying that only 2 computers can be so
> networked. But I've also seen diagrams implying that an ad-hoc network
can
> be expanded beyond 2 nodes (no AP), using more than 2 ad-hoc nodes.
>
> So what happens if there are 3 computers with a 802.11g ad-hoc, all
> configured with the same SSID? Will all 3 be able to see and talk to each
> other without having to disconnect from one and connect with the other? A
> with B with C?
>
> Or is 3 computers (one adhoc device per computer) with the same ad-hoc
SSID
> (within range of each other and on the same channel) illegal?
>
> Thanks,
> Bruce.
>
>

Ad-hoc networks can have as many stations as the bandwidth will support.
These networks are called point-to-point to distinguish them from the usual
infrastructure network, which is a hub. The difference is that, in ad-hoc,
each station transmits directly to the receiver - therefore point-to-point,
although the receiver could be any station in the net - while in the
infrastructure (hub) network, all stations transmit to the AP, which
retransmits to the receiver.

"Bruce Chastain" <(E-Mail Removed)> wrote in message
news:uHTGc.5018$(E-Mail Removed) ink.net...
> I have a question about 802.11g ad-hoc mode. Everything I read refers to
> ad-hoc mode as point-to-point, implying that only 2 computers can be so
> networked. But I've also seen diagrams implying that an ad-hoc network
can
> be expanded beyond 2 nodes (no AP), using more than 2 ad-hoc nodes.
>
> So what happens if there are 3 computers with a 802.11g ad-hoc, all
> configured with the same SSID? Will all 3 be able to see and talk to each
> other without having to disconnect from one and connect with the other? A
> with B with C?
>
> Or is 3 computers (one adhoc device per computer) with the same ad-hoc
SSID
> (within range of each other and on the same channel) illegal?
>
> Thanks,
> Bruce.
>
>

> Ad-hoc networks can have as many stations as the bandwidth will support.
> These networks are called point-to-point to distinguish them from the usual
> infrastructure network, which is a hub. The difference is that, in ad-hoc,
> each station transmits directly to the receiver - therefore point-to-point,
> although the receiver could be any station in the net - while in the
> infrastructure (hub) network, all stations transmit to the AP, which
> retransmits to the receiver.

Does that mean that in infrastructure mode, an 11Mb/s link can only
transfer a maximum of about 500KB/s between two nodes (vs 1MB/s between
the hub and any other node) ?


Stefan

"gary" <(E-Mail Removed)> wrote in message
news:%TUGc.11795$(E-Mail Removed) om...
> Ad-hoc networks can have as many stations as the bandwidth will support.
> These networks are called point-to-point to distinguish them from the
usual
> infrastructure network, which is a hub. The difference is that, in ad-hoc,
> each station transmits directly to the receiver - therefore
point-to-point,
> although the receiver could be any station in the net - while in the
> infrastructure (hub) network, all stations transmit to the AP, which
> retransmits to the receiver.

Interesting. Thanks for the helpful answer!

One more thing confuses me. If A and B are in range, and B and C are in
range, but A is not in range of C, will A and C automatically use B as a
relay point? Or is ad-hoc limited to direct connections with no hops?

Thanks again!
Bruce.

Yes, an infrastructure network cuts station-station throughput in half. It's
half-duplex - the same antenna can't be used to transmit and receive
concurrently.

"Stefan Monnier" <(E-Mail Removed)> wrote in message
news:jwvn02bn725.fsf-monnier+(E-Mail Removed)...
> > Ad-hoc networks can have as many stations as the bandwidth will support.
> > These networks are called point-to-point to distinguish them from the
usual
> > infrastructure network, which is a hub. The difference is that, in
ad-hoc,
> > each station transmits directly to the receiver - therefore
point-to-point,
> > although the receiver could be any station in the net - while in the
> > infrastructure (hub) network, all stations transmit to the AP, which
> > retransmits to the receiver.
>
> Does that mean that in infrastructure mode, an 11Mb/s link can only
> transfer a maximum of about 500KB/s between two nodes (vs 1MB/s between
> the hub and any other node) ?
>
>
> Stefan

"Bruce Chastain" <(E-Mail Removed)> wrote in message
news:boVGc.5107$(E-Mail Removed) ink.net...
> "gary" <(E-Mail Removed)> wrote in message
> news:%TUGc.11795$(E-Mail Removed) om...
> > Ad-hoc networks can have as many stations as the bandwidth will support.
> > These networks are called point-to-point to distinguish them from the
> usual
> > infrastructure network, which is a hub. The difference is that, in
ad-hoc,
> > each station transmits directly to the receiver - therefore
> point-to-point,
> > although the receiver could be any station in the net - while in the
> > infrastructure (hub) network, all stations transmit to the AP, which
> > retransmits to the receiver.
>
> Interesting. Thanks for the helpful answer!
>
> One more thing confuses me. If A and B are in range, and B and C are in
> range, but A is not in range of C, will A and C automatically use B as a
> relay point? Or is ad-hoc limited to direct connections with no hops?

