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'''Associativity-Based Routing'''<ref>{{citation |title="Associativity-based routing for ad hoc mobile networks" |url=https://scholar.google.com/citations?view_op=view_citation&hl=en&user=YTwSsH4AAAAJ&citation_for_view=YTwSsH4AAAAJ:d1gkVwhDpl0C}}</ref><ref>{{citation |title="A novel distributed routing protocol to support ad-hoc mobile computing" |url=https://scholar.google.com/citations?view_op=view_citation&hl=en&user=YTwSsH4AAAAJ&citation_for_view=YTwSsH4AAAAJ:2osOgNQ5qMEC}}</ref><ref name="auto">[[Chai Keong Toh]] Ad Hoc Mobile Wireless Networks, Prentice Hall Publishers, 2002. ISBN 978-0-13-007817-9</ref><ref>{{citation |title="Long-lived ad-hoc routing based on the concept of Associativity" |url=https://scholar.google.com/citationsview_op=view_citation&hl=en&user=YTwSsH4AAAAJ&citation_for_view=YTwSsH4AAAAJ:YsMSGLbcyi4C}}</ref> (commonly known as '''ABR''') is a mobile routing protocol invented for [[wireless ad hoc networks]] or also known as [[Mobile Ad Hoc Networks]] (MANETs) and [[Wireless Mesh Network]]. ABR was invented in 1993, filed for a USA patent in 1996, and granted the patent in 1999. ABR was invented by [[Chai Keong Toh]] while doing his Ph.D. at Cambridge University. In the 1990s, our Internet is still largely wired. Toh was working on a different Internet – that of a rapidly deployable, infrastructureless, self-organizing, self-configuring mobile Internet. The challenges in such a network is mobility of nodes and link dynamics. Toh's prime argument is that there is no point in choosing a node to route packets if the route is unstable or going to be broken soon. So, he introduced a new routing metric (known as associativity ticks) and the concept of associativity, i.e., link stability among nodes over TIME and SPACE. Hence, ABR was born.
==Explanation==
In the early 1990s, the Internet is still largely wired. To achieve anytime anywhere computing, computers must be able to connect to each other wirelessly and automatically. The [[Internet Protocol]] at that time did not address mobility, and the formation of an rapidly deployable mobile Internet. The underlying protocols for Internet were TCP/UDP/IP. Those protocols do not support spontaneous network creation, and do not handle dynamics due to mobility of computers. The assumption was end host are static host, and they do not move. Another assumption was the network is wired (with copper wires or fiber).
Since existing Internet protocols cannot support ad hoc mobile computing, a new mobile Internet is need. This calls for a new network layer software that will enable anytime and anywhere mobile computing, while at the same time, retains compatibility with IP/UDP/TCP protocols already present in the wired Internet. ABR is an on-demand routing protocol, i.e., routes are created only as and when needed. This, in contrast, to the existing Internet where routes are immediately available and routing tables are constantly updated among routers. According to the publications,<ref name="auto"/> on-demand routing is chosen because it can reduce the amount of control packet traffic and this is suitable for a wireless network because bandwidth is limited.▼
▲This, in contrast, to the existing Internet where routes are immediately available and routing tables are constantly updated among routers. According to the publications,<ref name="auto"/> on-demand routing is chosen because it can reduce the amount of control packet traffic and this is suitable for a wireless network because bandwidth is limited.
==Route discovery phase==
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==Route reconstruction phase==
Because ABR chooses route that are long-lived or associativity-stable, most route so established will seldom experience link breaks. However, if one or more links are broken, there ABR will immediately respond and invoke the RRC – route reconstruction phase. The RRC basically repairs the broken link by having the upstream node (which sense the link break) doing a localized route repair. The localized route repair is in the form of localized broadcast query, in the search for an alternative long-lived partial route to the destination.
ABR route maintenance consists of:
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==Route deletion phase==
When a discovered route is no longer needed, a RD (Route Delete) packet will be initiated by the source node so that all intermediate nodes in the route will update their routing table entries and stopped relay data packets associated with this deleted route.
In addition to using RD to delete a route, ABR can also implement a soft state approach where route entries are expired or invalidated after timed out, when there is no traffic activity related to the route over a period of time.
