Internet DRAFT - draft-manyfolks-gaia-community-networks
draft-manyfolks-gaia-community-networks
Global Access to the Internet for All J. Saldana, Ed.
Internet-Draft University of Zaragoza
Intended status: Informational A. Arcia-Moret
Expires: July 25, 2015 Universidad de Los Andes
B. Braem
iMinds
L. Navarro
U. Politecnica Catalunya
E. Pietrosemoli
ICTP
C. Rey-Moreno
University of the Western Cape
A. Sathiaseelan
University of Cambridge
M. Zennaro
Abdus Salam ICTP
January 21, 2015
Alternative Network Deployments. Taxonomy and characterization
draft-manyfolks-gaia-community-networks-02
Abstract
This document presents a taxonomy of "Alternative Network
deployments", and a set of definitions and shared characteristics.
This term includes a set of network access models emerged in the last
decade with the aim of bringing Internet connectivity to people,
using topological, architectural and business models different from
the so-called "traditional" ones, where a company deploys the network
infrastructure for connecting the users, who pay for it.
Several initiatives throughout the world have built large scale
networks that are alternative to the traditional network operator
deployments using predominately wireless technologies (including long
distance) due to the reduced cost of using the unlicensed spectrum.
Wired technologies such as Fiber are also used in some of these
alternate networks. There are several types of such alternate
network: networks such as community networks are self-organized and
decentralized networks wholly owned by the community; networks owned
by individuals who act as wireless internet service providers
(WISPs), networks owned by individuals but leased out to network
operators who use such networks as a low-cost medium to reach the
underserved population and finally there are networks that provide
connectivity by sharing wireless resources of the users.
The emergence of these networks can be motivated by different causes
such as the reluctance, or the impossibility, of network operators to
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provide wired and cellular infrastructures to rural/remote areas. In
these cases, the networks have self sustainable business models that
provide more localised communication services as well as Internet
backhaul support through peering agreements with traditional network
operators. Some other times, networks are built as a complement and
an alternative to commercial Internet access provided by
"traditional" network operators.
The present classification considers different existing network
models such as Community Networks, open wireless services, user-
extensible services, traditional local Internet Service Providers
(ISPs), new global ISPs, etc. Different criteria are used in order
to build a classification as e.g., the ownership of the equipment,
the way the network is organized, the participatory model, the
extensibility, if they are driven by a community, a company or a
local (public or private) stakeholder, etc.
According to the developed taxonomy, a characterization of each kind
of network is presented, in terms of specific network characteristics
related to architecture, organization, etc.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 5
2. Classification . . . . . . . . . . . . . . . . . . . . . . . 5
2.1. Community Networks . . . . . . . . . . . . . . . . . . . 5
2.1.1. Free Networks . . . . . . . . . . . . . . . . . . . . 6
2.2. Wireless Internet Service Providers WISPs . . . . . . . . 7
2.3. Shared infrastructure model . . . . . . . . . . . . . . . 7
2.4. Crowdshared approaches, led by the people and third party
stakeholders . . . . . . . . . . . . . . . . . . . . . . 8
2.5. Testbeds for research purposes . . . . . . . . . . . . . 9
3. Scenarios where Alternative Networks are deployed . . . . . . 9
3.1. Digital Divide and Alternative Networks . . . . . . . . . 9
3.2. Urban vs. rural areas . . . . . . . . . . . . . . . . . . 11
4. Technologies employed . . . . . . . . . . . . . . . . . . . . 12
4.1. Wired . . . . . . . . . . . . . . . . . . . . . . . . . . 12
4.2. Wireless . . . . . . . . . . . . . . . . . . . . . . . . 12
4.2.1. Antennas . . . . . . . . . . . . . . . . . . . . . . 13
4.2.2. Link length . . . . . . . . . . . . . . . . . . . . . 14
4.2.2.1. Line-of-Sight . . . . . . . . . . . . . . . . . . 14
4.2.2.2. Transmitted and Received Power . . . . . . . . . 15
