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Optimized for bulk file transfer. ... Send. ✓ If size of message >= MTU. • Fragment & send. ✓ 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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