Communication" technologies" are" currently" being" designed" for" constrained" WSN" environments" that" promise" to" enable" the" integration" of" WSN" with" the" Internet" communications" infrastructure." Thus," in" this" integration" scenario" WSN" devices" are" able" to" communicate" directly" with" external" or" Internet" entities," at" diverse" protocol" layers." This" vision" is" currently" becoming" a" reality" thanks" to" communication" technologies" developed"
based" on" the" 6LoWPAN" [69][70][71]" adaptation" layer." The" employment" of" Internet" communication" technologies" on" WSN" environments" can" also" require" the" evolution" of" existing"Internet"security"mechanisms"and"solutions"to"encompass"WSN"environments"and" sensing"devices,"an"aspect"that"deeply"motivates"the"research"efforts"described"throughout" the"thesis."
The" communication" technologies" currently" being" designed" to" enable" Internet" communications"on"WSN"environments"are"also"a"result"of"efforts"from"working"groups"of" organizations" such" as" the" Internet" Engineering" Task" Force" (IETF)." Also" relevant" are" efforts" conducted" in" the" context" of" the" ETSI" Technical" Committee" on" M2M" communications" [60]," which" is" working" to" develop" an" endNtoNend" highNlevel" architecture" for" M2M" and" also" standards"fulfilling"the"gaps"where"other"standards"bodies"or"groups"are""unable"to"do"so." The" ITUNT" (Telecommunication" Standardization" Sector" of" the" International" Telecommunication"Union)"[72]"is"working"on"recommendations"related"to"USN"(Ubiquitous" Sensor" Networks)" and" NGN" (next" generation" networks)," with" the" goal" of" designing" a" conceptual" network" built" over" existing" physical" networks," which" provides" knowledge" services"by"making"use"of"sensorial"data."
"
Figure!2.2!K!A!standardized!protocol!stack!for!the!Internet!of!Things![73]!
Internet" communication" technologies" for" WSN" are" being" designed" accordingly" to" the" constraints" and" characteristics" of" lowNenergy" sensing" devices" and" lowNrate" wireless" communications"that"are"typical"of"such"environments."Although"such"characteristics"have" also"influenced"previous"designs"of"applications"employing"WSN"isolated"from"the"Internet," the" new" solutions" are" being" designed" to" guarantee" interoperability" with" existing" Internet" standards"and"guarantee"that"sensing"devices"are"able"to"communicate"with"other"Internet" entities"in"the"context"of"future"IoT"distributed"applications."The"communication"protocols" available"or"currently"being"designed"with"this"purpose"already"enable"a"reference"protocol" PHY (IEEE 802.15.4) MAC (IEEE 802.15.4, IEEE 802.15.4e) Adaptation (6LoWPAN) Network/routing (IPv6, ROLL RPL) In te rn et e n d- to -en d in te g ra tio n
stack"for"the"employment"of"Internet"communication"technologies"[73],"which"is"illustrated" in"Figure"2.2."
The" communication" technologies" at" particular" layers" of" the" protocol" stack" illustrated" in" Figure" 2.2" are" designed" to" be" appropriate" to" the" employment" of" lowNenergy" devices" and" wireless" communications," while" providing" acceptable" reliability" and" not" compromising" the" lifetime"of"sensing"applications."As"previously"discussed,"many"sensing"devices"are"powered" by"batteries"and,"in"consequence,"new"communication"and"security"solutions"developed"for" WSN" environments" are" required" to" carefully" balance" the" communications" rate," reliability" and"energy"usage."From"a"bottomNup"perspective,"the"following"are"the"main"characteristics" of"the"various"standard"protocols"forming"the"stack"illustrated"in"Figure"2.2:"
! LowNenergy" communications" at" the" physical" (PHY)" and" Medium" Access" Control" (MAC)" layers"may"be"supported"by"IEEE"802.15.4"[74],"including"more"recent"addendums"to"the" standard"as"IEEE"802.15.4e"[75]."IEEE"802.15.4"sets"the"rules"for"communications"at"the" lower"layers"and"lays"the"ground"for"the"development"of"WSN"Internet"communication" technologies"at"higher"layers"of"the"stack."
! LowNenergy" communication" environments" using" IEEE" 802.15.4" support" at" most" 102" bytes"for"the"transmission"of"data"at"higher"layers"of"the"stack,"a"value"much"less"than" the"maximum"transmission"unit"(MTU)"of"1280"bytes"required"for"IPv6."Addressing"this" issue,"6LoWPAN"[69][70][71]"provides"an"adaptation"layer"for"the"transmission"of"IPv6" packets" over" IEEE" 802.15.4," by" implementing" fragmentation" and" reassembly" of" IPv6" packets,"among"other"required"mechanisms,"as"we"detail"later."
! Routing"over"6LoWPAN"WSN"environments"may"be"supported"by"the"Routing"Protocol" for" LowNpower" and" Lossy" Networks" (RPL)" [76]." RPL" provides" a" framework"that" may" be" adapted"to"the"requirements"of"particular"applications."ApplicationNspecific"profiles"are" defined"to"identify"the"corresponding"routing"requirements"and"optimization"goals."
! The" Constrained" Application" Protocol" (CoAP)" [34]" supports" communications" at" the" application" layer." CoAP" is" currently" being" designed" to" provide" interoperability" at" the" application"layer,"in"conformance"with"the"REST"architecture"prevalent"on"the"web."
