Embed Size (px)
Citation preview
Redes Inalámbricas – Tema 3Wireless Mesh NetworksRedes Inalámbricas – Tema 3Wireless Mesh Networks
�Overview of the technology�Study case: Guifi.net�Routing: metrics�IEEE 802.11s
REDES INALÁMBRICAS Máster de Ingeniería de Computadores 2008/2009
�IEEE 802.11s
MIC
2008/2
009 Overview
2
Wireless routers
Gateways
Printers, servers
Intra-mesh wireless links
Stationary client access
Mobile client access
Node Types Link Types
RE
DE
S I
NA
LÁ
MB
RIC
AS
Printers, servers
Mobile clients
Stationary clients
Mobile client access
Internet access links
MIC
2008/2
009 Gateways
�Multiple interfaces (wired & wireless)
�Mobility�Stationary (e.g. rooftop) – most common case
�Mobile
3R
ED
ES
IN
AL
ÁM
BR
ICA
S
�Mobile (e.g., airplane, busses/subway)
�Serve as (multi-hop) “access points” to user nodes
�Relatively few are needed, (can be expensive)
GW
MIC
2008/2
009 Wireless Routers
4
� At least one wireless interface.
� Mobility
� Stationary (e.g. rooftop)
� Mobile (e.g., airplane,
busses/subway).
� Provide coverage (acts as a mini-
RE
DE
S I
NA
LÁ
MB
RIC
AS
� Provide coverage (acts as a mini-cell-tower).
� Do not originate/terminate data flows
� Many needed for wide areas, hence, cost can be an issue.
MIC
2008/2
009 Users
�Typically one interface.�Mobility
�Stationary�Mobile
�Connected to the mesh network through wireless
RE
DE
S I
NA
LÁ
MB
RIC
AS
network through wireless routers (or directly to gateways)
�The only sources/destinations for data traffic flows in the network.
5
MIC
2008/2
009 User – Wireless Router Links
�Wired� Bus (PCI, PCMCIA, USB)� Ethernet, Firewire, etc.
�Wireless� 802.11x� Bluetooth
RE
DE
S I
NA
LÁ
MB
RIC
AS
�
� Proprietary� Point-to-Point or Point-to-
Multipoint� If properly designed is not a
bottleneck.� If different from router-to-
router links we’ll call them access links
6
MIC
2008/2
009 Router to Router Links
�Wireless�802.11x�Proprietary
�Usually multipoint to multipoint
RE
DE
S I
NA
LÁ
MB
RIC
AS
multipoint�Sometimes a collection of point to point
�Often the bottleneck�If different from router-to-user links we’ll call them backbone links
7
MIC
2008/2
009 Gateway to Internet Links
�Wired�Ethernet, TV Cable, Power Lines
�Wireless�802.16�Proprietary
RE
DE
S I
NA
LÁ
MB
RIC
AS
�Proprietary
�Point to Point or Point-to-Multipoint
�We’ll call them backhaullinks
�If properly designed, not the bottleneck
8
MIC
2008/2
009 How it Works
�User-Internet Data Flows� In most applications the main data flows
�User-User Data Flows
RE
DE
S I
NA
LÁ
MB
RIC
AS
�User-User Data Flows� In most applications a small percentage of data flows
9
MIC
2008/2
009 Taxonomy
10
WirelessNetworking
Multi-hopSingleHop
RE
DE
S I
NA
LÁ
MB
RIC
AS
Infrastructure-less(ad-hoc)
Infrastructure-based(Hybrid)
Infrastructure-less(MANET)
CellularNetworks Wireless Sensor
NetworksWireless Mesh
Networks
Car-to-car Networks(VANETs)
Infrastructure-based(hub&spoke)
802.11 802.16 Bluetooth802.11
MIC
2008/2
009 Broadband Internet Access
11
RE
DE
S I
NA
LÁ
MB
RIC
AS
MIC
2008/2
009 Layer 2 Connectivity
�The entire wireless mesh cloud becomes one (giant) Ethernet switch
�Simple, fast installation�Short-term events
12
RE
DE
S I
NA
LÁ
MB
RIC
AS
�Short-term events (e.g., conferences, conventions, shows)
�Where wires are not desired (e.g., hotels, airports)
�Where wires are impossible (e.g., historic buildings)
InternetInternet
MIC
2008/2
009 Community Networks
13
� Grass-roots broadband Internet Access
� Several neighbors may share their broadband connections with many
RE
DE
S I
NA
LÁ
MB
RIC
AS
Source: research.microsoft.com/mesh/
connections with many other neighbors
� Not run by ISPs
� Possibly in the disadvantage of the ISPs
MIC
2008/2
009
14
RE
DE
S I
NA
LÁ
MB
RIC
AS
Introducció a guifi.net
<Lloc>
<Data>
MIC
2008/2
009 Temes
� Volem explicar-vos:� què és guifi.net ?� com ho fem ?� com funciona ?� què s'està fent per <Zona> ?� com hi podré connectar des de casa ?� quins continguts hi ha a la xarxa ?� la plataforma de guifi.net
15
RE
DE
S I
NA
LÁ
MB
RIC
AS
� la plataforma de guifi.net� com hi puc col·laborar ?
