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Simplemux. A generic multiplexing protocol
draft-saldana-tsvwg-simplemux-12

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Author Jose Saldana
Last updated 2024-01-02
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draft-saldana-tsvwg-simplemux-12
TSVWG                                                         J. Saldana
Internet-Draft                                   CIRCE Technology Center
Intended status: Standards Track                        28 December 2023
Expires: 30 June 2024

              Simplemux.  A generic multiplexing protocol
                    draft-saldana-tsvwg-simplemux-12

Abstract

   The high amount of small packets present in nowaday's networks
   results in a low efficiency, as the size of both the headers and the
   payload in these packets can be comparably large, often falling
   within the same order of magnitude.  In some situations, multiplexing
   (i.e. aggregating) a number of small packets into a bigger one is
   desirable to improve the efficiency.  For example, a number of small
   packets can be sent together between a pair of machines if they share
   a common network path.  This may happen between machines in different
   locations or even inside a datacenter with a number of servers
   hosting virtual machines.  The traffic profile can be shifted from
   small to larger packets, thus reducing the network overhead and the
   number of packets per second to be managed by intermediate devices.

   This document describes Simplemux, a protocol able to encapsulate a
   number of packets belonging to different protocols into a single
   packet.  Small headers (separators) are added at the beginning of
   each multiplexed packet, including some flags, the packet length and
   a "Protocol" field.  The presence of this "Protocol" field allows it
   to aggregate packets belonging to any protocol (the "multiplexed
   packets"), in a single packet belonging to other (or the same)
   protocol (the "tunneling protocol").

   To reduce the overhead, the size of the multiplexing headers is kept
   very low (it may be a single byte when multiplexing packets of small
   size).

About This Document

   This note is to be removed before publishing as an RFC.

   Status information for this document may be found at
   https://datatracker.ietf.org/doc/draft-saldana-tsvwg-simplemux/.

   Discussion of this document takes place on the Transport Area Working
   Group (tsvwg) Working Group mailing list (mailto:tsvwg@ietf.org),
   which is archived at https://mailarchive.ietf.org/arch/browse/tsvwg/.
   Subscribe at https://www.ietf.org/mailman/listinfo/tsvwg/.

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Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on 30 June 2024.

Copyright Notice

   Copyright (c) 2023 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Conventions . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Benefits of multiplexing  . . . . . . . . . . . . . . . . . .   5
   4.  Existing multiplexing protocols . . . . . . . . . . . . . . .   6
     4.1.  Tmux  . . . . . . . . . . . . . . . . . . . . . . . . . .   6
     4.2.  PPPmux  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     4.3.  Advantages of Simplemux . . . . . . . . . . . . . . . . .   7
   5.  Scenarios of interest . . . . . . . . . . . . . . . . . . . .   7
   6.  Protocol description  . . . . . . . . . . . . . . . . . . . .   7
     6.1.  Fast flavor . . . . . . . . . . . . . . . . . . . . . . .   8
     6.2.  Compressed flavor . . . . . . . . . . . . . . . . . . . .   8
       6.2.1.  First Simplemux header  . . . . . . . . . . . . . . .   8
       6.2.2.  Non-first Simplemux header  . . . . . . . . . . . . .  11
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  16
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  16

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   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  16
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  16
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  17
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  17

1.  Introduction

   The high amount of small packets present in nowaday's networks
   results in a low efficiency, when the size of the headers and the
   payload fall within the same order of magnitude.  In some situations,
   multiplexing (i.e. aggregating) a number of small packets into a
   bigger one is desirable to improve the efficiency.  In these cases, a
   number of small packets can be sent together between a pair of
   machines if they share a common network path.  This may happen
   between machines in different locations or even inside a datacenter
   with a number of servers hosting virtual machines.  The traffic
   profile can be shifted from small to larger packets, thus reducing
   the overhead and the number of packets per second to be managed by
   intermediate devices.

   This document describes Simplemux, a protocol able to encapsulate a
   number of packets belonging to different protocols into a single
   packet.

   Simplemux generic: it includes a "Protocol" field, so it can be used
   to aggregate a number of packets belonging to any protocol, in a
   single packet belonging to other (or the same) protocol.