The" communication" technologies" forming" the" protocol" stack" of" Figure" 2.2" enable" communications"between"wireless"sensing"devices"and"external"hosts"at"the"various"protocol" layers." Such" technologies" may" enable" more" full" integration" approaches," and" also" motivate" new"challenges"in"respect"to"the"fulfillment"of"appropriate"security"guarantees"in"the"context" of" InternetNintegrated" WSN." This" aspect" raises" the" question" of" what" mechanisms" are" available" to" guarantee" security" in" the" presence" of" endNtoNend" communications" using" the" technologies"illustrated"in"Figure"2.2.""
The"complexity"of"protecting"WSN"domains"in"such"more"full"integration"approaches"is"also" related" to" the" fact" that" endNtoNend" communications" with" sensing" devices" may" take" place"
from" the" networkNlayer" up," and" as" such" WSN" devices" and" communications" may" be" more" open" to" a" plethora" of" threats" and" attacks" originated" at" external" communication" environments" or" the" Internet." As" most" WSN" devices" are" expected" to" remain" constrained," endNtoNend" communication" and" security" technologies" must" be" employed" parsimoniously," and" one" possible" strategy" in" this" context" is" to" complement" such" mechanisms" with" appropriate" security" mechanisms" supported" by" more" resourceful" devices," as" we" consider" later."On"the"other"hand,"endNtoNend"security"is"in"reality"only"part"of"the"problem,"as"many" security" aspects" may" require" appropriate" crossNlayer" approaches." Later" in" the" chapter" we" discuss" such" aspects" in" greater" detail," together" with" the" employment" of" 6LoWPANNbased" communication"technologies"in"WSN"environments."
The" gradual" adoption" of" 6LoWPANNbased" communication" technologies" for" WSN" is" also" visible" in" existing" commercial" offerings." For" example," the" popular" ZigBeeN2006" [50]" specification"is"evolving"to"adopt"the"ZigBee"IP"stack"[52],"which"also"provides"support"for" 6LoWPAN," RPL" [76]" and" CoAP" [34]." Despite" the" adoption" of" a" networking" stack" oriented" towards" 6LoWPAN," we" must" observe" that" ZigBee" remains" a" commercial" and" closed" specification," in" the" sense" that" communications" related" with" ZigBee" applications" that" are" transported"over"the"Internet"remain"restricted"to"such"applications."Other"proposals"such" as" those" from" Sensinode" [77]" also" adopt" IPNbased" 6LoWPAN" communication" technologies." Sensinode" currently" offers" the" NanoStack" 6LoWPAN" protocol" stack" and" the" NanoRouter" platform,"which"supports"applications"requiring"6LoWPANNInternet"routing"infrastructures." We" may" also" observe" that" a" few" research" proposals" have" contributed" to" the" idea" of" integrating"WSN"with"the"Internet"via"the"Internet"communication"technologies"developed" for"such"environments."As"in"other"research"proposals,"the"exploratory"nature"of"such"works" justifies" the" absence" of" appropriate" security" solutions" in" such" proposals." The" research" proposals"in"[78]"[79]"do"not"address"security,"instead"focusing"on"the"intelligent"placement" of"gateways"in"order"to"reduce"data"latency"in"scalable"and"sustainable"WSN"deployments."A" few"initial"research"proposals"also"focus"on"the"integration"of"WSN"with"the"Internet"via"web" services," in" particular" exploring" the" usage" of" web" services" directly" on" constrained" sensing" devices."As"in"the"previous"works,"we"also"observe"the"lack"of"appropriate"security"solutions" in"such"proposals."In"[80]"and"[81]"the"authors"focus"only"on"the"communication"aspects"of" the"integration."In"the"StreamFeeds"proposal"[82]"the"authors"discuss"that"applications"may" be"able"to"inherit"security"mechanisms"supporting"authentication"and"privacy"services"from" the" web" services" technology" employed" in" the" Internet," while" doesn’t" specifying" how" this" may" be" achieved" in" practice." In" conclusion," given" the" preliminary" nature" of" such" research" proposals,"security"is"either"absent"or"mostly"undefined."
The"integration"of"WSN"with"the"Internet"via"Internet"WSN"communication"technologies"was" initially"addressed"in"the"design"of"mechanisms"to"enable"communications"with"web"services" running"directly"on"constrained"WSN"sensing"devices"[80][81]."Such"proposals"thus"represent" an" evolution" and" complement" other" proposals" focused" on" the" integration" via" frontNend" gateways,"which"we"discuss"later."The"employment"of"web"services"on"constrained"sensing"
devices" was" initially" proposed" and" evaluated" in" [80]," and" in" [81]" the" authors" describe" a" RESTful"web"service"architecture"allowing"external"servers"to"communicate"directly"over"TCP" with" IPNenabled" sensor" devices" using" web" services." The" architecture" described" in" this" proposal" employs" a" sessionNaware" powerNsaving" MAC" protocol" running" over" XNMAC" [83]," which" synchronizes" wakeNup" periods" of" devices" with" TCP" control" messages," and" on" the" employment"of"the"HTTP"(Hypertext"Transfer"Protocol)"conditional"mechanisms"to"avoid"the" transmission"of"nonNchanging"data"from"the"server"to"the"client."Stream"Feeds"[82]"identifies" streams"of"data"from"sensing"devices"using"URLs"that"may"be"hyperlinked"to"other"objects"on" the"web,"thus"enabling"such"streams"to"be"indexed"by"search"engines."
In"our"following"discussion"we"analyze"the"communication"technologies"identified"in"Figure" 2.2," and" also" the" security" technologies" and" approaches" that" may" be" considered" in" the" context" of" its" employment." This" analysis" also" serves" our" purpose" of" identify" the" currently" open" issues" regarding" security," which" motivate" the" research" solutions" described" and" evaluated"later"in"the"thesis."