SWE 622- Distributed Systems

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• SWE 622- Distributed Systems
• Project Phase I
• Eric Barnes, David Chang, David Nelson
• Fisayo Oluwadiya, Xiang Shen

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Architecture
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Message Format I

• For business transactions, the messages are line
  based and each field is separated by a colon. The
  format is
• OpexchangeNametraderNameproductquantityprice
  timeStamp
• For example
• Trader Messages
• sellExchange1Trader2product_one043.530
• buyExchange2Trader1product_two3400
• Exchange Messages
• sellExchange1Trader2product_one0123.4512372
  37965973
• buyExchange1Trader2product_one756123.451237
  237970443

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Message Format II

• For clock synchronization , the messages are line
  based and each field is separated by a colon as
  well. The format is
• Time request from trader to exchange
• timeexchangeNametraderNametime
• Time response from exchange to trader
• timetime
• For example
• Trader Messages
• timeE1T21237237964619
• Exchange Messages
• time1237237964534

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Synchronization

• Problem Traders (clients) need to determine the
  age of a message from Exchanges (servers).
• Clocks are not guaranteed to be synchronized.
• There may be non-trivial latency in the network
• A solution is needed to determine clock-skew and
  network latency to compensate.

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Synchronization

• Clients will query Servers for timestamps.
• Client will take a timestamp, and send a message
  to server for server time.
• Server will take a timestamp upon receipt and
  immediately send it back to and the original
  client.
• Client takes another timestamp upon receipt of
  the server response.
• Client will calculate the network latency and
  clock skew.
• Network latency will be one half of the
  difference between the two client timestamps.
• Clock Skew will be the difference between the
  average of the two client timestamps and the
  server timestamp.
• Client will maintain the clock skews for the
  Servers it receives messages from and use those
  values to determine message age.

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Synchronization Mechanism
Server
Client
t1
t2
t3

• After acknowledgement message has been received
  from the server, client will have client
  timestamps for t1 and t3, and a server timestamp
  for t2.
• Client will assume that the network latency is
  approximately symmetrical, and that the server
  processing time is negligible.
• The clock offset will be calculated by
  t2-(t1t3)/2.
• This value will be stored in the client and used
  to determine message age.

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Implementation For Synchronization

• Assuming the server processing time is
  negligible.
• Samples are taken every 5 seconds.
• Each sample is averaged by three requests.
• Only the latest sample is saved.

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Deployment For Evaluation

• More than one Exchange will be created
• More than one trader will be created
• Exchanges and traders will be deployed to team
  members laptops and/or GMU servers such as
  mason.gmu.edu or zeus.ite.gmu.edu

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Test Cases For Exchange

1. Exchange comes online and is ready to accept sell
   requests
2. Exchange receives first sell order
3. Exchange receives first buy order
4. Exchange is already selling a product and
   receives another selling order and successfully
   processes it within set time limit
5. Exchange is currently processing a buy order and
   receives another and successfully processes it
   within set time limit
6. Exchange is shutdown after processing all orders
7. Exchange shuts down normally
8. Exchange crashes

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Test Cases For Trader

1. Trader comes online and is ready to send buy/sell
   orders
2. Trader sends buy order
3. Trader sends sell order
4. Trader receives confirmation for buy/sell order
5. Trader doesnt receive confirmation for buy/sell
   order within expected time limit
6. Trader is unable to connect to Exchange
7. Trader shuts down normally
8. Trader crashes

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Fault Simulation

• Simulate clock skew
• Modify the system clocks for exchanges and
  traders
• Simulate Exchange/Trader failure
• Use kill or task manager to terminate exchanges
  and traders
• Simulate Network failure
• Unplug the network cable
• Shutdown the NIC, Network switch etc.
• Simulate Network latency
• Connect the trader and exchange via a SOCKS proxy
  server
• Use open source server such as Simple SOCKS
  Server for Perl
• Modify the code and randomly sleep a few seconds
  before forwarding the packets

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Methods For Verification

• Manually run the system and use our eye balls
• Check the log files for verification
• Possible automation via scripting, such as using
  Perl Win32GuiTest etc.