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Mobile Database Systems Vijay Kumar Computer Sc. Telecommunications University of Missouri-Kansas City 5100 Rockhill Road Kansas City, MO 64110, USA

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Presentation on theme: "Mobile Database Systems Vijay Kumar Computer Sc. Telecommunications University of Missouri-Kansas City 5100 Rockhill Road Kansas City, MO 64110, USA"— Presentation transcript:

1 Mobile Database Systems Vijay Kumar Computer Sc. Telecommunications University of Missouri-Kansas City 5100 Rockhill Road Kansas City, MO 64110, USA kumar@cstp.umkc.edu

2 Mobile Database Systems Outline  Fully Connected Information Space  Personal Communication System (PCS)  Mobile Database Systems (MDS)  Transaction Management  Data Caching  Query Processing  Data Classification  Conclusion

3 Mobile Database Systems Fully connected information space

4 Mobile Database Systems Fully connected information space  Each node of the information space has some communication capability.  Some node can process information.  Some node can communicate through voice channel.  Some node can do both

5 Mobile Database Systems Fully connected information space Can be created and maintained by integrating legacy database systems, and wired and wireless systems (PCS, Cellular system, and GSM)

6 Mobile Database Systems A system with the following structural and functional properties  Distributed system with mobile connectivity  Full database system capability  Complete spatial mobility  Built on PCS/GSM platform  Wireless and wired communication capability What is a Mobile Database System (MDS)?

7 Mobile Database Systems What is a mobile connectivity? A mode in which a client or a server can establish communication with each other whenever needed. Intermittent connectivity is a special case of mobile connectivity.

8 Mobile Database Systems A node in which only the client can establish communication whenever needed with the server but the server cannot do so. What is intermittent connectivity?

9 Personal Communication System (PCS)  Architecture  Wireless communication  Bandwidth limitations  Frequency reuse Part 1

10 Personal Communication System (PCS) A system where wired and wireless networks are integrated for establishing communication.

11 Personal Communication System (PCS) PCS refers to variety of wireless access (communication) and personal mobility services provided through a small terminal at any place, and in any form. Business opportunities (E-commerce) for such services are tremendous, since every person, every organization, etc., could be equipped. Several PCS systems have been developed to meet rapid growth prompted by market demand. Most of them are connected to Public Switched Telephone Network (PSTN) to integrate with the wired service. Two of the most popular PCS systems are:  Cellular telephony  Cordless and low-tier PCS telephony

12 Personal Communication System (PCS) Cellular telephony overview Four popular cellular telephony networks are:  Advanced Mobile Phone Service (AMPS)  Global System for Mobile Communication (GSM)  EIA/TIA IS-136 Digital Cellular System  EIA/TIA IS-95 Digital Cellular System

13 Personal Communication System (PCS) Cellular telephony overview Advanced Mobile Phone Service (AMPS) AMPS was the first cellular system, which was developed during the 1970s by Bell Lab. From 1974 to 1978, a large scale AMPS trial was conducted in Chicago. Commercial AMPS service has been available since 1983. It is based on frequency division multiple access (FDMA), AMP was designed as a high capacity system based on a frequency reuse scheme. A total of 50 MHz in the 824-849 MHz and 869- 894 MHz bands is allocated for AMPS.This spectrum is divided into 832 full-duplex channels using 1664 discrete frequencies, that is, 832 downlinks and 832 uplinks. In AMPS, the typical frequency reuse plan employs either a 12-group frequency cluster using omnidirectional antennas or a 7-group cluster using three sectors per base stations. Thus, there are about 50 channels per cell.

14 Personal Communication System (PCS) Cellular telephony overview Global System for Mobile Communication (GSM) GSM is a digital cellular system developed by Groupe Special Mobile of Conference Europeenne des Postes et Telecommunications (CEPT) and its successor European Telecommunications Standard Institute (ETSI). GSM combines time divisioin multiple access (TDMA) and FDMA. With TDMA, the radio hardware in the base station can be shared among multiple users. In GSM the frequency carrier is divided into eight time slots where the speech coding rate is 13 Kbps. In a GSM base station, every pair of radio transceiver-receiver supports eight voice channels, whereas an AMPS base station needs one such pair for every voice channel. The GSM development process was similar to that of AMPS, except that no large scale trial was conducted.

15 Personal Communication System (PCS) Cellular telephony overview EIA/TIA IS-136 Digital Cellular System This system is also referred to as digital AMPS (DAMPS), American Digital Cellular (ADC), or North American TDMA (NA-TDMA), IS-136, the successor to IS-54, supports a TDMA air interface similar to that of GSM. IS-54 was renamed IS-136 when it reached revision C. It supports three voice channels, where the speech coding rate is 7.95 Kbps. IS-136 capacity is around three times that of AMPS. An existing AMPS system can be easily upgraded to IS-136 0n a circuit-by-circuit basis.

