Nomadic ommunications Wireless Mesh Networks Renato Lo igno Loigno@disi.unitn.it - Tel: 2026 Home Page: http://isi.unitn.it/locigno/index.php/teaching-duties/nomadic-communications opyright Quest operaèprotettadallalicenza: reative ommons ttribuzione-non commerciale-nonopere derivate 2.5 Italia License Per i dettagli, consultare http://creativecommons.org/licenses/by-nc-nd/2.5/it/ locigno@disi.unitn.it 2 d-hoc and WMN d-hoc network non permanent general purpose or specific (sensors) single or multi-hop, normally mobile may require routing (see OV and OLR) Wireless Mesh Networks (WMN) more structured than d-hoc may be hierarchical semi-permanent, some nodes are fixed requires routing locigno@disi.unitn.it 3
WMN: a general view locigno@disi.unitn.it 4 Mesh d-hoc network d-hoc can be meshed non single broadcast channel multi-hop require routing locigno@disi.unitn.it 5 Mesh: asic scenarios () xtended WLN access imple configuration no routing imple 802. handover support ouble radio guarantees good performance ingle radio creates resource conflicts 3 on the same channel suitable for low-cost low-performance locigno@disi.unitn.it 6 2
Mesh: asic scenarios (2) W is broadcast (GW) can be a bottleneck xtended WLN access Routing required imple 802. handover support ouble radio guarantees good performance ingle radio creates serious resource conflicts n+ on the same channel locigno@disi.unitn.it 7 Mesh: asic scenarios (3) locigno@disi.unitn.it 8 Mesh: asic scenarios (3) xtended WLN access asic infrastructuring ingle radio operation very difficult Multiple external gateways sophisticated, flow-based routing Non standard handover support flow based routing requires exporting the context address management require coordination W may be multi-hop How many channels? Point-to-point and broadcast channels in W locigno@disi.unitn.it 9 3
Mesh: asic scenarios (3) ddress management (HP) is a problem Flow-based routing may be impossible Joining/splitting of partitions is an open issue locigno@disi.unitn.it 0 Moving between belonging to different Mesh/W Mesh d-hoc: OV d-hoc On-demand istance Vector routing rfc356 V (see RIP) protocol for next-hop based routing On-emand: maintains routes only for nodes that are communicating Must build routes when requested Route Request (RRQ) are flooded through the network Nodes set-up reverse path pointers to the source OV assumes symmetric links locigno@disi.unitn.it Mesh d-hoc: OV The intended receiver sends back a Route Reply (RR) RR follow the reverse path set-up by intermediate nodes (unicast) establishing a shortest path route memorized by intermediate nodes Paths expire if not used protocol & transmission overhead guarantee of stability in dynamic, non reliable networks Usual V problems count to infinity, slow convergence,... in a dynamic environment may be too much throughput going to zero locigno@disi.unitn.it 2 4
OV Loop Freedom estination sequence numbers to order routing events in time Ordering among <seqno, hop count> tuples at different nodes on a path higher seqno has precedence if same seqno, lower hop count has precedence The final selection will be the shortest path (w.r.t. some metric, not necessarily hop-count) locigno@disi.unitn.it 3 Mesh d-hoc: OV Next-hop based (other proposals are based on source routing) Flat protocol: all nodes are equal an manage only one route per s-d pair can be inefficient in presence of highly variable link quality and persistence Good for sporadic communications ad for high mobility slow convergence difficulty in understanding topology changes. locigno@disi.unitn.it 4 Mesh d-hoc: OMV d-hoc On-demand Multipath istance Vector Routing in d Hoc Networks n extension to OV OMV computes multiple loop-free and link-disjoint paths Using dvertised Hop-count guarantees Loop-freedom variable, which is defined as the maximum hop count for all the paths. node only accepts an alternate path to the destination if it has a lower hop count than the advertised hop count for that destination Link-disjointness of multiple paths is achieved by using a particular property of flooding Performance comparison of OMV with OV shows that OMV improves the end-to-end delay, often more than a factor of two OMV reduces routing overheads by about 20% locigno@disi.unitn.it 5 5