4.2.2.3. Medium Access Protocol . . . . . . . . . . . . . 16
4.2.3. Layer 2 . . . . . . . . . . . . . . . . . . . . . . . 16
4.2.3.1. 802.11 (Wi-Fi) . . . . . . . . . . . . . . . . . 16
4.2.3.2. GSM . . . . . . . . . . . . . . . . . . . . . . . 18
4.2.3.3. Dynamic Spectrum . . . . . . . . . . . . . . . . 18
5. Network and architecture issues . . . . . . . . . . . . . . . 20
5.1. Layer 3 . . . . . . . . . . . . . . . . . . . . . . . . . 20
5.1.1. IP addressing . . . . . . . . . . . . . . . . . . . . 20
5.1.2. Routing protocols . . . . . . . . . . . . . . . . . . 20
5.1.2.1. Traditional routing protocols . . . . . . . . . . 21
5.1.2.2. Mesh routing protocols . . . . . . . . . . . . . 21
5.2. Upper layers . . . . . . . . . . . . . . . . . . . . . . 21
5.2.1. Services provided by Alternative Networks . . . . . . 22
5.2.1.1. Intranet services . . . . . . . . . . . . . . . . 22
5.2.1.2. Access to the Internet . . . . . . . . . . . . . 23
5.3. Topology . . . . . . . . . . . . . . . . . . . . . . . . 23
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 24
7. Contributing Authors . . . . . . . . . . . . . . . . . . . . 24
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25
9. Security Considerations . . . . . . . . . . . . . . . . . . . 25
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 25
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10.1. Normative References . . . . . . . . . . . . . . . . . . 25
10.2. Informative References . . . . . . . . . . . . . . . . . 28
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 32
1. Introduction
Several initiatives throughout the world have built large scale
networks that are alternative to the traditional network operator
deployments using predominately wireless technologies (including long
distance) due to the reduced cost of using the unlicensed spectrum.
Wired technologies such as Fiber are also used in some of these
alternate networks. There are several types of such alternate
network: networks such as community networks are self-organized and
decentralized networks wholly owned by the community; networks owned
by individuals who act as wireless internet service providers
(WISPs), networks owned by individuals but leased out to network
operators who use such networks as a low cost medium to reach the
underserved population and finally there are networks that provide
connectivity by sharing wireless resources of the users.
The emergence of these networks can be motivated by different causes,
as the reluctance, or the impossibility, of network operators to
provide wired and cellular infrastructures to rural/remote areas
[Pietrosemoli]. In these cases, the networks have self sustainable
business models that provide more localised communication services as
well as Internet backhaul support through peering agreements with
traditional network operators. Some other times, they are built as a
complement and an alternative to commercial Internet access provided
by "traditional" network operators.
One of the aims of the Global Access to the Internet for All (GAIA)
IRTF initiative is "to document and share deployment experiences and
research results to the wider community through scholarly
publications, white papers, Informational and Experimental RFCs,
etc." In line with this objective, this document is intended to
propose a classification of these "Alternative Network deployments".
This term includes a set of network access models emerged in the last
decade with the aim of bringing Internet connectivity to people,
following topological, architectural and business models different
from the so-called "traditional" ones, where a company deploys the
infrastructure connecting the users, who pay for it. The document is
intended to be largely descriptive providing a broad overview of
initiatives, technologies and approaches employed in these networks.
Research references describing each kind of network are also
provided.
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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].
2. Classification
This section classifies Alternative Networks (ANs) according to their
intended usage. Each of them has different incentive structures,
maybe common technological challenges, but most importantly
interesting usage challenges which feeds into the incentives as well
as the technological challenges.
This classification is agnostic from the technical point of view.