16 Personal Communication System (PCS) Cellular telephony overview EIA/TIA IS-95 Digital Cellular System This digital cellular system was developed by Qualcomm, and has been operating in USA since 1996. IS-95 is based on Code Division Multiple Access (CDMA) technology. It allows many users to share a common frequency/time channel for transmission. The channel bandwidth used by IS-95 is 1.25 MHz, which has been extended to 5 MHz in the third generation wideband CDMA proposal. The speech coding rate for IS-95 is 13 Kbps or 8 Kbps. IS-95’s capacity is estimated to be 10 times that of AMPS.

17 Personal Communication System (PCS) Cordless telephony technologies Cordless Telephone, Second Generation (CT2) Developed in Europe, and has been available since 1989. CT2 is allocated 40 FDMA channels with a 32-Kbps speech coding rate. For a user, both baseptop handset signals and handset- to-base signals are transmitted in the same frequency. The maximum transmit power of a CT2 handset is 10 mW. In the call setup procedure, CT2 moves a call path from one radio channel to another after three seconds of handshake failure. CT2 also supports data transmission rates of up to 2.4 Kbps through the speech code and up to 4.8 Kbps with an increased rate. CT2 does not support handoff and in a public CT2 system, call delivery is not supported.

18 Personal Communication System (PCS) Digital European Cordless Telephone (DECT) The Digital European Cordless Telephone has been replaced by Digital Enhanced Cordless Telephone to denote global acceptance of DECT. DECT supports high user density with a picocell design. There are 12 voice channels per frequency carrier. Sleep mode is employed to converse handset power. DECT also supports seamless handoff. DECT is typically implemented as a wireless-PBX (Private Brach Exchange) connected to PSTN. DECT can interwork with GSM to allow user mobility. Cordless telephony technologies

19 Personal Communication System (PCS) Low-tier PCS telephony overview Personal Handy Phone System (PHS) PHS is a standard developed by the Research and Development Center for Radio Systems (RCR), a private standardization organization in Japan. PHS is a low-tier digital PCS system that offers telecommunication services for homes, offices, and outdoor environment, using radio access to the public telephone network or other digital networks. PHS uses TDMA. Sleep mode enables PHS to support five hours of talk time, or 150 hours of standby time. PHS operates in the 1895-1918.1 MHz band. The bandwidth is partitioned into 77 channels, each with 300 KHz bandwidth. The band 1906.1-1918.1 MHz (40 channels) is designed for public systems, and the band 1895-1906.1 MHz (37 channels) is used for home/office applications.

20 Personal Communication System (PCS) Low-tier PCS telephony overview Personal Access Communications Systems (PACS) PACS is a low-power PCS system developed at Telcordia (formerly Bellcore). TDMA is used in PACS with eight voice channels per frequency carrier. In FDD mode, the PACS uplink and downlink utilizes different RF carriers, similar to cellular systems.

21 Personal Communication System (PCS) Cordless and low-tier PCS telephony overview SystemHigh-tier CellularLow-tier PCSCordless Cell sizeLarge (0.4-22 mile)Medium (30-300’)Small (30-60’) User speed High (  160 mph)Medium (  60 mph) Low (  30 mph) Coverage areaLarge/Continuous macrocell Medium. Micro and picocell Small/Zonal, picocell Handset complexity HighLow H-set power useHigh (100-800 mW)Low (5-10 mW) Speech coding rate Low (8-13 Kbps)High (32 Kpbs) Delay or latency High (  600 ms)Low (  10 ms)Low (  20 ms)

22 Personal Communication System (PCS) Wireless Components Base Station (BS): A network element that interconnects the mobile station (or Mobile unit (MU)) to the network via the air interface. Each cell in the network has a BS associated with it. The primary function of a BS is to maintain the air interface, or medium, for communication to any mobile unit within its cell. Other functions of BS are call processing, signaling, maintenance, and diagnostics. The BS communicates to its mobile unit via the air interface, and to MTSO by dedicated communication link such as T1 trunks. Communication links on the BS to the MTSO interface are also classified into voice links and signaling link.

23 Personal Communication System (PCS) Wireless Components Mobile Units (MU): Also called Mobile Systems (MS) or Mobile Hosts (MH). It consists of three components: (a) transceiver, (b) antenna, and (c) user interface. The user interface exists only at MU, which consists of a display, a keypad for entering information, and an audio interface for speaking and hearing voice conversation. This can be a laptop, a palmtop, or a cell phone, or any other mobile device. A MU also stores (a) Mobile Identification Number (MIN), (b) Electronic Serial Number (EIN), and (C) Station Class Mark (SCM). These are transmitted upon power on, cell initiated sampling, and cell origination.

