Request for Comments: November 1996

Transcription

1 Netwrk Wrking Grup Request fr Cmments: 2009 Categry: Experimental T. Imielinski J. Navas Rutgers University Nvember 1996 GPS-Based Addressing and Ruting Status f this Mem This mem defines an Experimental Prtcl fr the Internet cmmunity. This mem des nt specify an Internet standard f any kind. Discussin and suggestins fr imprvement are requested. Distributin f this mem is unlimited. IANA Nte: This dcument describes a pssible experiment with gegraphic addresses. It uses several specific IP addresses and dmain names in the discussin as cncrete examples t aid in understanding the cncepts. Please nte that these addresses and names are nt registered, assigned, allcated, r delegated t the use suggested here. Table f Cntents 1. Intrductin b. General Architecture c. Scenaris f Usage: Interface Issues Addressing Mdel a. Using GPS fr Destinatin Addresses Ruting a. GPS Multicast Ruting Scheme (GPSM) a-i. Multicast Trees a-ii. Determining the GPS Multicast Addressing a-iii. Building Multicast Trees a-iv. Ruting a-v. DNS Issues a-vi. Estimatins b. "Last Mile" Ruting b-i. Applicatin Level Filtering b-ii. Multicast Filtering b-iii. Cmputers n Fixed Netwrks c. Gemetric Ruting Scheme (GEO) c-i. Ruting Overview c-ii. Supprting Lng-Duratin GPScasts. 16 3c-iii. Discvering A Ruter s Service Area 17 Imielinski & Navas Experimental [Page 1]

2 3c-iv. Hierarchical Ruter Structure and Multicast Grups c-v. Ruting Optimizatins c-vi. Ruter-Failure Recvery Scheme c-vii. Dmain Name Service Issues Ruter Daemn and Hst Library a. GPS Address Library - SendTGPS() b. Establishing A Default GPS Ruter c. GPSRuteD c-i. Cnfiguratin d. Multicast Address Reslutin Prtcl (MARP) 23 4e. Internet GPS Management Prtcl (IGPSMP) Wrking Withut GPS Infrmatin a. Users Withut GPS Mdules b. Buildings blck GPS radi frequencies What then? Applicatin Layer Slutin Reliability Security Cnsideratins References Authrs Addresses Intrductin In the near future GPS will be widely used allwing a brad variety f lcatin dependent services such as directin giving, navigatin, etc. In this dcument we prpse a family f prtcls and addressing methds t integrate GPS int the Internet Prtcl t enable the creatin f lcatin dependent services such as: Multicasting selectively nly t specific gegraphical regins defined by latitude and lngitude. Fr example, sending an emergency message t everyne wh is currently in a specific area, such as a building r train statin. Prviding a given service nly t clients wh are within a certain gegraphic range frm the server (which may be mbile itself), say within 2 miles. Advertising a given service in a range restricted way, say, within 2 miles frm the server, Imielinski & Navas Experimental [Page 2]

3 Prviding cntiguus infrmatin services fr mbile users when infrmatin depends n the user s lcatin. In particular prviding lcatin dependent bk-marks, which prvides the user with any imprtant infrmatin which happens t be lcal (within a certain range) pssibly including ther mbile servers. The slutins which we present are flexible (scalable) in terms f the target accuracy f the GPS. We als discuss cases when GPS cannt be used (like inside buildings). The main challenge is t integrate the cncept f physical lcatin int the current design f the Internet which relies n lgical addressing. We see the fllwing general families f slutins: a) Unicast IP ruting extended t deal with GPS addresses b) GPS-Multicast slutin c) Applicatin Layer Slutin using extended DNS The first tw slutins are presented in this mem. We nly sketch the third slutin. 1b. General Architecture We will assume a general cellular architecture with base statins called Mbile Supprt Statins (MSS). We will cnsider a wide variety f cells, including utdr and indr cells. We will discuss bth cases when the mbile client has a GPS card n his machine and cases when the GPS card des nt wrk (i.e. - inside buildings). We will assume that each MSS cvers a cell with a well defined range specified as a plygn f spatial crdinates and that the MSS is aware f its wn range. 1c. Scenaris f Usage and Interface Issues Belw, we list sme pssible scenaris f usage fr the gegraphic messaging. Cnsider an example situatin, f an area f land near a river. During a severe rain strm, the lcal authrities may wish t send a fld warning t all peple living within a hundred meters f the river. Imielinski & Navas Experimental [Page 3]

4 Fr the interface t such messaging system we prpse t use a zmable map similar t the U.S. Census Bureau s Tiger Map Service. This map wuld allw a user t view a gegraphical area at varying degrees f magnitude. He culd then use a pinting device, such as a muse, t draw a bunding plygn arund the area which will receive the message t be sent. The cmputer wuld then translate the drawn plygn int GPS crdinates and use thse crdinates when sending and ruting the message. Gegraphical regins specified using this zm-able map culd be stred and recalled at a later time. This zm-able map is analgus t the IP address bks fund in many prgrams. T cntinue with the abve example, lcal fficials wuld call up a map cntaining the river in danger f verflwing. They wuld then hand-draw a bunding plygn arund all f the areas at least a hundred yards frm the river. They wuld specify this t be the destinatin fr a fld warning t all residents in the area. The warning wuld then be sent. Similar applicatins include traffic management (fr example, reaching vehicles which are stuck in traffic) and security enfrcement. Other applicatins invlve general client server applicatins where servers are selected n the basis f the gegraphic distance. Fr example, ne may be interested in finding ut all car dealers within 2 miles frm his/her lcatin. This leads t an extensin f the Web cncept in which lcatin and distance play imprtant rles in selecting infrmatin. We are currently in the prcess f implementing lcatin dependent bk-marks (ht lists) in which pages assciated with static and mbile servers which are present within a certain distance frm the client are displayed n the client s terminal. 2. Addressing Mdel Tw-dimensinal GPS psitining ffers latitude and lngitude infrmatin as a fur dimensinal vectr: <Directin, hurs, minutes, secnds> where Directin is ne f the fur basic values: N, S, W, E; hurs ranges frm 0 t 180 (fr latitude) and 0 t 90 fr lngitude, and, finally, minutes and secnds range frm 0 t 60. Thus <W, 122, 56, 89> is an example f lngitude and <N, 85, 66, 43> is an example f latitude. Imielinski & Navas Experimental [Page 4]

