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Versions: 00 01 02 draft-irtf-gaia-alternative-network-deployments

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-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   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
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   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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