24 Personal Communication System (PCS) Wireless Components

25 Personal Communication System (PCS) Wireless channels are limited ItemEurope (MHz)US (MHz)Japan (MHz) Mobile Phones NMT: 453-457, 463-467 GSM: 890-915, 935-960, 1710-1785, 1805-1880 AMPS, TDMA, CDMA 824-849, 869-894 GSM, TDMA, CDMA 1850-1910, 1930-1990 PDC: 810-826 940-956, 1429-1465, 1477-1513. Cordless Phones CT1+: 885-887, 930-932 CT2: 864-868 DECT: 1880-1900 PACS 1850-1910,1930-1990; PACS-UB: 1910-1930 PHS 1895-1918; JCT: 254-380 NMT:Nordic Mobile Telephone PDC:Pacific Digital Cellular PACS:Personal Access Communications System PHS:Personal Handyphone System PACS-UB:PACS Unlicensed Band JCT:Japanese Cordless Telephone (Taken from Mobile Communications by Jochen Schiller)

26 Personal Communication System (PCS) Limited channels must be utilized efficiently. It is done so by (a) Frequency reuse and (b) Mobile cell Frequency reuse The goal of every mobile service provider is to manage as many simultaneous calls as possible. In USA each cellular provider is allocated 25 MHz of spectrum, 12.5 MHz for transmitting (downstream) and 12.5 MHz for receiving (upstream). Cellular system is duplex because transmitting and receiving are allocated their own frequencies. A person on a mobile call only needs the allocated frequency of the cell, thus there is no reason somebody else on the other end of the town cannot be using the same frequency in a different cell. The concept of multiple users using the same frequency at the same time for communication is called frequency reuse.

27 Personal Communication System (PCS) Frequency reuse (continued) For frequency reuse to work correctly it is imperative that each base station has just sufficient power to reach its cell boundary. If it puts out too much power, then it will not only reach the intended cell site, it will reach unintended cell sites, which others may be using at the same frequency for a totally different conversation. This limitation on transmitted power, however, is also an advantage because the cellular phone’s battery will last longer.

28 Personal Communication System (PCS) Within the cellular allocation the USA is divided into Metropolitan Statistical Areas (MSAs) and Rural Statistical Areas (RSAs). There are six PCS service providers authorized to provide mobile service in each of these areas. Within their geographical region, each service provider divides their area into smaller segments called cells. Each of this cell has a Base Station. Ideally, the system has a large number of very small hexagons (cell). The greater the number of hexagons, the more simultaneous calls the system can handle. However, larger number of hexagons increases the cost of implementation. Thus, cell coverage is a dynamic activity, which is constantly changing in response to increases in demand. Mobile cell

29 Personal Communication System (PCS) Mobile cells

30 Personal Communication System (PCS) Mobile cells The entire coverage area is a group of a number of cells. The size of cell depends upon the power of the base stations.

31 Personal Communication System (PCS) Frequency reuse D = distance between cells using the same frequency R = cell radius N = reuse pattern (the cluster size, which is 7). Thus, for a 7-cell group with cell radius R = 3 miles, the frequency reuse distance D is 13.74 miles.

32 Personal Communication System (PCS) Problems with cellular structure  How to locate of a mobile unit in the entire coverage area? Solution: Location management  How to maintain continuous communication between two parties in the presence of mobility? Solution: Handoff  How to maintain continuous communication between two parties in the presence of mobility? Solution: Roaming

33 Personal Communication System (PCS) Handoff A process, which allows users to remain in touch, even while breaking the connection with one BS and establishing connection with another BS.

34 Personal Communication System (PCS) Handoff To keep the conversation going, the Handoff procedure should be completed while the MS (the bus) is in the overlap region.

35 Personal Communication System (PCS) Handoff issues  Handoff detection  Channel assignment  Radio link transfer

36 Personal Communication System (PCS)  Mobile-Controlled handoff (MCHO)  Network-Controlled handoff (NCHO)  Mobile-Assisted handoff (MAHO) Handoff detection strategies

37 Personal Communication System (PCS) Mobile-Controlled Handoff (MCHO) In this strategy, the MS continuously monitors the radio signal strength and quality of the surrounding BSs. When predefined criteria are met, then the MS checks for the best candidate BS for an available traffic channel and requests the handoff to occur. MACHO is used in DECT and PACS.

38 Personal Communication System (PCS) Network-Controlled Handoff (NCHO) In this strategy, the surrounding BSs, the MSC or both monitor the radio signal. When the signal’s strength and quality deteriorate below a predefined threshold, the network arranges for a handoff to another channel. NCHO is used in CT-2 Plus and AMPS.

