The Hazy-Sighted Link State Routing Protocol ( HSLS ) is a wireless mesh network routing protocol being developed by the CUWiN Foundation. This is an algorithm allowing computers communicating via digital radio in a mesh network to forward messages to computers that are out of reach of direct radio contact. Its network overhead is theoretically optimal, utilizing both proactive and reactive link-state routing to limit network updates in space and time. Its inventors believe it is a more efficient protocol to route wired networks as well. HSLS was invented by researchers at BBN Technologies .
34-465: HSLS was made to scale well to networks of over a thousand nodes, and on larger networks begins to exceed the efficiencies of the other routing algorithms. This is accomplished by using a carefully designed balance of update frequency, and update extent in order to propagate link state information optimally. Unlike traditional methods, HSLS does not flood the network with link-state information to attempt to cope with moving nodes that change connections with
68-431: A change in the connectivity map happens, it is necessary to recompute the shortest-path tree and then recreate the routing table. BBN Technologies discovered how to compute only that part of the tree which could have been affected by a given change in the map. In some cases, it is reasonable to reduce the number of nodes that generate LSA messages. For this reason, a topology reduction strategy can be applied, in which only
102-487: A failed node until former neighbors send long-distance announcements. Thus, HSLS may fail in some circumstances requiring high assurance. While the papers describing HSLS do not focus on security, techniques such as digital signatures on routing updates can be used with HSLS (similar to OSPF with Digital Signatures ), and BBN has implemented HSLS with digital signatures on neighbor discovery messages and link state updates. Such schemes are challenging in practice because in
136-418: A link-state protocol, the only information passed between nodes is connectivity related . Link-state algorithms are sometimes characterized informally as each router "telling the world about its neighbors." In link-state routing protocols, each router possesses information about the complete network topology. Each router then independently calculates the best next hop from it for every possible destination in
170-741: A mechanism that would calculate routes more quickly when network conditions changed and thus lead to more stable routing. The technique was later adapted for use in the contemporary link-state routing protocols IS-IS and OSPF. Cisco literature refers to Enhanced Interior Gateway Routing Protocol (EIGRP) as a "hybrid" protocol, despite the fact it distributes routing tables instead of topology maps. However, it does synchronize routing tables at start-up as OSPF does and sends specific updates only when topology changes occur. In 2004, Radia Perlman proposed using link-state routing for layer 2 frame forwarding with devices called routing bridges , or Rbridges. The Internet Engineering Task Force has standardized
204-429: A multi-cloud environment. Variable access nodes across the interface protocol may also bypass the simultaneous access node problem. The Optimized Link State Routing Protocol (OLSR) is a link-state routing protocol optimized for mobile ad hoc networks (which can also be used on other wireless ad hoc networks ). OLSR is proactive and uses hello and topology control messages to disseminate link-state information into
238-418: A network without any moving nodes. The algorithm has a few special features to cope with cases that are common in radio networks, such as unidirectional links, and looped-transmission caused by out-of-date routing tables . In particular, it reroutes all transmissions to nearby nodes whenever it loses a link to an adjacent node. It also retransmits its adjacency when this occurs. This is useful precisely because
272-401: A short message, the link-state advertisement , which: This message is sent to all the nodes on a network. As a necessary precursor, each node in the network remembers, for every one of its neighbors, the sequence number of the last link-state message which it received from that node. When a link-state advertisement is received at a node, the node looks up the sequence number it has stored for
306-563: A subset of the network nodes generate LSA messages. Two widely studied approaches for topology reduction are multipoint relays that are at the base of the Optimized Link State Routing Protocol (OLSR) but have also been proposed for OSPF and connected dominating sets that were again proposed for OSPF. With Fisheye State Routing (FSR), the LSA are sent with different time-to-live values to restrict their diffusion and limit
340-413: Is O ( N 1.5 ) {\displaystyle O(N^{1.5})} compared to standard link state which scales as O ( N 2 ) {\displaystyle O(N^{2})} , where N is the number of nodes in the network. Because HSLS sends distant updates infrequently, nodes do not have recent information about whether a distant node is still present. This issue
