    Independent Submission                                         R. Hinden
    Request for Comments: 6921                          Check Point Software
    Category: Informational                                     1 April 2013
    ISSN: 2070-1721

        Design Considerations for Faster-Than-Light (FTL) Communication

    Abstract

       We are approaching the time when we will be able to communicate
       faster than the speed of light.  It is well known that as we approach
       the speed of light, time slows down.  Logically, it is reasonable to
       assume that as we go faster than the speed of light, time will
       reverse.  The major consequence of this for Internet protocols is
       that packets will arrive before they are sent.  This will have a
       major impact on the way we design Internet protocols.  This paper
       outlines some of the issues and suggests some directions for
       additional analysis of these issues.

    Status of This Memo

       This document is not an Internet Standards Track specification; it is
       published for informational purposes.

       This is a contribution to the RFC Series, independently of any other
       RFC stream.  The RFC Editor has chosen to publish this document at
       its discretion and makes no statement about its value for
       implementation or deployment.  Documents approved for publication by
       the RFC Editor are not a candidate for any level of Internet
       Standard; see Section 2 of RFC 5741.

       Information about the current status of this document, any errata,
       and how to provide feedback on it may be obtained at
       http://www.rfc-editor.org/info/rfc6921.

    Copyright Notice

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       document authors.  All rights reserved.

       This document is subject to BCP 78 and the IETF Trust's Legal
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    RFC 6921       Design Considerations for FTL Communication  1 April 2013

    Table of Contents

       1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 2
       2.  Protocol Design Considerations for FTL Communication  . . . . . 3
         2.1.  Related Issues  . . . . . . . . . . . . . . . . . . . . . . 4
       3.  FTL Communication Research  . . . . . . . . . . . . . . . . . . 5
       4.  IETF Recommendations  . . . . . . . . . . . . . . . . . . . . . 5
       5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
       6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 6
       7.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 6
         7.1.  Normative References  . . . . . . . . . . . . . . . . . . . 6
         7.2.  Informative References  . . . . . . . . . . . . . . . . . . 6

    1.  Introduction

       We are approaching the time when we will be able to communicate
       faster than the speed of light.  It is well known that as we approach
       the speed of light, time slows down.  Logically, it is reasonable to
       assume that as we go faster than the speed of light, time will
       reverse.  The major consequence of this for Internet protocols is
       that packets will arrive before they are sent.  This will have a
       major impact on the way we design Internet protocols.  This paper
       outlines some of the issues and suggests some directions for
       additional analysis of these issues.

       There is a lot of discussion in the physics community about faster-
       than-light travel and communication.  In fact, it even has a well
       known acronym "FTL".  This acronym will be used in the remainder of
       this document.

       FTL issues have been discussed in the scientific literature for a
       long time.  For example, it was discussed in 1917 in the section
       "Velocities Greater than that of Light" on page 54 of "The Theory of
       the Relativity of Motion" [Tolman].  A good overall description of
       the effects of FTL communication can be found in [Goldberg].

       [Ardavan] describes a "polarization synchrontron", which pushes radio
       waves faster than the speed of light.  In the paper, the author
       explains:

          ...though no superluminal source of electromagnetic fields can be
          point-like, there are no physical principles preventing extended
          faster-than-light sources.  The coordinated motion of aggregates
          of subluminally-moving charged particles can give rise to
          macroscopic polarization currents whose distribution patterns move
          superluminally.  Further relevant progress occurred with the
          theoretical prediction that extended sources that move faster than
          their own waves could be responsible for the extreme properties of

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    RFC 6921       Design Considerations for FTL Communication  1 April 2013

          both the electromagnetic emission from pulsars (rapidly spinning,
          magnetized neutron stars) and the acoustic emission by supersonic
          rotors and propellers.

       This may be a viable approach for transmitting data FTL.

