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Internet Engineering Task Force                                  A. Jain
Internet-Draft                                                 A. Terzis
Intended status: Informational                                    Google
Expires: September 14, 2017                                    H. Flinck
                                                             N. Sprecher
                                                          S. Arunachalam
                                                          Nokia Networks
                                                                K. Smith
                                                                Vodafone
                                                          V. Devarapalli
                                                            R. Bar Yanai
                                                         Vasona Networks
                                                          March 13, 2017


          Mobile Throughput Guidance Inband Signaling Protocol
             draft-flinck-mobile-throughput-guidance-04.txt

Abstract

   The bandwidth available for end user devices in cellular networks can
   vary by an order of magnitude over a few seconds due to changes in
   the underlying radio channel conditions, as device mobility and
   changes in system load as other devices enter and leave the network.
   Furthermore, packets losses are not always signs of congestion.  The
   Transmission Control Protocol (TCP) can have difficulties adapting to
   these rapidly varying conditions leading to inefficient use of a
   cellular network's resources and degraded application performance.
   Problem statement, requirements and the architecture for a solution
   is documented in [Req_Arch_MTG_Exposure].

   This document proposes a mechanism and protocol elements that allow
   the cellular network to provide near real-time information on
   capacity available to the TCP server.  This "Throughput Guidance"
   (TG) information would indicate the throughput estimated to be
   available at the radio downlink interface (between the Radio Access
   Network (RAN) and the mobile device (UE)).  TCP server can use this
   TG information to ensure high network utilization and high service
   delivery performance.  The document describes the applicability of
   the proposed mechanism for video delivery over cellular networks; it
   also presents test results from live operator's environment.

Status of This Memo

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





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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Contributing Authors  . . . . . . . . . . . . . . . . . .   3
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
     1.3.  Acronyms and Abbreviations  . . . . . . . . . . . . . . .   3
     1.4.  Definitions . . . . . . . . . . . . . . . . . . . . . . .   4
     1.5.  Assumptions and Considerations for the Solution . . . . .   4
   2.  Protocol  . . . . . . . . . . . . . . . . . . . . . . . . . .   6
     2.1.  Message Format  . . . . . . . . . . . . . . . . . . . . .   8
     2.2.  Authentication  . . . . . . . . . . . . . . . . . . . . .  10
   3.  Applicability to Video Delivery Optimization  . . . . . . . .  10
     3.1.  Test Results  . . . . . . . . . . . . . . . . . . . . . .  11
   4.  Manageability considerations  . . . . . . . . . . . . . . . .  12
   5.  Security considerations . . . . . . . . . . . . . . . . . . .  12
   6.  IANA considerations . . . . . . . . . . . . . . . . . . . . .  13
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  13
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  14
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  14
   Appendix A. . . . . . . . . . . . . . . . . . . . . . . . . . . .  15



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   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  15

1.  Introduction

   The problem statement related to the behavior of the TCP in cellular
   networks is provided in [Req_Arch_MTG_Exposure].  That same document
   specifies the requirements, reference architecture and proposed
   solution principles for a mobile throughput guidance exposure
   mechanism that can be used to assist TCP in cellular networks,
   ensuring high utilization and high service delivery performance.

   This document presents a set of considerations and assumptions for
   the development of a solution.  It specifies a protocol that
   addresses the requirements and the architecture stated in the
   [Req_Arch_MTG_Exposure].  This document describes also the
   applicability of the proposed mechanism to video delivery over
   cellular networks with test results from live production environment.

1.1.  Contributing Authors

   The editors gratefully acknowledge the following additional
   contributors: Peter Szilagyi/Nokia, Csaba Vulkan/Nokia, Ram Gopal/
   Nokia, Guenter Klas/Vodafone and Peter Cosimini/Vodafone.

1.2.  Terminology

   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].

