Redes Inalámbricas – Tema 4 Wireless Mesh Networks - GRC

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Oct 29, 2013 (3 years and 10 months ago)

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REDES
INALÁMBRICAS






Máster de Ingeniería
de
Computadores
-
DISCA

Redes Inalámbricas


Tema 4

Wireless Mesh Networks


Terminology


Study case: Guifi.net


Mesh HW and SW


Elements of mesh routing


IEEE 802.11s


Thanks

to

Sebastian
Büttrich
, wire.less.dk

REDES INALÁMBRICAS




MIC 2009/2010

Mesh topology


a typical scenario

2

REDES INALÁMBRICAS




MIC 2009/2010

Community Networks


Broadband Internet Access
technology


Several neighbors may share
their broadband connections
with many other neighbors


Not run by ISPs


Possibly in the
disadvantage of the ISPs


3

Source:
research.microsoft.com/mesh/


REDES INALÁMBRICAS




MIC 2009/2010

Overview

4


Wireless routers


Gateways



Printers, servers



Mobile clients



Stationary clients

Intra
-
mesh wireless links

Stationary client access


Mobile client access




Internet access links

Node Types

Link Types

REDES INALÁMBRICAS




MIC 2009/2010


Advantages of Mesh Networking


Self
-
forming


The wireless mesh network forms automatically once the mesh nodes have been
configured and activated.


Fault tolerance


If redundant routes exist in the network, information flow is not interrupted in the rest
of the network when one node fails. The network will dynamically reroute the
information via the next available route.


Self
-
healing


Once restored, a node rejoins the mesh network seamlessly.


Community ownership


Ownership of the network is shared, hence the burden of network support does not
rest with a single person.


Low cost of infrastructure


Mesh nodes can be built from low cost, common
-
off
-
the
-
shelf equipment.


Incremental cost of network expansion is low


With the addition of one extra node, at the marginal cost of that node, the reach and
value of the network is increased.


Ease of deployment


With little training members of a community can build their own nodes, configure and
deploy them in the community.

5

REDES
INALÁMBRICAS






Máster de Ingeniería
de
Computadores
-
DISCA

Redes Inalámbricas


Tema 4

Wireless Mesh Networks


Terminology


Study case: Guifi.net


Mesh HW and SW


Elements of mesh routing


IEEE 802.11s


Thanks

to

Sebastian
Büttrich
, wire.less.dk

REDES INALÁMBRICAS




MIC 2009/2010

From Ramon Roca talk
at:




Study case: Guifi.net

REDES INALÁMBRICAS




MIC 2009/2010

What?

Enabling users to become infrastructure providers


Extending the Internet network neutrality up to the last mile


Embracing the Openness paradigm:


By peer to peer connection agreements open to all, not restricted to telecoms/


Open standards, software, hardware... Networks!


Free as in freedom:


No single ownership


Same rules for all


Lowering TCO by being cost oriented/real value instead of price dominance
(How much it costs vs how much user can pay...)

REDES INALÁMBRICAS




MIC 2009/2010

guifi.net experience


Started in 2,004 in country
-
side Catalonia


Envisioned as a New Generation of Free Networks / Wireless
Communities


Lead and originally founded by the civil society


Currently a non
-
profit NGO (Foundation)


As of Aug 2,009:


7,500 online nodes


10,000
kms
. of network links


Sustained growth



REDES INALÁMBRICAS




MIC 2009/2010

How?


By building end
-
user oriented platform to enable the deployment of
neutral networks at the last mile


Same P2P agreement for all


Web 2.0 style collaborative platform including


IP Provisioning


Network Monitoring (traffic, status...)


GIS applications (maps)


Device Configuration


Technology agnostic


Low cost wireless intensively used, but not restricted to (now extending to
fiber)

REDES INALÁMBRICAS




MIC 2009/2010

Example: The node page

Complete menus providing many
features

Detailed drill/down information and
maps

Graphs & Network statistics

REDES INALÁMBRICAS




MIC 2009/2010

Example: The node page II


List of nodes & availability


Real time

REDES INALÁMBRICAS




MIC 2009/2010

Example
: The
node page III


Suggested links, check for Line
-
of
-
Sight (
LoS
)

REDES INALÁMBRICAS




MIC 2009/2010

And now is time for...


Launching FFTH
-

FFTF
projects


Fiber From The Farms /
Houses, NOT just “To”...