Any two stations that want to communicate in an ad-hoc network must be in
range of one another. All communication is direct, and there is no relaying.
It is a common problem in ad-hoc networks for two or more stations to be
out of range of one another. This is called the hidden-node problem, and it
can shut the network down. 802.11 uses carrier sense and collision
avoidance. If B is in range of A and C, but A and C are out of range of one
another, A and C can transmit concurrently. This results in unrecoverable
interference at B, and since A and C don't know they are causing a problem,
they will never co-ordinate access to the network.

>
> Thanks again!
> Bruce.
>
>

In an ad-hoc network, all stations are supposed to be within range of every
other station. This differs from an infrastructure network, in which all
stations must be within range of the access point, but not each other.

Ron Bandes, CCNP, CTT+, etc.

"gary" <(E-Mail Removed)> wrote in message
news:%TUGc.11795$(E-Mail Removed) om...
> Ad-hoc networks can have as many stations as the bandwidth will support.
> These networks are called point-to-point to distinguish them from the
usual
> infrastructure network, which is a hub. The difference is that, in ad-hoc,
> each station transmits directly to the receiver - therefore
point-to-point,
> although the receiver could be any station in the net - while in the
> infrastructure (hub) network, all stations transmit to the AP, which
> retransmits to the receiver.
>
> "Bruce Chastain" <(E-Mail Removed)> wrote in message
> news:uHTGc.5018$(E-Mail Removed) ink.net...
> > I have a question about 802.11g ad-hoc mode. Everything I read refers
to
> > ad-hoc mode as point-to-point, implying that only 2 computers can be so
> > networked. But I've also seen diagrams implying that an ad-hoc network
> can
> > be expanded beyond 2 nodes (no AP), using more than 2 ad-hoc nodes.
> >
> > So what happens if there are 3 computers with a 802.11g ad-hoc, all
> > configured with the same SSID? Will all 3 be able to see and talk to
each
> > other without having to disconnect from one and connect with the other?
A
> > with B with C?
> >
> > Or is 3 computers (one adhoc device per computer) with the same ad-hoc
> SSID
> > (within range of each other and on the same channel) illegal?
> >
> > Thanks,
> > Bruce.
> >
> >
>
>

On Wed, 07 Jul 2004 16:19:19 GMT, "Bruce Chastain"
<(E-Mail Removed)> wrote:

>One more thing confuses me. If A and B are in range, and B and C are in
>range, but A is not in range of C, will A and C automatically use B as a
>relay point? Or is ad-hoc limited to direct connections with no hops?

Direct only. B cannot be used as a repeater to get from A to C.
There's also no access point to use as a client to client repeater.
Clients that can't see each other can't communicate.

You can setup a dedicated repeater to extend the range and coverage
for peer to peer, but it will need to be configured with all the MAC
addresses involved, which could grow quite large. Store-n-forward
will also cut your thruput in half. There are also some client radios
that can act as repeaters, which are the basis of a mesh network.

Peer-to-peer also has some collision issues as there is no access
point to arbitrate transmission times with flow control packets.

Incidentally, 802.11g does NOT officially support peer-to-peer
communications at the faster speed and is limited to 802.11b speeds
for peer-to-peer.


--
Jeff Liebermann (E-Mail Removed)
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 AE6KS 831-336-2558

"Jeff Liebermann" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> On Wed, 07 Jul 2004 16:19:19 GMT, "Bruce Chastain"
> <(E-Mail Removed)> wrote:
>
> >One more thing confuses me. If A and B are in range, and B and C are in
> >range, but A is not in range of C, will A and C automatically use B as a
> >relay point? Or is ad-hoc limited to direct connections with no hops?
>
> Direct only. B cannot be used as a repeater to get from A to C.
> There's also no access point to use as a client to client repeater.
> Clients that can't see each other can't communicate.
>
> You can setup a dedicated repeater to extend the range and coverage
> for peer to peer, but it will need to be configured with all the MAC
> addresses involved, which could grow quite large. Store-n-forward
> will also cut your thruput in half. There are also some client radios
> that can act as repeaters, which are the basis of a mesh network.
>
> Peer-to-peer also has some collision issues as there is no access
> point to arbitrate transmission times with flow control packets.
>
> Incidentally, 802.11g does NOT officially support peer-to-peer
> communications at the faster speed and is limited to 802.11b speeds
> for peer-to-peer.

Actually, I can't find support anywhere in the 802.11g standard for this
claim. It is true that many, if not most, vendors limit ad-hoc to 802.11b
mode, and the reason is understandable. An ad-hoc network cannot be hybrid.
If you have an ad-hoc net of all "g" devices, and a "b" device tries to
join, all clients must detect this and switch to 802.11b mode. This would be
complex and expensive to do correctly, although it's fairly easy for an AP
to do it in an infrastructure setting.

As I read the standard, it simply does not require clients to support ERP in
ad-hoc - it doesn't prohibit it. In fact clause 7 devotes a lot of time to
describing how to handle non-ERP stations joining an all-ERP IBSS. See
7.3.2.13, for example, about setting the nonERP_Present bit in an IBSS when
a beacon from a non-ERP station is received.

>
>
> --
> Jeff Liebermann (E-Mail Removed)
> 150 Felker St #D http://www.LearnByDestroying.com
> Santa Cruz CA 95060 AE6KS 831-336-2558