Chapter 8 LOCATION SERVICES

Transcription

1 Disribued Compuing Group Chaper 8 LOCATION SERVICES Mobile Compuing Winer 2005 / 2006 Overview Mobile IP Moivaion Daa ransfer Encapsulaion Locaion Services & Rouing Classificaion of locaion services Home based GLS MLS Disribued Compuing Group Mobile Compuing R. Waenhofer 8/2 Moivaion for Mobile IP Requiremens on Mobile IP (RFC 2002) Rouing based on IP desinaion address, nework prefix (e.g ) deermines physical subne change of physical subne implies change of IP address o have a opological correc address (sandard IP) or needs special enries in he rouing ables Changing he IP-address? adjus he hos IP address depending on he curren locaion almos impossible o find a mobile sysem, DNS updaes are oo slow TCP connecions break securiy problems Change/Add rouing able enries for mobile hoss? worldwide! does no scale wih he number of mobile hoss and frequen changes in heir locaion Compaibiliy suppor of he same layer 2 proocols as IP no changes o curren end-sysems and rouers required mobile end-sysems can communicae wih fixed sysems Transparency mobile end-sysems keep heir IP address coninuaion of communicaion afer inerrupion of link possible poin of connecion o he fixed nework can be changed Efficiency and scalabiliy only lile addiional messages o he mobile sysem required (connecion ypically via a low bandwidh radio link) world-wide suppor of a large number of mobile sysems Securiy auhenicaion of all regisraion messages Disribued Compuing Group Mobile Compuing R. Waenhofer 8/3 Disribued Compuing Group Mobile Compuing R. Waenhofer 8/4

2 Daa ransfer from mobile sysem Daa ransfer o mobile sysem FA foreign nework 2 FA foreign nework 3 home nework (physical home nework of ) home nework 1 User (end-sysem) Mobile Node (mobile end-sysem) User (end-sysem) 1. Sender sends o he IP of, inerceps packe (proxy ARP) 2. unnels packe o FA by encapsulaion 3. FA forwards packe o he Disribued Compuing Group Mobile Compuing R. Waenhofer 8/5 Disribued Compuing Group Mobile Compuing R. Waenhofer 8/6 Daa ransfer back o Terminology home nework User (end-sysem) FA sends o he IP address of he receiver () as usual, FA works as defaul rouer. foreign nework Mobile Node () sysem (node) ha can change he poin of connecion o he nework wihou changing is IP address Home Agen () sysem in he home nework of he, ypically a rouer regisers he locaion of he, unnels IP daagrams o he COA Foreign Agen (FA) sysem in he curren foreign nework of he, ypically a rouer ypically he defaul rouer for he Care-of Address (COA) address of he curren unnel end-poin for he (a FA or ) acual locaion of he from an IP poin of view can be chosen, e.g., via DHCP Corresponden Node () Disribued Compuing Group Mobile Compuing R. Waenhofer 8/7 Disribued Compuing Group Mobile Compuing R. Waenhofer 8/8

3 Overview home nework User (end-sysem) COA FA unnels packes o he COA of he FA foreign nework How i works Agen Adverisemen and FA periodically send adverisemen messages ino heir physical subnes lisens o hese messages and deecs if i is in he home or a foreign nework (sandard case for home nework) reads a COA from he FA adverisemen messages Regisraion (always limied lifeime!) signals COA o he via he FA, acknowledges via FA o hese acions have o be secured by auhenicaion Adverisemen adverises he IP address of he (as for fixed sysems), i.e. sandard rouing informaion rouers adjus heir enries, hese are sable for a longer ime ( responsible for a over a longer period of ime) packes o he are sen o he independen of changes in COA/FA Disribued Compuing Group Mobile Compuing R. Waenhofer 8/9 Disribued Compuing Group Mobile Compuing R. Waenhofer 8/10 Agen adverisemen IP-in-IP Encapsulaion ype code checksum #addresses addr. size lifeime rouer address 1 preference level 1 rouer address 2 preference level 2... ype lengh sequence number regisraion lifeime R B H F M G V reserved COA 1 COA 2... Mandaory in RFC 2003 unnel beween and COA ver. IHL TOS lengh IP idenificaion flags fragmen offse TTL IP-in-IP IP checksum IP address of Care-of address COA ver. IHL TOS lengh IP idenificaion flags fragmen offse TTL lay. 4 pro. IP checksum IP address of IP address of COA TCP/UDP/... payload Disribued Compuing Group Mobile Compuing R. Waenhofer 8/11 Disribued Compuing Group Mobile Compuing R. Waenhofer 8/12