   In this document we will talk about the "multiplexed" protocol, and
   the "tunneling" protocol, being Simplemux the "multiplexing"
   protocol.  The "external header" will be the one of the "tunneling"
   protocol.  In this document, we will also refer to the Simplemux
   header with the terms "separator," "Simplemux separator" or "mux
   separator".  In the figures we will also use the abbreviation "Smux".
   These elements are presented in Figure 1.

       +--------------------------------+
       |       Multiplexed Packet       |     Multiplexed protocol
       +--------------------------------+
       |   Simplemux header/separator   |     Multiplexing protocol
       +--------------------------------+
       |       Tunneling header         |     Tunneling protocol
       +--------------------------------+

                                  Figure 1

   A Simplemux packet will have the structure shown in Figure 2.

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     +-------------++-------------+------++-------------+------+
     |tunneling hdr||Simplemux hdr|packet||Simplemux hdr|packet|  ...
     +-------------++-------------+------++-------------+------+

                                  Figure 2

   As an example, if a number of small IPv6 packets have to traverse an
   IPv4 network, they can be multiplexed together into a single IPv4
   packet.  In this case, IPv4 will be the "tunneling" protocol and IPv6
   will be the "multiplexed" protocol.  The IPv4 header is called in
   this case the "tunneling" or the "external" header.  The scheme of
   this packet will be(the "Protocol" field inside the Simplemux header
   will be 41 (IPv6), according to IANA Assigned Internet Protocol
   Numbers):

     +------++-------------+-----------++-------------+-----------+
     | IPv4 ||Simplemux hdr|IPv6 packet||Simplemux hdr|IPv6 packet|...
     +------++-------------+-----------++-------------+-----------+

                                  Figure 3

   Another example is the tunneling of Ethernet frames between different
   networks using UDP.  In this case, IPv4/UDP will be the "tunneling"
   protocol and Ethernet will be the "multiplexed" protocol.  The IPv4/
   UDP header is called in this case the "tunneling" or the "external"
   header.  The scheme of this packet will be (the "Protocol" field
   inside the Simplemux header will be 143 (Ethernet), according to IANA
   Assigned Internet Protocol Numbers):

     +------+---++-------------+---------++-------------+---------+
     | IPv4 |UDP||Simplemux hdr|Eth frame||Simplemux hdr|Eth frame|...
     +------+---++-------------+---------++-------------+---------+

                                  Figure 4

   Simplemux has two flavors:

   *  Fast: all the separators are 3-byte long, and all have the same
      structure, so it sacrifices some compression on behalf of speed.

   *  Compressed: it tries to compress the separators as much as
      possible.  For that aim, some single-bit fields are used.

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2.  Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Benefits of multiplexing

   The benefits of multiplexing are:

   - Tunneling a number of packets together.  If a number of packets
   have to be tunneled through a network segment, they can be
   multiplexed and then sent together using a single external header.
   This will avoid the need for adding a tunneling header to each of the
   packets, thus reducing the overhead.

   - Reduction of the amount of packets per second in the network.
   Network equipment has a limitation in terms of the number of packets
   per second it can manage, i.e. many devices are not able to send
   small packets back to back due to processing delay.

   - Bandwidth reduction.  The presence of high rates of tiny packets
   translates into an inefficient usage of network resources, so the
   overhead introduced by low-efficiency flows can be reduced.  When
   combined with header compression, as done in TCRTP [RFC4170]
   multiplexing may produce significant bandwidth savings, which are
   interesting for network operators, since they may alleviate the
   traffic load in their networks.

   - Energy savings: a lower amount of packets per second will reduce
   energy consumption in network equipment since, according to [Bolla],
   internal packet processing engines and switching fabric require 60%
   and 18% of the power consumption of high-end routers respectively.
   Thus, reducing the number of packets to be managed and switched will
   reduce the overall energy consumption.  The measurements deployed in
   [chab] on commercial routers corroborate this: tests showed that
   energy consumption gets reduced, since a non-negligible amount of
   energy is associated to header processing tasks, and not only to the
   sending of the packet itself.

   Some tests measuring the benefits of Simplemux were published in
   [Saldana].

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4.  Existing multiplexing protocols

   Different multiplexing protocols have been approved by the IETF in
   the past:

4.1.  Tmux

   TMux [RFC1692] is able to combine multiple short transport segments,
   independent of application type, and send them between a server and
   host pair.  As stated in the reference, "The TMux protocol is
   intended to optimize the transmission of large numbers of small data
   packets.  In particular, communication load is not measured only in
   bits per seconds but also in packets per seconds, and in many
   situation the latter is the true performance limit, not the former.
   The proposed multiplexing is aimed at alleviating this situation."