asic OV Route iscovery RRQ (broadcast) When a route is needed, source floods a route request for the destination. locigno@disi.unitn.it 6 asic OV Route iscovery RRQ (broadcast) Reverse Path Reverse path is formed when a node hears a non-duplicate route request. ach node forwards the request at most once (pure flooding). locigno@disi.unitn.it 7 asic OV Route iscovery RRQ (broadcast) Reverse Path Reverse path is formed when a node hears a non-duplicate route request. ach node forwards the request at most once (pure flooding). locigno@disi.unitn.it 8 6
asic OV Route iscovery Reverse Path Observation: uplicate RRQ copies completely ignored. Therefore, potentially useful alternate reverse path info lost. locigno@disi.unitn.it 9 Use of duplicate RRQ: the wrong way Reverse Path Form reverse paths using all duplicate RRQ copies causes routing loops alternate loop-free reverse paths are build in OMV using some selected duplicate RRQ copies? locigno@disi.unitn.it 20 Loop Freedom Impose ordering among nodes in every path. Notion of upstream/downstream nodes Never form a route at a downstream node via an upstream node Prune portions of paths that are longer urviving s-d path will be disjoint and loop-free i j d locigno@disi.unitn.it 2 7
OMV Loop Freedom equence number rule: Keep only routes for the highest dest seqno (like in OV). For the same dest seqno, Route advertisement rule: Keep multiple routes but always advertise only one of them to others. Hop count of that path is the advertised hop count Which one? Longest path at the time of first advertisement Why? Maximize chances of forming more paths Route acceptance rule: ccept a route from a neighbor only if it has a smaller or equal advertised hop count. reak ties using node ids. No need for coordination with upstream nodes locigno@disi.unitn.it 22 OMV Routing Table ntry est eqno dvertised hop count Hop count Next hop Hop count 2 Next hop 2 locigno@disi.unitn.it 23 Multiple Loop-free Reverse Paths RRQ (broadcast) 0 uppose RRQ from includes highest seqno for itself. locigno@disi.unitn.it 24 8
Multiple Loop-free Reverse Paths RRQ (broadcast) Reverse Path 0 locigno@disi.unitn.it 25 Multiple Loop-free Reverse Paths 2 RRQ (broadcast) Reverse Path 0 2 locigno@disi.unitn.it 26 Multiple Loop-free Reverse Paths 2 Reverse Path 0 2 locigno@disi.unitn.it 27 9
Multiple Loop-free Forward Paths 2 Forward Path 0 2 nother modification to basic OV route discovery: multiple replies from destination. locigno@disi.unitn.it 28 How Many Paths? Too many paths are not useful Overhead proportional to # paths. iminishing utility with larger # paths. nalytical study in olution: isjoint paths utomatically fewer paths Paths fail independently, more robust Node or link disjoint? Too few node disjoint paths in dense networks using flooding link disjoint locigno@disi.unitn.it 29 Finding Link-disjoint Paths How? xamples Maintain last hop info in routing table nsure that next hops and last hops before destination are unique dest seq. next last hop no hop hop count N L N2 L2 This requires route request and replies to carry first hop info locigno@disi.unitn.it 30 0
Mesh d-hoc: OLR Optimized Link-tate Routing Protocol (rfc3626) Proactive, link-state routing protocol ased on the notion of MultiPoint Relay (MPR) Three main components: Neighbor ensing mechanism MPR Flooding mechanism topology iscovery (diffusion) mechanism. uxilary features of OLR: network association - connecting OLR to other networks locigno@disi.unitn.it 3 Mesh d-hoc: OLR asic neighbor sensing: periodic exchange of HLLO messages; HLLO messages list neighbors + "neighbor quality HR - link may be asymmetric YM - link is confirmed to be symmetric MPR - link is confirmed to be symmetric N neighbor selected as MPR Providing: topology information up to two hops MPR selector information notification locigno@disi.unitn.it 32 Mesh d-hoc: OLR ach node selects from among its neighbors an MPR set such that an emitted flooding message, relayed by the MPR nodes, can be received by all nodes in the 2-hop neighborhood Goals: reduce flooding overhead (select minimal sets) provide optimal flooding distances locigno@disi.unitn.it 33