4 Minimal Encapsulaion Daa ransfer from he mobile sysem opional avoids repeiion of idenical fields such as TTL, IHL, version, TOS only applicable for unfragmened packes, no space lef for fragmen idenificaion FA foreign nework ver. IHL TOS lengh IP idenificaion flags fragmen offse TTL min. encap. IP checksum IP address of care-of address COA lay. 4 prooc. S reserved IP checksum IP address of IP address of (only if S=1) TCP/UDP/... payload home nework User (end-sysem) Problems: - Firewall a - TTL - Mulicas Disribued Compuing Group Mobile Compuing R. Waenhofer 8/13 Disribued Compuing Group Mobile Compuing R. Waenhofer 8/14 Reverse unneling (RFC 2344) Mobile IP wih reverse unneling 2 FA foreign nework 1 accep ofen only opologically correc addresses (firewall!) a packe from he encapsulaed by he FA is now opologically correc furhermore mulicas and TTL problems solved (TTL in he home nework correc, bu is oo far away from he receiver) home nework User (end-sysem) 3 1. sends o FA 2. FA unnels packes o by encapsulaion 3. forwards he packe o he receiver (sandard case) Reverse unneling does no solve problems wih firewalls, he reverse unnel can be abused o circumven securiy mechanisms (unnel hijacking) opimizaion of daa pahs, i.e. packes will be forwarded hrough he unnel via he o a sender (double riangular rouing) Reverse unneling is backwards compaible he exensions can be implemened easily and cooperae wih curren implemenaions wihou hese exensions Disribued Compuing Group Mobile Compuing R. Waenhofer 8/15 Disribued Compuing Group Mobile Compuing R. Waenhofer 8/16

5 Opimizaion of packe forwarding Triangular Rouing sender sends all packes via o higher laency and nework load Soluions sender learns he curren locaion of direc unneling o his locaion informs a sender abou he locaion of big securiy problems Change of FA packes on-he-fly during he change can be los new FA informs old FA o avoid packe loss, old FA now forwards remaining packes o new FA his informaion also enables he old FA o release resources for he Change of foreign agen FA old FA new reques updae updae ACK daa ACK daa regisraion warning daa updae ACK daa daa regisraion daa daa changes locaion Disribued Compuing Group Mobile Compuing R. Waenhofer 8/17 Disribued Compuing Group Mobile Compuing R. Waenhofer 8/18 Locaion services Home based georouing in a MANET Service ha maps node names o (geographic) coordinaes Should be disribued (no require for specialized hardware) Should be efficien Lookup of he posiion (or COA) of a mobile node Mobile IP: Ask home agen Home agen is deermined hrough IP (unique ID) of Possibly long deours even hough sender and receiver are close OK for Inerne applicaions, where laency is (normally) low Oher applicaion: Rouing in a MANET MANET: mobile ad hoc nework No dedicaed rouing hardware Limied memory on each node: canno sore huge rouing ables Nodes are mosly baery powered and have limied energy Nodes roue messages, e.g. using georouing How can he sender learn he curren posiion of anoher node? Flooding he enire nework is undesirable (raffic and energy overhead) Home based approach Similar o Mobile IP, each node has a home node, where i sores and regularly updaes is curren posiion The home is deermined by he unique ID of he node. One possibiliy is o hash he ID o a posiion p and use he node closes o p as home. Thus, given he ID of a node, every node can deermine he posiion of he corresponding home. Home based rouing 1. Roue packe o h, he home of he desinaion 2. Read he curren posiion of 3. Roue o s h p Disribued Compuing Group Mobile Compuing R. Waenhofer 8/19 Disribued Compuing Group Mobile Compuing R. Waenhofer 8/20

