Redes Inalámbricas – Tema 4 Wireless Mesh Networks

REDES INALÁMBRICAS Máster de Ingeniería de Computadores-DISCA

Redes Inalámbricas – Tema 4Wireless Mesh Networks

TerminologyStudy case: Guifi.netMesh HW and SWElements of mesh routingIEEE 802.11s

Thanks to Sebastian Büttrich, wire.less.dk

RED

ES IN

ALÁ

MB

RIC

AS

MIC

200

9/20

102

Mesh topology – a typical scenario

RED

ES IN

ALÁ

MB

RIC

AS

MIC

200

9/20

103

Community Networks

Broadband Internet Access technology

Several neighbors may share their broadband connections with many other neighbors

Not run by ISPsPossibly in the

disadvantage of the ISPs

Source: research.microsoft.com/mesh/

http://www.research.microsoft.com/mesh/

RED

ES IN

ALÁ

MB

RIC

AS

MIC

200

9/20

10 Overview4

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

RED

ES IN

ALÁ

MB

RIC

AS

MIC

200

9/20

105

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.

RED

ES IN

ALÁ

MB

RIC

AS

MIC

200

9/20

10

From Ramon Roca talk at:

Study case: Guifi.net

RED

ES IN

ALÁ

MB

RIC

AS

MIC

200

9/20

10What?

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 ownershipSame rules for allLowering TCO by being cost oriented/real value instead of price

dominance (How much it costs vs how much user can pay...)

RED

ES IN

ALÁ

MB

RIC

AS

MIC

200

9/20

10 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

RED

ES IN

ALÁ

MB

RIC

AS

MIC

200

9/20

10 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 ProvisioningNetwork Monitoring (traffic, status...)GIS applications (maps)Device Configuration

Technology agnosticLow cost wireless intensively used, but not restricted to (now

extending to fiber)

RED

ES IN

ALÁ

MB

RIC

AS

MIC

200

9/20

10 Example: The node page

Complete menus providing many features

Detailed drill/down information and maps

Graphs & Network statistics

RED

ES IN

ALÁ

MB

RIC

AS

MIC

200

9/20

10 Example: The node page II

List of nodes & availability Real time

RED

ES IN

ALÁ

MB

RIC

AS

MIC

200

9/20

10 Example: The node page III Suggested links, check for Line-of-Sight (LoS)

RED

ES IN

ALÁ

MB

RIC

AS

MIC

200

9/20

10 And now is time for...

Launching FFTH - FFTF projectsFiber From The Farms /

Houses, NOT just “To”...Launched in Summer

2,009Reuse of existing copper

infrastructure / posts

RED

ES IN

ALÁ

MB

RIC

AS

MIC

200

9/20

10 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.

RED

ES IN

ALÁ

MB

RIC

AS

MIC

200

9/20

1017 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

RED

ES IN

ALÁ

MB

RIC

AS

MIC

200

9/20

1018 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.

RED

ES IN

ALÁ

MB

RIC

AS

MIC

200

9/20

1019 Mesh Hardware: Commercial & proprietary

Tropos BelAir Strix And:

Nortel Nokia Cisco …

RED

ES IN

ALÁ

MB

RIC

AS

MIC

200

9/20

1020 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 MHzWRT54GS 32 8 200 MHz

Processor: Broadcom Price: circa 60€ (WRT54G)

RED

ES IN

ALÁ

MB

RIC

AS

MIC

200

9/20

1021 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, …

http://www.cuwin.net/

RED

ES IN

ALÁ

MB

RIC

AS

MIC

200

9/20

1022 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, ....

RED

ES IN

ALÁ

MB

RIC

AS

MIC

200

9/20

1023 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

RED

ES IN

ALÁ

MB

RIC

AS

MIC

200

9/20

1025 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.

RED

ES IN

ALÁ

MB

RIC

AS

MIC

200

9/20

1026 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.

RED

ES IN

ALÁ

MB

RIC

AS

MIC

200

9/20

1027 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).

RED

ES IN

ALÁ

MB

RIC

AS

MIC

200

9/20

1028 Select the network topology type

Simple mesh network plot

Clustered mesh with backbone

RED

ES IN

ALÁ

MB

RIC

AS

MIC

200

9/20

1029 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.