MIC
2008/2
009 Què és guifi.net?
� fer xarxa oberta, lliure i neutral� Es forma a base d'interconnexió del tram de xarxa que aporta cada participant
�Oberta a la participació de tothom�Lliure perquè no hi ha un propietari que imposi restriccions�Neutral perquè és independent dels seus continguts
� Comuns Sensefils� http://guifi.net/ComunsSensefils
16
RE
DE
S I
NA
LÁ
MB
RIC
AS
MIC
2008/2
009 Com ho fem?
� projecte obert:� coordinació:
�entre els interessats d’un lloc per poder muntar la infraestructura comuna necessària per fer la xarxa
� col·laboració:�particulars, empreses i administracions
� no té una ubicació geogràfica determinada� molt estès per les comarques centrals
17
RE
DE
S I
NA
LÁ
MB
RIC
AS
� molt estès per les comarques centrals
� un lloc web:� amb informació, eines i coneixement� sobre xarxes, autoservei
Aviat 8.896!!
MIC
2008/2
009 Què NO és guifi.net?
� NO és una iniciativa comercial� NO és una “xarxa d'aficionats”
� Hi destaquen els usos professionals� És una de les xarxes més grans del món d'aquestes característiques
� NO és un proveïdor de serveis d’Internet (ISP) � NO és un sistema de pagament� NO és una tecnología en concret
18
RE
DE
S I
NA
LÁ
MB
RIC
AS
� NO és una tecnología en concret� És una combinació de moltes tecnologies portades a la pràctica
MIC
2008/2
009 Què NO és guifi.net?
� NO és una associació, comunitat, ajuntament o empresa� És un conjunt de tot això� Hi ha una Fundació que li dona suport
� NO representa cap organisme oficial� NO exigeix res a ningú
� cadascú aporta el que vol� sense cap tipus d’obligació
19
RE
DE
S I
NA
LÁ
MB
RIC
AS
� sense cap tipus d’obligació
MIC
2008/2
009 Com funciona?
� els usuaris tenim el nostre node a casa� connectem el node de casa amb la resta de nodes� com ?
� usem supernodes, el bon rendiment depèn de que n'hi hagi forces� tipus d'enllaços:
�casa – supernode�supernode – supernode
20
RE
DE
S I
NA
LÁ
MB
RIC
AS
�supernode – supernode�casa - casa
MIC
2008/2
009 Com és el node de casa?
� necessitem:� un ordinador� un router amb antena externa
�n'hi han que ja ho porten tot plegat� un fil de xarxa entre el router i l'ordinador
21
RE
DE
S I
NA
LÁ
MB
RIC
AS
MIC
2008/2
009 Com és el node de casa?
� important:�el millor enllaç
�poca potència�visió directa
�antena a la teulada�com la de la TV�apuntant al Punt d'Accés (AP)
22
RE
DE
S I
NA
LÁ
MB
RIC
AS
�apuntant al Punt d'Accés (AP) que ens dona cobertura
�Fer servir equips que se sàpiga que funcionaran, no tots serveixen ni fan la mateixa feina
http://wind.awmn.net/?page=nodes&n
ode=72
MIC
2008/2
009 Com és el node de casa?
�com ho faig ...� router i antena externa a la teulada�cable curt, 1 a 3 m�caixa estanca o sota teulada
�cable de xarxa entre el router i l'ordinador
23
Teulada
Antena
i router
Ordinador
RE
DE
S I
NA
LÁ
MB
RIC
AS
i l'ordinador� fins a 100 m
Ordinador
Portàtil
sense fils
Interior Exterior
Cable
xarxa
Cable
xarxa
Cable
xarxa
Router
sense fils
Sense
fils
MIC
2008/2
009 Com és el node de casa?
� i si ...� tinc dos o més ordinadors ?�som diferents veïns d'un edifici ?
