Community Networks. Definition and taxonomy
draft-manyfolks-gaia-community-networks-00
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Replaced".
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|---|---|---|---|
| Authors | Jose Saldana , Andres Arcia-Moret , Bart Braem , Leandro Navarro , Ermanno Pietrosemoli , Carlos Rey-Moreno, Arjuna Sathiaseelan , Marco Zennaro | ||
| Last updated | 2014-06-18 | ||
| Replaced by | draft-irtf-gaia-alternative-network-deployments, draft-irtf-gaia-alternative-network-deployments, RFC 7962 | ||
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draft-manyfolks-gaia-community-networks-00
Global Access to the Internet for All J. Saldana, Ed.
Internet-Draft University of Zaragoza
Intended status: Informational A. Arcia-Moret
Expires: December 20, 2014 Universidad de Los Andes
B. Braem
University of Antwerp - iMinds
L. Navarro
U. Politecnica Catalunya
E. Pietrosemoli
Escuela Latinoamericana de Redes
C. Rey-Moreno
University of the Western Cape
A. Sathiaseelan
University of Cambridge
M. Zennaro
Abdus Salam ICTP
June 18, 2014
Community Networks. Definition and taxonomy
draft-manyfolks-gaia-community-networks-00
Abstract
Several communities have developed initiatives to build large scale,
self-organized and decentralized community wireless networks that use
wireless technologies (including long distance) due to the reduced
cost of using the unlicensed spectrum. This can be motivated by
different causes: Sometimes the reluctance, or the impossibility, of
network operators to provide wired and cellular infrastructures to
rural/remote areas has motivated the rise of these networks. Some
other times, they are built as a complement and an alternative to
wired Internet access.
These community wireless networks have self sustainable business
models that provide more localised communication services as well as
providing Internet backhaul support through peering agreements with
traditional network operators who see such community led networks as
a way to extend their reach to rural/remote areas at lower cost.
This document defines these networks, summarizes their technological
characteristics and classifies them, also talking about their socio-
economic sustainability models.
There exist other networks, also based on sharing wireless resources
of the users, but not built upon the initiative of the users
themselves, nor owned by them. The characterization of these
networks is not the objective of this document.
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Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on December 20, 2014.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
1.2. Definition . . . . . . . . . . . . . . . . . . . . . . . 4
1.3. Scenarios . . . . . . . . . . . . . . . . . . . . . . . . 4
1.3.1. Developing countries . . . . . . . . . . . . . . . . 4
1.3.2. Rural areas . . . . . . . . . . . . . . . . . . . . . 6
2. Technologies employed . . . . . . . . . . . . . . . . . . . . 7
2.1. Antennas . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2. Link length . . . . . . . . . . . . . . . . . . . . . . . 8
2.3. Layer 2 . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.3.1. The 802.11 standard . . . . . . . . . . . . . . . . . 10
2.3.2. Deployment planning for 802.11 wireless networks . . 11
2.3.3. 802.11af (TVWS) . . . . . . . . . . . . . . . . . . . 13
2.3.4. Other options . . . . . . . . . . . . . . . . . . . . 13
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2.4. Layer 3 . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.4.1. IP addressing . . . . . . . . . . . . . . . . . . . . 13
2.4.2. Routing protocols . . . . . . . . . . . . . . . . . . 13
2.4.2.1. Traditional routing protocols . . . . . . . . . . 13
2.4.2.2. Mesh routing protocols . . . . . . . . . . . . . 14
2.5. Upper layers . . . . . . . . . . . . . . . . . . . . . . 14
2.5.1. Services provided by these networks . . . . . . . . . 15
2.5.1.1. Intranet services . . . . . . . . . . . . . . . . 15
2.5.1.2. Access to the Internet . . . . . . . . . . . . . 16
3. Topology . . . . . . . . . . . . . . . . . . . . . . . . . . 16
4. Classification . . . . . . . . . . . . . . . . . . . . . . . 17
4.1. Community led Wireless Mesh, led by the people . . . . . 17
4.2. Crowdshared approaches, led by the people and third party
stakeholders . . . . . . . . . . . . . . . . . . . . . . 17
4.3. Testbed . . . . . . . . . . . . . . . . . . . . . . . . . 18
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 18
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
7. Security Considerations . . . . . . . . . . . . . . . . . . . 18
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 18
8.1. Normative References . . . . . . . . . . . . . . . . . . 18
8.2. Informative References . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22
1. Introduction
Several communities have developed initiatives to build large scale,
self-organized and decentralized community wireless networks that use
wireless technology (including long distance) due to the reduced cost
of using the unlicensed spectrum. This can be motivated by different
causes: Sometimes the reluctance, or the impossibility, of network
operators to provide wired and cellular infrastructures to rural/
remote areas has motivated the rise of these networks [Pietrosemoli].
Some other times, they are built as a complement and an alternative
to wired Internet access.
These community wireless networks have self sustainable business
models that provide more localised communication services as well as
providing Internet backhaul support through peering agreements with
traditional network operators who see such community led networks as
a way to extend their reach to rural/remote areas at lower cost.