374-400: Is "The total overhead is defined as the amount of bandwidth used in excess of the minimum amount of bandwidth required to forward packets over the shortest distance (in number of hops) by assuming that the nodes had instantaneous full-topology information." They then made some reasonable assumptions and used a mathematical optimization to find the times to transmit link state updates, and also
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#1732859098149408-411: Is in the network, because complete, though out-of-date routing information is present in every node. However, this is not the same as knowing whether a node is in the network. This guess may be adequate for most tariff network use, like telephony, but it may not be adequate for safety-related military or avionics . HSLS has good scalability properties. The asymptotic scalability of its total overhead
442-415: Is present to some extent in all link state protocols, because the link state database may still contain an announcement from a failed node. However, protocols like OSPF will propagate a link state update from the failed nodes neighbors, and thus all nodes will learn quickly of the failed node's demise (or disconnection). With HSLS, one can't disambiguate between a node that is still present 10 hops away and
476-401: Is quite simple. The routing information and the data transfer are decentralized, and should therefore have good reliability and performance with no local hot spots. The system requires capable nodes with large amounts of memory to maintain routing tables. Fortunately, these are becoming less expensive all the time. The system gives a very quick, relatively accurate guess about whether a node
510-489: Is that every node constructs a map of the connectivity to the network in the form of a graph , showing which nodes are connected to which other nodes. Each node then independently calculates the next best logical path from it to every possible destination in the network. Each collection of best paths will then form each node's routing table . This contrasts with distance-vector routing protocols, which work by having each node share its routing table with its neighbors, in
544-529: The Transparent Interconnection of Lots of Links (TRILL) protocol to accomplish this. More recently, this hierarchical technique was applied to wireless mesh networks using the Optimized Link State Routing Protocol (OLSR). Where a connection can have varying quality, the quality of a connection can be used to select better connections. This is used in some ad hoc routing protocols that use radio frequency transmission. The first main stage in
578-408: The ad hoc environment reachability of public key infrastructure servers cannot be assured. Like almost all routing protocols, HSLS does not include mechanisms to protect data traffic. (See IPsec and TLS .) Link-state routing protocol Link-state routing protocols are one of the two main classes of routing protocols used in packet switching networks for computer communications ,
612-401: The breadth of nodes that the link state updates should cover. Basically, both should grow to the power of two as time increases. The theoretical optimal number is very near to two, with an error of only 0.7%. This is substantially smaller than the likely errors from the assumptions, so two is a perfectly reasonable number. A local routing update is forced whenever a connection is lost. This is
646-405: The candidate list. (When there are none, all the nodes in the network will have been added to the tree.) This procedure ends with the tree containing all the nodes in the network. For any given destination node, the best path for that destination is the node which is the first step from the root node, down the branch in the shortest-path tree which leads toward the desired destination node. Whenever
680-465: The first adaptive routing network of computers, using link-state routing, was designed and implemented during 1976–1977 by a team from Plessey Radar led by Bernard J Harris; the project was for "Wavell" – a system of computer command and control for the British Army . The first link-state routing concept was published in 1979 by John M. McQuillan (then at Bolt, Beranek and Newman ) as
714-414: The link-state algorithm is to give a map of the network to every node. This is done with several subsidiary steps. First, each node needs to determine what other ports it is connected to over fully working links; it does this using reachability protocol that it runs periodically and separately with each of its directly connected neighbours. Each node periodically (and in case of connectivity changes) sends
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#1732859098149748-425: The mobile ad hoc network. Using hello messages, each node discovers two-hop neighbor information and elects a set of multipoint relays (MPRs). MPRs make OLSR distinct from other link-state routing protocols. Individual nodes use the topology information to compute next-hop paths regarding all nodes in the network using shortest-hop forwarding paths. Asymptotic Too Many Requests If you report this error to