�vull moure'm amb un portàtil ?
� ...
24
RE
DE
S I
NA
LÁ
MB
RIC
AS
� ...
MIC
2008/2
009 Com és un “supernode”?
� És un conjunt de ràdios amb antenes sectorials de cobertura i direccionals per a connexions a distància
25
RE
DE
S I
NA
LÁ
MB
RIC
AS
MIC
2008/2
009 Exemple de “supernode”
26
Connexionsd'usuaris
des de les cases
Connexió a altressupernodes
RE
DE
S I
NA
LÁ
MB
RIC
AS
8.4 Km
MIC
2008/2
009 Fotografies de “Supernodes”
27
RE
DE
S I
NA
LÁ
MB
RIC
AS
MIC
2008/2
009 Com m'hi podré connectar des de casa
� necessites tenir un trasto+antena que se sap que funciona� Linksys, Búffalo + antena� Nanostation, Mikrotik CPE...
� afegir-te en tres passos:� lloc on vius� router que tens� enllaç que fas
http://guifi.net/trespassos
28
RE
DE
S I
NA
LÁ
MB
RIC
AS
� http://guifi.net/trespassos
MIC
2008/2
009 Algunes fotografies
29
RE
DE
S I
NA
LÁ
MB
RIC
AS
MIC
2008/2
009 Quines coses hi ha a la xarxa?
�+ 8.896 nodes funcionant� la majoria entrellaçats
�més de 100 serveis icontinguts�Portes d'accés a Internet� Intercanvi d'arxius
30
RE
DE
S I
NA
LÁ
MB
RIC
AS
�Telèfon�Xat�Càmeres, Correu, webs, ...
MIC
2008/2
009 La xarxa a Catalunya
31
RE
DE
S I
NA
LÁ
MB
RIC
AS
MIC
2008/2
009 La xarxa a la Castellon
32
RE
DE
S I
NA
LÁ
MB
RIC
AS
MIC
2008/2
009 Quins continguts hi ha a la xarxa?
�servidors de pàgines web propis
�servidors de correu�servidors de disc i ftp�centraletes telefòniques�portes a Internet
33
RE
DE
S I
NA
LÁ
MB
RIC
AS
�portes a Internet�P2P intern�xat, emissora de ràdio, càmeres web, ...
IRC-Catalunya.org
#guifi
MIC
2008/2
009 Portes a Internet
�particulars�obertes�compartides
�públiques� sortida per proxy federat amb nom d'usuari
34
RE
DE
S I
NA
LÁ
MB
RIC
AS
nom d'usuari�navegar per internet�correu, missatgeria instantània...
Xarxa sense fils
PROXY: usuari i contrasenya
internetinternet
MIC
2008/2
009 Com hi puc col·laborar?
� participant connectant-te a la xarxa� particular, institució, empresa, ...
� estenent xarxa� Supernodes, apadrinant
� aportant continguts
35
RE
DE
S I
NA
LÁ
MB
RIC
AS
� aportant continguts� buscant o fent portes a Internet
� compartint el què vulguis
MIC
2008/2
009 La plataforma de guifi.net
�Aprovisionament de�Adreces IP�Configurador d'aparells� Informació sobre l'estat de la xarxa�Estat de les connexions, tràfic�Estadístiques y gràfiques
36
RE
DE
S I
NA
LÁ
MB
RIC
AS
�Estadístiques y gràfiques descentralitzades
�GIS per a la planificació de desplegaments
�Traces de camins, “pings”....� I moltes més coses!
MIC
2008/2
009 Exemple: La pàgina d'un node I
37
Menú d'utilitats (distàncies, línea de visió, edició...)
