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E-tickets validation protocols in mobile environment

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E-tickets validation protocols in mobile environment

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  1. E-tickets validation protocols in mobile environment • MSS:verification server maintains a list of E-tickets validated by it. • MH:submit the E-ticket • E-ticket validation problem:validation process • The same sequence of an E-ticket should not get validated more than once. • An E-ticket should get validated at least once. That is, at least one MSS should accept this sequence of an E-ticket.

  2. E-tickets validation protocols in mobile environment • E-ticket problem can be defined in short by the following two properties: • (P.1) If a MSS accepts the E-ticket T and it does not crash, then no other MSS accepts T and a MSS does not accept the same E-ticket more than once. • (P.2) Let δ(T) be the set of MSSs that validate the same E-ticket T. If not all MSSs in δ(T) crashes then there is at least one MSS in δ(T) that accepts T.

  3. E-tickets validation protocols in mobile environment • Two Phase E-ticket Validation Protocol (TPEP) • Flat scheme algorithm • Tree-Based Protocol (TBP) • Hierarchical scheme algorithm

  4. Two Phase E-ticket Validation Protocol • When MH send the E-ticket to the MSS • Phase I • The MSS sends an inquiry to all other MSSs in the system visited by the MH, and it validates an E-ticket if none of the responses received from all other MSSs for the same E-ticket is negative. • Phase II • It only starts if the MSS gets at least one negative acknowledgment. When more than one MSS tries to validate an E-ticket in Phase II, the MSS that is in the same cell as the MH will validate the E-ticket and all others will reject it.

  5. Two Phase E-ticket Validation Protocol • At the end of the protocol, the MSS Si informs the decision on the validation of the E-ticket T to the mobile host, Hi, holding T. • If Hi is disconnected, Si waits for the reconnection of Hi and delivers the message.

  6. NEWTKT REQUESTACK ACK POSITIVE NEGATIVE REJECT ACCEPT Message Type MH將E-ticket傳送給MSS做認證 MSS詢問其他MSSs 1.驗證過此E-ticket ? 2.其他MSS發送相同的REQUESTACK ? MSS回覆REQUESTACK 此E-ticket沒有被認證過且沒有其他MSS發送過此E-ticket的REQUESTACK給我 同時有其他MSS正為此E-ticket作認證 此E-ticket我已認證過了 MSS通知所有MSSs此E-ticket已被我認證了

  7. Wait replies MH Hi MSS Si Other MSSs Phase I NEWTKT REQUESTACK Already validated Already received Otherwise ACKs ACK-NEGATIVE ACK-POSITIVE ACK-REJECT All Positive Has Negative Has Reject REJECT ACCEPT Phase II

  8. MH Hi MH Hi MH Hi MSS Sj MSS Si Phase II • More than one MSS tries to validate the same E-ticket T in case the same ticket is submitted for validation by Hi from several places. Phase II Reject Phase II Phase II Accept Reject MSS Sk E-Ticket E-Ticket E-Ticket cell cell cell

  9. Two Phase E-ticket Validation Protocol • Si :the mobile support station (MSS) • Hi :the mobile host (MH) • λS:the set of MSSs • λH:the set of MHs • δHi:the set of MSSs where Hi visited • visited_ list ( Hi ) → 回傳 Hi 之前拜訪過的 MSS List • Search ( Hi ) → 回傳目前正在服務 Hi 的 MSS • Nearst ( CurrentMSS , List ) → 回傳 List 中離 CurrentMSS最近的 MSS

  10. E-ticket’s attribute • status : accept or reject • ackStatus : positive, negative or reject • currentValidator : the set of validators which are validating this E-ticket

  11. Two Phase E-ticket Validation Protocol Algorithm to be executed at each MSS SiFormat: (Message Type, ticket, sender, receiver) 存放 REQUESTACK紀錄 (MSS,T)