A Community Network MAY or MAY NOT be organized as a company, but in
any case this document only considers those operated and owned by the
community members (e.g. as a cooperative). The fact of setting up a
company is sometimes an advantage: it not only permits the provision
of the service within the current regulatory framework (in some
countries, in order to charge for the services, even in a cost-
recovery mode only, you need to have a licence), but it also allows
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to obtain wholesale prices from other operators when peering, which
are way cheaper than those offered for normal clients, prices which
influence greatly on the uptake of the service and in the financial
sustainability of the Community Network.
There exist other networks, also based on sharing wireless resources
of the users, but not built upon the initiative of the users
themselves, nor owned by them. The characterization of these
networks is not the objective of this document.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
1.2. Definition
Community Networks are large-scale, distributed, self-managed
networks which are built and organized in a decentralized and open
manner. Community Networks start and grow organically, they are open
to participation from everyone agreeing to an open peering agreement.
Knowledge about building and maintaining the network and ownership of
the network itself is decentralized and open. Hardware and software
used in community networks CAN be very diverse, even inside one
network. A Community Network CAN have both wired and wireless links.
The network CAN be managed by multiple routing protocols or network
topology management systems. The network CAN serve as a backhaul for
providing a whole range of services and applications, from completely
free to even commercial services.
1.3. Scenarios
Scenarios where CNs are interesting or have been deployed.
1.3.1. Developing countries
There is no definition for what a developing country represents that
has been recognized internationally, but the term is generally used
to describe a nation with a low level of material well-being. In
this sense, one of the most commonly used classification is the one
by the World Bank, who ranks countries according to their Gross
National Income (GNI) per Capita: low income, middle income, and high
income, being those falling within the low and middle income groups
considered developing economies. Developing countries have been also
defined as those which are in transition from traditional lifestyles
towards the modern lifestyle which began in the Industrial
Revolution. Additionally, the Human Development Index, which
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considers not only the GNI but also life expectancy and education,
has been proposed by the United Nations to rank countries according
to the well-being of a country and not solely based on economic
terms. These classifications are used to give strong signals to the
international community to the need of special concessions in support
of these countries, implying a correlation between development and
increased well-being.
However, at the beginning of the 90's the debates about how to
quantify development in a country were shaken by the appearance of
Internet and mobile phones, which many authors consider the beginning
of the Information Society. With the beginning of this Digital
Revolution, defining development based on Industrial Society concepts
started to be challenged, and links between digital development and
its impact on human development started to flourish. The following
dimensions are considered to be meaningful when measuring the digital
development state of a country: infrastructures (availability and
affordability); ICT sector (human capital and technological
industry); digital literacy; legal and regulatory framework; and
content and services. The lack or less extent of digital development
in one or more of these dimensions is what has been referred as
Digital Divide. This divide is a new vector of inequality which - as
it happened during the Industrial Revolution - generates a lot of
progress at the expense of creating a lot economic poverty and
exclusion. The Digital Divide is considered to be a consequence of
other socio-economic divides, while, at the same time, a reason for
their rise.
In this context, the so-called developing countries, worried of being
left behind of this incipient digital revolution, motivated the World
Summit of the Information Society which aimed at achieving "a people-
centred, inclusive and development-oriented Information Society,
where everyone can create, access, utilize and share information and
knowledge, enabling individuals, communities and peoples to achieve
their full potential in promoting their sustainable development and
improving their quality of life" [WSIS], and called upon
"governments, private sector, civil society and international
organisations" to actively engage to accomplish it [WSIS].
Most efforts from governments and international organizations focused
initially on improving and extending the existing infrastructure for
not leaving their population behind. Universal Access and Service
plans have taken different forms in different countries over the
years, with very uneven success rates, but in most cases inadequate
to the scale of the problem. Given its incapacity to solve the
problem, some governments included Universal Service and Access
obligations to mobile network operators when liberalizing the
telecommunications market. In combination with the overwhelming and
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unexpected uptake of mobile phones by poor people, this has mitigated
the low access indicators existing in many developing countries at
the beginning of the 90s [Rendon].
Although it is undeniable the contribution made by mobile network
operators in decreasing the access gap, its model presents some
constraints that limits the development outcomes that increased
connectivity promises to bring. Prices, tailored for the more
affluent part of the population, remain unaffordable to many, who
invest large percentages of their disposable income in
communications. Additionally, the cost of prepaid packages, the only
option available for the informal economies existing throughout
developing countries, is high compared with the rate longer-term
subscribers pay.
The consolidation of many Community Networks in high income countries
sets a precedent for civil society members from the so-called
developing countries to become more active in the search for
alternatives to provide themselves with affordable access.
Furthermore, Community Networks could contribute to other dimensions
of the digital development like increased human capital and the
creation of contents and services targeting the locality of each
network.