   A TMux message appears as:

    +------++--------+-----------------++--------+-----------------+
    |IP hdr||TMux hdr|Transport segment||TMux hdr|Transport segment|...
    +------++--------+-----------------++--------+-----------------+

                                  Figure 5

   Therefore, the Transport Segment is not an entire IP packet, since it
   does not include the IP header.

   TMux works "between a server and host pair," so it multiplexes a
   number of segments between the same pair of machines.  However, there
   are scenarios where a number of low-efficiency flows share a common
   path, but they do not travel between the same pair of end machines.

4.2.  PPPmux

   PPPMux [RFC3153] "sends multiple PPP encapsulated packets in a single
   PPP frame.  As a result, the PPP overhead per packet is reduced."
   Thus, it is able to multiplex complete IP packets, using separators.

   However, the use of PPPMux requires the use of PPP and L2TP to
   multiplex a number of packets together, as done in TCRTP [RFC4170].
   Thus, it introduces more overhead and complexity.

   Using PPPMux, an IP packet including a number of packets appears as:

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    +------++-------+-------++----------+------++----------+------+
    |IP hdr|L2TP hdr|PPP hdr||PPPMux hdr|packet||PPPMux hdr|packet| ...
    +------++-------+-------++----------+------++----------+------+

                                  Figure 6

   The scheme proposed by PPPMux is similar to the Compound-Frames of
   PPP LCP Extensions [RFC1570].  The key differences are that PPPMux is
   more efficient and that it allows concatenation of variable sized
   frames.

4.3.  Advantages of Simplemux

   The definition of a protocol able to multiplex complete packets,
   avoiding the need of using other protocols as e.g.  PPP is seen as
   convenient.  The multiplexed packets MAY belong to any protocol,
   since a "Protocol" field is added to each of them.  Note that
   Ethernet frames can also be aggregated together.

5.  Scenarios of interest

   Simplemux works between a pair of machines.  It creates a tunnel
   between an "ingress" and an "egress".  They MAY be the endpoints of
   the communication, but they MAY also be middleboxes able to multiplex
   packets belonging to different flows.  Different mechanisms MAY be
   used in order to classify flows according to some criteria (sharing a
   common path, kind of service, etc.) and to select the flows to be
   multiplexed and sent to the egress (see Figure 7).

   +-------+
   |       |       +---------+                          +---------+
   |       | --->  |Simplemux|        _  _              |Simplemux| -->
   |classif| --->  | ingress | ===>  ( `   )_     ===>  | egress  | -->
   |       |       +---------+      (  Network  `)      +---------+
   |       |                       (_   (_ .  _) _)
   +-------+
                              <--------Simplemux-------->

                                  Figure 7

6.  Protocol description

   Simplemux has two flavors:

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   *  Fast: all the separators are 3-byte long, and all have the same
      structure, so it sacrifices some compression on behalf of speed.

   *  Compressed: it tries to compress the separators as much as
      possible.  For that aim, some single-bit fields are used.

6.1.  Fast flavor

   In Fast flavor, all the Simplemux headers have the same format, with
   two fields:

   - Length (LEN, 16 bits) of the multiplexed packet (in bytes).

   - Protocol (8 bits) of the multiplexed packet, according to IANA
   "Assigned Internet Protocol Numbers".

              0                   1                   2
              0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
             +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
             |                               |               |
             |           Length              |   Protocol    |
             |          (16 bits)            |   (8 bits)    |
             +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                  Figure 8

6.2.  Compressed flavor

   In Compressed flavor, the Simplemux header has two different forms:
   one for the "First Simplemux header," and another one for the rest of
   the Simplemux headers (called "Non-first Simplemux headers"):

6.2.1.  First Simplemux header

   In is placed after the tunneling header, and before the first
   multiplexed packet.

   In order to allow the multiplexing of packets of any length, the
   number of bytes expressing the length is variable, and a field called
   "Length Extension" (LXT, one bit) is used to flag if the current byte
   is the last one including length information.  This is the structure
   of a First Simplemux header:

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   - Single Protocol Bit (SPB, one bit) only appears in the first
   Simplemux header.  It is set to 1 if all the multiplexed packets
   belong to the same protocol (in this case, the "Protocol" field will
   only appear in the first Simplemux header).  It is 0 when each packet
   MAY belong to a different protocol.