Launched in Summer 2,009


Reuse of existing copper
infrastructure / posts



REDES INALÁMBRICAS




MIC 2009/2010

Open Spectrum Alliance


Whitespaces

+ “
smart

technologies

= new
opportunities

for
spectrum

efficiency


The Open Spectrum Alliance is united by the goal of realizing the potential social
and economic benefits of this underutilized natural resource by promoting
innovative public policies.

REDES
INALÁMBRICAS






Máster de Ingeniería
de
Computadores
-
DISCA

Redes Inalámbricas


Tema 4

Wireless Mesh Networks


Terminology


Study case: Guifi.net


Mesh HW and SW


Elements of mesh routing


IEEE 802.11s


Thanks

to

Sebastian
Büttrich
, wire.less.dk

REDES INALÁMBRICAS




MIC 2009/2010

Mesh hardware


Ranges from (almost no
-
cost) refurbished computers over modified
home user Access points for 50


to mid
-
price embedded boards to
carrier grade equipment for several thousand



Challenge: to balance total cost of ownership, quality, requirements


as with all other network hardware.


Market is in dynamic development


Open platforms and standards enable open development

17

REDES INALÁMBRICAS




MIC 2009/2010

Mesh hardware: Meshnode by Saxnet


Debian

GNU Linux 2.6er Kernel


Processor

AMD Geode LX x86


WLAN Standards 802.11
a/b/c/g/
i
/f


Security

WPA2 (AES), WEP
64/128/156, 802.1x, Firewall,
MAC Filter, HTTPS, Port
Forward


Management

Web GUI,
root access over SSH2, SNMP
V3 (read), Network
Management System


Services

PPPoE

(DSL & 3G) ,
DHCP server, SSH, HTTP,
DynDNS


Built into a waterproof outdoor
enclosure.


18

REDES INALÁMBRICAS




MIC 2009/2010

Mesh Hardware: Commercial & proprietary


Tropos


BelAir


Strix


And:


Nortel


Nokia


Cisco




19

REDES INALÁMBRICAS




MIC 2009/2010

Mesh hardware: Linksys WRT54G


Not originally meant as a mesh device


Due to low price and GPL firmware, one of the most interesting and
versatile low budget options


Many firmware distributions available:
OpenWRT
, EWRT,
Batbox
,
Sveasoft
,
FreifunkFirmware
, and many more


Hardware specs:

RAM / Flash / CPU speed

WRT54G v2


16

4

200 MHz

WRT54GS


32

8

200 MHz





Processor: Broadcom


Price: circa 60


(WRT54G)


20

REDES INALÁMBRICAS




MIC 2009/2010

Mesh software packages


Zebra/
Quagga


GNU Zebra is free software that manages TCP/IP based routing protocols. Part of
the GNU Project, distributed under the GNU GPL


Mesh protocols included: BGP
-
4 (RFC1771, A Border Gateway Protocol 4), RIPv1,
RIPv2, OSPFv2, IPv6 ready.


Fork:
Quagga

adds RIPv3, OSPFv3


Meshlinux

by

elektra


@ http://zolder.scii.nl/~elektra/


Based on
Slackware
, circa 50 MB ISO


Targetted

at reuse of (older) laptops


Mesh protocols included:
MobileMesh
, OLSR, BGP, OSPF, RIP, AODV


CUWiN

(the Champaign
-
Urbana Community Wireless Network)


@
http://www.cuwin.net/


Various mesh protocols included: HSLS, ETX, …



21

REDES INALÁMBRICAS




MIC 2009/2010

Mesh software packages:
OpenWRT


OpenWrt

is a
linux

distribution for the Linksys WRT54G, a minimal
firmware with support for add
-
on packages, custom
tunable


http://openwrt.org/


It includes other chipsets, manufacturers and device types, including
Netgear
, D
-
Link,
Asus

routers and many others.


Readonly

core provides: network
initalization

(
ethernet

and wireless),
firewalling,
dhcp

client / server, caching
dns

server, telnet server and
busybox

environment


ssh

and web interfaces available via
ipkg


Many more packages, e.g. asterisk


Mesh protocols: OLSR, AODV, ....