6 Home based locaion service how good is i? Classificaion of locaion services Visiing he home of a node migh be waseful if he sender and receiver happen o be close, bu he home far away The rouing srech is defined as srech := lengh of roue lengh of opimal roue We wan rouing algorihms wih low srech. Simulaneous message rouing and node movemen migh cause problems Can we do beer? s h p h p s Proacive Mobile node divulges is posiion o all nodes whenever i moves E.g. hrough flooding Reacive Sender searches mobile hos only when i wans o send a message E.g. hrough flooding Hybrid Boh, proacive and reacive. Some nodes sore informaion abou where a node is locaed Arbirarily complicaed sorage srucures Suppor for simulaneous rouing and node mobiliy Disribued Compuing Group Mobile Compuing R. Waenhofer 8/21 Disribued Compuing Group Mobile Compuing R. Waenhofer 8/22 Locaion services: Lookup & Publish The Grid Locaion Service (GLS), Li e. al (2000) Any node A can invoke o basic operaions: Lookup(A, B): A asks for he posiion of B Publish(A, x, y): A announces is move from posiion x o y Open quesions How ofen does a node publish is curren posiion? Where is he posiion informaion sored? How does he lookup operaion find he desired informaion? Canno ge reasonable srech wih one single home. Therefore, use several homes (locaion servers) where he node publishes is posiion. The locaion servers are seleced based on a grid srucure: The area in which he nodes are locaed is divided ino squares All nodes agree on he lower lef corner (0,0) and upper righ corner (2 M, 2 M ), which forms he square called level-m Recursively, each level-n square is spli ino 4 level-(n-1) squares The recursion sops for level-1 Disribued Compuing Group Mobile Compuing R. Waenhofer 8/23 Disribued Compuing Group Mobile Compuing R. Waenhofer 8/24

7 The Grid Addressing of nodes Level-1 (2 M,2 M ) Unique IDs are generaed for each node (e.g. by using a hashfuncion) ID space (all possible hash values) is circular Every node can find a leas greaer node w.r.. he ID space (he closes node) Level-M Example: Le he ID space range from 1 o 99 and consider he IDs {3, 43, 80, }. Then, he leas greaer node wih respec o he given ID space is 3 43; 43 80; 80 ; 90 3 (0,0) Level-(M-1) Disribued Compuing Group Mobile Compuing R. Waenhofer 8/25 Disribued Compuing Group Mobile Compuing R. Waenhofer 8/26 Selecing locaion servers Each node A recruis locaion servers using he underlying grid: In each of he 3 level-1 squares ha, along wih A, make up a level-2 square, A chooses he node closes o is own ID as locaion server. The same selecion process is repeaed on higher level squares Disribued Compuing Group Mobile Compuing R. Waenhofer 8/ Example for node, which selecs he nodes {23, 17, 11} on he level-1 and {2, 3, 31} on level-2. Complee example , 72, 76, 81, 1, 5, 6, 10, 12, 82, 84, 14, 37, 62, 70, 90, Disribued Compuing Group Mobile Compuing R. Waenhofer 8/ , 35, 37, 45, 50, 51, 82 1, 5, 16, 37, 16, 17, 19, 21, 19, 35, 39, 45, 39, 41, 43 62, 63, 90, 23, 26, 28, 31, 51, 82 32, 35 1, 62, 70, 90 1, 5, 16, 37, 39, 41, 43, 45, 50, 51, 55,, 1, 2, 16, 37, 35, 39, 45, 50 19, 35, 39, 45, 62, 70, 90, 50, 51, 55,, 62, 63, 70, 72, 76, 81 62,, 19, 20, 21, 23, 26, 28, 31, 32, 51, 82 14, 17, 19, 20, 2, 17, 20, 63 2, 17, 23, 26, 21, 23, 31, 32, 43, 55,, 62 14, 23, 26, 31, 32, 43, 55,, 63, 81, 82, 84 1, 2, 5, 6, 10, 12, 14, 16, 17, 82, 84,, 90,, 19 28, 31, 32, 35, 10, 20, 21, 28, 37, 39 41, 43, 45, 50, 51, 55,, 62, 63, 70 2, 12, 26,, 1, 17, 23, 63, 2, 12, 14, 16, 6, 10, 20, 21, 81,, 23, 63 23, 26, 41, 72, 76, 84 6, 72, 76, , 81, 31, 32, 81,, 12, 43, 45, 50, 12, 43, 55 1, 2, 5, 21, 76, 6, 10, 20, 76 6, 10, 12, 14, 90, 51, 84,, 90,, 16, 17, 19, 84 31, 32, 43, 55,, 63, 70, 72, 76, 2, 12, 14, 17, 23, 26, 28, 32, 81, 12, 14, 17, 23, 26, 31, 32, 35, 37, 39, 41, 55, 2, 5, 6, 10, 6, 21, 28, 41, 20, 21, 28, 41, 43, 55,, 72 72, 76, 81, 82 63, 81,,