5 Fur bytes f addressing space (ne byte fr each f the fur dimensins) are necessary t stre latitude and fur bytes are als sufficient t stre lngitude. Thus eight bytes ttal are necessary t address the whle surface f earth with precisin dwn t 0.1 mile! Ntice that if we desired precisin dwn t mile (1.8 meters) then we wuld need just five bytes fr each cmpnent, r ten bytes tgether fr the full address (as military versins prvide). The future versin f IP (IP v6) will certainly have a sufficient number f bits in its addressing space t prvide an address fr even smaller GPS addressable units. In this prpsal, hwever, we assume the current versin f IP (IP v4) and we make sure that we manage the addressing space mre ecnmically than that. We will call the smallest GPS addressable unit a GPS-square. 2a. Using GPS fr Destinatin Addresses A destinatin GPS address wuld be represented by ne f the fllwing: Sme clsed plygn such as: circle( center pint, radius ) plygn( pint1, pint2, pint3,..., pintn) where each pint wuld be expressed using GPS-square addresses. This ntatin wuld send a message t anyne within the specified gegraphical area defined by the clsed plygn. site-name as a gegraphic access path This ntatin wuld simulate the pstal mail service. In this manner, a message can be sent t a specific site by specifying its lcatin in terms f real-wrld names such as the name f a specific site, city, twnship, cunty, state, etc. This frmat wuld make use f the directry service detailed later. Imielinski & Navas Experimental [Page 5]

6 Fr example, if we were t send a message t city hall in Fresn, Califrnia, we culd send it by specifying either a bunding plygn r the mail address. If we specify a bunding plygn, then we culd specify the GPS limits f the city hall as a series f cnnected lines that frm a clsed plygn surrunding it. Since we have a list f cnnected lines, we just have t recrd the endpints f the lines. Therefre the address f the city hall in Fresn culd lk like: plygn([n , W ], [N , W ],... ) Alternatively, since city hall in Fresn is a well-defined gegraphical area, it wuld be simpler t merely name the destinatin. This wuld be dne by specifying "pstal-like" address such as city_hall.fresn.califrnia.usa. Fr "ad hc" specified areas such as, say a quad between 5th and 6th Avenue and 43 and 46 street in New Yrk, the plygn addressing will be used. Unfrtunately, we will nt be able t assume that we have enugh addressing space available in the IP packet addressing space t address all GPS squares. Instead we will prpse a slutin which is flexible in terms f the smallest GPS addressable units which we call atms. In ur slutin, a smaller available addressing space (in the IP packet) will translate int bigger atms. Obviusly, we can use as precise addressing as we want t in the bdy f the gegraphic messages - the space limitatins apply nly t the IP addressing space. By a gegraphic address we mean an IP address assigned t a gegraphic area r pint f interest. Our slutin will be flexible in terms f the gegraphic addressing space. Belw, we will use the fllwing tw terms: Atms: fr smallest gegraphic areas which have gegraphic address. Thus, atms culd be as small as GPS squares but culd be larger Partitins: These are larger, gegraphical areas, which will als have a gegraphic address. A state, cunty, twn etc. may cnstitute a partitin. A partitin will cntain a number f atms. Imielinski & Navas Experimental [Page 6]

7 Here are sme examples f pssible atms and partitins: A rectangle, defined by truncating either lngitude r latitude part f the GPS address by skipping ne r mre least significant digits A circle, centered in a specific GPS address with a prespecified radius. Irregular shapes such as administrative dmains: states, cunties, twnships, brughs, cities etc Partitins and Atms (which are f curse special atmic partitins) will therefre have gegraphic addresses which will be used by ruters. Areas f smaller size than atms, r f "irregular shape" will nt have crrespnding gegraphic addresses and will have t handled with the help f applicatin layer. 3. Ruting Let us nw describe the suggested ruting schemes respnsible fr delivering a message t any gegraphical destinatin. We will distinguish between tw legs f the cnnectin frm the sender t the receiver: the first leg frm the sender t the MSS (base statin) and the secnd leg frm the MSS t the receiver residing in its cell. Our tw slutins will differ n the first leg f the cnnectin and use the same ptins fr the secnd leg, which we call "last mile". 3a. GPS-Multicast Ruting Scheme Here, we discuss the first leg f ruting: frm the sender t the MSS. We start with the multicasting slutin. Each partitin and atm is mapped t a multicast address. The exact frm f this mapping is discussed further in this subsectin. We first sketch the basic idea. Imielinski & Navas Experimental [Page 7]