22

REDES INALÁMBRICAS




MIC 2009/2010

Mesh software packages:
OpeWRT

derivatives


Many other
forware

s are available that derive in
vaious

percentages
from the original
OpenWRT
. The most important are:


Freifunk


@ http://start.freifunk.net/


Uses OLSR


DD
-
WRT


@ http://www.dd
-
wrt.com/


Commercial


Sveasoft


@ http://sveasoft.com/


Talisman
/
Mesh

Firmware

23

REDES
INALÁMBRICAS






Máster de Ingeniería
de
Computadores
-
DISCA

Redes Inalámbricas


Tema 4

Wireless Mesh Networks


Terminology


Study case: Guifi.net


Mesh HW and SW


Elements of mesh routing


IEEE 802.11s


Thanks

to

Sebastian
Büttrich
, wire.less.dk

REDES INALÁMBRICAS




MIC 2009/2010

Wireless Mesh Networking Principles


Communication between mesh nodes are
typically

based on
Wi
-
Fi radios (IEEE 802.11 a/b/g) attached to directional or
omni
-
directional antennas.


All radios are set to ad
-
hoc mode (not client mode or infrastructure
(access point) mode).


Each node in the WMN has the same ESSID (name) and BSSID
(number)
-

the BSSID should be fixed to prevent partitioning of the
wireless network.


All nodes in the WMN will operate on the same channel (frequency).


In an ideal WMN, each node should be able to “see” at least two other
nodes in the WMN. This allows full fail
-
over in case any node goes out
of commission (e.g. due to a hardware failure or power failure).


A mesh routing protocol, like OLSR, will route IP traffic between the
wireless interfaces of the mesh nodes.

25

REDES INALÁMBRICAS




MIC 2009/2010

Important Considerations


Various obstructions may interfere with the signals and should be
considered:


Trees and plants


water on leaves negatively impact on signal strength


Construction materials


metal objects like roofs or reinforcing in concrete walls
affect the signal strength.


Electronics are susceptible to lightning damage and lightning
protection should be considered, especially for outdoor installations of
Wi
-
Fi equipment.


Each country has a regulatory body that regulates the use of wireless
equipment. Check with your local regulator.


There is a trade
-
off between the cost of planning and building of a
network well at the start of the project and the cost of maintaining a
badly designed network. It is worth the effort to plan thoroughly, get
the appropriate equipment and to create redundant routes in the
wireless mesh network wherever possible.

26

REDES INALÁMBRICAS




MIC 2009/2010


Important Considerations: channel allocation


Channel allocation for the backbone and mesh network


Adding a backbone effectively adds another wireless network that has to work
independent from the other mesh network. The “normal” mesh network will
therefore work at channel 6 and the backbone at channel 11. This will ensure that
the two networks do not interfere with each other.



Channel allocation for home / office users


A third wireless network is possible within this framework;
a hotspot
. A hotspot is
usually required at home or the office when one wants to create a local wireless
network to connect laptops and other wireless equipment. The hotspot will require
a wireless access point (Linksys) to be connected to the mesh node. The two
Linksys boxes are connected together back
-
to
-
back with an LAN cable (via the
Ethernet switch ports).


27

REDES INALÁMBRICAS




MIC 2009/2010


Select the network topology type

28

Simple
mesh

network

plot

Clustered

mesh

with

backbone

REDES INALÁMBRICAS




MIC 2009/2010

Plan the IP address allocation


Addresses are allocated according to
RFC 1918
which provides details
of the private address space.


The IP addressing scheme should ensure unique addresses for each
node and PC on the network.


The first thing one has to choose is an available subnet.


According to RFC 1918, the subnets available for private
IP networks that will not be connected to the internet are:



10. 0.0.0
-

10.255.255.255 (10/8 prefix)


172. 16.0.0
-

172. 31.255.255 (172.16/12 prefix)


192.168.0.0
-

192.168.255.255 (192.168/16 prefix)


Once the subnet has been selected, one can assign IP numbers to
mesh nodes and PCs randomly.


It is much better to choose a method of assigning IP numbers and to
stick to it very rigorously.

29

REDES INALÁMBRICAS




MIC 2009/2010


A Method of assigning IP numbers (wireless interface):

a proposal


Backbone node:


Wireless interface:
10.0.1.x/24

where 1 ≤ x < 255


Ethernet interface:
10.3.x.y/24

where 1 ≤ y < 255


“Normal” mesh node:


Wireless interface:
10.1.1.a/24

where 1 ≤ a < 255


Ethernet interface:
10.2.a.b/24

where 1 ≤ b < 255.


Note that “mesh” nodes will be in the lower range, but other PCs and laptops
connected to a node will be numbered from 100 according to the DHCP
settings.


Access Point (Hotspots):


One would connect a wireless access back
-
to
-
back to a “normal”
mesh node. The subnet assigned to the wireless LAN or hotspot will therefore be
the same as with an Ethernet LAN connected to the mesh node.