   - Length Extension (LXT, one bit) is 0 if the current byte is the
   last byte where the length of the first packet is included, and 1 in
   other case.

   - Length (LEN, 6, 13, 20, etc. bits): This is the length of the
   multiplexed packet (in bytes).  If the length of the multiplexed
   packet is less than 64 bytes (less than or equal to 63 bytes), the
   first LXT is 0 and the 6 bits of the length field are the length of
   the multiplexed packet.  If the length of the multiplexed packet is
   equal or greater than 64 bytes, additional bytes are added.  The
   first bit of each of the added bytes is the LXT.  If LXT is set to 1,
   it means that there is an additional byte for expressing the length.
   This allows to multiplex packets of any length (see the next
   figures).

   - Protocol (8 bits) of the multiplexed packet, according to IANA
   "Assigned Internet Protocol Numbers."

   A First Simplemux header before a packet smaller than 64 (2^6) bytes
   will be 2 bytes long:

    0                   1
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |S|L|           |               |
   |P|X|  Length   |   Protocol    |
   |B|T| (6 bits)  |   (8 bits)    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ^
      |
      0

                                  Figure 9

   A First Simplemux header before a packet with a length greater or
   equal to 64 bytes, and smaller than 8192 bytes (2^13) will be 3 bytes
   long:

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    0                   1                   2
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |S|L|           |L|             |               |
   |P|X| Length 1  |X|  Length 2   |   Protocol    |
   |B|T| (6 bits)  |T|  (7 bits)   |   (8 bits)    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ^             ^
      |             |
      1             0

                                 Figure 10

   In this case, the length of the packet will be the number expressed
   by the concatenation of the bits of Length 1 and Length 2 (total 13
   bits).  Length 1 includes the 6 most significant bits and Length 2
   the 7 less significant bits.

   A First Simplemux header before a packet with a length greater of
   equal to 8192 bytes, and smaller than 1048576 bytes (2^20), will be 4
   bytes long:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |S|L|           |L|             |L|             |               |
   |P|X| Length 1  |X|  Length 2   |X|  Length 3   |   Protocol    |
   |B|T| (6 bits)  |T|  (7 bits)   |T|  (7 bits)   |   (8 bits)    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ^             ^               ^
      |             |               |
      1             1               0

                                 Figure 11

   In this case, the length of the packet will be the number expressed
   by the concatenation of the bits of Length 1 , Length 2 and Length 3
   (total 20 bits).  Length 1 includes the 6 most significant bits and
   Length 3 the less 7 significant bits.

   More bytes can be added to the length if required, using the same
   scheme: 1 LXT byte plus 7 bits for expressing the length.

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6.2.2.  Non-first Simplemux header

   The Non-first Simplemux headers also employ a format allowing the
   multiplexing of packets of any length, so the number of bytes
   expressing the length is variable, and the field Length Extension
   (LXT, one bit) is used to flag if the current byte is the last one
   including length information.  This is the structure of a Non-first
   Simplemux header:

   - Length Extension (LXT, one bit) is 0 if the current byte is the
   last byte where the length of the packet is included, and 1 in other
   case.

   - Length (LEN, 7, 14, 21, etc. bits): This is the length of the
   multiplexed packet (in bytes), not including the length field.  If
   the length of the multiplexed packet is less than 128 bytes (less
   than or equal to 127 bytes), LXT is 0 and the 7 bits of the length
   field represent the length of the multiplexed packet.  If the length
   of the multiplexed packet is greater than 127 bytes, additional bytes
   are added.  The first bit of each of the added bytes is the LXT.  If
   LXT is set to 1, it means that there is an additional byte for
   expressing the length.  This allows to multiplex packets of any
   length (see the next figures).

   - Protocol (8 bits) field of the multiplexed packet, according to
   IANA "Assigned Internet Protocol Numbers".  It only appears in Non-
   first headers if the Single Protocol Bit (SPB) of the First Simplemux
   header is set to 1.