Technology in this case must be taken as implementation. Moreover,
many of these networks are implemented in a way that several
technologies (Ad-Hoc Wi-Fi, Infrastructure Wi-Fi, Optical Fiber,
IPv4, IPv6, RFC1918, OLSR, BMX6, etc.) coexist.
2.1. Community Networks
Community Networks are large-scale, distributed, self-managed
networks sharing these characteristics:
- They are built and organized in a decentralized and open manner.
- They start and grow organically, they are open to participation
from everyone, sometimes agreeing to an open peering agreement.
Community members directly contribute active network infrastructure
(not just passive infrastructure).
- Knowledge about building and maintaining the network and ownership
of the network itself is decentralized and open. Community members
have an obvious and direct form of organizational control over the
overall operation of the network in their community (not just their
own participation in the network).
- The network CAN serve as a backhaul for providing a whole range of
services and applications, from completely free to even commercial
services.
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.
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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]. These networks are effective in
enhancing and extending digital Internet rights following a
participatory model.
The fact of the users adding new infrastructure (i.e. extensibility)
can be used to formulate another definition: A Community Network is a
network in which any participant in the system may add link segments
to the network in such a way that the new network segments can
support multiple nodes and adopt the same overall characteristics as
those of the joined network, including the capacity to further extend
the network. Once these link segments are joined to the network,
there is no longer a meaningful distinction between the previous
extent of the network and the new extent of the network.
In Community Networks, the profit can only be made by services and
not by the infrastructure itself, because the infrastructure is
neutral, free, and open (traditional Internet Service Providers,
ISPs, base their business on the control of the infrastructure). In
Community Networks, everybody keeps the ownership of what he/she has
contributed.
Community Networks MAY also be called "Free Networks" or even
"Network Commons". [FNF]. The majority of Community Networks
accomplishes the definition of Free Network, included in the next
subsection.
2.1.1. Free Networks
A definition of Free Network (which MAY be the same as Community
Network) is proposed by the Free Network Foundation (see
http://thefnf.org) as:
"A free network equitably grants the following freedoms to all:
Freedom 0 - The freedom to communicate for any purpose, without
discrimination, interference, or interception.
Freedom 1 - The freedom to grow, improve, communicate across, and
connect to the whole network.
Freedom 2- The freedom to study, use, remix, and share any network
communication mechanisms, in their most reusable forms."
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The principles of Free, Open and Neutral Networks have also been
summarized (see http://guifi.net/en/FONCC) this way:
- You have the freedom to use the network for any purpose as long as
you do not harm the operation of the network itself, the rights of
other users, or the principles of neutrality that allow contents and
services to flow without deliberate interference.
- You have the right to understand the network, to know its
components, and to spread knowledge of its mechanisms and principles.
- You have the right to offer services and content to the network on
your own terms.
- You have the right to join the network, and the responsibility to
extend this set of rights to anyone according to these same terms.
2.2. Wireless Internet Service Providers WISPs
WISPs are commercially-operated wireless Internet networks that
provide Internet and/or Voice Over Internet (VoIP) services. They
are most common in areas not covered by incumbent telcos or ISPs.
WISPs often use wireless point-to-point or point-to-multipoint in the
unlicensed frequencies but licensed frequency use is common too
especially in regions where unlicensed spectrum is either perceived
as crowded or where unlicensed spectrum may have regulatory barriers
impeding its use.
Most WISPs are operated by local companies responding to a perceived
market gap. There is a small but growing number of WISPs, such as
AirJaldi [Airjaldi] in India that have expanded from local service
into multiple locations.
Since 2006, the deployment of cloud-managed WISPs has been possible
with companies like Meraki and later OpenMesh and others. Until
recently, however, most of these services have been aimed at
industrialised markets. Everylayer [Everylayer], launched in 2014,
is the first cloud-managed WISP service aimed at emerging markets.
2.3. Shared infrastructure model
These networks are owned by individuals but leased out to network
operators who use them as a low cost medium to reach the underserved
population.