8 Querying locaion of oher nodes Lookup(A, B): Find a locaion server of node B 1. Node A sends he reques (wih georouing) o he node wih ID closes o B for which A has locaion informaion 2. Each node on he way forwards he reques in he same way 3. Evenually, he query reaches a locaion server of B, which forwards i o B. Example: Send packe from 81 o 23 14, 17, 19, 20, 21, 23, 26 14, 23, 26, 31, 32, 43, 55,, 63, 81, 82, , 12, 26,, 14 31, 81, 31, 32, 81,, 90, 31, 32, 43, 55,, 63, 70, 72, 76, 2, 12, 14, 17, 23, 26, 28, 32, 81, 31 2, 17, 20, 63 2, 17, 23, 26, 31, 32, 43, 55,, 62 1, 17, 23, 63, 81,, , 43, 45, 50, 51, 55 12, 14, 17, 23, 26, 31, 32, 35, 37, 39, 41, 55, , 12, 14, 16, 23, 63 12, 43, , 5, 6, 10, 43, 55,, 63, 81,, 12 Lookup Example Lookup for 17 from 76, 39 and , 72, 76, 81, 82, 84, 31 1, 5, 6, 10, 12, 14, 37, 62, 70, 90, 1, 5, 16, 37, 16, 17, 19, 62, 63, 90, 21, 23, 26, 28, 31, 32, 35 1, 62, 70, 90 1, 5, 16, 37, 39, 41, 43, 45, 50, 51, 55,, , 35, 37, 45, 50, 51, 82 19, 35, 39, 45, 39, 41, 43 51, 82 1, 2, 16, 37, 35, 39, 45, 50 19, 35, 39, 45, 62, 70, 90, 50, 51, 55,, 62, 63, 70, 72, 76, 81 62,, 19, 20, 21, 23, 26, 28, 31, 32, 51, 82 14, 17, 19, 20, 2, 17, 20, 63 2, 17, 23, 26, 21, 23, 31, 32, 43, 55,, 62 14, 23, 26, 31, 32, 43, 55,, 63, 81, 82, 84 1, 2, 5, 6, 10, 12, 14, 16, 82 17, 84,, 90,, 19 28, 31, 32, 35, 10, 20, 21, 28, 37, 39 41, 43, 45, 50, 51, 55,, 62, 63, 70 2, 12, 26,, 1, 17, 23, 63, 2, 12, 14, 16, 6, 10, 20, 21, 81,, 23, 63 23, 26, 41, 72, 76, 84 31, 81, 31, 32, 81,, 12, 43, 45, 50, 12, 43, 55 1, 2, 5, 21, 76, 6, 10, 20, 76 90, 51, 84,, 90,, 31, 32, 43, 55,, 63, 70, 72, 76, 2, 12, 14, 17, 23, 26, 28, 32, 81, 12, 14, 17, 23, 26, 31, 32, 35, 37, 39, 41, 55, 2, 5, 6, 10, 43, 55,, 63, 81,, 6, 72, 76, , 21, 28, 41, 20, 21, 28, 41, 72, 76, 81, , 10, 12, 14, 16, 17, 19, Disribued Compuing Group Mobile Compuing R. Waenhofer 8/29 Disribued Compuing Group Mobile Compuing R. Waenhofer 8/30 Analysis of GLS Theorem 1: A query needs no more han k locaion query seps o reach a locaion server of he desinaion when he sender and receiver are colocaed in a level-k square. Theorem 2: The query never leaves he level-k square in which he sender and desinaion are colocaed. GLS has no wors case guaranees The lookup cos beween wo nodes migh be arbirarily high even hough he nodes are very close The publish cos migh be arbirarily high even hough a node only moved a very shor disance In sparse neworks, rouing o he locaion server may have wors case cos, while rouing direcly can be more efficien 1, 5, 16, 37, 62, 63, 90, 1, 62, 70, , 17, 19, 20, 21, 23, 14, 23, 26, 31, 32, 43, 55,, 63, 81, 82, , 72, 76, 81, 82, 84, 90 1, 5, 16, 37, 39, 41, 43, 45, 50, 51, 55,, , 5, 6, 10, 12, 14, 37, 62, 70, 90, 16 1, 2, 16, 37, 62, 70, 90, , 17, 19, 21, 23, 26, 28, 31, 32, , 35, 39, 45, 51, , 39, 45, 50 62,, 19, 20, 21, 23, 26, 28, 31, 32, 51, 82 2, 12, 26,, 31, 81, 31, 32, 81,, 90, 31, 32, 43, 55,, 63, 70, 72, 76, 2, 12, 14, 17, 23, 26, 28, 32, 81, 2, 17, 20, 63 2, 17, 23, 26, 31, 32, 43, 55,, 62 1, 17, 23, 63, 81,, 12, 43, 45, 50, 51, 12, 14, 17, 23, 26, 31, 32, 35, 37, 39, 41, 55, 2, 12, 14, 16, 23, 63 28, 31, 32, 35, 37, 39 12, 43, 55 1, 2, 5, 21, 76, 84,, 90,, A B 2, 5, 6, 10, 43, 55,, 63, 81,, 6, 10, 20, 21, 23, 26, 41, 72, 76, 84 6, 10, 20, 76 6, 21, 28, 41, , 35, 37, 45, 50, 51, 82 39, 41, , 2, 5, 6, 10, 12, 14, 16, 17, 82, 84,, 90,, 10, 20, 21, 28, 41, 43, 45, 50, 51, 55,, 62, 63, 70 6, 72, 76, 84 20, 21, 28, 41, 72, 76, 81, , 35, 39, 45, 50, 51, 55,, 62, 63, 70, 72, 76, 81 6, 10, 12, 14, 16, 17, 19, Disribued Compuing Group Mobile Compuing R. Waenhofer 8/31 Disribued Compuing Group Mobile Compuing R. Waenhofer 8/32

