Re: Netgear MA814 Slow file sharing

> I spent 2 hours on the phone with netgear. They had me trying all sorts
> of stuff. Forcing 5.5Mbps. Forcing 11Mbps.

You do realize of course, that 11Mbps is 5.5 in each direction, right?

It's not 11Mbps in one direction, going both ways.

> You do realize of course, that 11Mbps is 5.5 in each direction, right?
>
> It's not 11Mbps in one direction, going both ways.

Sorry, misinformation.

The signalling rate is 11Mbps period.

What you get in terms of throughput from a half duplex system once you
add on protocol overhead is something completely different.

It's 11Mbps in either direction but not at the same time. That's quite
different from 5.5 each way.



David.

On Mon, 23 Jun 2003 14:23:15 +0100, David Taylor wrote:

> What you get in terms of throughput from a half duplex system once you
> add on protocol overhead is something completely different.

Now now, let's not spread more misinformation. 802.11b is NOT
half-duplex, it's TDD (Time Division Duplexing). This means that the radio
must switch between transmit (Tx) and receive (Rx). The checksums in
802.11b are not transmitted over the air. A checksum is performed in the
MAC and if a packet does not pass, no ACK is sent back to the transmitter.

For 802.11b (which has a theoretical peak and total bandwidth
of 11Mbps) you could either send or receive 11Mbps in "half-duplex" mode
or switch to a "full-duplex" type of operation that lets you send at
5.5Mbps and receive 5.5Mbps simultaneously, or any mixture that totals 11
Mb. You cannot send TCP traffic at more than 5.5Mbps on 802.11b, because
you still need that amount of ACK coming back. If you want to send at
9Mbps outbound, you need enough in the protocol to allow 9Mbps back, i.e.
18Mbps, which 802.11b is not.

So I should be getting 5.5Mbps. I'm getting 2.3Mbps. Where's the
difference? Interference?

Thanks.

Ryan


"John Doe" <(E-Mail Removed)> wrote in message news:<(E-Mail Removed)>...
> On Mon, 23 Jun 2003 14:23:15 +0100, David Taylor wrote:
>
> > What you get in terms of throughput from a half duplex system once you
> > add on protocol overhead is something completely different.
>
> Now now, let's not spread more misinformation. 802.11b is NOT
> half-duplex, it's TDD (Time Division Duplexing). This means that the radio
> must switch between transmit (Tx) and receive (Rx). The checksums in
> 802.11b are not transmitted over the air. A checksum is performed in the
> MAC and if a packet does not pass, no ACK is sent back to the transmitter.
>
> For 802.11b (which has a theoretical peak and total bandwidth
> of 11Mbps) you could either send or receive 11Mbps in "half-duplex" mode
> or switch to a "full-duplex" type of operation that lets you send at
> 5.5Mbps and receive 5.5Mbps simultaneously, or any mixture that totals 11
> Mb. You cannot send TCP traffic at more than 5.5Mbps on 802.11b, because
> you still need that amount of ACK coming back. If you want to send at
> 9Mbps outbound, you need enough in the protocol to allow 9Mbps back, i.e.
> 18Mbps, which 802.11b is not.

> Now now, let's not spread more misinformation. 802.11b is NOT
> half-duplex, it's TDD (Time Division Duplexing). This means that the radio

Ok, splitting hairs, TDD and half duplex are the same thing. Half
duplex, transmit/receive but only in one direction at a time.

> For 802.11b (which has a theoretical peak and total bandwidth
> of 11Mbps) you could either send or receive 11Mbps in "half-duplex" mode

No theory about it, the signalling rate *IS* 11Mbps.

> or switch to a "full-duplex" type of operation that lets you send at
> 5.5Mbps and receive 5.5Mbps simultaneously,

So tell me, how are you going to do that simultaneously with a single
radio...

> you still need that amount of ACK coming back. If you want to send at
> 9Mbps outbound, you need enough in the protocol to allow 9Mbps back, i.e.
> 18Mbps, which 802.11b is not.

If what you suggest were true, any asymmetric connection such as ADSL
would need to have the same upstream bandwidth and well, it doesn't.

David.