NOTE


The
10.0.1.x/24

notation translates to:

IP address:
10. 0. 1.x

where 1 ≤ x < 255, and

subnet mask:
255.255.255.0

30

Or

sometimes

(x
-
1)…

REDES INALÁMBRICAS




MIC 2009/2010

Example layout of a wireless mesh network

31

REDES INALÁMBRICAS




MIC 2009/2010

Routing Protocols


Proactive:


OLSR (Optimized Link State
Protocol)


B.A.T.M.A.N.

(Better
Approach to Mobile Ad
-
Hoc
Networking)


Reactive:


AODV (Ad
-
hoc on Demand
Distance Vector)


SrcRR

(MIT
Roofnet
)


Hybrid:


HSLS (Hazy Sighted Link
State Routing,
CuWin
)


These are just some of the
most relevant protocols in
our context ... there are
many other protocols!


TBRPF (Topology Broadcast
based on Reverse
-
Path
Forwarding routing protocol)


MMRP (Mobile Mesh Routing
Protocol), short:
MobileMesh


OSPF (Open Shortest Path
First)


32

REDES INALÁMBRICAS




MIC 2009/2010

Mesh routing protocols: Metrics


Metric calculation deals with the cost assigned to a certain route


In principle, the routing protocol is independent from the metrics
calculation


it just needs to know how 'good' the route is, not where
that value comes from


Yet sensible metrics are the core of wireless ad hoc networking

33

REDES INALÁMBRICAS




MIC 2009/2010

Link Quality Metrics


Per
-
hop Round Trip Time (RTT)



Per
-
hop Packet
-
Pair (
PktPair
)



Expected transmissions (
ETX
)



Minimum
-
hop routing (HOP)


Binary link quality


34

REDES INALÁMBRICAS




MIC 2009/2010

Metric 1: Per
-
hop RTT


Node periodically pings each of its neighbors


Unicast

probe/probe
-
reply pair



RTT samples are averaged using TCP
-
like low
-
pass filter


Exponential smoothing





Path with least sum of RTTs is selected

35

REDES INALÁMBRICAS




MIC 2009/2010

Metric 1: Per
-
hop RTT


Advantages


Easy to implement


Accounts for link load and bandwidth


Also accounts for link loss rate


802.11 retransmits lost packets up to 7 times


Lossy links will have higher RTT



Disadvantages


Expensive


Self
-
interference due to queuing


36

REDES INALÁMBRICAS




MIC 2009/2010

Metric 2: Per
-
hop Packet
-
Pair


Node periodically sends two back
-
to
-
back probes to each neighbor


First probe is small, second is large



Neighbor measures delay between the arrival of the two probes;
reports back to the sender



Sender averages delay samples using low
-
pass filter



Path with least sum of delays is selected

37

REDES INALÁMBRICAS




MIC 2009/2010

Metric 2: Per
-
hop Packet
-
Pair


Advantages


Self
-
interference due to queuing is not a problem


Implicitly takes load, bandwidth and loss rate into account



Disadvantages


More expensive than RTT

38

REDES INALÁMBRICAS




MIC 2009/2010

Metric 3: Expected Transmissions (ETX)


Estimate number of times a packet has to be retransmitted on each
hop


Each node periodically broadcasts a probe


802.11 does not retransmit broadcast packets



Probe carries information about probes received from neighbors



Node can calculate loss rate on forward (Pf) and reverse (Pr) link to
each neighbor






Select the path with least total ETX

39

REDES INALÁMBRICAS




MIC 2009/2010

Metric 3: Expected Transmissions


Advantages


Low overhead


Explicitly takes loss rate into account



Disadvantages


Loss rate of broadcast probe packets is not the same as loss rate of data packets


Probe packets are smaller than data packets


Broadcast packets are sent at lower data rate


Does not take data rate or link load into account


40

REDES INALÁMBRICAS




MIC 2009/2010

Mesh Testbed

41



23 Laptops running Windows XP.

802.11a cards: mix of Proxim and Netgear.

Diameter: 6
-
7 hops.

REDES INALÁMBRICAS




MIC 2009/2010

Link bandwidths in the testbed

42



Cards use Autorate




Total node pairs:


23x22/2 = 253




90 pairs have non
-
zero
bandwidth in both directions.





Bandwidths vary significantly; lot of asymmetry.

