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Yuriy Sheynin, Elena Suvorova,

Providing guaranteed packet delivery time in SpaceWire networks Session: SpaceWire networks and protocols. Yuriy Sheynin, Elena Suvorova, St. Petersburg State University of Aerospace Instrumentation 67, Bolshaya Morskaya st.   190 000, St. Petersburg   RUSSIA

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Yuriy Sheynin, Elena Suvorova,

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  1. Providing guaranteed packet delivery time in SpaceWire networksSession: SpaceWire networks and protocols Yuriy Sheynin, Elena Suvorova, St. Petersburg State University of Aerospace Instrumentation67, Bolshaya Morskaya st.   190 000, St. Petersburg   RUSSIA E-mail: sheynin@online.ru, suvorova@aanet.ru

  2. In this presentation we evaluate • The minimal distance between two transmission phases • The interval between start of last packet transmission and end of transmission phase for TDMA communications based on • time triggered mechanism • global slot mechanism We compare these parameters for different topologies and evaluate real transmission rate and real throughput of links

  3. The minimum distance between two sequential transmission phases (1) time-triggered communication: sources of difference between terminal nodes clocks Not in all cases we can place Time_codes source to centre of interconnection graph (1) Not in all cases we can set same speed for all links in system (or symmetric speed for all paths from time_codes source to other nodes) (2) For output links of one switch previous symbols could be differ and state of sending these symbols could be differ (3) The minimal distance between transmission phases is equal to the maximal difference between terminal nodes clocks

  4. The minimum distance between two sequential transmission phases (2) shortest path, rapid links Ts – the Time-code processing time in transit switch (1) Tb – time of one bit transmission for most slowly link, Tbi – for i link, (2,3) Tt - waiting to send previous code time(3) a – the max number of bits in previous symbol (14 or 10)(3) Ttdmax - the maximal delivery time for Time-code Ttdmin - the minimal delivery time for Time-code Ttmax maximum distance of local clocks in the system and the minimal distance between two sequential transmission phases Longest path, slowly links

  5. Interval between start of last packet transmission and end of transmission phase Tp Tp –whole packet transmission time Th - maximal header of packet transmission time Td - the maximal interval between arriving of header and of packet end to destination node Tb - the time of one bit transmission in transit link(Tbi – for input, Tbo – for output link) Zp - length of last packet , number of bytes Tsh – header processing time Ta – arbitration time + max output port waiting time in case when in one transmission phase some paths between source and destination nodes share links

  6. Example 1 Physical throughput of T0-S0 link Is equal to summary throughputs of T1-S1, … T40-S4 links 400Mbit/s 10Mbit/s Real transmission rate is 0.028Mbit/s Real transmission rate and throughput in 40 times less than potential

  7. Example 2 126 data symbols Ttmax=3175 ns 400Mbit/s 10Mbit/s in case of the transmission time for pairs includes to one slot is essentially differ this distribution is not rational in this case the big number of slots results to bid time will be lost because of inter slots intervals.

  8. Conclusion • For many different systems using of global slots leads to not rationale using of system resources: • In some cases the size of interval between two transmission phases is equal to time for transmission of packet in some network regions. • In some cases real network throughput is in ten times less than physically reachable

  9. Thank you!

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