1.3.  Acronyms and Abbreviations




















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   This document uses the following acronyms:

   ECGI     E-UTRAN Cell Global Identifier format
   ECN      Explicit Congestion Notification
   HMAC     Hash-based Message Authentication Code
   HTTP     Hypertext Transfer Protocol
   HTTPS    Hypertext Transfer Protocol Secure
   IP       Internet Protocol
   IV       Initialization Vector
   LTE      Long Term Evolution
   MTG      Mobile Throughput Guidance
   RAN      Radio Access Network
   RCTP     RTP Control Protocol
   RTT      Round Trip Time
   SACK     Selective Acknowledgement
   TCP      Transmission Control Protocol
   TCP-EDO  TCP Extended Data option
   TG       Throughput Guidance
   UE       User Equipment

1.4.  Definitions

   Throughput Guidance Provider:

      A functional element that has access to the radio network
      information and signals to the TCP server, information about the
      (near-real time) throughput estimated to be available to a UE at
      the radio downlink interface

1.5.  Assumptions and Considerations for the Solution

   This document specifies a solution protocol that is complies with the
   requirements and architecture specified in [Req_Arch_MTG_Exposure].
   The protocol is used by the cellular network to provide throughput
   guidance information to the TCP server; this information indicates
   the throughput estimated to be available at the radio downlink
   interface for the TCP connection.  The protocol allows the
   information to be provided in near real time in situations where the
   network conditions are changing frequently or the user is moving.

   While the implementation details can vary according to the access
   technology, the resource allocation is abstracted as the capacity of
   the "radio link" between the RAN and the UE.  For example, in the
   case of an LTE network, the number of physical resource blocks
   allocated to a UE, along with the modulation scheme and coding rate
   used, can be translated into radio link capacity in Megabits per
   second (Mbit/s).  From the derived UE's total throughput and with the




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   UE's TCP flow information, Throughput guidance for the TCP connection
   can be computed.

   The TCP server can use this explicit information to inform several
   congestion control decisions.  For example: (1) selecting the initial
   congestion window size, (2) deciding the value of the congestion
   window during the congestion avoidance phase, and (3) adjusting the
   size of the congestion window when the conditions on the "radio link"
   change.  In other words, with this additional information, TCP
   neither has to congest the network when probing for available
   resources (by increasing its congestion window), nor rely on
   heuristics to decide how much it should reduce its sending rate after
   a congestion episode.

   The same explicit information can also be used to optimize
   application behavior given the available resources.  For example,
   when video is encoded in multiple bitrates, the application server
   can select the highest encoding rate that the network can deliver.

   This solution specified in this document also satisfies the following
   assumptions and considerations:

   o  The end-to-end traffic is delivered via HTTP.

   o  The end-to-end traffic is encrypted (through HTTPS), thus HTTP
      header enrichment cannot be used by intermediate elements between
      the client and the server.

   o  TCP is used to deliver the HTTPS traffic.

   o  The Real-time Transport Protocol (RTP) network protocol is not
      used for traffic delivery.

   The protocol specified in this document assumes that a trustful
   relationship between the Throughput Guidance Provider and the TCP
   server has been formed using the means discussed in the Security
   considerations section.

   The solution in this document satisfies the considerations and the
   assumptions presented above, and proposes an in-band exposure
   mechanism where the throughput guidance information is added to the
   TCP headers of the relevant upstream packets.  HTTP and TCP are the
   most prevalent protocols in the Internet, used even by the most
   popular streaming application.  Throughput guidance at TCP level can
   be shared among multiple applications; it is not limited to any
   particular application level optimization only but it offers a
   generic approach that works even if application level end-to-end
   encryption, such as HTTPS, is applied.



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   In particular, the Throughput Guidance Providers adds the throughput
   guidance information to the Options field of the TCP header (see RFC
   0793 [RFC0793]) of packets from the TCP client to the TCP server.  An
   in-band mechanism is proposed because it does not require a separate
   interface, reference value, or correlation mechanism that would be
   needed with out of band approaches such as with RCTP that is limited
   to only certain types of applications.  Furthermore, an in-band
   mechanism can keep up with the rapid changes in the underlying radio
   link throughput.  Unlike existing mechanisms such as ECN, where an
   ECN- aware router sets a mark in the IP header in order to signal
   impending congestion (see [RFC3168]).  The proposed scheme provides
   explicit information, (termed "Throughput Guidance") about the
   estimated throughput available for the TCP connection at the radio
   link between the RAN and the UE.

   Note that once standardized and implemented, TCP Extended Data option
   (TCP-EDO) can be used to carry the throughput guidance information as
   specified in [tcp-edo] and simplify the use of the TCP Option fields
   by extending the space available for TCP options.  Currently the TCP-
   EDO is still work in progress and not available in production.
   Therefore, the use of TCP-EDO to carry throughput guidance is left
   for the later drafts.

