Problems with mesh networks

Ofcom's radio carve-up could cut out mesh
<http://www.theregister.co.uk/2008/01/09/sur_proposal/>

Ofcom has published the first of its consultation documents looking
at how Spectrum Usage Rights (SURs) are going to work in the real
world, and the future looks bad for mesh networks with their lack of
centralised control.

The document is a follow-up to the Ofcom statement on SURs, published
last December, and represents a refinement of that proposal. It deals
with specific instances where owners of neighbouring blocks of
spectrum could experience interference, and how Ofcom intends to
respond to any complaints on the matter.

While most of the document (pdf) is pretty technical, it does admit
that control of spectrum usage is dependent on centralised control of
transmitters, something impossible in mesh networks were every node
is responsible for its own communications. Or, as the document puts
it:

In a pure mesh there appears to be no easy way to control the
mobile density or transmitted power. Therefore, it appears to us
at the moment that an operator could not change from an existing
licence to this type of deployment and still be able to
demonstrate that they met their SUR requirements.

Mesh networks have demonstrated their ability to operate in
unlicensed frequency bands,

My comment: Operate, yes, but not in a way that's both efficient and
friendly to other users of that spectrum.

but it's hard to imagine how a company
could make money from licensing spectrum and operating a mesh
network, so the problem may be moot.

Ofcom states they'd be interested in hearing suggestions of how a
mesh could be shown to conform to the SUR, if an operator applies for
a change of use to deploy a mesh - but it's interesting to see how
the open, flexible model can throw up its own technical limitations.

For more on mesh network problems, see
<http://www.dailywireless.org/2004/06/28/ugly-truth-about-mesh-networks/>

Ugly truths about mesh networks - they dont scale - for now.
by Francis daCosta

As founder and CTO of a Wireless Mesh networking company, I have
pondered long and hard about whether or not I should submit this.

The buzz on mesh networking certainly works in our favor. However,
there is more hype than reality around mesh networking. Its time for
a reality check on what mesh can and cannot do.

First, Mesh networks are not a new concept. In some ways, the
internet is a mesh network. And it works, despite its size - because
it does not suffer from the limitations of conventional wireless mesh
networks:

1- Radio is a shared medium and forces everyone to stay silent while
one person holds the stage. Wired networks, on the other hand, can
and do hold multiple simultaneous conversations.

2- In a single radio ad hoc mesh network, the best you can do is
(1/2)^^n at each hop. So in a multi hop mesh network, the Max
available bandwidth available to you degrades at the rate of 1/2,
1/4, 1/8. By the time you are 4 hops away the max you can get is 1/16
of the total available bandwidth.

3- That does not sound too bad when you are putting together a
wireless sensor network with limited bandwidth and latency
considerations. It is DISASTROUS if you wish to provide the level of
latency/throughput people are accustomed to with their wired
networks. Consider the case of just 10 client stations at each node
of a 4 hop mesh network. The clients at the last rung will receive
-at best- 1/(16,0000) of the total bandwidth at the root.

4- Why has this not been noticed as yet? Because first there are not
a lot of mesh networks around and second, they have not been tested
under high usage situations. Browsing and email don t count. Try
video - where both latency and bandwidth matter - or VOIP where the
bandwidth is a measly 64Kbps but where latency matters. Even in a
simple 4 hop ad hoc mesh network with 10 clients, VOIP phones wont
work well beyond the first or second hop the latency and jitter
caused by CSMA/CA contention windows (how wireless systems avoid
collisions) will be unbearable.

Mesh networks are a great concept. But the challenge lies in managing
the dynamics of mesh networks so users receive an acceptable level of
performance in terms of both latency and throughput.

Its time to focus on solving some real problems to make mesh networks
scale and provide stable performance.

--
Best regards, FAQ for Wireless Internet: <http://Wireless.wikia.com>
John Navas FAQ for Wi-Fi: <http://wireless.wikia.com/wiki/Wi-Fi>
Wi-Fi How To: <http://wireless.wikia.com/wiki/Wi-Fi_HowTo>
Fixes to Wi-Fi Problems: <http://wireless.wikia.com/wiki/Wi-Fi_Fixes>

John Navas wrote:

Multi snipped
> For more on mesh network problems, see
> <http://www.dailywireless.org/2004/06/28/ugly-truth-about-mesh-networks/>
>
> Ugly truths about mesh networks - they dont scale - for now.
> by Francis daCosta

> 2- In a single radio ad hoc mesh network, the best you can do is
> (1/2)^^n at each hop. So in a multi hop mesh network, the Max
> available bandwidth available to you degrades at the rate of 1/2,
> 1/4, 1/8. By the time you are 4 hops away the max you can get is 1/16
> of the total available bandwidth.
>

> Mesh networks are a great concept. But the challenge lies in managing
> the dynamics of mesh networks so users receive an acceptable level of
> performance in terms of both latency and throughput.
>
> Its time to focus on solving some real problems to make mesh networks
> scale and provide stable performance.
>
A 2004 document and only concentrating on a single radio system.
What about more up to date info about mesh systems with multiple radios?