782-418: The most valuable, long-distance links are also the least reliable in a radio network. The network establishes pretty good routes in real time, and substantially reduces the number and size of messages sent to keep the network connected, compared to many other protocols. Many of the simpler mesh routing protocols just flood the whole network with routing information whenever a link changes. The actual algorithm
816-405: The neighbors is recomputed and then flooded throughout the network whenever there is a change in the connectivity between the node and its neighbors, e.g., when a link fails. The second main stage in the link-state algorithm is to produce routing tables by inspecting the maps. Each node independently runs an algorithm over the map to determine the shortest path from itself to every other node in
850-494: The network grows larger. The best algorithms seem to be in a sweet spot in the middle. The routing information is called a "link state update." The distance that a link-state is copied is the " time to live " and is a count of the number of times it may be copied from one node to the next. HSLS is said to optimally balance the features of proactive, reactive, and suboptimal routing approaches. These strategies are blended by limiting link state updates in time and space. By limiting
884-402: The network using local information of the topology. The collection of best next hops forms the routing table. This contrasts with distance-vector routing protocols , which work by having each node share its routing table with its neighbours. In a link-state protocol, the only information passed between the nodes is the information used to construct the connectivity maps. What is believed to be
918-419: The network; generally, some variant of Dijkstra's algorithm is used. A node maintains two data structures: a tree containing nodes which are "done", and a list of candidates . The algorithm starts with both structures empty; it then adds to the first one the node itself. The variant of a greedy algorithm then repetitively does the following: The two steps are repeated as long as there are any nodes left in
952-467: The others being distance-vector routing protocols . Examples of link-state routing protocols include Open Shortest Path First (OSPF) and Intermediate System to Intermediate System (IS-IS). The link-state protocol is performed by every switching node in the network (i.e., nodes which are prepared to forward packets; in the Internet , these are called routers ). The basic concept of link-state routing
986-505: The overhead due to control messages. The same concept is used also in the Hazy Sighted Link State Routing Protocol . If all the nodes are not working from exactly the same map, routing loops can form. These are situations in which, in the simplest form, two neighboring nodes each think the other is the best path to a given destination. Any packet headed to that destination arriving at either node will loop between
1020-407: The reactive part of the algorithm. A local routing update behaves just the same as the expiration of a timer. Otherwise, each time that the delay since the last update doubles, the node transmits routing information that doubles in the number of network-hops it considers. This continues up to some upper limit. An upper limit gives the network a global size and assures a fixed maximum response time for
1054-531: The rest of the network. Further, HSLS does not require each node to have the same view of the network. Link-state algorithms are theoretically attractive because they find optimal routes, reducing waste of transmission capacity. The inventors of HSLS claim that routing protocols fall into three basically different schemes: proactive (such as OLSR ), reactive (such as AODV ), and algorithms that accept sub-optimal routings. If one graphs them, they become less efficient as they are more purely any single strategy, and
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1088-448: The source of that link-state message; if this message is newer (i.e., has a higher sequence number), it is saved, the sequence number is updated, and a copy is sent in turn to each of that node's neighbors. This procedure rapidly gets a copy of the latest version of each node's link-state advertisement to every node in the network. The complete set produces the graph for the map of the network. The link-state message giving information about
1122-453: The time to live the amount of transmission capacity is reduced. By limiting the times when a proactive routing update is transmitted, several updates can be collected and transmitted at once, also saving transmission capacity. The designers started the tuning of these items by defining a measure of global network waste. This includes waste from transmitting route updates, and also waste from inefficient transmission paths. Their exact definition
1156-403: The two, hence the name. Routing loops involving more than two nodes are also possible. This can occur since each node computes its shortest-path tree and its routing table without interacting in any way with any other nodes. If two nodes start with different maps, it is possible to have scenarios in which routing loops are created. In certain circumstances, differential loops may be enabled within
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