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Transport Area Working Group                                  J. Saldana
Internet-Draft                                      J. Fernandez Navajas
Intended status: Standards Track                             J. Ruiz Mas
Expires: September 3, 2018                        University of Zaragoza
                                                           March 2, 2018


              Simplemux.  A generic multiplexing protocol
                    draft-saldana-tsvwg-simplemux-09

Abstract

   The high amount of small packets present in nowaday's networks
   results in a low efficiency, as the size of the headers and the
   payload of these packets can be in the same order of magnitude.  In
   some situations, multiplexing a number of small packets into a bigger
   one is desirable in order 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.  Thus, the traffic
   profile can be shifted from small to larger packets, reducing the
   network overhead and the number of packets per second to be managed
   by intermediate routers.

   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.  This allows the inclusion of a number of packets
   belonging to different protocols (the "multiplexed packets") on a
   packet of another protocol (the "tunneling protocol").

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

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any




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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on September 3, 2018.

Copyright Notice

   Copyright (c) 2018 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
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
     1.2.  Existing multiplexing protocols . . . . . . . . . . . . .   3
     1.3.  Benefits of multiplexing  . . . . . . . . . . . . . . . .   5
   2.  Description of the scenario . . . . . . . . . . . . . . . . .   6
   3.  Protocol description  . . . . . . . . . . . . . . . . . . . .   6
   4.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  13
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  13
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

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 are in the same order of magnitude.  In some situations,
   multiplexing a number of small packets into a bigger one is desirable
   in order 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.  Thus, 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 routers.

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




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   packet.  This can be useful e.g. for grouping small packets and thus
   reducing the number of packets per second in a network.

   Simplemux is a generic multiplexing protocol, i.e. it can be used to
   aggregate a number of packets belonging to a protocol, on a single
   packet belonging to other (or the same) protocol.  One example of
   this is the fallback from QUIC to TLS over TCP
   [I-D.ietf-quic-applicability], which requires stream multiplexing.
   This is not provided by TCP, and could be implemented in other
   layers.

   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 (see the figure (Figure 1))


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


                                 Figure 1

   As an example, if a number of small IPv6 packets have to travel over
   an IPv4 network, they can be multiplexed and put into a single IPv4
   packet.  In this case, IPv4 is the "tunneling" protocol and IPv6 is
   the "multiplexed" protocol.  The IPv4 header is called in this case
   the "tunneling" or the "external" header.  The simplified scheme of
   this packet would be:

   |IPv4 hdr||Simplemux hdr|IPv6 packet||Simplemux hdr|IPv6 packet||...|

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

1.2.  Existing multiplexing protocols

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




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   o  TMux [RFC1692]

   TMux 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||...|

   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 machines.

   o  PPPMux [RFC3153]

   PPPMux "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 in order
   to multiplex a number of packets together, as done in TCRTP
   [RFC4170].  Thus, it introduces more overhead and complexity.

   An IP packet including a number of them using PPPMux appears as:

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

   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.

                                    ***

   The definition of a protocol able to multiplex complete packets,
   avoiding the need of other protocols as PPP is seen as convenient.
   The multiplexed packets can be of any kind, since a "Protocol Number"
   field can be added to each of them.  Not all the packets multiplexed



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   together must belong to the same protocol.  The general scheme of
   Simplemux is:

   |tunnel hdr||Simplemux hdr|packet||Simplemux hdr|packet||...|

   The Simplemux header includes the "Protocol Number" field, so it
   permits the multiplexing of different kinds of packets in the same
   bundle.

   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".

   When applied to IP packets, the scheme of a multiplexed packet
   becomes:

   |tunnel hdr||Simplemux hdr|IP packet||Simplemux hdr|IP packet||...|

1.3.  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.  It
   is desirable for two main reasons: first, 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 there
   is a need for mechanisms able to reduce the overhead introduced by
   low-efficiency flows.  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



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   [Chabarek]on commercial routers corroborate this.  A study using
   different packet sizes was presented, and the tests with big packets
   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.

2.  Description of the scenario

   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 2).

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


                                 Figure 2

3.  Protocol description

   A Simplemux packet consists of:

   - An external header that is used as the tunneling header for the
   whole packet.

   - A series of pairs "Simplemux header" + "packet" of the multiplexed
   protocol.

