Ch'21 : Mobility Support for Sales and Inventory Applications

1
Ch.21 Mobility Support for Sales and Inventory
Applications

• Naranan Krishnakumar and Ravi jain
• 1995
• CA Lab. CS Dept
• Winam kwon

2
Contents

• Introduction
• Application Scenario
• Mobile Sales Inventory
• System Architecture
• Database System Design
• Mobile Sales Transactions
• Maintaining Service Profiles
• Conclusions

3
Intro.(1) - PISA

• Personal Information Service Application
• Services
• Mbile sales inventory service,
• Financial and stock market information,
• Electronic magazines, News clipping services,
• Traveler information,
• File access, and etc
• ISAP(Information Service and Application
  Provider)
• PCS network
• Session
• Sequence of transactions
• Unit of comm. unaware any disruption in service
  as users move
• Service handoff
• Virtual mobility of a server by users mobility.

4
Intro.(2) - Issues

• Focused service
• Mobile sales and inventory application
• Design Principles
• Minimize the aspects which are needed solely to
  support users mobility
• Application Level Issues
• Design and management of application DB in mobile
  env.
• Infrastructure Level Issues
• Management of service profile data

5
Application Scenario

• Mobile Sales Inventory

6
System Architecture

• Distributed Server Architecture
• Service area
• Local server
• PCS nets support for ISAP
• Physical conn. during a session w/o disruption
• Call handoff protocol physical conn. transfer
• User location protocol registering, locating
  delivering calls
• Service handoff
• The local server at the new service area takes
  over the service.
• Physical conn. Transfer context info. Transfer
• By matchmaker

7
DB System Design(1) Trx. Control

• Transaction Processing
• Control concurrent access to shared data for the
  consistency
• Correctness
• Serializability
• One-copy serializability
• Concurrency control protocol
• to ensure serializability
• Co-ordination protocol
• Transactions are commited or aborted at all sites.

8
DB System Design(2) Trx. Control

• Concurrency control protocol
• Strict two-phase locking protocol
• Multiple read locks and one write lock on a
  signle shared data
• Transaction is serialized in the order of
  releasing locks
• Available copies algorithm
• On shared data with replicas in sites
• Read from its own copy and Write on all replicas
• Co-ordination protocol
• Two-phase commit protocol
• Broadcast a prepare msg to all replicas
• Each replica votes (commit/abort)
• If all replica voted commit, commit.
• Otherwise, abort!

9
DB System Design(3) Trx. Control

• Replicated DB Management with
• Available copies algorithm and
• ! Acquiring locks at all sites whenever to access
• Two-phase commit protocol
• ! Synchronized voting of all sites whenever to
  commit
• ! Blocking protocol
• Wait for the failed coordinator to recover
• ! At least two rounds of messages

10
DB System Design(4) Escrow

• Escrow Techniques
• Assume reliable the 3rd parties
• Consistency of replicas
• Salem lt Totalm for a sale item m
• Transaction escrow
• Site escrow
• Site-transaction escrow
• Transaction escrow
• for access to hot-spots in a single-copy DB
• escrow log
• log successful escrow operations
• escrow operation
• place resources in reserve
• Short-term lock on escrow log
• not wait for the commit/abort of T but
• wait during the log update operation

11
DB System Design(5) Escrow

• Site escrow
• Partition instances across servers
• Upperlimit amount of instances at site A, Au
• Selled or requested amount at site A, A
• If A lt Au then handle it locally
• Else, initiate demarcation protocol to
  reconfigure Au and handle it locally.
• Demarcation protocol
• Satisfy integrity but unavailable resources
• Require reliable transport protocol
• Site-transaction escrow
• Site escrow but also transaction escrow in local
  transaction.

12
Mobile Sales Transactions(1)

• Why Site-Transaction Escrow in Mobile Env.
• Limited power
• Quick response doze mode
• Service handoff
• Lesser context info. quick service handoffs
• Limited wireless bandwidth
• cache instances in mobile itself
• Principle
• Minimize the aspects specific to users mobility
• Proposed Solution
• Design mobile sales transaction with
  site-transaction escrow

13
Mobile Sales Transactions(2)

• Discrete Mobility
• Complete a session in a service area
• Continuous Mobility service handoff
• Context transfer of a session from the old to
  the new server, before physical conn. transfer.
• Handoff
• Context info.
• Transaction id and uncommited transaction list
• No lock info and no performed op
• Reconfiguration of instances
• Decrement Totalm by the amount alloced to the trx
  at the old server
• Increment Totalm by the amount alloced to the trx
  at the new server
• Unavailable resource problem
• Pair-wise two-phase commit protocol btwn the old
  and the new servers

14
Mobile Sales Transactions(3)

• Example

15
Maintaining Service Profiles(1)

• IS-41 Protocol in PCS network
• HLR Home Location Register
• VLR Visitor Location Register
• MSC Mobile Switching Center
• A user info can be in more than one VLR at one
  time, possibly leading to race condition
• Twice same update transaction by two servers

16
Maintaining Service Profiles(2)

• Protocol
• HSD Home Service DB
• VSD Visitor Service DB
• Define unactive user

17
Conclusions

• Distributed replicated server architecture for
  delivery of PISA
• Service handoffs
• DB design based on a site escrow method for
  mobile sales and inventory services
• Two-level hierarchy of DB for maintaining service
  profiles for mobiles and update protocol