  12. PHASE I 傳回結果給Hi Hi 之前拜訪過的MSS清單 紀錄其他 MSSs 回覆訊息的數量 紀錄 Positive ACK 的數量 紀錄其他同時認證此 ticket 之MSSs

  13. Already validated 此 ticket是否有其他 MSS 同時在認證? Already received 將該MSS加入 Otherwise

  14. Has Reject 從other MSSs 接收的ACK 回應 Positive ACK Negative ACK 記錄目前正在驗證 的MSS

  15. 當 replies >= (RequestACK / 2) All Positive 告知所有的MSS,此ticket已被我驗證過 Otherwise

  16. 更新 vTkts , aTkts資訊

  17. PHASE II 查處Hi目前所在的MSS Si是否為Hi目前所在的MSS中? Nearest Accept Other Reject

  18. Hi 在Si 範圍且 Hi未斷線 則傳遞 Hi 在Si 範圍且 Hi斷線 則等 △t 時間後再傳 Hi 不在Si 範圍 則搜尋 Hi所在的 Si

  19. MSS S1 MSS S2 MSS S3 MSS S4 Correctness of protocol Req_Ack Accept Req_Ack H1 submits T T accepted NewTkt +ACK +ACK Req_Ack Req_Ack Req_Ack Accept H1 submits T T rejected NewTkt -ACK Reject

  20. MSS S1 MSS S2 MSS S3 MSS S4 Correctness of protocol Phase II Req_Ack Req_Ack H1 submits T T rejected NewTkt Req_Ack +ACK -ACK Req_Ack Req_Ack H1 submits T T accepted NewTkt +ACK -ACK -ACK

  21. Analysis of protocol • Three types of messages exchanged in the Phase I of the protocol • REQUESTACK • ACK • ACCEPT • Best Case : MH is residing in only one cell. In this case the number of messages exchanged will be zero. • Worst Case : MH is highly mobile and may cover the entire network. In this case the number of messages exchanged will be 3(m-1) where m is the number of MSSs. • Avg. Case : The mobile host is limited to a few cells. The number of messages exchanged will be 3(δMH-1) where δMH < m is the number of cells that MH visited.

  22. Tree-based protocol • Hierarchy of geographical region • Each node is a MSS • Each region is a collection of some MSS’s information and is represented by a internal node. • The root node represents the total area spanning over the entire region • Each MSS in a higher level of hierarchy knows the information about E-tickets validated by the lower level nodes • Use the timestamp to choose nearest MSS

  23. Tree-Based Protocol S1 Has information of validated ticket S4 S7 Has information of validated ticket Has information of validated ticket S8 S6 S3 S2 S5

  24. Tree-Based Protocol S1 Already validated S4 S7 Reject Req_Ack Req_Ack S8 S6 S3 S2 S5 NewTkt NewTkt

  25. Tree-Based Protocol • Algorithm to be executed at each MSS SiFormat: (Message Type, ticket, sender, receiver)

  26. 將Request ACK往Parent送

  27. 表此 ticket 已被驗證過 回傳 Negative ACK 若此 MSS 為 root,且此 ticket 未被驗證過 回傳 Positive ACK Otherwise 將Request ACK往上傳

  28. 判斷路由Stack是否為空 表此MSS為驗證的源起者 表此MSS非驗證的源起者 將ACK訊息往下傳

  29. Hi 在Si 範圍且 Hi未斷線 則傳遞 Hi 在Si 範圍且 Hi斷線 則等 △t 時間後再傳 Hi 不在Si 範圍 則搜尋 Hi所在的 Si

  30. Correctness of protocol If S4 , S5 At the same time If S4 faster than S5 S5’s timestamp > S4’s timestamp S1 +ACK -ACK -ACK +ACK Req_Ack S4 S7 NewTkt Req_Ack S8 S6 S3 S2 S5 NewTkt

  31. Analysis of protocol • Two types of messages exchanged in the protocol • REQUESTACK • ACK • Best Case : The server that gets the ticket and the root being the same, the number of messages is zero. • Worst Case : The server that gets the ticket is at the highest level, the number of messages will be 2(h - 1) where h is the height of the tree. • Avg. Case : The server that gets the ticket is at a level i, the number of messages will be 2(h – i - 1), where h is the height of the tree.

  32. Comparsion of the protocol • Assumption • Without failure • The same E-ticket is used once by the users • Comparsion • Resilience • Latency • The number of messages exchanged to validate an E-ticket.

  33. Comparsion of the protocol Request & ACK Request & ACK & Accept Request & ACK Θ : maximum message delay δs : the number of servers visited by the client h : the height of tree