1.3.2. Rural areas
The Digital Divide presented in the previous section is not only
present between countries, but within them too. This is specially
the case for rural inhabitants, which represents approximately 55% of
the World's population, from which 78% inhabit in developing
countries. Although it is impossible to generalize among them, there
exist some common features that have determined the availability of
ICT infrastructure in these regions. The disposable income of their
dwellers is lower than those inhabiting urban areas, with many
surviving on a subsistence economy. Many of them are located in
geographies difficult to access and exposed to extreme weather
conditions. This has resulted in the almost complete lack of
electrical infrastructure. This context, together with their low
population density, discourages telecommunications operators to
provide similar services to those provided to urban dwellers, since
they do not deemed them profitable
The cost of the wireless infrastructure required to set up a
Community Network, including powering them via solar energy, is
within the range of availability if not of individuals at least of
entire communities. The social capital existing in these areas can
allow for Community Network set-ups where a reduced number of nodes
may cover communities whose dwellers share the cost of the
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infrastructure and the gateway and access it via inexpensive wireless
devices. In this case, the lack of awareness and confidence of rural
communities to embark themselves in such tasks can become major
barriers to their deployment. Scarce technical skills in these
regions have been also pointed as a challenge for their success, but
the proliferation of urban Community Networks, where scarcity of
spectrum, scale, and heterogeneity of devices pose tremendous
challenges to their stability and to that of the services they aim to
provide, has fuelled the creation of robust low-cost low-consumption
low-complexity off-the-self wireless devices which make much easier
the deployment and maintenance of these alternative infrastructures
in rural areas.
2. Technologies employed
These networks employ different technologies [WNDW]. They can be
classified according to different criteria:
2.1. Antennas
Three kinds of antennas are suitable to be used in community
networks: omnidirectional, directional and high gain antennas.
For local access, omnidirectional antennas are the most useful, since
they provide the same coverage in all directions of the plane in
which they are located. Above and below this plane, the received
signal will diminish, so the maximum benefits are obtained when the
client is at approximately the same height as the Access Point.
When using an omnidirectional antenna outdoors to provide
connectivity to a large area, people often select high gain antennas
located at the highest structure available to extend the coverage.
In many cases this is counterproductive, since a high gain
omnidirectional antenna will have a very narrow beamwidth in the
vertical plane, meaning that clients that are below the plane of the
antenna will receive a very weak signal (and by the reciprocity
property of all antennas, the omni will also receive a feeble signal
from the client). So a moderate gain omnidirectional of about 8 to
10 dBi is normally preferable. Higher gain omnis antennas are only
advisable when the farthest way client are roughly in the same plane.
For indoor clients, omnis are generally fine, because the numerous
reflections normally found in indoor environments negate the
advantage of using directive antennas.
For outdoor clients, directive antennas can be quite useful to extend
coverage to an Access Point fitted with an omni.
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When building point to point links, the highest gain antennas are the
best choice, since their narrow beamwidth mitigates interference from
other users and can provide the longest links [Flickenger] [Zennaro].
24 to 34 dBi antennas are commercially available at both the
unlicensed 2.4 GHz and 5 GHz bands, and even higher gain antennas can
be found in the newer unlicensed bands at 17 GHz and 24 GHz.
Despite the fact that the free space loss is directly proportional to
the square of the frequency, it is normally advisable to use higher
frequencies for point to point links when there is a clear line of
sight, because it is frequently easier to get higher gain antennas at
5 GHz. Deploying high gain antennas at both ends will more than
compensate for the additional free space loss. Furthermore, higher
frequencies can make due with lower altitude antenna placement since
the Fresnel zone is inversely proportional to the square root of the
frequency.
On the contrary, lower frequencies offer advantages when the line of
sight is blocked because they can leverage diffraction to reach the
intended receiver.
It is common to find dual radio Access Points, at two different
frequency bands. One way of benefiting from this arrangement is to
attach a directional antenna to the high frequency radio for
connection to the backbone and an omni to the lower frequency to
provide local access.
Of course, in the case of mesh networking, where the antenna should
connect to several other nodes, it is better to use omnidirectional
antennas.
Keep also in mind that the same type of polarisation must be used at
both ends of any radio link. For point to point links, some vendor
use two radios operating at the same frequency but with orthogonal
polarisations, thus doubling the achievable throughput, and also
offering added protection to multipath and other transmission
impairments.
2.2. Link length
For short distance transmission, there is no strict requirement of
line of sight between the transmitter and the receiver, and multipath
can guarantee communication despite the existence of obstacles in the
direct path.
For longer distances, the first requirement is the existence of an
unobstructed line of sight between the transmitter and the receiver.
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For very long path the earth curvature is an obstacle that must be
cleared, but the trajectory of the radio beam is not strictly a
straight line due to the bending of the rays as a consequence of non-
uniformities of the atmosphere. Most of the time this bending will
mean that the radio horizon extends further than the optical horizon.
Another factor to be considered is that radio waves occuppy a volume
around the optical line, which must be unencumbered from obstacles
for the maximum signal to be captured at the receiver. This volume
is known as the Fresnel ellipsoid and its size grows with the
distance between the end points and with the wavelength of the
signal, which in turn is inversely proportional to the frequency.
So, for optimum signal reception the end points must be high enough
to clear any obstacle in the path and leave extra "elbow room" for
the Fresnel zone. This can be achieved by using suitable masts at
either end, or by taking advantage of existing structures or hills.
Once a clear radio-electric line of sight (including the Fresnel zone
clearance) is obtained, one must ascertain that the received power is
well above the sensitivity of the receiver, by what is known as the
link margin. The greater the link margin, the more reliable the
link. For mission critical applications 20 dB margin is suggested,
but for non critical ones 10 dB might suffice.