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2.4. Crowdshared approaches, led by the people and third party
stakeholders
These networks can be defined as a set of nodes whose owners share
common interests (e.g. sharing connectivity; resources; peripherals)
regardless of their physical location. The node location exhibits a
space and time correlation which is the basis to establish a robust
connectivity model over time.
These networks conform to the following approach: the home router
creates two wireless networks: one of them is normally used by the
owner, and the other one is public. A small fraction of the
bandwidth is allocated to the public network, to be employed by any
user of the service in the immediate area. Some examples are
described in [PAWS] and [Sathiaseelan_c]. Other example is
constituted by the networks created and managed by City Councils
(e.g., [Heer]).
In the same way, some companies [Fon] 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, and people can join the network in
different ways: they can buy a 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 revenue 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.
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 low priority, a less-than-best-
effort or scavenger approach, so as not to harm the traffic of the
owner of the connection [Sathiaseelan_a].
The elements involved in a crowd-shared network are summarised below:
- Interest: a parameter capable of providing a measure (cost) of the
attractiveness of a node towards a specific location, in a specific
instance in time.
- Resources: A physical or virtual element of a global system. For
instance, bandwidth; energy; data; devices.
- The owner: End users who sign up for the service and share their
network capacity. As a counterpart, they can access another owners'
home access for free. The owner can be an end user or an entity
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(e.g. operator; virtual operator; municipality) that is to be made
responsible for any actions concerning his/her device.
- The user: a legal entity or an individual using or requesting a
publicly available electronic communications' service for private or
business purposes, without necessarily having subscribed to such
service.
- The Virtual Network Operator (VNO): An entity that acts in some
aspects as a network coordinator. It may provide services such as
initial authentication or registering, and eventually, trust
relationship storage. A VNO is not an ISP given that it does not
provide Internet access (e.g. infrastructure; naming). A VNO is
neither an Application Service Provider (ASP) since it does not
provide user services. Virtual Operators MAY also be 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.
2.5. Testbeds for research purposes
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], [Bernardi].
3. Scenarios where Alternative Networks are deployed
Alternative Network deployments are present in every part of the
world. Even in some high-income countries, these networks have been
built as an alternative to commercial ones managed by traditional
network operators. This section discusses the scenarios where
Alternative Networks have been deployed.
3.1. Digital Divide and Alternative Networks
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
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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 also been
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
considers not only the GNI but also life expectancy and education,
has been proposed by the United Nations to rank countries according
to their well-being and not solely based on economic terms. These
classifications are used to give strong signals to the international
community about 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 (Information and Communications Technology)
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", in order not
to be 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].
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Most efforts from governments and international organizations focused
initially on improving and extending the existing infrastructure in
order not to leave their population behind. As an example, one of
the goals of the Digital Agenda for Europe [DAE] is "to increase
regular internet usage from 60% to 75% by 2015, and from 41% to 60%
among disadvantaged people."
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 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 the contribution made by mobile network operators in
decreasing the access gap is undeniable, their model presents some
constraints that limit 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 Alternative Networks (e.g. 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, Alternative 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.
3.2. Urban vs. 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
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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 deem them profitable.
The cost of the wireless infrastructure required to set up a network,
including powering it 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 Alternative
Network set-ups where a reduced number of nodes may cover communities
whose dwellers share the cost of the infrastructure and the gateway
and access it via inexpensive wireless devices. Some examples are
presented in [Pietrosemoli] and [Bernardi].
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 the services they aim to provide,
has fuelled the creation of robust low-cost low-consumption low-
complexity off-the-shelf wireless devices which make much easier the
deployment and maintenance of these alternative infrastructures in
rural areas.
4. Technologies employed
4.1. Wired
In many (developed or developing) countries it may happen that
national service providers may decline to provide connectivity to
tiny and isolated villages. So in some cases the villagers have
created their own optical fiber networks. It is the case of
Lowenstedt in Germany [Lowenstedt].
