Subject: Re: 45th IETF: Wireless LAN

From: Graham Klyne <[email-masked]>
Date: Thu, 24 Jun 1999 11:03:22 +0100

At 09:21 23/06/99 -0400, John C Klensin wrote:

>From a marketplace standpoint, if one is a lot better in some 
>environments and the other is a lot better in others, I'd expect
>to see:
>
> -- some vendors offering both, with appropriate advertising and 
>    positioning.

FWIW, my take on this, based on DEC literature is:

- Direct Sequence (DS) is faster, giving about 2Mbps.

- Frequency Hopping (FH) is not so fast (at about 1.5Mbps), but is more
robust (noise immune, etc.)

> -- advertising that highlights those differences and advantages

I agree it's not crystal clear.  I'd particularly like to understand how
they compare, performance-wise, under conditions of "moderate interference".

> -- someone working on a dual-mode device

Now that could be nice!

I would also like to know the state of interoperability between different
wireless vendors.  The most recent information I could find (a year or so
old) suggested that MAC/Datalink level interoperability (roughly 802.11, I
think) was quite good, but that higher level protocol interoperability (for
roaming, etc.) was pretty poor.

#g

------------
Graham Klyne
([email-masked])

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From: Amlan Saha <[email-masked]>
Date: Thu, 24 Jun 1999 19:54:57 +0730 (SST)

> robust (noise immune, etc.)

You say FHSS provides for 1.5 Mbps at most and so does a host of other 
literature that I rummaged through.  However, I have with me right
know the manual for the BreezeCOM (from Israel) FHSS cards which are 
marked as Ericsson WLAN Card C3, and in it the promise is for upto 3 
Mbps.  Although, I have not had the time to do measurements and see
the truth of it, I am slightly skeptical.  

What is the general opinion on this ?

-amlan.

-- 
Amlan Saha 		      [email-masked], [email-masked]
Mobile Computing and Protocols Group  
Center for Wireless Comms, 20 Science Park Rd, Singapore 117674
+65.8709.265 (Tel) +65.779.5441 (Fax)   **I speak only for myself**

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From: Amlan Saha <[email-masked]>
Date: Thu, 24 Jun 1999 19:54:57 +0730 (SST)

-amlan.

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From: "Arnoud Zwemmer" <[email-masked]>
Date: Fri, 25 Jun 1999 19:27:05 +0200

Let me brief you on some more recent developments in 
the wireless LAN world. 

DSSS has indeed been standardized for 2 Mbps, 
but the 802.11 High Rate committee is now finalizing
the 11 Mbps standard, which some vendors (such as we)
already offer and others (3Com, Nokia, AiroNet, Symbol) 
have announced products for. This is all DSSS. So, for 
bandwidth, DSSS is definitely the way to go and vendors 
have started realizing that. Interoperability at UNH is 
also further for DSSS than for FHSS.

Resistance to interference, where FHSS used to be better 
in the past, has much improved with the new Harris radios 
mentioned in another mail on this thread. Also, this 
multipath interference is only noticeable in very large 
industry halls and not really at an IETF meeting.

--
Arnoud Zwemmer - [email-masked]
Network Technology Engineer
No Wires Needed, The Netherlands
http://www.nwn.com

> -----Original Message-----
> From: Amlan Saha [mailto:[email-masked]]
> Sent: Thursday, June 24, 1999 2:25 PM
> To: Graham Klyne
> Cc: John C Klensin; ietf
> Subject: Re: 45th IETF: Wireless LAN
> 
> 
> Graham Klyne writes:

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From: "Arnoud Zwemmer" <[email-masked]>
Date: Fri, 25 Jun 1999 19:27:05 +0200

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From: Bill Sommerfeld <[email-masked]>
Date: Fri, 25 Jun 1999 15:05:44 -0400

This is getting into RF esoterica, about which I'm not particularly
expert, but..

> Also, this 

I was confused about the claim that FH dealt better with multipath
than DS.

I recall seeing a presentation from Phil Karn a number of years ago
about Qualcomm's CDMA direct sequence spread spectrum in which he
claimed that the direct sequence decoders that Qualcomm used actually
dealt very well with multipath (I recall that it had something to do
with independantly locking on to the signal at several different
delays and then adding the signals together).  

But I imagine this depends on the exact implementation of the decoder
and I can easly see that capability not being included in a low cost
system..

					- Bill

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From: Bill Sommerfeld <[email-masked]>
Date: Fri, 25 Jun 1999 15:05:44 -0400

- Bill

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From: Henning Schulzrinne <[email-masked]>
Date: Fri, 25 Jun 1999 16:12:09 -0400

http://www.wavelan.com/about/wavelan.html provides a whitepaper
describing the technical differences. While the author(s) obviously are
not exactly unbiased, some of the statements seem at least be subject to
verification and proof rather than just conjecture. Two interesting
facts seem to be the limited packet size for FHSS and the claimed longer
delay due to hopping.
-- 
Henning Schulzrinne   http://www.cs.columbia.edu/~hgs

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From: Henning Schulzrinne <[email-masked]>
Date: Fri, 25 Jun 1999 16:12:09 -0400

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From: "Theodore Y. Ts'o" <[email-masked]>
Date: Fri, 25 Jun 1999 17:01:20 -0400

Date: Fri, 25 Jun 1999 15:05:44 -0400
   From: Bill Sommerfeld <[email-masked]>

As was I....

I remember this as well; in fact, I believe the (counter-intuitive)
assertion that was made was that with DS and a proper decoder, multipath
can *help*.

						- Ted

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From: "Theodore Y. Ts'o" <[email-masked]>
Date: Fri, 25 Jun 1999 17:01:20 -0400

As was I....

						- Ted

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From: [email-masked] (Jim Thompson)
Date: Sat, 26 Jun 1999 01:14:33 -0500

> assertion that was made was that with DS and a proper decoder, multipath

I can attest to this in a real-world situation.  The 'B' concourse at
ORD has 802.11 DS in it.  I thought the multipath would kill the
performance, but one AP covers to within 50' of each end.

Someday I'll go back and put the beamy 'patch' antennas on the AP, and 
pick up the rest of the terminal.  I know of about 20 hotels with
802.11 DS in them as well.  Works great.

Jim

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From: [email-masked] (Jim Thompson)
Date: Sat, 26 Jun 1999 01:14:33 -0500

Jim

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From: Takashi TSUTSUI <[email-masked]>
Date: Sat, 26 Jun 1999 15:52:28 +0900

Multipath is quite common even in a room behind refrigerators, behind wall,
anywhere present.
And moving multipath is quite common in seminar hall.

But fast moving multipath is made by car outdoors.
And DS is not CDMA.

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From: Takashi TSUTSUI <[email-masked]>
Date: Sat, 26 Jun 1999 15:52:28 +0900

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From: Takashi TSUTSUI <[email-masked]>
Date: Sat, 26 Jun 1999 15:56:21 +0900

This mail list is for the expert engineers so, I think this information resource
is better.
You can study basic idea here.

http://grouper.ieee.org/groups/802/11/Tutorial/index.html

But if you need to know in deep, here it is:
ftp://ftp.cs.utwente.nl/pub/doc/802.11/ibmpc/

10 year expert discussion archive is here (^^)\
Here is a better information resource than any selling books.

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From: Takashi TSUTSUI <[email-masked]>
Date: Sat, 26 Jun 1999 15:56:21 +0900