8 This slutin prvides flexible mix f the multicast and applicatin level filtering fr the gegraphic addressing. The key idea here is t apprximate the addressing plygn f the smallest partitin which cntains it and using the multicast address crrespnding t that partitin as the IP address f that message. The riginal plygn is a part f the packet s bdy and the exact matching is dne n the applicatin layer in the secnd leg f the rute. Hw is the multicast ruting perfrmed? 3a-i. Multicast Trees The basic idea fr the first level f ruting using multicast is t have each base statin jin multicast grups fr all partitins which intersect its range. Thus, MSS is nt nly aware f its wn range but als has a cmplete infrmatin abut system defined partitins which its range intersects. This infrmatin can be btained upn MSS installatin, frm the gegraphic database stred as a part f DNS. If the prper multicast trees are cnstructed (using fr example link state multicast prtcl) than the sender can simply determine the multicast address f the partitin which cvers the riginal plygn he wants t send his message t, use this multicast address as the address n the packet and put the riginal plygn specificatin int the packet cntent. In this way, multicast will assure that the packet will be delivered t the prper MSS. Example Fr instance the MSS in New Brunswick may have its range intersect the fllwing atms and partitins: Busch, Cllege Avenue, Duglass and Livingstn Campuses f Rutgers University (atms), New Brunswick dwntwn area (atm), the Middlesex cunty partitin and the NJ state partitin. Each f these atms and partitins will be mapped int a multicast address and the New Brunswick s MSS will have t jin all such multicast grups. The message will be then specified and sent as fllws: The user will btain the map f the New Brunswick area pssibly frm the DNS extended prperly with relevant maps. He will specify the intended destinatin by drawing a plygn n the map which will be translated int the sequence f crdinates. In the same time the plygn will be "apprximated" by the smallest partitin which cntains that plygn. The multicast address crrespnding t that partitin will be the IP address fr packets carrying ur message. The exact destinatin plygn will be a part f each packet s bdy. In this way the packet will be delivered using multicast ruting t Imielinski & Navas Experimental [Page 8]

9 the set f MSS which are members f the specified multicast grup (that is all MSS whse ranges intersect the given partitin). Each such MSS nw will fllw the "last mile" ruting which is described in detail, further in the prpsal. Briefly speaking, the MSS culd then multicast the message further n the same multicast address and the client will perfrm the final filtering applicatin layer, matching its lcatin (btained frm GPS) with the plygn specified in the packet s bdy. Other slutins based entirely n multicasting are als pssible as described belw. End_Example Hwever, things cannt be as simple as described. Fr such a large ptential number f multicast grups if we build entire multicast trees, the ruting tables culd be t large. Frtunately it is nt necessary t build cmplete multicast trees. Indeed, it in nt imprtant t knw precise lcatin f each atm in Califrnia, frm a remte lcatin, say in NJ. Thus, we mdify ur simple slutin by implementing the fllwing intuitin: The smaller is the size f the partitin (atm) the mre lcally is the infrmatin abut that partitin (atm) prpagated. Thus, nly multicast grup membership fr very large partitins will be prpagated acrss the whle cuntry. Fr example, a base statin in Menl Park, Califrnia can intersect several atms ) and several larger which cver Menl Park, such say a partitin which cvers the entire San Mate cunty, next which cver the entire Califrnia and finally next which may cver the entire west cast. This base statin will have t jin multicast grups which crrespnd t all these rectangles. Hwever, nly the infrmatin abut multicast grup crrespnding t the West Cast partitin will be prpagated t the East Cast ruters. Hwever, a simple address aggregatin scheme in which nly a "mre significant prtin" f address prpagates far away wuld nt wrk. Indeed, in this case a remte ruter, say in NJ, culd have several aggregate links leading t Califrnia - in fact, in the wrst case, all its links culd pint t Califrnia since it culd have received a ruting infrmatin t sme lcatin in Califrnia n any f thse links. T avid this, fr each partitin we distinguish ne r a few MSS which act as designated ruter(s) fr that partitin. Fr example, the Califrnia partitin, may have nly three designated ruters, ne Imielinski & Navas Experimental [Page 9]

10 in Eureka, anther in Sacrament and yet anther in LA. Only the ruting entries frm the designated ruters wuld be aggregated int the aggregate address fr Califrnia. Infrmatin cming frm ther city ruters will simply be drpped and nt aggregated at all. This, in additin t a standard selectin f the shrtest rutes, wuld restrict the number f links which lead t an aggregate address. In particular, when there is nly ne designated ruter per partitin, there wuld nly be ne aggregate link in any ruter. This culd lead t nn-ptimal ruting but will slve the prblem f redundant links. Even with a designated ruters, it may happen that the same packet will arrive at a given base statin mre than nce due t different alternative rutes. Thus, a prper mechanism fr discarding redundant cpies f the same packet shuld still be in place. In fact, due t the pssible intersectins between ranges f the base statins the pssibility f receiving redundant cpies f the same packets always exist and has t be dealt with as a part f any slutin. 3a-ii. Determining the gegraphic Multicast Addressing Here we describe mre specifically, the prpsed addressing scheme and the crrespnding ruting. The addressing will be hierarchical. We will use the fllwing cnventin - each multicast address crrespnding t a partitins r an atms will have the fllwing frmat: 1111.GPS.S.C.x where GPS is the specific cde crrespnding t the gegraphic addressing subspace f the verall multicast addressing space. The S, C and x parts are described belw: S - Encding f the state. Each state partitin will have the address S/0/0. C - Cunty within a state. Each cunty partitin having the address S/C/0. x - Atm within a cunty. where 0 s refer t the sequences f 0 bits n psitins crrespnding t the "C part" and "x part" f address. Fr example if GPS part is 6 bit,s which gives 1/64 f existing multicast addresses t the gegraphic addressing we have 22 bits left. The S part will take first 6 bits, C part next 6 bits (say) and then the next 10 bits encde different atms (within a cunty). Imielinski & Navas Experimental [Page 10]