Bear in mind that the sensitivity of the receiver decreases with the
transmission speed, so more power is needed at greater transmission
speeds.
The received power is determined by the transmitted power, the gain
of the transmitting and receiving antennas and the propagation loss.
The propagation loss is the sum of the free space loss (proportional
to the square of the the frequency and the square of the distance),
plus additional factors like attenuation in the atmosphere by gases
or meteorological effects (which are strongly frequency dependent),
multipath and diffraction losses.
Multipath is more pronounced in trajectories over water, if they
cannot be avoided special countermeasures should be taken.
So to achieve a given link margin (also called fade margin), one can:
a) increase the output power.The maximum transmitted power is
specified by the country's regulation, and for unlicensed frequencies
is much lower than for licensed frequencies.
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b) Increase the antenna gain. There is no limit in the gain of the
receiving antenna, but high gain antennas are bulkier, present more
wind resistance and require sturdy mounts to comply with tighter
alignment requirements. The transmitter antenna gain is also
regulated and can be different for point to point as for point to
multipoint links. Many countries impose a limit in the combination
of transmitted power and antenna gain, the EIRP (Equivalent
Isotropically Irradiated Power) which can be different for point to
point or point to multipoint links.
c) Reduce the propagation loss, by using a more favourable frequency
or a shorter path.
d) Use a more sensitive receiver. Receiver sensitivity can be
improved by using better circuits, but it is ultimately limited by
the thermal noise, which is proportional to temperature and
bandwidth. So one can increase the sensitivity by using a smaller
receiving bandwidth, or by settling to lower throughput even in the
same receiver bandwidth. This step is often done automatically in
many protocols, in which the transmission speed can be reduced say
from 150 Mbit/s to 6 Mbit/s if the receiver power is not enough to
sustain the maximum throughput.
A completely different limiting factor is related with the medium
access protocol. WiFi was designed for short distance, and the
transmitter expects the reception of an acknowledgment for each
transmitted packet in a certain amount of time, if the waiting time
is exceeded, the packet is retransmitted. This will reduce
significantly the throughput at long distance, so for long distance
application it is better to use a different medium access technique,
in which the receiver does not wait for an acknowledge of the
transited packet. This strategy of TDMA (Time Domain Multiple
Access) has been adopted by many equipment vendors who offer
proprietary protocols alongside the standard WiFi in order to
increase the throughput at longer distances. Low cost equipment
using TDMA can offer high throughput at distances over 100
kilometres.
2.3. Layer 2
2.3.1. The 802.11 standard
Wireless standards ensure interoperability and usability by those who
design, deploy and manage wireless networks. The Standards used in
the vast majority of Community Networks come from the IEEE Standard
Association's IEEE 802 Working Group.
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The standard we are most interested in is 802.11 a/b/g/n, as it
defines the protocol for Wireless LAN. Different 802.11 amendments
have been released, as shown in the table below, also including their
frequencies and approximate ranges.
|802.11| Release | Freq |BWdth | Data Rate per | Approx range (m) |
|prot | date | (GHz)|(MHz) |stream (Mbit/s) | indoor | outdoor |
+------+---------+------+------+----------------+--------+----------+
| a |Sep 1999 | 5 | 20 | 6,9,12, 18, 24,| 35 | 120 |
| | | | | 36, 48, 54 | | |
| b |Sep 1999 | 2.4 | 20 | 1, 2, 5.5, 11 | 35 | 140 |
| g |Jun 2003 | 2.4 | 20 | 6,9,12, 18, 24,| 38 | 140 |
| | | | | 36, 48, 54 | | |
| n |Oct 2009 | 2.4/5| 20 | 7.2, 14.4, 21.7| 70 | 250 |
| | | | | 28.9, 43.3, | | |
| | | | | 57.8, 65, 72.2 | | |
| n |Oct 2009 | 2.4/5| 40 | 15, 30, 45, 60,| 70 | 250 |
| | | | | 90, 120, | | |
| | | | | 135, 150 | | |
| ac |Nov 2011 | 5 | 20 | Up to 87.6 | | |
| ac |Nov 2011 | 5 | 40 | Up to 200 | | |
| ac |Nov 2011 | 5 | 80 | Up to 433.3 | | |
| ac |Nov 2011 | 5 | 160 | Up to 866.7 | | |
In 2012 IEEE issued the 802.11-2012 Standard that consolidates all
the previous amendments. The document is freely downloadable from
IEEE standards [IEEE].
2.3.2. Deployment planning for 802.11 wireless networks
Before packets can be forwarded and routed to the Internet, layers
one (the physical) and two (the data link) need to be connected.
Without link local connectivity, network nodes cannot talk to each
other and route packets.
To provide physical connectivity, wireless network devices must
operate in the same part of the radio spectrum. This is means that
802.11a radios will talk to 802.11a radios at around 5 GHz, and
802.11b/g radios will talk to other 802.11b/g radios at around 2.4
GHz. But an 802.11a device cannot interoperate with an 802.11b/g
device, since they use completely different parts of the
electromagnetic spectrum. More specifically, wireless interfaces
must agree on a common channel. If one 802.11b radio card is set to
channel 2 while another is set to channel 11, then the radios cannot
communicate with each other.