    2.  Protocol Design Considerations for FTL Communication

       Most, if not all, Internet protocols were designed with the basic
       assumption that the sender would transmit the packet before the
       receiver received it.  For example, in the Transmission Control
       Protocol (TCP) [RFC0793], protocol activity is shown in timing
       diagrams such as Figure 7:

           TCP A                                                TCP B

       1.  CLOSED                                               LISTEN

       2.  SYN-SENT    --> <SEQ=100><CTL=SYN>               --> SYN-RECEIVED

       3.  ESTABLISHED <-- <SEQ=300><ACK=101><CTL=SYN,ACK>  <-- SYN-RECEIVED

       4.  ESTABLISHED --> <SEQ=101><ACK=301><CTL=ACK>       --> ESTABLISHED

       5.  ESTABLISHED --> <SEQ=101><ACK=301><CTL=ACK><DATA> --> ESTABLISHED

               Basic 3-Way Handshake for Connection Synchronization

                                Figure 7 of RFC 793

       In an FTL communication environment, this assumption is no longer
       true, because TCP B will receive the first SYN before TCP A
       transmitted it.  For example, the first part of a TCP 3-way handshake
       in an FTL environment will look like:

           TCP A                                                TCP B

       1.  CLOSED                                               LISTEN

       2.                  <SEQ=100><CTL=SYN>               --> SYN-RECEIVED

       3.  SYN-SENT    --> <SEQ=100><CTL=SYN>

       The exact operation will depend on the difference between the
       backward time (i.e., from the future to the past) and the processing
       time to process a packet.  If the processing time is greater than the
       backward time shift, then even though the packets are received out of
       order, TCP should still work due to the TCP symmetrical 3-way

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       handshake mechanism.  If the processing time is smaller than the
       backward time shift, then it gets much harder, as many packets will
       be received before they are sent.  The faster the communication is
       above the speed of light, the more severe the problem becomes.

       Assuming the first case where the processing time is equivalent or
       larger than the backward time shift (i.e., after an exchange of
       packets the backward time offset is canceled out), the TCP 3-way
       handshake in an FTL environment would look like:

           TCP A                                                TCP B

       1.  CLOSED                                               LISTEN

       2.                  <SEQ=100><CTL=SYN>               --> SYN-RECEIVED

       3.  SYN-SENT    --> <SEQ=100><CTL=SYN>

       4.  ESTABLISHED <-- <SEQ=300><ACK=101><CTL=SYN,ACK>      SYN-RECEIVED

       5.  ESTABLISHED     <SEQ=300><ACK=101><CTL=SYN,ACK>  <-- SYN-RECEIVED

       6.  ESTABLISHED     <SEQ=101><ACK=301><CTL=ACK>      --> ESTABLISHED

       7.  ESTABLISHED --> <SEQ=101><ACK=301><CTL=ACK>          ESTABLISHED

       It shows remarkable forethought by the inventors of the TCP protocol
       that the 3-way handshake works in an FTL communication environment.
       This is due to the symmetrical nature of the 3-way handshake and its
       ability to deal with dropped packets.  It should be possible to use
       dropped packets as a way to mimic an FTL communication environment.
       In fact, this may provide a good vehicle to analyze and test
       protocols to see how they will work in an FTL communication
       environment.

    2.1.  Related Issues

       Additional work is needed to think about protocol design
       considerations when the backward time shift is much greater than the
       processing time.  This would create challenges where it would be
       necessary to have received all of the data before the connection
       could be established.  This is left to future researchers.  In
       practical terms, this scenario isn't likely to happen for a long
       time.  That said, FTL communication might lead to FTL travel, where
       we can travel into the past.  It may be necessary to start working on
       this yesterday.

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    RFC 6921       Design Considerations for FTL Communication  1 April 2013

       There is a large amount of work that has been done in a related area,
       Delay-Tolerant Networks.  For example, [RFC4838] defines an
       architecture for Delay-Tolerant Networks.  An FTL communication
       environment is similar to Delay-Tolerant Networks with the major
       difference that the packets arrive at the destination with a negative
       delay.  Documents that will need review include "A One-way Delay
       Metric for IPPM" [RFC2679] and "A Delay Bound alternative revision of
       RFC 2598" [RFC3248].