39 Personal Communication System (PCS) Mobile-Assisted Handoff (MAHO) It is a variant of NCHO strategy. In this strategy, the network directs the MS to measure the signal from the surrounding BSs and to report those measurements back to the network. The network then uses these measurements to determine where a handoff is required and to which channel. MACHO is used in GSM and IS-95 CDMA.

40 Personal Communication System (PCS) Handoff types with reference to the network  Intra-system handoff or Inter-BS handoff The new and the old BSs are connected to the same MSC.

41 Personal Communication System (PCS) Intra-system handoff or Inter-BS handoff Steps 1. The MU (MS) momentarily suspends conversation and initiates the handoff procedure by signaling on an idle (currently free) channel in the new BS. Then it resumes the conversation on the old BS.

42 Personal Communication System (PCS) Intra-system handoff or Inter-BS handoff 2. Upon receipt of the signal, the MSC transfers the encryption information to the selected idle channel of the new BS and sets up the new conversation path to the MS through that channel. The switch bridges the new path with the old path and informs the MS to transfer from the old channel to the new channel.

43 Personal Communication System (PCS) Intra-system handoff or Inter-BS handoff 3. After the MS has been transferred to the new BS, it signals the network and resumes conversation using the new channel.

44 Personal Communication System (PCS) Intra-system handoff or Inter-BS handoff 4. Upon the receipt of the handoff completion signal, the network removes the bridge from the path and releases resources associated with the old channel.

45 Personal Communication System (PCS) Handoff types with reference to the network  Intersystem handoff or Inter-MSC handoff The new and the old BSs are connected to different MSCs.

46 Personal Communication System (PCS) Handoff types with reference to link transfer  Hard handoff The MS connects with only one BS at a time, and there is usually some interruption in the conversation during the link transition.  Soft handoff The two BSs are briefly simultaneously connected to the MU while crossing the cell boundary. As soon as the mobile's link with the new BS is acceptable, the initial BS disengages from the MU.

47 Personal Communication System (PCS) Handoff types with reference to link transfer Hard handoff 1. MU temporarily suspends the voice conversation by sending a link suspend message to the old BS. 2. MU sends a handoff request message through an idle time slot of the new BS to the network. 3. The new BS sends a handoff ack message and marks the slot busy. 4. The MU returns the old assigned channel by sending a link resume message to the old BS.

48 Personal Communication System (PCS) Handoff types with reference to link transfer Hard handoff 5. MU continues voice communication while the network prepares for the handoff. 6. Upon receipt of a handoff request message, the new BS sends a handoff ack message and reconfigures itself to effect the handoff. 7. The MSC inserts a bridge into the conversation path and bridges the new BS. 8. Finally, the network informs the MU to execute the handoff via both the new and old BSs by sending the handoff execute message.

49 Personal Communication System (PCS) Handoff types with reference to link transfer Hard handoff 9. MU releases the old channel by sending an access release message to the old BS. 10. Once the MU has made the transfer to the new BS, it sends the network a handoff complete message through the new channel, and resumes the voice communication. The network removes the bridge from the path and frees up the resources associated with the old channel.

50 Personal Communication System (PCS) Handoff types with reference to link transfer Soft handoff 1. MU sends a pilot strength measurement message to the old BS, indicating the new BS to be added. 2. The old BS sends a handoff request message to the MSC. If the MSC accepts the handoff request, it sends a handoff request message to the new BS. 3. The BS sends a null traffic message to the MU to prepare the establishment of the communication link.

51 Personal Communication System (PCS) Handoff types with reference to link transfer Soft handoff 4. The new BS sends a join request message to the MSC. The MSC bridges the connection for the two BSs, so that the handoff can be processed without breaking the connection. 5. The new BS sends a handoff ack message to the old BS via the MSC. The old BS instructs the MU to add a link to the new BS by exchanging the handoff command and handoff complete messages.

52 Personal Communication System (PCS) Handoff types with reference to link transfer Soft handoff 6. The old BS and the MSC conclude this procedure by exchanging the required handoff information. The quality of the new link is guaranteed by the exchange of the pilot measurement request and the pilot strength measurement message pair between the MU and the new BS.

53 Personal Communication System (PCS) Roaming Roaming is a facility, which allows a subscriber to enjoy uninterrupted communication from anywhere in the entire coverage space. A mobile network coverage space may be managed by a number of different service providers. They must cooperate with each other to provide roaming facility. Roaming can be provided only if some administrative and technical constraints are met.

54 Personal Communication System (PCS) Roaming Administrative constraints  Billing.  Subscription agreement.  Call transfer charges.  User profile and database sharing.  Any other policy constraints.

55 Personal Communication System (PCS) Roaming Technical constraints  Bandwidth mismatch. For example, European 900MHz band may not be available in other parts of the world. This may preclude some mobile equipment for roaming.  Service providers must be able to communicate with each other. Needs some standard.  Mobile station constraints.

