Re: [gaia] draft-irtf-gaia-alternative-network-deployments. Distinction between 2.4 and 5GHz

You are right, Ermanno!

   Different specifications of 802.11 operate in different frequency
   bands. 802.11b/g/n operates in 2.4 GHz, but 802.11a/n/ac operates in
   5GHz.  This fact is used in some Community Networks in order to
   separate ordinary and "backbone" nodes:

   o  Typical routers running mesh firmware in homes, offices, public
      spaces operate on 2.4 GHz.

   o  Special routers running mesh firmware as well, but broadcasting
      and receiving on the 5 GHz band are used in point-to-point
      connections only.  They are helpful to create a "backbone" on the
      network that can both connect neighborhoods to one another when
      reasonable connections with 2.4 GHz Nodes are not possible, and
      ensure that users of 2.4 GHz nodes are within a few hops to strong
      and stable connections to the rest of the network.

Sorry for the confusion,

Jose 

De: gaia [mailto:gaia-bounces@irtf.org] En nombre de Ermanno Pietrosemoli
Enviado el: jueves, 14 de abril de 2016 11:09
Para: Jose Saldana <jsaldana@unizar.es>
CC: gaia <gaia@irtf.org>; Mitar <mmitar@gmail.com>
Asunto: Re: [gaia] draft-irtf-gaia-alternative-network-deployments. Distinction between 2.4 and 5GHz

Hi Jose,

I suggest a minor modification to this paragraph:

 " o  Special routers running mesh firmware as well, but broadcasting
      and receiving on the 5 GHz band that can travel longer distances
      than 2.4GHz, are used in point-to-point connections only.  They
      are helpful to create a "backbone" on the network that can both:
      connect neighborhoods to one another when reasonable connections
      with 2.4GHz Nodes are not possible, and ensure users of 2.4GHz
      nodes are within a few hops to strong and stable connections to
      the rest of the network "

It is not true that;
"the 5 GHz band that can travel longer distances
      than 2.4GHz"
The propagation losses at 5 GHz are about 6 dB greater than at 2.4 GHz,

In practice, 5 GHz is preferred for point to point longer distances because it is easer to get high gain antennas at this frequency, which more than compensates for the greater propagation loss, leaving a positive balance.

Since this explanation is too long for the already crowded document, I would suggest to only  remove a few words in the paragraph leaving it as:

Special routers running mesh firmware as well, but broadcasting
      and receiving on the 5 GHz band  are used in point-to-point connections only.  They
      are helpful to create a "backbone" on the network that can both
      connect neighborhoods to one another when reasonable connections
      with 2.4GHz Nodes are not possible, and ensure that users of 2.4GHz
      nodes are within a few hops to strong and stable connections to
      the rest of the network

Good day,

Ermanno

On Thu, Apr 14, 2016 at 10:21 AM, Jose Saldana <jsaldana@unizar.es <mailto:jsaldana@unizar.es> > wrote:
Hi,

I think this could be said in section 6.2.1.1. 802.11 (Wi-Fi). I have added some content at the end:

6.2.1.1.  802.11 (Wi-Fi)

   The standard we are most interested in is 802.11 a/b/g/n/ac, as it
   defines the protocol for Wireless LAN.  It is also known as "Wi-Fi".
   The original release (a/b) was issued in 1999 and allowed for rates
   up to 54 Mbit/s.  The latest release (802.11ac) approved in 2013
   reaches up to 866.7 Mbit/s.  In 2012, the IEEE issued the 802.11-2012
   Standard that consolidates all the previous amendments.  The document
   is freely downloadable from IEEE Standards [IEEE].

   The MAC protocol in 802.11 is called CSMA/CA (Carrier Sense Multiple
   Access with Collision Avoidance) and was designed for short
   distances; the transmitter expects the reception of an acknowledgment
   for each transmitted unicast packet; if a certain waiting time is
   exceeded, the packet is retransmitted.  This behavior makes necessary
   the adaptation of several MAC parameters when 802.11 is used in long
   links [Simo_b].  Even with this adaptation, distance has a
   significant negative impact on performance.  For this reason, many
   vendors implement alternative medium access techniques that are
   offered alongside the standard CSMA/CA in their outdoor 802.11
   products.  These alternative proprietary MAC protocols usually employ
   some type of TDMA (Time Division Multiple Access).  Low cost
   equipment using these techniques can offer high throughput at
   distances above 100 kilometers.

   Different specifications of 802.11 operate in different frequency bands.
   802.11b/g/n operates in 2.4 GHz, but 802.11a/n/ac operates in 5GHz.
   This fact is used in some Community Networks in order to separate
   ordinary and "backbone" nodes:

   o  Typical routers running mesh firmware in homes, offices, public
      spaces operate on 2.4 GHz.

   o  Special routers running mesh firmware as well, but broadcasting
      and receiving on the 5 GHz band that can travel longer distances
      than 2.4GHz, are used in point-to-point connections only.  They
      are helpful to create a "backbone" on the network that can both:
      connect neighborhoods to one another when reasonable connections
      with 2.4GHz Nodes are not possible, and ensure users of 2.4GHz
      nodes are within a few hops to strong and stable connections to
      the rest of the network .

Thanks,

Jose

> -----Mensaje original-----
> De: Mitar [mailto:mmitar@gmail.com <mailto:mmitar@gmail.com> ]
> Enviado el: miércoles, 13 de abril de 2016 12:43
> Para: Jose Saldana <jsaldana@unizar.es <mailto:jsaldana@unizar.es> >
> CC: gaia <gaia@irtf.org <mailto:gaia@irtf.org> >
> Asunto: Re: [gaia] draft-irtf-gaia-alternative-network-deployments. Mitar review,
> question #10 Traffic management
>
> Hi!
>
> On Wed, Apr 13, 2016 at 1:33 AM, Jose Saldana <jsaldana@unizar.es <mailto:jsaldana@unizar.es> > wrote:
> >> In community networks is also pretty common to run the network itself
> >> on
> > different
> >> frequencies than the APs. Some first generation mesh networks ran
> > everything
> >> (backbone over ad-hoc) and client-serving APs on the same channel,
> >> but
> > with 5
> >> GHz spectrum and cheap dual-band devices this is often separated now.
> >
> > I think this is interesting. Do you have any reference or example to
> > support this statement?
>
> Hm, this is so common that I am unsure how to reference this. See diagrams here
> for an example:
>
> https://sudoroom.org/wiki/Mesh/Diagrams
>
>
> Mitar
>
> --
> http://mitar.tnode.com/
> https://twitter.com/mitar_m

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-- 
Professor Ermanno Pietrosemoli
Telecommunications/ICT for Development Laboratory (T/ICT4D)
Abdus Salam International Centre for Theoretical Physics  Strada Costiera 11, Trieste 34151, Italy
ermanno@ictp.it <mailto:ermanno@ictp.it>        http://wireless.ictp.it <http://wireless.ictp.it/> 
-------
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Fundación Escuela Latinoamericana de Redes (EsLaRed)
www.EsLaRed.net <http://www.EsLaRed.net> 