4.2. Wireless
Different wireless technologies [WNDW] can be employed in Alternative
Network deployments. Below we summarise topics to be considered in
such deployments:
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4.2.1. Antennas
Three kinds of antennas are suitable to be used in these 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 antenna will also receive a feeble
signal from the client). A moderate gain omnidirectional of about 8
to 10 dBi is normally preferable. Higher gain omnidirectional
antennas are only advisable when the farthest way client is roughly
in the same plane.
For indoor clients, omnidirectional antennas are generally fine,
because the numerous reflections normally found in indoor
environments negate the advantage of using directional antennas.
For outdoor clients, directional antennas can be quite useful to
extend coverage to an Access Point fitted with an omnidirectional
one.
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 normally 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 do with lower altitude antenna placement since
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the Fresnel ellipsoid (the volume around the optical line occuppied
by radio waves, which should be free from obstacles), 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 omnidirectional one to the lower
frequency to provide local access.
In the case of mesh networking, where the antenna should connect to
several other nodes, it is better to use omnidirectional antennas.
The same type of polarisation must be used at both ends of any radio
link. For point-to-point links, some vendors 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.
4.2.2. Link length
4.2.2.1. Line-of-Sight
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.
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 the Fresnel zone (the volume
around the optical line) must be unencumbered from obstacles for the
maximum signal to be captured at the receiver. The size of the
Fresnel ellipsoid grows with the distance between the end points and
with the wavelength of the signal, which in turn is inversely
proportional to the frequency.
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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.
4.2.2.2. Transmitted and Received Power
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.
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.
In order to achieve a given link margin (also called "fade margin"),
one can:
a) Increase the output power.The maximum transmitted power is
specified by each country's regulation, and for unlicensed
frequencies is much lower than for licensed frequencies.
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, 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 favorable frequency
or a shorter path.
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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. 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 from
150 Mbit/s to 6 Mbit/s if the receiver power is not enough to sustain
the maximum throughput.
4.2.2.3. Medium Access Protocol
A completely different limiting factor is related to the medium
access protocol. Wi-Fi 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 significantly
reduce the throughput at long distance, so for long distance
applications it is better to use a different medium access technique,
in which the receiver does not wait for an acknowledgement 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 Wi-Fi in order to
increase the throughput at longer distances. Low cost equipment
using TDMA can offer high throughput at distances over 100
kilometers.
4.2.3. Layer 2
4.2.3.1. 802.11 (Wi-Fi)
Wireless standards ensure interoperability and usability to 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.
The standard we are most interested in is 802.11 a/b/g/n,
[IEEE.802-11A.1999], [IEEE.802-11B.1999], [IEEE.802-11G.2003],
[IEEE.802-11N.2009] 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.
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|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].
4.2.3.1.1. 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 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.
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
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wireless interface creates a network with a specified name (called
the SSID, Service Set IDentifier) 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 associated with the master.
Managed mode interfaces do not communicate with each other directly,
and 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 traffic 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. Managed mode clients cannot communicate with
each other directly, so a high repeater site is required 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.
4.2.3.2. GSM
GSM has also been used in Alternative Networks as Layer 2 option, as
explained in [Mexican].
4.2.3.3. Dynamic Spectrum
Some Alternative Networks make use of TV White Spaces - a set of UHF
and VHF television frequencies that can be utilized by secondary
users in locations where it is unused by licensed primary users such
as television broadcasters. Equipment that makes use of TV White
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Spaces is required to detect the presence of existing unused TV
channels by means of a spectrum database and/or spectrum sensing in
order to ensure that no harmful interference is caused to primary
users. In order to smartly allocate interference-free channels to
the devices, cognitive radios are used which are able to modify their
frequency, power and modulation techniques to meet the strict
operating conditions required for secondary users.
