Subject: [manet] MAC layer

From: "Ioannis C. Avramopoulos" <[email-masked]>
Date: Fri, 21 Nov 2003 23:33:28 -0500

Dear fellows,

I have a question on the MAC layer used in ad hoc networks.

In 802.11 nodes share the medium, i.e. they use the same
frequency hopping pattern or chip sequence. Had nodes used
orthogonal hopping patterns, spectrum utilization would
significantly increase and, furthermore, the impact of
malicious nodes with respect to jamming would be severely 
mitigated.

I am interested in the reasons that schemes of the latter
type are not considered in the ad hoc community. I would
appreciate it if you could point me to any papers discussing
such issues.

Kind regards,
Yannis

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---

From: Joe Macker <[email-masked]>
Date: Mon, 24 Nov 2003 10:28:29 -0500

>appreciate it if you could point me to any papers discussing

802.11 is "widely available and inexpensive" and has an ad hoc mode 
which makes broadcast neighbor association simple.  

There are NO fundamental reasons why it has to be the MAC layer.
There are many possibilities here.  You've point out one.

There is plenty of work here and you can go back to the 1980s..

---

From: "Petar Popovski" <[email-masked]>
Date: Mon, 24 Nov 2003 21:17:19 +0100

Hello,

In addition to the previous comments, I think that the usage of a single
spreading code can be also related to the fact that WLAN operates in an
unlicensed spectrum. The single random access channel gives some guarantees
about the interference level that a WLAN or group of collocated WLANs can
make to the other collocated entities that operate in the same spectrum.
This is due to the usage of CSMA and the limited number of successful
transmission that can occur simultaneously at the certain spatial point
(clearly, more than one e.g. due to reuse possibility for an exposed
terminal). If there are more spreading codes, the WLANs will have increased
throughput, but at the expense of increased interference level for the other
proximate license-free devices.

Regards,
Petar

---

From: "John Mullen" <[email-masked]>
Date: Mon, 24 Nov 2003 13:47:45 -0700

Hi Joe,

I guess it is good to bear in mind that this is an evolving situation.
My first wireless phone did OK out in the country, but when I moved to
the "big city" I found I needed a phone with more channels to avoid
interference with neighbors.  I think as MANETs and other wireless
solutions become more common, it will become more necessary to include
more sophisticated methods and the simpler, less expensive, alternatives
will be phased out.  In addition, as new technology is developed, the
more sophisticated options will become less and less expensive.
Eventually, manufacturers will not want to support both the older and
newer technology and the old stuff will be phased out.

That is, we'll be able to tell our grand kids about the "good old days"
when there were hot spots, antennas were omni and the leading MAC
protocol was 802.11.

John Mullen
Who remembers crystal radios, 33, 45 and 78 rpm records, when Hollerith
cards were an innovation, and when everybody had to set their watch
every day.

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf Of
Joe Macker
Sent: Monday, November 24, 2003 8:28 AM
To: Ioannis C. Avramopoulos; [email-masked]
Subject: Re: [manet] MAC layer

At 11:33 PM 11/21/2003, Ioannis C. Avramopoulos wrote:

>In 802.11 nodes share the medium, i.e. they use the same frequency 
>hopping pattern or chip sequence. Had nodes used orthogonal hopping 
>patterns, spectrum utilization would significantly increase and, 
>furthermore, the impact of malicious nodes with respect to jamming 
>would be severely mitigated.
>
>type are not considered in the ad hoc community. I would appreciate it 
>if you could point me to any papers discussing such issues.

There are NO fundamental reasons why it has to be the MAC layer. There
are many possibilities here.  You've point out one.

---

From: Joe Macker <[email-masked]>
Date: Mon, 24 Nov 2003 16:30:41 -0500

>newer technology and the old stuff will be phased out.

Absolutely, did you think I wasn't agreeing ? I am.
(Even in the short history since IETFish MANET).
802.11 was relatively expensive and just becoming a standard
while many of use were developing routing solutions and looking
for a cheap off-the-shelf digital radio.  

We had heterogeneous wireless in mind. (there was early
diffused IR work even)..and we still do keep this idea
alive.  Heterogeneity is what IP is good at...and its
partly why we started this WG in this forum.

This is not a research group, but better MACs are certain to 
evolve (the 802 series will move on).  

Some MAC/PHY combinations when they become
widespread realities will likely require some redesign of the 
routing layer interface functions (e.g., different interface type classes).

I worked on a variety of MAC types, including CDMA, in the 80s.,
and I expect to run UWB in my house as a grandad someday...
...let's trade 78s I have some Caruso but its going to cost you ;->

-------------------------

---

From: "John Mullen" <[email-masked]>
Date: Mon, 24 Nov 2003 16:03:35 -0700

Hi Joe,

I figured you would agree.

:-)

Technology is wonderful, when it works.  I suppose one problem in this
working group is trying to come up with a MANET protocol that works, not
only in the variety of situations that exist today, but also in those
likely to exist in the near future.

BTW, we are looking for some "cheap off-the-shelf digital radio" that we
can use over a distance of a few hundred meters.  The only catch is we
are looking for devices that we can connect to a computer and that will
allow us to monitor the received power and/or S/N ratio.  Any
suggestions?

