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CIS 725

CIS 725. High Speed Networks. High-speed networks. High bandwidth, high latency Low error rates Message loss mainly due to congestion. Example: A and B connected via a 1 Gps link RTD = 60ms. Go Back N Selective repeat. Parallelism. Thread models - thread per layer

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CIS 725

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  1. CIS 725 High Speed Networks

  2. High-speed networks • High bandwidth, high latency • Low error rates • Message loss mainly due to congestion

  3. Example: A and B connected via a 1 Gps link RTD = 60ms

  4. Go Back N • Selective repeat

  5. Parallelism • Thread models - thread per layer - thread per module - thread per message - thread per connection

  6. Thread per layer m1 m2 m3 T1 T2 T3 T4 • One thread for each layer • Pipelining

  7. Thread per function Send function Receive function • One thread for each function • More than one function may be possible in a layer

  8. Thread per message reordering • Interface • * recv_msg() Thread pool m1 m2 - Synchronization overhead

  9. Thread per connection • A separate thread is created • for each connection • All messages for a connection • are processed by the same thread

  10. Blast Protocol • Transmission occurs in blasts • Optimistic Assumption: - Next packet to arrive is the expected one - A blast is not interrupted by other packets - Location of a data packet is known

  11. data APP APP header DLL DLL temp • Normal Path - copy data packets into temp buffer check header copy into final location • Optimistic path - copy data packet into final location check header if incorrect then do recovery

  12. Selective retransmission based protocol window = blast size selective ack sent at end of blast

  13. If unexpected packet is received - wait until end of blast recopy items send nack

  14. Performance results • Blast size = 32k • raw data rate = 9.4Mbs • Using normal processing = 63% • Best case optimistic = 85% • Worst case optimistic = 53%

  15. Image Transfer Protocol • Purpose = transfer of stored images • Many images itself have certain degree of uncertainty • Most images have spatial redundancy • Neighboring pixels are highly correlated

  16. No retransmissions - a message should not contain any two neighboring pixels

  17. Protocol must handle packets out of order and in parallel • The source image is decomposed into messages, each containing info to deduce the position of the pixels • Image is pre-processed and stored as exact messages to be transferred

  18. Congestion control: - increases the transfer rate until the maximum acceptable loss rate is achieved

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