9 GLS and mobiliy Improving GLS Node crosses boundary line: wha happens o he node s role as locaion server? Mus redisribue all informaion in he old level Gaher new informaion in he new level Publish cos is arbirarily high compared o he moved disance A lookup happening in parallel wih node movemen migh fail. Thus, GLS does no guaranee delivery for real concurren sysems, where nodes migh move independenly a any ime. 14, 17, 19, 20, 21, 23, 26 14, 23, 26, 31, 2, 12, 26,, 32, 43, 55,, 63, 81, 82, 84 31, 81, 31, 32, 81,, 90, 32 31, 32, 43, 55,, 63, 70, 72, 76, , 12, 14, 17, 23, 26, 28, 32, 81, 31 2, 17, 20, 6 2 1, 17, 23, 6 81,, 12, 43, 45 50, 51, 5 12, 14, 17 26, 31, 32 37, 39, 41 4 Goals for MLS Publish cos only depends on moved disance Lookup cos only depends on he disance beween he sender and receiver Nodes migh move arbirarily a any ime, even while oher nodes issue lookup requess Deermine he maximum allowed node speed under which MLS sill guaranees delivery Disribued Compuing Group Mobile Compuing R. Waenhofer 8/33 Disribued Compuing Group Mobile Compuing R. Waenhofer 8/34 Locaion poiners (aka locaion servers) Locaion poiner & Noaion Difference o GLS: Only one locaion poiner (LP) per level (L) (GLS: 3 locaion servers) The locaion poiner only knows in which sub-level he node is locaed (GLS: he locaion server knows he exac posiion) Noaion: LP k Locaion poiner for node on level-k L k Level-k ha conains node L M LP M L 0 The locaion poiners are placed depending on heir ID, as in he home-based lookup sysem. LP 1 L 1 The posiion of is obained by hashing he ID of node o a posiion in. The locaion poiner is sored on he neares nodes. L k LP k LP M 1 L 2 LP 2 L M 1 Disribued Compuing Group Mobile Compuing R. Waenhofer 8/35 Disribued Compuing Group Mobile Compuing R. Waenhofer 8/36