2.  Protocol

   This section describes the protocol mechanism and the message format
   that needs to be communicated from the RAN to the TCP remote
   endpoint.  We describe the protocol mechanism and message format for
   throughput guidance.  The protocol mechanism is defined in an
   extensible way to allow additional information to be specified and
   communicated.  The protocol specification is based on the existing
   experiments and running code.  It is recommended to insert the
   throughput guidance information to the TCP segments that flow from
   client to server (see reasoning in "Assumptions and Considerations"
   section).  Most of the time, TCP segments are ACK packets from a
   client to the server and hence packets are unlikely to be fragmented.
   However, the described protocol solution can deal with fragmentation.

   The Mobile Throughput Guidance Signaling message conveys information
   on the throughput estimated to be available at the down link path for
   a given TCP connection.  The information is sent to the uplink end-
   point of the connection (i.e, the TCP server).  The TCP server MAY
   use this information to adapt TCP behavior and to adjust application-
   level behavior to the link conditions as defined in
   [Req_Arch_MTG_Exposure].

   A good example is a content optimizer or a cache that can adapt the
   application-level coding to match the indicated downlink radio



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   conditions.  As radio link conditions may change rapidly, this
   guidance information is best carried in-band using TCP options
   headers rather than through an out-of-band protocol.

   Using the TCP options to carry throughput guidance associates the
   guidance information with an ongoing TCP connection and explicitly
   avoids separate session identification information.  The proposed
   mechanism neither impacts the TCP state machine nor the congestion
   control algorithms of the TCP protocol.

   The Options field enables information elements to be inserted into
   each packet with a 40-byte overall limit; this needs to be shared
   with the standardized and widely-used option elements, such as the
   TimeStamp and SACK.  (Use of TCP-EDO will lift this constraint once
   available and deployed).  The TCP Options field uses a Kind-Length-
   Value structure that enables TCP implementations to interpret or
   ignore information elements in the Options field based on the Kind.

   In this draft, we define a message format for encoding information
   about the estimated capacity of a radio access link between the RAN
   and the UE which is traversed by a TCP connection.  The intention is
   to define a generic container to convey in-band information within
   the limited TCP Option space with optional authentication
   capabilities.  This document conveys throughput guidance information.
   Additional information can be specified in future.

   The Throughput Guidance Provider functional element inserts Mobile
   Throughput Guidance TCP options only if there is enough space in the
   TCP header.  The Throughput Guidance Provider has access to the radio
   network information and is typically co-located with the RAN
   functionality.

   The Throughput Guidance information must be delivered in a secure
   way, such than an intermediate node cannot modify it.  The
   information can be provided as plain text in a secure and closed
   network.  In other cases, the information should be authenticated
   (between the Throughput Guidance Provider and the TCP server).  An
   acceptable level of authentication (according to best common
   practices) may require more data than fits into a single TCP header
   (maximum of 40 bytes if no other options are present).  As described
   below, fragmenting information across multiple packets will be used
   if such is the case.

   Two transfer modes are defined to deal with security of exchanged
   throughput guidance information in this document; namely, plain-text
   mode and authenticated mode.  A third mode, encryption with
   authentication mode, is equally feasible and may be described in a




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   future revision of this protocol.  The flags field indicate which
   mode is used.

2.1.  Message Format

   Mobile Throughput Guidance Signaling uses the common TCP options
   structure as in [RFC0793] with experimental identifier as defined in
   [RFC6994].  The followign defines the message format:


        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
                                       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                       |      kind     |    Length     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |             ExID              |      Ver      |Resvd|Frag |P|T|
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |          Seq number           |              SBR              |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |  CL   |KeyIndx|              Auth MAC (20 bytes)              |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                                 Figure 1

    Kind:

      Code point 253 for Experimental Option for 16-bit ExID [RFC6994].
      The size of this field is 1 byte.

    Length:

      A 1-byte field, length of the option in bytes as defined in
      RFC793.

    ExID:

      Two bytes Experimental Identifier according to [RFC6994].  Code
      point 0x6006.

    Ver:

      Version of the protocol, set to 1.

    Flags:

      One byte of MTG protocol flag field as defined below.