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When two wireless interfaces are configured to use the same protocol
on the same radio channel, then they are ready to negotiate data link
layer connectivity. Each 802.11a/b/g device can operate in one of
four possible modes:
1.Master mode (also called AP or infrastructure mode) is used to
create a service that looks like a traditional access point. The
wireless interface creates a network with a specified name (called
the SSID) and channel, and offers network services on it. While in
master mode, wireless interfaces manage all communications related to
the network (authenticating wireless clients, handling channel
contention, repeating packets, etc.) Wireless interfaces in master
mode can only communicate with interfaces that are associated with
them in managed mode.
2.Managed mode is sometimes also referred to as client mode.
Wireless interfaces in managed mode will join a network created by a
master, and will automatically change their channel to match it.
They then present any necessary credentials to the master, and if
those credentials are accepted, they are said to be associated with
the master. Managed mode interfaces do not communicate with each
other directly, and will only communicate with an associated master.
3.Ad-hoc mode creates a multipoint-to-multipoint network where there
is no single master node or AP. In ad-hoc mode, each wireless
interface communicates directly with its neighbours. Nodes must be
in range of each other to communicate, and must agree on a network
name and channel. Ad-hoc mode is often also called Mesh Networking.
4.Monitor mode is used by some tools (such as Kismet) to passively
listen to all radio traHc on a given channel. When in monitor mode,
wireless interfaces transmit no data. This is useful for analysing
problems on a wireless link or observing spectrum usage in the local
area. Monitor mode is not used for normal communications.
When implementing a point-to-point or point-to-multipoint link, one
radio will typically operate in master mode, while the other(s)
operate in managed mode. In a multipoint-to-multipoint mesh, the
radios all operate in ad-hoc mode so that they can communicate with
each other directly. Remember that managed mode clients cannot
communicate with each other directly, so it is likely that you will
want to run a high repeater site in master or ad-hoc mode. Ad-hoc is
more flexible but has a number of performance issues as compared to
using the master / managed modes.
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2.3.3. 802.11af (TVWS)
Some Community Networks make use of TV White Spaces, using 802.11af
standard.
2.3.4. Other options
802.11 is not the only layer 2 option to be used in Community
Networks.
2.4. Layer 3
2.4.1. IP addressing
Most known Community Networks started in or around the year 2000.
IPv6 was fully specified by then, but most almost all Community
Networks still use IPv4. A community networks survey [Avonts]
indicated that IPv6 rollout forms a challenge to Community Networks.
Most Community Networks use private IPv4 address ranges, as defined
by RFC 1918 [RFC1918]. The motivation for this was the lower cost
and the simplified IP allocation because of the large available
address ranges.
2.4.2. Routing protocols
Community Networks are composed of possibly different layer 2
devices, resulting in a mesh of Community Network nodes. Connection
between different nodes is not guaranteed, the link stability can
vary strongly over time. To tackle this, some Community Networks use
mesh network routing protocols while other networks use more
traditional routing protocols. Some networks operate multiple
routing protocols in parallel. E.g., they use a mesh protocol inside
different islands and use traditional routing protocols to connect
islands.
2.4.2.1. Traditional routing protocols
The BGP protocol, as defined by RFC 4271 [RFC4271] is used by a
number of Community Networks, because of its well-studied behavior
and scalability.
For similar reasons, smaller Community Networks opt to run the OSPF
protocol, as defined by RFC 2328 [RFC2328].
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2.4.2.2. Mesh routing protocols
A large number of Community Networks use the OLSR routing protocol as
defined in RFC 3626 [RFC3626]. The pro-active link state routing
protocol is a good match with Community Networks because it has good
performance in mesh networks where nodes have multiple interfaces.
The Better Approach To Mobile Adhoc Networking (B.A.T.M.A.N.)
[Abolhasan]protocol was developed by member of the Freifunk
community. The protocol handles all routing at layer 2, creating one
bridged network.
Parallel to BGP, some networks also run the BMX6 protocol [Neumann].
This is an advanced version of the BATMAN protocol which is based on
IPv6 and tries to exploit the social structure of Community Networks.
2.5. Upper layers
From crowd shared perspective, and considering just regular TCP
connections during the critical sharing time, the Access Point
offering the CN service is likely to be the bottleneck of the
connection. This is the main concern of sharers, having several
implications. There should be an adequate Active Queue Management
(AQM) mechanism that implement a Less than Best Effort policy for the
CN user and protect the sharer. Achieving LBE behaviour requieres
the appropriate tuning of the well known mechanisms such as ECN, or
RED, or others more recent AQM mechanisms such as CoDel and PIE that
aid on keeping low latency RFC 6297 [RFC6297].
The CN user traffic should not interfere with the sharers traffic.
However, other bottlenecks besides client's access bottleneck may not
be controlled by previously mentioned protocols. And so, recently
proposed transport protocols like LETBAT [reference required] with
the purpose of transporting scavenger traffic may be a solution.
LEDBAT requieres the cooperation of both the client and the server to
achieve certain target delay, therefore controlling the impact of the
CN user all along the path.
There are applications that manage aspects of CN from the sharer side
and from the client side. From sharer's side, there are applications
to centralise the management of the APs conforming the CN that have
been recently proposed by means of SDN [Sathiaseelan_a] [Suresh].