I posted these in Dec but you must have missed them.
<http://www.belairnetworks.com/resources/pdfs/Mesh_Capacity_BDMC00040-C02.pdf>
<http://www.belairnetworks.com/resources/pdfs/WP%5FMunicipal%5FBDMC00080%2DA01%2Epdf>
http://www.govtech.com/dc/articles/173754
http://www.ci.minneapolis.mn.us/news...sMplsAward.asp

On Thu, 10 Jan 2008 05:17:57 +0000, LR <(E-Mail Removed)> wrote in
<(E-Mail Removed)>:

>John Navas wrote:
>
>Multi snipped
>> For more on mesh network problems, see
>> <http://www.dailywireless.org/2004/06/28/ugly-truth-about-mesh-networks/>
>>
>> Ugly truths about mesh networks - they dont scale - for now.
>> by Francis daCosta

>A 2004 document and only concentrating on a single radio system.
>What about more up to date info about mesh systems with multiple radios?
>
>I posted these in Dec but you must have missed them.
><http://www.belairnetworks.com/resources/pdfs/Mesh_Capacity_BDMC00040-C02.pdf>
><http://www.belairnetworks.com/resources/pdfs/WP%5FMunicipal%5FBDMC00080%2DA01%2Epdf>
>http://www.govtech.com/dc/articles/173754
>http://www.ci.minneapolis.mn.us/news...sMplsAward.asp

I didn't miss them -- I just didn't find them persuasive.
Mesh networks are still an abomination.

--
Best regards, FAQ for Wireless Internet: <http://Wireless.wikia.com>
John Navas FAQ for Wi-Fi: <http://wireless.wikia.com/wiki/Wi-Fi>
Wi-Fi How To: <http://wireless.wikia.com/wiki/Wi-Fi_HowTo>
Fixes to Wi-Fi Problems: <http://wireless.wikia.com/wiki/Wi-Fi_Fixes>

John Navas wrote:

> I didn't miss them -- I just didn't find them persuasive.
> Mesh networks are still an abomination.
>
You are entitled to your opinion, however the title of "The Register"
article "Ofcom's radio carve-up could cut out mesh" is misleading.
The document by Ofcom refers to licensed spectrum and does not cover
licensed-exempt spectrum, where they are not applying SUR's.

http://www.ofcom.org.uk/consult/condocs/surs/surs.pdf
Mesh networks
2.39 An extension of the situation set out above is a pure mesh network
where there are no base stations and mobile devices communicate between
themselves. Our view is that such networks are unlikely to be deployed
in licensed spectrum. Instead they would be deployed in licence-exempt
spectrum where we do not currently propose to apply SURs. Nevertheless,
we give them some consideration here.

They also ask:-
Q10: Is this an appropriate approach to pure mesh networks?

It is after all a consultation document and they will expect a response
from those with an interest.

On Thu, 10 Jan 2008 12:53:26 +0000, LR <(E-Mail Removed)> wrote in
<i5Cdnd0JdZ-(E-Mail Removed)>:

>John Navas wrote:
>
>> I didn't miss them -- I just didn't find them persuasive.
>> Mesh networks are still an abomination.
>>
>You are entitled to your opinion, however the title of "The Register"
>article "Ofcom's radio carve-up could cut out mesh" is misleading.
>The document by Ofcom refers to licensed spectrum and does not cover
>licensed-exempt spectrum, where they are not applying SUR's.

Interference is an issue whether the spectrum is licensed or unlicensed.

--
Best regards, FAQ for Wireless Internet: <http://Wireless.wikia.com>
John Navas FAQ for Wi-Fi: <http://wireless.wikia.com/wiki/Wi-Fi>
Wi-Fi How To: <http://wireless.wikia.com/wiki/Wi-Fi_HowTo>
Fixes to Wi-Fi Problems: <http://wireless.wikia.com/wiki/Wi-Fi_Fixes>

John Navas wrote:
> On Thu, 10 Jan 2008 12:53:26 +0000, LR <(E-Mail Removed)> wrote in
> <i5Cdnd0JdZ-(E-Mail Removed)>:
>
>> John Navas wrote:
>>
>>> I didn't miss them -- I just didn't find them persuasive.
>>> Mesh networks are still an abomination.
>>>
>> You are entitled to your opinion, however the title of "The Register"
>> article "Ofcom's radio carve-up could cut out mesh" is misleading.
>> The document by Ofcom refers to licensed spectrum and does not cover
>> licensed-exempt spectrum, where they are not applying SUR's.
>
> Interference is an issue whether the spectrum is licensed or unlicensed.
>
Doesn't seem to have stopped people from buying WiFi devices.

On Thu, 10 Jan 2008 15:51:46 +0000, LR <(E-Mail Removed)> wrote in
<(E-Mail Removed)>:

>John Navas wrote:
>> On Thu, 10 Jan 2008 12:53:26 +0000, LR <(E-Mail Removed)> wrote in
>> <i5Cdnd0JdZ-(E-Mail Removed)>:
>>
>>> John Navas wrote:
>>>
>>>> I didn't miss them -- I just didn't find them persuasive.
>>>> Mesh networks are still an abomination.
>>>>
>>> You are entitled to your opinion, however the title of "The Register"
>>> article "Ofcom's radio carve-up could cut out mesh" is misleading.
>>> The document by Ofcom refers to licensed spectrum and does not cover
>>> licensed-exempt spectrum, where they are not applying SUR's.
>>
>> Interference is an issue whether the spectrum is licensed or unlicensed.
>>
>Doesn't seem to have stopped people from buying WiFi devices.

True enough -- the benefits of wireless are greater than the hassles of
interference, but the hassles of interference are widespread and real,
as evidenced by the posts here.

--
Best regards, FAQ for Wireless Internet: <http://Wireless.wikia.com>
John Navas FAQ for Wi-Fi: <http://wireless.wikia.com/wiki/Wi-Fi>
Wi-Fi How To: <http://wireless.wikia.com/wiki/Wi-Fi_HowTo>
Fixes to Wi-Fi Problems: <http://wireless.wikia.com/wiki/Wi-Fi_Fixes>