The use of the term "White Spaces" is often used to describe "TV
White Spaces" as the VHF and UHF television frequencies were the
first to be exploited on a secondary use basis. There are two
dominant standards for TV white space communication: (i) the 802.11af
standard [IEEE.802-11AF.2013] - an adaptation of the 802.11 standard
for TV white space bands and (ii) the IEEE 802.22 standard
[IEEE.802-22.2011] for long-range rural communication.
4.2.3.3.1. 802.11af
802.11af [IEEE.802-11AF.2013] is a modified version of the 802.11
standard operating in TV White Space bands using Cognitive Radios to
avoid interference with primary users. The standard is often
referred to as White-Fi or Super WiFi and was approved in February
2014. 802.11af contains much of the advances of all the 802.11
standards including recent advances in 802.11ac such as up to four
bonded channels, four spatial streams and very high rate 256-QAM
modulation but with improved in-building penetration and outdoor
coverage. The maximum data rate achievable is 426.7 Mbps for
countries with 6/7 MHz channels and 568.9 Mbps for countries with 8
MHz channels. Coverage is typically limited to 1km although longer
range at lower throughput and using high gain antennas will be
possible.
Devices are designated as enabling stations (access points) or
dependent stations (clients). Enabling stations are authorized to
control the operation of a dependent station and securely access a
geolocation database. Once the enabling station has received a list
of available white space channels it can announce a chosen channel to
the dependent stations for them to communicate with the enabling
station. 802.11af also makes use of a registered location server - a
local database that organizes the geographic location and operating
parameters of all enabling stations.
4.2.3.3.2. 802.22
802.22 [IEEE.802-22.2011] is a standard developed specifically for
long range rural communications in TV white space frequencies and
first approved in July 2011. The standard is similar to the 802.16
(WiMax) [IEEE.802-16.2008] standard with an added cognitive radio
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ability. The maximum throughput of 802.22 is 22.6 Mbps for a single
8 MHz channel using 64-QAM modulation. The achievable range using
the default MAC scheme is 30 km, however 100 km is possible with
special scheduling techniques. The MAC of 802.22 is specifically
customized for long distances - for example, slots in a frame
destined for more distant CPEs are sent before slots destined for
nearby CPEs.
Base stations are required to have a GPS and a connection to the
Internet in order to query a geolocation spectrum database. Once the
base station receives the allowed TV channels, it communicates a
preferred operating white space TV channel with the Client Premises
Equipment (CPE) devices. The standard also has a co-existence
mechanism that uses beacons to make other 802.22 base stations aware
of the presence of a base station that is not part of the same
network.
5. Network and architecture issues
5.1. Layer 3
5.1.1. IP addressing
Most known Alternative Networks started in or around the year 2000.
IPv6 was fully specified by then, but almost all Alternative Networks
still use IPv4. A survey [Avonts] indicated that IPv6 rollout
presents 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.
5.1.2. Routing protocols
Alternative Networks are composed of possibly different layer 2
devices, resulting in a mesh of nodes. Connection between different
nodes is not guaranteed and the link stability can vary strongly over
time. To tackle this, some Alternative Networks use mesh network
routing protocols while other networks use more traditional routing
protocols. Some networks operate multiple routing protocols in
parallel. For example, they use a mesh protocol inside different
islands and use traditional routing protocols to connect islands.
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5.1.2.1. 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 networks opt to run the OSPF protocol,
as defined by RFC 2328 [RFC2328].
5.1.2.2. Mesh routing protocols
A large number of Alternative Networks use the OLSR routing protocol
as defined in RFC 3626 [RFC3626]. The pro-active link state routing
protocol is a good match with Alternative Networks because it has
good performance in mesh networks where nodes have multiple
interfaces.
The Better Approach To Mobile Adhoc Networking (BATMAN) [Abolhasan]
protocol was developed by members 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 Alternative
Networks.