11 Thus, in ur terminlgy the prpsed addressing scheme has tw types f partitins: states and cunties. We will assume that the GPS netwrk will cnsist f all base statins (MSS) in additin the rest f the fixed netwrk infrastructure. The designated GPS ruters hwever, will nly be selected frm the ppulatin f MSS. Specifically, there will be state dedicated and cunty dedicated ruters. The cncept f the designatin will be implemented as fllws. Frm the set f all MSS, nly certain MSS will play a rle f designated ruters fr cunty and state partitins. Nn-designated MSS will nly jin multicast grups which crrespnd t the GPS atms but nt GPS partitins that they intersect. The MSS which is a designated ruter fr a cunty partitin will jin the multicast grup f the cunty in which it is lcated, but nt the state. Finally the state designated ruter will als jin the multicast address crrespnding t the state it is lcated in. 3a-iii. Building Multicast Trees We assume that each ruter has gegraphic infrmatin attached t it - in the same frmat as we use fr multicast mapping, S/C/x - it encdes the atm that cntains the ruter. The multicast tree is built by a ruter prpagating its multicast memberships t the neighbring ruters. A given ruter will nly retain certain addresses thugh, t fllw the intuitin f nt retaining a specific infrmatin which is far away. This is dne as fllws: the ruter (nt necessarily the MSS based ruter) with the address S/C/x will nly retain addresses abut S /0/0, S/C /0 fr S and C different frm S and C and S/C/x fr all x. Thus, it will drp all the addresses f the frm S /C /y fr all S different that S except thse with C =0 and y=0, as well as all the addresses f the frm S/C /y with C different frm C except thse with y=0. Hence, these addresses will nt be frwarded any further either. Thus, ntice that nly the infrmatin cming frm designated ruters will be frwarded further away, since the nn-designated ruters are nt allwed t jin the multicast grups which crrespnd t the states and cunties. Cnsequently, their multicast membership infrmatin will be nt be prpagated. In this way a ruter at S/C/x will nt bther abut specific lcatins within S /C /y since they are "t far". Imielinski & Navas Experimental [Page 11]

12 Ntice that this service may nt be prvided everywhere s we may nt have t use all multicast addresses even within thse assigned fr gegraphic addresses. Ntice als that all f this is flexible - if we have mre multicast addresses available (IP v 6) we will get mre precise addressing due t smaller atms. 3a-iv. GPS Ruting Given a packet we always lk fr the "clsest" match in the ruting table. If there is a cmplete match we fllw such a link, if nt we fllw the address with the x-part 0 d in (cunty address) if there is nne with the cunty which agrees with the destinatin cunty than we lk at the entry which agrees with the state part f the destinatin address. 3a-v. DNS Issues Hw des the client find ut the multicast address n which the packet is t be sent? We assume that the lcal name server has the cmplete state/cunty hierarchy and that each cunty map can be prvided pssibly with the "grid" f atms and partitins already clearly marked. Pints f interests within a cunty can be attached multicast address just as atms. Then a given base statin wuld have t jin multicast grups f the pints f interests that it cvers. The final stage is fr the receiver t lk at the plygn (pint f interest) which is encded in the bdy f the multicast packet and decide n the basis f its wn GPS lcatin if this packet is t be received r nt. Ding it n the applicatin layer simplifies many ruting issues. There is a tradeff, hwever, specially when we have very shrt S/C/x addresses and base statins which d nt cver the given plygn in fact are reached unnecessarily. This may happen and it needs t be determined what is the number f the multicast addresses which are necessary t reduce this "false" alarms t the minimum. 3a-vi. Estimatins Assume average cell size f, say, 2km x 2km and the average state size: say 200,000 square km, the average cunty size: say 4,000 square km. A reasnable size f the atm is arund the size f the cell since then we d nt hit wrng cells t ften. Imielinski & Navas Experimental [Page 12]

13 Therefre we need the x addressing part f the S/C/x t encde 4,000/4 cells: atms. Thus we need 10 bits fr x part. With 6 bits fr the state and 6 bits fr the cunty that gives 22 bits which is 1/64 f the ttal IP v4 multicast addressing space. With IPv6 we will have, f curse, much mre addressing space which we can use fr the GPS multicast ruting. 3b. "Last Mile" Ruting Multicasting will be used fr the last mile ruting in bth ur slutins (i.e the ne just discussed and the gemetric ruting slutin described next), but in different ways. 3b-i. Applicatin Level Filtering The MSS will frward the gegraphic message n its wireless link under a multicast address. This multicast address will either be the same fr all lcatins in the range f the MSS s cell r, there will be several addresses crrespnding t atms which intersect the given cell. Additinally, a cmplete GPS address (fr example in the frm f the plygn) will be prvided in the bdy f the packet and the exact address matching will be perfrmed n the applicatin layer. The receiver, knwing its GPS psitin uses it t match against the plygn address. The GPS psitin can be btained by the receiver either frm the GPS card r, indrs, frm the indr base statin which itself knws its GPS psitin as a part f cnfiguratin file. 3b-ii. Multicast Filtering In multicast level filtering, the base statin assigns a temprary multicast address t the addressing plygn in a message. It will send ut a directive n the cell s specially assigned multicast address. All mbile clients wh reside in that cell are members f that special multicast grup (ne per MSS). The directive sent by the MSS will cntain the pair cnsisting f the temprary multicast address tgether with the plygn. T imprve the reliability this message will be multicast several times. The clients, knwing their GPS psitins will than jin the temprary multicast grups if their current lcatins are within the advertised plygn. The MSS will then send ut the real message using the temprary multicast address. The temprary multicast address wuld be cached fr a perid f time. If mre packets fr the same plygn arrive in a shrt perid f time, they will be sent ut n the same multicast address. If nt, then the multicast address is drpped and purged frm the cache. Filtering n the client s statin is then perfrmed entirely n the IP level. This slutin intrduces additinal delay (needed t jin Imielinski & Navas Experimental [Page 13]