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           0 1 2 3 4 5 6 7
          +-+-+-+-+-+-+-+-+
          |Resvd|Frag |P|T|
          +-+-+-+-+-+-+-+-+


               Flag field of common Kind-Lenght-Value header

                                 Figure 2

    Frag:

      Three bits that provide information about how to reassemble
      information if fragmented into multiple packets.  If no
      fragmentation across multiple TCP packet headers is needed, these
      bits are set to zero.  Otherwise, Frag is a counter starting from
      1 and incremented by 1 for each subsequent packet of the same type
      (see P- and T-bits below).  For the last fragment, the Fragment is
      always 7 (binary 111) to indicate that the information is
      complete.

    P and T bits:

      These two bits encode the packet type: Plaintext (P=0, T= 0),
      Cipher text (P=0, T=1), Nonce (IV) (P=1, T=0) or Authentication
      (P=1, T=1).  For Plaintext, the Fragment bits are always zero.

     Seq Number:

      16-bit sequence number to protect against replay attacks

     SBR:

      Suggested bit rate for the data session in Mbps.  The 12 most
      significant bits are used for the integer value while the bottom 4
      bits correspond to the decimal portion of the throughput value.

     CL:

      Cell Congestion Level (0, 1, 2, 3).  A 4-bit field that indicates
      the current cell congestion level. "0" indicates no congestion and
      "3" indicates high congestion value.

     Key Index:

      A 4-bit field to identify the key used for integrity protection.

     Auth MAC:



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      20 bytes of MAC that protects the TCP option

2.2.  Authentication

   Authentication covers the entire TCP option, exlcuding the Flags
   field and the Auth MAC field.  The authentication uses HMAC codes
   (e.g.  HMAC- SHA2-224), 128 bits (16 bytes) key size, 256 bits (32
   bytes) digest size.  Multiple keys (at most 256) for authentication
   with the same information receiver can be used.  Truncation is
   possible but at least 160 bits (20 bytes) must be used from the
   digest to meet the typical security level of mobile networks.

   Authentication takes a key, the input (arbitrary length) and produces
   a 32 byte long digest, which is truncated to 20 bytes (keeping the
   most significant bytes).  The HMAC algorithm and truncation can be
   negotiated via key management (out of scope of this document).

   The order in which the fields are included into the message
   authentication code is the same as the order in which the bytes
   appear in the message format.

   In case the option packets used as input to the HMAC are fragmented
   into multiple TCP headers, they are processed so that headers with
   cipher text option are processed first, followed by IV/Nonce option
   packets.

   The options containing the result of the HMAC are marked by setting
   both P- and T-bits of the flag-field to one.  Key Index is set to
   point to the used authentication key, followed by the resulting
   authentication code.  If the option doesn't fit into the free option
   space in the TCP header, it is fragmented across multiple TCP headers
   in the same way as the cipher text options.

3.  Applicability to Video Delivery Optimization

   The applicability of the protocol specified in this document to
   mobile video delivery optimization has been evaluated and tested in
   different network load scenarios.

   In this use case, TCP traffic, for which throughput guidance
   information is required, passes through a Radio Analytics application
   which resides in a Mobile-edge Computing (MEC) server (see
   [MEC_White_Paper]).  This Radio Analytics application acts as the
   Throughput Guidance Provider and sends throughput guidance
   information for a TCP connection using the Options field in the TCP
   header (according to the message specification provided in section
   2).  The TCP server MAY use this information to assist TCP congestion
   control decisions as described above.  The information MAY also be



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   used to select the application level coding so that it matches the
   estimated capacity at the radio downlink for that TCP connection.

   All of these improvements aim to enhance the quality of experience of
   the end user by reducing the time-to-start of the content as well as
   video stall occurrences.

3.1.  Test Results

   Nokia Networks and Google tested the video delivery optimization use
   case in a live production LTE network.  Google server was placed
   close to the packet core network of LTE (SGi-interface of LTE).
   Different network load scenarios were taken into consideration.  TCP
   CUBIC was used in these tests [MTG_ICCRG].

                      Field trial performance results

   +-------------------+-----------------------+-----------------------+
   |    Performance    |     Difference of     |      Diff of 99th     |
   |       metric      |      Averages (%)     |      percentiles      |
   +-------------------+-----------------------+-----------------------+
   |    Time to play   |         -8.0%         |          -12%         |
   | Number of formats |         +4.1%         |         +29.9%        |
   |  Client bandwidth |         +0.7%         |         +8.0%         |
   |     Ave Video     |         +6.2%         |         +5.6%         |
   |     resolution    |                       |                       |
   |   Re-buffer time  |         -19.7%        |         -5.1%         |
   +-------------------+-----------------------+-----------------------+

                         Table 1: Performance Data

   These user experience improvements results into better video play and
   are likely to offer longer battery life.