There are also other proposals such as Wi2Me [Lampropulos] that
manage the connection to several CNs from the client's side. This
application have shown to improve the client performance compared to
a single-CN client.
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On the other hand, transport protocols inside a multiple hop wireless
mesh network are likely to suffer performance degradation for
multiple reasons, e.g., hidden terminal problem, unnecessary delays
on the TCP ACK clocking that decrease the throughout or route
changing [Hanbali]. So, there are some options for network
configuration. The implementation of an easy-to-adopt solution for
TCP over mesh networks may be implemented from two different
perspectives. One way is to use a TCP-proxy to transparently deal
with the different impairments RFC 3135 [RFC3135]. Another way is to
adopt end-to-end solutions for monitoring the connection delay so
that the receiver adapts the TCP reception window (rwnd)
[Castignani_c]. Similarly, the ACK Congestion Control (ACKCC)
mechanism RFC 5690 [RFC5690] could deal with TCP-ACK clocking
impairments due to inappropriate delay on ACK packets. ACKCC
compensates in an end-to-end fashion the throughput degradation due
to the effect of media contention as well as the unfairness
experienced by multiple uplink TCP flows in a congested WiFi access.
2.5.1. Services provided by these networks
This section provides an explaining of the services between hosts
inside the CN. They can be divided into Intranet services,
connecting hosts between them, and Internet services, connecting to
nodes outside the network.
2.5.1.1. Intranet services
- VoIP (e.g. with SIP)
- remote desktop (e.g. using my computer and my Internet connection
when I am on holidays in a village).
- FTP file sharing (e.g. distribution of Linux software).
- P2P file sharing.
- public video cameras.
- DNS.
- online games servers.
- jabber instant messaging.
- IRC chat.
- weather stations.
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- NTP.
- Network monitoring.
- videoconferencing / streaming.
- Radio streaming.
2.5.1.2. Access to the Internet
2.5.1.2.1. Web browsing proxies
A number of federated proxies provide web browsing service for the
users. Other services (file sharing, skype, etc.) are not usually
allowed.
2.5.1.2.2. Use of VPNs
Some "micro-ISPs" may use the CN as a backhaul for providing Internet
access, setting up VPNs from the client to a machine with Internet
access.
3. Topology
These networks follow different topology patterns, as studied in
[Vega].
Regularly rural areas in CNs are connected through long-distance
links (the so-called community mesh approach) which in turn convey
the Internet connection to relevant organisations or institutions.
In contrast, in urban areas, users tend to share and require mobile
access. Since these areas are also likely to be covered by
commercial ISPs, the provision of wireless access by Virtual
Operators like FON is the way to extend the user capacity (or gain
connection) to the network. Other proposals like Virtual Public
Networks [Sathiaseelan_a] can also extend the service.
As in the case of main Internet Service Providers in France,
Community Networks for urban areas are conceived as a set of APs
sharing a common SSID among the clients favouring the nomadic access.
For CNs users in France, ISPs promise to cause a little impact on
their service agreement when the CN service is activated on clients'
APs. Nowadays, millions of APs are deployed around the country
performing services of nomadism and 3G offloading, however as some
studies demonstrate, at peatonal speed, there is a fair chance of
performing file transfers [Castignani_a] [Castignani_b]. In studied
scenarios in France and Luxembourg the density of APs around the
urban areas (mainly in downtown and residential areas) there is a
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crowded deployment of APs for the different ISPs. Moreover,
performed studies reveal that aggregating available networks can be
beneficial to the client by using an application that manage the best
connection among the different CNs. For improving the scanning
process (or topology recognition), which consumes the 90% of the
connection/reconnection process to the Community Network, the client
may implement several techniques for selecting the best AP
[Castignani_c].
4. Classification
This section classifies Community Networks according to their
intended usage. Each of them have different incentive structures,
maybe common technological challenges but most importantly
interesting usage challenges which feeds into the incentives as well
as technological challenges
Some networks exist, which they are outside the scope of the present
document. A first example are the networks created and managed by
City Councils (e.g., [Heer]).Some companies [FON reference missing]
develop and sell Wi-Fi routers with a dual access: a Wi-Fi network
for the user, and a shared one. A user community is created, an
people can join it different ways: they can buy a dual router, so
they share their connection and in turn they get access to all the
routers associated to the community. Some users can even get some
revenues every time another user connects to their Wi-Fi spot. Other
users can just buy some passes in order to use the network. Some
telecommunications operators can collaborate with the community,
including in their routers the possibility of creating these two
networks.
4.1. Community led Wireless Mesh, led by the people
These networks grow organically, since they are formed by the
aggregation of nodes belonging to different users. A minimum
governance infrastructure is required in order to coordinate IP
addressing, routing, etc. A clear example of this kind of Community
Network is described in [Braem].
4.2. Crowdshared approaches, led by the people and third party
stakeholders
These networks follow the next approach: the home router creates two
wireless networks, one of them to be normally used by the owner, and
the other one is public. A small fraction of the bandwidth is
allocated to the public network (as e.g. Less-than-best-effort or
scavenger traffic), to be employed by any user of the service in the
immediate area. An example is described in [PAWS].