56 Personal Communication System (PCS) Roaming Technical constraints  Integration of a new service provider into the network. A roaming subscriber must be able to detect this new provider.  Service providers must be able to communicate with each other. Needs some standard.  Quick MU response to a service provider’s availability.  Limited battery life.

57 Personal Communication System (PCS) Roaming Two basic operations in roaming management are  Registration (Location update): The process of informing the presence or arrival of a MU to a cell.  Location tracking: the process of locating the desired MU.

58 Personal Communication System (PCS) Roaming Registration (Location update): There are six different types of registration.  Power-down registration. Done by the MU when it intends to switch itself off.  Power-up registration. Opposite to power-down registration. When an MU is switched on, it registers.  Deregistration. A MU decides to acquire control channel service on a different type of network (public, private, or residential).

59 Personal Communication System (PCS) Roaming Registration (Location update): There are six different types of registration.  New system/Location area registration: when the location area of the MU changes, it sends a registration message.  Periodic registration: A MU may be instructed to periodically register with the network.  Forced registration: A network may, under certain circumstances, force all MUs to register.

60 Personal Communication System (PCS) Registration Two-Tier Scheme HLR: Home Location Register A HLR stores user profile and the geographical location. VLR: Visitor Location Register A VLR stores user profile and the current location who is a visitor to a different cell that its home cell.

61 Personal Communication System (PCS) Registration Two-Tier Scheme steps. MU1 moves to cell 2.

62 Personal Communication System (PCS) Registration Steps 1. MU1 moves to cell 2. The MSC of cell 2 launches a registration query to its VLR 2. 2. VLR2 sends a registration message containing MU’s identity (MIN), which can be translated to HLR address. 3. After registration, HLR sends an acknowledgment back to VLR2. 4. HLR sends a deregistration message to VLR1 (of cell 1) to delete the record of MU1 (obsolete). VLR1 acknowledges the cancellation.

63 Personal Communication System (PCS) Location tracking Steps 1. VLR of cell 2 is searched for MU1’s profile. 2. If it is not found, then HLR is searched. 3. Once the location of MU1 is found, then the information is sent to the base station of cell 1. 4. Cell 1 establishes the communication.

64 Personal Communication System (PCS) Location tracking Two-Tier Scheme steps location search

65 Personal Communication System (PCS) Location tracking Two-Tier Scheme steps location update

66 Mobile Database Systems (MDS) Part 2  Architecture  Data categorization  Data management  Transaction management  Recovery

67 Mobile Database Systems (MDS) A Reference Architecture (Client-Server model)

68 Mobile Database Systems (MDS) MDS Applications  Insurance companies  Emergencies services (Police, medical, etc.)  Traffic control  Taxi dispatch  E-commerce  Etc.

69 Mobile Database Systems (MDS) MDS Limitations  Limited wireless bandwidth  Wireless communication speed  Limited energy source (battery power)  Less secured  Vulnerable to physical activities  Hard to make theft proof.

70 Mobile Database Systems (MDS) MDS capabilities  Can physically move around without affecting data availability  Can reach to the place data is stored  Can process special types of data efficiently  Not subjected to connection restrictions  Very high reachability  Highly portable

71 Mobile Database Systems (MDS) Objective To build a truly ubiquitous information processing system by overcoming the inherent limitations of wireless architecture.

72 Mobile Database Systems (MDS) MDS Issues  Data Management Data Caching Data Broadcast (Broadcast disk) Data Classification  Transaction Management Query processing Transaction processing Concurrency control Database recovery

73 Mobile Database Systems (MDS) MDS Data Management Issues How to improve data availability to user queries using limited bandwidth? Possible schemes  Semantic data caching: The cache contents is decided by the results of earlier transactions or by semantic data set.  Data Broadcast on wireless channels

74 Mobile Database Systems (MDS) MDS Data Management Issues How to improve data availability to user queries using limited bandwidth? Semantic caching  Client maintains a semantic description of the data in its cache instead of maintaining a list of pages or tuples.  The server processes simple predicates on the database and the results are cached at the client.

75 Mobile Database Systems (MDS) MDS Data Management Issues Mobile Database Systems (MDS) Data Broadcast (Broadcast disk) A set of most frequently accessed data is made available by continuously broadcasting it on some fixed radio frequency. Mobile Units can tune to this frequency and download the desired data from the broadcast to their local cache. A broadcast (file on the air) is similar to a disk file but located on the air.

76 Mobile Database Systems (MDS) MDS Data Management Issues Mobile Database Systems (MDS) Data Broadcast (Broadcast disk) The contents of the broadcast reflects the data demands of mobile units. This can be achieved through data access history, which can be fed to the data broadcasting system. For efficient access the broadcast file use index or some other method.