       Congestion control algorithms will also need serious review --
       specifically, how to handle negative round-trip time (RTT) on TCP
       congestion control or the corner case where the RTT comes out at
       exactly zero.  Do any of the control equations include a divide-by-
       RTT or sqrt(RTT)?  It should also be noted that there may be the
       possibility for significant advancements in congestion algorithms
       given the properties of FTL communication.  Specifically, it maybe
       possible to stop network congestion before it starts.  This could be
       an important new approach for congestion control researchers.

    3.  FTL Communication Research

       FTL communication has great potential for the networking research
       community.  It is clearly an exciting area for new research and
       considerable time could be spent working on it.  It is very important
       that we fully understand all of its aspects before we know how to
       achieve FTL communication.  Funding agencies should take this into
       account when allocating money and make sure that all new research
       projects look at FTL communication environments.

    4.  IETF Recommendations

       The Internet Engineering Steering Group (IESG), which is the part of
       Internet Engineering Task Force (IETF) that manages the standards
       process, has area reviews as part of its review process.  For
       example, the Security area reviews proposed protocols for security
       issues.  The IETF Chair also has a General area that does overall
       reviews.

       The author recommends that the IETF create a new review group to
       evaluate all new Internet protocols to verify that FTL communication
       has been taken into consideration in the design of the protocol.
       This would be similar to what is done to make sure that new Internet
       protocols are secure or are designed to run over IPv4 and IPv6.  As
       we look forward to FTL communication, it is critical that all
       Internet protocols are designed to work in this environment.

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    RFC 6921       Design Considerations for FTL Communication  1 April 2013

       Further, the author recommends that the IESG start a review process
       to do a detailed analysis of all existing Internet protocols to make
       sure they have been designed to work in FTL communication
       environments.  For protocols that do not work in this environment,
       the IESG should add work items to exiting working group charters or
       charter new working groups to update these protocols so that they
       will work in FTL communication environments.

    5.  Security Considerations

       It is early to fully understand security issues relating to FTL
       communication.  The main issue is likely to be related to the
       characteristic of FTL communication that the receiver will receive a
       packet before it is sent.  Many exploits are likely to be written to
       take advantage of this property.  Also, given the number of exploits
       that are being discovered that don't have any protections available,
       it may be that the malware community is already taking advantage of
       the properties of FTL communication.

    6.  Acknowledgements

       Valuable comments and support were provided by Brian Carpenter and
       Rodney Van Meter.

    7.  References

    7.1.  Normative References

       [RFC0793]   Postel, J., "Transmission Control Protocol", STD 7, RFC
                   793, September 1981.

    7.2.  Informative References

       [Ardavan]   Ardavan, A., Singleton, J., Ardavan, H., Fopma, J.,
                   Hallida, D., and W. Hayes, "Experimental demonstration of
                   a new radiation mechanism: emission by an oscillating,
                   accelerated, superluminal polarization current", eprint
                   arXiv:physics/0405062, May 2004.

       [Goldberg]  Goldberg, D., "Do faster than light neutrinos let you
                   change the past?", October 2011, <http://io9.com/5846519/
                   do-faster-than-light-neutrinos-let-you-change-the-past>.

       [RFC2679]   Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way
                   Delay Metric for IPPM", RFC 2679, September 1999.

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    RFC 6921       Design Considerations for FTL Communication  1 April 2013

       [RFC3248]   Armitage, G., Carpenter, B., Casati, A., Crowcroft, J.,
                   Halpern, J., Kumar, B., and J. Schnizlein, "A Delay Bound
                   alternative revision of RFC 2598", RFC 3248, March 2002.

       [RFC4838]   Cerf, V., Burleigh, S., Hooke, A., Torgerson, L., Durst,
                   R., Scott, K., Fall, K., and H. Weiss, "Delay-Tolerant
                   Networking Architecture", RFC 4838, April 2007.

       [Tolman]    Tolman, R., "The Theory of the Relativity of Motion",
                   Berkeley: University of California Press, 1917.

    Author's Address

       Robert M. Hinden
       Check Point Software
       959 Skyway Road
       Suite 300
       San Carlos, CA  94070
       USA

       EMail: bob.hinden@gmail.com

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