RED

ES IN

ALÁ

MB

RIC

AS

MIC

200

9/20

1030

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

Or sometimes (x-1)…

RED

ES IN

ALÁ

MB

RIC

AS

MIC

200

9/20

1031 Example layout of a wireless mesh network

RED

ES IN

ALÁ

MB

RIC

AS

MIC

200

9/20

1032 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)

RED

ES IN

ALÁ

MB

RIC

AS

MIC

200

9/20

1033 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

RED

ES IN

ALÁ

MB

RIC

AS

MIC

200

9/20

1034 Link Quality Metrics

Per-hop Round Trip Time (RTT)

Per-hop Packet-Pair (PktPair)

Expected transmissions (ETX)

Minimum-hop routing (HOP)Binary link quality

RED

ES IN

ALÁ

MB

RIC

AS

MIC

200

9/20

1035 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

RED

ES IN

ALÁ

MB

RIC

AS

MIC

200

9/20

1036 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 timesLossy links will have higher RTT

Disadvantages Expensive Self-interference due to queuing

RED

ES IN

ALÁ

MB

RIC

AS

MIC

200

9/20

1037 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

RED

ES IN

ALÁ

MB

RIC

AS

MIC

200

9/20

1038 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

RED

ES IN

ALÁ

MB

RIC

AS

MIC

200

9/20

1039 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

)P1(*)P1(1

rf ETX

RED

ES IN

ALÁ

MB

RIC

AS

MIC

200

9/20

1040 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

packetsProbe packets are smaller than data packetsBroadcast packets are sent at lower data rate

Does not take data rate or link load into account

RED

ES IN

ALÁ

MB

RIC

AS

MIC

200

9/20

10 Mesh Testbed41

Approx. 61 m

Appr

ox. 3

2 m

23 Laptops running Windows XP. 802.11a cards: mix of Proxim and Netgear.

Diameter: 6-7 hops.

RED

ES IN

ALÁ

MB

RIC

AS

MIC

200

9/20

10 Link bandwidths in the testbed42

0

5

10

15

20

25

30

0 5 10 15 20 25 30Higher Bandwidth (Mbps)

Low

er B

andw

dith

(Mbp

s)

• Cards use Autorate •Total node pairs: 23x22/2 = 253

• 90 pairs have non-zero bandwidth in both directions.

Bandwidths vary significantly; lot of asymmetry.

RED

ES IN

ALÁ

MB

RIC

AS

MIC

200

9/20

1043 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

RED

ES IN

ALÁ

MB

RIC

AS

MIC

200

9/20

1044

Median Throughput

0

200

400

600

800

1000

1200

1400

1600

HOP ETX RTT PktPair

Med

ian

Thro

ughp

ut (K

bps)

ETX performs best. RTT performs worst.

RED

ES IN

ALÁ

MB

RIC

AS

MIC

200

9/20

1045

0

1

2

3

4

5

6

7

8

0 1 2 3 4 5 6 7 8

Path Length with ETX

Path

Len

gth

with

HO

P

Impact on Path Lengths

Path length is generally higher under ETX.

RED

ES IN

ALÁ

MB

RIC

AS

MIC

200

9/20

1046

Throughput vs path length

PktPair

0

2000

4000

6000

8000

10000

12000

0 1 2 3 4 5 6 7 8

Average Pathlength (Hops)

Thro

ughp

ut (K

bps)

ETX

0

20004000

6000

800010000

12000

0 1 2 3 4 5 6 7 8

Average Path Length (Hops)

Thro

ughp

ut (K

bps)

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

RED

ES IN

ALÁ

MB

RIC

AS

MIC

200

9/20

10 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

RED

ES IN

ALÁ

MB

RIC

AS

MIC

200

9/20

10 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

RED

ES IN

ALÁ

MB

RIC

AS

MIC

200

9/20

10 Joining the MeshEach 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

MP3MP4

Unified Channel Graph

RED

ES IN

ALÁ

MB

RIC

AS

MIC

200

9/20

10 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 authentication5. If authentication is succesfully completed, MP1 is connected

to the mesh

51

RED

ES IN

ALÁ

MB

RIC

AS

MIC

200

9/20

10 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

RED

ES IN

ALÁ

MB

RIC

AS

MIC

200

9/20

1053 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

Redes Inalámbricas – Tema 4 Wireless Mesh Networks

Documents

Transcript of Redes Inalámbricas – Tema 4 Wireless Mesh Networks