10 Rouing in MLS Rouing in MLS (2) Rouing from a node s o a node consiss of wo phases: 1. Find a locaion poiner LP k 2. Once a firs locaion poiner is found on level-k, we know in which of he 4 sub-squares is locaed and hus in which L k 1 has published anoher locaion poiner LP. k 1 Recursively, he message is roued owards locaion poiners on lower levels unil i reaches he lowes level, from where i can be roued direcly o. When a node s wans o find a locaion poiner of a node, i firs searches in is immediae neighborhood and hen exends he search area wih exponenial growing coverage. Firs, ry o find a locaion poiner LP 0 in L s 0 or one of is 8 neighboring levels. Repea his search on he nex higher level unil a is found The lookup pah draws a spiral-like shape wih exponenially increasing radius unil i finds a locaion poiner of. Once a locaion poiner is found, he lookup reques knows in which sub-square i can find he nex locaion poiner of. LP k s Disribued Compuing Group Mobile Compuing R. Waenhofer 8/37 Disribued Compuing Group Mobile Compuing R. Waenhofer 8/38 Suppor for mobiliy in MLS Lazy publishing A locaion poiner only needs o be updaed when he node leaves he corresponding sub-square. LP 2 is OK as long as remains in he shaded area. Mos of he ime, only he closes few locaion poiners need o be updaed due o mobiliy. LP i+2 LP 1 LP 2 Idea: Don updae a level poiner as long as is sill somewha close o he level L k where poins. LP i+2 LP i+1 LP k LP k No enough: If a node moves across a level boundary, many poiners need o be updaed. E.g. a node oscillaes beween he wo poins a and b. LP i+1 LP i+1 LP i LP i+1 Breaks he lookup: poins o a level ha does no conain LP i LP i LP i a b Disribued Compuing Group Mobile Compuing R. Waenhofer 8/39 Disribued Compuing Group Mobile Compuing R. Waenhofer 8/40

11 Lazy publishing wih forwarding poiners Concurrency in MLS No problem, add a forwarding poiner ha indicaes in which neighboring level he locaion poiner can be found. LP i+2 Allowing for concurren lookup requess and node mobiliy is somewha ricky, especially he deleion of poiners. Noe ha a lookup reques needs some ime o ravel beween locaion poiners. The same holds for requess o creae or delee locaion (or forwarding) poiners. LP i+1 FP i LP i Example: A lookup reques follows LP i+1, and node moves as indicaed updaes is LP iand LP i+1 and removes he FP i and he old LP i The lookup reques fails if i arrives afer he has been removed FP i LP i+1 FP i LP i LP i Disribued Compuing Group Mobile Compuing R. Waenhofer 8/41 Disribued Compuing Group Mobile Compuing R. Waenhofer 8/42 Concurrency in MLS (2) Properies of MLS No problem eiher: Insead of removing a locaion poiner or forwarding poiner, replace i wih a emporary poiner ha remains here for a shor ime unil we are sure ha no lookup reques migh arrive anymore on his oudaed pah. Similar o he forwarding poiner, a emporary poiner redirecs a lookup o he neighbor level where he node is locaed. LP i+1 TP i LP i TP i Consan lookup srech The lengh of he chosen roue is only a consan longer han he opimal roue Publish cos is O(d log d) where moved disance is d Even if nodes move considerably, he induced message overhead due o publish requess is moderae. Works in a concurren seup Lookup requess and node movemen migh inerleave arbirarily Nodes migh no move faser han 1/15 of he underlying rouing speed We can deermine he maximum node speed ha MLS suppors. Only if nodes move faser, here migh arise siuaions where a lookup reques fails. Disribued Compuing Group Mobile Compuing R. Waenhofer 8/43 Disribued Compuing Group Mobile Compuing R. Waenhofer 8/44

12 MLS Conclusions I s somewha ricky o handle concurrency properly Use of emporary forwarding poiners MLS is he firs locaion service ha deermines he maximum speed a which nodes migh move Wihou he speed limiaion, no delivery guaranees can be made! Drawbacks MLS uilizes an underlying rouing algorihm ha can deliver messages wih consan srech given he posiion of he desinaion MLS requires a relaively dense node populaion Disribued Compuing Group Mobile Compuing R. Waenhofer 8/45