   As an example, a Non-first Simplemux header before a packet smaller
   than 128 bytes, when the protocol bit has been set to 0 in the First
   header, will be 1 byte long:

       0
       0 1 2 3 4 5 6 7
      +-+-+-+-+-+-+-+-+
      |L|             |
      |X|   Length    |
      |T|  (7 bits)   |
      +-+-+-+-+-+-+-+-+
       ^
       |
       0

   SPB = 1 in the first header

                                 Figure 12

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   A Non-first Simplemux header before a packet witha a length greater
   or equal to 128 bytes, and smaller than 16384 (2^14), when the
   protocol bit has been set to 0 in the First header, will be 2 bytes
   long:

       0                   1
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |L|             |L|             |
      |X|  Length 1   |X|  Length 2   |
      |T|  (7 bits)   |T|  (7 bits)   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       ^               ^
       |               |
       1               0

   SPB = 1 in the first header

                                 Figure 13

   A Non-first Simplemux header before a packet with a length greater or
   equal to 16384 bytes, and smaller than 2097152 bytes (2^21), when the
   protocol bit has been set to 0 in the First header, will be 3 bytes
   long:

       0                   1                   2
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |L|             |L|             |L|             |
      |X|  Length 1   |X|  Length 2   |X|  Length 3   |
      |T|  (7 bits)   |T|  (7 bits)   |T|  (7 bits)   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       ^               ^               ^
       |               |               |
       1               1               0

   SPB = 1 in the first header

                                 Figure 14

   In this case, the length of the packet will be the number expressed
   by the concatenation of the bits of Length 1, Length 2 and Length 3
   (total 21 bits).  Length 1 includes the 7 most significant bits and
   Length 3 the 7 less significant bits.

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   More bytes can be added to the length if required, using the same
   scheme: 1 LXT byte plus 7 bits for expressing the length.

   A Non-first Simplemux header before a packet smaller than 128 bytes,
   when the protocol bit has been set to 1 in the First header, will be
   2 bytes long:

       0                   1
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |L|             |               |
      |X|   Length    |   Protocol    |
      |T|  (7 bits)   |   (8 bits)    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       ^
       |
       0

   SPB = 0 in the first header

                                 Figure 15

   A Non-first Simplemux header before a packet with a length greater or
   equal to 128 bytes, and smaller than 16384 (2^14), when the protocol
   bit has been set to 1 in the First header, will be 3 bytes long:

       0                   1                   2
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |L|             |L|             |               |
      |X|  Length 1   |X|  Length 2   |   Protocol    |
      |T|  (7 bits)   |T|  (7 bits)   |   (8 bits)    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       ^               ^
       |               |
       1               0

   SPB = 0 in the first header

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                                 Figure 16

   A Non-first Simplemux header before a packet with a length greater of
   equal to 16384 bytes, and smaller than 2097152 bytes (2^21), when the
   protocol bit has been set to 1 in the first header, will be 4 bytes
   long:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |L|             |L|             |L|             |               |
      |X|  Length 1   |X|  Length 2   |X|  Length 3   |   Protocol    |
      |T|  (7 bits)   |T|  (7 bits)   |T|  (7 bits)   |   (8 bits)    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       ^               ^               ^
       |               |               |
       1               1               0

   SPB = 0 in the first header

                                 Figure 17

   In this case, the length of the packet will be the number expressed
   by the concatenation of the bits of Length 1, Length 2 and Length 3
   (total 21 bits).  Length 1 includes the 7 most significant bits and
   Length 3 the 7 less significant bits.

   More bytes can be added to the length if required, using the same
   scheme: 1 LXT byte plus 7 bits for expressing the length.

   Next, some examples of the whole bundles are presented

   Case 1: All the packets belong to the same protocol: The first
   Simplemux header will be 2 or 3 bytes (for usual packet sizes), and
   the other Simplemux headers will be 1 or 2 bytes.  For small packets
   (length < 128 bytes), the Simplemux header will only require one
   byte.

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          LXT                 LXT        LXT   LXT
           |                   |          |     |
           V                   V          V     V
   +---++-+-+---+--------+---++-+---+---++-+---+-+---+---++
   |tun||1|0|len|Protocol|pkt||0|len|pkt||1|len|0|len|pkt||...
   +---++-+-+---+--------+---++-+---+---++-+---+-+---+---++
         ^    ^                   ^          ^     ^
         |    |                   |          |     |
       SPB   (6 bits)           (7 bits)    (14 bits)

          LXT   LXT                 LXT        LXT   LXT
           |     |                   |          |     |
           V     V                   V          V     V
   +---++-+-+---+-+---+--------+---++-+---+---++-+---+-+---+---++
   |tun||1|1|len|0|len|Protocol|pkt||0|len|pkt||1|len|0|len|pkt||..
   +---++-+-+---+-+---+--------+---++-+---+---++-+---+-+---+---++
         ^    ^     ^                   ^          ^     ^
         |    |     |                   |          |     |
       SPB   (13 bits)               (7 bits)     (14 bits)

                                 Figure 18

   Case 2: Each packet MAY belong to a different protocol: All the
   Simplemux headers will be 2 or 3 bytes (for usual packet sizes).