5.2. Upper layers
From crowdshared perspective, and considering just regular TCP
connections during the critical sharing time, the Access Point
offering the 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 implements a Less than Best Effort (LBE) policy
for the user and protects the sharer. Achieving LBE behaviour
requires 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 user traffic should not interfere with the sharer's traffic.
However, other bottlenecks besides client's access bottleneck may not
be controlled by the previously mentioned protocols. Therefore,
recently proposed transport protocols like LEDBAT [Ros], [Komnios]
with the purpose of transporting scavenger traffic may be a solution.
LEDBAT requires the cooperation of both the client and the server to
achieve certain target delay, therefore controlling the impact of the
user along all the path.
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There are applications that manage aspects of the network 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
network 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 Community
Networks from the client's side. These applications have shown to
improve the client performance compared to a single-Community Network
client.
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]. 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 Wi-Fi access.
5.2.1. Services provided by Alternative Networks
This section provides an overview of the services between hosts
inside the network. They can be divided into Intranet services,
connecting hosts between them, and Internet services, connecting to
nodes outside the network.
5.2.1.1. Intranet services
Intranet services can include, but are not limited to:
- VoIP (e.g. with SIP)
- Remote desktop (e.g. using my home 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.
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- Public video cameras.
- DNS.
- Online games servers.
- Jabber instant messaging.
- IRC chat.
- Weather stations.
- NTP.
- Network monitoring.
- Videoconferencing / streaming.
- Radio streaming.
5.2.1.2. Access to the Internet
5.2.1.2.1. Web browsing proxies
A number of federated proxies MAY provide web browsing service for
the users. Other services (file sharing, skype, etc.) are not
usually allowed in many Alternative Networks due to bandwidth
limitations.
5.2.1.2.2. Use of VPNs
Some "micro-ISPs" may use the network as a backhaul for providing
Internet access, setting up VPNs from the client to a machine with
Internet access.
5.3. Topology
Alternative Networks follow different topology patterns, as studied
in [Vega].
Regularly rural areas in these networks 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] may constitute a way to extend the user
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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 users in France, ISPs promise to cause a little impact on their
service agreement when the shared network 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 walking speed, there is a fair chance of
performing file transfers [Castignani_a], [Castignani_b]. Scenarios
studied in France and Luxembourg show that the density of APs in
urban areas (mainly in downtown and residential areas) is quite big
and from different ISPs. Moreover, performed studies reveal that
aggregating available networks can be beneficial to the client by
using an application that manages the best connection among the
different networks. 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].
6. Acknowledgements
This work has been partially funded by the CONFINE European
Commission Project (FP7 - 288535).
The editor and the authors of this document wish to thank the
following individuals who have participated in the drafting, review,
and discussion of this memo:
Paul M. Aoki, Roger Baig, Jaume Barcelo, Steven G. Huter, Rohan
Mahy, Rute Sofia, Dirk Trossen.
A special thanks to the GAIA Working Group chairs Matt Ford and
Arjuna Sathiaseelan for their support and guidance.
7. Contributing Authors
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Ioannis Komnios
Democritus University of Thrace
Department of Electrical and Computer Engineering
Kimmeria University Campus
Xanthi 67100
Greece
Phone: +306945406585
Email: ikomnios@ee.duth.gr
Steve Song
Village Telco Limited
Halifax
Canada
Phone:
Email: stevesong@nsrc.org
David Lloyd Johnson
Meraka, CSIR
15 Lower Hope St
Rosebank 7700
South Africa
Phone: +27 (0)21 658 2740
Email: djohnson@csir.co.za
8. IANA Considerations
This memo includes no request to IANA.
9. Security Considerations
No security issues have been identified for this document.
10. References
10.1. Normative References
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[IEEE.802-11A.1999]
"Information technology - Telecommunications and
information exchange between systems - Local and
metropolitan area networks - Specific requirements - Part
11: Wireless LAN Medium Access Control (MAC) and Physical
Layer (PHY) specifications - High-speed Physical Layer in
the 5 GHZ Band", IEEE Standard 802.11a, Sept 1999,
<http://standards.ieee.org/getieee802/
download/802.11a-1999.pdf>.