   Table 3 summarizes the results from a field trial in the 3G network
   of a Tier 1 mobile network operator in the Americas.  As in the
   previous case, the Google servers were located close to the packet
   core network while the network elements from Vasona Networks
   generated the Throughput Guidance messages.

   It is interesting to note that the improvements that Throughput
   Guidance provides are qualitatively different in LTE and 3G networks.
   LTE networks generally have capacities that cannot be fully utilized
   by CUBIC;s initial sending rate.  On the other hand, Throughput
   Guidance tends to be more conservative in 3G networks leading to
   higher time to play.  Video re-buffering is smaller in both cases.





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                    3G field trial preformance results

   +-------------------+-----------------------+-----------------------+
   |    Performance    |     Difference of     |      Diff of 99th     |
   |       metric      |      Averages (%)     |      percentiles      |
   +-------------------+-----------------------+-----------------------+
   |    Time to play   |         +0.8%         |         +4.6%         |
   | Number of formats |         -1.2%         |         +0.0%         |
   |  Client bandwidth |         +2.5%         |         -0.5%         |
   |     Ave Video     |         +0.5%         |         -1.9%         |
   |     resolution    |                       |                       |
   |   Re-buffer time  |         -13.9%        |         -10.9%        |
   +-------------------+-----------------------+-----------------------+

               Table 2: Performance Data from 3G field trial

4.  Manageability considerations

   The application in the RAN SHOULD be configured with a list of
   destinations to which throughput guidance should be provided.  The
   application in RAN will supply mobile throughput guidance information
   to more than one TCP server simultaneously based on the list of
   destinations.

   In addition, it SHOULD be possible to configure the frequency (in
   milliseconds) at which throughput guidance needs to be signaled as
   well as the required security level and parameters for the encryption
   and the authentication if supported.

5.  Security considerations

   Throughput guidance SHOULD be provided in a secure way.  The
   information can be provided as plain text in a secure and closed
   network (e.g. inside operator network).  In other cases, the
   information should be authenticated (between the Throughput Guidance
   Provider and the TCP server).

   Section 2 described how the TCP Header information is protected.  An
   out-of-band mechanism is currently used to agree upon the set of keys
   used to authenticate the messages exchanged between the endpoint and
   the network element that generates the throughput guidance headers.
   For example, service providers/OTTs can provide a portal that network
   providers can use to configure the keys they use to encrypt/sign the
   throughput guidance information.  Then, a service behind the portal
   ensures that the keys are distributed to the servers that need them.

   As stated in [Req_Arch_MTG_Exposure], the policy configuration of the
   Throughput Guidance Provider and the server endpoint, as well as the



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   key management are beyond the scope of this protocol definition.  The
   protocol assumes that a trustful relationship has been formed between
   the Throughput Guidance Provider and the TCP server and that the
   required security level is already configured by the operator and
   agreed between the entities ( i.e.  authentication, encryption or
   both).

   The identity of the Mobile Throughput Guidance provider that injects
   the throughput guidance header must be explicitly known to the
   endpoint receiving the information.  Omitting such information would
   enable malicious third parties to inject erroneous information.

   Fortunately, the issue of malicious disinformation can be easily
   addressed using well known techniques.  First, the network entity
   responsible for injecting the throughput guidance header can include
   a cryptographically secure message authentication code.  In this way
   the transport endpoint that receives the throughput guidance header
   can check that the information was sent by a legitimate entity and
   that the information has not been tampered with.

   Furthermore, the throughput guidance information should be treated
   only as an estimate to the congestion control algorithm running at
   the transport endpoint.  The endpoint that receives this information
   should not assume that it is always correct and accurate.
   Specifically, endpoints should check the validity of the information
   received and if they find it erroneous they should discard it and
   possibly take other corrective actions (e.g., discard all future
   throughput guidance information from a particular IP prefix).
   Endpoints MUST process throughput guidance information only from TCP
   segments that would be otherwise be accepted as part of the standard
   TCP input process.  For example, the receiver should ignore
   throughput guidance information included in TCP ACKs whose
   acknowledgement sequence numbers fall outside the range of valid
   sequence numbers.