14 the temprary multicast grup) but reduces the number f irrelevant packets received by the client. This especially imprtant fr very lng messages. 3b-iii. Cmputers n Fixed Netwrks Fixed-netwrk cmputers shuld als mnitr all f the mandatry multicast addresses fr their site and GPS square. In this manner, the fixed cmputers will als receive messages sent t specific GPSaddresses. Mdified base statins wuld still be in charge f multicasting the messages t the cmputers. These base statins wuld have the same GPS-ruting functinality as the mbile cmputer base statins. Their main difference wuld be that the mbile cmputer base statins wuld use radi frequencies t multicast their messages and the fixed netwrk base statins use the lcal Ethernet r Tken Ring netwrk. The next scheme differs frm the GPS multicast scheme described abve nly n the first leg f the rute, frm the sender t the MSS. The "last mile" frm the MSS t the final destinatin will have the same ptins as described abve. 3c. Gemetric Ruting Scheme (GEO) The Gemetric Ruting Scheme (GEO) uses the plygnal gegraphic destinatin infrmatin in the GPScast header directly fr ruting. GEO ruting is ging t be implemented in the Internet Prtcl (IP) Netwrk layer in a manner similar t the way multicast ruting was first implemented. That is, a virtual netwrk which uses GPS addresses fr ruting will be verlayed nt the current IP internetwrk. We wuld accmplish this by creating ur wn GPSaddress ruters. These ruters wuld use tunnels t ship data packets between them and between the ruters and base statins. 3c-i. Ruting Overview Sending a GPScast message invlves three steps: sending the message, shuttling the message between ruters, and receiving the message. Sending a GPScast message is very similar t sending a UDP datagram. The prgrammer wuld use the GPScast library rutine SendTGPS(). Amng ther parameters, this rutine will accept the GPS plygnal destinatin address and the bdy f the message. The SendTGPS() rutine will encapsulate the GPScast message in a UDP datagram and send it t the class E address Previusly, the system administratr will have specified in the /etc/rc.lcal r /etc/rc.ip file a rute cmmand that will specify that packets with the address Imielinski & Navas Experimental [Page 14]

15 will instead be sent t the address f the lcal GPS ruter. This will have the effect f sending the datagram t the nearest GPS ruter. Befre explaining hw the GPS ruters shuttle the GPScast message t its destinatin, an intrductin t ruters and their different parts is in rder. Fr scalability purpses, GPS ruters are arranged in a hierarchical fashin. Each layer wuld crrespnd t a distinct gegraphic area, such as a state r a city. At the tp wuld be cuntry-wide ruters in charge f mving messages frm ne end f the cuntry t anther. At the bttm wuld be campus r department ruters in charge f mving messages between the base statins. See Figure 1. Cuntry-Ruter(s) / \ State-Ruter(s) / \ City-Ruter(s) / \ Ruter Ruter / \ \ Base Base Base Base Base Figure 1: Hierarchy f ruters. A GPS ruter essentially cnsists f three parts: a service area table cntaining the gegraphic area serviced by the ruter and each f its hierarchical children, a hashed cache f previus actins, and a table cntaining the IP addresses f at least the ruter s children and the ruter s parent. In the case f a bttm-layer campus ruter, the service area table will cntain plygns describing the gegraphic reach f each child base statin s cell. The plygn created frm the unin f all f the ruter s child base statins plygns defines the service area f the ruter. Once the datagram arrives at a GPS ruter, the ruter strips the datagram ff, thereby, leaving it with the riginal GPScast message. First the ruter must determine if it services any part f the area f the destinatin plygn. T d this, the ruter finds the intersectin between the destinatin plygn and the plygn describing the ruter s service area. The plygn intersectin algrithm used is described by O Rurke in his paper, A New Linear Algrithm fr Intersecting Cnvex Plygns. This algrithm requires rder N-squared time in the wrst case. If the intersectin result is null, then the ruter simply sends the message t its parent ruter. Imielinski & Navas Experimental [Page 15]

16 Destinatin Plygn A B Ruter s Service Area Plygn C Figure 2: Plygn Difference Hwever, if the result is nt null, then the ruter des service the area described by the intersectin plygn. The ruter nw subtracts its service area frm the destinatin plygn and sends the rest t it s parent ruter. This subtractin step is actually a by-prduct f the intersectin algrithm. Using the example in Figure 2, the destinatin plygn and the ruter s service area plygn intersect at the regin labeled B. Therefre, the ruter will subtract ut the B sectin and send the remaining sectins A and C t its parent ruter. Cntinuing with the example, the ruter nw uses the intersectin plygn B t t determine which base statin (r statins) will receive the GPScast message. The ruter finds the intersectin between the regin B and the plygn f each base statin s cell. Thse base statin plygns which intersect the regin B will be sent the GPScast message. Prcesses n Mbile Hsts serviced by these base statins will nw use the rutine RecvFrmGPS() t receive the GPScast message. 3c-ii. Supprting Lng-Duratin GPScasts Mst likely, there will be a need t supprt sending real-time cntinuus media t a GPS destinatin. This cntinuus media culd be an audi GPScast r a vide GPScast. This wuld require that jitter be reduced in rder t minimize disturbing artifacts in the audi r vide playback. Cntinually checking the destinatin gemetry f each packet wuld incur unnecessary delays and may prmte jitter. Therefre, the ruter will keep a hashed cache f the latest GPScast packets and their destinatins. Each cache item will be hashed using the Sender Identificatin included in the header f GPScast messages as the key. Each cache item will cntain a time stamp and a list f the next hps fr that GPScast. When the time stamp exceeds a certain limit, then the cache item will be drpped. The list f next hps is a list f the IP addresses f the base statins, peer ruters, and parent ruter which are t receive a cpy f the GPScast messages. Imielinski & Navas Experimental [Page 16]

