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Redes Inalámbricas – Tema 4 Wireless Mesh Networks

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. Mesh topology – a typical scenario. Community Networks . Broadband Internet Access technology

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Redes Inalámbricas – Tema 4 Wireless Mesh Networks

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  1. Redes Inalámbricas – Tema 4Wireless Mesh Networks Terminology Study case: Guifi.net Mesh HW and SW Elements of mesh routing IEEE 802.11s ThankstoSebastian Büttrich, wire.less.dk

  2. Mesh topology – a typical scenario

  3. 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 Source: research.microsoft.com/mesh/

  4. Overview Link Types Node Types Intra-mesh wireless links Stationary client access Mobile client access Internet access links Wireless routers Gateways Printers, servers Mobile clients Stationary clients

  5. 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.

  6. Redes Inalámbricas – Tema 4Wireless Mesh Networks Terminology Study case: Guifi.net Mesh HW and SW Elements of mesh routing IEEE 802.11s ThankstoSebastian Büttrich, wire.less.dk

  7. Study case: Guifi.net From Ramon Roca talk at:

  8. 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...)

  9. 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

  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 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)

  11. Example: The node page Complete menus providing many features Detailed drill/down information and maps Graphs & Network statistics

  12. Example: The node page II • List of nodes & availability • Real time

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

  14. 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

  15. Open Spectrum Alliance • Whitespaces + “smart” technologies = new opportunities for spectrumefficiency • 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.

  16. Redes Inalámbricas – Tema 4Wireless Mesh Networks Terminology Study case: Guifi.net Mesh HW and SW Elements of mesh routing IEEE 802.11s ThankstoSebastian Büttrich, wire.less.dk

  17. 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

  18. 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.

  19. Mesh Hardware: Commercial & proprietary • Tropos • BelAir • Strix • And: • Nortel • Nokia • Cisco • …

  20. 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 speedWRT54G v2 16 4 200 MHzWRT54GS 32 8 200 MHz • Processor: Broadcom • Price: circa 60€ (WRT54G)

  21. 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 • Meshlinuxbyelektra • @ 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, …

  22. 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, ....

  23. 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

  24. Redes Inalámbricas – Tema 4Wireless Mesh Networks Terminology Study case: Guifi.net Mesh HW and SW Elements of mesh routing IEEE 802.11s ThankstoSebastian Büttrich, wire.less.dk

  25. 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.

  26. 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.

  27. 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).

  28. Select the network topology type Simple meshnetworkplot Clusteredmeshwithbackbone

  29. 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.

  30. A Method of assigning IP numbers (wireless interface):a proposal Orsometimes (x-1)… • 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

  31. Example layout of a wireless mesh network

  32. 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)

  33. 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

  34. Link Quality Metrics • Per-hop Round Trip Time (RTT) • Per-hop Packet-Pair (PktPair) • Expected transmissions (ETX) • Minimum-hop routing (HOP) • Binary link quality

  35. 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

  36. 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

  37. 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

  38. 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

  39. 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

  40. 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

  41. Mesh Testbed 23 Laptops running Windows XP. 802.11a cards: mix of Proxim and Netgear. Diameter: 6-7 hops.

  42. Link bandwidths in the testbed • Cards use Autorate • Total node pairs: • 23x22/2 = 253 • 90 pairs have non-zero bandwidth in both directions. Bandwidths vary significantly; lot of asymmetry.

  43. 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

  44. Median Throughput ETX performs best. RTT performs worst.

  45. Impact on Path Lengths Path length is generally higher under ETX.

  46. Throughput vs path length PktPair suffers from self-interference only on multi-hop paths.

  47. Redes Inalámbricas – Tema 4Wireless Mesh Networks Terminology Study case: Guifi.net Mesh HW and SW Elements of mesh routing IEEE 802.11s

  48. 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.

  49. 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

  50. 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 Unified Channel Graph MP1 MP2 MP4 MP3

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