77 Mobile Database Systems (MDS) MDS Data Management Issues How MDS looks at the database data? Data classification  Location Dependent Data (LDD)  Location Independent Data (LID)

78 Mobile Database Systems (MDS) MDS Data Management Issues Location Dependent Data (LDD) The class of data whose value is functionally dependent on location. Thus, the value of the location determines the correct value of the data. Location Data value Examples: City tax, City area, etc.

79 Mobile Database Systems (MDS) MDS Data Management Issues The class of data whose value is functionally independent of location. Thus, the value of the location does not determine the value of the data. Example: Person name, account number, etc. The person name remains the same irrespective of place the person is residing at the time of enquiry. Location Independent Data (LID)

80 Mobile Database Systems (MDS) MDS Data Management Issues Location Dependent Data (LDD) Example: Hotel Taj has many branches in India. However, the room rent of this hotel will depend upon the place it is located. Any change in the room rate of one branch would not affect any other branch. Schema: It remains the same only multiple correct values exists in the database.

81 Mobile Database Systems (MDS) MDS Data Management Issues Location Dependent Data (LDD) LDD must be processed under the location constraints. Thus, the tax data of Pune can be processed correctly only under Pune’s finance rule. Needs location binding or location mapping function.

82 Mobile Database Systems (MDS) MDS Data Management Issues Location Dependent Data (LDD) Location binding or location mapping can be achieved through database schema or through a location mapping table.

83 Mobile Database Systems (MDS) MDS Data Management Issues Location Dependent Data (LDD) Distribution MDS could be a federated or a multidatabase system. The database distribution (replication, partition, etc.) must take into consideration LDD. One approach is to represent a city in terms of a number of mobile cells, which is referred to as “Data region”. Thus, Pune can be represented in terms of N cells and the LDD of Pune can be replicated at these individual cells.

84 Mobile Database Systems (MDS) MDS Data Management Issues In a data region the entire LDD of that location can be represented in a hierarchical fashion. Concept Hierarchy in LDD

85 Mobile Database Systems (MDS) MDS Query processing Query types  Location dependent query  Location aware query  Location independent query

86 Mobile Database Systems (MDS) MDS Query processing Location dependent query A query whose result depends on the geographical location of the origin of the query. Example What is the distance of Pune railway station from here? The result of this query is correct only for “here”.

87 Mobile Database Systems (MDS) MDS Query processing Location dependent query Situation: Person traveling in the car desires to know his progress and continuously asks the same question. However, every time the answer is different but correct. Requirements: Continuous monitoring of the longitude and latitude of the origin of the query. GPS can do this.

88 Mobile Database Systems (MDS) MDS Transaction Management Transaction properties: ACID (Atomicity, Consistency, Isolation, and Durability). Too rigid for MDS. Flexibility can be introduced using workflow concept. Thus, a part of the transaction can be executed and committed independent to its other parts.

89 Mobile Database Systems (MDS) MDS Transaction Management Transaction fragments for distribution.

90 Mobile Database Systems (MDS) MDS Transaction Management Transaction fragments for distributed execution Execution scenario: User issues transactions from his/her MU and the final results comes back to the same MU. The user transaction may not be completely executed at the MU so it is fragmented and distributed among database servers for execution. This creates a Distributed mobile execution.

91 Mobile Database Systems (MDS) MDS Transaction Management A mobile transaction (MT) can be defined as T i is a triple ; where F = {e 1, e 2, …, e n } is a set of execution fragments, L = {l 1, l 2, …, l n } is a set of locations, and FLM = {flm 1, flm 2, …, flm n } is a set of fragment location mapping where  j, flm i (e i ) = l i

92 Mobile Database Systems (MDS) MDS Transaction Management An execution fragment e ij is a partial order e ij = {  j,  j } where   i = OS j  {N i } where OS j =  k O jk, O jk  {read, write}, and N j {Abort L, Commit L }.  For any O jk and O jl where O jk = R(x) and O jl = W(x) for data object x, then either O jk  j O jl or O jl  j O jk.

93 Mobile Database Systems (MDS) MDS Transaction Management Mobile Transaction Models Kangaroo Transaction: It is requested at a MU but processed at DBMS on the fixed network. The management of the transaction moves with MU. Each transaction is divided into subtransactions. Two types of processing modes are allowed, one ensuring overall atomicity by requiring compensating transactions at the subtransaction level.

94 Mobile Database Systems (MDS) MDS Transaction Management Mobile Transaction Models Reporting and Co-Transactions: The parent transaction (workflow) is represented in terms of reporting and co-transactions which can execute anywhere. A reporting transaction can share its partial results with the parent transaction anytime and can commit independently. A co-transaction is a special class of reporting transaction, which can be forced to wait by other transaction.