John Mullen

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf Of
Joe Macker
Sent: Monday, November 24, 2003 2:31 PM
To: John Mullen; [email-masked]
Subject: RE: [manet] MAC layer

At 03:47 PM 11/24/2003, John Mullen wrote:
>more sophisticated methods and the simpler, less expensive, 
>alternatives will be phased out.  In addition, as new technology is 
>developed, the more sophisticated options will become less and less 
>expensive. Eventually, manufacturers will not want to support both the 
>older and newer technology and the old stuff will be phased out.

Absolutely, did you think I wasn't agreeing ? I am.
(Even in the short history since IETFish MANET).
802.11 was relatively expensive and just becoming a standard while many
of use were developing routing solutions and looking for a cheap
off-the-shelf digital radio.  

We had heterogeneous wireless in mind. (there was early diffused IR work
even)..and we still do keep this idea alive.  Heterogeneity is what IP
is good at...and its partly why we started this WG in this forum.

Some MAC/PHY combinations when they become
widespread realities will likely require some redesign of the 
routing layer interface functions (e.g., different interface type
classes).

I worked on a variety of MAC types, including CDMA, in the 80s., and I
expect to run UWB in my house as a grandad someday... ...let's trade 78s
I have some Caruso but its going to cost you ;->

---

From: Joe Macker <[email-masked]>
Date: Mon, 24 Nov 2003 19:04:30 -0500

>likely to exist in the near future.

True...

>allow us to monitor the received power and/or S/N ratio.  Any

We are looking for something similar... ;-)

While some selected drivers, cards, and other wireless devices 
allow some level of this .. things could be improved. If you
are going to do something with the information metric provided
at a routing layer or neighbor discovery/management layer 
its also important to know how it was measured and potentially filtered
or not.

IMHO, some general improvements here would be welcome.

-joe

---

From: "John Mullen" <[email-masked]>
Date: Tue, 25 Nov 2003 09:34:40 -0700

Hi Joe,

That's what we figure here, too.  At this point, we're looking for the
card with a S/N or power monitoring port more to validate our stochastic
propagation models, but expect we can use this capability later in other
ways.  If I find something I'll drop a note.

John Mullen

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf Of
Joe Macker
Sent: Monday, November 24, 2003 5:05 PM
To: John Mullen; [email-masked]
Subject: RE: [manet] MAC layer

At 06:03 PM 11/24/2003, John Mullen wrote:
>working group is trying to come up with a MANET protocol that works, 
>not only in the variety of situations that exist today, but also in 
>those likely to exist in the near future.

True...

>BTW, we are looking for some "cheap off-the-shelf digital radio" that 
>we can use over a distance of a few hundred meters.  The only catch is 
>we are looking for devices that we can connect to a computer and that 
>will allow us to monitor the received power and/or S/N ratio.  Any 
>suggestions?

While some selected drivers, cards, and other wireless devices 
allow some level of this .. things could be improved. If you are going
to do something with the information metric provided at a routing layer
or neighbor discovery/management layer 
its also important to know how it was measured and potentially filtered
or not.

-joe

---

From: David Young <[email-masked]>
Date: Tue, 25 Nov 2003 14:11:07 -0600

> ways.  If I find something I'll drop a note.

John,

Virtually all 802.11 radios tell the RSSI for each Rx packet. Some tell
the noise level, also. Are you looking for something different?

Just for example, Lucent and Intersil Prism-based radios tell signal &
noise in ~dB.  I think that Cisco Aironet cards do, also.  Finally, the
Atheros-based radios are most versatile of all the 802.11a/b/g radios,
but AFAIK they only tell Rx signal strength---no noise figure.

I don't know about Linux, but in NetBSD & FreeBSD you can get at the
signal strength information using the Berkeley Packet Filter. Both those
BSDs provide the information through an extensible, hardware-independent
radio header. I have patches for tcpdump that make it interpret the
header. For example, monitoring an Atheros radio:

% sudo ./tcpdump -ne -y ieee802_11_radio -i ath0
listening on ath0, link-type IEEE802_11_RADIO (802.11 plus radio information header), capture size 96 bytes
14:00:58.351473 11.0 Mb/s 2442 MHz (0x00a0) 52dB signal antenna 1
  BSSID:ff:ff:ff:ff:ff:ff DA:ff:ff:ff:ff:ff:ff SA:00:05:5d:da:b0:a9 Probe
  Request (cuw) [1.0* 2.0* 5.5* 11.0* Mbit]

Monitoring a Prism radio:

% sudo ./tcpdump -ne -y ieee802_11_radio -i wi0
listening on wi0, link-type IEEE802_11_RADIO (802.11 plus radio information header), capture size 96 bytes
14:02:20.331138 11.0 Mb/s 2422 MHz BSSID:00:05:5d:89:6a:33
  SA:00:05:5d:da:ac:a8 DA:ff:ff:ff:ff:ff:ff Data IV:3aaaa Pad 0 KeyID 0
14:02:20.334116 11.0 Mb/s 2422 MHz -79dB signal -100dB noise
  DA:00:05:5d:da:ac:a8 BSSID:00:05:5d:89:6a:33 SA:00:05:5d:89:6a:33 Data
  IV:3aaaa Pad 0 KeyID 0

Dave

-- 
David Young             OJC Technologies
[email-masked]      Urbana, IL * (217) 278-3933