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A Virtual Private Network (VPN) is created for public traffic, so it
is completely secure and separated from the owner's connection. The
network capacity shared may employ a less-than-best-effort approach,
so as not to harm the traffic of the owner of the connection
[Sathiaseelan_a].
There are three actors in the scenario:
- End users who sign up for the service and share their network
capacity. As a counterpart, they can access anyone's home broadband
for free.
- Virtual Network Operators (VNOs) are stakeholders with socio-
environmental objectives. They can be a local government, grass root
user communities, charities, or even content operators, smart grid
operators, etc. They are the ones who actually run the service.
- Network operators, who have a financial incentive to lease out the
unused capacity [Sathiaseelan_b] at lower cost to the VNOs.
VNOs pay the sharers and the network operators, thus creating an
incentive structure for all the actors: the end users get money for
sharing their network, the network operators are paid by the VNOs,
who in turn accomplish their socio-environmental role.
4.3. Testbed
In some cases, the initiative to start the network is not from the
community, but from a research entity (e.g., a university), with the
aim of using it for research purposes [Samanta].
5. Acknowledgements
6. IANA Considerations
This memo includes no request to IANA.
7. Security Considerations
No security issues have been identified for this document.
8. References
8.1. Normative References
[RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
E. Lear, "Address Allocation for Private Internets", BCP
5, RFC 1918, February 1996.
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.
[RFC3135] Border, J., Kojo, M., Griner, J., Montenegro, G., and Z.
Shelby, "Performance Enhancing Proxies Intended to
Mitigate Link-Related Degradations", RFC 3135, June 2001.
[RFC3626] Clausen, T. and P. Jacquet, "Optimized Link State Routing
Protocol (OLSR)", RFC 3626, October 2003.
[RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
Protocol 4 (BGP-4)", RFC 4271, January 2006.
[RFC5690] Floyd, S., Arcia, A., Ros, D., and J. Iyengar, "Adding
Acknowledgement Congestion Control to TCP", RFC 5690,
February 2010.
[RFC6297] Welzl, M. and D. Ros, "A Survey of Lower-than-Best-Effort
Transport Protocols", RFC 6297, June 2011.
8.2. Informative References
[Abolhasan]
Abolhasan, M., Hagelstein, B., and J. Wang, "Real-world
performance of current proactive multi-hop mesh
protocols", In Communications, 2009. APCC 2009. 15th Asia-
Pacific Conference on (pp. 44-47). IEEE. , 2009.
[Avonts] Avonts, J., Braem, B., and C. Blondia, "A Questionnaire
based Examination of Community Networks", Proceedings
Wireless and Mobile Computing, Networking and
Communications (WiMob), 2013 IEEE 8th International
Conference on (pp. 8-15) , 2013.
[Braem] Braem, B., Baig Vinas, R., Kaplan, A., Neumann, A., Vilata
i Balaguer, I., Tatum, B., Matson, M., Blondia, C., Barz,
C., Rogge, H., Freitag, F., Navarro, L., Bonicioli, J.,
Papathanasiou, S., and P. Escrich, "A case for research
with and on community networks", ACM SIGCOMM Computer
Communication Review vol. 43, no. 3, pp. 68-73, 2013.
[Castignani_a]
Castignani, G., Loiseau, L., and N. Montavont, "An
Evaluation of IEEE 802.11 Community Networks Deployments",
Information Networking (ICOIN), 2011 International
Conference on , vol., no., pp.498,503, 26-28 , 2011.
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[Castignani_b]
Castignani, G., Monetti, J., Montavont, N., Arcia-Moret,
A., Frank, R., and T. Engel, "A Study of Urban IEEE 802.11
Hotspot Networks: Towards a Community Access Network",
Wireless Days (WD), 2013 IFIP , pp.1,8, 13-15 , 2013.
[Castignani_c]
Castignani, G., Arcia-Moret, A., and N. Montavont, "A
study of the discovery process in 802.11 networks",
SIGMOBILE Mob. Comput. Commun. Rev., vol. 15, no. 1, p. 25
, 2011.
[Flickenger]
Flickenger, R., Okay, S., Pietrosemoli, E., Zennaro, M.,
and C. Fonda, "Very Long Distance Wi-Fi Networks", NSDR
2008, The Second ACM SIGCOMM Workshop on Networked Systems
for Developing Regions. USA, 2008 , 2008.
[Hanbali] Hanbali, A., Altman, E., and P. Nain, "A Survey of TCP
over Ad Hoc Networks", IEEE Commun. Surv. Tutorials, vol.
7, pp. 22-36 , 2005.
[Heer] Heer, T., Hummen, R., Viol, N., Wirtz, H., Gotz, S., and
K. Wehrle, "Collaborative municipal Wi-Fi networks-
challenges and opportunities", Pervasive Computing and
Communications Workshops (PERCOM Workshops), 2010 8th IEEE
International Conference on (pp. 588-593). IEEE. , 2010.
[IEEE] Institute of Electrical and Electronics Engineers, IEEE,
"IEEE Standards association", 2012.
[Lampropulos]
Lampropulos, A., Castignani, G., Blanc, A., and N.