95 Mobile Database Systems (MDS) MDS Transaction Management Mobile Transaction Models Clustering: A mobile transaction is decomposed into a set of weak and strict transactions. The decomposition is done based on the consistency requirement. The read and write operations are also classified as weak and strict.

96 Mobile Database Systems (MDS) MDS Transaction Management Mobile Transaction Models Semantics Based: The model assumes a mobile transaction to be a long lived task and splits large and complex objects into smaller manageable fragments. These fragments are put together again by the merge operation at the server. If the fragments can be recombined in any order then the objects are termed reorderable objects.

97 Mobile Database Systems (MDS) MDS Transaction Management Mobile Transaction execution.

98 Mobile Database Systems (MDS) MDS Transaction Management Serialization of concurrent execution.  Two-phase locking based (commonly used)  Timestamping  Optimistic Reasons these methods may not work satisfactorily  Wired and wireless message overhead.  Hard to efficiently support disconnected operations.  Hard to manage locking and unlocking operations.

99 Mobile Database Systems (MDS) MDS Transaction Management New schemes based on timeout, multiversion, etc., may work. A scheme, which uses minimum number of messages, especially wireless messages is required. Serialization of concurrent execution.

100 Mobile Database Systems (MDS) MDS Transaction Management Database update to maintain global consistency. Database update problem arises when mobile units are also allowed to modify the database. To maintain global consistency an efficient database update scheme is necessary.

101 Mobile Database Systems (MDS) MDS Transaction Management In MDS a transaction may be fragmented and may run at more than one nodes (MU and DBSs). An efficient commit protocol is necessary. 2-phase commit (2PC) or 3-phase commit (3PC) is no good because of their generous messaging requirement. A scheme which uses very few messages, especially wireless, is desirable. Transaction commit.

102 Mobile Database Systems (MDS) MDS Transaction Management Transaction commit. One possible scheme is “timeout” based protocol. Concept: MU and DBSs guarantee to complete the execution of their fragments of a mobile transaction within their predefined timeouts. Thus, during processing no communication is required. At the end of timeout, each node commit their fragment independently.

103 Mobile Database Systems (MDS) MDS Transaction Management Transaction commit. Protocol: TCOT-Transaction Commit On Timeout Requirements Coordinator: Coordinates transaction commit Home MU: Mobile Transaction (MT) originates here Commit set: Nodes that process MT (MU + DBSs) Timeout: Time period for executing a fragment

104 Mobile Database Systems (MDS) MDS Transaction Management  MT arrives at Home MU.  MU extract its fragment, estimates timeout, and send rest of MT to the coordinator.  Coordinator further fragments the MT and distributes them to members of commit set.  MU processes and commits its fragment and sends the updates to the coordinator for DBS.  DBSs process their fragments and inform the coordinator.  Coordinators commits or aborts MT. Protocol: TCOT-Transaction Commit On Timeout

105 Mobile Database Systems (MDS) MDS Transaction Management Transaction and database recovery. Complex for the following reasons  Some of the processing nodes are mobile  Less resilient to physical use/abuse  Limited wireless channels  Limited power supply  Disconnected processing capability

106 Mobile Database Systems (MDS) MDS Transaction Management Desirable recovery features  Independent recovery capability  Efficient logging and checkpointing facility  Log duplication facility Transaction and database recovery.

107 Mobile Database Systems (MDS) MDS Transaction Management  Independent recovery capability reduces communication overhead. Thus, MUs can recover without any help from DBS  Efficient logging and checkpointing facility conserve battery power  Log duplication facility improves reliability of recovery scheme Transaction and database recovery.

108 Mobile Database Systems (MDS) MDS Transaction Management Possible approaches  Partial recovery capability  Use of mobile agent technology Transaction and database recovery.

109 Mobile Database Systems (MDS) MDS Transaction Management Possible MU logging approaches  Logging at the processing node (e.g., MU)  Logging at a centralized location (e.g., at a designated DBS)  Logging at the place of registration (e.g., BS)  Saving log on Zip drive or floppies. Transaction and database recovery.

110 Mobile Database Systems (MDS) Mobile Agent Technology A mobile agent is an independent software module capable of  Migrating to any node on the network  Capable of spawning and eliminating itself  Capable of recording its own history

111 Mobile Database Systems (MDS) Mobile Agent Technology  Centralized and distributed logging  Log carrier. A Mobile unit may need to carry its log with it for independent recovery  Log processing for database recovery  Transaction commit or abort A mobile agent can be used for the following activities, which are essential for recovery.

