- WiFi activists on free Web crusade - Nov. 29, 2002 (fwd)

Eugen Leitl eugen at
Sun Dec 1 02:39:37 PST 2002

On Sat, 30 Nov 2002, Tyler Durden wrote:

> I just don't see how a single WiFi cloud will be able to scale very far. All 
> the WiFi users within "eyeshot" of each other are always going to contend 
> for bandwidth, no? It'll be just like the old half-duplex 10BaseT copper 

There is limited bandwidth within a cell, if you use omni radiators. How 
high is the limit? No one knows, but you can get 100 MBits/s with current 
ultrabroadband prototypes. Then you have stuff like

Wireless Transfer Rate of 10 Gbps Possible, NTT says

Always stretching the boundaries of wireless communications is Japanese 
telecom NTT.

The company?s most recent accomplishment was achieving a peak data 
transfer rate of 2.5 Gbps, breaking the recorded rate of 1 Gbps; NTT 
researchers now believe they will eventually break the 10 Gbps barrier.

As the airwaves become increasingly congested, exploring uncharted 
airwaves could pay NTT high dividends in the future.

As an article in ComputerWire explains, NTT's solution has been to harness 
new electronic and optical technologies to access the empty 120 GHz radio 
band. Optical systems are used to generate the original signal which is 
passed, using amplitude modulation to a 300 GHz photodiode, which creates 
an electrical signal that is passed to a direct slot antenna. The key to 
the whole process is the 300 GHz photodiode, which harnesses optical 
technology, in this case the Lithium Niobate substrate originally designed 
for light switching, to the business of generating an electrical signal.

Commercial viability is still a ways off. At the moment, the sustained 
1.25 Gbps signal generates a range of only 50 cm. Nevertheless, as demand 
for wireless services out strips available spectrum, NTT will no doubt 
find itself swarmed by partners and competitors alike.

Then, you have funky stuff like antenna arrays. People have started 
tinkering on MEMS galvanometers lately, which would allow to use line of 
sight lasers across free space without need for manual alignment; possibly 
dynamically tracking moving objects.

> LANs. And I still don't understand how a WiFi router will help you...if the 

Current routers use an omni to cover local area, and directional aeries to 
create a mesh with their peers. Directional aerials for long-range 
connections have both a longer range and are less sensitive to crosstalk 
from the omni.

> different Layer2 LANs overlap in space at all, they'll interfere with each 
> other optically even if they are on different segments. (With copper you 

Photons are bosons, so they don't interact with each other. Photon 
detectors can and usually have anisotropic sensitivity. Sure you can never 
beat fiber, but line of sight is free...

> didn't even have this problem.) Thus, aren't you stuck with zillions o 
> little WiFi islands that must not overlap without things getting very slow?

> As for service providers not wanting freeloaders, I'd point out that DSL 
> "cares" much less....the DSL connection is mapped over ATM and is basically 

If I have a P2P infrastructure run on end-user owned hardware (little 
boxes glued to windowpanes) across an urban area with ~100 MBps/cell there 
is not all that much use for an ISP.

Things only become difficult if you want to crosslink cities. Here you 
have to use fiber, or similiar.

> a dedicated connection to a router port, with fixed bandwidth in either 
> direction. Whether that port is processing lots of freeloader packets or 
> idle packets from a single dedicated user shouldn't matter much.
> Uh, but now that I think of it ATM does allow for some oversubscription, so 
> in order to maximize the conection between the DSLAM and the ATM switch 
> that's in front of the router (it might be in thesame box as the router, I 
> know!), maybe they'l discourage freeloading. BUT, DSL companies have been 
> touting that they're very happy for you to put a home-based LAN on your side 
> of the connection (Cable Modem providers don't normally like that).

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