Technical Considerations for Transport Layer Protocols Optimization for Satellite Networks (T4SAT)
draft-xiong-tsvwg-technical-considerations-t4sat-00

tsvwg                                                           Q. Xiong
Internet-Draft                                           ZTE Corporation
Intended status: Informational                                    J. Liu
Expires: 12 December 2025                                      GEE Space
                                                            10 June 2025

Technical Considerations for Transport Layer Protocols Optimization for
                       Satellite Networks (T4SAT)
          draft-xiong-tsvwg-technical-considerations-t4sat-00

Abstract

   This document analyses the gaps of the existing transport layer
   technologies and provides technical considerations for Transport
   Layer Protocols Optimization for Satellite Networks (T4SAT).

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   This Internet-Draft will expire on 12 December 2025.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Definition of Terms . . . . . . . . . . . . . . . . . . . . .   2
   3.  Technical Considerations for T4SAT  . . . . . . . . . . . . .   2
     3.1.  Optimization of Congestion Control Algorithms . . . . . .   3
     3.2.  Enhancement of Congestion Notification  . . . . . . . . .   3
     3.3.  Adaptations of Transport Protocols  . . . . . . . . . . .   3
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   6.  Informative References  . . . . . . . . . . . . . . . . . . .   4
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   4

1.  Introduction

   It demands high-bandwidth and high-throughput data transmission in
   LEO (Low Earth Orbit) satellite networks as described in
   [I-D.yang-tsvwg-leo-transport-req].  The performance of transport
   protocols will be impacted by the unique characteristics such as
   networks-highly dynamic topologies, long and variable propagation
   delays and time-varying channel errors.  The optimization of
   transport layer technologies in LEO satellite networks should
   consider:

   *the congestion control algorithms should be optimized to adapt the
   increasing bursty packet loss and significant delay variability.

   *the congestion control should decouple channel errors from
   congestion signals while adapting to rapid topology changes.

   *the ACK mechanism should adapt the transport layer to reduce
   spurious retransmissions.

   This document analyses the gaps of the existing transport layer
   technologies and provides technical considerations for Transport
   Layer Protocols Optimization for Satellite Networks (T4SAT).

2.  Definition of Terms

   This document uses the terms defined in
   [I-D.yang-tsvwg-leo-transport-req]:

3.  Technical Considerations for T4SAT

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3.1.  Optimization of Congestion Control Algorithms

   As per [I-D.yang-tsvwg-leo-transport-req], frequent handovers and
   connection switching will increase packet loss ratio (e.g. over 60%).
   The congestion control algorithms should be selected and optimized to
   tolerate the high packet loss ratio and predict bandwidth to control
   the congestion before the queues overflow.

   Bottleneck Bandwidth and Round-trip propagation time (BBR) is a
   congestion-based congestion control algorithm for TCP, which actively
   measures bottleneck bandwidth (BtlBw) and round-trip propagation time
   (RTprop) based on the model to calculate the bandwidth delay product
   (BDP) and then to adjust the transmission rate to maximize throughput
   and minimize latency.  In LEO satellite networks, the dynamic
   topology could add significant delay variability beyond the inherent
   propagation latency and it also consumes valuable satellite capacity.
   The congestion control algorithms should be optimized to adapt
   seamlessly to latency variations and RTT fluctuation based on precise
   RTT measurements.

3.2.  Enhancement of Congestion Notification

   As per [I-D.yang-tsvwg-leo-transport-req], random packet loss will
   lead to the failure of congestion control mechanisms.  For example,
   when receiving a congestion notification with packet loss, the loss-
   based congestion control algorithms, such as Congestion-based Upon
   Bandwidth-Information (CUBIC), will reduce the congestion window and
   the throughput will dramatically decrease.

   In LEO satellite networks, the packet loss will be divided into
   channel-error loss and congestion-based loss.  The time-varying
   channel-error loss will occur when packets are corrupted or dropped
   due to physical layer impairments in the communication channel.  It
   needs to retransmit the lost packets without reducing congestion
   window.  The congestion notification should distinguish channel-error
   loss and congestion-based loss.  Explicit Congestion Notification
   (ECN) can be used to achieve an end-to-end congestion notification
   and the type of packet loss could be encoding in the ECN markings.

3.3.  Adaptations of Transport Protocols

   As per [I-D.yang-tsvwg-leo-transport-req], long and variable
   propagation delay is one of unique characteristics in LEO satellite
   networks.  The propagation delays (e.g.20-150ms RTT) are higher
   exceeding the terrestrial networks.  The Retransmission Timeout (RTO)
   mechanism will frequently misinterpret propagation delay as
   congestion.  The acknowledgments (ACKs) are not arriving on time,
   leading to unnecessary congestion window reduction and packet

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   retransmissions.  Moreover, asymmetric uplink and downlink capacities
   cause ACK congestion and buffer overflows.  The ACK mechanism in LEO
   satellite networks should adapt the transport layer to give ACKs
   higher priority during handovers and guarantee ACK delivery even
   during orbital transitions, reducing spurious retransmissions caused
   by orbital motion.

4.  Security Considerations

   To be discussed in future versions of this document.

5.  IANA Considerations

   Currently this document does not make an IANA requests.

6.  Informative References

   [I-D.yang-tsvwg-leo-transport-req]
              Yang, F. and T. Tsou, "Transport Layer Protocol
              Requirement for LEO satellite", Work in Progress,
              Internet-Draft, draft-yang-tsvwg-leo-transport-req-00, 16
              March 2025, <https://datatracker.ietf.org/doc/html/draft-
              yang-tsvwg-leo-transport-req-00>.

Authors' Addresses

   Quan Xiong
   ZTE Corporation
   Email: xiong.quan@zte.com.cn

   Jie Liu
   GEE Space
   Email: jie.liu33@geely.com

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