Optimized for bulk file transfer. ... Send. â If size of message >= MTU. ⢠Fragment & send. â The fragmentation and reassembly of ... Sending small messages:.
Seamless Aeronautical Networking through integration of Data links, Radios, and Antennas
Reliable Aeronautical Services Protocol: Laboratory Testing and Verification M. Muhammad, T. de Cola, C. Kissling, M. Berioli German Aerospace Center (DLR) Presented by R. Hermenier SANDR A - Seamless Aeronautical Networking through integration of Data links, Radios, and Antennas
Agenda Properties of Aeronautical Services State-of-the-art Protocols Reliable Areonautical Services Protocol (RASP) • Design • Operation
Simulation Test-bed Tests Results
SANDR A - Seamless Aeronautical Networking through integration of Data links, Radios, and Antennas
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Properties of Aeronautical Services ATM messages vary in: • Size (few bytes some kilobytes); • Bursty inter-arrival times (up to several minutes); • Latency requirements (few seconds).
Forward link
APT TMA
ORP ENR
Return link
SANDR A - Seamless Aeronautical Networking through integration of Data links, Radios, and Antennas
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Reliable User Datagram Protocol (RUDP) Represents an extension of basic UDP functionalities by providing: • window and flow control mechanisms; • connection set-up and tear-down, thus • almost mimicking the TCP behavior.
• Acknowledgment mechanism. • Retransmission of lost packets.
As such, the real benefit in aeronautical networks is minimal • since the ATM services are message oriented, and • the content size is in the order of few kilobytes.
SANDR A - Seamless Aeronautical Networking through integration of Data links, Radios, and Antennas
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Datagram Congestion Control Protocol (DCCP) A further enhancement of UDP; Has different profiles CCID 2 and 3, consisting in the implementation of TCPlike and TFRC congestion control; The more recent CCID-4 offers also improvements to CCID-3 in the case small packets are to be transmitted. • Even though the protocol presents interesting features, it still shows weak points with respect to the efficient transport of aeronautical services: • the congestion control, which is actually not necessary in this domain.
SANDR A - Seamless Aeronautical Networking through integration of Data links, Radios, and Antennas
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Transmission Control Protocol (TCP) Byte streaming Optimized for bulk file transfer. Connection initiation: 3-way handshake • Waiting time for first byte = 2 x RTT.
Congestion control • Congestion window (cwnd) closes after long idle period • Large messages require longer time to be delivered.
• Big messages: 20KB 15 IP packets delivery time: 2 x RTT.
TCP source transferring aeronautical messages will experience some inactive periods due to the burstiness of the traffic.
SANDR A - Seamless Aeronautical Networking through integration of Data links, Radios, and Antennas
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Reliable Areonautical Services Protocol (RASP) End-to-End; UDP-based • Connection-less (no connection initiation & shutdown).
Reliable message delivery • every message is treated as an independent file, • honor message boundaries.
No congestion & flow control mechanisms • Sparseness & small size of the messages; • Dimensioned environment.
Timers to control message transfer: • Sender side (retransmission timer: RTx) RTT, • Receiver side (fragmentation timer: FTx) one-way delay. SANDR A - Seamless Aeronautical Networking through integration of Data links, Radios, and Antennas
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RASP Design – (cont) If size of message < MTU • Send
If size of message >= MTU • Fragment & send
The fragmentation and reassembly of messages • At the RASP layer
Only fully received messages are passed to the higher layers • This is done to prevent messages from being received more than once by the application, in case of retransmissions.
Light weight and easy to implement message based communications protocol.
SANDR A - Seamless Aeronautical Networking through integration of Data links, Radios, and Antennas
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RASP in Action! Sending small messages: sender
receiver
RTx: start RTx: stop … RTx: start
RTx: start expire RTx: stop
SANDR A - Seamless Aeronautical Networking through integration of Data links, Radios, and Antennas
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RASP in Action! Sending large messages: sender RTx: start RTx: update RTx: stop
1 2 3 4 5
receiver FTx: start FTx: FTx: restart stop
… RTx: start RTx: update RTx: restart RTx: stop
1 2 3 4 5
FTx: start
2 4
FTx: expire
FTx: restart
FTx: restart stop
SANDR A - Seamless Aeronautical Networking through integration of Data links, Radios, and Antennas
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Simulation Test-bed The adopted configuration is as follows: • Offered data rate (BW): 512 Kbps on both forward and return links (FL and RL); • Round Trip Time (RTT): 500 ms; • Link errors: Packet erasure rate (PER) set to 10−2 and defined at interface between IP and Ethernet layer; • The buffer size of the mobile router was set to 8388608 Bytes to represent the large buffer case; • The small buffer size at the mobile router was set to 50 KBytes, which is to some extent larger than the Bandwidth-Delay Product of the satellite link under consideration.
SANDR A - Seamless Aeronautical Networking through integration of Data links, Radios, and Antennas
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Simulation Results – transmitted bytes Large buffer size at mobile router
Tx RASP TCP_Cubic TCP_Hybla TCP_Reno
Rx
Link FL
App 735414
TL 748550
TL 735414
App 735414
RL FL
175534 866007
175836 874800
175836 874800
175534 866007
RL FL
174755 862169
175218 871496
175218 871496
174755 862169
RL FL
171519 888776
174392 904704
174392 904704
171519 888776
RL
169488
169787
169787
169488
SANDR A - Seamless Aeronautical Networking through integration of Data links, Radios, and Antennas
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Simulation Results – transmitted bytes Small buffer size at mobile router
Tx RASP TCP_Cubic TCP_Hybla TCP_Reno
Link FL RL FL RL FL RL FL RL
App 845095 174609 847846 168297 779506 180576 890698 172372
Rx TL 853082 180116 852322 168297 789642 181061 907164 175410
TL 845095 177353 852322 168297 789642 181061 907164 175410
App 845095 174609 847846 168297 779506 180576 890698 172372
SANDR A - Seamless Aeronautical Networking through integration of Data links, Radios, and Antennas
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Simulation Results – average delivery delay Small buffer size at mobile router
RASP TCP_Cubic TCP_Hybla TCP_Reno
Link FL RL FL RL FL RL FL RL
RTT Small Buffer 0.53 0.51 0.62 0.51 0.64 0.52 0.66 0.52
Large Buffer 0.55 0.52 0.61 0.51 0.61 0.52 0.69 0.51
SANDR A - Seamless Aeronautical Networking through integration of Data links, Radios, and Antennas
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Conclusion A detailed description regarding: • design, implementation and testing for future and safety-critical aeronautical communications. • it was implemented in the Linux operating system network stack. • The test campaigns confirmed the benefits of RASP over TCP in terms of: • average message delivery delay, and • efficiency of recovery functions.
Main advantages of RASP: • • • •
Simple to implement Achieves similar performances as TCP Reliable protocol Suitable for message-based communication (e.g. aeronautical)
SANDR A - Seamless Aeronautical Networking through integration of Data links, Radios, and Antennas
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Thank you for your attention Questions?
SANDR A - Seamless Aeronautical Networking through integration of Data links, Radios, and Antennas
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