17 When a ruter receives a GPScast packet, it will use the incming packet s Sender Id as a key int the hashed cache. If this is nt the first packet t arrive fr this destinatin and if the timer n the hash table entry has nt yet expired, then the hashed cache will return a list f all f the destinatin addresses t which cpies f the packet must be sent. Cpies f the packet are sent t all f these destinatins and the hash entry s time stamp is updated. If n hash table entry is fund (i.e.- this is the first packet encuntered fr this destinatin address), then the nrmal gemetry checking rutine wuld take ver. A new cache entry is made recrding all f the next-hp destinatin addresses f the GPScast. In this manner, if several ther packets with the same GPS destinatin fllw this first packet, the ruter can use the hash table t lk-up the destinatin base statins instead f calculating it using gemetry. 3c-iii. Discvering A Ruter s Service Area When the ruter is initiated, it will cnsult its cnfiguratin file. One f the items it will find in the file will be the multicast address f the base statin grup t which all f its child base statins are members. The ruter will jin this grup and then send ut Service Area Query messages t this multicast grup peridically t discver and t refresh its knwledge f its children base statins and the gegraphical areas serviced by them. Queries are issued infrequently (n mre than nce every five minutes) s as t keep the IGPSMP verhead n the netwrk very lw. Hwever, since the query is issued using unreliable multicast datagrams, there is a chance that sme base statins may nt receive the query. This is imprtant in tw cases: when a child nde fails and when a ruter first bts up. The case f a failed child nde will be explained later. Hwever, when a ruter first bts up, it can issue several queries in a small amunt f time in rder t guarantee that base statins will receive the query and t, therefre, build up its knwledge abut its child base statins quickly. Base statins respnd t a Service Area Query by issuing a Service Area Reprt. This reprt is issued n the same multicast grup address that all f the base statins have jined. The reprt cntains the gegraphical service area f the base statin. In rder t avid a sudden cngestin f reprts being sent at the same time, each base statin will initiate a randm delay timer. Only when the timer expires will the base statin send its reprt. Imielinski & Navas Experimental [Page 17]

18 Fr every base statin that respnds, the ruter will create an IP tunnel between it and the base statin. This tunnel will carry the GPScast packet traffic between the base statin and the ruter. Each respnding base statin and its gegraphic area f service will als be included in the ruter s gemetric ruting table as a pssible destinatin fr GPScast packets. Any base statin that des nt respnd fr ten cntinuus Service Area Queries will be cnsidered unreachable and will be drpped frm the ruting table. 3c-iv. Hierarchical Ruter Structure and Multicast Grups R R6 / \ / \ R R2 R R4 / \ / \ / \ / \ b1 b2 b3 b4 b5 b6 b7 b8 b9 b10 b11 b12 Figure 3: Tw peer ruters (R5 and R6) cperatively servicing fur child ruters (R1 - R4). Fr scalability purpses, a hierarchy f ruters is used t transprt messages frm a sender t a receiver. Each layer f peer ruters wuld have its wn multicast grup address fr the exchange f Service Area Queries and Reprts between the peer ruters. Hwever, ruters in distinct subtrees need nt knw abut the ruters in ther subtrees. Therefre, multicast grup addresses will als differ between hierarchy subtrees. See figure 3. Fr instance, ruters R1 and R2 wuld share a multicast grup and wuld knw abut each ther. At the same time, ruters R3 and R4 wuld share a different multicast grup and wuld knw abut each ther. Hwever, ruters R1 and R2 wuld nt knw abut R3 and R4, and vice versa. But hw will the ruter knw the lcatin and number f its peer ruters and wh its parent ruter is? As mentined befre, the ruter cnsults its cnfiguratin file upn start-up. Included in this cnfiguratin file will be the the address f its parent ruter and the multicast grup address that the peer ruters will use. This peer multicast grup address will be used in the same manner as the base statin multicast grup address. It will be used t send and receive Service Area Queries and Reprts between the parent ruter and the peer ruters. There is nly ne difference. When a ruter sends a Service Area Reprt, in additin t reprting its gegraphical service area, a ruter will include the multicast address f its children base statins. The reasn fr this is explained in the ruter-failure recvery scheme described belw. Imielinski & Navas Experimental [Page 18]

19 3c-v. Ruting Optimizatins The ptimizatin described here attempts t reduce the latency f a GPScast. It des s by reducing the the number f hps a packet must traverse befre finding its destinatin. The intuitin behind the idea is this: instead f ging t the parent ruter and then t the sibling, simply g t the sibling directly. As an additinal benefit, this methd prevents the parent ruter frm becming a bttleneck r a pint f failure in the ruting scheme. In this ptimizatin, when a ruter attempts t determine wh will receive the GPS packet, it cnsiders its peer ruters as if they were als its children in the ruting hierarchy. This means that the ruter will cnsider its service area t be the unin f the service areas f its children and its peer ruters. Als, when the destinatin plygn intersects the ruter s service area plygn, the ruter will frward a cpy f the GPScast packet t any child r peer ruter whse gegraphic service area cntains r tuches the packet s GPS destinatin plygn. Hwever, befre it sends a cpy f the packet t a peer ruter, it first finds the plygn: P = D /\ S where D stands fr the packet s destinatin GPS plygn, S is the plygn representing the service area f the peer ruter, and P is the plygn that represents the intersectin f D and S. The plygn P is substituted fr the destinatin plygn D in the packet and nly then is the packet frwarded t the peer ruter. This is necessary because the peer ruter will be using that same ruting algrithm. Therefre, if the peer ruter receives a packet with the riginal destinatin plygn D, it will als rute cpies f the packet t all f its qualifying peer ruters causing a chain f packet cpies being bunced back and frth. 3c-vi. Ruter-Failure Recvery Scheme In the case f a ruter failure, the system shuld be able t rute arund the failed ruter and cntinue t service GPScast messages. The respnsibility f detecting whether a ruter has failed r nt falls t the parent ruter. Using Figure 3 as an example ruter hierarchy, the parent ruter R5 peridically sends ut Service Area Query IGPSMP messages n its children s multicast grup address. Thus, the child ruters R1 and R2 will bth receive this query. Nrmally, bth ruters will respnd with a Service Area Reprt message. This message cntains a plygn describing their service areas and the multicast grup address f their children. Imielinski & Navas Experimental [Page 19]