[IEEE.802-11AF.2013]
"Information technology - Telecommunications and
information exchange between systems - Local and
metropolitan area networks - Specific requirements - Part
11: Wireless LAN Medium Access Control (MAC) and Physical
Layer (PHY) specifications - Amendment 5: Television White
Spaces (TVWS) Operation", IEEE Standard 802.11af, Oct
2009, <http://standards.ieee.org/getieee802/
download/802.11af-2013.pdf>.
[IEEE.802-11B.1999]
"Information technology - Telecommunications and
information exchange between systems - Local and
metropolitan area networks - Specific requirements - Part
11: Wireless LAN Medium Access Control (MAC) and Physical
Layer (PHY) specifications - Higher-Speed Physical Layer
Extension in the 2.4 GHz Band", IEEE Standard 802.11b,
Sept 1999, <http://standards.ieee.org/getieee802/
download/802.11b-1999.pdf>.
[IEEE.802-11G.2003]
"Information technology - Telecommunications and
information exchange between systems - Local and
metropolitan area networks - Specific requirements - Part
11: Wireless LAN Medium Access Control (MAC) and Physical
Layer (PHY) specifications - Amendment 4: Further Higher
Data Rate Extension in the 2.4 GHz Band", IEEE Standard
802.11g, Jun 2003, <http://standards.ieee.org/getieee802/
download/802.11g-2003.pdf>.
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[IEEE.802-11N.2009]
"Information technology - Telecommunications and
information exchange between systems - Local and
metropolitan area networks - Specific requirements - Part
11: Wireless LAN Medium Access Control (MAC) and Physical
Layer (PHY) specifications - Amendment 5: Enhancements for
Higher Throughput", IEEE Standard 802.11n, Oct 2009,
<http://standards.ieee.org/getieee802/
download/802.11n-2009.pdf>.
[IEEE.802-16.2008]
"Information technology - Telecommunications and
information exchange between systems - Broadband wireless
metropolitan area networks (MANs) - IEEE Standard for Air
Interface for Broadband Wireless Access Systems", IEEE
Standard 802.16, Jun 2008,
<http://standards.ieee.org/getieee802/
download/802.16-2012.pdf>.
[IEEE.802-22.2011]
"Information technology - Telecommunications and
information exchange between systems - Local and
metropolitan area networks - Specific requirements - Part
22: Cognitive Wireless RAN Medium Access Control (MAC) and
Physical Layer (PHY) specifications: Policies and
procedures for operation in the TV Bands", IEEE Standard
802.22, Jul 2011, <http://standards.ieee.org/getieee802/
download/802.11af-2013.pdf>.
[RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
E. Lear, "Address Allocation for Private Internets", BCP
5, RFC 1918, February 1996.
[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.
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[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.
10.2. 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.
[Airjaldi]
Rural Broadband (RBB) Pvt. Ltd., Airjaldi., "Airjaldi
service", Airjaldi web page, www.airjaldi.net , 2015.
[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.
[Bernardi]
Bernardi, B., Buneman, P., and M. Marina, "Tegola tiered
mesh network testbed in rural Scotland", Proceedings of
the 2008 ACM workshop on Wireless networks and systems for
developing regions (WiNS-DR '08). ACM, New York, NY, USA,
9-16 , 2008.
[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
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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
iMinds
Gaston Crommenlaan 8 (bus 102)
Gent 9050
Belgium
Phone: +32 3 265 38 64
Email: bart.braem@iminds.be
Saldana, et al. Expires July 25, 2015 [Page 32]
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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
ICTP
Via Beirut 7
Trieste 34151
Italy
Phone: +39 040 2240 471
Email: ermanno@ictp.it
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
Saldana, et al. Expires July 25, 2015 [Page 33]