Montavont, "Wi2Me: A Mobile Sensing Platform for Wireless
Heterogeneous Networks", 32nd International Conference on
Distributed Computing Systems Workshops (ICDCS Workshops),
2012, pp. 108-113 , 2012.
[Neumann] Neumann, A., Lopez, E., and L. Navarro, "An evaluation of
bmx6 for community wireless networks", In Wireless and
Mobile Computing, Networking and Communications (WiMob),
2012 IEEE 8th International Conference on (pp. 651-658).
IEEE. , 2012.
[PAWS] Sathiaseelan, A., Crowcroft, J., Goulden, M.,
Greiffenhagen, C., Mortier, R., Fairhurst, G., and D.
McAuley, "Public Access WiFi Service (PAWS)", Digital
Economy All Hands Meeting, Aberdeen , Oct 2012.
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[Pietrosemoli]
Pietrosemoli, E., Zennaro, M., and C. Fonda, "Low cost
carrier independent telecommunications infrastructure", In
proc. 4th Global Information Infrastructure and Networking
Symposium, Choroni, Venezuela , 2012.
[Rendon] Rendon, A., Ludena, P., and A. Martinez Fernandez,
"Tecnologias de la Informacion y las Comunicaciones para
zonas rurales Aplicacion a la atencion de salud en paises
en desarrollo", CYTED. Programa Iberoamericano de Ciencia
y Tecnologia para el Desarrollo , 2011.
[Samanta] Samanta, V., Knowles, C., Wagmister, J., and D. Estrin,
"Metropolitan Wi-Fi Research Network at the Los Angeles
State Historic Park", The Journal of Community
Informatics, North America, 4 , May 2008.
[Sathiaseelan_a]
Sathiaseelan, A., Rotsos, C., Sriram, C., Trossen, D.,
Papadimitriou, P., and J. Crowcroft, "Virtual Public
Networks", In Software Defined Networks (EWSDN), 2013
Second European Workshop on (pp. 1-6). IEEE. , 2013.
[Sathiaseelan_b]
Sathiaseelan, A. and J. Crowcroft, "LCD-Net: Lowest Cost
Denominator Networking", ACM SIGCOMM Computer
Communication Review , Apr 2013.
[Suresh] Suresh, L., Schulz-Zander, J., Merz, R., Feldmann, A., and
T. Vazao, "Towards Programmable Enterprise WLANs with
ODIN", In Proceedings of the first workshop on Hot topics
in software defined networks (HotSDN '12). ACM, New York,
NY, USA, 115-120 , 2012.
[Vega] Vega, D., Cerda-Alabern, L., Navarro, L., and R. Meseguer,
"Topology patterns of a community network: Guifi. net.",
Proceedings Wireless and Mobile Computing, Networking and
Communications (WiMob), 2012 IEEE 8th International
Conference on (pp. 612-619) , 2012.
[WNDW] Wireless Networking in the Developing World/Core
Contributors, "Wireless Networking in the Developing
World, 3rd Edition", The WNDW Project, available at
wndw.net , 2013.
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[WSIS] International Telecommunications Union, ITU, "Declaration
of Principles. Building the Information Society: A global
challenge in the new millenium", World Summit on the
Information Society, 2003, at http://www.itu.int/wsis,
accessed 12 January 2004. , Dec 2013.
[Zennaro] Zennaro, M., Fonda, C., Pietrosemoli, E., Muyepa, A.,
Okay, S., Flickenger, R., and S. Radicella, "On a long
wireless link for rural telemedicine in Malawi", 6th
International Conference on Open Access, Lilongwe, Malawi
, Nov 2008.
Authors' Addresses
Jose Saldana (editor)
University of Zaragoza
Dpt. IEC Ada Byron Building
Zaragoza 50018
Spain
Phone: +34 976 762 698
Email: jsaldana@unizar.es
Andres Arcia-Moret
Universidad de Los Andes
Facultad de Ingenieria. Sector La Hechicera
Merida 5101
Venezuela
Phone: +58 274 2402811
Email: andres.arcia@ula.ve
Bart Braem
University of Antwerp - iMinds
Middelheimlaan 1
Antwerp B-2020
Belgium
Phone: +32 (0)3 265.38.64
Email: bart.braem@iminds.be
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Leandro Navarro
U. Politecnica Catalunya
Jordi Girona, 1-3, D6
Barcelona 08034
Spain
Phone: +34 934016807
Email: leandro@ac.upc.edu
Ermanno Pietrosemoli
Escuela Latinoamericana de Redes
Apartado 514
Merida 5101
Venezuela
Phone: +58 0274 2403327
Email: ermanno@ula.ve
Carlos Rey-Moreno
University of the Western Cape
Robert Sobukwe road
Bellville 7535
South Africa
Phone: 0027219592562
Email: crey-moreno@uwc.ac.za
Arjuna Sathiaseelan
University of Cambridge
15 JJ Thomson Avenue
Cambridge CB30FD
United Kingdom
Phone: +44 (0)1223 763781
Email: arjuna.sathiaseelan@cl.cam.ac.uk
Marco Zennaro
Abdus Salam ICTP
Strada Costiera 11
Trieste 34100
Italy
Phone: +39 040 2240 406
Email: mzennaro@ictp.it
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