20 Hwever, if a ruter, R1, des nt respnd t ten cntinuus queries, then it must be cnsidered t have failed. Upn detecting this, the parent ruter R5 will send a Set Service Area message t the child ruter, R2 telling it t assume respnsibility fr the base statins underneath the failed R1 ruter. In this Set Service Area message, the parent ruter includes the multicast grup address f R1 s children. The R2 ruter uses this multicast address t learn the service areas and IP addresses f R1 s children. The R2 ruter then issues a Service Area Reprt advertising its new enlarged service area respnsibilities. All peer and parent ruters will then update their ruting tables t include this new infrmatin. When the failed ruter, R1, restarts, it will declare that it is alive and that it is again servicing its area. All ruters will then again update their ruting tables. In the case that there is n parent ruter, such as at the tp f the ruting hierarchy, then each peer ruter will keep track f its neighbrs. If a neighbr ruter fails, then the first neighbr ruter t declare that it is taking ver the base statins fr the failed ruter will take respnsibility. The rest cntinues as befre. 3c-vii. Dmain Name Service Issues Dmain Name Servers (DNS) culd be used t facilitate the use f GPS gegraphic addressing fr sites f interest. The aim is t describe specific gegraphic sites in a mre natural and real-wrld manner using a pstal-service like addressing methd. Essentially, the DNS wuld reslve a pstal-service like address, such as City_Hall.New_Yrk_City.New_Yrk, int the IP address f the GPS ruter respnsible fr that site. The GPS ruter wuld then rute the message t all available recipients in the site. The DNS wuld be used when a message is sent using the site-cde.city-cde.state-cde.cuntry-cde addressing scheme. The DNS wuld evaluate the address in reverse starting with the cuntry cde, then the state cde, etc. This is the same methd used currently by the IP DNS service t return IP addresses based n the cuntry r gegraphic dmains. Imielinski & Navas Experimental [Page 20]

21 4. Ruter Daemn and Hst Library 4a. GPS Address Library - SendTGPS() A library fr GPS address ruting will be cnstructed. The main rutines cntained in this library will be the SendTGPS() and RecvFrmGPS() cmmands. SendTGPS() has the fllwing syntax: SendTGPS(int scket, GPS-Address *address, char *message, int size) where scket is a previusly created datagram scket, address is a filled GPS-Address structure with the fllwing frm: typedef _GPS-Address { enum { pint, circle, plygn } type; char *mail-address; struct { enum { Nrth, Suth, West, East } dir; int hurs, minutes, secnds; } *pints; } GPS-Address; and message and size specify the actual message and its size. The SendTGPS() rutine will take the GPS-addressed message, encapsulate it in an IP packet, and then send it as a nrmal IP datagram. The message is encapsulated in the fllwing manner: IP Header with destinatin address set t Sender Identifier Address Type - Circle Plygn Actual GPS Address (see belw) Bdy f Message where the Sender Identifier wuld cnsist f a cmbinatin f the sender s prcess id, hst IP address, and the center f the destinatin plygn. The Actual Address wuld be ne f the fllwing: circle - single GPS address and range measured in centiminutes. Imielinski & Navas Experimental [Page 21]

22 plygn - list f GPS addresses terminated by the impssible address: N RecvFrmGPS() has the fllwing syntax: RecvFrmGPS(int scket,gps-address *address,char *message,int size) where scket is a previusly created datagram scket, address is an empty GPS-Address structure, and message and size specify message buffer and its size. 4b. Establishing A Default GPS Ruter The default GPS ruter is determined using the unicast ruting table fund in the UNIX kernel. The lcal system administratr will have previusly adjusted the table s that all GPScast messages are sent t the lcal GPS ruter. Hwever, if there is n rute fr GPScast messages in the table, then all messages will, by default, be sent t the default gateway. If the default gateway des nt supprt GPScast messages, then all attempts t send a GPScast will return an errr. By default, all GPScast messages will initially have as their destinatin the class E address A rute will be added t the kernel ruting table by the system administratr fr this address. The rute will specify the lcatin f the lcal GPS ruter. The "rute" cmmand will be used t affect the ruting table and it can be placed in the /etc/rc.lcal r /etc/rc.ip files s that it will take effect each time the cmputer is bted. Fr example, t specify that GPScast messages addressed t shuld, by default, be sent t the ruter which resides n a cmputer n the same subnet with lcal address , use the fllwing: /etc/rute add hst If the default destinatin fr GPScast messages is a hst that des nt supprt GPS addressing, then Netwrk Unreachable errrs will be returned t any prcess attempting t rute GPScasts thrugh that hst. 4c. GPSRuteD In rder t prvide the capability f GPS address ruting thrughut an IPv4-based internetwrk, special-purpse ruters will be created t supprt GPS address ruting n tp f the current Internet. These ruters, which will be called GPSRuteD, will use virtual pint-tpint links called tunnels in rder t cnnect tw GPSRuteDs tgether ver regular unicast netwrks. The tunnels wrk by encapsulating the GPS address messages in IP datagrams and then Imielinski & Navas Experimental [Page 22]