RE
DE
S I
NA
LÁ
MB
RIC
AS
Detall de daades i mapa
Gràfiques i estadístiques
MIC
2008/2
009 Exemple: La pàgina d'un node II
� Llistat d'enllaços i disponibilitat
38
RE
DE
S I
NA
LÁ
MB
RIC
AS
MIC
2008/2
009 Exemple: La pàgina d'un node III
� Llistat de connexions possibles (LOS)
39
RE
DE
S I
NA
LÁ
MB
RIC
AS
MIC
2008/2
009 Exemple: La pàgina d'un node IV
�Buscador de serveis i camins (traceroute) �Des d'un punt, cerca el camí cap a altres punts o descobreix serveis
�Busca el camí més curt�Es representa en un mapa
40
RE
DE
S I
NA
LÁ
MB
RIC
AS
�Es representa en un mapa
MIC
2008/2
009 Preguntes freqüents
� De qui és guifi.net ?� De qui en forma part
� Qui paga guifi.net ?� Els participants, aportant infraestructures i serveis
� Quin cost té entrar a guifi.net ?� Cap� Comprar-te el material i fer-te o encarregar la instal·lació
41
RE
DE
S I
NA
LÁ
MB
RIC
AS
� Comprar-te el material i fer-te o encarregar la instal·lació
� Hi ha quotes periòdiques ?� No� Pots participar en les millores de material d'ús comú
MIC
2008/2
009 Preguntes freqüents
� Puc connectar-me directament amb el portàtil ?� Així m'estalvio uns 'calerons'� No! (excepte en zones habilitades) � Els portàtils ... :� Connexions bidireccionals� Tenen antenes petites� Veuen els punts d'accés...
...pero no emeten fins als AP
42
RE
DE
S I
NA
LÁ
MB
RIC
AS
...pero no emeten fins als AP� Connecten només en un
rang de metres
MIC
2008/2
009 Preguntes freqüents
� I, això és legal ?�Sí !�Liberalització Unió Europea�Llei de Telecomunicacions
�Autoprestacions
�Quadre de Freqüències:�Ús comú: 2.4 i 5 GHz
43
RE
DE
S I
NA
LÁ
MB
RIC
AS
�Ús comú: 2.4 i 5 GHz
� I, això és segur ?�La seguretat la proporciona la gestió de la disponibilitat de la xarxa i l'encriptació de les comunicacions quan és necessari.
MIC
2008/2
009
Some Key Characteristics of (Radio) Wireless Communications
� “Unshielded” or “open” in the air, i.e., electromagnetic fields� (Multi-Path) Fading and Shadowing
� path loss: due to attenuation, (atmospheric) absorption, … � multi-path effect: due to refraction, reflection, …� “shadowing”: reflection from objects and nodes (esp. in motion)
� Environmental noises and Interference from other nodes� Hence: “connectivity” between two nodes depends on
44
RE
DE
S I
NA
LÁ
MB
RIC
AS
� Hence: “connectivity” between two nodes depends on� where two nodes are, and their specific “environment” at the time
�distance, terrain, noises, … � interference from other surrounding nodes� transmission power of sender� specifics of receiver decoding algorithm/hardware design � ……
� Typical physical layer metrics:� power, distance, signal-to-noise ratio (SNR), signal-to-noise-and-interference ratio
(SNIR), bit error rate (BER)
MIC
2008/2
009 Protocols should exploit intermediate-quality links
� Link-quality-aware routing (ETX, LQSR)� ETX: use expected # of transmissions over a certain time period (e.g., a second)
measured via broadcast [Mobicom’03]� ETX as “link weight” metric used in ExOR
� Opportunistic protocols (ExOR, OMAC)� ExOR: extremely opportunistic routing
� Other mechanisms/protocols, e.g.,
45
RE
DE
S I
NA
LÁ
MB
RIC
AS
� 802.11 transmit bit-rate selection� Multicast data distribution
MIC
2008/2
009 Traditional Routing (used in MANET)
46
packet packet
A B
RE
DE
S I
NA
LÁ
MB
RIC
AS
� Abstract radio to look like a wired link� Identify a route, forward over links
packet src dst
C
MIC
2008/2
009 Radios aren’t wires!
47
A B
RE
DE
S I
NA
LÁ
MB
RIC
AS
�Every packet is broadcast�Reception is probabilistic
1 2 3 4 5 61 2 3 63 51 42 3 4 561 2 4 5 6 src dst
C
MIC
2008/2
009 Hop Count Metric
� Maximizes the distance traveled by each hop� Minimizes signal strength -> Maximizes the loss ratio� Uses a higher TxPower -> Interference
� Possibly many shortest routes� Avoid lossy links?