==Practicality==
In 1998, ABR was successfully implemented<ref>{{citation |title="Mobile Computing Magazine Interview Article, 1999 |url=http://init.unizar.es/images/MobiCompMag1999.pdf}}</ref><ref>{{citation |title="Implementation and evaluation of an adaptive routing protocol for infrastructureless mobile networks" |url=https://www.semanticscholar.org/paper/Implementation-and-evaluation-of-an-adaptive-Toh-Lin/422dbbb6a624855a4636bed56c65e0d1278f9e6a}}</ref><ref>{{citation |title="Evaluating the communication performance of an ad hoc wireless network" |url=https://scholar.google.com/citations?view_op=view_citation&hl=en&user=YTwSsH4AAAAJ&citation_for_view=YTwSsH4AAAAJ:WF5omc3nYNoC}}</ref><ref>{{citation |title="Experimenting with an Ad Hoc wireless network " |url=http://dl.acm.org/citation.cfm?id=377622}}</ref> into Linux kernel, in various different branded laptops (IBM Thinkpad, COMPAQ, Toshiba, etc.) that are equipped with [[WaveLAN]] 802.11a PCMCIA wireless adapters. A working 6-node wide [[wireless ad hoc network]] spanning a distance of over 600 meters was achieved and the successful event was published in Mobile Computing Magazine in 1999. Various tests were performed with the network:
*[1] Transmission of up to 100MBytes of data from source to destination over 3-hop route.
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*[5] Route repair delay
In 2002, TRW Tactical Systems Incorporation implemented<ref>{{citation |title="Next-Generation Tactical Ad Hoc Mobile Wireless Networks" |url=https://www.researchgate.net/publication/228887934_Next-Generation_Tactical_Ad_Hoc_Mobile_Wireless_Networks}}</ref> an enhancement of the ABR protocol and successfully implemented on ORiNOCO WaveLAN 802.11b over an X windows system running Linux 5.2 Operating System on DELL laptops. The implementation and field test were done in an outdoor setting in [[Carson, California]] over a 6-node ad hoc network. The enhancement made to the protocol include:
* Network layer QoS
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* Route pre-emption
TRW investigators successfully transmitted 10Gbytes of large files, and did tests on route discovery, route repair, and measurements on delays. They recommended the use of Multi-Input Multi-Output (MIMO) spectrum-aware MAC and the consideration of logical clustering to scale to 100,000 or more large scale ad hoc networks.
==Patent and applications==
ABR was granted a US patent 5987011<ref>{{citation |title="A Routing Method for Ad Hoc Mobile Networks" |url=https://www.google.com/patents/US5987011}}</ref> and the assignee being [[King's College Cambridge]], UK. ABR was subsequently licensed to a US defense corporation. Tactical Mobile Ad Hoc Networks bloom with US defense spending<ref>{{citation |title="US Defense Spending Outlook" |url=https://cit.com/thought-leadership/us-defense-spending-industry-outlook/?cmp=paidsearch&gclid=Cj0KEQiAperBBRDfuMf72sr56fIBEiQAPFXszXJSUmhVzQx8nvTO-_D_DomeLEkW4rqNBnL09JQb8l4aAuaU8P8HAQ&jcpid=8a8ae4cd56581431015659d1200a185b&jsf=790d9e37-8253-492c-9760-301ebc6d7513:35584}}</ref> over $2 Billion in programs and research by [[DARPA]], DoD, Air Force, Coast Guards, and US Navy.<ref>{{citation |title="Naval Communications" |url=https://www.nap.edu/read/11605/chapter/8#153}}</ref>
In October 2013, the '''Storm Disaster Sandy''' hit the USA, and US Coast Guards used mobile ad hoc networking technology to quickly established networks to facilitate rescue operations. Many lives were saved.<ref>{{citation |title="After Sandy hit, Coast Guard comms got ... better" |url=https://gcn.com/articles/2013/10/07/gcn-award-coast-guard-trident.aspx}}</ref>
In '''US Operation Enduring Freedom''' on wars with Afghanistan, tactical ad hoc mobile communications is used in the battlefield.<ref>{{citation |title="Army networking radios improve communications at tactical edge" |url=https://www.army.mil/article/68498/Army_networking_radios_improve_communications_at_tactical_edge}}</ref>
'''Globally''', defense and national science organizations in other countries have also invested heavily on research programs related to mobile ad hoc networks. Such countries include USA, UK,<ref>{{citation |title="UK MoD High Capacity Tactical Ad Hoc Radio" |url=https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/514562/HOCS_F0I_2016_11086____Information_on_use_at_High_Capacity_Data_Radio__HCDR_.pdf}}</ref> Canada, Sweden, Singapore, Australia,<ref>{{citation |title="Australia DSTO Military ad-hoc wireless network" |url=http://www.acorn.net.au/show/project/57/}}</ref> Germany, Norway,<ref>{{citation |title="Research Council of Norway, VERDIKT Program" |url=http://wiki.unik.no/media/Swacom/SwacomProjectProposal.pdf}}</ref> France, Switzerland, Taiwan, Japan, Korea, China, Spain, Italy, Denmark, Finland, etc.
Many industries have since contributed to the development of tactical ad hoc mobile radios and networking products, including:▼
▲since contributed to the development of tactical ad hoc mobile radios and networking
* Harris
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