Mesh d-hoc: OLR xchanges topology information with other nodes of the network regularly MPRs announce their status periodically in control messages In route calculation, the MPRs are used to form the route from a given node to any destination in the network Uses MPRs to facilitate efficient flooding of control messages The presence of a 2-tiear topology (MPRs are sort of supernodes) makes it complex and prone to failures locigno@disi.unitn.it 34 MPR selection algorithm ach point u has to select its set of MPR. Goal : select in the -neighborhood of u N(u) a set of nodes as small as possible which covers the whole 2-neighborhood of u N2(u) one in two steps: tep : elect nodes of N(u) which cover stub nodes of N2(u) stub nodes are those that are connected to one N(u) node only tep 2: elect among the nodes of N(u) not selected at the first step, the node which covers the highest number of nodes in N2(u) not yet connected locigno@disi.unitn.it 35 Repeat tep 2 until all N2(u) is reached MPR selection step stub node u elect nodes (light blue) in N(u) which cover stub nodes of N2(u) locigno@disi.unitn.it 36 2
MPR selection step 2 u elect the node in N(u) which cover the largest number of non-stub nodes in N2(u) locigno@disi.unitn.it 37 TMN etter pproach To Mesh d-hoc Networking V protocol using Link Qualities ased on periodic roadcast of Originator Messages OGM Link Quality metric is the number of received OGMs Path Metric is the product of link metric roadcast is always at minimum PHY rate... difficult to distinguish high speed paths OGM have TTL fields to avoid too long paths TTL must be tailored to the MH dimension locigno@disi.unitn.it 38 TMN TMN is a level 2.5 routing solution Uses M addresses to identify stations, avoiding the problem of changing IP addresses to deliver frames Not pure layer 2 since it runs in the kernel and is not integrated in NI cards or drivers Relies on Layer 2 info, like link quality end UP packets and not Layer 2 frames for routing purposes TMN does not have handover enhancement support low convergence makes connection fail We are proposing one (already in the distribution) with a colleague of yours from last year locigno@disi.unitn.it 39 3
TMN F G X wants to reach X locigno@disi.unitn.it 40 TMN :0 F :9 G X Nodes broadcast originator messages (OGM's) every second OGM's are rebroadcast Other nodes measure how many OGM's are received in a fixed time window locigno@disi.unitn.it 4 TMN F :8 :7 G X :7 TMN routing table Final routing table TO VI Q TO VI 8 7 locigno@disi.unitn.it 42 4
TMN :0 F :4 :6 :7 G X G TMN routing table G Final routing table TO VI Q TO VI 6 7 locigno@disi.unitn.it 43 TMN F X TMN routing table G :5 X :6 X Final routing table TO VI Q TO VI G 5 6 locigno@disi.unitn.it 44 TMN F X TMN routing table TMN routing table TO VI Q 9 G TMN routing table TO VI Q 7 4 TO VI Q G 5 6 X locigno@disi.unitn.it 45 5
urrent GW selection techniques GW2 Minimum hop count to gateways F G X Used by routing protocols like OV reates single over congested gateways GW locigno@disi.unitn.it 46 urrent GW selection techniques GW2 est link quality to GW 3.5 2.2 F G 2 X Used by source routing protocols like MIT rcr Link state protocols like OLR Prevents congested links to GW Not global optimum of GW W usage GW locigno@disi.unitn.it 47 urrent GW selection techniques 3 Mbps GW2 9 0 7 F 4 G 8 7 0 52 kbps GW 7 TMN has advanced a little further GW can advertise downlink speed User can choose GW selection based on GW with best W table GW (need history) X GW W x LQ an't trust advertised GW W oesn't achieve fairness locigno@disi.unitn.it 48 6