6.  IANA considerations

   In the current version of the document and for field tests, the
   experimental value 253 is used for the "Throughput Guidance" TCP
   option kind.  ExpID SHOULD be set to 0x6006 (16 bits)

7.  Acknowledgements

8.  References







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8.1.  Normative References

   [RFC0793]  Postel, J., "Transmission Control Protocol", STD 7,
              RFC 793, DOI 10.17487/RFC0793, September 1981,
              <http://www.rfc-editor.org/info/rfc793>.

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

   [RFC6994]  Touch, J., "Shared Use of Experimental TCP Options",
              RFC 6994, DOI 10.17487/RFC6994, August 2013,
              <http://www.rfc-editor.org/info/rfc6994>.

8.2.  Informative References

   [I-D.narten-iana-considerations-rfc2434bis]
              Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", draft-narten-iana-
              considerations-rfc2434bis-09 (work in progress), March
              2008.

   [MEC_White_Paper]
              ETSI, "Mobile-Edge Computing - Introductory Technical
              White Paper", 2014.

   [MTG_ICCRG]
              Szilagyi, P., and Terzis, A., "Mobile Content Delivery
              Optimization based on Throughput Guidance", Presentation
              at ICCRG meeting IETF93 (work in progress), July 2015.

   [Req_Arch_MTG_Exposure]
              Jain, A., , Terzis, A., , Sprecher, N., , Arunachalam, S.,
              , Smith, K., , and G. Klas, "Requirements and reference
              architecture for Mobile Throughput Guidance Exposure",
              draft-sprecher-mobile-tg-exposure-req-arch-01.txt (work in
              progress), February 2015.

   [RFC2629]  Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
              DOI 10.17487/RFC2629, June 1999,
              <http://www.rfc-editor.org/info/rfc2629>.

   [RFC3168]  Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
              of Explicit Congestion Notification (ECN) to IP",
              RFC 3168, DOI 10.17487/RFC3168, September 2001,
              <http://www.rfc-editor.org/info/rfc3168>.




Jain, et al.           Expires September 14, 2017              [Page 14]


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   [RFC3552]  Rescorla, E. and B. Korver, "Guidelines for Writing RFC
              Text on Security Considerations", BCP 72, RFC 3552,
              DOI 10.17487/RFC3552, July 2003,
              <http://www.rfc-editor.org/info/rfc3552>.

   [RFC4413]  West, M. and S. McCann, "TCP/IP Field Behavior", RFC 4413,
              DOI 10.17487/RFC4413, March 2006,
              <http://www.rfc-editor.org/info/rfc4413>.

   [RFC5925]  Touch, J., Mankin, A., and R. Bonica, "The TCP
              Authentication Option", RFC 5925, DOI 10.17487/RFC5925,
              June 2010, <http://www.rfc-editor.org/info/rfc5925>.

   [tcp-ao-encrypt]
              Touch, J., , "A TCP Authentication Option Extension for
              Payload Encryption", draft-touch-tcp-ao-encrypt-
              02.txt (work in progress), November 2014.

   [tcp-edo]  Touch, J., and Eddy, W., "TCP Extended Data Offset
              Option", draft-ietf-tcpm-tcp-edo-01.txt (work in
              progress), October 2013.

Appendix A.

Authors' Addresses

   Ankur Jain
   Google
   1600 Amphitheatre Parkway
   Mountain View, CA  94043
   US

   Phone: +1-925-526-5879
   Email: jankur@google.com


   Andreas Terzis
   Google
   1600 Amphitheatre Parkway
   Mountain View, CA  94043
   US

   Phone: +1-650-214-5270
   Email: aterzis@google.com







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   Hannu Flinck
   Nokia Networks
   Karaportti 13
   Espoo
   FI

   Phone: +358504839522
   Email: hannu.flinck@nokia-bell-labs.com


   Nurit Sprecher
   Nokia Networks
   Hod HaSharon
   IL

   Phone: +97297751229
   Email: nurit.sprecher@nokia.com


   Swaminathan Arunachalam
   Nokia Networks
   Irving, TX
   US

   Phone: +19723303204
   Email: swaminathan.arunachalam@nokia.com


   Kevin Smith
   Vodafone
   One Kingdom Street, Paddington Central
   London  W2 6BY
   UK

   Phone: +19723303204
   Email: kevin.smith@vodafone.com


   Vijay Devarapalli
   Vasona Networks

   Email: vijay@vasonanetworks.com


   Roni Bar Yanai
   Vasona Networks

   Email: rbaryanai@vasonanetworks.com



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