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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 Máster de Ingeniería de Computadores-DISCA 2 MIC 2009/2010 REDES INALÁMBRICAS Mesh topology – a typical scenario 3 MIC 2009/2010 REDES INALÁMBRICAS 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 MIC 2009/2010 Overview Node Types Wireless routers Gateways Printers, servers Link Types Intra-mesh wireless links Stationary client access Mobile client access Mobile clients REDES INALÁMBRICAS Stationary clients Internet access links 5 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. REDES INALÁMBRICAS 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. 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 Máster de Ingeniería de Computadores-DISCA MIC 2009/2010 Study case: Guifi.net REDES INALÁMBRICAS From Ramon Roca talk at: MIC 2009/2010 REDES INALÁMBRICAS 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...) 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: REDES INALÁMBRICAS 7,500 online nodes 10,000 kms. of network links Sustained growth MIC 2009/2010 How? By building end-user oriented platform to enable the deployment of neutral networks at the last mile REDES INALÁMBRICAS 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) MIC 2009/2010 Example: The node page Complete menus providing many features REDES INALÁMBRICAS Detailed drill/down information and maps Graphs & Network statistics MIC 2009/2010 REDES INALÁMBRICAS Example: The node page II List of nodes & availability Real time MIC 2009/2010 REDES INALÁMBRICAS Example: The node page III Suggested links, check for Line-of-Sight (LoS) MIC 2009/2010 And now is time for... Launching FFTH - FFTF projects REDES INALÁMBRICAS Fiber From The Farms / Houses, NOT just “To”... Launched in Summer 2,009 Reuse of existing copper infrastructure / posts MIC 2009/2010 Open Spectrum Alliance Whitespaces + “smart” technologies = new opportunities for spectrum efficiency REDES INALÁMBRICAS 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 – 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 Máster de Ingeniería de Computadores-DISCA 17 MIC 2009/2010 REDES INALÁMBRICAS 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 MIC 2009/2010 REDES INALÁMBRICAS 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 MIC 2009/2010 Mesh Hardware: Commercial & proprietary Tropos BelAir Strix And: REDES INALÁMBRICAS Nortel Nokia Cisco … 20 MIC 2009/2010 REDES INALÁMBRICAS 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) 21 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 REDES INALÁMBRICAS CUWiN (the Champaign-Urbana Community Wireless Network) @ http://www.cuwin.net/ Various mesh protocols included: HSLS, ETX, … 22 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/ REDES INALÁMBRICAS 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 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: REDES INALÁMBRICAS Freifunk @ http://start.freifunk.net/ Uses OLSR DD-WRT @ http://www.dd-wrt.com/ Commercial Sveasoft @ http://sveasoft.com/ Talisman/Mesh Firmware 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 Máster de Ingeniería de Computadores-DISCA 25 MIC 2009/2010 REDES INALÁMBRICAS 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 omnidirectional 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 MIC 2009/2010 Important Considerations Various obstructions may interfere with the signals and should be considered: REDES INALÁMBRICAS 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 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 REDES INALÁMBRICAS 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 MIC 2009/2010 REDES INALÁMBRICAS Select the network topology type Simple mesh network plot Clustered mesh with backbone 29 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: REDES INALÁMBRICAS 10. 0.0.0 172. 16.0.0 192.168.0.0 - 10.255.255.255 172. 31.255.255 192.168.255.255 (10/8 prefix) (172.16/12 prefix) (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 MIC 2009/2010 A Method of assigning IP numbers (wireless interface): a proposal Backbone node: Or sometimes (x-1)… 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. REDES INALÁMBRICAS 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 MIC 2009/2010 REDES INALÁMBRICAS Example layout of a wireless mesh network 32 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: REDES INALÁMBRICAS 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 MIC 2009/2010 REDES INALÁMBRICAS 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 MIC 2009/2010 Link Quality Metrics Per-hop Round Trip Time (RTT) Per-hop Packet-Pair (PktPair) Expected transmissions (ETX) Minimum-hop routing (HOP) REDES INALÁMBRICAS Binary link quality 35 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 REDES INALÁMBRICAS Path with least sum of RTTs is selected 36 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 REDES INALÁMBRICAS Expensive Self-interference due to queuing 37 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 REDES INALÁMBRICAS Path with least sum of delays is selected 38 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 REDES INALÁMBRICAS More expensive than RTT 39 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 REDES INALÁMBRICAS ETX 1 (1 P ) * (1 P ) f Select the path with least total ETX r 40 MIC 2009/2010 Metric 3: Expected Transmissions Advantages Low overhead Explicitly takes loss rate into account Disadvantages REDES INALÁMBRICAS 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 REDES INALÁMBRICAS Approx. 32 m MIC 2009/2010 Mesh Testbed Approx. 61 m 23 Laptops running Windows XP. 802.11a cards: mix of Proxim and Netgear. Diameter: 6-7 hops. 42 Lower Bandwdith (Mbps) MIC 2009/2010 Link bandwidths in the testbed 30 • Cards use Autorate 25 •Total node pairs: 23x22/2 = 253 20 • 90 pairs have non-zero bandwidth in both directions. 15 10 5 REDES INALÁMBRICAS 0 0 5 10 15 20 25 Higher Bandwidth (Mbps) 30 Bandwidths vary significantly; lot of asymmetry. 43 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: REDES INALÁMBRICAS Throughput Number of paths Path may change during transfer Average path length Weighted by fraction of packets along each path 44 MIC 2009/2010 Median Throughput 1600 Median Throughput (Kbps) 1400 1200 1000 800 600 400 REDES INALÁMBRICAS 200 0 HOP ETX RTT ETX performs best. RTT performs worst. PktPair 45 MIC 2009/2010 Impact on Path Lengths 8 Path Length with HOP 7 6 5 4 3 2 REDES INALÁMBRICAS 1 0 0 1 2 3 4 5 6 7 Path Length with ETX Path length is generally higher under ETX. 8 46 MIC 2009/2010 Throughput vs path length Throughput (Kbps) ETX 12000 10000 8000 6000 4000 2000 0 0 1 2 3 4 5 6 7 8 Average Path Length (Hops) PktPair Throughput (Kbps) REDES INALÁMBRICAS 12000 10000 8000 6000 4000 2000 0 0 1 2 3 4 5 6 7 8 Average Pathlength (Hops) PktPair suffers from self-interference only on multi-hop paths. 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 Máster de Ingeniería de Computadores-DISCA 48 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. REDES INALÁMBRICAS 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 MIC 2009/2010 REDES INALÁMBRICAS 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 MIC 2009/2010 REDES INALÁMBRICAS 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 51 MIC 2009/2010 REDES INALÁMBRICAS 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 52 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 REDES INALÁMBRICAS 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) 53 MIC 2009/2010 REDES INALÁMBRICAS 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