23 transmitting the message t the hst n the ther end f the tunnel. In this manner, the GPS address messages lk like nrmal unicast packets t all IPv4 ruters in between the tw GPS address ruters. At the end f the tunnel, the receiving GPSRuteD remves the GPS address message frm the datagram and cntinues the ruting prcess. By using tunnels, the GPS ruters can be established as a virtual internetwrk thrughut the current Internet withut regard fr the physical prperties f the underlying netwrks. Mrever, the use f tunnels means that the hst n which the ruter daemn is running need nt be cnnected t mre than ne subnet in rder fr the ruter t frward GPS messages. This virtual internetwrk wuld be respnsible fr ruting GPS address messages nly. This virtual netwrk, hwever, is nt intended t be a permanent slutin and is nly intended t prvide a means f supprting GPS address ruting until it gains wider acceptance and supprt in the Internet infrastructure. 4c-i. Cnfiguratin When a GPSRuteD initially executes, it first checks the file /etc/gpsruted.cnf fr cnfiguratin cmmands t add tunnel and multicast links t ther GPS address ruters. There are tw kinds f cnfiguratin cmmands: multicast <multicast-address> <peer child> tunnel <lcal-addr> <remte-addr> <parent peer child hst> <service-area> The tunnel cmmand is used t create a tunnel between the lcal hst n which the GPSRuteD executes and a remte hst n which anther GPSRuteD executes. The tunnel must be set up in the GPSRuteD.cnf files at bth ends befre it will be used. The multicast cmmand tells the ruter which multicast addresses t jin. These addresses will carry IGPSMP messages and replies. The ruter will use these IGPSMP messages t build up and keep current its wn internal ruting table. 4d. Multicast Address Reslutin Prtcl (MARP) Of curse, this begs the questin, hw will the individual cmputers knw which multicast addresses t jin? Fr example, an MH wuld have t jin the multicast address f its current cell s that it can receive GPScast messages (using applicatin-level filtering) r directins t jin ther multicast grups (using multicast filtering). We have designed a prtcl called Multicast Address Imielinski & Navas Experimental [Page 23]

24 Reslutin Prtcl (MARP) that wrks the same way as Reverse Address Reslutin Prtcl (RARP). Hwever, instead f returning the IP address f the MH, it will return multicast grup address f the cell the MH is currently in. The MH wuld then jin this multicast grup. 4e. Internet GPS Management Prtcl (IGPSMP) The Internet GPS Management Prtcl (IGPSMP) is used by GPS ruters t reprt, query, and infrm their ruter cunterparts abut their gegraphical service areas. The IGPSMP will als be used t verify that ruters are crrectly functining. The vcabulary f IGPSMP will cnsist f six wrds: set service area - Used by the parent ruter t set the gegraphic service area f a ruter. This is needed in rder t autmatically respnd t ruter failure r new ruter bt-up. cnfirm service area - cnfirms that a ruter has received its service area. gegraphical service area query - This message will be used by a ruter t build up its gegraphical ruting table. It is sent t all ruters n the same level. service area reprt - This message is sent in respnse t a query request. It cntains a bunding clsed plygn described using GPS crdinates which cntains the service area fr the ruter. ping - This message is sent peridically t ascertain whether the ruter is currently functining prperly. Usually sent by the parent ruter in the hierarchy tree. alive signal - Usually sent as a reply t the ping message. Used by a ruter t indicate that it is functining crrectly. It is als sent immediately after a ruter bts. All f IGPSMP messages will be sent n an all-ruters multicast address fr a particular hierarchy level. The exact multicast address can be set in the ruter cnfiguratin file. Nte that fr the GPS-Multicast ruting scheme, the time-t-live value f the service area reprts will be varied in rder t cntrl the distributin f the infrmatin. In GPS-Multicast ruting, nly Imielinski & Navas Experimental [Page 24]

25 the multicast grup membership fr very large partitins will be distributed thrughut the cuntry. Smaller partitin may nly be distributed t neighbr ruters. 5. Wrking Withut GPS Infrmatin 5a. Users Withut GPS Mdules Mbile users withut GPS mdules can still participate - thugh at a very reduced level. When an MH enters a cell, it can use an MARP t discver the lcal multicast grup fr that cell r atm. As the user rams frm cell t cell, the mbile hst can keep track f the current cell that the user is in and adds r drps the multicast grups pertaining t thse cells. The user s GPS address can be set t be the center f the current cell. 5b. Buildings blck GPS radi frequencies. What then? Each rm can have a radi beacn placed n the ceiling. The beacn will be weak enugh s that it will nt penetrate walls. Each radi beacn will have its wn GPS-address assciated with it which it will bradcast. When a mbile user enters a rm, his MH will detect the beacn and read the beacn s GPS address. The GPS-address f the MH will be set t the GPS-address f the beacn. The MH will then use this beacn s GPS address in rder t perfrm any message filtering that it needs t d. Nw the mbile user can have a GPS-address assciated with him even thugh he is indrs and his GPS-mdule is useless. 6. Applicatin Layer Slutin In this subsectin we sketch a third slutin which relies mre heavily n the DNS. In the applicatin layer slutin the gegraphic infrmatin is added t the DNS which prvides the full directry infrmatin dwn t the level f the IP address f each base statin and its area f cverage represented as a plygn f crdinates. A new first level dmain - "gegraphic" is added t the set f first level dmains. The secnd level dmain names include states, the third, cunties and finally, the furth: plygns f crdinates, r s called pints f interests. We can als allw, plygns t ccur as elements f secnd, third dmains t enable sending messages t larger areas. Imielinski & Navas Experimental [Page 25]