48
RE
DE
S I
NA
LÁ
MB
RIC
AS
MIC
2008/2
009 ETX
� The predicted number of data transmissions required to send a packet over a link
� The ETX of a path is the sum of the ETX values of the links over that path
� Examples:� ETX of a 3-hop route with perfect links is 3� ETX of a 1-hop route with 50% loss is 2
49
RE
DE
S I
NA
LÁ
MB
RIC
AS
MIC
2008/2
009 ETX continued…
� Expected probability that a transmission is successfully received and acknowledged is df x dr� df is forward delivery ratio� dr is reverse delivery ratio
� Each attempt to transmit a packet is a Bernoulli trial, so…
50
RE
DE
S I
NA
LÁ
MB
RIC
AS
MIC
2008/2
009 Details of ETX
� Based on delivery ratios, which affect throughput� Detects and handles asymmetry by incorporating loss ratios in each
direction� Uses precise link loss ratios measurements to make fine-grained
decisions between routes� Assumes you can measure these ratios precisely
� Penalizes routes with more hops, which have lower throughput due to
51
RE
DE
S I
NA
LÁ
MB
RIC
AS
� Penalizes routes with more hops, which have lower throughput due to inter-hop interference� Assumes loss rates are equal over links
� Tends to minimize spectrum use, which should maximize overall system capacity (reduce power too)� Each node spends less time retransmitting data
MIC
2008/2
009 Acquiring ETX values
� Measured by broadcasting dedicated link probe packets with an average period τ (jittered by ±0.1τ)
� Delivery ratio:
� count(t-w,t) is the # of probes received during window w� w/τ is the # of probes that should have been received
� Each probe contains this information
52
RE
DE
S I
NA
LÁ
MB
RIC
AS
� Each probe contains this information
MIC
2008/2
009 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
53
RE
DE
S I
NA
LÁ
MB
RIC
AS
� All the ideas have been merged into two different proposals, called “See-Mesh” and “Wi-Mesh”.
MIC
2008/2
009 The standard 802.11s: history
�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.
� Actually (as of January 2009) the draft is D2.0 and the 802.11s Task Group is working on comments received during the 2009 ballot.
54
RE
DE
S I
NA
LÁ
MB
RIC
AS
MIC
2008/2
009 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.
55
TRANSPORT
APPLICATIONLAYER 5
4
RE
DE
S I
NA
LÁ
MB
RIC
AS
PHYSICALLAYER
DATA LINKLAYER
NETWORKLAYER
TRANSPORTLAYER
The TCP/IP model
4
3
2
1
MIC
2008/2
009 Classes of devices
� 802.11s D1.00 contains a distinction between:� MP (Mesh Point): it establishes peer links with neighbour nodes� MAP (Mesh Access Point): a MP with a double interface: mesh towards other
MAPs, traditional AP towards the clients� MPP (Mesh Portal): gateway between the MESH infrastructure and a traditional
external network� STA (Station): traditional client connected to a MAP
56
RE
DE
S I
NA
LÁ
MB
RIC
AS
MIC
2008/2
009 Key issues
� How can a new node join the network?� How do we protect from unauthorized access?� How can a Mesh network route the packets?� How can co-exist mesh Infrastructured or Mixed networks and
traditional networks?
57
RE
DE
S I
NA
LÁ
MB
RIC
AS
MIC
2008/2
009 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
58
Unified Channel
Graph
RE
DE
S I
NA
LÁ
MB
RIC
AS
stations�Each MP has a table with a
priority list for every active channel
MP2
MP1
MP3
MP4
MIC
2008/2
009 Steps in joining a Mesh
1. MP1 “feels” some mesh frames in the air2. 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
59
RE
DE
S I
NA
LÁ
MB
RIC
AS
4. Start of authentication5. If authentication is succesfully completed, MP1 is connected to the
mesh
MIC
2008/2
009 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
60
RE
DE
S I
NA
LÁ
MB
RIC
AS
MIC
2008/2
009 Authentication and Privacy
� 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.
61
RE
DE
S I
NA
LÁ
MB
RIC
AS
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)
MIC
2008/2
009 Routing techniques
�D1.00 defines one “Mandatory Protocol” for the Path Selection (HWMP, inspired by AODV and Tree-based routing), but any vendor of 802.11s could define any other protocol
�An optional protocol (RA-OLSR) is described in the 802.11s draft
�MWLAN Capability Element is used to inform new nodes of which protocol is in use
RE
DE
S I
NA
LÁ
MB
RIC
AS
which protocol is in use�There are two kind of routing techniques:
� Proactive routing� Reactive routing
62