112 Mobile Database Systems (MDS) Mobile Agent Technology  Agent broadcast on a dedicated wireless channel  Pool of agents at every processing node  Agent migration to a required node. Possible approaches

113 Mobile Database Systems (MDS) Mobile E-commerce Mapping of business activity on the network. The network may be mobile of ad-hoc in which case the scope of business activities significantly increases. What is E-commerce?

114 Mobile Database Systems (MDS) Mobile E-commerce To make business activity free from spatial constraints. This allows tremendous flexibility to customers as well as to vendors. Important gain: Making information available at the right time, at the right location, and in a right format. Why mobile E-commerce?

115 Mobile Database Systems (MDS) Mobile E-commerce  Security  Reliability  Efficient  Customer trust  Quality of service Requirements for a mobile E-system

116 Mobile Database Systems (MDS) Mobile E-commerce Security Conventional key approaches needs revision. Reliability Hard to provide mainly because of the unreliability and limitations of resources. These requirements are difficulty and complex to achieve

117 Mobile Database Systems (MDS) Mobile E-commerce Efficient This capability can be easily improved mainly because of the elimination of spatial constraints. Customer trust A time consuming activity. Customer do not easily trust electronic communication and always wants to see a reliable backup service. These requirements are difficulty and complex to achieve

118 Mobile Database Systems (MDS) Mobile E-commerce These requirements are difficulty and complex to achieve Quality of service Mobility and web provides ample scope for improving the quality of service. An integration of mobility, web, data warehousing and workflow offers tremendous growth potential and a very controlled way of managing business activities.

119 Mobile Database Systems (MDS) Conclusions and summary Wireless network is becoming a commonly used communication platform. It provides a cheaper way to get connected and in some cases this is the only way to reach people. However, it has a number of easy and difficult problems and they must be solved before MDS can be built. This tutorial discussed some of these problems and identified a number of possible approaches.

120 Mobile Database Systems (MDS) Conclusions and summary The emerging trend is to make all service providing disciplines, such as web, E-commerce, workflow systems, etc., fully mobile so that any service can be provided from any place. Customer can surf the information space from any location at any time and do their shopping, make flight reservation, open bank account, attend lectures, and so on. This is what the wireless technology driving us to.

121 Mobile Database Systems (MDS) References 1. Acharya, S., Alonso, R., Franklin, M., and Zdonik, S. Broadcast Disks: Data management for Asymmetric Communication Environments. Proc. ACM SIGMOD Conf., San Jose, May, 1995. 2. Alonso, R., and Korth, H. Database Systems Issues in Nomadic Computing. Proc. ACM SIGMOD International Conf. on management of Data, May 1993.

122 Mobile Database Systems (MDS) References 3. Barbara, D., and Imielinski, T. Sleepers and Workaholics: Caching Strategies in Mobile Environments. Proc. ACM SIGMOD Conf., Minneapolis, May, 1994. 4. Chrysanthis, P. K., Transaction Processing in Mobile Computing Environment, in IEEE Workshop on Advances in Parallel and Distributed Systems, October 1993.

123 Mobile Database Systems (MDS) References 5. Dhawan, C. Mobile Computing. McGraw-Hill, 1997. 6. Dunham, M. H., Helal, A., and Balakrishnan, S., A Mobile Transaction Model That Captures Both the Data and Movement Behavior, ACM/Baltzer Journal on Special Topics in Mobile Networks and Applications, 1997. 7. Forman, H. George and Zahorjan, J. The Challenges of Mobile Computing, IEEE Computers, Vol. 27, No. 4, April 1994.

124 Mobile Database Systems (MDS) References 8. Pitoura, E. and Bhargava, B., Maintaining Consistency of Data in Mobile Distributed Environments. Proceedings of 15th International Conference on Distributed Computing Systems., 1995. 9. Pitoura, E. and Bhargava, B., Building Information Systems for Mobile Environments, Proc. 3rd. Int. conf. on Information and Knowledge Management, Washington, DC, No. 1994.

125 Mobile Database Systems (MDS) References 10. Vijay Kumar, “Timeout-based Mobile Transaction Commit Protocol”, 2000 ADBIS- DASFAA Symposium on Advances in Databases and Information Systems, Prague, Sep. 5-8, 2000. 11. Shaul Dar, Michael Franklin, Bjorn T. Johnsson, Divesh Srivastava, and Michael Tan, “Semantic Data Caching and Replacement”, Proc. Of the 22 nd VLDB Conference, Mumbai, India, 1996.

126 Mobile Database Systems (MDS) References 12. E. Pitoura and G. Samaras, “Data Management for Mobile Computing”, Kluwer Academic Publishers, 1998. 13. E. Turban, at. el., “Electronic Commerce: A Managerial Perspective”, Prentice Hall, 2000. 14. L. Loeb, “Secure Electronic Transactions”, Artech House, 1998.


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