   This is the scheme of a Simplemux packet:

   |tun hdr||Simplemux hdr|packet||Simplemux hdr|packet||...|

   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"):

   o  First Simplemux header (after the tunneling header, and before the
      first multiplexed packet):



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   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:

   |SPB(1 bit)|LXT(1 bit)|length (6 bits)||LXT(1 bit)|length (7
   bits)||...||Protocol (8 bits)|

   - 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 set to 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), not including the length field.  If
   the length of the multiplexed packet is less than 64 bytes (less than
   or equal to 63 bytes), the first LXT is set to 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) is the Protocol field of the multiplexed packet,
   according to IANA "Assigned Internet Protocol Numbers."

   As an example, a First Simplemux header before a packet smaller than
   64 (2^6) bytes would 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 3




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   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:

       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 4

   In this case, the length of the packet will be the number expressed
   by the concatenation of the bits of Length 1 - 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) would 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 5

   In this case, the length of the packet will be the number expressed
   by the concatenation of the bits of Length 1 - Length 2 - 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.

   o  Subsequent (Non-first) Simplemux headers (before the other
      packets):



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   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:

   |LXT(1 bit)|length (7 bits)||LXT(1 bit)|length (7
   bits)||...||Protocol (8 bits, optional)|

   - 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 set to 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) is the Protocol 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, would be 1 byte long:

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

   SPB = 0 in the first header

                                 Figure 6




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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 = 0 in the first header

                                 Figure 7

   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 = 0 in the first header

                                 Figure 8

   In this case, the length of the packet will be the number expressed
   by the concatenation of the bits of Length 1 - Length 2 - 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.




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   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 = 1 in the first header

                                 Figure 9

   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 = 1 in the first header

                                 Figure 10

   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:










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       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 = 1 in the first header

                                 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 - 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.

   These would be some examples of the whole bundles:

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


   |tun||1|0|len|Protocol|pkt||0|len|pkt||1|len|0|len|pkt||...|
              |                   |          |     |
              v                   v          v     v
           (6 bits)             (7 bits)    (14 bits)


   |tun||1|1|len|0|len|Protocol|pkt||0|len|pkt||1|len|0|len|pkt||...|
              |     |                   |          |     |
              v     v                   v          v     v
             (13 bits)               (7 bits)     (14 bits)


                                 Figure 12

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





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|tun||0|0|len|Prot|pkt||0|len|Prot|pkt||1|len|0|len|Prot|pkt||...|
           |               |               |     |
           v               v               v     v
        (6 bits)         (7 bits)         (14 bits)


|tun||0|1|len|0|len|Prot|pkt||0|len|Prot|pkt||1|len|0|len|Prot|pkt||...|
           |     |               |               |     |
           v     v               v               v     v
          (13 bits)           (7 bits)          (14 bits)


                                 Figure 13

4.  Acknowledgements

   This work has been partially funded by the EU H2020 Wi-5 project
   (Grant Agreement no: 644262) and the Spanish Ministry of Economy and
   Competitiveness project TIN2015-64770-R, in cooperation with the
   European Regional Development Fund.

5.  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.

6.  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 (being N the
   number of multiplexed packets) to 1.

7.  References

7.1.  Normative References

   [I-D.ietf-quic-applicability]
              Kuehlewind, M. and B. Trammell, "Applicability of the QUIC
              Transport Protocol", draft-ietf-quic-applicability-01
              (work in progress), October 2017.



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

   [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>.

   [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>.

   [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>.

7.2.  Informative References

   [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.

   [Chabarek]
              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.

Authors' Addresses

   Jose Saldana
   University of Zaragoza
   Dpt. IEC Ada Byron Building
   Zaragoza  50018
   Spain

   Phone: +34 976 762 698
   Email: jsaldana@unizar.es




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   Julian Fernandez Navajas
   University of Zaragoza
   Dpt. IEC Ada Byron Building
   Zaragoza  50018
   Spain

   Phone: +34 976 761 963
   Email: navajas@unizar.es


   Jose Ruiz Mas
   University of Zaragoza
   Dpt. IEC Ada Byron Building
   Zaragoza  50018
   Spain

   Phone: +34 976 762 158
   Email: jruiz@unizar.es

































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