REDES INALÁMBRICAS




MIC 2009/2010

Experiment 1


3
-
Minute TCP transfer between each node pair


23 x 22 = 506 pairs


1 transfer at a time


Long transfers essential for consistent results



For each transfer, record:


Throughput


Number of paths


Path may change during transfer


Average path length


Weighted by fraction of packets along each path

43

REDES INALÁMBRICAS




MIC 2009/2010

44

Median Throughput

ETX performs best. RTT performs worst.

REDES INALÁMBRICAS




MIC 2009/2010

45

Impact on Path Lengths

Path length is generally higher under ETX.

REDES INALÁMBRICAS




MIC 2009/2010

46

Throughput
vs

path length

PktPair

suffers from self
-
interference only on multi
-
hop paths.

REDES
INALÁMBRICAS






Máster de Ingeniería
de
Computadores
-
DISCA

Redes Inalámbricas


Tema 4

Wireless Mesh Networks


Terminology


Study case: Guifi.net


Mesh HW and SW


Elements of mesh routing


IEEE 802.11s


REDES INALÁMBRICAS




MIC 2009/2010

The standard 802.11s: history


The Mesh Standard 802.11s is currently under development and
unapproved.


The development started in September 2003 and a Call for Proposals
was issued in May 2005.


The 15 proposals received by the IEEE were submitted to vote in July
2005.


All the ideas have been merged into two different proposals, called “See
-
Mesh”
and “Wi
-
Mesh”.


Wi
-
Mesh (sponsored by Nortel, Accton, Thomson, Philips, InterDigital, MITRE,
NextHop and Comnets) has been merged to See
-
Mesh (sponsored by Intel, Nokia,
Motorola, Texas Instruments and NTT DoCoMo) in January 2006.


The TGs goal for the March 2010 IEEE 802.11 meeting is to resolve all
outstanding comments, produce Draft 5.0, and
recirculate
.


48

REDES INALÁMBRICAS




MIC 2009/2010

The standard 802.11s and D1.00


802.11s is an extension of the traditional 802.11 protocol for WLAN
communication and adds MESH functionality (routing) at Link layer
(Level 2).


802.11s (MESH) is transparent for higher levels.


802.11s Device Classes
:


Stations (STA): Non
-
mesh capable station


Mesh Points (MP): Mesh capable station


Mesh AP (MAP): MP + AP


Mesh Portal (MPP): Entry/exit to wired network. Support transparent
bridging, address learning, and bridge
-
to
-
bridge communication (spanning
tree etc).


Root Portal: MPP configured for topology building. Elected to become the
root of the default forwarding tree


49

REDES INALÁMBRICAS




MIC 2009/2010

Joining the Mesh


Each MP should have more
than one Radio Interface


more than one channel is
joined


Each channel belongs to a

Unified Channel Graph
”,
connecting more than two
stations


Each MP has a table with a
priority list for every active
channel

50

MP2

MP1

MP3

MP4

Unified Channel
Graph

REDES INALÁMBRICAS




MIC 2009/2010

Steps in joining a Mesh

1.
MP1 “feels” some mesh frames in the air

2.
MP1 tries to read the Mesh ID, the MWLAN Capability Element and
the Profile (eg. Link State)

3.
If MP1 can support the connection (in terms of protocol and profile),
it sends to “Candidate Neighbours” some frames to join the mesh

4.
Start of authentication

5.
If authentication is succesfully completed, MP1 is connected to the
mesh

51

REDES INALÁMBRICAS




MIC 2009/2010

Authentication and Privacy


No central authority or hierarchy


Security about


Authentication to the Mesh Network


Confidentiality and integrity of private data


Protection from DoS attacks


Open issues


A possible choice for having a secured authentication, provide a secure key
distribution and to prevent unauthorized connections could be the modification of
the 802.11i protocol, specifically designed for the traditional 802.11 security.


An option is to use a centralized server for primary authentication. Once the
authentication ends successfully, the Supplicant (new MP) and the Authenticator
(a MP connected to the Mesh network) can start an handshake and then establish
a secure connection.


Need to extend traditional 802.11i techniques for having fast
-
reconnect (still under
discussion as of today)


52

REDES INALÁMBRICAS




MIC 2009/2010

Routing techniques


D1.00 defines one “Mandatory Protocol” for the Path Selection (
Hybrid
wireless mesh protocol (HWMP)
, inspired by AODV and Tree
-
based
routing), but any vendor of 802.11s could define any other protocol


An optional protocol (
Radio Aware OLSR
) is described in the 802.11s
draft


MWLAN Capability Element is used to inform new nodes of which
protocol is in use

53