L xperimental RF 626 Found in many Linux releases V based on IP addresses problems with handovers and mobility Loop free, based on ideas similar to TMN, OV, V (estination equenced istance Vector) estination equenced locigno@disi.unitn.it 49 V Protocol Keep the simplicity of istance Vector Guarantee Loop Freeness New Table ntry for estination equence Number llow fast reaction to topology changes Make immediate route advertisement on significant changes in routing table but wait with advertising of unstable routes (damping fluctuations) locigno@disi.unitn.it 50 V (Table ntries) estination Next Metric eq. Nr Install Time table ata 0-550 00000 Ptr_ -02 00200 Ptr_ 3-588 00200 Ptr_ 4-32 00200 Ptr_ equence number originated from destination. nsures loop freeness. Install Time when entry was made (used to delete stale entries from table) table ata Pointer to a table holding information on how stable a route is. Used to damp fluctuations in network. locigno@disi.unitn.it 5 7
V (Route election) Update information is compared to own routing table. elect route with higher destination sequence number (This ensure to use always newest information from destination) 2. elect the route with better metric when sequence numbers are equal locigno@disi.unitn.it 52 V (Respond to Topology hanges) Immediate advertisements Information on new Routes, broken Links, metric change is immediately propagated to neighbors. Full/Incremental Update: Full Update: end all routing information from own table. Incremental Update: end only entries that has changed. (Make it fit into one single packet) locigno@disi.unitn.it 53 Fluctuations P Hops Q 0 Hops What are Fluctuations ntry for in : [, Q, 4, -00] makes roadcast with eq. Nr. -02 receives Update from P (, 5, -02) -> ntry for in : [, P, 5, -02] must propagate this route immediately. receives Update from Q (, 4, -02) -> ntry for in : [, Q, 4, -02] must propagate this route immediately. (,0,-02) This can happen every time or any other node does its broadcast and lead to unnecessary route advertisements in the network, so called fluctuations locigno@disi.unitn.it 54 8
amping Fluctuations P Hops Q 0 Hops How to damp fluctuations Record last and avg. ettling Time of every Route in a separate table. (table ata) eleting Time = Time between arrival of first route and the best route with a given seq. nr. still must update his routing table on the first arrival of a route with a newer seq. nr., but he can wait to advertising it. Time to wait is proposed to be 2*(avg. ettling Time). locigno@disi.unitn.it 55 Mesh Networks: 802.s Working group to deliver a standard for 802. (& around) base Mesh Networks There are drafts and early releases, but not yet a definitely released standard (as of 200) Tries to define a framework to support a Mesh network as a standard extended WLN with routing that goes beyond the standard minimum spanning tree of 802. interconnection locigno@disi.unitn.it 56 evice lasses in 802.s Mesh Point (MP) a point able to relay messages Mesh P (MP) a MP able to provide services to Ts Mesh Portal (MPP) a MP connected to a wired LN normally called a gateway and assumed to access the internet locigno@disi.unitn.it 57 9
Routing in 802.s Hybrid Wireless Mesh Protocol (HWMP) - Mandatory OV derived link-state protocol ased on trees for proaction and efficiency dd on-demand features (like OV) Radio ware OLR (R-OLR) Optional Radio aware metrics added to MPRs in OLR optional fish-eye routing capabilities association and discovery protocols for topology discovery and buildup locigno@disi.unitn.it 58 Routing in 802.s TMN probably supported Features for multi-gateway management upport for Vehicular networks, where some specialized features are needed Use only M addresses for routing Run directly in the diverse/ni cards Integration with the other 802. protocols... which is the real strength! locigno@disi.unitn.it 59 20