          LXT             LXT             LXT   LXT
           |               |               |     |
           V               V               V     V
   +---++-+-+---+----+---++-+---+----+---++-+---+-+---+----+---++
   |tun||0|0|len|Prot|pkt||0|len|Prot|pkt||1|len|0|len|Prot|pkt||..
   +---++-+-+---+----+---++-+---+----+---++-+---+-+---+----+---++
         ^    ^               ^               ^     ^
         |    |               |               |     |
       SPB   (6 bits)       (7 bits)         (14 bits)

          LXT   LXT             LXT             LXT   LXT
           |     |               |               |     |
           V     V               V               V     V
   +---++-+-+---+-+---+----+---++-+---+----+---++-+---+-+---+----+---++
   |tun||0|1|len|0|len|Prot|pkt||0|len|Prot|pkt||1|len|0|len|Prot|pkt||.
   +---++-+-+---+-+---+----+---++-+---+----+---++-+---+-+---+----+---++
         ^    ^     ^               ^               ^     ^
         |    |     |               |               |     |
       SPB   (13 bits)           (7 bits)          (14 bits)

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                                 Figure 19

7.  IANA Considerations

   A protocol number for Simplemux should be requested to IANA.

   As a provisional solution for IP networks, the ingress and the egress
   optimizers may agree on a UDP port, and use IP/UDP as the
   multiplexing protocol.

8.  Security Considerations

   Simplemux protocol has been developed in such a way that packet
   aggregation and security can be simultaneously applied to the same
   traffic flows, i.e. a single security header could protect a number
   of packets belonging to different flows.

   As a consequence, the overall efficiency could be improved, as the
   number of security headers could be reduced from N to 1 (being N the
   number of multiplexed packets).

9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC1570]  Simpson, W., Ed., "PPP LCP Extensions", RFC 1570,
              DOI 10.17487/RFC1570, January 1994,
              <https://www.rfc-editor.org/info/rfc1570>.

   [RFC3153]  Pazhyannur, R., Ali, I., and C. Fox, "PPP Multiplexing",
              RFC 3153, DOI 10.17487/RFC3153, August 2001,
              <https://www.rfc-editor.org/info/rfc3153>.

   [RFC4170]  Thompson, B., Koren, T., and D. Wing, "Tunneling
              Multiplexed Compressed RTP (TCRTP)", BCP 110, RFC 4170,
              DOI 10.17487/RFC4170, November 2005,
              <https://www.rfc-editor.org/info/rfc4170>.

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9.2.  Informative References

   [RFC1692]  Cameron, P., Crocker, D., Cohen, D., and J. Postel,
              "Transport Multiplexing Protocol (TMux)", RFC 1692,
              DOI 10.17487/RFC1692, August 1994,
              <https://www.rfc-editor.org/info/rfc1692>.

   [Bolla]    Bolla, R., Bruschi, R., Davoli, F., and F. Cucchietti,
              "Energy Efficiency in the Future Internet: A Survey of
              Existing Approaches and Trends in Energy-Aware Fixed
              Network Infrastructures", IEEE Communications Surveys and
              Tutorials vol.13, no.2, pp.223,244, 2011.

   [chab]     Chabarek, J., Sommers, J., Barford, P., Estan, C., Tsiang,
              D., and S. Wright, "Power Awareness in Network Design and
              Routing", INFOCOM 2008. The 27th Conference on Computer
              Communications. IEEE pp.457,465, 2008.

   [Saldana]  Saldana, J., Forcen, I., Fernandez-Navajas, J., and J.
              Ruiz-Mas, "Improving Network Efficiency with Simplemux",
              IEEE CIT 2015, International Conference on Computer and
              Information Technology pp. 446-453, 26-28 October 2015,
              Liverpool, UK., 2015.

Author's Address

   Jose Saldana
   CIRCE Technology Center
   Email: jmsaldana@fcirce.es

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